OC4 DeepCwindSemi Load Case 3.1

Wind & Water Computer-Aided Engineering Software Tools
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.

Sincerely,

Leo

2

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,