Significant Wave Height

Good Morning,

I am looking for a value of the significant wave height that would be typical for floating wind turbines. In the Certification Test file, NRELOffshrBsline5MW_OC4DeepCwindSemi_HydroDyn, the significant wave height is entered as 1.2646. Since this value is used in a Certification Test and there are 4 decimal places, I was wondering if there is an underlying basis for this number.

Arnold Ramsland

Dear Arnold,

Well NRELOffshrBsline5MW_OC4DeepCwindSemi_HydroDyn.dat came from a specific load case used with the IEA Wind Task 30 OC4 project. This is more of an example rather than a recommendation.

In general, the significant wave height is site specific and conditioned on mean wind speed (typically the higher the mean wind speed, the higher the wave height). Design standards dictate what significant wave height to use for each load case (e.g., the expected value conditioned on mean wind speed, a range of values based on the joint-probability distribution, the 1-year extreme value, or the 50-year extreme value).

Best regards,

Thank you.

Dear Jason,

I would like to know if i can get the distributed hydrodynamic loads of waves on the substructure portion above the MSL.

I’ve enabled the second order waves and put an output point righ above the MSL, so that is is located between the mean sea level and the significant wave amplitude. However, its output value is zero for all time steps.

Many thanks.


Dear Felipe,

Calculating wave kinematics and wave loads above MSL requires some sort of wave stretching implementation. We did have a project to add wave stretching into OpenFAST, but the project ran out of funding before a successful completion, and the solution was not numerically stable for structural flexible substructures; and we have not yet been funded to restart and finish the project. If you already have wave kinematics at all hydrodynamic analysis nodes, then you can use the WaveMod = 6 option to employ wave kinematics with wave stretching.

Best regards,