[overture] low massive rigid bodies
- From: Alessandro Orchini <aorchini@xxxxxxxxxx>
- To: <overture@xxxxxxxxxxxxx>
- Date: Fri, 2 Dec 2011 18:31:34 +0100
Hi,
I'm having a problem with 2D simulations involving a low massive thin flat
plate in a uniform flow. I think that since the density of the rigid body is
not much higher than the one of the fluid, there's a singularity in the
equation of motion: with a low inertia there are huge forces on the body, which
tries to assume the flow velocity in a small time.
I assume a possible solution would be to choose time-steps and t_max lower and
lower, but it would take an amount of time to run the entire simulation.
Furthermore, i've seen that if I constrain the motion in 1-D along and do not
modify any other parameter, the simulation works fine.
I wonder if there is another possible solution for this kind of problems. I
attach both cgins and ogen .cmd files in which are contained all the parameters
I'm using.
Thanks for the help
Alessandro.
********************************************************************************************************
create mappings
*************************
rectangle
set corners
-4, 16, -4, 4
mappingName
squarebig
lines
* 400, 200
200, 100
exit
************************
rectangle
set corners
-2, 8, -2, 2
lines
* 300, 300
150, 150
mappingName
squaresmall
boundary conditions
0,0,0,0
exit
**************************
rectangle
set corners
-1, 3, -1.0, 1.0
lines
* 300, 300
100, 80
mappingName
squaresmall2
boundary conditions
0,0,0,0
exit
***************************
smoothedPolygon
vertices
5
0. -0.025
1.0 -0.025
1.0 0.025
0. 0.025
0. -0.025
*sharpness
*120
*120
*120
*120
*120
n-dist
fixed normal distance
-0.5
lines
200,100
boundary conditions
-1, -1, 1, 0
n-stretch
2. 10. 0.00001
exit
******************************************
rotate/scale/shift
transform which mapping?
smoothedPolygon
* rotate
* -90
* 0,0
* shift
* 0.0, 0.0
mappingName
rotsmoothedPolygon
exit
***********************************************
rotate/scale/shift
transform which mapping?
squaresmall2
* rotate
* -90
* 0,0
* shift
* 0.0, 0.0
mappingName
rotsquaresmall2
exit
**********************************************
exit this menu
*********************************************
generate an overlapping grid
squarebig
squaresmall
* squaresmall2
* smoothedPolygon
rotsquaresmall2
rotsmoothedPolygon
done choosing mappings
compute overlap
change parameters
interpolation type
explicit for all grids
exit
compute overlap
exit
*************************************************
save a grid
smooth2.hdf
smooth2.hdf
exit
******************************************************************************************************************************
*
* cgins command file for flow past a thin flat plate
*
smooth2.hdf
* simulate grid motion only 1
* Specify the equations we solve:
incompressible Navier Stokes
standard model
* noTurbulenceModel
exit
*************************************
*************************************
*************************************
* Next specify the file to save the results in.
* This file can be viewed with Overture/bin/plotStuff.
show file options
compressed
open
thin.show
frequency to flush
20
frequency to save
100
* OBPSF:show variable: vorticity 1
exit
*************************************
*************************************
*************************************
* display parameters
turn off twilight zone
*************************************
*************************************
*************************************
final time 10
times to plot 0.00001
plot and always wait
** no plotting
*************************************
*************************************
*************************************
* choose implicit time stepping:
* use new advanceSteps versions
implicit
* but integrate the square explicitly:
choose grids for implicit
all=implicit
squarebig=explicit
squaresmall=explicit
rotsquaresmall2=explicit
done
*************************************
*************************************
*************************************
time stepping parameters...
