OC4 DeepCWind Phase II Load Case 2.2

Wind & Water Computer-Aided Engineering Software Tools
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Dear all,

I am a MS student who is very new to OpenFAST. I’m trying to run the load case 2.2 with irregular waves and obtain similar results as the documentation. I’ve ran the simulation and put the .outb file in BEMRosetta to visualize the motions. I have shown my work to my professor but she said that the B1(DOF) and Ptfm(DOF) graphs should not be identical. I assumed that the B1 is Body 1 from HydroDyn and the difference is that since Ptfm is an output of ElastoDyn, the output motion should be influenced by the rest of the structure unlike HydroDyn. I’m not sure if this is correct. I can not figure out how I can fix this problem or if it is a problem at all. I’m sorry if this is a ridiculous question, I’m a bit lost. Below I have attached the graphs I have obtained for surge and heave but the other 4 DOFs are the same.

Thank you.

Scatter plot1
Scatter plot11000×600 92.4 KB

Scatter plot
Scatter plot1000×600 69.4 KB

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Dear @Bilge.Kutay,

I would say this is not an issue. In the OpenFAST model you are using, ElastoDyn solves for the structural dynamics and HydroDyn solves for the hydrodynamics, with motions and loads passed back and forth at each coupling (time) step. The motion of the nodes in HydroDyn should follow the motion of the nodes in ElastoDyn, accounting for moment arms associated with any offsets in reference position, and the motion will be identical between the hydrodynamic and structural nodes if the reference positions are the same in the two modules.

Best regards,

1 Like
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Dear Jason,

Thank you for your reply, I will bring this up with my professor with ease of mind.