Convergence analysis and adaptive remeshing
Convergence analysis and adaptive remeshing
(OP)
Hi,
I'm working on a solid contact model involving sharp edges and small surfaces. I am trying to get my results to converge but I can't. I started with a coarse mesh (~8000 tetrahedral quad elements) and refined the mesh by using smaller global seeds in the area of interest while maintaining larger elements on the peripheries of the model far from the area of contact. The maximum stress values increase drastically when I use finer meshes and the values do not seem to converge. Also when I used smaller elements in the contact area the analysis aborts because of excessive distortion of some elements. I finally ended up with ~100,000 elements and the analysis has been running for 36 hours now and I am not even sure if the results will be accurate.
Is there any way to get around this problem? I thought adaptive remeshing might help but it did not reach the goal (5% error max stress) after several iterations.
Any suggestions
I'm working on a solid contact model involving sharp edges and small surfaces. I am trying to get my results to converge but I can't. I started with a coarse mesh (~8000 tetrahedral quad elements) and refined the mesh by using smaller global seeds in the area of interest while maintaining larger elements on the peripheries of the model far from the area of contact. The maximum stress values increase drastically when I use finer meshes and the values do not seem to converge. Also when I used smaller elements in the contact area the analysis aborts because of excessive distortion of some elements. I finally ended up with ~100,000 elements and the analysis has been running for 36 hours now and I am not even sure if the results will be accurate.
Is there any way to get around this problem? I thought adaptive remeshing might help but it did not reach the goal (5% error max stress) after several iterations.
Any suggestions





RE: Convergence analysis and adaptive remeshing
www.Roshaz.com
RE: Convergence analysis and adaptive remeshing
RE: Convergence analysis and adaptive remeshing
RE: Convergence analysis and adaptive remeshing
If this the case, Abaqus/Standard might not be the tool of choice here. Maybe you should give it a try first with Explicit and see what type of deformation you can expect. Do not worry about the stress accuracy at this time.
RE: Convergence analysis and adaptive remeshing
What I'm interested in is the max stress in the material around the screw in general (neglecting the stresses around the threads). How can I pick the most adequate element size for this purpose? Can I just create a similar model without the threads and just assume that the results will be similar?
RE: Convergence analysis and adaptive remeshing
corus
RE: Convergence analysis and adaptive remeshing
I tried to look up similar problems in the forum and I read somewhere you saying that the stress values at the corners may be ignored since they are a result of singularities. Let's say I decide to do this and ignore those values, can I just look at the second stress value in the color contour for comparison purposes? My main purpose is to see how the length of the screw for example affects stresses in the nearby area.
The problem is that I already created and modeled many similar models and working on hex elements or axisymmteric models means I have to start from scracth.
RE: Convergence analysis and adaptive remeshing
So, that being said, you might want to try putting a very small radius on those edges.
From the description of what you are looking for I don't see why a small radius would have a noticeable effect on the results. Even if you are a little off on the actual value.
RE: Convergence analysis and adaptive remeshing
I'd still spend half an hour looking at the mesh rather than wait 36 hours plus for results you're not even going to be confident about. It's also often useful to run simple 2D models first to get an idea of what is going on before going for the full razzamatazz of 3D models. Even then after running a 3D model you can then say with some confidence that the results from a 2D model are good enough for comparative studies. A little extra time at the beginning can save you a lot more in the end.
corus
RE: Convergence analysis and adaptive remeshing
I followed your advice and worked on a simple 2D model that gave me max stress values that converged easily. Would it be safe to extrapolate from there to the 3D models (i.e use a mesh density that gives similar max stress values as in the 2D model)?
I know for a fact that yielding will not occur under the conditions I am applying, I just want to compare different models.
RE: Convergence analysis and adaptive remeshing
corus
RE: Convergence analysis and adaptive remeshing
The only two options I can think of now is either to use a coarse 3D mesh with comparable values to the ones obtained in the 2D analysis or to use a fine mesh and ignore the peak stress values. Do you think this would work just for comparison?
I am sorry if I'm repeating myself. I appreciate your help, thanks a lot!
RE: Convergence analysis and adaptive remeshing
If your job is taking a long time to run and has contact in it, then check the time steps it's taking as these may be very small. Contact controls can make the job more stable and run faster. In addition, the use of quadrilateral elements increases the bandwidth of the problem and hence the run time and memory requirements. If you have contact in the problem then try and use linear hex elements, but more of them. Contact will converge better, and the job will run faster.
corus
RE: Convergence analysis and adaptive remeshing
RE: Convergence analysis and adaptive remeshing