I am trying to simulate response of structure with TLD using ANSYS APDL. I mesh the fluid volume and tanker so that they can have coincident nodes, merge the nodes, flagged on FSI for the interface areas plus I assign SURFACE-To_SURFACE contact between tanker and structure slab (which am not sure if it's the right way to assign connection between tanker and top slab). when i run modal analysis for the fluid filled tanker (with out attaching it to the structure) i find frequency value which is almost equal with Housner's equation, but when i do the modal analysis for the structure+TLD and check the deformed shape the fluid elements penetrate the structure boundary and don't know how to correct it. I would appreciate if any one can give me some recommendation how to solve the problem. For your reference i have attached the snip of the deformed shape. Thank you in advance