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6DOF RANS Simulations of Floating and Submerged Bodies using OpenFOAM
12th Numerical Towing Tank Symposium, Cortona, Italy4-6 October 2009
Eric Paterson, David Boger, Kevin Smith, Scott Miller, and Gina CasadeiApplied Research Laboratory, Penn State Univ, State College, PA, USA
Hrvoje JasakWikki Ltd., London, UK
Monday, October 5, 2009
Objectives
• Develop Multiphase CFD Tools for Naval Hydrodynamics using OpenFOAM
• Resistance and propulsion
• Bubbly wakes
• Seakeeping
• Wave-impact and green-water-on-deck forces
• Multi-body problems
Monday, October 5, 2009
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)
Monday, October 5, 2009
rasInterDyMFoam
Tool for Seakeeping, Ship motions, Wave Loads
Free SurfaceLarge-amplitude 6DOF Motions
Propulsion and Control Surfaces
Mesh Motion EOM Wave Model VOF/LS Outflow B.C. Body-force Direct Sim
•High-pass: Advective •Low-pass: Sponge Layer
•Actuator disk•BEM•3D RANS
•Regular waves•Irregular waves•Short crested waves
•Quarternions•Euler angles
•Dynamic mesh•GGI•Overset
•GGI•Overset
Monday, October 5, 2009
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
Monday, October 5, 2009
Wigley Hull
Transient solver: rasInterFoamMesh: 286,000 cells, y+ ~ 1002500 Δt for a converged solution
runTime ~ 5 hrsnumProc = 4
Monday, October 5, 2009
Bare-hull Model 5415
• Navy surface combatant ca. 1980.
• 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
Monday, October 5, 2009
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
Monday, October 5, 2009
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: rasInterFoamΔt ~ 1x10-4 (Co = 0.7)➙ 30,000 time steps for a steady solution!! Unacceptable.
Monday, October 5, 2009
LES of Free-surface flows
Froude number = 1.0 Froude number = 2.0
Monday, October 5, 2009
0
0.075
0.125
0.05
-0.1
-0.15
0
0.05
y(m)
-0.2
0
0.2
(b) Fr = 1.0
0
0.04 0
.08
-0.06
-0.10
0.04
y(m)
-0.2
0
0.2
(a) Fr = 0.8
0.2
0.3
-0.85
-0.75
-0.6
0
0
0.1
x (m)
y(m)
-0.2 0 0.2 0.4 0.6
-0.2
0
0.2
(c) Fr = 2.0
0
0.075
0.125
0.05
-0.1
-0.15
0
0.05
y(m)
-0.2
0
0.2
(b) Fr = 1.0
0
0.04 0
.08
-0.06
-0.10
0.04
y(m)
-0.2
0
0.2
(a) Fr = 0.8
0.2
0.3
-0.85
-0.75
-0.6
0
0
0.1
x (m)
y(m)
-0.2 0 0.2 0.4 0.6
-0.2
0
0.2
(c) Fr = 2.0
0
0.075
0.125
0.05
-0.1
-0.15
0
0.05
y(m)
-0.2
0
0.2
(b) Fr = 1.0
0
0.04 0
.08
-0.06
-0.10
0.04
y(m)
-0.2
0
0.2
(a) Fr = 0.8
0.2
0.3
-0.85
-0.75
-0.6
0
0
0.1
x (m)
y(m)
-0.2 0 0.2 0.4 0.6
-0.2
0
0.2
(c) Fr = 2.0
Mean wave elevation and axial velocity
Monday, October 5, 2009
Wave models
• Models required to generate waves
• regular waves, deep and shallow water
• irregular waves and wave spectra models
• short-crested or directional waves
Regular waves
Irregular seaway
Monday, October 5, 2009
groovyWaveTankhttp://openfoamwiki.net/index.php/Contrib_groovyBC#User-Cases
groovyWaveTank with nonzero forward speed (or current)
Monday, October 5, 2009
groovyWaveBasin
U
Uw
aves
groovyBC
advective
atmosphere
Monday, October 5, 2009
groovyWaveBasin
