openfast v2.3

Topics of general, but wind-related interest.

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Akheel.Kodambiyakamkizhakkakam
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Organization: NIT Calicut
Location: India

Re: openfast v2.3

Postby Akheel.Kodambiyakamkizhakkakam » Wed Nov 11, 2020 9:00 pm

Dear Sir,
I referred the paper 'Coupled modeling and structural vibration control for floating offshore wind turbine' by Yang et. al, 2020. I plotted the time series for surge under (load case 2 in the paper, Fig 16.a). I have attached a word file in which I have compared surge time series I obtained with the one in the paper. I have been trying to simulate this correctly for around two months. I could not understand where I am wrong.

Thanks
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SURGE COMPARISON.docx
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Jason.Jonkman
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Re: openfast v2.3

Postby Jason.Jonkman » Thu Nov 12, 2020 6:10 am

Dear Akheel,

Well, I'm not familiar with the Yang et al paper, nor with how you've set up your simulation, so, I can't really comment on what is different.

Regardless, the plot you are showing appears to be focused on the start-up transient, rather than the converged solution I would expect that you'd focus on when analyzing a forced vibration response. How does the solution look after all start-up transients decay away (much longer into the simulation)?

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

Akheel.Kodambiyakamkizhakkakam
Posts: 51
Joined: Wed Jul 15, 2020 5:28 am
Organization: NIT Calicut
Location: India

Re: openfast v2.3

Postby Akheel.Kodambiyakamkizhakkakam » Mon Nov 23, 2020 4:00 am

Dear Sir,
I have simulated a free vibration case with initial fore-aft displacement 10m. Then I incorporated a TMD into it. I could observe that the TMD vibration was shifted. Attached a plot for better understanding.
1. What could be the probable reason for it.
2. What do I need to infer if similar behavior is observed in any degree of freedom under wind or wave action
Attachments
FreeVibration.docx
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Jason.Jonkman
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Re: openfast v2.3

Postby Jason.Jonkman » Wed Nov 25, 2020 8:18 pm

Dear Akheel,

Regarding (1), are you asking why the heave displacement has a different mean when you incorporate a TMD? My guess is this is related to the increased weight within the system (because of the mass added by the TMD), which you have not compensated for in the floating wind turbine by increasing the static buoyancy or reducing the mooring pretension.

Regarding (2), I'm not sure I understand your question.

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

Akheel.Kodambiyakamkizhakkakam
Posts: 51
Joined: Wed Jul 15, 2020 5:28 am
Organization: NIT Calicut
Location: India

Re: openfast v2.3

Postby Akheel.Kodambiyakamkizhakkakam » Thu Nov 26, 2020 7:19 pm

Dear Sir,
Regardiung (2), I meant that if I see similar behavior (shift in mean position) for any dof (not necessarily Heave) under wind and wave, Will it be due to increased draft?

Jason.Jonkman
Posts: 5738
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

Re: openfast v2.3

Postby Jason.Jonkman » Fri Nov 27, 2020 6:32 am

Dear Akheel,

Sorry, but I still don't really understand what you are asking.

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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