Hello,
I have some doubts related to the stability analysis for the semisubmersible supporting 22 mw iea owt:
1º Regarding the IEA 22 MW semisubmersible (chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://iea-wind.org/wp-content/uploads/2024/04/iea-22-280-rwt-report.pdf) I would like to know whether there is a subdivision of the ballast tanks into bulkheads. I must know this in order to conduct damage stability over the platform.
2º Regarding down-flooding points for the damage stability analysis, shall I assume one randomly? I say this because I don’t know how the technical spaces are within the columns.
3º The 22 MW Semisubmersible report (linked before) claims the ballast water mass is 15,455 ton, which is 15078 m3. My doubt is where does this number come from? I say this because I assume the ballast water is placed only on the external columns, which its entire volume is less than 15000 m3 (this comes from 3 columns x 6.25^2 (squared radious) x pi x 40 m of height)
4º I understand that the weights within the 22MW IEA tabular excelfile of the RNA, blades and tower are associated with the conceptual design stage. In this case, as I want to perform a stability analysis of the semi-submersible that supports the 22 MW OWT, should I consider weight allowances for the weights of the RNA, blades and tower? Or should I not consider them due to the possible fact that these weights are accurate?
5º I have taken stability for only the ‘operation with sea growth’ load condition. I have seen stability reports where the analysis is done for idling condition as well. For the scope of my thesis (not more than 200 pages) , if i had to choose between idling and operating conditions , which one is better to analyse?
In case i did it for the operating condition I thought about analysing DLC 6.1 to be more conservative. Or is 1.6 better because it occurs much more often?
Thank you. Alberto
Hi Alberto,
I should note that stability was not considered during the initial design and any reasonable changes to the design that account for stability are welcome.
- Ballasts and bulkheads are defined in the
internal_structure of the windIO input, e.g., IEA-22-280-RWT/windIO/IEA-22-280-RWT_Floater.yaml at 68164bfd560acc87dc35e2433d82d1c74b6f1f43 · IEAWindSystems/IEA-22-280-RWT · GitHub, where the ballast is allowed to go up to 25% of the main column member, and there is a bulkhead placed there. Adding bulkheads should not drastically change the global performance, so if your analysis determines that more are necessary, please let us know.
- I might not randomly assume a down flooding point, but perhaps analyze where they are most impactful. We did not design accounting for a specific down flooding point.
- There is also water ballast in the lower pontoons.
- I would consider the weights in the RNA to be accurate considering the scope of your study and the previous work undertaken to design those components.
- I may need some help from my colleagues on this question. I would guess that the platform should be stable during both idling and operational conditions, unless there is a provable way to detect damage during operation. The IEC standards (or other codes) may have more to say on this topic.
I hope this helps.
Best, Dan
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Hello @Daniel.Zalkind , i really appreciate your reply.
About the upper pontoons, i guess this was a modification based on the initial design, wasn’t it? I say this because, according to the technical report “Definition of the IEA Wind 22-Megawatt Offshore Reference Wind Turbine“ (which was submitted in 2024), it does not include any upper pontoons. Plus, the paper “Novel conceptual design and performance analysis of a semi-submersible platform for 22 MW floating offshore wind turbine“ does not include any upper pontoons within the IEA 22 MW Semisub.
I was wondering if it is necessary to model the ring and longitudinal stiffeners of the outer columns. I am asking this if it could be possible that it could have a noticeable effect on the stability and hydrodynamic analyses.
Thank you. Alberto
Hi Alberto,
The design has always included upper pontoons, like the IEA-15MW VolturnUS platform. They are missing from Fig. 33 in the report, so we should note that.
The stiffeners will likely not have a large effect on the stability and hydrodynamic analyses. They will add some mass to the platform, but not affect the hydrodynamics. They are placeholders for future structural analysis, which was not part of the original scope.
Best, Dan