Thankyou for your suggestion sir. I tried to do the 1-way FSI as you said. But now I am getting this error, 'The normal of target element 184247 is not consistent with the normal of target element 184309 in real set 6561. Please use the ENORM command to correct it'. I read about it that the local axis of the two elements must not be matching so flip the element. Am I correct, But how can I find these elements. And also how can I use ENORM command or flip the same element. Note : I have got around 7000 elements in my model.nn