Heave Damping Coefficient

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Tomas.Cortes
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Heave Damping Coefficient

Postby Tomas.Cortes » Thu Jun 27, 2019 1:35 pm

Hi everybody,

I was plotting the damping coefficients calculated by WAMIT for the OC4 semi-submersible that are provided in the github repository. All coefficients seem to be ok but Heave. I would say that as frequency goes to zero, so should the damping coefficient. Is this correct? But what's happening is that there's a steep slope in the range [0Hz-0.7Hz] that I wouldn't be expecting...
I've uploaded an image with the coefficients in function of frequency, for Heave. Any idea?

Thanks for in advance,

Tomás
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heaveDampingCoef.JPG
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Jason.Jonkman
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Re: Heave Damping Coefficient

Postby Jason.Jonkman » Thu Jun 27, 2019 2:22 pm

Dear Tomás,

Are you sure you are plotting the WAMIT data correctly? (To dimensionalize the nondimensional WAMIT data, you must multiply by the angular frequency in addition to the water density and length scales.) The WAMIT data for the OC4-DeepCwind semi for the first-order radiation solution is plotted in Figure 4-3 of the specifications report: https://www.nrel.gov/docs/fy14osti/60601.pdf, which clearly shows that the damping tends toward zero at low frequency.

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Tomas.Cortes
Posts: 29
Joined: Fri Mar 15, 2019 7:18 am
Organization: Mr
Location: Portugal

Re: Heave Damping Coefficient

Postby Tomas.Cortes » Fri Jun 28, 2019 6:02 am

Dear Jason,

I was missing that part. It now looks exactly as the graphs in the report. Thank you for the help!

Best regards,

Tomás


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