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2012

Annual report

NORCOWE Annual report 2012

Norwegian Centre for Offshore Wind Energy page 1

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NORCOWE Annual report 2012

Welcome by Peter M. Haugan, UoB, Chair of NORCOWE executive board

2012 was a good year for NORCOWE. The strategy process that was completed during the year, has resulted in more focused efforts emphasising our strengths and profile with reduction from five to three work packages as we move into 2013. The first NORCOWE PhD students successfully completed their degrees in 2012 and many more will be finished in 2013. Together with many more master students, they will be available to support expansion in the offshore wind energy industry in the years to come. We have also welcomed several young scientists taking new roles in the centre management group. During 2012 we saw increasing international attention to NORCOWE. In addition to our European neighbors around the North Sea, there is now interest from Asia and America. These contacts will be followed up.

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We also lost Norwegian industry partners who have been with NORCOWE from the start, but now see that the prospects and conditions for industrial development in Norwegian waters are not as good as expected. While we regret this loss, it is also understandable. Even more reason then for us to keep a close watch on the international development and take roles where they emerge. Looking forward to a fruitful 2013 where we will complete several more PhD studies, maintain the industrial relevance in NORCOWE core activities as well as through an increasing number of spinoff projects. With assets such as the motion lab at University of Agder and expanding met-ocean measurement capabilities we are in a good position to develop procedures and projects to shape the future of the offshore wind industry.

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NORCOWE Annual report 2012

Table of contents Welcome 2 About the centre 4 NORCOWE 2012 4 Key figures 4 Scientific Activity Costs 4 Dear reader 5 Introduction 7 Centre Management Group 8 WP1 Met-Ocean data 10 LIDAR measurements for wind energy applications 12 NORCOWE Data storage solution 14 PhD student Martin Flügge 15 Report on the NORCOWE turbulence systems 16 WP2 Wind-Energy Estimation 18 Integrated Model Reduction and CFD Tool for Quick and Accurate Wind Farm Modelling 20 Validation of Large Eddy Simulations against FINO1 data 22 Data analysis for wind energy outcome forecast 23 PhD student Olav Krogsæter 24 WP3 Design, installation and operation of offshore wind turbines 25 Impacts of VSC-HVDC-based offshore wind power integration on power system transient stability 28 Motion Compensation Laboratory 30 PhD student Lene Eliassen 31 PhD student Tore Bakka 32 PhD student Erik Kostandyan 33 PhD student Arun Sarkar 34 PhD student Hongzhi Liu 35 PhD student Søren Christiansen 36 PhD student Trinh Nguygen 37 Associated projects 38 Gwind verification project – Status February, 2013 38 Decision support for installation of offshore wind turbines 39 Completed PhDs 40 NORCOWE Summer School 41 International cooperation 42 Public outreach 43 Appedix 45 Board and Committees 45 Equipment list 45 Scientific staff 46 Publications and reports 2012 50

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NORCOWE Annual report 2012

About the centre NORCOWE 2012

Committee for Innovation and Commercialization Lead: Jan Pedersen, Agder Energi

Scientific Committee Lead: Finn Gunnar Nielsen, UoB

General assembly All partners and EB chairman

International Scientific Advisory Committee Lead: Finn Gunnar Nielsen, UoB

Centre Administration Hosted by Christian Michelsen Research AS Centre Director Kristin Guldbrandsen Frøysa and Centre Coordinator Knut-Erland Brun

Executive board 9 representatives Chair: Peter M. Haugan, UoB.

Work Package 1 Lead: Angus Graham, Uni Research

Work Package 2 Lead: Jasna B. Jakobsen, UoS

Work Package 3 Lead: Ivar Langen, UoS

The NORCOWE research and industrial partners per 31.12.2012 Christian Michelsen Research (CMR) (host institution) Uni Research University of Agder (UoA) University of Bergen (UoB) University of Stavanger (UoS) Aalborg University (AAU) Agder Energi Aker Solutions Lyse Produksjon National Oilwell Varco Norway Origo Solutions Statkraft Development Statoil StormGeo Vestavind Offshore

Key figures PhD students: 15 Completed PhDs: 2 Post Docs: 3 Master students:22 Number of publications: 53 Reserach reports: 10 Patent applications: 2 page 4

Work Package 4 Lead: Lene SĂŚlen, CMR Gexcon

Work Package 5 Lead: Joachim Reuder, UoB

Scientific Activity Costs (kNOK)

WP 1 - Wind and ocean conditions

4 887

WP 2 - Offshore wind technology

2 651

WP 3 - Offshore deployment and operations

9 613

WP 4 - Wind farm optimisation

6 424

WP 5 - Common themes

5 672

Education

159

Equipment

635

Total costs

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NORCOWE Annual report 2012

Dear reader NORCOWE went through a strategy process in 2012. A new work package structure was set up as a result of that process. The current (2013) work packages are: WP1: Met/ocean data - Measurements and database WP2: Wind energy estimation - Wind resource assessment, energy yield and layout for offshore wind farms WP3: Design, installation and operation of offshore wind turbines We have chosen to present our scientific work and results under the new structure. For each work package, there is first an overview, then some results and activities are presented together with interviews of PhD students associated with the work package. The students presented are to complete their PhD in 2013. The last part of the annual report presents some associated projects and topics like the NORCOWE summer school, international cooperation, public outreach and publication list. The annual report gives only a snapshot of what is going on in NORCOWE. So please feel free to contact us if you want more information. It might also be a good idea to attend our two “Science meets industry conferences” in 2013. The first conference is in Stavanger 17th April; the second is in Bergen 10th September. I hope you will enjoy reading our annual report! Best regards, Kristin Guldbrandsen Frøysa Director NORCOWE

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NORCOWE Annual report 2012

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NORCOWE Annual report 2012

Introduction

In 2009 the European Wind Energy Association (EWEA) published the comprehensive report on offshore wind “Oceans of Opportunity”, where the installed accumulative capacity at the end of 2012 was estimated at 6.4 GW. At end 2011 3.8 GW capacity were in place and 2012 saw close to 1.2 GW additional capacity implying a total of 5 GW installed capacity by end 2012 in European waters, i.e. 78% of the capacity projected in 2009. Despite both technical and financial challenges offshore wind is happening now and shows steady and steep growth year by year. This is also being noticed by European industry and surprisingly enough also by leading international oil & gas contractors with record high backlogs as a result of the booming activity in the oil & gas sector. Accordingly, the two large global subsea contractors Subsea 7 and Technip have established offshore wind headquarters in Aberdeen. They bring their broad oil & gas heritage to the offshore wind industry and are taking strategic positions in order to make sure that they are ready when the market is. In other words, they strongly believe that offshore wind will be a large and profitable business for many years to come, otherwise they would never have bothered in view of how busy these companies are in the oil & gas sector. However, the sky is by far all blue. The industry is in its infancy and offshore wind is still much too expensive, businesses are loosing money and projects are delayed. However, Europe with UK and Germany leading the way seems determined to implement offshore wind as a major part of the European renewable energy system by offering generous financial incentives to the offshore wind sector. But, public financial incentives are a double edged sword and it is in the industry’s own interest to make offshore wind financially sustainable in a competitive market, i.e. free offshore wind from the necessity of public funding. Accordingly, there is a strong need for industrial innovation and new technologies in order to make the industry financially sustainable in the long run. This situation represents a unique opportunity to Norwegian industry. The research community has a lot to offer if we focus on areas where we can utilize our maritime heritage and broad offshore oil & gas competence.

• • • • • • • • •

Vessel traffic management systems Lifting equipment Cable installation services Marine installation services Maintenance and operation services Software for wind farm optimization and lay out Resource mapping Meteorological and oceanographic forecasts Production forecasts

Furthermore, Japanese companies are looking to Norway for technical expertise and solutions in their effort to implement offshore wind as a new renewable energy source in the wake of the Fukushima disaster in 2011. In a longer perspective it may be very attractive for Norwegian companies to develop offshore wind products and services built on solid offshore experience from the oil & gas industry. We know from past knowledge that the oil & gas industry is cyclic and standing on one leg only may prove to be a very risky business. The research community can play an important role in further development of the Norwegian offshore wind industry if the researches are able and willing to give priority to R&D of relevance to the industry and if more companies are willing to look over the horizon and put offshore wind on the agenda. In 2025 the 5 000 engineers employed in the many Norwegian offshore wind companies along the Western coast of Norway will be grateful for the courage and persistence shown by the businesses who dared to give some room to offshore wind among the plentiful and profitable oil & gas projects back in 2013. Asle Lygre, General Manager, Arena Norwegian Offshore Wind (Arena NOW)

Some Norwegian businesses have already spotted the potential within the offshore wind segment and are already supplying products and services to Europe despite the fact that the first offshore wind farm in Norwegian waters probably is many years away. Reading the press may give the false impression that offshore wind is dead and gone in Norway. This is not true and Norwegian businesses are providing a range of products and services to the international market such as • Substations • Foundations • Helidecks • Power export cables • Inter-array cables • Cable protection systems • Service vessels • Communication equipment page 7

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NORCOWE Annual report 2012

Centre Management Group Charlotte Obhrai, UoS

What is your scientific background? I am a metocean specialist currently working at the University of Stavanger as an Associate Professor in offshore wind research. My education is in the fields of mathematics, meteorology and hydrodynamics and I have experience leading challenging commercial and research projects in the coastal and offshore marine environment. During my career I have applied my numerical and physical modelling skills to a range of marine engineering problems including; offshore wind turbines, subsea structures, offshore breakwaters & reefs, seawalls, and mobile coastlines. Please give a brief description of your main research topic Representative models of the environmental actions are of prime importance for the assessment of fatigue and extreme loads on an offshore wind turbine, as well as the wind energy production. Extreme wind conditions are mainly associated with the so-called neutral atmospheric stability; however more frequent, operating wind conditions offshore are often dominated by the unstable conditions. Different atmospheric stability conditions imply different wind profiles (wind “shear”), turbulence intensities and wake characteristics, which affect both the structural loads as well as predicted energy production. At present, there is no consensus as to whether the current design standard (IEC 61400-1:2005 and IEC 64100-3:2009, which assumes neutral stability only) is conservative or not. What issue within offshore wind energy is addressed by your work? The current research project here at the University of Stavanger aims to assess current offshore wind energy standards

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with respect to structural design requirements and power production estimation. The methods used in the standards to determine the vertical wind profile are based Monin-Obukhov surface layer theory. Lower surface roughness and hence turbulence offshore can result in a reduction in the marine boundary layer height, as a result extrapolation of the profile above 60 m may no longer be valid. The turbulence models used in the standards have also been developed for use onshore but recent work has shown that wind wave effects result may result in very different turbulence characteristics offshore. Offshore wind data from the FINO platforms has been used to demonstrate the importance of including stability and thermal effects in offshore wind modelling.

Lene Sælen, CMR GexCon

What is your scientific background? I have a background from physics and a PhD from University of Bergen and Université de Paris in the field of atomic physics. In 2010 I changed from studying quantum systems to work with wind energy at CMR GexCon. There, I have been working with CFD (Computational Fluid Dynamics) for wind farm modelling within NORCOWE. In 2012 I was work package manager for WP4 Wind farm optimisation and I am currently deputy of WP2 Wind-energy estimation. Scientific scope The challenges within wind energy are both technical and multidisciplinary; they involve multiscale modelling and require a fundamental understanding of the underlying physics.

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NORCOWE Annual report 2012

In my research there are two main industrial challenges addressed: 1. How can we model the energy outtake in large wind farms (hundreds of wind turbines) efficiently and sufficiently accurately to be useful for investment decisions? 2. How much can you benefit in terms of production from efficient placement of wind turbines in a farm? We use CFD and also model reduction techniques together with CMR Computing to develop models and methods, which can answer the challenges above. The technical tasks include improving turbulence models, modelling of atmospheric conditions, models for wind turbines, energy capture and turbulence generation.

Joachim Reuder, UoB

What is your scientific background? I am professor in meteorology at the Geophysical Institute at UoB and work as experimental boundary layer meteorologist. I graduated in 1991 with a diploma in meteorology at the Ludwig-Maximilians-University in Munich, Germany. In 1998 I finished and defended my dissertation for the degree of Dr. rer. nat. at the BTU in Cottbus, Germany. Both during diploma and doctorate I have been working on the photochemical effects of solar UV radiation. After moving to Bergen in 2005 I started to work in atmospheric boundary layer research with focus on the polar boundary layer and air-sea interaction processes. Since the start of NORCOWE, I have worked with the marine atmospheric boundary layer for wind energy applications. Please give a brief description of your main research topic My research is mainly dedicated to improve the understanding of the atmospheric boundary layer and the relevant turbulent exchange processes. For that my group is working on the development of new measurement systems and techniques, e.g. the buoy based eddy-covariance system developed in NORCOWE or the Small Unmanned Meteorological Observer SUMO, a small and lightweight research drone. Another focus area is the application and further development of commercially available instrumentation. One example here is the extension of the measurement capabilities LIDAR wind profilers and LIDAR wind scanners for the investigation of turbulence. Last but not least we are also intensively working on the usage of the observational data for model initialization and validation purposes. What issue within offshore wind energy is addressed by your work? My main issue related to offshore wind energy is the descrip-

The centre manager group consists of (from left): Charlotte Obhrai, Angus Graham, Joachim Reuder, John Dalsgaard Sørensen, Lene Sælen, Finn Gunnar Nielsen, Geir Hovland and Stian Anfinsen page 9

tion and understanding of the manifold interactions between the atmospheric boundary layer and single wind turbines and wind farms. This includes the complex interaction between wind shear, turbulence and atmospheric stability, crucial parameters for the operation of wind farms with respect to energy output, loads and fatigue. The better understanding of single turbine and wind park wakes will directly improve future wind farm layouts. On the long term the improved understanding of the boundary layer processes will feed into our numerical models to increase the accuracy of wind and weather forecasts.

