Thanks Danb for Earlier reply...
now I have one more doubt regarding rigid modeling for Tank

I have a Tank of SIZE 33 meters dia X 9 meter in height

Pipeline connected to tank nozzle of 56" size at height of 2 meter from bottom.

If I model rigid element with Tank dia 33m (1300") then I get heavy downword longitudinal Force (42tonnes) as compared to modeling rigid Tank with pipeline size of 56" loads are (18 tonnes).

and If Same system without modeling tank (rigid elements) with only using radial displacements and settlement

I get lower downword longitudinal force (4 tonnes) but huge moments

could you pls enligten