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Simulation of Transient Performance of Podded Propulsion The Problem of Grid and Motion Generation A. Mountaneas, Diploma Engineer G. Politis, Associate Professor Department of Naval Architecture and Marine Engineering, NTUA 6/5/13

National Technical University of Athens


Contents 1.  2.  3.  4.  5.  6.  7.  8. 

Introduction - Motivation Grid Generation (Geometric Preprocessor) Motion Generation (Motion Preprocessor) Algorithm Outline UBEM (Main Processor) Preliminary Results Conclusions Future Work

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1. Introduction Motivation

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Why PODDED Propulsors? •  Electrical Power •  High Torque Capacity •  High Hydrodynamic Efficiency •  Dynamic Positioning •  All Electric Ship (AES) Integration •  High Maneuverability

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History (1) 1ST Generation: 1985 - 2004 Year

Ship Type

Ship Name

Power (MW)

Model

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Problems 1ST Generation: 1985 - 2004 •  Sealing •  Lubrication •  Bearings •  Electrical – Automation •  Reason:

Limited applied research and development

20 MW power per unit increase during a decade

•  Result:

Reliability loss and market shrinkage

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History (2) 2ND Generation: 2004 - … •  New models and companies warmed the market

•  Still limited application

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Other Computational Approaches •  RANS equations •  Boundary elements methods (BEM) •  Hybrid: RANS for pod body, BEM for propeller

•  Simulations mainly for straight course – static azimuthing angles

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Our Target

•  Investigation of transient hydrodynamic performance and behavior with Boundary Element Methods (BEM)

•  Calculation of loads excited by propulsor’s components during dynamic conditions: •  Azimuthing angle •  Non-linear path

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2. Grid Generation

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Geometric Breakdown (patches) Motor housing

Strut

Propeller •  Blades •  Boss •  Cap

Fillet

Fin

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Modelling Sequence 1.  Real Model

2.  Surface Description: •  • 

Offset e.g. propeller blades Mathematical Equations e.g. housing

3.  Surface Grid Generation • 

Interpolation Schemes

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Fillet Treatment

•  Core Idea: Work on plane defined by the hydrodynamically active component (e.g. blades, strut)

•  Lifting surfaces are hydrodynamically and computationally more important Simulation of Transient Performance of Podded Propulsion National Technical University of Athens

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Step 1: Vectors defining the plane are calculated by using bilinear quadrilateral boundary elements

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Step 2: Calculation of line and circle intersection points with housing

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Step 3: Conic curve definition

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Fillet Treatment Conics 1 − p )Q1x − 2pQ3x + (1 − p )Q2x }t 2 − 2{(1 − p )Q1x − pQ3x }t + (1 − p )Q1x ( { x (t ) = 2(1 − 2p )t 2 − 2(1 − 2p )t + 1 − p

(1 − p )Q1 y − 2pQ3 y + (1 − p )Q2 y }t 2 − 2{(1 − p )Q1 y − pQ3 y }t + (1 − p )Q1 y { y (t ) = 2(1 − 2p )t 2 − 2(1 − 2p )t + 1 − p

0.0 ≤ t , p ≤ 1.0 Strut / Blade

Fillet

Housing / Boss

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Grid Examples ABB Azipod 1575 elements 6746 elements 28218 elements

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Grid Examples Rolls Royce ABB 1493 elements 6746 elements 28218 elements

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Grid Examples Converteam Schottel SSP 2493 elements 10529 elements 27990 elements

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3. Motion Generation

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Motion Generation Motion superposition •  Superposition: 1.  Propeller rotation 2.  Propulsor rotation around vertical axis 3.  Translation

•  “Non incremental” superposition: t = 0 sec

t = tstep

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Motion Scenarios Rectilinear motion

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Motion Scenarios Linear motion & 45o yaw

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Motion Scenarios Linear motion, 45O yaw & reset

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4. Algorithm Outline

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Geometric Preprocessor Grid Data

INPUT

·∙

pod_geometry_parameters.txt

·∙

prop_geom1

·∙

prop_geom2

·∙

grid_blade_parameters1

·∙

grid_blade_parameters2

Grid &  Motion  Data

·∙ ·∙   ·∙   ·∙  

Azipod_pod_grid_parameters.txt Mermaid_pod_grid_parameters.txt SSP_pod_grid_parameters.txt CRP_pod_grid_parameters.txt

