Discussion Forum

Posted: 1 decade ago 2010年4月8日 GMT-4 07:48

Hi Probably they are referring to the fact that you can define a surface function (of any shape) and use the ALE (moving mesh) starting from a regular shape and to optimise its shape to adapt to the overall surface function (with the given mesh resolution), then you save that mesh shape and you do your simulations. this is teached in one of the comsol courses, probably the advanced one Good luck Ivar

Posted: 1 decade ago 2010年4月8日 GMT-4 10:41

Ivar, thank you for your reply. Do you have the course slides or manuals may be I can take a look?

Posted: 1 decade ago 2010年4月8日 GMT-4 11:18

Hi unfortunately no I do not have any specific doc, but I can advise you to get hands on the book of zimmermann (http://www.comsol.com/academic/books/mmwfem/) and go through some of the examples at the beginning of the book, it gives you an excellent introduction on how to use COMSOL to solve simple equations, as well as function optimisation, which is the first step, to define an error function that should be minimised to "0" between the ALE surface and your defined function. Good luck Ivar

Posted: 1 decade ago 2010年4月9日 GMT-4 01:50

Hi I quickly generate an example, this gives the idea: Start Comsol in 2D with just a moving mesh ALE mode, draw a rectangle 1 m in x, 0.2 m in y Define an analytical function "Wave" with argument "x" and expression something like 0.05*sin(2*pi*3.5*x) I have choosen a half total wavenumber just to make the funtion symmetric between x = 0 and 1, this is no necessity, test it by plotting it in the Function GUI for 0 < x < 1. Then you define the boundary conditions: lower edge "2": fixed mesh dx=dy=0 left and right edges "1,4": fixed along dx=0 and dy not selected = free top edge "3": fixed along dx=0 and dy=Wave(x) forced to the Wave function You mesh and hit refinement once to get a reasonnable mesh, w.r.t. the wave periode and you solve. To see the mesh, use "postprocessing - plot parameters - General tab: Element refinement OFF and value "1" its toward the middle-bottom part of the GUI, and in Surface tab: Coloring: FLAT Fill Style Wireframe there you are. now you can save this "deformed" mesh as a geometry, but you might need to "remesh it" as the mesh quality might become poor, also if the mesh was rather rough you might not have a very clean geometry, once saved, with a few "spikes, that might need some tweaking. have fun COMSOLING

Posted: 1 decade ago 2010年4月14日 GMT-4 10:21

Hi Ivar, Have tried this small example, though it is SMALL but helped me A LOT, now I have some idea about the solution. Really thank you a lot.

Posted: 1 decade ago 2010年8月25日 GMT-4 08:17

Dear all, The solution presented above probably refers to version 3.5. I would like to implement a similar solution in 4.0a how can I do that? Is it possible to set a similar boundary condition in 4.0a? If so, how? BR Mehdi

Posted: 1 decade ago 2010年9月21日 GMT-4 08:58

I have a similiar problem with Comsol 4. In the Model Builder>Moving Mesh there is no option to set the boundary conditions of single edges. You can only set the prescribed mesh displacement but that doesn't work at my system. Thanks Matthias

Posted: 1 decade ago 2010年9月21日 GMT-4 10:40

Hi first be sure you have the latests patch 4.0.0.993 for me today ;) Then if you rightclick the Moving mesh node you can see the domain and boundary prescribed displacement that allows you to define boundary or point meshing constriants. By dfault everything is fixed, sou you must also add a free mesh domain node and select which are "free" to move -- Good luck Ivar

