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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