Dynamic mesh issue

moloykb · September 12, 2012, 06:20

Dear all,
I am trying to simulate the flow through a artery in the presence of stenosis with surface irregularities. The artery wall is assumed to oscillate with a velocity of sinusoidal variation. In order to define the motion of the wall I am using the Dynamic mesh feature of Fluent with the following compiled udf to define the motion of the wall.

#include "udf.h"

DEFINE_CG_MOTION(wave, dt, vel, omega, time, dtime)
{
vel[1]=-.0001*7.543*sin(7.543*time);
}
For the unsteady simulation I am using a time step size of 0.0001 sec and as a mesh method I am using Layering approach with a split and collapse factor of 0.4 and zone type as rigid body.
But unfortunately when I try to run the simulation it shows the error Update-dynamic mesh failed: negative cell volume detected.
Please help me.

cfd seeker · September 12, 2012, 11:21

try reducing your time step size and also play with dynamic mesh parameters, also turn on smoothing

moloykb · September 13, 2012, 01:32

Dear cfd seeker
thanks for your reply. I have already reduced the time step upto 0.000001 sec, but till the same problem exists.Regarding the parameters how to choose the proper value of those.

nimbus1947 · September 13, 2012, 04:38

Try using triangular mesh and use re-meshing instead of layering.

If you insist on going with quad mesh try the following
1. Set the udf motion for the fluid (the quad mesh region)
2.Set the boundary as stationary.

cfd seeker · September 13, 2012, 07:03

Quote:

Originally Posted by nimbus1947

Try using triangular mesh and use re-meshing instead of layering.

If you insist on going with quad mesh try the following
1. Set the udf motion for the fluid (the quad mesh region)
2.Set the boundary as stationary.

which boundary to set as stationary?

moloykb · September 13, 2012, 07:17

dear nimbus1947
how to set the udf motion for the fluid zone and what is the stationary boundary. Would u please elaborate something?

nimbus1947 · September 13, 2012, 08:56

upload the picture of your full domain with boundary names.

fluentworkshop · September 24, 2012, 08:02

Hi guys
Cell height of wall (in dynamic mesh zones) must not be zero.
or you must use another wall as stationary and also quad zone must be move with same udf.

cfd seeker · September 24, 2012, 13:07

Quote:

Originally Posted by fluentworkshop

Hi guys
Cell height of wall (in dynamic mesh zones) must not be zero.
or you must use another wall as stationary and also quad zone must be move with same udf.

didn't get your point?

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September 12, 2012, 11:21		#2
cfd seeker Senior Member Join Date: Mar 2011 Location: Germany Posts: 552 Rep Power: 20	try reducing your time step size and also play with dynamic mesh parameters, also turn on smoothing

September 13, 2012, 01:32		#3
moloykb Member Dr. Moloy Kumar Banerjee Join Date: Jun 2011 Posts: 71 Rep Power: 15	Dear cfd seeker thanks for your reply. I have already reduced the time step upto 0.000001 sec, but till the same problem exists.Regarding the parameters how to choose the proper value of those.

September 13, 2012, 04:38		#4
nimbus1947 New Member Join Date: Sep 2009 Location: IIT Kharagpur Posts: 10 Rep Power: 17	Try using triangular mesh and use re-meshing instead of layering. If you insist on going with quad mesh try the following 1. Set the udf motion for the fluid (the quad mesh region) 2.Set the boundary as stationary.

September 13, 2012, 07:17		#6
moloykb Member Dr. Moloy Kumar Banerjee Join Date: Jun 2011 Posts: 71 Rep Power: 15	dear nimbus1947 how to set the udf motion for the fluid zone and what is the stationary boundary. Would u please elaborate something?

September 13, 2012, 08:56		#7
nimbus1947 New Member Join Date: Sep 2009 Location: IIT Kharagpur Posts: 10 Rep Power: 17	upload the picture of your full domain with boundary names.

September 24, 2012, 08:02		#8
fluentworkshop New Member CFD man Join Date: Sep 2012 Location: Earth Posts: 12 Rep Power: 14	Hi guys Cell height of wall (in dynamic mesh zones) must not be zero. or you must use another wall as stationary and also quad zone must be move with same udf.