Posted: 1 decade ago 2010年10月9日 GMT-4 01:52

Hi Could you please be more specific about this example in version 4.0a? I am confused about the following: lower edge "2": fixed mesh dx=dy=0 left and right edges "1,4": fixed along dx=0 and dy not selected = free top edge "3": fixed along dx=0 and dy=Wave(x) forced to the Wave function You mesh and hit refinement once to get a reasonnable mesh, w.r.t. the wave periode and you solve. Are these settings in Prescribed Mesh Displacement under Moving Mesh (ALE) node? And where are the "Mesh" and "Refinement" actions? Thanks very much. [QUOTE] Hi I quickly generate an example, this gives the idea: Start Comsol in 2D with just a moving mesh ALE mode, draw a rectangle 1 m in x, 0.2 m in y Define an analytical function "Wave" with argument "x" and expression something like 0.05*sin(2*pi*3.5*x) I have choosen a half total wavenumber just to make the funtion symmetric between x = 0 and 1, this is no necessity, test it by plotting it in the Function GUI for 0 < x < 1. Then you define the boundary conditions: lower edge "2": fixed mesh dx=dy=0 left and right edges "1,4": fixed along dx=0 and dy not selected = free top edge "3": fixed along dx=0 and dy=Wave(x) forced to the Wave function You mesh and hit refinement once to get a reasonnable mesh, w.r.t. the wave periode and you solve. To see the mesh, use "postprocessing - plot parameters - General tab: Element refinement OFF and value "1" its toward the middle-bottom part of the GUI, and in Surface tab: Coloring: FLAT Fill Style Wireframe there you are. now you can save this "deformed" mesh as a geometry, but you might need to "remesh it" as the mesh quality might become poor, also if the mesh was rather rough you might not have a very clean geometry, once saved, with a few "spikes, that might need some tweaking. have fun COMSOLING [/QUOTE]

Posted: 1 decade ago 2010年10月10日 GMT-4 06:33

Hi you are right in V4 "ale" is under "Mathematics - Deformed mesh" Then by default V4 comes with Fixed Mesh "all" for the full/all volume so you must add: Free Deformation and select domain 1 (the only one or the one you want to deform if several) Thereafter you might define your boundary Prescribed mesh displacements in V4 I ususally leave the two default entries Fixed Mesh 1 and Prescribed Mesh Displacement 1 as is and add my own thereafter. For this example: 1x Free Displacement (on the domain) and 3x Prescribed Mesh Displacements on the Boundaries sa described. The mesh "size" is in the "SIZE" subnode of the mesh, the first subnode is a global settings (or the one you add to a partial meshing command) The mesh refinement is somewhat hidden in the sub-node: right-click_on_Mesh + More_Operations + Refine Then solve, to see the mesh, use a mesh plot (right click under Results - 2D Plot Group) -- Good luck Ivar

Attachments:

• Capturea.PNG

Posted: 1 decade ago 2010年10月10日 GMT-4 16:42

Problem solved:) Thank you very much! I am really a total beginner of COMSOL so this might be a stupid question: How to save the deformed mesh as a geometry? How to use the formed geometry in other models?

Posted: 1 decade ago 2010年10月11日 GMT-4 12:19

Hi normally there is an Export to file as right-click option for the meshing -- Good luck Ivar

Posted: 1 decade ago 2010年10月11日 GMT-4 12:55

Hi Ivar, There is an Export to file as right-click option for the Mesh node, but the exported mhpbin file is just the mesh that before the sine wave edge was formed. How can I exported the deformed mesh? Best Regards

Posted: 1 decade ago 2010年10月11日 GMT-4 15:38

Hi Good remark, in V4 I cannot find any saved deformed mesh or make geoemtry of deformed mesh, could be that it is not yet implemented ? -- Good luck Ivar

Posted: 1 decade ago 2010年10月12日 GMT-4 00:36

Hi Ivar, Is it possible to make a deformed mesh in 3.5a and then export it and use it in v4? I don't have 3.5a but I can ask some else to try this. Best Regards Steven

Posted: 1 decade ago 2011年1月31日 GMT-5 10:26

Hello Ivar, I have some problems in reconstructing the example you described above. Could you post the file you have created the screenshot from? So I could check out what I have missed in the boundary conditions or somewhere else. Thanks a lot, Thomas

Posted: 7 years ago 2017年1月25日 GMT-5 10:32

Dear Ivar, can you please explain this little more. To see the mesh, use "postprocessing - plot parameters - General tab: Element refinement OFF and value "1" its toward the middle-bottom part of the GUI, and in Surface tab: Coloring: FLAT Fill Style Wireframe