6DOF RANS Simulations of Floating and Submerged Bodies using OpenFOAM

Transcription

1 6DOF RANS Simulations of Floating and Submerged Bodies using OpenFOAM Eric Paterson, David Boger, Kevin Smith, Scott Miller, and Gina Casadei Applied Research Laboratory, Penn State Univ, State College, PA, USA Hrvoje Jasak Wikki Ltd., London, UK 12th Numerical Towing Tank Symposium, Cortona, Italy 4-6 October 2009

2 Objectives Develop Multiphase CFD Tools for Naval Hydrodynamics using OpenFOAM Resistance and propulsion Bubbly wakes Seakeeping Wave-impact and green-water-ondeck forces Multi-body problems

3 Approach OpenFOAM ~4 years of experience at PSU/ARL Initial validation efforts performed as part of student theses Now being used for real-world design, analysis, and acquisition programs Development of overset methods: foamedover Why OpenFOAM? Open-source, extensible C++, code architecture, existing models and algorithms Capability for multi-physics simulations and custom solvers world-wide user base (2500+ users)

4 rasinterdymfoam Tool for Seakeeping, Ship motions, Wave Loads Large-amplitude 6DOF Motions Free Surface Propulsion and Control Surfaces Mesh Motion EOM Wave Model VOF/LS Outflow B.C. Body-force Direct Sim Dynamic mesh GGI Overset Quarternions Euler angles Regular waves Irregular waves Short crested waves High-pass: Advective Low-pass: Sponge Layer Actuator disk BEM 3D RANS GGI Overset

5 rasinterdymfoam rasinterfoam extended for dynamic Mesh forces and moments include buoyancy (floatingbody class) equations of motion formulated using quaternions (sixdofqode class) 13 variables (linear displacement from Earth-fixed system (3), linear velocity (3), rotational velocity (3), quaternions (4)) Runge-Kutta ODE solver

6 Wigley Hull Transient solver: rasinterfoam Mesh: 286,000 cells, y + ~ Δt for a converged solution runtime ~ 5 hrs numproc = 4

7 Bare-hull Model 5415 Navy surface combatant ca Sonar dome and transom stern, propulsion is provided through twin open-water propellers driven by shafts supported by struts CFD Validation Database Used at the Gothenburg 2000, Tokyo 2005, Gothenburg 2010 workshops

8 Bare-hull Model 5415 Grid Pointwise ~5M hex cells, y + ~ 100 Simulation 128 processors on 4400-core Woodcrest cluster OF compiled with icc, linked to optimized MPI

9 Bare-hull Model 5415 Grid Pointwise ~5M hex cells, y + ~ 100 Simulation 128 processors on 4400-core Woodcrest cluster OF compiled with icc, linked to optimized MPI Transient solver: rasinterfoam Δt ~ 1x10-4 (Co = 0.7) 30,000 time steps for a steady solution!! Unacceptable.

10 LES of Free-surface flows Froude number = 1.0 Froude number = 2.0

11 0.05 Mean wave elevation and axial velocity 0.2 (b) Fr = (c) Fr = 2.0 y(m) y(m) x(m) x(m)

12 Wave models Models required to generate waves regular waves, deep and shallow water Regular waves irregular waves and wave spectra models short-crested or directional waves Irregular seaway

13 groovywavetank groovywavetank with nonzero forward speed (or current)

14 atmosphere groovywavebasin advective U Uwaves groovybc

15 groovywavebasin input for U This is probably the limit: more complexity custom BC

16 Outflow b.c. Two approaches used in tandem: advection BC: high-pass filter, best for filtering long waves ineffective for zero forward speed, but good for other cases Numerical beach: low-pass filter, best for damping short waves

17 Numerical beach ρu t + (ρuu) = p + µ U + ρg σκn ν d (x)ργu ν d is a scalar dissipation function Zero everywhere except in the sponge layer region ν d (x) defined as a cubic (Clement, 1996) Grid expansion is also effective at filtering short waves

18 Numerical beach Studied numerous lengths and magnitudes. Evaluated by defining a reflection coefficient No Sponge Layer ν d,max = 6, L = 4 ν d,max = 100, L = 4

19 Surface-piercing cyclinder in waves zero Forward speed

20 Wigley Hull in waves nonzero Forward speed

21 Wigley Hull in waves response of boundary layer & wake

22 Wave impact loads Wave impact pressure on block Experiment done at NSWCCD (Fullerton et al., 2009) Breaking and non-breaking waves tested Block face and angle varied Data taken from slam panels and pressure gages Pressures and forces taken relative to calm water level Average load of 75 to 150 wave impacts

23 Wave impact loads EFD data

24 Prescribed motions Tumblehome geometry 2D midship slice

25 Roll damping & wave-excited roll Results: Damping Factor ζ CFD BR: CFD No BR: Experiment: Bilge radius reduces damping Sources of error 2D approximation Experimental setup has more damping due to friction at fixed axis of barge Wave parameters: λ = 1.56 m, H = m

26 foamedover Overset meshing requires the following modifications to a CFD solver Blank out regions of the mesh Interpolation of fringe and outer boundary cells from donor meshes (tri-linear interpolation) Modification of algebraic solvers (Hard part) Breaks symmetry of pressure Poisson equation. Solution: PETSc GMRES solver Momentum and turbulence solved with 2-stage Jacobi Future work: modify OpenFOAM solvers (GAMG, PGC, BiCGStab, etc.) and compare to PETSc solvers

27 rasinterdymfoam OpenFOAM libraries (OpenCFD) OpenSource CFD Toolbox PETSc libraries (ANL) OpenSource data structures and solvers libsuggar++ and DiRTlib (PSU/ARL) OpenSource Overset Tools foamedover libraries Interface between OpenFOAM - PETSc - libsuggar++/dirtlib custom libraries waves b.c., floatingbody class

28 foamedover start with potentialfoam potential field 4 new lines of code to create oversetpotentialfoam

29 foamedover oversetsimplefoam 6 lines of new code required to link with foamedover library pressure field velocity field

30 foamedover oversetrasinterfoam 7 lines of new code required to link with foamedover library gamma field pressure field

31 3DOF rising buoyant body Overset GGI capsize of floating box

32 Conclusions Different CFD formulations required for various aspects of Ship Hydrodynamics Steady VOF - URANS - LES/DES - vehicle motions: all have unique challenges interfoam-class solvers work well for transient problems such as wave propagation, wave slap, wave forces Develop work required to stitch everything together Boundary-condition formulation for oblique/beam/trailing seas needs attention Overset has been implemented and tested. Needs to be compared to GGI/dynamic mesh for seakeeping simulations

33 Overset Symposium 9th Symposium (2008): Penn State University 10th Symposium (2010): NASA Ames, CA

34 OpenFOAM Ship Hydro SIG

35 OpenFOAM Workshop 1st Workshop (2006): Zagreb, Croatia 2nd Workshop (2007): Zagreb, Croatia 3rd Workshop (2008): Milan, Italy 4th Workshop (2009): Montreal, Canada 5th Workshop (2010): Gothenburg, Sweden