dynamic pressure boundary?
 

Hi,

I want to simulate something like a silencer, a tube with holes that open into another chamber. One end would have the inlet from the pump on partial load, the other end would be the outlet but it has a closing valve to it so it would have some sort of water hammer. Wouldn't this end be an inlet, too, since you would have some pressure input? Plus the pressure would not be static, but all I can find is static pressure.
How can I simulate this, what would be the boundary conditions for dummies? Plus wouldn't the result be dynamic, a pressure wave moving through the device, hope its dampened somehow?

Thanks,

Steffen