Skip to main content

Unintended Mesh Interference

If you're not careful, you'll end up like me with unintended interference. The problem can be illustrated with a pin and hole-part assembly. Three identical geometry assemblies are created. From left to right, firstly a Tet mesh, then two others of different Hex mesh controls (Figure 1). Though the pin has the same diameter as the hole diameter, there may be interference in the model due to geometry discretization.

Figure 1: Identical Geometry but Different Mesh

The difference in results are clear from the contact pressure shown in Figure 2:
Figure 2: Contact Pressure at Frictionless Contacts

The coarse Tet mesh does not 'curve' well (Figure 3) thus bumping into each other. The interference in the second assembly with hex mesh is less acute but still present (Figure 4). The third assembly with hex mesh with nodes of both the pin and hole aligned has no interference (Figure 5) hence almost no pressure.

Figure 3: End View Tet Mesh Shows Interference at Hole

Figure 4: End View of Hex Mesh (Not Aligned) Has Interference

Figure 5: End View of Aligned Hex Mesh

In summary, a good mesh size and controlled hexahedral meshing does make a difference. The v18.1 archived WB file can be downloaded here.

Comments

Popular posts from this blog

ANSYS User Defined Results

There is an abundant of options in ANSYS classic when one wishes to post process results. ANSYS workbench default pull down menu post processing options are more limited but they can still be accessed via the User Defined Results. One way not commonly used but can come in handy is as follows: Zeroth: Under Analysis Settings, there is "Output Controls" where you can toggle to "Yes" what you would like to save before the solution starts. This is like OUTRES in APDL. Output Controls First: After solving the model, click on Solution in the tree to highlight it. Solution Second: Click on Worksheet in the toolbar. Worksheet Third: In the worksheet, you will see list of results that are saved. Right click on it to create the User Defined Results. Create User Defined Results So here we have it. You could of look up the different expressions in the help document but I find this method of accessing the results convenient.  Example: Aspec

Export Stiffness Matrix from Ansys

It is sometimes useful to extract the mass and stiffness matrix from Ansys.     *SMAT, MatK, D, IMPORT, FULL, file.full, STIFF       *PRINT, matk, matk, txt Exporting mass matrix would be similar:       *SMAT, MatM, D, import, full, file.full, MASS The above script uses APDL Math to get the job done. (Please see previous post for another example). The ordering of the matrix is unfortunately not concurrently exported. To verify the sequencing is as expected, we will work to replicate a truss example in the  Finite Element Trusses course notes by Bob Greenlee. Figure 1: Truss Problem Setup Model Creation Script to create model: /prep7 !! Creates Model to reflect course notes ! Properties et ,1,1  mp , ex, 1, 29.5e6 r , 1, 1 ! Geometry n ,1 $  n ,2, 40 $  n ,3, 40, 30 $  n ,4, 0, 30 e ,1,2 $  e ,2,3 $  e ,1,3 $  e ,3,4 ! Boundary Conditions d ,1,ux,0 $  d ,1,uy,0 d ,2,uy,0 d ,4,ux,0 $  d ,4,uy,0 f ,2,fx,20e3 f ,3,fy,-25e3 ! solves /solu eqslv , sparse

ANSYS APDL Syntax Highlighting editor

Notepad++ with APDL User Defined Language The editor of my choice is Notepad++  with the available User Defined Language Files for APDL . You can install it without administrative privileges via the zip file. The best part of it is, it's FREE! After installing Notepad++, go to "Language>Define Your Language..." then "Import" the XML file downloaded from the above link. Remember to restart Notepad++ so that the language changes will take into effect. Opening up any *.inp or *.ans files should automatically switch highlighting to APDL. I made some minor edits. Here's my XML file: LINK . I also heard Sublime Text and  Ultraedit  has more advance features but they aren't (totally) free.