Finn Gunnar Nielsen, Statoil/UoB

What is your scientific background? NTNU Marine Technology, PhD in Marine Hydrodynamics (1980). Presently Senior Advisor at Statoil Research and Innovation and adjunct professor at Geophysical Institute, UoB. Previously adjunct professor in marine technology, marine operations at NTNU. Please give a brief description of your main research topic My main research is with marine technology, interaction between ocean environment and marine structures in general. Lately my work has mostly been related to floating offshore wind systems; working with dynamic properties and loads. I headed the R&D project developing Hywind and I am currently involved in several international committees on marine renewable energy. What issue within offshore wind energy is addressed by your work? Floating offshore wind has been the main focus. Developing methods to computed coupled dynamics, including loads due to wind, waves and control system. I am also teaching offshore wind and marine renewables at the University of Bergen.

Angus Graham

What is your scientific background? I lead the Environmental Flow Group at Uni Computing, Uni Research in Bergen. I have a degree in physics from the University of Sussex, UK, and a doctorate in applied mathematics from the University of Southampton. I have ten years’ research experience in physical oceanography, gained at Southampton Oceanography Centre, and ten years’ research experience in meteorology and air quality, gained at Manchester Metropolitan University. Please give a brief description of your main research topic I have expertise in geophysical boundary layers; air-sea interaction and surface waves; wakes, jets and plumes; remote measurement techniques and image processing; and stochastic simulation. What issues within offshore wind energy are addressed by your work? 1. The role of waves on ambient hub-height winds. 2. The interaction of turbine wakes with their environment and one another, and their merging and transition to a mesoscale wake.

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NORCOWE Annual report 2012

WP1 Met-Ocean data – Measurement and database by Joachim Reuder (UoB)

Wind LIDARs at Stavanger Airport Sola

The planning, realization and operation of offshore wind farms is utterly dependent on the understanding of the marine atmospheric boundary layer (MABL) and the oceanic mixed layer (OML). The main objective of WP1 is therefore the collection and interpretation of high quality meteorological and oceanographic data sets relevant for offshore wind energy applications and the provision of structure and database for an efficient data exchange within NORCOWE. This task includes the coordination and organization of the required instrumentation, test facilities and measurement infrastructure, as well as the further development and maintenance of the NORCOWE met-ocean data base. The activities under WP 1 have been organized in 5 thematic sub-packages.

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WP1.1 – Measurements Atmosphere The main activities are dedicated to improve the availability of relevant data sets of the MABL relevant for offshore wind energy applications. Two main focus areas have been identified for this sub-package. The first one is the direct measurement of surface-near turbulence and turbulent exchange by a newly developed buoy-mounted eddy-covariance measurement system, including the development and test of corresponding motion correction algorithms (see page 16). The second and rather new research activity is dedicated to the application and further development of state-of-the-art LIDAR technology for detailed investigations of the 3D wind field and its potential for application toward the study of wake effects from single turbines and complete wind farms (see page 12). This topic has been pointed out as one of the strategic areas in NORCOWE by the board.

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NORCOWE Annual report 2012

For the year 2014 we envisage a larger international field campaign in an operative wind farm. The idea is to combine well established remote sensing techniques, as LIDAR and sodar wind profilers, and microwave temperature profilers with new and experimental approaches, e.g. the use of very small small unmanned aircrafts, for a comprehensive description of the atmospheric boundary layer in and around a wind farm. The atmospheric measurements will be complemented by corresponding oceanic observations on wavefield and oceanic mixed layer turbulence. This sub-task requires close interaction between all participating institutions and all NORCOWE partners are invited to participate with own measurements. A particular focus in this task will be set on the interaction between the measurement (WP1) and modelling (WP2) community to clearly define requirements and limitations of observational data sets for the purpose of model initialization and model test and validation. Sonic anemometer for atmospheric flux measurements front bow of R/V Håkon Mosby.

WP1.2 – Measurements Ocean This sub-task will address the improved understanding of the OML under the aspect of offshore wind energy applications. Waves and turbulence are the key parameters determining loads on bottom mounted foundations and movements of floating foundations for wind turbines. WP1.2 addresses at the moment two main topics. The first is the direct measurement of ocean turbulence, including motion correction, using a specifically developed and designed turbulence probe. The second investigates the interaction of the upper ocean with large wind farms, combining measurements and modeling activities (see page 16).

WP1.5 – Data storage and management Within NORCOWE it will be of crucial importance to collect, quality control, store, and manage a continuously increasing amount of data, both from ongoing and envisaged measurement activities and model simulations. A particular focus has to be set on the long term safe storage of the data and a safe and easy way for data access for all NORCOWE partners to ensure the exchange of relevant information between various partners and across the different WPs. The main activities in the beginning will be to assist the experimental meteorologists and oceanographers in data conversion and upload of new datasets. On the longer term, the database will be extended by modeling data (see page 14).

WP1.3 – Data collection and interpretation This sub package will coordinate the collection and interpretation of offshore met-ocean data sets of broader interest for different partners within NORCOWE, in particular from external sources (e.g. the German FINO platforms) and data that are or will be made available in the future by NORCOWE industrial partners. The data will be quality controlled and prepared for upload into the NORCOWE data base. This process will if necessary include the averaging of raw data to time intervals relevant for other project partners. One of the main benefits will be an increased visibility of existing data sets and the avoidance of duplication of work. The sub-task will also bridge the observational tasks of WP1 to the modelling activities in WP2 and has of course a direct link to sub-task 1.5 on data storage and management. WP1.4 – Coordination of measurement activities and international field campaign This sub-task covers mainly three activities: 1. Administration of NORCOWE owned met-ocean instrumentation, in particular the two wind LIDAR systems. 2. Planning and design of related research infrastructure. 3. Planning of future measurement campaigns for the characterization of the MABL and OML and for the investigation of wake effects, both of single wind turbines and entire wind farms.

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Unboxing the new scanning wind LIDAR

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NORCOWE Annual report 2012

LIDAR measurements for wind energy applications By Valerie Kumer (UoB)

What is LIDAR and why using this technique? As wind energy is one of the rising branches in green energy production, lots of effort is put into optimizing the productivity of every single wind turbine and wind farms. One key issue is the improvement of our knowledge on the atmospheric boundary layer (ABL), the lowest part of the atmosphere that is distinctly influenced by the Earth’s surface. The increase in turbine size and nacelle height in the recent years makes wind measurements via traditional meteorological masts more and more difficult. In response to that, there has been an increase in the use of remote sensing methods based on light detection and ranging (LIDAR) technology. The determination of wind profiles is not only necessary for wind farm siting but also for power production forecast. Therefore the accuracy of these wind profiles is of uttermost importance. LIDAR wind profilers can measure the wind to altitudes of several hundreds of meters and enable a detailed analysis of the relevant boundary layer processes. To detect the wind field, short light pulses are sent into the atmosphere. The emitted photons are scattered back to the device by atmospheric aerosol particles that move with the wind. Scattering at moving targets leads to a slight shift in wavelength of the returned signal. This so-called Doppler Effect can also be experienced daily by the change of frequency of the sound waves e.g. from a car that is passing by, with higher frequency while approaching and lower frequency after passage. One single measurement gives the velocity component in the direction of the beam. By measuring in different directions and elevation angles, wind profiles and cross sections of the wind field can be derived.

The retrieved wind information is not only for commercial use in terms of power forecasts, but also applies to scientific studies of for example turbulence characteristics of the atmospheric boundary layer and turbulence generation by wind turbines and wind farms. Turbulence is in general of interest as it extracts energy from the mean flow and therefore represents an energy loss for wind farm operators. In particular energy losses due to the wake of upstream turbines are of vast importance for the overall productivity of a wind farm. Measurements with the scanning wind LIDAR system within NORCOWE will provide highly required data as both input to and for testing or validation of numerical models. Current LIDAR research activities at UoB: Measurement campaign at Sola A scanning wind-LIDAR system (WindCube 100S from Leosphere) was purchased by NORCOWE in spring 2012. The performance was already tested with measurements on the rooftop of the Geophysical Institute at UoB (GFI). As such systems have entered the wind energy community very recently, another test deployment started in the scope of a measurement campaign of a NORCOWE PhD project at UoB on February 25th this year. The Windcube 100S is located together with a Windcube v1 on the rooftop of an Avinor building next to the runway of Stavanger Airport Sola (Figure 2). Additionally a second Windcube v1 was placed next to the radio sounding launching system from Met.no. This setup allows comparisons of measurements collected by the scanning Windcube 100S not only to data from the Windcube v1, but also to meteorological measurements of the tower and to wind profiles of rising weather balloons.

Figure 1: Increase in wind turbine size from mid 80s until today (illustration by EWEA)

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NORCOWE Annual report 2012

The aim of this campaign is to evaluate uncertainties of the Windcube 100S, including investigations in different scanning regimes as well as testing its limitations. This will lead to more experience and knowledge of reliable scanning patterns, that can later be applied in upcoming on- and offshore wind farm measurement campaigns in the Netherlands and UK. Data collected during these upcoming campaigns will be used for detailed investigations of the interaction between wind turbines and the ABL, including wake effects of a single wind turbine as well as disturbances of a whole wind farm. What are the expected results and how do they benefit wind energy production? With the gained information and experiences in the first field deployments we want to improve and adapt measurement characteristics of the scanning WindCube 100S through testing different scan speeds and scan patterns. That will result in a setup optimized for specific meteorological application in wind energy. In terms of the analysis of the collected data, dependent on the deployment, we expect to see wake effects in horizontal wind speed deficits as well as the helix structure of the wake itself. This is already known from wind tunnel experiments and model simulations but is not yet verified by measurements in real atmospheric conditions. Considering this knowledge in the operation of wind farms is crucial for the operators as it could lead to more efficient lifetime power production of wind farms. This is done by taking wake effects into account, leading to reduced loads and fatigue and therefore prolonging the overall lifetime of the wind turbines. Moreover the gained information can be used for optimizing layouts of new wind farms as well as for intelligent operation of already existing ones.

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Figure 2: Scanning wind LIDAR at Stavanger Airport Sola

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NORCOWE Annual report 2012

NORCOWE Data storage solution by Stian Anfinsen and Junyong You (CMR Computing) Several of the experiments and measurement campaigns in NORCOWE generate (large) data sets. As a general rule such data sets often end up in a drawer being inaccessible for other researchers and partners. As part of the NORCOWE strategy for distributing and promoting data access and collaboration, the storage solution MetaWind (hosted and developed by Met.no) has been set up (http://metawind.met.no). The solution stores data and metadata together behind a searchable service interface. NORCOWE develops and maintains a conversion tool from the various data formats, including LIDAR, MAST, Bouy, QuikSCAT, Windcube100S, and SODAR measurement data currently. New conversion routines will be developed as new data sets become available.

Data Type

Conversion Routines

LIDAR measurement (ASCII format, Available binary format) MAST measurement data

Available

Buoy measurement data

Available

QuikSCAT satellite data

Available

Windcube100S data (ASCII format)

Available

Covariance Flux System measurement data

Available soon

SODAR measurement data

Available

Step-by-step description of how to get a copy of the conversion routines and run them on your own system has been produced, enabling the data producers themselves to convert and upload their data. The documentation of MetaWind and the conversion routines are available to the NORCOWE partners in ProjectPlace.

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NORCOWE Annual report 2012

PhD student Martin Flügge

What is your scientific background? I obtained a bachelor’s degree in meteorology and oceanography in 2007 and a master’s degree in geophysics (climate) in 2009. Currently, I am taking my PhD at the University of Bergen and work in the research field of boundary layer meteorology. What topic is addressed in your PhD? My main research is on the characterization of the Marine Atmospheric Boundary Layer (MABL). The project focus is to investigate the turbulent exchange processes of momentum and heat between the ocean and the atmosphere. These processes govern the stability of the MABL and thus the winds that will affect offshore wind turbines. I use the NORCOWE turbulence system mounted on a ship or a buoy in order to quantify the turbulent exchange processes. This measurement technique is still under development and my research project will also contribute to improve it.

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What are you main results? During the last two years, we have developed the NORCOWE Direct Covariance Flux System in collaboration with the turbulence group at the University of Ireland. The system is utilized for offshore applications and can easily be mounted on ships and buoys. Measurements of turbulent air-sea exchange processes from floating platforms are contaminated by platform motions. A correction algorithm has been successfully used for measurements taken from ships in the late 1990’s. Based on this algorithm, we have found that turbulence measurements of heat and momentum taken from buoys can be corrected to give accurate results. The usage of buoys for these kinds of offshore measurements makes the site specific investigation of the vertical turbulence structure cheaper as buoys has lower operation costs and easily can be deployed within a wind farms.

