The calculated surge motion decays quickly compared to orcaflex

[ZhouYmi]

Dear Pere,
I have question about my data, the surge motion of my model, decays quickly compared to orcaflex. Is this related to the type of waves? Because I didn't see the Stokes second-order option in Orcaflex, I used the Jonswap wave.
Best,
Zhou

[ZhouYmi]

Sorry to bother you. Later, I tested the free decay motion of my floating platform model, and its free decay speed was too fast compared to Orcaflex. Why did this happen?@fronterapp

[fronterapp]

Dear Zhou,

From the image you sent, it seems you are using the K03 example which replicates the 15MW RWT with the VolturnUS platform. Note that I never tested nor validated this model in my thesis, where I considered a 5MW floating turbine.

When dealing with different models (CFD vs. Diffraction), it is important to acknowledge the differences between them before comparing the results. For example:

• Wave Spectra: irregular (OrcaFlex) vs. regular (CFD)
• Mooring: FEM (OrcaFlex) vs analytic catenary (CFD)
• Aerodynamics: BEM (OrcaFlex) vs ALM (CFD)
• Control: PI Controller (OrcaFlex) vs Constant Speed (CFD)
• Drag: Linear + Quadratic matrices (OrcaFlex) vs full non-linear (CFD)
• Tower: Flexible (OrcaFlex) vs none (CFD)

My recommendation is that you first compare your model with already validated results, the OC6 from IEA Task 30 might be a good place to start.

Best regards,
Pere

[ZhouYmi]

Dear Zhou,

From the image you sent, it seems you are using the K03 example which replicates the 15MW RWT with the VolturnUS platform. Note that I never tested nor validated this model in my thesis, where I considered a 5MW floating turbine.

When dealing with different models (CFD vs. Diffraction), it is important to acknowledge the differences between them before comparing the results. For example:

* **Wave Spectra**: irregular (OrcaFlex) vs. regular (CFD)

* **Mooring**: FEM (OrcaFlex) vs analytic catenary (CFD)

* **Aerodynamics**: BEM (OrcaFlex) vs ALM (CFD)

* **Control**: PI Controller (OrcaFlex) vs Constant Speed (CFD)

* **Drag**: Linear + Quadratic matrices (OrcaFlex) vs full non-linear (CFD)

* **Tower**: Flexible (OrcaFlex) vs none (CFD)

My recommendation is that you first compare your model with already validated results, the OC6 from IEA Task 30 might be a good place to start.

Best regards, Pere

Dear Pere @fronterapp ,
Thank you very much for your serious reply. It has been very helpful for me to learn CFD. I used your code to test the VolturnUS platform and its 15MW wind turbine in the past period. The free decay motion I calculated does not match the numerical simulation data released by IEA, which is why I am confused.
Do you mean the wind turbines and platform models which have undergone physical experiments or real sea test when you say 'already validated results'? For example, regarding OC6 from IEA Task 30 that you mentioned.
Also, there is a small question about mooring. I noticed that you are using a quasi-steady mooring model. If I want to modify it to a lumped-mass model or FEM model, what part should I modify from?Do I need to install Moody? I would greatly appreciate it if you could give me some advice.
Finally, thank you very much for your suggestion. I will test OC6 from IEA Task 30 In the following time. : )
Best,
Zhou