Thursday, April 9, 2009

Abaqus: Bottom-up mesh example

So swept meshing and structured meshing have failed or aren't available but bottom-up meshing is complicated and hard right? Not as much as you might think. Here is a sample of how I meshed a region of a part using bottom-up meshing technique. This is using Abaqus version 6.7 and I'm skipping the parts about seeding, partitioning, and element type that you have to do to make a mesh. Be sure you seed the region before you mesh it or it will not mesh.

Step 1: Select Mesh > Controls... > Hex (in this case it could be something else but hex looks the most professional) > Bottom-up. Then you select the region (partition, cell) of the part you wish to mesh with bottom-up technique.



Step 2: Click on Mesh > Create Bottom-Up Mesh... Then select the cell (region, partition) that you just gave mesh controls to. The "Create Bottom-Up Mesh" box will appear.


Step 3: Select the Source side. Click "Done" when you have selected the source side. This is the side where the mesh will be created in two dimensions, essentially the bottom of the part, so that the mesh can be swept through the volume.
Step 4: Then select at least one connecting side in this example I choose five connecting sides. The more sides you have the more structured the mesh will be. When you have selected the side(s) click "Done". In some cases you have have to specify a Target side but in general is is not necessary.

Step 5: Click "Apply" in the "Create Bottom-Up Mesh" box and you are done! So that you know the details this mesh had 2304 elements, with 0 analysis errors and 48 analysis warnings. (That means it's pretty good.)


If you have any questions just ask, although I might not respond quickly.

24 comments:

  1. Hi,

    I read your post on bottom-up meshing in ABAQUS and I have a question. I'm trying to mesh a thin walled pipe with a through hole to evaluate the Findley criterion for my master thesis. I need to have the mesh mapped in the hole in order to find the critical plane.

    My question is: can I mesh a thin walled pipe with a through hole with quad-elements? When I try, I get the message that "the connecting side has to be bound with at least 4 edges". This can obvoiusly never be the case for a pipe.

    Can you help me?

    //Veronica Waatz, Royal Institute of Technology, Sweden.

    ReplyDelete
  2. Sorry it took me so long to reply I was out of the country and office most of the summer.

    Try to partition the cylinder. I think that perhaps creating a partition along the length of the cylinder that goes through the center of the hole as well as a partition that is perpendicular to that along the length of the cylinder. I would then create another partition around the circumference that passes through the the center of the hole.

    At that point you should now have eight sections to your cylinder and I would think you can mesh everything separately with a bottom-up mesh. I am unfamiliar with meshing in a hole but when I have had to mesh around a hole in the past I was able to partition the surrounding material into four pieces and I used hex elements, which in Abaqus is "An eight node linear brick" and they look like little cubes. The "hex" refers to the number of faces I believe.

    I hope some of that helps and it is not too late.

    ReplyDelete
    Replies

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  3. can you give soluton to this problem?i have this problem..I am investigating crack propagation in brittle solids using abaqus for my undergraduate thesis. I am brand new to abaqus and am working my way through tutorials and examples. My goal is to create a 2d planar model that will show the process of crack initiation and propagation. I am getting stuck however when I try to create adjacent regions of differing mesh densities. For my model, I need an internal region of very fine mesh, and an outer region of very coarse mesh. The way I am trying to create this is by creating two parts and seeding them separately, and then joining them. So far it is working, however I have seen an example in the problems manual (1.4.4) that uses an orphan mesh as the main part of the model. I am now trying to create an orphan mesh similar as the one in the manual, but on a very basic level.

    I am creating two square parts of 10x10 units, that will be joined along a common boundary.

    Part-1 is 10x10 size and has a 1x1 mesh using CPS8 elements.

    Part-2 is 10x10 size and has a 2x2 mesh also using CPS8 elements.

    I want to merge these two parts into one part retaining the mesh orientations described above.

    My current method of achieving this is as follows:

    1.create each part in the Part module assign the seeds and generate the mesh
    2.once the mesh is generated I create a mesh part (also called an orphan mesh I believe) of each part, so now I have 4 parts (2x 10x10 parts and 2x 10x10 orphan meshes)
    3.I now merge the two orphan meshes in the Assembly module, merging the nodes that are overlapping
    4.run job analysis and view results
    Now what I find is that the two meshes behave as normal, except that at the boundary where the nodes are merged, the element edges are opbviously not merged, and deflect according to the applied load ie. deflect apart. What I need is for those elements along the boundary to also merge.

    The model that I have been looking at as a guide is example 1.4.4 in the Abaqus Example Problems Manual (abaqus doc v6.7). This is the crack growth in a beam with 3-point loading. As you can see in this model, the creator has made an orphan mesh including a few regions of differing mesh densities. I have read through much of the abaqus manual, but I am just not sure which parts are relevant to this particular problem.

    I would appreciate any help at all. I feel as though I am on the right path, but may be missing something simple.

    I have attached a sketch of my model as described above, just to give you a visual of what I am talking about.

    ReplyDelete
  4. I have not worked with orphan meshes so I can not comment on what you may or may not be doing wrong. I also do not see the sketch that you attached. However, I would suggest creating one part instead of two and using partitions to divide the part in half or quarters or some other number of regions. Then you can seed the edges of each region and develop a dense mesh in one region and a coarse mesh in another region. You might also be able to use an edge biased mesh as well. Perhaps one part with a partition in the middle and an edge biased mesh on both sides so that near the middle the mesh is very dense but near the outside the mesh is coarse. Also, I am unsure what you mean by 1x1 and 2x2 meshes. If that is the size of the elements you can probably make a much denser mesh or have the entire simulation be 1x1 size elements. I know the speed of computers vary but anything up to about 50,000 nodes only takes a few hours to run and simulations of 100s of nodes generally take less than a minute. Also your simulation is 2D which helps things to run faster.