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NORCOWE Annual report 2012

Report on the NORCOWE turbulence systems by Mostafa Bakhoday Paskyabi, Martin Flügge, Joachim Reuder and Ilker Fer (UoB) The improvement of offshore wind farms energy output continuous to increase as larger and more effective turbines are developed and placed in deeper water further offshore. For wind farm operators it is desirable to gain knowledge about the vertical wind profile up to the turbine height. Wind shear and turbulence increase loads and fatigue on the rotor blades and have to be addressed as a safety aspect. In the Marine Atmospheric Boundary Layer (MABL) these processes are a direct consequence of turbulent air-sea interaction that feedbacks on both the upper layers of the ocean and the lower 200 meters of the atmosphere. Wind blowing over the open ocean transfers momentum into the sea surface, driving surface currents and contributing to wave formation and upper ocean turbulence. Waves formed by the wind will disturb the smooth horizontal wind flow over the ocean and feedback on the lower part of the MABL, thus introducing atmospheric turbulence that will affect wind turbines. The present knowledge of these turbulent air-sea interaction processes are limited as only a few sporadic measurement sites for real offshore conditions are available. The theory used today to predict wind profiles and boundary layer turbulence was developed in the late 1960’s and is based on field measurements over land. Experiences from offshore wind farms showed that the land based wind profile laws are not applicable for offshore conditions. As a matter of fact, vertical wind profiles might behave differently for each wind farm. Water depth, distance to shore, mean wind speed and location of the wind farm are key parameters that determine the turbines energy output. For example, shallow water might lead to higher wave height as waves approach the shore, which in turn lead to increased turbulence in the MABL, thus leading to an increased fatigue on the turbines. In deeper water, swell wave traveling faster than the wind might feedback on the lower part of the MABL, thus introducing atmospheric turbulence that will affect wind farms. As the atmosphere and ocean are coupled, measurements in both the ocean and atmospheric boundary layers are highly needed to increase our understanding of the turbulent air-sea exchange processes. A better knowledge of these processes will enable researches to develop better models for the prediction of the vertical and horizontal wind and ocean current profiles at each specific wind farm site. This will lead to increased turbine safety as loads and fatigue will be limited, more reliable environmental assessments as the ocean circulation response in the vicinity of wind farms will be better understood, and increased wind farm productivity as the wind predictions are better constrained. How do researchers investigate turbulent air-sea exchange processes? Observations of air-sea interaction processes, background ocean currents, and surface gravity waves were made during the cruise of the R/V Håkon Mosby between 28 and 30 November 2012. The measurement site was approximately 30 km southwest of Bergen at 20 m of water depth. The deployment site is less than 5 km east of the 200 m isobath of the Norwegian trench (Fig. 1). Ancillary atmospheric data were logged page 16

Figure 1. Map shows cruise area where all instruments were deployed during November 28-30, 2012.

from the ship’s meteorological mast at 15 m height. During three days of cruise, the atmospheric turbulence measurements were made using a Direct Eddy Covariance Systems that has been purchased through NORCOWE (Fig. 2). The system consists of a sonic anemometer, an Inertial Measuring Unit (IMU) and a data logger, all in packed in watertight hous-

Figure 2.The NORCOWE Direct Eddy Correlation System mounted at the front bow of R/V Håkon Mosby. The sonic anemometer is mounted directly above the Inertial Measuring Unit which is contained in the black housing www.norcowe.no


NORCOWE Annual report 2012

ings. The anemometer records high frequency measurements of wind speed and temperature to capture the turbulent momentum and heat transport across the air-sea interface. Measurement of air-sea interaction processes involves measurements from floating platforms such as ship or buoys. As a consequence, the anemometer measurements will be contaminated by platform motions induced by the waves and by the translational motion of the platform itself. In order to correct recorded data for these motions in data post-processing an Inertial Measuring Unit has been added to the system to keep track of the platforms attitude, e.g. roll, pitch and yaw. Observations of ocean microstructure, background currents, and surface gravity waves were made during the cruise using a Moored Autonomous Turbulence System (MATS) and a bottom mounted frame equipped with different oceanographic sensors. The MATS has been designed to collect long time series of pressure, mean current, small scale turbulence velocity vectors and temperature data at a fixed level. The platform is a low–drag buoy custom modified to fit turbulence sensors, an Acoustic Doppler Velocimeter (ADV) and a motion sensor (Fig. 3-Top). During the field cruise, the MATS was the upper element of a bottom–anchored mooring line; aligned itself with the currents and acquired data in the upper 10 m Figure 3. (Top) MATS deployment and different components, and (Below) Bottom mounted frame with different equipped oceanographic sensors

of the ocean. The MATS recorded samples of 15-min bursts every one hour and the shear probes and thermistors data are used to estimate turbulent dissipation near the sea surface. Furthermore, the high-resolution pressure sensor mounted on the MATS is used to estimate wave bulk parameters such as significant wave heights and wave mean period. Additionally, a bottom mounted frame (BMF) was deployed in the area close to the MATS during this experiment. The BMF was equipped with an AWAC (Acoustic Wave and Current Profiler), an uplooking Aquadopp, and an ADV with a horizontal plate and a 45° slanted bracket (Fig. 3). The AWAC performs dual measurements of both ocean currents and surface gravity waves from a single fixed installation. The upward-looking Aquadopp provided background current measurements. In contrast to the MATS, implementation of the ADV into the Bottom Mounted Frame enabled us to record high resolution flow and turbulent flux measurements without any need for motion correction. Similar to the MATS, the ADV collected samples of 15-min bursts per hour. This experimental set up provided different approaches to estimate surface gravity waves and ocean microstructure from both moving and fixed platforms, using the independent BMF as reference. Our preliminary data analysis showed that the MATS successfully estimates wave bulk parameters and dissipation rates of turbulent kinetic energy near the sea surface.

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WP2 Wind-Energy Estimation

- Wind resource assessment, energy yield and layout for offshore wind farms Angus Graham (Uni Research)

WP2 is concerned with predicting wind-farm energy yields. Flow modelling takes place on a wide range of scales, from mesoscale (synoptic) down to rotor-blade element. This circumvents having to make somewhat arbitrary distinctions between meteorology and computational fluid dynamics (CFD). The reality is that there is considerable two-way coupling across the scales, particularly in the case of large farms of 100+ turbines (which represents the trend offshore). The geophysical response to the presence of a farm, over the downwind extent of the farm and many times this downwind, may thus need consideration. The use of interpolative predictive techniques, free of an inherent flow model, with time series of flow measurements or estimates is also under evaluation. Improved tools for wind-resource assessment Much of the work is directed at improved, validated, tools for assessing the wind resource, optimum layout and associated energy yield of a prospective wind farm. There is need to reduce investment risks here, through greater accuracy, and a quantification of uncertainties at all relevant flow scales. Estimation of the wind climatology at an offshore site should take account of local mesoscale and coastal effects, and a wave field that is only partially developed. It should yield a joint probability density function of hub-height wind speed and direction and stability parameter, applicable over the design lifetime of the farm (twenty years being typical). The energy yield over the lifetime might then be calculated from this density via a reduced model of the farm flow (as described further below), with an interactive or iterative repositioning of turbines and substations in the model ultimately being possible. Wind climatology is supplied globally at synoptic scales by

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the national and international meteorological agencies. Our research involves a state-of-the-art numerical downscaling of these hindcasts to the mesoscale, using the Weather Research and Forecasting (WRF) model. The model can be run with nested grids to accommodate complex boundary features such as bluff topography or wind farms. Offshore, it can be coupled to a spectral surface wave model such as that supplied by the international Wave Modelling Group (WAM), or a variant of this like the Simulating Waves Near-Shore (SWAN) model. The high resolution and computational complexity work against studying climatologically reliable periods of time (ie. decades), so machine-learning techniques are also being applied to correlate synoptic and short, site-specific, downscaled climatologies. Site biases established accordingly can then be applied over decadal periods. Wind-farm modelling The interaction of wind and turbines is being studied using blade-element and actuator line and disk representations of the rotor, with the WRF being coupled to suitable CFD models (CMR-Wind and OpenFOAM). Treatment of the dynamics as statistically steady (through Reynolds averaging) is being complemented by large-eddy simulation (LES), in a statistically unsteady coupling (see page 22). This reflects a pressing need to parameterise better certain unsteady effects, particularly wake meandering, in steady-state models. A reduced-order model of farm flow is also being developed. This uses a set of discretised conditions, and associated ensemble of CFD solutions, to compute a general solution, combining realisations so as still to satisfy the equations of fluid dynamics (see page 20) .

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Validation of models and wind-farm layout There is joint work with WP1 in the use and appraisal of measurement techniques in model assimilation and validation, and in the use of simulations to inform the planning of fieldwork. There is also joint work with WP3 in wind-farm layout design, balancing cabling installation costs and power losses (lowest where turbines are close together) with power losses from wakes (lowest where turbines are far apart). Nowcasting Work is jointly underway with WP3 on the nowcasting of turbulent fluctuations in the wind field in the vicinity of a turbine. Prediction follows from the flow history measured at an upwind mast or using Lidar, or indirectly using turbine power as a proxy for wind speed. Nowcasting underpins the mechanical control of turbines, wherein resistive torque and blade pitch are continuously adjusted to enhance power outputs and limit blade fatigue. A validated predictive algorithm which improves on state-of-the-art is sought, capable of being implemented in real time. Machine-learning techniques will be evaluated, perhaps against a dynamical and diagnostic model of ambient and wake turbulence in which LES results are drawn upon (see page 23). A key effect that can then be captured is turbines sometimes being in the wake of an upwind neighbour, as a result of wake meandering, and sometimes not. Marine operations and weather forecasting Work is also jointly underway with WP3 on forecasting for the purposes of scheduling marine operations and in energy page 19

load-balancing and trading. The wind industry needs to see a reduction in offshore costs greater than that realised onshore, and a connection with the grid that allows demand to be better met. Better decision-support software, accommodating probabilistic meteorological estimates, should help here, and a decision-support system for marine operations is accordingly under development. Real-time measurements of conditions at sea are typically only sparsely available for operational decision-making. This is particularly so during construction at a hitherto undeveloped site. Measurements are furthermore rarely available along the complete route from port to site. Capturing all relevant uncertainties in local conditions over an operational period may thus require a state-of-the-art downscaling - in both space and time - of ensemble synoptic forecasts. Relations used in offshore engineering will be applied to convert a given realisation of wind and waves to an equipment response. An appropriate economic cost level will then be predicted for the operation, such as the expected cost, or, in the case of a oneoff operation, a cost there is a small, given, chance of exceeding. The lowest-cost route will then be found, balancing journey length, time and conditions, and associated loadings on equipment. The associated cost will allow a decision on whether to proceed. Results achieved in this work are expected to reduce the number of unnecessary delayed marine operations due to uncertainties in wave and weather forecasts.

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Integrated Model Reduction and CFD Tool for Quick and Accurate Wind Farm Modelling By Yngve Heggelund and Chad Jarvis (CMR Computing), Lene SĂŚlen and Marwan Khalil (CMR GexCon)

ing approach. This puts limits on the level of detail of the wind resource statistics that can be included in yearly and longterm energy yield estimates. The computational bottleneck effectively prohibits such a CFD approach from being used in layout design, except for testing a small number of design possibilities. The goal of our work is thus to develop methods which can provide fast wind farm simulations without compromising the accuracy of CFD.

Industrial Challenge Current commercial methods for wind farm modelling are characterized by large uncertainties and often over predict production. This is especially true for large, offshore wind farms.

Method CMR is developing tools for efficient and accurate wind farm modelling through reduced solution of CFD models. In general, such strategies are called Model Reduction Techniques, and the technique here is based on the RANS (Reynolds averaged Navier-Stokes) equations for fluid flow. Instead of solving these in the full solution space (CFD), model reduction tool generates a basis from a set of CFD simulations and utilises only the main modes through orthogonal decomposition. This dramatically reduces the dimensionality of the problem and a solution can be achieved within a few tenths of a second com-

Wakes from upstream turbines are responsible for a considerable increase in the cost of energy (COE) due to lost energy potential and increased turbine loading. The lost energy potential is of size 5 - 20% (compared to free-stream operating turbines) for entire farms and up to 40% for individual turbines (EWEA, 2009). The aim of the work described in this brief report is to further reduce the current COE and project risk through better placement of turbines within wind farms and provide better accuracy in the estimated long-term energy production. Technical challenge The current state-of-the-art in wind farm modelling is to use Computational Fluid Dynamics (CFD) with modelling of the wind turbines (e.g. Actuator Disk, Actuator Line or similar). CFD in wind farm modelling is, however, not yet an industry standard. Most commercial actors still use simplified wake models for the turbines which have severe limitations in describing both the complex wake-wake interactions and the interaction between the wind turbine wakes and the ambient flow. Due to inherent shortcomings of the simplified methods, the industry is moving towards more extensive use of CFD (including turbine modelling) for accurate predictions of annual production. CFD is, however, a computationally demandpage 20

One of the advantages with model reduction techniques is the opportunity to evaluate non-regular layouts for offshore wind farms (right), rather than regular layouts (left). www.norcowe.no


NORCOWE Annual report 2012

Figure 1 Left: A scenario with three turbine rows and the wind blowing from west. Right: A scenario with six rows (21 turbines) for testing the scalability of the method.

pared to hours for a full CFD solution. The CFD basis simulations are generated in advance and this involve a small initial (computational) cost. In addition the CFD simulations are performed only on parts of the wind farm exploiting the modularity of the problem further reducing the (computational) cost of CFD. Control of convergence and accuracy of the method is done by comparing with CFD for selected control cases.