* forward Euler
* adams order 2
* adams PC
* adams PC order 4
* midpoint
* Runge-Kutta
* implicit
* variable time step PC
* steady state RK
* steady state RK-line
*************************************
* useOldImplicitMethod
* useNewImplicitMethod
*************************************
* implicitViscous
* implicitAdvectionAndViscous
* implicitFullLinearized
*************************************
* second order accurate
* fourth order accurate
*************************************
* solve for steady state
* second order accurate in time
* fourth order accurate in time
*************************************
* first order predictor
* second order predictor
* third order predictor
* fourth order predictor
* default order predictor
*************************************
* adjust dt for moving bodies 1
*************************************
* final time 5.000e+01
* max iterations 10000
cfl 0.7
dtMax 0.00001
* implicit factor 0. (1=BE,0=FE)
recompute dt every 1 steps
* slow start 0.2 (seconds)
* slow start cfl 0.1
* fixup unused frequency 4
* cflMin, cflMax 0.81, 0.95
* preconditioner frequency 1
number of PC corrections 4
*************************************
close time stepping
*************************************
*************************************
*************************************
*************************************
*************************************
*************************************
pde parameters
* use curl-curl boundary condition
* use old pressure boundary condition
* use p.n=0 boundary condition
*************************************
* OBPDE:project initial conditions 1
* OBPDE:second-order artificial diffusion 1
* OBPDE:fourth-order artificial diffusion 1
* OBPDE:sixth-order artificial diffusion 1
* OBPDE:use implicit fourth-order artificial diffusion 1
* OBPDE:use split-step implicit artificial diffusion 1
* OBPDE:use new fourth order boundary conditions 0
* OBPDE:use split-step implicit artificial diffusion 1
* OBPDE:use self-adjoint diffusion operator 1
* OBPDE:use self-adjoint diffusion operator 0
* OBPDE:include artificial diffusion in pressure equation 1
* OBPDE:include artificial diffusion in pressure equation 0
*************************************
* Kinematic Viscosity
OBPDE:nu 0.0001
* OBPDE:nu 0.001
* OBPDE:divergence damping 1
* OBPDE:cDt div damping 0.25
* turn off second order artificial diffusion
* OBPDE:ad21,ad22 1,1
* OBPDE:ad41,ad42 2,2
* OBPDE:ad61,ad62 2,2
*************************************
* gravity
* 0 5 0
***********
fluid density
1.0
* fluid density
* 1.225
*************************************
* use old pressure boundary condition
* use p.n=0 boundary condition
* use default outflow
check for inflow at outflow
* expect inflow at outflow
* use Neumann BC at outflow
* use extrapolate BC at outflow
* order of time extrapolation for p
*************************************
*************************************
*************************************
OBPDE:check for inflow at outflow
* OBPDE:expect inflow at outflow
*
turn on second order artificial diffusion
OBPDE:ad21,ad22 2,2
* OBPDE:fourth-order artificial diffusion 1
* OBPDE:ad41,ad42 1,1
done
*************************************
*************************************
*************************************
*
* OBPSF:show variable: vorticity 1
* OBPSF:show variable: divergence 1
*
*
*************************************
*************************************
*************************************
*
general options...
* iterative implicit interpolation 1
* axisymmetric flow 0
* check for floating point errors 1
* check for floating point errors 0
* axisymmetric flow 0
* maximum iterations for implicit interpolation -1
* reduce interpolation width 3
*************************************
pressure solver options
* choose best direct solver
choose best iterative solver
*multigrid
******************************************
* multigrid parameters
* save the multigrid composite grid
* mg.hdf
* exit
******************************************
PETSc
**generalized minimal residual
**number of incomplete LU levels
**0
bi-conjugate gradient stabilized
additive Schwarz preconditioner
reverse Cuthill McKee ordering
relative tolerance
1.e-4
*absolute tolerance
*1.e-3
use iterative improvement
*number of incomplete LU levels
*1
exit
*************************************
implicit time step solver options
* choose best direct solver
choose best iterative solver
PETSc
**generalized minimal residual
**number of incomplete LU levels
**0
bi-conjugate gradient stabilized
additive Schwarz preconditioner
reverse Cuthill McKee ordering
relative tolerance
1.e-4
*absolute tolerance
*1.e-3
use iterative improvement
*number of incomplete LU levels
*1
exit
*************************************
close general options
*
*************************************
*************************************
*************************************
*
*
boundary conditions
all=noSlipWall
squarebig(0,0)=inflowWithVelocityGiven, uniform(p=1.0, u=1.0, v=0.0)
* squarebig(0,0)=inflowWithVelocityGiven, ramp(ta=0.0, tb=0.05, ua=0.0,
ub=2.7, va=0.0, vb=0.0),
squarebig(1,0)=outflow
squarebig(0,1)=slipWall
squarebig(1,1)=slipWall
*************************************
* squarebig(0,0)=inflowWithVelocityGiven, ramp(ta=0.0, tb=0.05, ua=0.0,
ub=2.7, va=0.0, vb=0.0),
* square(1,0)=outflow, pressure(1.*p+1.*p.n=0.)
* square(1,0)=outflow, pressure(1.*p+0.*p.n=1.)
** squarebig(1,0)=outflow,
* squarebig(0,0)=outflow, pressure(1.*p+1.*p.n=0.)
* squarebig(1,0)=outflow, pressure(1.*p+1.*p.n=0.)
* squarebig(0,1)=slipWall
* squarebig(1,1)=slipWall
*************************************
done
*
*
*************************************
*************************************
*************************************
*************************************
*************************************
*************************************
*************************************
moving grid options...
turn on moving grids
specify grids to move
rigid body
mass
0.495
density
* -1 is for unknow density
* -1
10.0
moments of inertia
0.0404
initial centre of mass
******** per naca verticale
0.5 0.0 0.0
initial velocity
0. 0. 0.
initial angular velocity
0. 0. 0.
body force
0 0 0
* position has no constraint
position is constrained to a plane
1 0 0
0 1 0
* position is constrained to a line
* 1 0 0
* 0 1 0
* position is fixed
* rotation has no constraint
rotation is constrained to a plane
1 0 0
0 1 0
* rotation is constrained to a line
* rotation is fixed
done
rotsmoothedPolygon
rotsquaresmall2
done
done
*************************************
initial conditions
* read from a show file
* band35.show
* -1
* OBIC:initial time 0.0
uniform flow
p=1.0, u=1.0, v=0.0
exit
project initial conditions
*************************************
exit
** debug 3
continue
movie mode
finish
************************************************************************************************************************************
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