Hello,
I am trying to carry out a fatigue analysis of an offshore wind monopile structure in SACS using a spectral wave load and damage equivalent wind loads (DEWL) provided from the wind generator turbine manufacturer.
I have input these DEWLs in the SACS input file and created a Sea State file with the spectral wave load. However, I am not sure if the spectral fatigue analysis actually uses the DEWLs at all.
Should I carry out a separate deterministic fatigue analysis with the DEWLs and combine the damage with the one obtained from the fatigue spectral analysis with the spectral wave? How do I do that, if I do not know the number of occurrences of the DEWLs?
Same thing with the generated pile super element. I am not sure if SACS is using this at all in the fatigue analysis. Happy to share the input files.
Thanks and regards
Marcelo da Silva Machado
The only way to combine your DEWL wind fatigue damage with a spectral wave fatigue analysis is to sum the damage of each independent fatigue analysis. In this case you would need to use a deterministic fatigue analysis using the DEWL and a spectral wave fatigue analysis and then combine the damage. The reason for this is that the spectral wave fatigue analysis is a probabilistic analysis which uses the wave spectra to determine the damage which is not associated with any particular wind load. This is fine if you do not expect coupling to occur (i.e. the wind does not affect the wave response), but that is typically not the case for wind turbines. Because of this, wind turbine fatigue design is typically done with a time-history approach. The wind response is combined with the wave response into a single time-history which can then be used to determine the fatigue damage. Our Wind Turbine utilities in SACS are intended to be used for these types of analyses. You can check out some of our sample files here:
https://communities.bentley.com/products/offshore/m/mediagallery/273278
https://communities.bentley.com/products/offshore/m/mediagallery/273280
You might also want to read the Wind Turbine documentation to learn more about the different wind turbine solutions that SACS offers.
In regards to the question about the pile superelement, the superelement is only required to determine the mode shape. The pile model can be used in the wave response solution by selecting the Foundation Option in the Analysis Generator. You should then be able to specify the psi input file for your analysis.
Regards,
Geoff
Dear Geoff,
Thanks for the Answer.
In both provided Zip files, the referred fatigue input files outside the folders are corrupted and cannot be edited. When you open the Zip files, you can see the ftginp files are partially downloaded. Can you please check and send the correct files to me again?
I understand your explanation but to carry out a deterministic fatigue analysis with wave response, I would need to know the wave response caused by the DEWL. I have not been provided with this information, other than the final static DEWL. The analysis is for conceptual design purposes and it would be fine to assume uncoupled effects. In this case, how would I include the DEWL in the uncoupled fatigue analysis? I am sending you the loads.