2-dimensional tail gate in ansys fluent
 

Hi!!
I am simulating hydraulic jump in a 2-d rectangular flume(channel). The channel has inlet at left and a tailgate at right. I want the tail-gate to be vertically raised or lowered at :
some specified rate ,
upto some specified height ,during calculations.

In other words, while the flow is being calculated , I wish to raise the tail-gate i.e I want the boundary condition at the tail-gate to gradually change from "wall" to "pressure-outlet" at some rate. Also I may want to lower the tail-gate i.e change the boundary back from "pressure-outlet" to "wall".

Can you please provide me an UDF / scheme to do this. I am totally ignorant about Coding.