Time dependent gate opening
 

Dear friends, I have a problem with time dependent gate opening in a particulate flow chamber. The gate is located at the bottom of the chamber. It opens while the mass stacked on it over a certain weight. Generally it takes 2-3 mins. Could you please suggest how to resolve that gate boundary? Now I am using wall boundary there, but I don't know how to put time dependent movement of that gate. Please suggest some idea. Thx

krish