Computing hydrodynamic loads

Hi everybody,
I am working on my master thesis, which concerns developing a floating support structure for a wind turbine with an elliptical tower cross section and a yaw bearing at the tower base. I am thinking of several possible support structure concepts (barge, TLP, buoy or semi-submersible) and I have to calculate the hydrodynamic loads on the submerged structure. I can see from the test 22, 23 and 24 files that the hydrodynamic loads are frequency dependent and have been calculated using the software WAMIT. Unfortunately, my institution does not have a license for WAMIT and I now ask if anyone know of a free, open-source software that can generate the same type of files as WAMIT (.hst, .1 and .3) that can be read by FAST8? I have looked a little into NEMOH, but it does not appear to be able to generate the 3 file types needed for FAST8.

Best regards

Jacob K. Pedersen

Dear Jacob,

NEMOH is the only open-source WAMIT-type code that I’m aware of. I only have a little experience with NEMOH myself, but I’ve heard that NEMOH is quite good compared to WAMIT. I’m not sure whether NEMOH can directly output to the WAMIT output format needed by FAST’s HydroDyn module, but if not, it should not be hard to convert to WAMIT output format yourself—the format of the WAMIT-generated output files (*.1, *.3, and *.hst, etc.) can be found in Chapter 4 of the WAMIT User’s Manual, available online:

NEMOH is limited to the first-order problem (and second-order mean-drift loads that can derived from the first-order problem); if you need second-order terms, you’ll have to buy WAMIT (or an equivalent commercial code) anyway.

Best regards,

Dear Jason,

Thanks for your reply, I will have a closer look at Nemoh.