Dear Dr. Jonkman,
Thank you for your reply very much.
I used the half of hydrodynamic load to make the simulation, and response of blade seems to be normal as shown below. The reason for half hydrodynamic load is that the response of surge of Offshore Model is about two times as large as response of OpenFAST. I extract the hydrodynamic load -HydroFxi from OpenFAST and compare it with hydrodynamic load from Offshore Model. The results show that the hydrodynamic load of Offshore Model is two times as large as the hydrodynamic load obtained by OpenFAST.
I get the generalized hydrodynamic load by the principle of virtual work:
DOFs: q_k
Virtual displacement of jth element: deltaR_j_i(q_k,t), i=1~3 means 3 displacements along x, y, z
Morison force of jth element: dF_j_i
Virtual work of jth element: delta_dW_j = sum(deltaR_j_i*dF_j_i), I = 1, 2, 3
Total virtual work of platform: delta_W = sum(delta_dW_j), j = 1~n_element
The displacement and Morison force are described in global coordinate system. Then I can get the generalized force by deriving virtual work (delta_W) with respect to DOFs (q_k).
And I have check that Offshore Model and OpenFAST have same wave field, i.e. for a sine wave, the wave height is twice the amplitude.
Is there any mistake I made? Could you give me some suggestions?
Thank you in advance.
Best regards,
Xing Tan