How to export single variable of a single surface?

zeitistgeld · September 25, 2009, 08:08

Does any body know how to export single variable of a single surface when doing a transient caculation. I don't want to export all the mesh and all the variables in trn files just in case my disk space will be used up. It seems that single varialbe of all the mesh is possible, but the TRN file size is still large. I have to save hundreds of trn files for a cycle. Thanks!

ckleanth · September 25, 2009, 08:12

while defining the tranisent save setup from the output control you can chose to save only selected variables. you diont export the mesh or anything else so if you do it this way whatever size you get this is what you have to live with.

zeitistgeld · September 25, 2009, 08:23

Thanks George. The problem is that I have to do integration over that surface mesh, so I have to export the single surface mesh.

ckleanth · September 25, 2009, 08:29

I assume the surface mesh area changes over timestep?

zeitistgeld · September 25, 2009, 08:37

Yes, George. The surface mesh is pitching as a matter of fact. It's a pitching airfoil. to solve the problem I encountered in the thread I posted long ago http://www.cfd-online.com/Forums/cfx...tml#post226063 .
if I can get the surface mesh and pressure of the airfoil I can get the drag through integration in the X direction and the viscous force is not included of course.

ckleanth · September 25, 2009, 09:01

not sure if you can export only a part of the mesh and to be honest I dont think you can however you can ask ansys and get the official version.

btw i was thinking about that problem you have/had with drag. if you are integrating the pressure to get the force I assume you use absolute pressure in your equation...

ghorrocks · September 26, 2009, 07:37

I think you are looking for a bad solution to a problem which should not exist. You should be able to calculate forces on surfaces using the CEL force_x/y/z functions and then you have no need to output anything except the final force value.

As I said in my previous post I cannot explain the differences you are seeing between the monitor points and the out file but you should investigate this further. If you can show one or the other (or both!) is wrong then you should report it as a bug and get it fixed.

It may be simply that the mesh motion is inconsistently applied between the CEL expression and the out file. Dunno, that's just a guess, you need to check this.

But I think you are going in the wrong direction by trying to export the datasets to do it elsewhere. Fix the real problem instead.

September 25, 2009, 08:08	How to export single variable of a single surface?	#1
zeitistgeld Member zeitistgeld Join Date: Apr 2009 Posts: 37 Rep Power: 17	Does any body know how to export single variable of a single surface when doing a transient caculation. I don't want to export all the mesh and all the variables in trn files just in case my disk space will be used up. It seems that single varialbe of all the mesh is possible, but the TRN file size is still large. I have to save hundreds of trn files for a cycle. Thanks!

September 25, 2009, 08:12		#2
ckleanth Senior Member George Join Date: Mar 2009 Location: Birmingham, UK Posts: 257 Rep Power: 18	while defining the tranisent save setup from the output control you can chose to save only selected variables. you diont export the mesh or anything else so if you do it this way whatever size you get this is what you have to live with. __________________ Top 4 tips 1. Knowledge is everything and Ignorance is dangerous. 2. Understand your limitations and try to eliminate them. 3. Get yerself a bike and hoon the chuffer. You will soon learn why dogs like to hang their heads out the car window. 4. Please before asking any questions on how to run simulations in CFX, go though all the tutorials

September 25, 2009, 08:29		#4
ckleanth Senior Member George Join Date: Mar 2009 Location: Birmingham, UK Posts: 257 Rep Power: 18	I assume the surface mesh area changes over timestep? __________________ Top 4 tips 1. Knowledge is everything and Ignorance is dangerous. 2. Understand your limitations and try to eliminate them. 3. Get yerself a bike and hoon the chuffer. You will soon learn why dogs like to hang their heads out the car window. 4. Please before asking any questions on how to run simulations in CFX, go though all the tutorials

September 25, 2009, 09:01		#6
ckleanth Senior Member George Join Date: Mar 2009 Location: Birmingham, UK Posts: 257 Rep Power: 18	not sure if you can export only a part of the mesh and to be honest I dont think you can however you can ask ansys and get the official version. btw i was thinking about that problem you have/had with drag. if you are integrating the pressure to get the force I assume you use absolute pressure in your equation... __________________ Top 4 tips 1. Knowledge is everything and Ignorance is dangerous. 2. Understand your limitations and try to eliminate them. 3. Get yerself a bike and hoon the chuffer. You will soon learn why dogs like to hang their heads out the car window. 4. Please before asking any questions on how to run simulations in CFX, go though all the tutorials

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September 25, 2009, 08:23		#3
zeitistgeld Member zeitistgeld Join Date: Apr 2009 Posts: 37 Rep Power: 17	Thanks George. The problem is that I have to do integration over that surface mesh, so I have to export the single surface mesh.

September 25, 2009, 08:37		#5
zeitistgeld Member zeitistgeld Join Date: Apr 2009 Posts: 37 Rep Power: 17	Yes, George. The surface mesh is pitching as a matter of fact. It's a pitching airfoil. to solve the problem I encountered in the thread I posted long ago http://www.cfd-online.com/Forums/cfx...tml#post226063 . if I can get the surface mesh and pressure of the airfoil I can get the drag through integration in the X direction and the viscous force is not included of course.

September 26, 2009, 07:37		#7
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	I think you are looking for a bad solution to a problem which should not exist. You should be able to calculate forces on surfaces using the CEL force_x/y/z functions and then you have no need to output anything except the final force value. As I said in my previous post I cannot explain the differences you are seeing between the monitor points and the out file but you should investigate this further. If you can show one or the other (or both!) is wrong then you should report it as a bug and get it fixed. It may be simply that the mesh motion is inconsistently applied between the CEL expression and the out file. Dunno, that's just a guess, you need to check this. But I think you are going in the wrong direction by trying to export the datasets to do it elsewhere. Fix the real problem instead.