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Estimating Torque Demands of Electric Driven Pods and Thrusters A. Mountaneas, MEng

G. Politis, Associate Professor Department of Naval Architecture and Marine Engineering, NTUA 13-2-2014

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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Electric motors & PODs Problems • High failure rate of motor parts: • Stator windings and core • Rotor windings • Slip ring connectors

• Main reason: High temperature in windings • Excessive overheating stresses

• Conclusion: Motors mismatched with operational conditions

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Our Target • Investigation of torque demands during transient operation with Boundary Element Methods (BEM)

• Calculation of loads excited by propulsor’s components during dynamic conditions: • Azimuthing angle • Non-linear path • Blade rotation about spindle axis (controllable pitch)

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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 – given pitch

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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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Modeling 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 Estimating torque demands of electric driven pods and thrusters 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 Mermaid 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. 2. 3. 4.

Propeller rotation Blade rotation around spindle axis Propulsor rotation around vertical axis 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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Motion Scenarios Blade rotation 0o to nominal pitch angle

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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 Estimating torque demands of electric driven pods and thrusters National Technical University of Athens

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5. U nsteady B oundary E lement M odeling* *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 – podded propulsor 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 – podded propulsor 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

15

Yaw angle [ degrees ]

• Rectilinear motion (0o yaw)

Rectilinear Yaw +20O Yaw -20O

10 5 0 -5 -10

velocity -15 -20 0

0.5

1

1.5

2

2.5

Time [ sec ] Estimating torque demands of electric driven pods and thrusters National Technical University of Athens

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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) Torque around propeller axis

• Oscillation due to strut – propeller interaction

• Strut yaw affects loads

Torque [ tons*m ]

80

60

Rectiinear Yaw +20O Yaw -20O

40

20

0

0

1

2

3

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Preliminary Results (sparse grid) Force along propeller axis

Fo rc e [ to ns ]

80

60

Rectilinear Yaw +20O Yaw -20O

40

20

0

0

1

2

3

T im e [ se c ]

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7. Conclusions

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Conclusions Flexible & highly configurable algorithm • BEM can be used on various motion scenarios • Different configurations easily implemented • Motion scenarios easily generated • 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 • Implementation of various motion scenarios and strategies • 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


? Questions

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1. Estimating torque demands of electric driven pods and thrusters  
1. Estimating torque demands of electric driven pods and thrusters  
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