1. Propulsor  (excl.  propeller)  Data  Read

3.Propeller &  Boss  Grid  Generation

read_input_pod_geom_params

Propeller_module_fore Propeller_module

read_input_pod_grid_params

system_geometry.f90

lecup_grid 2. Data  Processing Propeller_module_aft Propeller_module

Basic_geometries

lecup_grid

4. Strut  Grid  Generation

OUTPUT

strut_grid

system_geometry

5. Fillet  Grid  Generation

fillet2

MPP_prop_simple_1[193]_parameters

Housing Grid  Generation

torpedo_grid

MPP_prop_simple_1[193]_inmotion

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INPUT

Motion Preprocessor System_geometry

MPP_prop_simple_1[193]_parameters

MPP_prop_simple_1[193]_inmotion

1. Input  Read

OUTPUT

MPP_prop_simple1_[193].f90

read_system_geometry

read_motion_data

2. Drag  Coefficient  Estimation find_cdrag

3. Position  Calculation  and    Output  #1   Write

4. Position  Calculation  and  Output  #2   Write

find_propeller_position_and_orientation

find_propeller_position_and_orientation

write_system geometry_at_time_t

write_system geometry_at_time_t

system_motion_0

MPP_prop_output

system_motion_1

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Final Οutput Automatic data generation for UBEM •  Identical motion with Δt lapse

Flow velocity calculation for every surface element control point Simulation of Transient Performance of Podded Propulsion National Technical University of Athens

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5. U nsteady B oundary E lement M odelling* *Politis G.K., 2011, ‘Application of a BEM time stepping Algorithm in understanding complex unsteady propulsion hydrodynamic phenomena’, Ocean Engineering 38 (699-711).

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UBEM Assumptions •  Solution of unsteady flow around systems of bodies using a Potential based (Morino) formulation with free vortex sheets (for lifting bodies). •  Position of free vortex sheets is calculated by UBEM by applying the vorticity transport equation in a time step by step base. Vortex sheet motion instabilities are suppressed using Gaussian filters (exact solutions of N-S equations). •  Free vortex sheet – body interaction heuristically taken using ‘shields’. •  Corrections for viscous drag using a surface frictional drag coefficient (can depend from the local Reynolds). •  Separation can not be modeled.

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6. Preliminary Results

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Case Study Parameters •  Configuration:

Azipod XO 2100

•  Propeller:

∅6m, z=4, AE/A0=0.7, P/D= 1.0

•  Strut airfoil:

NACA 0012

•  Scenarios:

Rectilinear, Yaw +/-20o

•  Advance speed:

7.2 m/s @ 93 RPM

•  Grid:

Sparse - 1648 elements

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Case Study Scenarios 20

•  Azimuthing angle scenarios: •  Yaw

+20o

(const. rate turn)

•  Yaw -20o (const. rate turn)

•  X-axis velocity pattern: •  Step 1-30: Const. acceleration •  Step 31-240: Const. x-axis velocity

15

Y a w a ng le [ de gre e s ]

•  Rectilinear motion (0o yaw)

Rectilinear Yaw +20O Yaw -20O

10 5 0 -5 -1 0 -1 5 -2 0 0

0.5

1

1.5

T im e [ s e c ]

2

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3


Vorticity Sheet Generation Rectilinear Motion

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Vorticity Sheet Generation Yaw +20o & reset

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Vorticity Sheet Generation Yaw -20o & reset

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Preliminary Results (sparse grid) Force along propeller axis

•  Oscillation due to strut – propeller interaction

F o rc e [ to n s ]

80

60

Rectilinear Yaw +20O Yaw -20O

40

•  Strut yaw affects loads 20

0

0

1

2

3

T im e [ s e c ]

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Preliminary Results (sparse grid) Torque around propeller axis

Torque [ tons*m ]

80

60

Rectiinear Yaw +20O Yaw -20O

40

20

0

0

1

Time [ sec ]

2

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7. Conclusions

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Conclusions Flexible & highly configurable algorithm

•  Different podded propulsor configurations easily implemented •  User has total control of geometry

•  Adjustable grid density of propulsor patches

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8. Future Work

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Future Work •  Additional types (e.g. ducted podded propulsor, bow thruster) •  New geometries investigation (e.g. asymmetric strut) •  Verification with experimental data •  Alternative grid generation using B-splines or/and differential equations schemes

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ACKNOWLEDGMENT THE

WORK PRESENTED IN THIS PAPER HAS BEEN DEVELOPED WITHIN THE

THALES-DEFKALION PROJECT. THIS RESEARCH HAS BEEN COFINANCED BY THE EUROPEAN UNION (EUROPEAN SOCIAL FUND – ESF) AND GREEK NATIONAL FUNDS THROUGH THE OPERATIONAL PROGRAM "EDUCATION AND LIFELONG LEARNING" OF THE NATIONAL STRATEGIC REFERENCE FRAMEWORK (NSRF) - RESEARCH FUNDING PROGRAM: THALES: REINFORCEMENT OF THE INTERDISCIPLINARY AND/OR INTER-INSTITUTIONAL RESEARCH AND INNOVATION.

FRAMEWORK OF THE


9. Questions ?

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Simulation of transient performance of a PODED propulsion  
Simulation of transient performance of a PODED propulsion  
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