Heave difference between Openfast and simpack for semi-submersibles

1

Dear all，

I did heave free decay in Simpack and compared it with Openfast, both of them give an initial displacement of 8m, but the result of simpack has a negative offset in the Z direction compared to Openfast, I want to know Why is that.

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Best regards，
Monge.

2

Dear @Monge.Low,

Do both models have the same total mass, undisplaced buoyancy, and vertical mooring pretension?

Best regards,