OC4 Task 30 Phase II Load case 2.1

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Bertrand.Canetti
Posts: 23
Joined: Thu Oct 31, 2019 6:35 pm
Organization: University College of Cork
Location: Ireland

OC4 Task 30 Phase II Load case 2.1

Postby Bertrand.Canetti » Thu Nov 28, 2019 10:55 am

Dear all,

For the load case 2.1, deterministic waves, I have respected the following conditions:

- AeroDyn and InflowWind = 0
- ServoDyn = 0
- HydroDyn = 1 with H = 6 m, T = 10 s
- Support DOF (platform + tower enabled)

And yet, I do obtain a weird slow frequency in my surge response.

Image

I did not find where this additional frequency could come from. I have tried disabling the tower DOF, it is the same.

Thank you for your help,

Bertrand

Jason.Jonkman
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Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

Re: OC4 Task 30 Phase II Load case 2.1

Postby Jason.Jonkman » Fri Nov 29, 2019 9:03 am

Dear Bertrand,

What you are seeing is the surge natural period of the OC4-DeepCwind semisubmersible (which is around 120 s).

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

Bertrand.Canetti
Posts: 23
Joined: Thu Oct 31, 2019 6:35 pm
Organization: University College of Cork
Location: Ireland

Re: OC4 Task 30 Phase II Load case 2.1

Postby Bertrand.Canetti » Fri Nov 29, 2019 1:20 pm

Dear Jason,

Thank you for your answer.

Ok, but could you explain why this frequency is not visible in the surge OC4 results for load case 2.1 in the Code Comparison paper, page 8, figure 6?

Image

Best regards,
Bertrand

Jason.Jonkman
Posts: 4394
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

Re: OC4 Task 30 Phase II Load case 2.1

Postby Jason.Jonkman » Fri Nov 29, 2019 5:24 pm

Dear Bertrand,

The response you are showing from OC4 is taken after all start-up transients die out. The surge oscillation at its natural frequency results from the nonequilibrium condition and will decay away over time.

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


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