There are many meshers in market which are able to make mesh with minimum user input. But still they need manual work for fine tuning the mesh in important regions which software does not know at all. Moreover for hexa mesh, automatic meshers will find hard time for complicated models.
But I would always go for good tet mesh than the bad Hexa mesh. Author has emphasized importance of experienced users and Hexa mesh. Which implies if you have option to create Hexa mesh you should go for it. Which is really a contradiction!!! But there are many situations in which it is not possible to create hexa mesh or the problem is not highly dependent on mesh.
Last but not the least, you always need a good Hexa mesh if you want to have good results and your model shall be used for different design points simulation e. However, for most not-so-experienced users, automation tools are valuable.
Point 2 : As we increase the no of faces hexa, polygonal in a cell, we can have more information from neighbouring cells. Since tet cells have less neighbouring cells therefore it needs more dense mesh in those critical regions. This is what we learned in our CFD classes. Take an example of backward facing step validation case. You can easily observe HEX meshes have clear advantages. However for quick design iterations for complex geometries, it is better to go for tet type meshes, which easily adopt the themselves to geometry.
How we are going to estimate uncertainty with tet mesh to the time needed for hex mesh generation? Which one is more important? Doubts on results from tet meshes or time consumed in Hex mesh?
I find this post as well as the follow-up discussion-comments very helpful and valuable. I wonder if anybody has done detailed comparison between finite volume method and finite element method with the same mesh containing non-orthogonality, skewness, non-uniformity. To my understanding with some level of experience with the finite element method on hex-quad meshes , the finite element method is quite robust or insensitive with high aspect ratio meshes and large element-to-element size ratios nonuniformity.
But finite volume method, based on central difference or so, will theoretically lose accuracy on nonuniform meshes. Am I correct? But the problem i am facing is how to decide the mesh element size for a particular geometry. Sir, can you please suggest me about how to decide mesh element size max face size of element, mini element size and max element size. Thank You. As far as some modeling is not compare with experimental datas even the mesh size may be badly estimated.
In these days, not always a tethraedral mesh can be better than hexaedral mesh, and in that few cases you MUST be capable of discern if your solution is ok. Try to simulate hertz contact between 2 cylinders do it in 3D with tethraedral mesh, and you will know to which I refer.
However I am new in abaqus but some of the thing that I got from my simulation is that meshing with tet element creates a large number of element as compared to hex or hex-dominated element.
And tet element takes more computational time as compared to hex. So, I want to know, Is there any way to reduce the number of element in tet meshing. The second thing is that which is better, to spend time in partition to generate hex or hex-dominated type meshing or simply go for tet meshing.
Thanks to many improvements over the years, meshing has transformed from a very tedious, manual process into a quick and easy automated one. Is it a good mesh? From here you will see a lot of information about your mesh that can help you make informed decisions about your simulation. Specifically, you will be able to qualify whether or not the mesh is in fact good.
How elements transition in size can greatly impact how a model uses the mesh. In general, a gradual change in element size functions makes for a better mesh for most models. A poor mesh will have a quick change in elements size, acute interior angles, and thin triangles. The solution for smoothing out the element transition is to adjust the spacing of the arc vertices in the mesh generator coverage and to examine the proximity of the arcs. In general, arcs that are close to each other should have a similar number of vertices.
Arcs that are further apart can have a greater disparity of vertices. When creating quadrilateral elements in a mesh using a patch, it is important that the spacing of the vertices be precise. Parallel arcs need to have the same number of vertices when creating a patch or the result will be an uneven patch. It is recommended to always preview the mesh when using the patch option, then adjust the number of vertices to make certain the patch is even.
I'd never seen that trick of inverting the number of nodes and using the trend line equation to extract a "correct" answer. I tried it out on a simple hook example 2D elements, static analysis , with "quick and dirty" mesh refinement and it raised a couple of questions.
From the normal Nodes x stress graph, I get nice convergence graph so it looks like a nice direction. Intuitively, changing the curve from linear to exponential seemed a bit of a risk, but again the normal nodes vs stress curve resemble a logarithmic, so the inverse being exponential doesn't seem so farfetched. I'm just curious on your thoughts on this, and the implications as it were.
The elements on my final run were very small and the stress had increased again to MPa so it could be a case of reaching a "too small" element size and the stress will keep increasing. As to your question, this is a tricky thing. I've talked with Angus Ramsay about it a few years ago, and this method leaves something to be desired. You see, you should not assume that the mesh converges linearly, and I never claimed such a thing - that is the case in some situations of course, but not always the case.
