Dear Rob, Thank you again for your reply. I used a new thread, because this topic is different with my previous one.
This model, I want to simulated this process: the moving pipe solidification and melting in a hot melt, the melted parts will follow in the melt (momentum equation works), but for the un-melted part, it still keeps its original velocity (DEFINE_CG_MOTION works).
The reality is that: during the pipe motion, the pipe has been partly melted.
Yes, I agree with you to use a material & energy source term. However, I found, the method easily causes the solution unsteady, that can not converge well.
I also test some other methods, such as directly fixing the pipe velocity. But when I fixed the pipe motion, the melted parts flow in the melt can not been simulated. Even I used some "if" statement to control the open and shut of the fixed velocity. I guess, once we use the fixed velocity, it will work in the whole modelling. Please correct me, if I am incorrect.
I wonder, if there are any other robust methods for simulating a similar process? something like controlling the switch from a solid zone to a fluid zone according to a specific "if" statement. If so, we can specify the un-melted part surface as a solid wall, while set the melted part wall as a interior (fluid zone).
Thank you in advance.