Hi all, I have following problem. The geometry is very simple: air enters the pipe from one side under pressure. On the other side there is valve: the valve could be in one of two positions: "closed" where no flow is possible (pipe closed from one side) and "opened" where sucking occurs through the valve. The valve opens and closes periodicaly. I am using UDF to represent changes of the valve state in time but I dont know how to simulated closed valve with pressure BC.

Any ideas? Luk

Why don´t you change your pressure outlet to wall and backwards ?

Is it possible with UDF? I mean is it possible to periodicaly change type of BC for specified surface/face?

I didn´t work much with UDF´s. But I´m sure you can handle that with a journal file. The question is how often do you open and close?

About 100/sec. The size of the pipe is few cm in diameter and about 50cm length. Pressures are rather low.

O.K., i tried some things. To change the boundary condition with a journal file is possible. To start the journal file with an execute-comand works too. So there is a posibility to automate the whole thing but it´s a long way.

Maybe someone else knows an alternative.

Dear Sir, Thanks for Your kind help! I'll try this solution today in few hours.

Luk

last chance for me to help you is tomorrow, then I´m on holiday for 2 weeks - Jippie!!!!

The execute comand to start the journal is easy :

file read-journal nameofjournal

the journal comands to switch from wall to pressure outlet :

define boundary-condition modify-zones zone-type ( ID number of your face you want to switch ) pressure-outlet ( or wall when you switch back )

but be careful the settings of your pressure outlet are set to the default values. you can change them with :

define boundary-condition pressure-outlet

good luck

I wish Your nice holydays! Could You be so kind and send me email for further contact: my address is Lukasz.Czopyk@ifj.edu.pl. I promise not to disturb Your free time anyway.

Luk