moving wall with grid_motion?

Joerg

Hello i have a problem. i want to move a piston. the piston is in a membrane. so i have to simplify the problem. my problems are the walls next to the piston. they have to move with the piston. one side of the wall is fixed an the other side is moving. i hope you understand my problem. so my question is, which define macro should i use? the define_geom, the define_grid_motion or another? and how should i read the udf. i have problems to understand the example of the udf manual, because there are instructions i could not find in the index. like: NV_D NODE_X(v) NODE_POS_NEED_UPDATE(v) NODE_POS_UPDATE(v) NODE_COORD

i hope somebody can help me.

Thanks Joerg