mesh displacement in CFX

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 April 22, 2014, 22:59 mesh displacement in CFX #1 New Member   Ma.L Join Date: May 2013 Location: ShangHai,China Posts: 17 Rep Power: 9 I want to know the displacement of a particle in one certain direction,for example direction Y,so i use the motion mesh.But there are two kinds of displacement:Total Mesh Displacement Y and Mesh Displacement Y.If i want to know the motion trail of a particle in direction Y,which one i should refer to?Namely,what is the difference between the two kinds of displacement? Thanks!

 April 23, 2014, 00:12 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 16,471 Rep Power: 128 I suspect you are getting confused between all the different displacements. "Mesh Displacement" and "Total Mesh Displacement" refer to the motion of the MESH during a moving mesh simulation. It has nothing to do with the fluid flow or the motion of particles. The variable "velocity" is the velocity of the FLUID. Neither of these variables tell you anything about the motion of a particle. If you are using lagrangian particle tracking then I think it is "Particle velocity". If you are using eularian particle models then you will have to do some work to extract the particle motions - maybe a streamline of the particle phase velocity field. If you are doing a rigid body simulation then it is in the rigid body variables.

April 27, 2014, 04:21
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Ma.L
Join Date: May 2013
Location: ShangHai,China
Posts: 17
Rep Power: 9
Quote:
 Originally Posted by ghorrocks I suspect you are getting confused between all the different displacements. "Mesh Displacement" and "Total Mesh Displacement" refer to the motion of the MESH during a moving mesh simulation. It has nothing to do with the fluid flow or the motion of particles. The variable "velocity" is the velocity of the FLUID. Neither of these variables tell you anything about the motion of a particle. If you are using lagrangian particle tracking then I think it is "Particle velocity". If you are using eularian particle models then you will have to do some work to extract the particle motions - maybe a streamline of the particle phase velocity field. If you are doing a rigid body simulation then it is in the rigid body variables.
Dear Glenn Horrocks,
Thanks for you reply.
I am using motion mesh for processing the simulation of the vortex-induced vibration for a cylinder.Now,i want to know the displacement of cylinder during the VIV, so i create a monitor particle on the center of cylinder,then i monitor this point I create when CFX is on solving.The question is that I have monitor the "Mesh Displacement" and "Total Mesh Displacement" for the user point, however i don't know which one is the real displacement of the point.Namely,what's the difference of the "Mesh Displacement" and "Total Mesh Displacement".
At last,I attached three graphic for this problem.
Kind regardsviv.JPG

mesh disp Y.jpg

total mesh disp Y.jpg

 April 27, 2014, 07:37 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 16,471 Rep Power: 128 It depends on how you have set it up, but Mesh displacement will probably be the change in mesh position from the last time step, and total mesh displacement is the absolute position of the mesh. The total mesh displacement is the integral of the mesh position.

 May 21, 2016, 05:24 Viv cylinder #5 New Member   abubakar izhar Join Date: Oct 2015 Posts: 9 Rep Power: 7 Dear I am trying to simulate VIV of CYLINDER IN CFX rigid body solver. I have made a sub domain around cylinder which follows the rigid body motion. Which type of mesh motion should I set on both sides of fluid fluid INTERFACE between the sub domain and outer fluid domain. If I use rigid body motion on both sides then mismatch between the mesh occurs on both sides of INTERFACE. SHOULD I USE conservative INTERFACE FLUX on both sides. What are effects of both. Moreover when I use conservative INTERFACE FLUX on both sides I get negative volume mesh but when I use rigid body solution on both sides I don't get negative volumes . The stiffness is set to 1[m5 /s]*VOLUME OF FINITE VOLUMES. Please guide.

 May 21, 2016, 07:19 #6 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 16,471 Rep Power: 128 The FAQ on this issue (http://www.cfd-online.com/Wiki/Ansys..._went_wrong.3F) has a tip on visualising the mesh motion. This is highly recommended for debugging mesh motion simulations.

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