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How to calculate the quality matrix using fx_getMats.m #2422
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Dear @lk73438702, Regarding the "triplet" warnings from the MBC3 scripts in the MATLAB Toolbox, these warning are associated with the write outputs from ElastoDyn, Best regards, |
Dear @lk7343870, The linearization functionality of OpenFAST will not export the full-system mass matrix (rather, OpenFAST linearization produces a linear model in 1st-order form, where in the state matrix “A”, the mass matrix has been inverted and multiplied by the stiffness and damping matrices). You can often derive the rigid-body mass matrix from the linearized "D" matrix, but this same approach does not work for the generalized mass matrix (including structural flexibility). Best regards, |
Dear @jjonkman, |
Dear @lk73438702, You can use an OpenFAST linearization analysis to calculate the 6x6 mass matrix of a rigid ElastoDyn model of a wind turbine using the approach outlined in the following topic on our forum: https://forums.nrel.gov/t/openfast-2nd-order-linearization/2249. Best regards, |
Dear @jjonkman |
Dear @lk73438702, As stated in the forum post I linked to, you should take the 6x6 matrix subset from ElastoDyn's "D" matrix associated with the 6 platform load inputs and 6 platform acceleration outputs. The platform load inputs will automatically be included when you select Best regards, |
Dear @jjonkman |
Dear @lk73438702, I can't see the image you tried to upload, so, I can't really answer your first question. Regarding the reference point for the center of gravity and inertia values, this would be the user-specified platform reference point in ElastoDyn, which unless you've changed it was set to Best regards, |
Dear @jjonkman, |
Dear @lk73438702, Can you share the 6x6 mass matrices you derived for these two cases with and without the tower mass? What value of Best regards, |
Dear @jjonkman , |
Dear @lk73438702, It sounds like you are following the correct process and the mass matrices look like I would expect in terms of the various quadrants of the 6x6 matrices. I'm not sure why the masses are not matching what you are expecting. The total mass is also written to the ElastoDyn summary (.ED.sum) file; do they match what you are seeing in upper-left quadrant of the 6x6 matrices? Best regards, |
Dear @jjonkman , |
Dear @lk73438702, Well, at least the OpenFAST ElastoDyn summary file and linearization results are self-consistent. I'm not sure why these masses are not matching the values reported in the IEA Wind 15-MW reference documentation. Did you change the OpenFAST model in terms of mass or geometry? If not, this is probably a better question for the IEA Wind 15-MW repository: https://github.com/IEAWindTask37/IEA-15-240-RWT. Best regards, |
The MATLAB command line window will have the problem shown in Figure 1. The output result obtained by using fx_getMats.m is Figure 2. Does Figure 1 have any impact? How to get the mass matrix
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