How to update components of face boundary zone?
 

I am doing a laser cladding model, where mass flow is added in a moving molten pool (convection flow inside) on workpiece. I need to trace the growth of clad hump. If the workpiece top surface boundary can be updated at each time step, the face zone thread needs to be re-grouped. I think fluent does not allow to do so in UDF. So I am thinking to use multiphase model - consider a bigger domain which include workpiece and some null elements (air) above the workpiece. I can update the clad shap by some method. But how to add the boundary condition at the air/clad interface, such as laser power, convection and radiation heat transfer? Any suggestion is appreciated!