{"id":248363,"date":"2023-02-01T23:01:48","date_gmt":"2023-02-01T23:01:48","guid":{"rendered":"\/forum\/forums\/topic\/issues-with-gravitational-sag-measurements-in-static-structural\/"},"modified":"2023-02-01T23:01:48","modified_gmt":"2023-02-01T23:01:48","slug":"issues-with-gravitational-sag-measurements-in-static-structural","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/issues-with-gravitational-sag-measurements-in-static-structural\/","title":{"rendered":"Issues with Gravitational Sag Measurements in Static Structural"},"content":{"rendered":"

I am looking at the gravitational sag of an object held at 4 supports (visible in the picture below, which is a bottom view of the system). The supports are implemented as displacements with the y component (the direction of gravity) set to 0 and the other components set free. I noticed the following 2 issues:<\/p>\n

1: If I apply this boundary condition to point-like supports (the 4 points at the centers of the holes in the picture) convergence with the mesh size is poor for some of the displacements I try to measure and the results don’t always respect the symmetry of the problem (for instance there is one mirror plane with respect to which results should be symmetric and they are not). If I instead apply it to finite disks, convergence is better, but measured displacements in the y direction get bigger as the radius of the disks decreases and don’t seem to converge to some limit as the disks become smaller (and below a certain radius I start running again into mesh convergence issues). I would appreciate any suggestions on how to improve these simulations in the small contact surface limit.<\/p>\n

<\/p>\n

2: I want to measure the tilts on the inner surfaces of the two flat disks at the ends due to bending of the object under its own weight. I am implementing a remote point out of a few mesh points on a line parallel with the y-axis, as seen in the image below, and using the ROTX  APDL command to look at rotations around the x-axis. The measured tilts are inconsistent when I change the mesh size or make small changes in the support positions or even on multiple runs of the same simulation. If I look at the difference in tilts between the two sides, those results are consistent, though, which makes it look like maybe there is an offset added to the two tilts due to rigid body rotation. I expected some erroneous rigid body motion in the xz-plane due to the lack of constraints there (and I see it, but it’s easy to subtract and not a problem for me), but did not expect this rotation, and I am not sure how to measure the actual deformation\/bending when it’s covered by it. What makes things tricky is that the material is anisotropic, so the two tilts are not expected to be symmetric\/equal. Is there a way to eliminate this rotation from the results?<\/p>\n

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