    Here is an example of edge biased mesh: http://www.isaiahjanzen.com/2009/05/abaqus-edge-biased-structured-mesh.html

    I hope this helps.

    ReplyDelete
  5. Hi, I am very new to Abaqus, and I am having my thesis on the Abaqus and what I am trying to do is, trying to get contact analysis of the gear tooth meshing, by using python script and trying to automate the whole precess, to optimise the gear tip relief.
    My main question is I am trying to use the script in C++. Can you give me some idea how can I use python script in C++. All I am trying to do is by just one click on c++ program and some inputs, and that will give me output window of the Abaqus with the results on it. All the solution and pre processing and post prossing I am trying to get done in the script via c++. I know I can copy some python script to model and first analysis iteration through macro manager, and then I want to iterate that script by C++.

    can you help me to put all of these together. C++ python script and abaqus.

    Note I have gone through scripting manual and all but couldnt get strong understanding to develope code to make c++ program.

    ReplyDelete
  6. To be honest I can not help you. My C++ is so weak and my python is even worse. I recommend you contact Simulia: http://simulia.custhelp.com/cgi-bin/abaqus.cfg/php/enduser/home.php
    or ask on the Eng-Tips forum: http://www.eng-tips.com/threadminder.cfm?pid=727&page=10

    Chances are someone at either of those places will be able to help you.

    ReplyDelete
  7. hi this karthik... i have a problem in meshing the tyre model... i find trouble in meshing the groove portions of the tyre.. pls help me out..
    karthik
    tvs tyres...

    ReplyDelete
  8. Hi, i am trying to do a pressure analysis on a water tank, i am fixing the bottom part of tank to ground(Encastre). When i use bottom up mesh, however the model gets meshed, i am having error while submitting the job , it says, the boundary condition regions are not assigned to mesh, could you suggest some suggestion for this

    ReplyDelete
  9. My bottom up mesh doesn't seem to be properly associated with the part geometry since when I try to run the job I get the error that the boundary conditions reference regions that are not associated with the mesh. Any ideas on how to fix this? Thanks.

    ReplyDelete
  10. Hello, could you please help me to create cohesive elements in simple 2D-mesh.
    I heard that one should use orphan mesh. So first i create Part, created two materials, one is for elastic behaviour, another cohesive behaviour. Then i created sections. First for elöastic material, second for cohesive material. But when i assign the section properties i couldnot select the region with cohesive elements. Could you give me some advice what should i do to create the layer of cohesive elements between normal plane strain elements,

    ReplyDelete
  11. How to subtract one solid from another in Abaqus?

    ReplyDelete
  12. Hi,

    I try to convert an orphan mesh part to modified part. Can you help me to do this.

    Thanks

    ReplyDelete
  13. Hi

    I want to do modal analysis on a cracked beam so I need to simulate it, I have read that because I do not want to check crack propagation I can simulate the crack with detaching nodes after I had meshed the model but there is not any choice for this purpose in “edit mesh” part in mesh module.
    I would become so much thankful if you can help me.

    Regards

    ReplyDelete
  14. Hi

    Is there a way to specify Abaqus to choose automatically choose global size while scripting Abaqus ?

    p.seedPart(size=1.0, deviationFactor=0.1, minSizeFactor=0.1)

    ReplyDelete
  15. Hi

    what are the connecting sides you were talking about (I'm a complete novice and can only follow detailed instructions!)

    ReplyDelete
  16. Hi,

    I am using bottom-up meshing for my fluid part,but it gives an error saying that the region which contains geometry entities are not associated with mesh.Ho can I solve this problem??

    Best Regards,
    P.S.I have already post my question here but did not see.so I am writing it here once again.Sorry for repeating!

    ReplyDelete
  17. do u have any documents about meshing technique. Thanks a lot

    ReplyDelete
  18. My bottom up mesh doesn't seem to be properly associated with the part geometry since when I try to run the job I get the error that the boundary conditions reference regions that are not associated with the mesh. Any ideas on how to fix this? Thanks.

    ReplyDelete
  19. @shreya parmar : same thing happening with me as well..

    ReplyDelete
  20. Hi
    I would like to mesh a steel I beam which is divided into many partition surfaces, I used bottom up mesh method as well but couldn't work.
    Does anyone help in this regard.

    ReplyDelete
  21. شركة تتميز بجميع الخبرات في تقديم اعمالها المتميزة في الكشف عن التسريبات من خلال شركة كشف تسربات المياه بجدة التي تعطي كل ما لديها في اصلاح العديد من المشاكل التي تحدث نتيجة كسر او عطل مفاجئ في امدادت المياه لذلك ننصحم ان تعتمد علي شركة كشف تسربات بجدة لديه سباكين وفنين لديهم الخبرة في حل هذه المشكلة بكل سهولة كما نمتلك لديها القدرة علي تنفيذ اعمال العوازل من خلال شركة عزل اسطح بالرياض التي تعالج تسريبات المياه في الاسقف والحوائط كما نقدم خدمة العزل السليمة للخزانات الارضي والعلوي الخرسانية بواسطة فني متميزة لديه القدرة علي معالجة كل ذلك بسهولة من خلال شركة عزل خزانات بالرياض تمتلك مواد ذات جودة متميزة

    ReplyDelete
  22. Hi
    I am meshing a disk of different thickness. While creating bottom mesh, i want to make layers in different proportion(say first and last quarter of height into 4 layer and mid-half into 10 layers). Is it possible to do with bottom mesh?

    ReplyDelete

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