Dear Jason,
the seed in FAST’s HydroDyn module is found in the Platform file (for the offshore 5MW monopile-supported wind turbine) right?
6 seeds should be enough? So for every wind speed I still need 6 seeds in total (66 simulations for DLC 1.2).
Thank you again for everything
Best regards,
Thanasis Petridis
Yes, I agree.
Dear Jason,
hello again. I have one more question regarding the Weibull parameters needed in MLife.
Since, most Weibull distributions regard wind speeds at u[size=60]10[/size] (wind speed 10m above ground), the weibull scale and shape factors are also calculated for these wind speeds. So, when I need to input these two parameters in MLife, shall I use these parameters, or should I somehow convert them for wind speed in hub height?
i.e. Weibull scale parameter is in m/s calculated with wind speeds 10m above ground and is proportional to the mean wind speed. Assuming a power law wind profile, increase the parameter to a higher value matching the “average” wind speed at hub height level. That’s because the actual mean wind speed at hub height is significantly higher than the Weibull scale parameter calculated.
k is the Weibull form parameter. It specifies the shape of a Weibull distribution and takes on a value of between 1 and 3. A small value for k signifies very variable winds, while constand winds are characterized by a larger k.
So, by calculating wind speeds at hub height, the range of wind speeds increases from the initial k calculated (with wind speeds 10m above ground)
What should be the inputs in MLife and do you have any suggestions?
Best regards
Thanasis Petridis
Dear Thanasis,
The wind speed distribution specified in MLife should be for the reference height used in the loads analysis, which presumably is hub height. If you are designing to site-specific conditions with wind speeds known only at 10 m, then yes, you would have to use the (possibly assumed) shear profile to scale the wind speeds to hub height. Often though, loads analysis is based only on generic wind classes defined in the IEC standards.
Best regards,
Dear Jason,
thank you for your response, yet I don’t quite understand your last sentence (that is, “Often though, loads analysis is based only on generic wind classes defined in the IEC standards.”). Possibly I did not understand, since I have never taken a look at IEC standars other than BS_EN_61400-3_2009. Could you please rephrase it?
Also do you believe the Weibull shape parameter would also change, apart from the Weibull scale parameter?
Thank you once again.
Best regards
Thanasis Petridis
Dear Thanasis,
The generic wind classes in the IEC standard assumes a Rayleigh wind-speed distribution (k=2) with V_average = 0.2*V_ref, where V_ref is determined by the wind turbine class (V_ref = 50 m/s for class I, V_ref = 42.5 m/s for II, and V_ref = 37.5 m/s for III).
Best regards,
Dear Jason,
So, if k=2 and mean wind speed is a fixed value, Weibull scale parameter is also a fixed value [c=(2*v_average)/(sqrt(π))].
My actual wind data and their probabilty of occurance are not accounted anywhere. Is this a safe assumption? Or did I misinterpret something?
Thank you,
Best regards
Thanasis Petridis
Dear Thanasis,
Yes, your understanding is correct.
Normally the loads analysis used for turbine design is based on a generic IEC wind class. When selecting whether a given turbine design is suitable at a specific installation site involves a site-suitability analysis, where you could perform a loads analysis with site-specific inflow conditions (e.g., based on measured wind-speed distribution, shear, turbulence intensities, etc.).
Best regards,
Dear Jason,
thank you very much for all your immediate responses, even on irrelevant-to-NREL questions.
Best regards
Thanasis Petridis
Dear Jason,
Apologies for replying on an old post, I’m just looking for some clarity in regards to using TurbSim to create the necessary wind speed bins for fatigue analysis.
In a previous reply you said:
“With Vin = 3 m/s and Vout = 25 m/s, normally a fatigue analysis would involve 11 wind speed bins (of width 2 m/s), each with 6 seeds, for a total of 66 10-minute simulations”.
To achieve this in TurbSim would you vary the value of ‘Uref’ in the input file between Vin and Vout for the centre of each wind speed bin (e.g.for Vin = 3m/s and Vout = 25m/s, set Uref to: 4m/s, 6m/s, 8m/s etc.), whilst also varying the value of the ‘RandSeed1’ for each wind speed bin input file?
Thank you very much in advance,
Kind Regards,
John Boundy
Dear John,
Yes, your understanding is correct. This is documented a bit in Appendix B of the TurbSim User’s Guide.
Best regards,
Dear Jason,
Thanks for getting back to me so quickly and clearing that up for me.
Just one more question;
Am I correct in thinking that for fatigue analysis of different DLCs that have the same wind conditions (e.g. DLC 1.2 and 2.4 - NTM, Vin<Vhub<Vout), the same TurbSim wind files can be used?
It is just FAST that will have to be adjusted to account for the difference between cases (e.g. in this case where DLC 2.4 describes power production loading with a control system fault,electrical fault or loss of electrical network)?
Thanks again,
Kind Regard,
John Boundy
Dear John,
Yes, you are correct again.
Best regards,
Thanks for all your help Jason,
All the best,
John Boundy
Dear Jason,
Please help me check whether the calculation parameters of these variables in fig. 1 are correct.
In your paper “FAST.Farm load validation for single wake situations at alpha ventus”, I found the “blade-root bending moment in the Flapwise direction” calculated by you, as shown in Fig. 2, I would like to confirm whether this parameter is “RootMyb1”. If not, please correct me. And I would like to know the parameters in MCru input file of “NSlopes”, “SNslopeLst”, “BinWidth”, “TypeLMF”, “LUlt” for"blade-root bending moment in the Flapwise direction" DEL calculation. Thanks!
Bset regard,
Liye Zhao
Dear Liye,
Matthias Kretschmer was the lead author of this paper and generated all of the results. I do not have access to all of his input files. But the paper mentions the flapwise bending moment, which is “RootMyb1” in ElastoDyn, so, I assume that is correct. The paper also describes the formula used to calculate the DEL and it is the short-term DEL only, without considering the Goodman correction for mean loads and weighting across load case that is necessary for long-term DEL calculation. The values of N_eq (= 600) and the material exponents (4 for the tower, and 10 for the blades) are also stated in the paper.
Best regards,
Dear Jason,
The paper “FAST.Farm load validation for single wake situations at alpha ventus” authored by Matthias Kretschmer and you has DEL for 5MW turbines in wind farm. Is there any published literature on DEL for isolated NREL 5MW turbine? I understand that the land to sea ratios of DEL for 5MW turbine are available in the literature “Model development and loads analysis of an offshore wind turbine on a TLP with comparison to other floating turbine concepts” by Matha.
Thank you
Dear @Keerthana.Mohan,
The fatigue loads for the land-based version of the NREL 5-MW turbine were calculated as damage-equivalent loads (DELs) for a range of material exponents (m) and ultimate load factors (ULF), as described in the calculation process documented in section 4.3 of Matha’s report you reference: http://www.nrel.gov/docs/fy10osti/45891.pdf.
Best regards,
Dear Jason,
I want to know the Vref for the IEA-15-240-RWT turbine .
Looking forward to your reply.
Best regards,
Dear @Cuizhi.Zhu,
According to the IEA Wind 15-MW RWT specifications report (https://www.nrel.gov/docs/fy20osti/75698.pdf), this turbine is designed for IEC class IB. A class I wind turbine implies a V_ref of 50 m/s.
Best regards,