What I'm doing is, I'm calculating several meshes, and if I see that "toward the smaller elements" all the values are more or less in a single line, THAN I assume I can extrapolate it in a line. So if the chart is not a line, I would be very careful with this. However, if you start with an ultra coarse mesh which I never do you would get a super crazy start of the chart - so be careful with that.
Hope this helps, but if you have any followup questions - just let me know Thanks for your reply. I was mulling over it and came to the same conclusion, the starting mesh was perhaps too coarse to use with that method. You raise some very good points about the validity of the method, I still think it has its merits as you mention in the article in the absence an analytical solution or physical testing data.
Like many things in FEA, it's another tool to use with a critical thinking cap on :. Thank you a lot for writing. Indeed this is not a perfect method, but it has some uses. The critical cap is always a good thing :. Hey Lukasz, What is the optimum value of the element quality mesh metrics in ansys workbench. Thank You. That is an impossible question Nithin! While there are some "rules" that I've developed, those come from us doing a LOT of similar problems But "from the outside" it will be super difficult for anyone to give you an answer - you will have to work it out yourself I'm afraid!
First of all, thank you very much for your explanations about refin mesh size. Generally, I do mesh convergence based-on von Mises stresses at vertical axis versus mesh sizes at horizontal axis. In this approach, I start from bigger size of mesh to smaller size, then I read von Mises stress for each mesh size. Therefore when the stresses of von Mises in two different mesh sizes that are close to each other reach almost the same value, I will stop test for mesh convergence.
Then I will consider that mesh size for analysis. However, may I know your idea about this method. This is more or less what I do, but I draw a chart as you see in the post so I see if the answers are converging. What I do not understand is the "von Mises stress at the vertical direction". But of course, the method you mentioned is fine regardless. Unless of course, I did not understand something - in that case, please let me know!
Hi , how to choose the global mesh size for a thin and long component say mm long and 3 mm thick? This is an impossible question - there is way too little to give a robust answer! Without such information, it will be super difficult to answer such a question specifically. If this is mmxmmx3mm plate loaded uniformly than use 2D mesh and perform a study I just described above hard to guess exactly, but you can start at 30mmx30mm which will give you a 10x10 mesh grid, and reduce from there.
Just assume several mesh sizes and see if the answers are constant if you reduce the mesh size Hi Lukas, 1. What is the lowest mesh size you have used in any of your electromagnetic problem?
Can you suggest how to mitigate it? I never solved a single electromagnetic problem. This is a difficult and rather long topic. I don't think I have a post about it, but maybe this will help you a little bit.
I am working on a problem that needs the result of elastic stresses as an input. I must obtain elastic solution which underestimate the stresses. Ali, I'm rather afraid to give you a "generic answer". You know, stuff is usually case-specific or at least I think it can be , and I don't want to give any misleading information I'm not sure if I get you right I would guess that a "reasonable overestimation" would be a better bet.
What kind of analysis are you doing really? If you need too small stress Please, treat what I will write here carefully, and it's best if you would do a mesh convergence check of your model. However, my experience is, that smaller elements provide higher local stresses. This is mostly because they average stress ok, it's more complicated but let's roll with that!
This is why smaller mesh is usually considered to be more accurate, but of course, you can go overboard with this approach and accuracy of calculations and rounding up starts to be a problem at some level I guess I never reached it I have a plate that is under repeated load in two direction. The behaviour of a structure under repeated loads depends on the intensity or amplitude of the load and can vary from elastic to non-restricted plastic flow behaviour.
I want to find a critical load limit below which the plate becomes stable under repeated loading and behaves elastically. This alternative method is based on two theorems of lower bound and upper bound. In this alternative solution, we must first find an elastic solution, then this elastic solution should be used in a mathematical programing and optimized to find the bounds of this limit load. My main problem is finding the elastic stresses that their value are less than the exact one. I thought that if I chose a coarse mesh and run elastic analysis, I would underestimate the exact value of elastic stresses.
Wow - you must be doing something pretty cool - I don't recall I ever heard about a procedure like that :. But since we already establish I have no idea what you are doing, let me get on my "expert podium" and give you a few bits of advice :P. Seriously though But this assumes that mesh quality is ok and all That being said and me being pragmatic Let's say the "correct answer" is MPa.
I assume that if you use the procedure and input 80MPa and 90MPa the outcomes you will receive will differ right? If that is the case who desides if it should be 80 or 90MPa, since they are both lower bound solution, and a reasonable one I assume.
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