In order to optimise turbine placement, factors such as installation costs, maintenance costs, cable costs, transmission losses, seabed conditions, turbine specification, etc. must be summed to give an overall picture of the net present value. In such a calculation, the energy capture in the farm is clearly a decisive contribution for which the confidence should be as high as possible.

The CFD model used here is an in-house code (CMR-Wind) where the wind turbines are represented by sub-grid models (Actuator Disk). We work in parallel on improving and validating this underlying CFD model including wind turbine models.

Status So far, the basic development and testing of the method is performed. The method is verified against CFD for scenarios of two and three turbine rows and a single wind direction, as can be seen in Figure 1 (left). The scalability in terms of the computational cost of the method is also tested by simulating a case with six rows (21 turbines), see Figure 1 (right). This case can be computed within 1 second on a single CPU with the reduced method, but has not yet been compared to CFD.

Application The Model Reduction Tool calculates the three-dimensional flow fields for both wind speed and turbulent kinetic energy in addition to energy production for each turbine. Access to the turbulence level in the wind farm is important to determine a safe placement of turbines in order to plan effective control of the turbines during operation. The short calculation time makes it possible to evaluate large sets of different scenarios for wind conditions. Those evaluations contribute to a better estimate of the energy exchange in the farm. The short computation time (on the order of seconds on a single CPU) makes it possible to evaluate various turbine configurations, and the tool can thus be used in the design and optimisation of the farm layout. The impact on production from slightly reducing or increasing turbine spacing is an example of investigation that can be answered quickly and accurately through this method. Another example is investigation of the sensitivity of wind resources on the annual production. Perhaps the most important point, however, is the possibility of investigating a large number of different layout possibilities.

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Development This year (2013) the focus will be on developing capabilities in relation to turbine placement, further verification against CFD for interpolation and extrapolation cases and validation of CFD. An example of an extrapolation case is to model n (>3) turbine rows using only modes from CFD calculations with two and three turbine rows. Demonstrating the scaling properties of the method is an important step towards application on large wind farms. The future goal is to demonstrate the method on full-scale wind farms with both regular and nonregular layout.

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Validation of Large Eddy Simulations against FINO1 data by Henning Heiberg-Andersen (Uni Research) Although computationally expensive, Large Eddy Simulation (LES) has a range of well-known advantages compared to Planetary Boundary Layer (PBL) schemes on the mesoscale and Reynolds-Averaged Navier-Stokes (RANS) models on the microscale. The latter approaches have in common that they solve the equations for a ”mean flow field” and try to imitate all turbulent effects through various closure models. In LES, on the other hand, a filtered set of equations is solved for the large eddies that carry most of the energy, while the effect of the smaller, dissipative components are modeled. While the parameterization of the vertical mixing in the PBL schemes is based on assumptions appropiate for large scales only, the various LES subfilter models are not subject to such restrictions, and so high-resolution LES simulations of real cases can be carried out. On the finest scale relevant for wind energy, LES can resolve features of turbine wakes that are averaged out in the RANS models. Our program is to cover all scales of the unsteady offshore PBL, and we are currently validating the LES implementation of the Weather Research and Forecasting model (WRF) against data from the FINO1 mast, which is located ~45 km off the island Borkum by the German coast. A comparison between the 10 min averages of simulated wind speeds 100 m above the sea leavel and corresponding cup anemometer measurements for May 16’th and 17’th 2005 is shown in Figure 1. This year we will couple LES fields from WRF to a CFD code (OpenFOAM) run in LES mode, where wind turbines will be represented as actuator disks.

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Figure 1: Comparison between LES simulation and and cup anemometer data from the FINO1 mast 100 m above the sea surface. Both the data and the simulated curve are 10 min averages. (Courtesy of German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety by Project Manager Juelich)

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Use of data-analysis techniques in wind-energy forecasts by Alla Sapronova (Uni Research) The importance of reliable forecasts for wind energy can hardly be overestimated: the need for precise estimation over time spans ranging from a few seconds to the lifetime of wind farms is driven by economic interests and governmental regulations. The large volume of data collected from turbines calls for fast, reliable and efficient methods of information processing and knowledge building, for tasks varying from weather forecasting and single-turbine control to energy-market prediction. Biologically inspired computational-intelligence methods, e.g. machine-learning algorithms, are consequently being applied by turbine manufacturers, park owners and grid operators. In NORCOWE, R&D activities involving the application of computational-intelligence methods are led by Uni Research. In 2012, for example, an artificial neural network (ANN) was used to model wind speeds and wind-turbine energy yields using data supplied by Fraunhofer IWES, Germany (via a research collaboration with NORCOWE). As shown in the figure, forecasts of wind speeds measured by the turbine’s nacelle-mounted anemometer are within 5% of subsequently observed values.

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The neural-network development will continue in 2013 in collaboration with the University of Aalborg. The aim is to improve prediction of wind-speed changes on very short time scales, 0.1 s – 1 min ahead, for better turbine control.

Figure 1: Five minutes ahead forecasted (purple) and observed (dark blue) wind speed at a wind turbine

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PhD student Olav KrogsĂŚter

What is your scientific background? Cand.Scient. degree from Geophysical Institute, University of Bergen, 1999. From 2000 to 2010 weather forecaster at StormGeo. PhD-student at StormGeo and UoB from 2010. What topic is addressed in your PhD? The main topic is to get a better understanding of the Marine Atmospheric Boundary Layer (MABL), which directly affects the wind turbines. Very few studies have addressed this, except for short case studies. Here we have done simulations for two years. Both observations, the atmospheric model WRF, and the wave model SWAN are used.

of the power-law equation (which is used in the ICE-standard) to estimate wind speeds at different heights have seriously shortcomings. A completely new two-way coupled system between WRF and SWAN is carried out. This new model setup shows slightly improvements in the wind speed forecasting in the range of 5-13 m/s in the40 m - 100 m level, but stronger winds are reduced too much. More testing and tuning may improve the results also for higher wind speeds. Small changes were found regarding significant wave height.

What are you main results? Testing of WRF with five different Planetary Boundary Layer (PBL) schemes, compared with observations, reveals that today’s state-of-the-art mesoscale models still suffer from representing several important physical parameters in the MABL in a good way, e.g. vertical wind profiles, PBL-height and stability. Observations and simulations also show that the use page 24

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WP3 Design, installation and operation of offshore wind turbines by Charlotte Obhrai (UoS)

The WP 3 aims to reduce the challenges related to design, deployment and operation of wind turbines offshore in both shallow and deep waters. The increase in size of offshore wind farms will result in increased the costs for installation, intervention, maintenance and operation compared to land based wind farms and there is a need for new cost reducing technology to make offshore wind energy competitive without large subsidies. The work package is divided in the following 4 subtasks: WP 3.1 Farm operation and maintenance This subtask aims to develop new operation and maintenance strategies to ensure the integrity of the offshore wind farm and at the same time reduce the life cycle cost significantly. This includes four PhD projects, two of which are near completion and two relatively new projects. One of the projects underway at the University of Stavanger aims to identify solutions for an integrated work management system for planning, decision-making and execution together with effective operation infrastructure to lower the cost of energy in a safe and environmentally friendly manner.

Figure 1: Subtask 3.1.2 - outline of wind farm controller.

Research projects at Aalborg University have worked to establish reliability models for those components, which are important for operation and maintenance planning. Their research has so far has shown that wind turbine convertor systems have the highest failure rates according to the published summaries of failure rates/downtimes. They have therefore focused on reliability assessment methods for power electronic components used in WT’s convertor systems. At the University of Agder they are developing a data integration framework for offshore wind farms in order to support work activities offshore more effectively and enable data exchange between offshore wind partners. A demonstration version of the system is expected this year and more details can be found in page 37.

The new crane at the motion compensation laboratory at UoA

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WP3.2 Wind farm control and optimized operations The integrity of the wind turbines and optimal use of the wind resources require a well-designed control system. A floating turbine is even more challenging to the control system due to the large movements of the floater. The activities within this subtask aim at developing more robust and fault tolerant control systems than what is in common use today both for the single turbine and for wind farms. www.norcowe.no


NORCOWE Annual report 2012

WP3.3 Marine operations The cost of marine operations related to installation, intervention and decommissioning of offshore wind turbines are unreasonably high when using state-of-the-art conventional technology. There is therefore a need for new thinking to develop safe, but less costly technology and procedures for these operations. This subtask proposes and analyses new installation and intervention methods that reduces these costs. A new experimental laboratory at the University of Agder includes two motion platforms capable of simulations wave motions with up to six degrees of freedom (heave, surge, sway, roll, pitch and yaw). This new facility is being used to develop methods for heave compensated transfer of payloads dedicated to offshore wind turbines and investigate the use of commercial vehicle loader cranes for payload transfer. This will lead to an increased weather window for operations and reduce the dynamic loading on both structures and the actuation system (see page 30) . A PhD project at the University of Stavanger has looked at installation methodologies for a monopole which can be adopted by floating vessels. The main idea involves using a pre-installed subsea structure which supports the monopile temporarily while driving which keeps it isolated from the vessel motions. Using this methodology critical load cases have

A research project at the University of Agder has focussed on new control strategies for a variable speed and pitch offshore wind turbine system. The main control objectives are to alleviate transient loads affecting the tower and to regulate and smooth power production (see page 28). The purpose of another project at Aalborg University is to reduce fatigue and maximise power output not for a single turbine but at the wind farm level (Figure 1). Standard operation for wind farms has been to let all turbines produce as much power as they can. This project will address if a time varying power set point for turbines within a wind park can reduce fatigue and maximise power. A new project also at Aalborg University aims to improve the electrical system design methods for wind farms to minimise costs and improve energy production while meeting operational requirements for power systems. The project will develop methods to optimise system topologies and voltage levels for different power levels. Another important aspect will be to create a new design program that allows offshore wind developers to optimise system costs, power losses associated with cables and transformers as well as connections between wind farms and the electric grid. Understandig all forces acting on a floating wind turbine is imptant when designing the control system. page 26

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been identified and studied numerically to address feasibility aspects. A new project is planned for 2013 that will continue this work but focus on methods for integrated installation of wind turbines in water depths of around 50 m taking into account that the design should be fit for operations on complex foundation sites. WP3.4 Impact of improved metocean knowledge on loads and operation criteria Understanding and estimating the dynamic response of offshore wind turbines under various environmental and operating conditions is essential for design and operation of the turbines. This subtask aims at establishing simple as well as more advanced numerical models for studying the dynamic behaviour of offshore wind turbines with respect to improved metocean knowledge. This will be achieved by improving the aerodynamic load models and then investigating the fatigue life and energy production under variable offshore wind conditions.

tion of wave loads on jacket type wind turbine foundations installed on shoals and in other areas were breaking wave are expected to occur. The following NORCOWE research and industry partners have activities within this work package • University of Agder (UoA): Condition based Maintenance, Single turbine control systems, Remote operations, Marine operations. • University of Stavanger (UoS): WP3 management, Asset management, Marine operations and impact of improved metocean knowledge on loads and design criteria. • Aalborg University (AAU):Single turbine control systems, Reliability analysis of wind turbines.

NORCOWE will also participate in new large scale experimental tests on wind turbine foundations subjected to loads from breaking waves in the Large Wave Flume in Hannover this summer. The main goal of this project will be improved estima-

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Impacts of VSC-HVDC-based offshore wind power integration on power system transient stability by Hongzhi Liu (AAU)

The potential of offshore wind energy has been commonly recognized and explored globally. Many countries have implemented and planned offshore wind farms to meet their increasing electricity demands and public environmental appeals, especially in Europe. With relatively less space limitation, an offshore wind farm could have a capacity rating to hundreds of MWs or even GWs that is large enough to compete with conventional power plants. Thus it is very important to thoroughly study and understand the impacts of large-scale offshore wind power integration on power system operation and stability. The impacts of offshore wind power integration on interconnected power systems are various and complex, depending to a large extent on the level of wind power penetration, size of the offshore wind farm and electrical grid size, type of the transmission system, and grid configuration and network parameters. In this article, the study of the transient stability of a power system with offshore wind power integration through VSC-HVDC transmission (high voltage direct current transmission based on voltage source converters) provides an essential understanding towards those impacts. The singleline diagram of the power system with offshore wind power integration is presented in Fig. 1.

