Learning Forum

[Max4]

Hi everyone,

As an attachment, an illustration of the problem. This models a cylinder with an inlet and outlet and piston movement.

- Case 1: When the piston goes down, we have mass flow at intlet and a closed outlet.

- Case 2: When the piston goes up, we have a closed inlet and a pressure at outlet.


I have write the UDF for the movement of the piston.

I want to write a UDF for the inlet and outlet depending on the movement of the piston, i.e. when the acceleration is negativ (Case 1) -> mass flow of x kg/s ; when the acceleration is positiv (Case 2) -> pressure of X Pa


Do i have to use UDM Macros ? In order to change the type of the boundary (mass flow inlet to wall), may I have to use a Scheme file and the TUI-Command or use a journal file?


Thank you.


Regards,


Maxime

[DrAmine]

Yes to change the kind of boundary you need to use scheme. So mixture of UDF and Scheme is required here. Or just use Dynamic Mesh Events to change a boundary type after certain time lasted.

[Max4]

Thank you for your reply. I can´t use Events because I want to do it for a random velocity profil, but good to know that it exists.

In the UDF for the movement of the piston, I have defined the velocity. Can I just define a variable (e.g. acceleration = -sin(..*time)) which has no effect for this UDF, but which is mandatory for the inlet/outlet boundaries UDF? In order to use this variable (acceleration) for the UDF of inlet/outlet, may I have to use UDM?

Regards,

Maxime

[DrAmine]

Yes you can use the UDM's as placeholder for that.