Dear Sarvenaz hoseini ghafari

I think that you could solve your problem by using buffer

In the manual, it mentioned that, buffer could be used for thin objects like the shells.

for the mesh part, you could combine various mesh techniques.

such as combined mesh (put some finer mesh box into coarser mesh box) which you see in this article

Article Investigation of Flow, Erosion, and Sedimentation Pattern ar...

Kind Regards,

Hanif

Thank for your answer. actually I have put diverse methods of mesh techniques but they have not work out as well as expected. mind you, I am facing a sort of complicated geometry. At any rate, I will try your propose.

Best regards

be careful about the mesh dimensions

coarser mesh should be 2 times max from finer mesh

Dear Wei Chek Moon

Thanks for your answer. would you please guide me more about " grid convergence test "! is it a particular simulating setting or an overall concept in simulation?

I had contemplated on simulating by part but unfortunately, it is not possible in this case.

have you had any experience on "Conforming Mesh"? If so, let me know please.

Best regards