Figure 2: Voltage of Bus10 while the given fault occurring at L4-2 at different wind penetration levels

Dynamic voltage stability To investigate the dynamic behavior of grid voltages, a severe three-phase ground fault is simulated at 90% of the line L4-2 near Bus10. This fault lasts for 200 ms and is cleared by tripping L4-2. Two levels of wind power penetration are also studied: 270 MW and 450 MW, and their corresponding VSCHVDC rating are 300 MVA and 500 MVA respectively. Fig. 2 shows the dynamic voltage of Bus10 in the events of the given fault occurring at different wind penetration levels. It still can be seen that the higher the wind power penetration, the lower the voltage of Bus10 during before- and post-fault periods. During the fault period, the voltage profile is on the contrary (zoom portion). The highest voltage is observed during the fault period in the maximum wind power injection case, whereas the voltage is the lowest with no wind power. These distinct voltage profiles are caused by the fact that the receiving end converter (REC) of VSC-HVDC adopts a different control strategy during grid disturbances, which intends to sacrifice REC’s active power delivery and guarantee its reactive power support first. Obviously, a larger converter is able to provide a larger amount of reactive power and thus has better voltage support capability during grid faults as could be observed.

Figure 1. Diagram of the power system with offshore wind power integration via VSC-HVDC page 28

Transient angle stability Transient angle stability here is characterized by critical clearing time (CCT), which is defined as maximal fault duration for which the system remains synchronous operation. It highly depends on system configuration and network parameters. Wind power integration affects power flows in the power system as well as the operation of conventional synchronous generators.

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In the studied power grid described in Figure 1, G1 is set as the reference machine and the system loads are constant. As the power flow is affected by the wind integration, the loading levels of G2, G3 and G4 climb slightly together with an obvious increase in their rotor angles while the wind penetration level gets higher, whereas G1’s loading declines as its active power generation is offseted by wind power. To calculate CCT, three-phase short circuit fault has been simulated at different individual lines and been cleared afterwards by tripping the faulted line. It is observed that the integration of wind power into the power grid via VSC-HVDC results in weakened transient angle stability for most of the studied cases. However, the wind integration does exert a positive impact on transient angle stability while the given fault happens at L4-1 near Bus10. This benefits from the reactive power support capability of the REC as explained above. Summary With increasing penetration level, wind power plays a more important role in maintaining power system stability. The impacts of large-scale offshore wind power integration via VSC-HVDC on system transient stability has been investigated here. page 29

During grid disturbances, the bus voltage is higher with higher wind penetration. It is due to the independent active and reactive power controllability of VSC-HVDC link, the control strategy of the REC and the fact that higher wind injection brings higher rating converters that can provide more reactive power support. The analysis of transient angle stability is actually a case-bycase issue, which is strongly influenced by system configuration and network parameters. The wind power integration changes the system power flow, loadings of generators and lines, generators’ rotor angles etc. For the studied power grid in this paper, the transient angle stability generally becomes worsen with higher wind penetration. However, an improvement in transient angle stability has actually been achieved when the given fault occurs at the line close to PCC owing to the reactive power support by the REC of VSC-HVDC transmission system.

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Motion Compensation Laboratory by Geir Hovland (UoA) Access to measurement data for offshore wind energy research is of great benefit in areas such as climatology of met/ocean conditions as well as marine operations and asset management. However, performing experiments and measurements in offshore environments is both costly and timeconsuming. As an alternative to offshore measurements, NORCOWE and the University of Agder have invested in a motion compensation laboratory consisting of two Stewart platforms, a vehicle loader crane and 600 m2 new laboratory facilities. A Stewart platform is a 6-legged parallel kinematic machine which can generate motion in 6 degrees of freedom (X,Y,Z translational motion as well as roll, pitch, yaw rotations). The smallest Stewart platform with a payload capacity of 1500 kg has been operational since 2011. The extended laboratory including the large Stewart platform with a payload capacity of 8000 kg and the vehicle load crane will be made operational during 2013.

The new motion laboratory under construction at UoA, Campus Grimstad

The advantages of the motion compensation laboratory are many, including: • R epeatable measurements can be generated in a stable laboratory environment. • No risk of damage to equipment and/or personnel due to harsh weather conditions. • Ability to generate realistic motions of payloads similar to wave-induced motion of vessels. So far, the following projects have been using the equipment: • C omparison of measurements from two stationary LIDARs against measurements from two moving LIDARs. Project organized by CMR Instrumentation. • Experiments with heave-compensated crane motions by PhD student Magnus Berthelsen Kjelland. • Experiments with sensor calibration for unmanned aerial vehicles by PhD student Øyvind Magnussen. • Experiments with heave-compensation using a topmounted crown compensator. Project by Master Mechatronics students Atle Aalerud and Tomas Klevmo in collaboration with industry partner National Oilwell Varco. When the extended facility becomes operational in the second half of 2013, NORCOWE will encourage both internal and external partners to make use of the available research infrastructure.

Testing new motion compensation algoritms on a downscaled top-compesator using the small Stewart platform. Experiment in collaboration with National Oilwell Varco, Norway. page 30

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Photo: Asbjørn_Jensen

PhD student Lene Eliassen

What is your scientific background? I have my master degree in mechanical engineering from NTNU. My master thesis was an experimental study on fracture mechanics of carbon anodes used in the aluminium industry. After my master studies I worked as an installation engineer at Subsea 7, and in relation to the work I had some courses in hydrodynamics. What topic is addressed in your PhD? The topic addressed in my PhD is the dynamic analysis of offshore wind turbines. My studies include aerodynamic analysis, fatigue analysis and study of offshore turbulence. What are you main results? I have found that if the atmospheric stability offshore is included in the estimates of the fatigue, it has an effect on the life time of a wind turbine. The distribution of the atmospheric stability was estimated based on measurement from the FINO1 platform, and the parameters characterizing the atmospheric turbulence were used to simulate wind fields in a time domain simulation. It was found that including the atmospheric stability as a parameter decreased the life time compared to a simulation that only had a neutral atmospheric stability for the whole fatigue simulation.

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In another study I have looked into the vortex method. This is a method that can be used to model the aerodynamic loads on the wind turbines. The advantage of using this method is that it models the flow across the rotor more physically correct than the BEM method that is more commonly used. The disadvantage is long computational time, and difficulties to model viscous flow. In my studies I have shown how one can reduce the time of the computation by using the graphics card of the computer, instead of the cpu. I have also used a two dimensional version of the code to estimate the aerodynamic damping of a floating wind turbine.

A potential vortex method is applied to a wind turbine rotor modeled with two-dimensional airfoils in a cascade configuration

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PhD student Tore Bakka

What is your scientific background? I have a bachelor degree in Electrical Engineering from the University of Stavanger and a master degree in Mechatronics from the University of Agder. What topic is addressed in your PhD? This project focuses on multi-objective and multivariable control strategies for offshore wind turbine systems. The main focus is to keep the closed loop system stable and performing according to prescribed performance measures, under the influence of above rated wind speed conditions.

ler which is valid in a larger operating region. These problems have been solved both with and without parameter dependent Lyapunov matrices. Lately we have been investigating how to utilize LPV techniques together with constrained information systems. By constrained information systems, we mean that a gain matrix which is in accordance with the information constraints in the system needs to be calculated.

What are your main results? During the last three years several topics have been examined. One of the first topics to be examined, was how a bond graph model of a wind turbine system can help us to better understand how it works. After a while the topics became more control related. We have mostly been using the software FAST connected with Matlab/Simulink to test our control design. The control problems have been formulated in terms of linear matrix inequalities (LMIs). Some of the topics have involved constructing a linear parameter-varying (LPV) model of the wind turbine. This makes it possible to design a control-

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NORCOWE Annual report 2012

PhD student Erik Kostandyan

What is your scientific background? I have completed my MS in Industrial Engineering and Systems Management from American University of Armenian in 2004 and a Ph.D. in Industrial Engineering from Western Michigan University, 2010. What topic is addressed in your PhD? Wind turbines (WT) convertor systems have the highest failure rates according to the published summaries of failure rates/ downtimes for WT’s critical subsystems. Research in this task has therefore focused on reliability assessment methods for power electronic components used in WT’s convertor systems. Insulated gate bipolar transistors (IGBTs) are one of the critical components in WT’s power converter systems. Standard wire-bonded IGBT has a multi-layered structure made of materials with various CTEs (coefficients of thermal expansion) like silicone, solder, copper, ceramics, etc. WT power production is directly influenced by wind speeds, which define the IGBT’s mission profiles. During its operation, an IGBT faces power losses in switching of high voltage and current, which causes temperature fluctuations in all layers of IGBT. This research is focused on reliability assessment of the standard wire-bonded IGBTs for the particular mission profile. The IGBTs reliability estimation models have to be developed so that they have to serve as a basis for not only IGBTs but also WTs reliability-based operation and maintenance strategies development, by considering system reliability and convertor fault effect on structural components reliability.

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What are your main results? A probabilistic model for reliability estimation of power electronics component (IGBTs) used in WTs is developed based on stochastic modeling techniques from structural reliability. This probabilistic model is used as basis for reliability analyses. Based on wind and output power mission profiles, the IGBT junction temperatures profile is estimated. The thermal fatigue failure mode in Power Semiconductor Devices (IGBTs) for WT applications is investigated and modeled. A physics of failure model is developed for the solder cracking failure mode related to crack propagation in the silicon chip. The model is used to estimate the reliability using structural and classical reliability techniques. A general model is developed for the reliability of WTs structural components in case of fault of the convertor system. The theoretical basis is described for assessment of systems (with dependent components) reliability considering as examples fatigue failure of welded details in offshore WT substructures and bond wire lift-off failure in IGBT systems.

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NORCOWE Annual report 2012

What is your scientific background? I hold bachelor degree in Civil Engineering from Bengal Engineering and Science University, India, and master’s degree in Ocean Engineering from Indian Institute of Technology, Madras. During my master’s thesis, I have contributed in developing an in-house FEM code for nonlinear analysis of offshore structures. I have been working in the offshore oil and gas industry for several years, where I have mainly dealt with the design of offshore structures, and the lifting analysis of subsea structures.

Photo: E. Tønnesen

PhD student Arun Sarkar

What topic is addressed in your PhD? My PhD thesis is focused on developing new installation technologies for a monopile supported offshore wind turbine which can be more robust in terms of the allowable installation seastate compared to the existing technologies. Large wastage of offshore work time have taken place in various projects in the North Sea area during the installation phase, as the existing installation technologies are normally suitable for significant wave heights up to 1.5 m. In my work, I have developed new installation technologies (along with the required installation aids), which involves only floating systems, and showed their potential to carry out the marine operation at a higher operating seastate. What are you main results? The overall concept used in my work is to install an offshore wind turbine as two separate modules, which are: a monopile, and a fully integrated upper structure (FIUS). A general arrangement for a FIUS, suitable for the proposed installation approach, is developed by incorporating an existing patented idea of using a telescopic tower, and keeping the blades orientated in a horizontal plane above the nacelle. The concept of an installation aid used in the methodologies, which is termed as SSIP structure, is also developed. The SSIP is essentially a floatable frame structure, fitted with a hull at the top, so that

it can be towed to the site and placed on the seabed. During a monopile installation, the SSIP provides temporary support to the monopile, i.e., it helps to keep the monopile isolated from the motions of the floating vessel. Afterwards, the SSIP is used to carry a FIUS to the site and to install it over a foundation by the float-over-pulling (FOP) method. The critical load cases appearing in the installation methodologies are identified and numerically studied. The results show the on-site technical feasibility of the installation methodologies for using them to install an offshore wind turbine at a significant wave height of 2.5 m.

SSIP installing a monopole (left) and a FIUS by FOP method (right) page 34

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NORCOWE Annual report 2012

PhD student Hongzhi Liu

What is your background? I received the B.Eng. from Taiyuan University of Technology, China, in 2000 and the M.Sc. from Northwestern Polytechnical University, China, in 2004, both in electrical engineering. After working in industry in China for a few years, I went to Australia in 2007 and got the M.Phil. in information technology from The University of Queensland in 2009. What topic is addressed in your PhD? The topic of my PhD is “Grid Integration of Offshore Wind Farms�. This work investigates the electrical characteristics of offshore wind farms and the associated connection systems. The work is mainly focused on key technical issues of grid integration of large-scale offshore wind farms, such as grid security and stability with high wind power penetration. The interaction between large-scale offshore wind farms and power systems as well as the steady-state and transient impact of large-scale wind power integration are studied and analysed in terms of grid stability, voltage control, frequency regulation etc.

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What are your main results? This research develops an understanding of the impact of large-scale offshore wind farms integration through VSCHVDC link (high voltage direct current transmission based on voltage source converters) on power transmission system reliability and performance. The supporting capability of VSCHVDC to the grid would reduce the negative impact on system voltage stability caused by high-penetration offshore wind power. Frequency regulations of wind turbines could effectively improve grid frequency excursion and the rate of change of frequency. The VSC-HVDC link could also provide limited frequency support with appropriate controls.

