Dear Jason

I am trying to model V-shaped semisubmersible in the ANSYS-AQWA, but unfortunately I am facing some problems in regard with Time-Domain analysis of the system.

I have got Time series of motions which are relative to COG(-30.6,0,-16) in six DoFs by AQWA. However, i want to get the motions in SWL（0,0,0）. I found the Tranmat martix in this Web. And the equation is q_cg=Transmat*q_swl. In other words,q_swl=Transmat^-1*q_cg.

Transmat=[1 0 0 0 16.2 0

0 1 0 -16.0 0 30.6

0 0 1 0 -30.6 0

0 0 0 1 0 0

0 0 0 0 1 0

0 0 0 0 0 1]

Transmat^-1=[1 0 0 0 -16.2 0

0 1 0 16.0 0 -30.6

0 0 1 0 30.6 0

0 0 0 1 0 0

0 0 0 0 1 0

0 0 0 0 0 1]

Then the displacement in Heave related to swl can be expressed Heave_swl=Heave_cg+30.6*Pitch_cg. In this paper, the aerodynamic force is simplified using a force-speed curve of NREL 5MW wind turbine. So the wind force can be converted to a steady thrust force in constat wind load case.

But after i calculate the heave motion related to SWl, the average heave motion is positive. However, the average motion in heave should be negative according to fig.1.

fig.1

fig.2

I would really appreciate it if you can help me!

best regards

Lixian.Zhang