Dear Bacha Munir ,

I think the following links can help you. In the first case, ignore the electric field.

- https://www.comsol.com/model/separation-through-electrocoalescence-8592

- https://www.comsol.com/model/droplet-breakup-in-a-t-junction-1994

Not clear exactly what you are comparing...the first experession is just the rewriting of the normal component of the velocity vector in terms of its cartesian component, the second expression is not clear at all, is x a vector position ? Are you considering a rigid translation in the flow?

Thank you my mistake. These are actually two kinematic boundary conditions, first one for interface normal motion and second one is the tangential component depends on time. (if i am wrong, please correct me).

My problem is, i want that the mesh move with the calculated x-component of velocity (using second condition) from left to right. In the attached figure, an elliptical shape bubble moving from left to right, but i do not know that second condition is correct or not for such interface motion to couple with fluid velocity. if correct, then how to apply it in comsol modeled based equations.

https://www.researchgate.net/post/How_to_remove_the_inverted_meshes_from_the_model, please also check it. thank you so much sir.

Is the movement of the bubble rigid and translating along x?

yes?. in fluid direction, from left to right.

I don't understand what you are...seems just the simulatuon of a flow around a fixed bluff body ... why do you need to move the mesh?

Dear Bacha Munir ,

I think the following links can help you. In the first case, ignore the electric field.

- https://www.comsol.com/model/separation-through-electrocoalescence-8592

- https://www.comsol.com/model/droplet-breakup-in-a-t-junction-1994

Thank you so much dear Farhad. Please, can you download for me that file, I am not able to download. I will be very thankful to you. Thank you.