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NORCOWE Annual report 2012

PhD student Søren Christiansen

What is your scientific background? I graduated from Aalborg University with a master in electronic engineering within the field of automation and control. The topic of my master thesis was adaptive control of a hydraulic blade pitch actuator for wind turbines. The project was proposed by Vestas Wind Systems, who later employed me as a wind turbine control engineer. What topic is addressed in your PhD? In my PhD I have addressed the control of a floating wind turbine exposed to wind and waves. A new control system designed for floating wind turbines is required since using conventional onshore control on floating wind turbines causes negative damping in the fore—aft tower motion. Furthermore, a floating wind turbine is subject to not only aerodynamics and wind induced loads, but also to hydrodynamics and wave induced loads. In contrast to a bottom fixed wind turbine, the floating structure, the hydrodynamics and the loads change the dynamic behavior of a floating wind turbine.

is estimated using an extended Kalman filter and the wave frequency, by an auto–regressive filter. To address the problem of negative damped fore–aft tower motion, additional control loops are suggested which stabilize the response of the onshore controller and reduce the impact of the wave induced loads. This research is then extended to model predictive control, to further address wave disturbances. A dynamic model of the undisturbed closed–loop system is used as a reference for the disturbed system within a framework based on model predictive control.

What are you main results? A time varying control model is presented based on the wind speed and wave frequency. Estimates of the wind speed and wave frequency are used as scheduling variables in a gain scheduled linear quadratic controller to improve the electrical power production while reducing fatigue. The wind speed page 36

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NORCOWE Annual report 2012

PhD student Trinh Nguyen

What is your scientific background? I received the specialist’s diploma in software engineering from Tomsk Polytechnic University, Russia in 2009. After that I spent 10 months at University of Trento, Italy where I worked as a research assistant. I started my PhD program in ICT at University of Agder in December 2010. During my PhD study, I was a visiting scholar at Georgia Institute of Technology, USA in 2012. My interests include data and knowledge management, business processes modeling and data modeling. What topic is addressed in your PhD? With more data available, it is possible to make better decisions, and thereby improve the recovery rates and reduce the operational costs. Besides, capturing failure data can help to analyze reliability of wind turbines using statistical methods. However, many partners and systems use their own applications and data formats. Hence, it is hard to enable data exchange and integration. Besides, many actors are reluctant to share data about their equipment, or to let third parties collect such data. Additionally, the process of agreement on data exchange only happens at the end of the development when the partners encounter integration problems with other partners. This process is time-consuming. Therefore, better ways to make data available and accessible would be desirable.

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In my PhD, I am looking for answers to the following questions: • How to connect between concepts, their properties, and relations in the offshore wind domain? • How can wind farm operators manage the fact that data comes from different sources with different formats? • Data sources are considered as autonomous, distributed and heterogeneous systems. How to manage, integrate, and unify them systematically? • How to solve semantic inconsistency which has become a problem for the explicit information or knowledge sharing among users or applications? • What are you main results? We have proposed a framework based on semantic technologies to overcome data integration challenges. The framework allows integrating and sharing a huge amount of data. In addition, we have developed an ontology which manages offshore wind metadata, enables knowledge sharing and data exchange in a semantic way.

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NORCOWE Annual report 2012

Associated projects

Gwind verification project – Status February, 2013 by Arnfinn Nergaard (UoS) The Gwind verification project started January 2012 and will run until the end of 2013. It is managed by TTO office Prekubator with Simen Malmin as project manager. The project is supported by the Norwegian Research Council through the FORNY-program with about 2.5 mill. NOK. CMR Prototech and University of Stavanger are partners in executing the project. The project is based on the patented gyrostabilized Vertical Axis Wind Turbine. The verification project has two main objectives; 1) to technically verify the effect of gyroscopic forces and 2) to perform early stage commercialization activities. Figure 1 shows an artistic impression of the Gwind concept.

A main activity in 2012 was performing scale model tank tests for a cylindrical hull, a spar type platform, in the towing tank at Bergen University College (HiB)

Figure 2: Results from testing the effect of the gyroscopic force on the overall pitch motion

Figure 1: Illustration of the Gwind project

The model was equipped with two small commercial gyros mounted inside the hull. The key objective was to verify the damping effect of the gyros. The model was exposed to a number of tests to determine natural frequencies of pitch, roll and heave and motion response from wave impact with gyros inactive and active.

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The tests were concluded successfully late October, 2012 with results verifying the effect of the gyroscopic force suppressing overall pitch motion, see Figure 2. As can be seen; in this case the gyro-effect practically eliminates the excessive motion that was experienced at excitation forces around the natural frequencies. The natural frequency resonance cannot even be identified in the case with active gyros, see the green triangles. The peak amplitude is reduced with about 80%. As a next step, Prekubator has acquired a commercial 1000 W turbine that shortly will be installed on a 3 m deep spar floater to be tested in the fjord during 2013. Independent of the gyroscopic effect it has been shown that the size of the hull may be reduced by some 20 % compared to a HAWT (horizontal axis wind turbine) due to the effect of moving loads (nacelle and gear) down below sea level. www.norcowe.no


NORCOWE Annual report 2012

Decision support for installation of offshore wind turbines by Yngve Heggelund (CMR Computing) Offshore operations such as the installation, maintenance, and repairs of equipment are complex and to a high degree weather sensitive. Operations are often carried out by specialized ships which are hired for a given time period. Waiting for weather windows for carrying out weather-sensitive phases of these operations (e.g. transportation, mooring, crane operations, etc.) is therefore very costly. The decision criteria used to commence operations are today related to simple parameters such as significant wave height and average wind velocity at a reference height. The actual limitations of the operations are however the physical limitations of the equipment used and come from the responses to the weather conditions (e.g. motions, accelerations, and forces). Installation of offshore wind turbines is an example where the present cost must be reduced to make the offshore wind industry competitive. To address this issue, partners in NORCOWE will combine their competences in a project funded by the Research Council of Norway and Statoil. The project is titled “Decision support for installation of offshore wind turbines� and is a 3-year competence building project (KPN) starting in 2013. The research partners are Uni Research, met.no, Aalborg University, MARINTEK, University of Bergen, and Christian Michelsen Research. Additionally, the universities of Stavanger and Agder will contribute master students on relevant topics.

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The project will develop methods for decision support which are based on real physical limitations of the equipment being used. A second contribution is taking uncertainties into account in the decision making. Uncertainties constitute an important aspect of weather-dependent data. Weather uncertainties will be transformed to uncertainties in equipment response. These uncertainties will be utilized in the decision support where the risks and consequences of failed operations are taken into account, enabling a risk based decision support. More specifically, local weather forecasts will be coupled with advanced dynamical models of the operations considered. Local weather forecasts will be improved with estimates of uncertainty based on improved capabilities of an ensemble prediction system, deterministic models and local measurements. The phases of selected operations will be described so that durations, dependencies and points of no return are identified. The cost of failed operations will be estimated so that the probabilities and consequences of exceeding critical levels for the response can be taken into account in the decision making. The anticipated final outcome is a prototype decision support system integrating the derived results and presenting them to the operation planners.

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NORCOWE Annual report 2012

Completed PhDs Local and Mesoscale Atmospheric Impacts of Wind Farms Anna C. Fitch, UoB, defended her thesis in August 2012.

Wind Farms: Modeling and Control

Maryam Soleimanzadeh ,AAU, defended her thesis in February 2012. About her work The primary purpose of this work has been to develop control algorithms for wind farms to optimize power production and augment the lifetime of wind turbines. A dynamical model has been developed for the wind flow in wind farms, based on the linearized Navier-Stokes equation combined with momentum theory. The model provides an approximate knowledge of what is happening downstream of a wind farm, and is represented in the form of ordinary differential equations to be applied in classic control algorithms. The wind farm control algorithms provide the power reference signal for each wind turbine of the farm such that the farm power set point is followed and also the structural load on wind turbines is minimized.

Impact of wind turbines on the wind speed and turbulence levels in the lower atmosphere can be observed several kilometers downwind from the wind farm

About her work: The rapid development of wind farms across the world has led to questions regarding their potential impacts on the environment. Wind farms extract energy from the wind to produce electricity. This extraction of energy may have the potential to impact the local weather and climate. Furthermore, the impact of wind farms on the atmosphere can in turn feed back onto the operation of wind farms, affecting the efficiency of power production, as has been observed in large wind farms. This work explores the interaction between large wind farms and the atmosphere, through developing a new computer model to represent the influence of wind farms on the atmosphere. Simulations of a large wind farm covering 10x10 km, similar in scale to the current largest offshore wind farms, show impacts on wind speed and turbulence, in both onshore and offshore cases. An impact is seen not only on the local wind, but also at distances of tens of kilometres downwind, at night, in the onshore case. There are major differences between daytime and night-time in the strength and structure of the wind farm wake. These differences in the wake in turn affect the power output of downwind wind turbines. The enhanced turbulence within the wind farm causes a very small change in temperature. The near-surface temperature change is found to be smaller than in previous climate model studies, with a maximum increase of 0.5 K at night. Little temperature change is seen during the day. Downwind, the temperature change is negligible. Current approaches for representing wind farms in climate models are found to be inappropriate and generally exaggerate the wind farm impacts seen. More sophisticated models such as the one developed in this work should be used instead. page 40

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NORCOWE Annual report 2012

NORCOWE Summer School The third NORCOWE Summer School “Wind Power Engineering” was held August 20-24 2012, at Skagen, Denmark. A total of 26 participants and lecturers attended, including eight guests from Statoil’s research department. The learning objectives for the summer school were: • Understand industry standard control systems that govern the energy capture • Understand the basics of operation and maintenance • Understand the most important grid integration problems addressed when designing wind farms • Understand fundamental issue in marine operations

Hovland (UoA) and Michael Rygaard Hansen (UoA). In addition to presentations by the organizers, presentations were given by other specialists from science and industry in the area. All students also presented a poster or made a pitch for their own work, and the programme included also a highly successful visit to Siemens Blades in Aalborg. Looking ahead, the 4th NORCOWE Summer School will be held at Preikestolen Fjellstue, Norway, August 26-30 2013. The school will address various aspects of geophysical and structural data. Analyses methods will be presented and the use of observations to validate and verify models will be discussed.

Each of these four topics included 3 hours of lectures and 3 hours of teamwork problems. Organizers were Thomas Bak (AAU), John Dalsgaard Sørensen (AAU), Zhe Chen (AAU), Geir

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NORCOWE Annual report 2012

International cooperation The international focus has been strengthened in NORCOWE during 2012. MoU NORCOWE has now MoU with DTU Wind, Fraunhofer IWES and The National Renewable Energy Lab (NREL) in USA. The agreement (MoU) with NREL was signed in March 2012. Scientific cooperation NORCOWE partners have scientific cooperation with a wide range of international research institutions, e.g. University of Strathclyde, Georgia Institute of Technology (USA), German Wind Energy Institute (DEWI), Leibniz Institute for Baltic Sea Research Warnem端nde, NUI Galway, Woods Hole Oceanographic Institution (WHOI), University of Connecticut, Klaipeda University (Lithuana), Stockholm University, Universitat Politecnica de Catalunya (UPC), University of Bremen, DTU Wind, National Centre for Atmospheric Research (NCAR) and Nelson Mandela University (NMU), Port Elizabeth, South Africa. NORCOWE and Fraunhofer IWES organized a joint workshop on meteorology and oceanography for offshore wind farms in Bergen 18th September. Topics for future cooperation were identified and we expect to see joint NORCOWE/Fraunhofer IWES projects as a result of the workshop. Cooperation with Fraunhofer IWES resulted in access to data sets from the Norderland wind farm for use in nowcasting.

have a deep insight in wind turbine modelling. PhD students Lene Eliassen and Tore Bakka have stayed at NREL for some months in 2012. UoS will do testing in the Large Wave Flume (GFD) in Hannover of wind turbine jacket foundation exposed to wave slamming loads during spring 2013. Standardization committees and international bodies AAU and UoS take part in three standardization groups: 1. Maintenance group for revision of IEC 61400-1: 2005: Wind turbines - Part 1: Design requirements 2. Maintenance group for revision of IEC 61400-3: 2009: Design requirements for offshore wind turbines 3. Project team for new wind turbine standard IEC 614006: Wind Turbines: Tower and foundation design NORCOWE partners participate in three IEA wind tasks: 1. IEA Wind Task 31- WakeBench: Benchmarking of wind farm flow models 2. IEA Wind Task 32 - LIDAR: Wind LIDAR Systems for Wind Energy Deployment 3. IEA Wind Task 33 - Reliability Data - Standardization of data collection for wind turbine reliability and operation & maintenance analyses NORCOWE partners are active in international bodies like EERA Wind, EWEA, TP Wind and EU projects.

The National Renewable Energy Lab (NREL) is natural to collaborate with because they put a large emphasis on issues related to coupling meso- and micro scale problems. They also

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NORCOWE Annual report 2012

Public outreach NORCOWE has two annual scientific meetings. The spring meeting in 2012 was held at UoA May 7-9 and included a guided tour at the motion laboratory. NORCOWE days took place in Bergen September 18-20. Arena NOW and NORCOWE organized two joint conferences (Science meets industry) in 2012. There will be similar conferences in 2013 (April 17 in Stavanger and September 10 in Bergen).

NORCOWE was presented at the large Japanese renewable conference RE2012 in Tokyo. There is a NORCOWE newsletter, with 4-6 issues a year. Please send an email to post(at)norcowe.no to subscribe to the newsletter. An overview over scientific papers is given in Appendix.

