Error running HydroDyn file

Discuss field testing of turbines and structural testing of components.

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Ka.Chang
Posts: 7
Joined: Sat Aug 08, 2020 9:13 pm
Organization: Jiangsu University
Location: China

Re: Error running HydroDyn file

Postby Ka.Chang » Fri Aug 14, 2020 3:31 am

Dear Dr. Jonkman,

Thank you very much!

I revised it as you suggested and recalculated the PtfmHeave value.I think the simulation result should be correct.Do you think it is right?

As you mentioned,the expected mean values of rotor speed and blade-pitch angle as a function of mean wind speed are given in Figure 9-1 of the NREL 5-MW specifications report.I only modified the rotor speed and blade pitch angle,However,I noticed that there are other parameters(TTDspFA,TTDspSS,OoPDefl,IPDefl) that need to be modified in the ElastoDyn.

Best regards,
Attachments
Tower Top Load curve.png
Tower Top Load curve.png (84.2 KiB) Viewed 1238 times

Jason.Jonkman
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Re: Error running HydroDyn file

Postby Jason.Jonkman » Fri Aug 14, 2020 6:35 am

Dear Ka.Ching,

Indeed, YawBrFzp is looking much better now. A very small adjustment to the initial PtfmHeave could likely eliminate the small lingering ringing.

The initial rotor speed and blade-pitch angle (and platform heave when using SubDyn) are the most critical initial conditions to get correct for a fixed-bottom offshore wind simulation. You could set the intial blade and tower-top deflections to their expected mean values as well, which will further reduce the start-up transients, but not by much.

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

Ka.Chang
Posts: 7
Joined: Sat Aug 08, 2020 9:13 pm
Organization: Jiangsu University
Location: China

Re: Error running HydroDyn file

Postby Ka.Chang » Sat Aug 15, 2020 8:39 am

Dear Dr. Jonkman,

That's very useful guidance on how to set the initial conditions in ElastoDyn.Thank you once again for your help.

Best regards,

Ka.Chang
Posts: 7
Joined: Sat Aug 08, 2020 9:13 pm
Organization: Jiangsu University
Location: China

Re: Error running HydroDyn file

Postby Ka.Chang » Thu Oct 29, 2020 7:05 pm

Dear Dr. Jonkman,

I'm sorry to trouble you again.I found RAO of the tower top(YawBrTDxp) under the unit regular wave(Hs=2m).I can get the resonant frequency from RAO.I study the motion response of the tower top under wave(still air:set CompInflow=0,CompAero = 2 and WakeMod = 0).condition i:regular wave(Hs=0.5m Tp=3.2258s/Resonance period),condition ii:Pierson-Moskowitz spectrum(Hs=0.5m Tp=3.2258s/Resonance period).however,I found that regular wave wave can cause tower top resonance and irregular wave can't cause resonance.Is the result reasonable?

I would be very happy if you could give me some guidance.
Best regards
Attachments
tower top motion results.zip
(198.66 KiB) Downloaded 48 times

Jason.Jonkman
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Re: Error running HydroDyn file

Postby Jason.Jonkman » Fri Oct 30, 2020 7:22 am

Dear Ka.Chang,

A resonance response will be impacted by the amplitude of excitation at the resonance frequency and the damping of the system. I would assume the system damping is set the same between the regular and irregular wave simulations. However, the amplitude of excitation quite different in the two cases. In the regular wave case, all of the energy is concentrated at the resonant peak. In the irregular wave case, the energy is spread across a range of frequencies, with less energy at the resonant peak. I'm sure you can induce more resonance in irregular seas if you increase the wave energy / signficant wave height.

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

Ka.Chang
Posts: 7
Joined: Sat Aug 08, 2020 9:13 pm
Organization: Jiangsu University
Location: China

Re: Error running HydroDyn file

Postby Ka.Chang » Sat Oct 31, 2020 8:34 am

Dear Dr. Jonkman,

the system damping is set the same between the regular and irregular wave simulations.I agree with you that increasing wave height can induce more resonance in irregular wave.But I still have some doubts.firstly,Can I come to the conclusion that regular wave can cause tower top resonance and irregular wave can't cause resonance under the environmental conditions mentioned above ? what's more,I found that the resonance amplitude didn't increase much under the conditions ii mentioned above,when I increased the simulation time from 800 seconds to 1500 seconds .Is the response of tower top motion at resonance frequency related to simulation time ?

