{"id":364996,"date":"2024-05-01T00:43:49","date_gmt":"2024-05-01T00:43:49","guid":{"rendered":"\/forum\/forums\/topic\/initial-oscillation-in-ls-dyna-following-static-structural-analysis\/"},"modified":"2024-05-01T00:55:58","modified_gmt":"2024-05-01T00:55:58","slug":"initial-oscillation-in-ls-dyna-following-static-structural-analysis","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/initial-oscillation-in-ls-dyna-following-static-structural-analysis\/","title":{"rendered":"Initial Oscillation in LS Dyna Following Static Structural Analysis"},"content":{"rendered":"

Hi, I am modeling a 3D object that is part of a hollow sphere which radius is 7.8 mm and its thickness is 0.536mm. From the side view, it makes a circular arc equal to 120 degrees. It is made of a linear elastic material with E = 0.3 Mpa. At the top vertex, a chain of steel spheres sits on this object, and their displacement is limited to the Y axis. The bottom corner face of the object is fixed and a constant pressure of 2400pa is applied on the interior surface of the object.
At first, I did a Static Structural analysis to find deformations related to gravity and the constant pressure, and then I wanted to do an explicit analysis for an impact through the chain using Ls Dyna for about 1 millisecond. Even though everything is the same for the Ls Dyna analysis, the curved object starts oscillating. I have used dynamic relaxation for Standard Earth Gravity and also option “Both” for Dynamic Relaxation Behavior of applying the pressure. So the oscillation amplitude is not too large according to the scale of the whole model. However, It is enlarging over time, and even this small oscillation will significantly affect my final results since I need high accuracy. Two attachments show the oscillation. The image below contains a graph showing deformation of the top vertex of the curved object. Why at the beginning of the Ls Dyna analysis, its deformation suddenly reduces from 0.0573mm (which is the result of the Static Structural analysis) to 0.055024mm and then gradually goes up again?<\/p>\n

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To solve the oscillation issue, is it a good idea to use an Ls Dyna Restart analysis for the impact after the Ls Dyna analysis and reduce the first Ls Dyna analysis end time from 1 ms to 0.2 ms to have the minimum oscillation amplitude before the impact (This approach significantly increases the ansys file size and I don’t know why!?)? If not, what should I do to completely dampen this oscillation?<\/p>\n

Also, I should mention that since I need to measure Nodal Contact Force through this analysis, my only option is to do a 3D analysis in Ls Dyna.<\/p>\n

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