OC4 DeepCwindSemi Load Case 3.1

Dear Dr. Jonkman,

I am trying to modify the “NRELOffshrBsline5MW_OC4DeepCwind.fst” file to run mooring analysis using the MoorDyn module for Load Case 3.1.

The sample file is currently set to run the analysis using the FAST-OrcaFlex interface without including the HydroDyn module.

After switching the mooring computing module from OrcaFlex to MoorDyn and adding the HydroDyn module to the sample code, I was able to run the simulation except I am receiving an error in the middle of final computation stage.

The simulation stops at 12 second of 60 seconds with the following:
CalcOutput: IFW_UniformWind_CalcOutput: GetWindSpeed:Height must not be negative.
IFW_UniformWind_CalcOutput: Error calculating the wind speed at position (-7.804, -10.742, -8.45430E-02) in the wind-file coordinates.

I am using the same Inflowwind data that the original code is referring to (NRELOffshrBsline5MW_Inflowind.dat), so I am not sure what adjustment I need to make in order to complete the simulation.

I just want to compare the simulation results between the FAST-MoorDyn cooupling and FAST-OrcaFlex coupling.

Any comment on how to resolve this issue would be greatly appreciated.

Also, is there a publicly available simulation result run by FAST for this Load Case? Please let me know.

Thank you for your time.



Dear Leo,

I’m not exactly sure why you are receiving that error. However, Test25 in the CertTest of the FAST v8 archive is a model of the NREL 5-MW turbine atop the OC4-DeepCwind semisubmersible using HydroDyn and MoorDyn: nwtc.nrel.gov/FAST8. While Test25 is set up to run IEA Wind Task 30 OC4 load case 3.7, it could quite easily be modified to run load case 3.1. I suggest comparing your model with the model available in Test25 to see what the differences are.

Best regards,