Hi Mike, That helped quite a lot, thanks. I implemented your second approach, and it seems like it's working.
Best regards, Paul Mike Taylor schrieb am Donnerstag, 23. Mai 2024 um 04:13:22 UTC+2: > Paul, > > Assuming this element works like ChElementHexaANCF_3843, these dimensions > are used to define the straight and undeformed element configuration. This > configuration is then mapped back to the bi-normalized configuration > (lengths of -1 to 1 for each side) for numerical integration as well as to > both the reference configuration (zero stress reference state of the > element - potentially a non-straight shape) and the current configuration > (defined by the current nodal locations). The code is setup to assume that > the initial locations of the nodes define the zero-stress reference > configuration. > > So again, assuming that this element works like ChElementHexaANCF_3843 as > I would expect, you should be able to use reasonable values for these > element length dimensions. One solution would be to use approximate > average element dimensions. Another solution would be to measure the > distance between the centers of the corresponding faces for each of the 3 > directions (e.g. Face ADEH to Face CBFG for the "x"/"u" direction). Note > that there is a text diagram of the brick element describing the nodal > ordering in ChElementHexaANCF_3843.h below the include statements. > > I hope this helps. > > Mike > On Tuesday, May 21, 2024 at 7:38:44 AM UTC-5 [email protected] wrote: > >> Hi Mike Taylor, >> >> Thank you for the reply. The problem is that you seem to have to know the >> dimensions of the elements. If I take, for instance, the >> "demo_FEA_hexaANCF_3813.cpp" demo and don't specify the InertFlexVec in >> line 167, the simulation starts, but nothing happens. >> >> If I use meshing software to create a hexahedral mesh, the elements don't >> necessarily need to have the same edge lengths per dimension. Thus, I can't >> set the InertFlexVec vector, can I? >> >> Kind regards, >> >> Paul >> >> Mike Taylor schrieb am Dienstag, 21. Mai 2024 um 04:32:27 UTC+2: >> >>> Paul, >>> >>> The "ChElementHexaANCF_3813" element is really a traditional 8 node >>> hexahedral element (nodes with only position coordinates). If you Google >>> "sphere hexahedral mesh" and look at the images, you'll see some approaches >>> to meshing a sphere with only hexahedral elements. If you are trying to >>> mesh an ellipsoid, one approach would be to start with the hexahedral mesh >>> of a sphere and then scale it along the three axes to match your >>> ellipsoid's geometry. A FEA meshing program might help here depending on >>> how fine a mesh you need. >>> >>> As for other "solid" elements, there is code for the >>> ChElementHexaANCF_3843 element (ChElementHexaANCF_3843_MR_Damp) that >>> implements a 2-term Mooney-Rivlin material law with a non-linear single >>> coefficient Kelvin-Voigt damping model in the fork I used for my PhD thesis >>> (https://github.com/taylome/chrono/tree/thesis/hyperelastics). This is >>> based on Chrono 7 and the code requires updates to use it in Chrono 9. >>> Also note that the ChElementHexaANCF_3843 element uses 12 coordinates per >>> node, 3 position coordinates and 3 position vector gradient coordinate >>> sets. The position vector gradient coordinates can make the element a >>> little harder to use from a meshing perspective. Long term, the goal is to >>> merge the hyperelastic code developed in this fork into the main Chrono >>> repository after some more additional development. >>> >>> Best Regards, >>> >>> Mike Taylor >>> On Friday, May 3, 2024 at 5:07:33 AM UTC-5 [email protected] wrote: >>> >>>> Hello everyone, >>>> >>>> I want to include an ellipsoidal geometry in my model and simulate it >>>> with finite elements. My problem now is that I want to use a hyperelastic >>>> material model (e.g. Mooney-Rivlin), and only the >>>> "ChElementHexaANCF_3813" element implements that. As I take it from the >>>> examples, you need a structured mesh where the hexahedral elements have >>>> known dimensions, which is difficult for an ellipsoid. >>>> >>>> I'm quite new to FEA and have only the following ideas: >>>> >>>> - divide the geometry into multiple simpler boxes (don't know how to >>>> do this automatically yet) >>>> >>>> - add the hyperelastic material model to the other elements >>>> >>>> - use an external FEM solver and implement an interface to Chrono >>>> (can't estimate how difficult this would be) >>>> >>>> Maybe you can help me find the best option. >>>> >>>> Thank you, and kind regards, >>>> >>>> Paul >>>> >>> -- You received this message because you are subscribed to the Google Groups "ProjectChrono" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/projectchrono/ff0e03f3-4a5f-4c05-894c-3884529c2401n%40googlegroups.com.
