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Static Analysis Realistic Setup and Symmetry Problems

Question asked by Ulrich Liebminger on Jan 24, 2019
Latest reply on Jan 25, 2019 by Bill McEachern

Hello Community,

I am currently simulating a problem representing a telescopic tubing assembly. How it looks like can be seen below. I would like to ask for your opinion if the setup is realistic, since I am quite new in simulation. Thank you, I really appreciate every bit of advice!





The pictures show the tubes in deployed, respectivley stowed position. The tubes are not sliding metal onto metal but there is a small gap between them (image on right hand side). For gliding, there are little plastic pads applied on each side, where the tubes are touching each other (red pads inside the lower tube, and green pads outside the upper tube). The actuation of the upper tube is performed by an internal drive, which means that the tube only absorbs moments and transverse forces, but no axial forces (they are absorbed by the actuation system)


Now to my simulation setup: I fixed the lowest face, where the tube is later mounted. Because of the fact that the upper tube can not move when the actuator is locked, I defined a global conctact (bonded). Is that representing reality in a good/sufficient way? I could also model the sliding pads and define a no penetration condition with friction, but that would result in a massiv increase of run time...


For meshing I used a solidmesh, because the geometry here on the pictures is much more simplified due to confidentiality reasons==> the real tubes have more details and changes in geometry which makes it difficult to have a shell mesh, I guess. For the solid mesh, I tried to have at least 2 elements along the wall thickness, in the areas of interest even 5-6. The aspect ratio for areas of interest are below 3. The energy norm error was also tried to be below 1 for critical areas. So, would the meshing experts say that this mesh is sufficiently fine for a reliable result? ( a convergence study is unfortunately not possible, because at the transition of lower to upper tube is a singularity due to the sudden change in geometry, which I decided to neglect. But: I observed the stress values at a radius of the notches for several meshes, and they seemed to converge...). Any advice on that issue?


The loading is introduced via a remote load (rigid connection), illustrated in the image below. The rigid connection is used, because the cross section should stay the same since there is an additional plate mounted onto the upper tube, restricting the cross section from deforming. Then the simulation can be started. For the simulation: is the stopping threshold of Solidworks (1e-04) sufficient, or is it a better practise to have it lower (e.g. 1e-08)?




Now comming to the symmetry issues:


In order to save simulation time, I would like to apply symmetry relations. Since there is one notch, which is different ( circled in red), I cannot use a quater of the model, but half.


Now I apply a remote loading (bending moments in two directions) and define a Symmetry Fixture, but no matter what surfaces I define as symmetric, the result is always different from the result obtained from the entire assembly. Is it just not possible to make a profile symmetric with different loading directions? (Because when I compare a bending moment in only one direction, the results seem to correlate...)


My guess would be that SolidWorks just doesn't account for the change of an open profile to a closed profile due to the symmetry? Is there any other way how I can make half of my model act like the entire one? Below there are also two pictures of a torsional loading case, where the inability of the symmetry relation is shown...





Thank you for reading this massiv thread!!!