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raymond September 17, 2001 06:11

Is it necessary to apply moving meshes?
Now I'm simulating the airflow in two room with a door connected. The door was closed at first, then opened suddenly under specific condition. That means that some solid cells in the domain can change to liquld material while doing calculation. Could it be possible to applying attachment boundary condition? But the attached cells are connected with face. Is there any method to do this kind of simulation?

John September 17, 2001 08:41

Re: Is it necessary to apply moving meshes?
STAR-CD's conditional attachment event could be what you are looking for - it's applied to the cell face such as the door between two rooms. You can specify the condition for the cells cut off by the door to see each other - before this condition is satified, the faces are treated as wall; when the condition is met, the wall condition becomes a normal cell face. You should be able to get further information from CD.

Richard September 17, 2001 09:07

Re: Is it necessary to apply moving meshes?
Moving mesh (i.e. conditional attach) is one possibility. But presumably you know a priori when the door is going to open and/or close. In this case you can just run an "Advanced Transient" analysis. Each boundary region can have its boundary condition re-defined at the start of each load-step - hence you could have a boundary region representing the door which changes from a wall to an "open" condition (inlet, pressure etc) when the door opens.

raymond September 17, 2001 23:08

Re: Is it necessary to apply moving meshes?
Thank you for your kindness help. I have thought about it before. But the problem is that the door is located between two rooms (inside the computational domain). It could not be defined as a boundary condition. Is it possible that I could change the cells representing the door to the fluid during the next time step? Does it affect the geometry file? If yes, what should I do?

raymond September 17, 2001 23:12

Re: Is it necessary to apply moving meshes?
Thanks. But the poroblem is that the door I defined has one cell thickness. The attechment event consider the door as a thin surface between two fluid cells. How do I apply attachment event to this kind of problem?

Philip Jones September 18, 2001 02:47

Re: Is it necessary to apply moving meshes?

In this case I think there is no need for moving meshes, you are simply taking a layer of cells that are not active in the first part of the calculation and turning them on in a second part of the calculation. There are two obvious ways to do this.
  1. Treat the run as two calculations. Perform the first run to the point the door opens. Then switch to a mesh with the door open and do a second run. Prostar has a command SMAP that allows the solution to be mapped from one mesh to another. The new cells where the door has just opened can be assigned default fluid values or those of neighbouring cells.
  2. Model the problem with the door cells always there but disable them, you could use porosity and set them to a high value in the firt part of the calculation and a low in the second or you could use user coded momentum to set the velocity in these cells to zero for the first part of the calculation (my prefered route the the whole problem). If you are solving for temperature you could also set the temperature of these cells.

Hope this helps


raymond September 18, 2001 20:58

Re: Is it necessary to apply moving meshes?
Thanks very much! For the second method, could you please tell me a little more clear? Which user subroution should be used to set up the velocity at each time step?

Philip Jones September 19, 2001 02:45

Re: Is it necessary to apply moving meshes?

Please note this is a forum, one definition of which is "A public meeting place for open discussion". This means that if you have a general question such as that you asked at the start of this thread then this is the place to air it and you have got sensible answers. You are now asking specific questions to a specific person, this is not a forum, you have my email address for private discussion but your proper route should now be to STAR-CD support who can help you on such details.

Crib sheet for experienced users only: sormom.f with some code like this freezes the velocity field in selective areas:
if(ictid.eq.2) then



raymond September 21, 2001 02:10

Re: Is it necessary to apply moving meshes?
Thanks anyway!

Sreenadh Jonnavithula October 1, 2001 17:11

Re: Is it necessary to apply moving meshes?
Aren't you getting carried away with minor details? What difference does it make if there is one extra layer of cells (on either domain)? i.e. treat the door as fluid cells always, but place an attach boundary on one side; when this is open, no flow through door (but the volume of one of the rooms is slightly higher); and when the door is open, attach the rooms together ..

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