An international workshop on “Predictive modeling and machine learning for renewable energy� was held on October 1-2, 2012 in Bergen, Norway.

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NORCOWE Annual report 2012

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NORCOWE Annual report 2012

Appedix

Board and Committees 31.12.2012

Board members

Anne Marie M. Seterlund (Statkraft), Gudmund Olsen (Statoil), Odd Henning Abrahamsen (Lyse Produksjon), Even Landsem (Aker Solutions), Rolf Hørsdal (National Oilwell Varco), Frank Reichert (University of Agder), Bjørn H Hjertager (University of Stavanger), John Dalsgaard Sørensen (Aalborg University), Peter M. Haugan (University of Bergen).

International (external, advisory) Scientific Committee Bill Leithead (University of Stratchlyde), Detlev Heinemann (University of Oldenburg), Line Gulstad (Vestas), Cecilie Kvamme (Institute of Marine Research), Trond Kvamsdal (SINTEF).

Internal Scientific Committee (main task: Education, in particular PhD)

Angus Graham (Uni Research), Birgitte Furevik (Met.no), Finn Gunnar Nielsen (Statoil/University of Bergen), Geir Hovland (University of Agder), Jasna Bogunović Jakobsen (University of Stavanger), Kristin Guldbrandsen Frøysa (Christian Michelsen Research), Paul Skeie (Storm Geo), Thomas Bak (Aalborg University).

Equipment list Equipment

Manufacturer

In use at

Stewart platform (small)

Bosh-Rexroth

University of Agder

Sonic Anemometers (2 pcs)

University of Bergen

Field computer

University of Bergen

Oceanographic turbulence equipment Rockland Scientific (Moored Autonomus Turbulence System, MATS)

University of Bergen

Aquadopp 1 MHz

NORTEK

University of Bergen

3D LIDAR Anemometer (Windcube 100S) Leosphere

University of Bergen

E-Motion 8-ton Stewart Platform

Bosh-Rexroth

University of Agder

Scientific camera

Kipp & Zonen, Campbell Scientific

University of Bergen

LIDAR Anemometer (Windcube V1)

Leosphere

University of Bergen

UiS structural monitoring instruments

Canterbury Seismic Instruments

University of Stavanger

UiS meteorological instruments

Gill, Vaisala, RM Young

University of Stavanger

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NORCOWE Annual report 2012

Scientific staff Key Researchers Name

Institution

Main research area

Bak

Thomas

Aalborg University

Control systems

Chen

Zhe

Aalborg University

Power system integration

Knudsen

Torben

Aalborg University

Control Engineering

Sørensen

John Dalsgaard

Aalborg University

Reliability & OM

Anfinsen

Stian

CMR Computing

Data management

Heggelund

Yngve

CMR Computing

Model reduction, decision support

Jarvis

Chad

CMR Computing

Model reduction

Magnus

Ingolf

CMR Computing

Data management, decision support system

Brun

Knut-Erland

CMR Energy

Centre Coordinator

Frøysa

Kristin Guldbrandsen

CMR Energy

Centre Director

Khalil

Marwan

CMR GexCon

CFD Turbulence modelling, Atmospheric flow, High-performance computing

Skjold

Trygve

CMR GexCon

Computational fluid dynamics

Sælen

Lene

CMR Gexcon

CFD for wind farm modelling

Hallanger

Anders

CMR Instrumentation

Computional Fluid Dynamics (CFD)

Kippersund

Remi A.

CMR Instrumentation

Measurements technology

Lohne

Kjetil Daae

CMR Instrumentation

Measurements technology

Sand

Ivar Øyvind

CMR Instrumentation

CFD for wind turbine modelling

Svardal

Benny

CMR Instrumentation

Measurements technology

Hanssen

Thomas

CMR Prototech

Wind Power Technology

Prakash

Ram

CMR Prototech

Wind Power Technology

Friisø

Trond

Origo Solutions

Condition based maintenance

Østhus

Karl Tore

Origo Solutions

Condition based maintenance

Hauge

Gard

StormGeo

Met/oecean conditions

Skeie

Paul

StormGeo

Met/oecean conditions

Winther

Nina

StormGeo

Met/oecean conditions

Adakudlu

Muralidhar

Uni Research

Meteorology

Alvesen

Helge

Uni Research

Wave modelling

Barstad

Idar

Uni Research

Mesoscale meteorology

Graham

Angus

Uni Research

Small scale oceanography

Heigberg-Andersen

Henning

Uni Research

LES (Large Eddy Simulation)

Lorenz

Torge

Uni Research

Mesoscale meteorological modelling and reserach

Mesquita

Michel

Uni Research

Large-scale meteorology

Sapronova

Alla

Uni Research

Artificial intelligence (AI)

Jenkins

Alastair

Uni Research /University of Bergen

Air sea interaction

Dahlgren

Thomas

Uni Research

Environment

Beyer

Hans-Georg

University of Agder

Energy Meterology

Hansen

Michael Rygaard

University of Agder

Marine Operations, Heave compensation and hydraulic systems

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NORCOWE Annual report 2012

Hovland

Geir

University of Agder

Condition monitoring, Asset Management, Marine Operations

Karimi

Hamid Reza

University of Agder

Turbine Control

Prinz

Andreas

University of Agder

Remote Operations

Reuder

Joachim

University of Bergen and Atmospheric boundary layer research Christian Michelsen Research

Nielsen

Finn Gunnar

University of Bergen and Statoil

Offshore wind turbines, dynamic response

Fer

Ilker

University of Bergen

Oceanic turbulence

Haugan

Peter M.

University of Bergen

Oceanography and offshore wind energy

Gudmestad

Ove T

University of Stavanger

Marine operations, marine technology

Jakobsen

Jasna Bogunovic

University of Stavanger

Dynamic analysis of OWT, Offshore structures

Langen

Ivar

University of Stavanger

Work package management, Engineering Mechanics

Liyanage

Jayantha

University of Stavanger

Asset management, operations and maintenance

Nergaard

Arnfinn

University of Stavanger

Design optimization, new concepts, Design of floating OWT, Subsea technology

Obhrai

Charlotte

University of Stavanger

Mathematics, meteorology and hydrodynamics

Postdoctoral researchers Name

Nationality

Period

Sex M/F

Topic

Severson    

Henning

Norwegian

2011-2012

M

Development and qualification of VAWT

Kettle

Anthony

British

2011-2015

M

Atmospheric turbulence and air-sea interaction

Tabatabaeipour

Seyed Mojtaba

Iranian

2011-2012

M

Fault tolerant control of wind turbine

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NORCOWE Annual report 2012

PhD students with financial support from the Centre budget Name

Nationality

Period

Sex M/F

Topic

Aarnes

Ole Johan

Norwegian

2008 - 2012

M

Oceanography

Bakhoday

Mostafa

Iranian

2010 - 2014

M

Experimental characterization of turbulence in the the oceanic mixed layer

Christiansen

Søren

Danish

2009 - 2012 M

Control of Floating wind turbine installation

Nguyen

Trinh H

Vietnamese

2010-2013

M

Model-based operation and maintenance for offshore wind

Sarkar

Arunjyoti

Indian

2010 - 2013

M

Marine operations

Kjelland

Magnus

Norwegian

2011-2014

M

Marine operations

Kostandyan

Erik

Armenian

2011-2014

M

Reliability of Wind Turbines

Liu

Hongzhi

Chinese

2010 - 2013

M

Gird Integration of Offshore Wind farms

PhD students working on projects in the centre with financial support from other sources Name

Funding

Nationality

Period

Sex M/F

Topic

Bakka

Tore

Ministry of education and research

Norway

2010 - 2013

M

Turbine Control

Eliassen

Lene

UoS

Norwegian

2010 - 2013

F

Dynamic analysis of floating OWT

Flügge

Martin

UoB

German

2010 - 2013

M

Experimental characterization of the marine atmospheric boundary layer

Kalvig

Siri M

RCN/StormGeo Norwegian

2010 - 2014

F

Energy forecast for Offshore wind farms

Krogsæter

Olav

RCN/StormGeo Norwegian

2010 - 2012

M

Validation and improvement of surface and boundary layer parameterization schemes for the marine atmospheric boundary layer

Kumer

Valerie

BKK/UoB

Austrian

2012 - 2015

F

Analysis LIDAR wind measurements and the potential of LIDAR measurements for investigations of wind turbine wakes

Endrerud

Ole-Erik Vestøl

UoS

Norwegian

2012 - 2015

M

Application of best engineering asset management practices from the O&G industry on the wind energy sector.

Completed PhDs Name

Institution

Topic

Soleimanzadeh

Maryam

AAU

Wind Farms - Modeling and Control

Fitch

Anna Camilla

UoB

Local and Mesoscale Atmospheric Impacts of Wind Farms

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NORCOWE Annual report 2012

Master Students (ongoing by november 2012) Name

Funding

Sex M/F

Topic

Christakos

Konstantinos

UoB

M

Characterization of the costal marine atmospheric boundary layer (MABL) for wind energy applications

Båserud

Line

UoB

F

Turbulence measurements with the MicroUAS SUMO

Olsson

Hans Martin

UoA

M

An asymmetric probability distribution for wind turbines

Skogstad

Joachim Gahrsen

UoA

M

IT Infrastructure for Condition-Based Maintenance

Jamtveit

Øystein

UoA

M

IT Infrastructure for Condition-Based Maintenance

Master Students Spring 2012 (AAU, HiB/CMR, UoS, 30 ECTs) Name

Funding

Sex M/F

Topic

Gudmundsen

Gunnar-Martin

UoS

M

Analysis of jacket structures for offshore wind turbines (OC4 wind turbine)

Mirza

Delsher

UoS

M

The effect of turbulence models on fatigue life (OC4 wind turbine)

Stava

Ole Magnus

UoS

M

The effect of wind profiles on fatigue life

Yuxiong

Lun

UoS

M

Analysis of an offshore floating wind turbine

Tangvald

Bjørn

UoS

M

Evaluation of methods to corrected stable offshore wind profiles using data from FINO 3

Olsen

Elin

UoS

F

Utmatting av vindturbin fundamenter på land (HøgJæren vindpark)

Torp

Birgitte

UoS

F

Analyse av vindmøllefundament

Madland

Stig

UoS

M

Dynamic analysUoS for installation of wind mill foundation

Korovkin

Pavel

UoS

M

Structural element for support during wind turbine foundation installation

Kverneland

Richard

UoS

M

Wind Energy; CFD simulation of wind-wave interactions

Andersen

Jan Terje

UoS

M

Use of wavelet analysis for identification of stiffness degradation in wind turbine blades

Engelsen

Christine

HiB/CMR

F

Samspill og kunnskapsflyt i NORCOWE

Rasmussen

Jens Saugmann

AAU

M

Reliability and Risk Analysis of Offshore Wind Turbines

Jensen

Rasmus Neigaard AAU Lund

M

Reliability and Risk Analysis of Offshore Wind Turbines

Poulsen

Anders S.

AAU

M

Probabilistic Design Of Gravity Based Foundations

Randers

Mads B.

