{"id":366293,"date":"2024-05-09T13:26:43","date_gmt":"2024-05-09T13:26:43","guid":{"rendered":"\/forum\/forums\/topic\/why-does-calculation-of-f-ku-using-exported-kmatrix-only-work-for-simple-model\/"},"modified":"2024-05-09T13:26:43","modified_gmt":"2024-05-09T13:26:43","slug":"why-does-calculation-of-f-ku-using-exported-kmatrix-only-work-for-simple-model","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/why-does-calculation-of-f-ku-using-exported-kmatrix-only-work-for-simple-model\/","title":{"rendered":"Why does calculation of F = KU using exported Kmatrix only work for simple model"},"content":{"rendered":"

Hi,<\/p>\n

I have exported a stiffness matrix from modal analysis using the DMAT command and then carried out a static analysis by applying a load on a specific node. Knowing the node where the force was applied and having the symmetric stiffness matrix, I attempted a simple static analysis in MATLAB using X=K\\F<\/code> to calculate displacement. For simple models, the results aligned well, and the relative error was very small except for a few exceptionally small values.<\/p>\n

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I checked how the node order changed in the left picture, and using the mapping vector in the right picture, I identified and the nodes where force was applied ( Z direction).<\/p>\n

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However, when extracting the stiffness matrix for slightly more complex models, the values completely change. Why does this situation occur?<\/p>\n

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Also, when performing transient analysis on a simple model using the generalized alpha (HHT-alpha) method, the results turn out well regardless of how short the time step dt is. However, for more complex models, the results diverge as (dt) decreases. Could both issues be related to problems with the stiffness matrix itself, or might they be due to issues within my code?<\/p>\n

I would be grateful if you could let me know where I might have gone wrong!<\/p>\n

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 <\/p>\n","protected":false},"template":"","class_list":["post-366293","topic","type-topic","status-closed","hentry","topic-tag-ansysworkbench-ansys-staticstructural"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t