CFD Analysis of a Novel Hull Design for an Offshore Wind Farm Service Vessel

Transcription

1 CFD Analysis of a Novel Hull Design for an Offshore Wind Farm Service Vessel M. Shanley 1, J. Murphy 1, and P. Molloy 2 1 Hydraulics and Maritime, Civil and Environmental Engineering University College Cork, Youngline Industrial Estate, Pouladuff Road, Togher, Ireland m.shanley@student.ucc.ie & jimmy.murphy@ucc.ie 2 Mechanical and Biomedical Engineering, College of Engineering and Informatics, University of Ireland Galway, Ireland padraig.molloy@nuigalway.ie Presented by: Matthew Shanley PhD Candidate University College Cork Hydraulics and Maritime m.shanley@student.ucc.ie (+353) (0) Funded through the Graduate Research Education Program in Engineering

2 Contents Research Motivation Current Vessels Weather Windows Safety Physical Model Testing Results Wind Farm Service Vessel Regulations Specification Computational Fluid Dynamics Setup Meshing Settings Output Computational Power and Memory Results Conclusions

3 Weather Windows Year round accessibility (% %) 100% 80% 60% 40% 20% 0% 1m 1.5m 2m 2.5m NorthSea 37km North Sea 100km M2 Irish Sea M1 71km M3 36 km O Connor M, Lewis T, Dalton GJ. Weather Windows analysis of Irish West Coast Wave Data with relevance to Operations and Maintenance of Marine Renewables Renewable Energy. Accepted In Proof 2012

4 Current Vessels

5 Safety Marine Lifting Operations Personnel Transfers Motion Induced Interruption The Renewable UK H&S 2011 Conference David Kirkly Submarine Technology Limited

6 Physical Model Testing

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8 Regulations General Regulations Det Norske Veritas Tentative Rules for Domestic Service Craft Stability Requirements 2000 High Speed Craft Code Note: Actual Personnel Transfer not governed under any regulations and is being worked on by DNV with the Carbon Trust

9 Vessel Specification Wind Farm Service Provider Category 1 odet Norske Veritas, (DNV) Regulations Displacement of 65 tonnes 24m Length 12 Passengers Operate at Hs 3m External diameter of tubes metres Horizontal spacing (S h ) metres Vertical spacing (S v ) 0.9 metres Number of tubes vertically 4 Number of tubes horizontally 7 The top of the deck is metres above the waterline Draft is metres

10 Modelling Software Potential Flow Frequency Domain Eg. WAMIT Time Domain Eg. TIMIT Constant waterplane area Time and Computationally inexpensive CFD Time Domain Viscous Flow Solves full Navier Stokes Equations Time and Computationally expensive

11 CFD Model Layout

12 Elevation and End View of Rigid Body

13 CFD Meshing Mesh Methods Patch Conforming Method - Throughout Body Sizing Face Sizing Inflation Vertex Sizing General Details Elements Nodes Element size capped at mm Min Element size 20.0 mm These details resulted form a Mesh Sensitivity Analysis

14 CFD Meshing

15 CFD - Meshing

16 CFD Meshing

17 CFX-PRE Settings Transient Analysis Rigid Body setting employed Restricted to 3 degrees of freedom Second Order Backward Euler - Simo Wong, Integration Method, Angular Momentum Equation Control (provides second order accuracy) The Domain is modelled using an air and water as a continuous fluid, with a density difference being the Fluid Buoyancy Model Free Surface Model Turbulence Model is Shear Stress Transport Timestep 0.05s (from Timestep sensitivity Analysis) Solver Control Continuity Equation Class Multiphase Control The initial Volume Fraction Smoothing is Volume-Weighted

18 CFX-PRE Settings Boundary Settings Rigid Body Surface No slip wall The mesh motion is governed by the Rigid Body Solution The fluid Mass Flux is 0 Kg m^-2 s^-1 Mass Flux Pressure Coefficient is

19 CFX-PRE Settings Boundary Settings Wave Maker No slip wall The Wave Maker motion is governed by the equation Where is determined from the wave maker formula for linear wave theory Reference: R.G. Dean, and R. A. Dalrymple, (1984). Water wave mechanics for engineers and scientists, Prentice-Hall Inc., New Jersy.

20 CFX-PRE Settings Boundary Settings The front and rear walls us a Symmetry boundary setting The top of the domain uses an Opening setting with the fluid volume fraction as 100% air The tank end, tank base and the Beach are modelled as fixed no slip walls Interfaces Conservative Interface Flux

21 CFX-PRE Settings Mesh Relaxation This relaxes mesh movement at the boundaries Expert Parameters linearly exact numerics = t solver relaxation fluids = 0.8 solver relaxation scalar = 0.8 solver target reduction fluids = 0.01 solver target reduction scalar = 0.01 max linsol passes fluids = 5 trilinear advection = f

22 CFX-PRE Settings Output Control Monitor the following variables, Pressure Total Mesh Displacement Velocity Water at 25 C.Volume Fraction Extract the Rigid body movements from the Solver as a.csv file Calculate wave heights in CFX post with a CCL Script

23 Computational Power and Memory NVIDIA1 Intel[R] XEON[R] 2.27 GHz 8 Dual Core Processors, 96.0GB RAM 1233GB Memory hmrccfd2 Del Precision PWS 490 Intel[R] XEON[R] CPU 2.66GHz Quad Core, 8GB RAM 297GB Memory

24 Computational Power and Memory NVIDIA1 Intel[R] XEON[R] 2.27 GHz 8 Dual Core Processors, 96.0GB RAM 1233GB Memory hmrccfd2 Del Precision PWS 490 Intel[R] XEON[R] CPU 2.66GHz Quad Core, 8 GB RAM 297GB Memory ICHEC-Stoney stoney.ichec.ie is a Bull Novascale R422-E2 cluster This results in a total of 496 cores and 2976GB of RAM available for jobs. External Hard Drives 1 Number 1TB 1 Number 4TB

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27 Vessel Motion Throughout A Wave T = 38.5s T = 41.55s T = 39.25s T = 42.3s T = 40.0s T = 43.05s T = 40.8s T = 43.7s

28 CFX Velocity Vectors & Vorticity

29 Physical Model Designs

30 Further Work Continue the CFD analysis in regular waves to determine the RAO s for a number of different wave conditions Physical Model Testing Test interaction with Wind Turbine Compare results from the physical model test with the CFD results

31 Summary The (larger) original physical model testing showed significant advantages over a conventional vessel The concept in this situation with this arrangement of tubes does not appear to have a noticeable effect compared to that of a conventional vessel CFD is particularly useful where; The water plane area is constantly changing Time Domain Analysis is required Viscous flow needs to be modelled Any detailed analysis which is not readily obtained from potential flow theory CFD issues; Set up time required to obtain an accurate and convergent solution Reliability of solution Need for Physical test for validation & verification Computationally Expensive Time Expensive

32 CFD Analysis of a Novel Hull Design for an Offshore Wind Farm Service Vessel M. Shanley 1, J. Murphy 1, and P. Molloy 2 1 Hydraulics and Maritime, Civil and Environmental Engineering University College Cork, Youngline Industrial Estate, Pouladuff Road, Togher, Ireland m.shanley@student.ucc.ie & jimmy.murphy@ucc.ie 2 Mechanical and Biomedical Engineering, College of Engineering and Informatics, University of Ireland Galway, Ireland padraig.molloy@nuigalway.ie Presented by: Matthew Shanley PhD Candidate University College Cork Hydraulics and Maritime m.shanley@student.ucc.ie (+353) (0) Funded through the Graduate Research Education Program in Engineering