Best regards
Attachments
Comparison chart of different time.png
Comparison chart of different time.png (152.64 KiB) Viewed 976 times

Jason.Jonkman
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Re: Error running HydroDyn file

Postby Jason.Jonkman » Mon Nov 02, 2020 7:05 am

Dear Ka.Ching,

After the initial growth during the start-up transient, the resonant response will be limited by the damping in the system and not grow indefinitely. So, I would not expect the resonant response to be strongly dependent on the simulation length. And I wouldn't say that regular waves can cause resonant response and irregular waves cannot cause resonance. Instead--as I implied in my prior post--you can increase the resonant response by adding energy at the resonant frequency or by decreasing the damping.

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

Yicheng.Fan
Posts: 6
Joined: Sat Dec 14, 2019 12:08 am
Organization: Huazhong University of Science and Technology
Location: China Wuhan

Re: Error running HydroDyn file

Postby Yicheng.Fan » Fri Jan 22, 2021 5:12 am

Dear Jason,

When I use OpenFAST to run 5MW_OC4Semi_WSt_WavesWN.fst, I set the environment to still air and regular waves, with a wave height of 7.56 m and a period of 10.6 s. The result of surge after running for 600 s is shown in the figure. The result seems to be wrong, because the result changes around 0 after the operation is stable, which seems incorrect. Could you please guide me where is the mistake? Thank you very much!
Attachments
surge.png
surge.png (36 KiB) Viewed 626 times
HydroDyn.png
HydroDyn.png (194.05 KiB) Viewed 626 times

Jason.Jonkman
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Re: Error running HydroDyn file

Postby Jason.Jonkman » Fri Jan 22, 2021 6:43 am

Dear Yicheng,

I don't really see anything unexpected with this response. The system appears to be initialized with zero initial conditions. And the initial platform velocities are zero. During the start-up transient, the system will want to pitch (due to the overhanging weight of the rotor), which induces surge motion. The periodic excitation from regular waves also gets applied at time zero. Eventually, the initial condition solution dies out and the periodic response from regular wave excitation dominates the response.

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

Yicheng.Fan
Posts: 6
Joined: Sat Dec 14, 2019 12:08 am
Organization: Huazhong University of Science and Technology
Location: China Wuhan

Re: Error running HydroDyn file

Postby Yicheng.Fan » Sat Jan 23, 2021 5:53 am

Dear Jason,

Thank you very much for your answers, what you said is correct, I set all initial conditions to 0. The correct result of this calculation is very useful to me. At the same time, I want to ask one more question. When I just only change the load environment to use P-M irregular waves (WaveMod = 2) and Kaimal turbulent wind, and then use the same files to calculate again, the results of the platform pitch and tower top fore-aft displacement make me feel very confused and doubt whether it is correct. Could you please answer my confusion? It would be greatly appreciated if you can guide me from which papers I can obtain the results and figures of floating wind turbines under the action of irregular waves or/and turbulent wind. Thank you in advance!

Best regards,
TTDSPFA.png
TTDSPFA.png (20.9 KiB) Viewed 612 times
pitch.png
pitch.png (17.9 KiB) Viewed 612 times

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

Re: Error running HydroDyn file

Postby Jason.Jonkman » Sat Jan 23, 2021 12:01 pm

Dear Yicheng,

Again, these results are expected. After the initial start-up transient, the structure is excited from the wind and waves. The mean pitch comes from the aerodynamic thrust force. As with any simulation, it is generally recommend to post-process the simulation results only after the start-up transient is over--which looks to be about 100 s in your case. You can minimize the start-up transient by setting proper initial conditions for the rotor speed, blade, pitch, platform surge, and platform pitch DOFs, based on their expected value for the given mean hub-height wind speed you are simulating.

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

Yicheng.Fan
Posts: 6
Joined: Sat Dec 14, 2019 12:08 am
Organization: Huazhong University of Science and Technology
Location: China Wuhan

Re: Error running HydroDyn file

Postby Yicheng.Fan » Sat Jan 23, 2021 8:13 pm

Dear Jason,

Thanks a lot! Your suggestions are very helpful.

Best regards,


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