AAU

M

Probabilistic Design Of Gravity Based Foundations

Sørensen

Torben

AAU

M

Probabilistic Design Of Gravity Based Foundations

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NORCOWE Annual report 2012

Publications and reports 2012 Scientific publications and conference papers Frøysa, Haugan and Nielsen (2012), The Norwegian Centre for Offshore Wind Energy (NORCOWE), OCEANS 2012 Yeosu (conference paper) Bakhoday Paskyabi, Fer, Jenkins (2012), Surface gravity wave effects on the upper ocean boundary layer: modification of a onedimensional vertical mixing model. Continental Shelf Research 38:63-78, 2012. Jenkins, Bakhoday Paskyabi, Fer, Gupta, Adakudlu (2012), Modelling the effect of ocean waves on the atmospheric and ocean boundary layers. Energy Procedia 24, 166-175, 2012 Barstad, I., Sorteberg, A. and Mesquita, M. dS. 2012. Present and future wind power potential in Northern Europe based on downscaled global climate runs with adjusted SST and sea-ice cover. J. Renewable Energy, 44, 398-405. Fitch, A., C., Olson, J. B., LundqUoSt, J. K., Dudhia, J., Gupta, A. K., Michalakes, J. and Barstad, I. 2012. Local and mesoscale impacts of wind farms as parameterised in a mesoscale NWP model. Month. Weather Rev., 140, 3017-3038. Barstad, I. and Jenkins, A. D. 2012. Challenges in modelling offshore wind – How to address them using observations. Modern Energy Rev., 4. Eliassen, L., Jakobsen, J.B. and Obhrai C. (2012), Offshore wind profile and fatigue life of offshore wind turbines, The Proceedings of The Twenty-second (2012) International Offshore and Polar Engineering Conference, Rhodes, Greece, June 17-22, Vols. 1-4: 330336, ISBN 978-1 880653 94-4 Eliassen, L., Knauer, A., Nielsen, F.G., and Jakobsen, J.B. (2012), Cascade Analysis of a Floating Wind Turbine, EAWE: Science of Making Torque Conference, Oldenburg, Oct 9-11. N. Nikitas, J.H.G. Macdonald, J.B. Jakobsen, T.L. Andersen (2012), Critical Reynolds number and galloping instabilities – Experiments on circular cylinders, Experiment in Fluids, 52: 1295-1306. J.B. Jakobsen, T.L. Andersen, J.H.G. Macdonald, N. Nikitas, G.L.L. Larose, M. G.Savage, B. R. McAuliffe (2012), Wind-induced response and excitation characteristics of an inclined cable model in the critical Reynolds number range, Journal of Wind Engineering & Industrial Aerodynamics, in press, http://dx.doi.org/10.1016/j.jweia.2012.04.025. O. Mikkelsen, J.B. Jakobsen (2012), Buffeting and aeroelastic response analysis of a long-span suspension bridge in time-domain, paper for the 10th UK Conference on Wind Engineering, Southampton, September 10-12. Tiusanen, R, Jännes,J and Liyanage, JP (2012) RAMSI management model and evaluation criteria for NORDIC offshore wind assets, VVT Technology 47 Tiusanen, R, Jännes,J and Liyanage, JP (2012) “ Identification and evaluation of RAMS+I factors affecting the value-added by different offshore wind turbine concepts in Nordic context “, Paper to be presented at ISOPE2012, Rhodes, Greece, June 17-22 Choux,M, Tyapin, I and Hovland, G,(2012) “Extended Friction Model of a Hydraulic Actuated System”, Annual Reliability and Maintainability Symposium (RAMS2012), Nevada, USA, Jan 23-26 2012. Choux,M, Tyapin, I and Hovland, G,(2012) “Leakage-Detection in Blade Pitch Control Systems for Wind Turbines”, Annual Reliability and Maintainability Symposium (RAMS2012), Nevada, USA, Jan 23-26 2012. Kostandyan, E.E. and Sørensen, JD (2012) “Reliability of Wind Turbine Components-Solder Elements Fatigue Failure”. Annual Reliability and Maintainability Symposium (RAMS2012), Jan 23-26 2012. Kostandyan, E.E. & J.D. Sørensen (2012): “Physics of Failure as a Basis for Solder Elements Reliability Assessment in Wind Turbines”. Accepted for Reliability Engineering & System Safety Kostandyan, E.E. & J.D. Sørensen (2012): “Weibull Parameters Estimation Based on Physics of Failure Model” to be presented at Industrial and Systems Engineering Research Conference, ISERC 2012,. Kostandyan, E. E. & K. Ma (2012) “Reliability Estimation with Uncertainties Consideration for High Power IGBTs in 2.3 MW Wind Turbine Convertor System” submitted to the European Symposium on Reliability of Electron Devices, Failure Physics and Analysis, ESREF 2012. page 50

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NORCOWE Annual report 2012

Kostandyan E.E., Sørensen J.D., (2012), Structural Reliability Methods for Wind Power Converter System Component Reliability Assessment, Proceedings on the 16th IFIP WG 7.5 Conference on Reliability and Optimization of Structural Systems, Yerevan, Armenia (in press). S. Christiansen, T. Bak, and T. Knudsen, “Damping wind and wave loads on a floating wind turbine,” IEEE Transactions on Control Systems Technology - submitted, 2012. S. Christiansen, T. Bak, and T. Knudsen, “Minimum thrust load control for floating wind turbine,” IEEE Multi-Conference on Systems and Control, 2012. S. Christiansen, T. Knudsen, and T. Bak, “Extended onshore control of a floating wind turbine with wave disturbance reduction”, The Science of Making Torque from Wind - submitted, 2012. S. Christiansen, S. M. Tabatabaeipour, T. Bak and T. Knudsen, Wave Disturbance Reduction of a Floating Wind Turbine Using a Reference Model–based Predictive Control. Submitted to ACC 2013. Tabatabaeipour, S. M., Odgaard, P. F., Bak, T. (2012) Fault detection of a benchmark wind turbine using internval analysis. In Proceedings of American Control Conference, pages 4387–4392. Tabatabaeipour, S. M., Stoustrup, J. and Bak, T. (2012) Control reconfiguration of linear parameter varying systems using virtual actuator and sensors. Accepted for presentation at Safeprocess, August, Mexico City, Mexico. Rosa, P., Casau, P., Silvestre, P., Tabatabaeipour, S. M. and Stoustrup, J. (2012) A set valued approach to FDI and FTC: Theory and implementation issues. Accepted for Presentation at Safeprocess, August, Mexico City, Mexico. Casau, P., Rosa, P. Tabatabaeipour, S. M., Silvestre, P. and Stoustrup, J. (2012) Fault detection and fault tolerant control of wind turbines using set values observers. Accepted for presentation at Safeprocess, August, Mexico City, Mexico. Tabatabaeipour, S. M., Odgaard, P.F., Bak, T., Stoustrup, J. (2012) Fault detection of wind turbine with uncertain parameters: A setmembership approach, Energies, 5(7):2224–2248. Tabatabaeipour, S. M. (2012) Active fault detection and isolation: a set-membership approach. Submitted to International Journal of Systems Science. T. Bakka, H.R. Karimi and N.A. Duffie, “Gain Scheduling for Output H∞ Control of Offshore Wind Turbine”, ISOPE 2012 – The 22nd International Offshore (Ocean) and Polar Engineering Conference & Exhibition, Greece, June 17−22, 2012. T. Bakka, H.R. Karimi, “Mixed H2/H∞ Control Design for Wind Turbine Systems with Pole Placement Constraints”, Proceedings of the 31st Chinese Control Conference, July 25-27, 2012, Hefei, China, p. 4775-4780. T. Bakka, H.R. Karimi, “Robust Output Feedback H∞ Control Synthesis with Pole Placement for Offshore Wind Turbine Systems: An LMI Approach”, accepted and to be presented at the IEEE Multi-conference on Systems and Control, October 3-5 2012. T. Bakka, H.R. Karimi, Robust H∞ Dynamic Output Feedback Control Synthesis with Pole Placement Constraints for Offshore Wind Turbine Systems, submitted to Mathematical Problems in Engineering. T. Bakka, H.R. Karimi, “Multi-objective Control Design with Pole Placement Constraints for Wind Turbine System”, Vibration Control, ISBN 979-953-307-807-5, InTech publisher. Nguyen, T.H., Prinz, A., Friisø, T., Nossum, R. (2012) “Smart Grid for offshore wind farms: Towards an information model based on the IEC 61400-25”, IEEE ISGT PES, Jan 16 - 19, Washington D.C., USA . Nguyen, T.H., Prinz, A. (2012) “Using semantics to facilitate data integration of offshore wind farms”, IEEE MELECON 2012, Mar 25 - 28, Tunisia. Nguyen, T.H., Rasta, K., Trinugroho, Y.B.D., Prinz, A. (2012) “Using Enterprise Service Bus for offshore wind farm data handling”, IADIS Applied Computing 2012, Oct 19 – 21, Madrid, Spain. Accepted Nguyen, T.H., Prinz, A., Friisø, T., Nossum, R., Tyapin, I. (2012) “A framework for data integration of offshore wind farms”, submitted to Renewable Energy. Sarkar, A and Gudmestad, O. T. (2012): “On the possibility of using a pendulum type liquid column damper (PLCD) for controlling the vibration of a structure - theoretical and experimental study”, Submitted April 2012 to Engineering Structures. Sarkar, A and Gudmestad,O.T. (2012): “Study on a new methodology proposed to install a monopile “, Proc. ISOPE, Greece. ISOPE 2012-TCP-0805

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Sarkar, A and Gudmestad, O. T. (2012): “Study on a new method for installing a monopile and a fully integrated offshore wind turbine upper structure - by using the SSIP structure”, Submitted August 2012 to Journal of Marine Structures Kjelland, M. B, Tyapin I, Hovland, G and Hansen,M.R; (2012) “Tool-Point Control for a Redundant Heave Compensated Hydraulic Manipulator”, IFAC Workshop on Automatic Control in Offshore Oil and Gas Production (ACOOG 2012), Trondheim, Norway. 1. June Kjelland, M.B and Hansen, M.R (2012) “Tool Point Tracking for Redundant Hydraulic Actuated Manipulator using Velocity Control”, 7th FPNI Ph.D. Symposium on Fluid Power, Reggio Emilia, Italy. 27-30 June Heggelund, Y., Skaar, I.M., & Jarvis, C. “Interactive design of wind farm layout using CFD and model reduction of the steady state RANS equations.” Proceedings of the 11th World Wind Energy Conference, Bonn, Germany, 3-5 July 2012. Liu, H. & Chen, Z., “Aggregated Modelling for Wind Farms for Power System Transient Stability Studies”, Asia-Pacific Power and Energy Engineering Conference, March 2012, Shanghai, China Liu, H. & Chen, Z., “Fault Ride-through and Grid Support of Permanent Magnet Synchronous Generator-based Wind Farms with HVAC and VSC-HVDC Transmission Systems”, International Energy Conference & Exhibition, September 2012, Florence, Italy Krogstad, P.-Å. and Eriksen, P.E. “Blind test” calculations of the performance and wake development for a model wind turbine, Renewable Energy 50 (2012) 225-33 Bakhoday Paskyabi, M., and I. Fer (2012), Upper ocean response to large wind farm effect in the presence of surface gravity waves, Energy Procedia, 24, 245-254. Reuder, J., Jonassen, M. O., & Olafsson, H. (2012). The Small Unmanned Meteorological Observer SUMO: Recent developments and applications of a micro-UAS for atmospheric boundary layer research. Acta Geophysica, DOI: 10.2478/s11600-012-0042-8, OnlineFirst. Reuder, J., & Jonassen, M. O. (2012). First results of turbulence measurements in a wind park with the Small Unmanned Meteorological Observer SUMO, Proceedings of the 9th Deep Sea Offshore Wind R&D Seminar, 19./20.01.2012,Energy Procedia, 24, 176-185. Flügge, M, Edson, J. B., & Reuder, J. (2012). Sensor movement correction for direct turbulence measurements in the marine atmospheric boundary layer, Proceedings of the 9th Deep Sea Offshore Wind R&D Seminar, 19./20.01.2012, Trondheim, Energy Procedia, 24, 159-165. Dahlgren, T.G., M-L Schläppy, A. Shashkov, M. Andersson, Y. Rzhanov, and I. Fer (2012). Assessing impact from wind farms at subtidal, exposed marine areas. In: Marine Renewable Energy and Environmental Interactions, Eds. M. A. Shields and A.I. L. Payne, Springer, accepted.

Reports Hansen, T., Torvanger, Ø., Design of an Offshore Vertical Axis Wind Turbine Part 1. Rotor size and geometry of the VAWT. Internal NORCOWE Research Report Hansen, T. (2012). Design of an Offshore Vertical Axis Wind Turbine Part 2. Energy capture and forces on the VAWT. NORCOWE Research Report Dahlgren et al, Assessing impact from wind farms at subtidal, exposed marine areas. Internal NORCOWE Report Kippersund, R. a., & Lohne, K. D., Ultrasonic condition monitoring of wind turbine blades, Internal NORCOWE Report Heggelund, Y., Skaar, I. M., & Jarvis, C., CFD Model Reduction for Wind Farm Layout Assessment, Internal NORCOWE Report Prakash, R & Hansen, T., Simulating a Model Wind Turbine using Navier-Stokes CFD -- Part two, Internal NORCOWE Report Sapronova, A., Forecasting wind speed with Hybrid Self Organizing Map (SOM) type artificial neural network (ANN), Internal NORCOWE Report Sapronova, A., Intelligent Power System Grid Integration -- Literature review, Internal NORCOWE Report Sælen, L. & Kahli, M., Modelling in FLACS Wind CMR-Wind, Internal NORCOWE Report Sand, I.Ø. & Hallanger, A., BEM-WTM Ext to Wind Shear, Internal NORCOWE Report page 52

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Commercial results (patent applications) Sarkar, A and Gudmestad, O T: ”Pendulum type liquid column damper (PLCD) for controlling the vibration of a structure” Sarkar, A and Gudmestad, O T: ”Installation technique for an offshore structure which is afloat with external buoyancy elements, onto a single submerged foundation by the use of a float-over-pulling(FOB) method”.

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Photos and illustrations by: Christian Michelsen Research Statoil Gephysical Institute, University of Bergen Europena Wind Energy Asociation Shutterstock CMR GexCon Germanischer Lloyd Uni Research Aalborg University University of Agder University of Stavanger Asbjørn Jensen E. Tønnesen CMR Prototech Japan Council For Renewable Energy

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Editor: Kristin Guldbrandsen Frøysa, Centre Director Knut-Erland Brun, Centre Coordinator Layout: Per Gunnar Lunde, Communication Officer

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NORCOWE Annual report 2012

Contact info Kristin Guldbrandsen Frøysa, Centre Director Annette Stephansen, Centre Coordinator Peter M. Haugan, Chair of Executive Board, University of Bergen Finn Gunnar Nielsen, Scientific Leader, University of Bergen Postal Address FME-NORCOWE Christian Michelsen Research AS P.O. Box 6031 NO-5892 Bergen, Norway Visiting Address Christian Michelsen Research AS Fantoftvegen 38 Bergen, Norway post(at)norcowe.no, Kristin(at)cmr.no. web: www.norcowe.no

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NORCOWE annual report 2012  

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