Dear rwoolhou,

Thank you for your answer. At the moment I have a relative easy model, please see attached, so I can figure out which node will move. For a complex geometry it will be a problem and I will have to figure it out later on. Basically, fluid is passing though the green area, it generates body forces of it and therefore I use ANSYS APDL to simulate the reaction of the green area.Then I export the new node position in a txt. file and try to use UDF to update the new node position. Would you give me any extra advice?