CFD modelling of floating body response to regular waves

Transcription

1 CFD modelling of floating body response to regular waves Dr Yann Delauré School of Mechanical and Manufacturing Engineering Dublin City University Ocean Energy Workshop NUI Maynooth, October 21, 2010

2 Table of contents 1 Introduction CFD Solutions Challenges Fine Marine 2 Formulation The Dambreak Problem The Rectangular Floating Barge The 6 DOF Floating Cylinder The Restrained 6 DOF Floating Cylinder

3 Introduction CFD Solutions CFD Solutions CFD modelling of wave structure interaction General Purpose CFD Software generally based on Finite Volume Methods Commercial Packages, e.g. Flow3D, ANSYS CFD (Fuent - CFX) STAR CD... OpenSource, e.g. OpenFOAM, OpenFVM... In-house codes CFD Solution for marine applications Numeca Fine Marine

4 Introduction Challenges Challenges Coupling of non linear unsteady Navier Stokes system with motion solver Motion may have 6DOF or may be restrained or constrained may involve large displacements Displacement may be larger than with boat dynamics boundary conditions Open boundary condition Wave generating boundary condition Specific physical models Turbulence modelling with implication on mesh resolution Free surface flow and interface deformation Mesh constraints Complex 3D shapes with possibility of narrow gaps Mesh deformation

5 Introduction Fine Marine Fine Marine / ISIS CFD Automated Meshing from geometry definition Segregated solution of RANS equations Mesh deformation and mesh refinement Parallel solution by domain decomposition External Forces including mooring option Integrated post processing Fine Marine [

6 Formulation Formulation PISO solver for the momentum and incompressible continuity equations VOF algebraic method for the advection of the free surface Broad range of RANS (including k ω SST) and LES turbulence models Domain decomposition for parallel computing Motion Solver Motion solver based on a Hamiltonian method Restraints and Constraints imposed as forces and moments Mesh distortion but no dynamic mesh refinement

7 The Dambreak Problem The Rectangular Floating Barge The Free Floating Cylinder The Contrained/Restrained Cylinder

8 The Dambreak Problem Problem Specifications

9 The Dambreak Problem Computational Setup Domain Dimensions: 3.2 x 1 x 1 m Time Step: Adaptive with Co max = 0.2 Number of Processors: 10, Mesh: 925,000 Hexahedral Cells Computational Time/Time Step: approx 5s

10 The Dambreak Problem Water Elevation History at probe H2

11 The Dambreak Problem Water Elevation History at probe H4

12 The Dambreak Problem Static pressure at probe P1

13 The Dambreak Problem Static pressure at probe P3

14 The Dambreak Problem Static pressure at probe P5

15 CFD modelling of floating body response to regular waves The Rectangular Floating Barge Domain Dimensions: 1 x 1 x 1 m Time Step: Adaptive with Comax = 0.2 Mesh: 95,000 Hexahedral Cells Floating Rectangular Barge: Density: 888 kg m 3 Dimensions: 0.3x0.3x0.12 Moments of Inertia: { , , 0.144}

16 The 6 DOF Floating Cylinder Deforming wave generation boundary Wall outlet with additional dissipation Open boundary at top

17 The 6 DOF Floating Cylinder Hollow Cylinder Mass: 1250 kg m 3 Mass: 512 kg Center of gravity: [m] (0, 0, 0.661) Origin of coordinate system: (0, 0, 0)

18 The 6 DOF Floating Cylinder Stable free floating solution

19 The 6 DOF Floating Cylinder Unstable free floating solution

20 The Restrained 6 DOF Floating Cylinder Consider the full cylinder under purely arbitrary restraints Restraints made of: Spring damper system for mooring to the bottom boundary Weaker spring-damper fixed to top boundary

21 The Restrained 6 DOF Floating Cylinder Rate of energy Extraction from Mooring Spring

22 Contact Dr Yann Delauré School of Mechanical and Manufacturing Engineering & Centre for Scientific Computing & Complex Systems Modelling (SCI-SYM) Acknowledgment This work was part supported by DCU s School of Mechanical and Manufacturing Engineering SCI-SYM and DCU s School of Computing for access to the Ampato Cluster