Our group do research on semi-submersible offshore wind turbine. We use the SESAM \ WADAM to do hydrodynamic calculation, and generate .1, .3, .hst file by processing the outcome file. This way is feasible. But on the second-order hydrodynamic calculation,we have not succeed. WADAM can generate .12d file itself, but the generated file now is not consistent with marin_semi.12d . My question is whether we can use WADAM to generate marin_semi.12d file? What factors should be taken into account in setting? Follow which steps?How to do post-processing?
I don’t use SESAM \ WADAM, so, I can’t really answer your questions. However, I’ll provide a few comments:
- Section 6.8.4 of the draft HydroDyn User’s Guide and Theory Manual provides some guidance on how to generate the second-order potential-flow solution needed by HydroDyn: wind.nrel.gov/nwtc/docs/HydroDyn_Manual.pdf.
- WAMIT need not be used as the pre-preprocessor for generating the second-order potential-flow hydrodynamic data needed by HydroDyn, but in the end, the WAMIT format is what is expected by HydroDyn. The format of the WAMIT-generated second output files (*.12d, etc.) can be found in Chapter 11 of the WAMIT User’s Manual, available online: wamit.com/manual6.4/Chap11.pdf.
- We’ve compared the second-order solutions calculated by WAMIT to those calculated by MARIN’s DIFFRAC code with reasonable (but not exact) agreement. Please find a paper summarizing this comparison here: nrel.gov/docs/fy14osti/61162.pdf.
I hope that helps.
Dear Dr. Jason Jonkman
Thank you for your prompt reply.
I read the HydroDyn User’s Guide and Theory Manual again, and there are three more questions:
- Mentioned in the manual that :
The second-order frequency-domain solution is dependent on first-order body motions, whose accuracy is impacted by setting the 6 × 6 rigid-body mass matrix and,Center of gravity of the complete floating wind system and the 6 × 6 mooring system restoring matrix.
my question is how to calculate the 6 × 6 mooring system restoring matrix,and consider the complete floating wind system or platform only when calculate the matrix.
2.Whether we should consider the Morrison model in the hydrodynamic calculation, that is,whether we should consider the pontoon and brace in calculation.
3.The .12d files loos like only consider the condition that wave incident angle is zero,because I can not find other angle’s message in the file.
Here are my answers to your questions:
The MAP++ mooring module of FAST can be used to calculate the 6x6 mooring-system restoring matrix: nwtc.nrel.gov/MAP.
For a semi-submersible floating platform for offshore wind turbines, I would normally recommend to model the hydrodynamics via a hybrid formulation that considers both a potential-flow solution (for the large-volume members) and a viscous drag from the strip-theory (Morison) solution (for the small-volume members, if not all members).
In general WAMIT *.12d files may contain the second-order difference-frequency quadratic transfer functions (QTFs) at multiple incident wave headings. However, due to the computational expense involved with running the second-order solution in WAMIT, rarely have we computed multi-directional QTFs.