Acoustic propagation simulation error

[qiangbo]

Hi,

I am trying to simulate the wave propagation process on a elastic material, which is surrounded by water. I am having the following error message when I try to run:

AN ACOUSTIC MEDIUM IS DEFINED FOR ELEMENT 50 INSTANCE WATER-1. ONLY ACOUSTIC ELEMENTS MAY HAVE THIS MATERIAL PROPERTY.

I searched but nothing seems to click. Anyone have a similar experience? What is the workaround?

Thanks.