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Problem with structure files
Dear developers,
Thanks for sharing QBlade. After I read the docs about the turbine structure, I do not fully understand and have some questions with creating my own turbine structure.
1. I have download the ‘NREL5 MW Onshore’ ‘NREL5 MW Offshore OC3’ ‘NREL5 MW Offshore Jacket’ files on your website, I know the structure of the files, but when I want to creat my own turbine structure, I have to fill the tables of subjoints, subelements, submembers….., but I am not quite understand how to calculate the figures, Is there a convinent way, like using the CAD software Solidworks,ProE to creat cad files and import them to QBlade?
2. By comparing the Tower.str files of ‘NREL5 MW Onshore’, ‘NREL5 MW Offshore OC3’ and ‘NREL5 MW Offshore Jacket’, I find the keywords in the Jacket tower files are different with the other two files(the uploaded files). I guess it is the old version. But I really don’t understand why there are the addmass in some locations for the Jacket type tower (‘ADDMASS_0.00_1900.00 ADDMASS_0.50_1400.0 ADDMASS_0.50_1000.0’) while for the other two types, there are no addmass? Besides, why not just write ‘ ADDMASS_0.50_2400.0’ instead of ‘ADDMASS_0.50_1400.0 ADDMASS_0.50_1000.0’? Is there any special meaning?
3. In the tower files, I know the diameter changes linearly for the top to bottom, but I don’t know how to calculate the MassDensity and EIx, EIy…. How can I do the calculation? Do you wirte codes to generate the figures automatically?
4. I want to creat the substructure file of OC4 turbine(the uploaded OC4-Error file), I do some changes in the OC3 turbine structure file, but sine I don’t know exactly how to calculate some figures, especially for the BEMUse.dat, SUB_HYDROADDEDMASS….. With this file, I can’t do the correct simulation, it just looks like that way from 3D view(the uploaded OC4-3D View).
I will appreciate it very much if you can help me.
Best regards.
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Hello Yueguotian,
let my try to answer you questions:
- The Tables for Joints, Members, Elements etc. have to be filled in manually. At present there is no tool that automates this process. Using a spreadsheet this should be straightfoward. From the substructure file that you attached I can see that you already managed to do this nicely.
- The Keyword ADDMASS allows to add a point mass to the tower structure. For the jacket tower these masses come from the OC4 Jacket definition document. Regarding the last point mass: ADDMASS_0.50_1000.0, this is an error and should be ADDMASS_1.00_1000.0. I’ll correct this.
- The cross sectional structural properties need to be obtained from a different software, CAD or similar, such as BECAS. For a simple circulat steel tower these values can also be calculated analytically.
- When looking at your substructure file I found a few issues: Your rigid elements (SUBELEMENTSRIGID) have a very small mass density (0.0001 kg/m), and you also dont have a hydrodynamic added mass coefficient > 0 assigned (CaN = 0). This can cause the structural model to diverge as the nodal mass becomes singular. Add some mass to the SUBELEMENTSRIGID, by slightly increasing the mass density, such as 0.1kg/m or use a nonzero CaN value in the HYDROMEMBERCOEFF table and the floater model should evaluate. Btw. in your SUBMEMBERS table you have not activated the buoyancy for the members, so the model will likely drown (IsBuoy = 0), set this to 1 to activate buoyancy. The POT_RAD_FILE and POT_EXC_FILE can be obtained from potential flow solvers such as NEMOH or WAMIT, likewise the SUB_HYDROADDEDMASS matrix. If you use morison elements with an added mass coefficient (CaN > 0) you can also just skip the SUB_HYDROADDEDMASS matrix alltogether.
In the near future we will also publish our version of the OC4 semisub model, so you will be able to check the model that you are building against it!
BR and happy modeling,
David
Thank you David, now I have a better understanding of the structure files, I will have a try and correct the file. Looking forward to the further development of your excellent work.
Best regards.
Yueguotian
Hi David, just one more thing, is it possible to create a sphere structure with the substructure file? Thank you.
Hi Yueguotian,
yes, thats possible if the sphere is approximated with cylindrical elements – see the attached image.
BR,
David
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I see, that’s nice, thank you David.