{ type groovyBC; refValue uniform (0 0 0); refGradient uniform (0 0 0); valueFraction uniform 1; value uniform (1 0 0); valueExpression "(pos().z<=A*cos(k*pos().x*cos(betaRad)+k*pos().y*sin(betaRad)-we*time())) ? vector(Us+cos(betaRad)*(A*w*exp(k*pos().z)*cos(k*pos().x*cos(betaRad)+k*pos().y*sin(betaRad)-we*time())), sin(betaRad)*(A*w*exp(k*pos().z)*cos(k*pos().x*cos(betaRad)+k*pos().y*sin(betaRad)-we*time())), A*w*exp(k*pos().z)*sin(k*pos().x*cos(betaRad)+k*pos().y*sin(betaRad)-we*time())) : vector(1,0,0)"; gradientExpression "vector(0,0,0)"; fractionExpression "(phi > 0) ? 0 : 1"; variables "l=1;A=0.05;Us=1;beta=45;betaRad=2.*pi*45.0/360.0;g=vector(0,0,-9.81);k=2*pi/l;w=sqrt(k*mag(g));we=w+k*Us*cos(betaRad);"; timelines (); }
input for U
This is probably the limit: more complexity ➙ custom BC
Monday, October 5, 2009
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
Monday, October 5, 2009
Numerical beach
• νd is a scalar dissipation function• Zero everywhere except in the sponge layer region• νd(x) defined as a cubic (Clement, 1996)• Grid expansion is also effective at filtering short waves
∂ρU∂t
+∇ · (ρUU) = −∇p +∇ · µ∇U + ρg − σκn− νd(x)ργU
Monday, October 5, 2009
• Studied numerous lengths and magnitudes.
• Evaluated by defining a reflection coefficient
Numerical beach
νd,max = 100, L = 4νd,max = 6, L = 4No Sponge Layer
Monday, October 5, 2009
Surface-piercing cyclinder in waveszero Forward speed
Monday, October 5, 2009
nonzero Forward speed
Wigley Hull in waves
Monday, October 5, 2009
response of boundary layer & wake
Wigley Hull in waves
Monday, October 5, 2009
• 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
Wave impact loads
Monday, October 5, 2009
EFD data
Wave impact loads
Monday, October 5, 2009
Prescribed motionsTumblehome geometry 2D midship slice
Monday, October 5, 2009
Roll damping & wave-excited roll Results: Damping Factor ζ
CFD BR: 0.0877 CFD No BR: 0.0980 Experiment: 0.106
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 = 0.044 m
Monday, October 5, 2009
• 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
foamedOver
Monday, October 5, 2009
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
rasInterDyMFoam
custom librarieswaves b.c., floatingBody class
Monday, October 5, 2009
foamedOver
• start with potentialFoam
• 4 new lines of code to create oversetPotentialFoam
■ include "oversetObject.H”■ include "createOverset.H" which instantiates the oversetObject object
■ add oversetOperations.swapValues(p) after pEqn.solve() to update the fringe values
■ add oversetOperations.blankEquations(pEqn,p) to modify the equations
potential field
Monday, October 5, 2009
foamedOveroversetSimpleFoam
–6 lines of new code required to link with foamedOver library
velocity fieldpressure field
Monday, October 5, 2009
foamedOver
–7 lines of new code required to link with foamedOver library
oversetRasInterFoam
gamma field pressure field
Monday, October 5, 2009
3DOF rising buoyant body
capsize of floating boxGGI
Overset
Monday, October 5, 2009
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
Monday, October 5, 2009
Overset Symposiumwww.oversetsymposium.org
9th Symposium (2008): Penn State University
10th Symposium (2010): NASA Ames, CA
Monday, October 5, 2009
OpenFOAM Ship Hydro SIGhttp://openfoamwiki.net/index.php/Sig_Ship_Hydrodynamics
Monday, October 5, 2009
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
Monday, October 5, 2009