Ansys Tips

Photo by  James Owen  on  Unsplash A surprisingly popular blog-post written here is Exporting Stiffness Matrix from Ansys . A sensible follow up question is what can one do with the exported stiffness matrix? In a recent Xansys Forum post, a question was raised on how we can edit the stiffness matrix of a superelement and use it for our model.  An approach presented below is to first create a superelement that has the same number of DOF and nodal location that will serve as a template. An APDL script can then be written to edit the stiffness matrix entries as desired before exporting to a new superelement *.SUB file for use in future models. The self-contained script below demonstrates this.  /prep7 et ,1, 185 mp , ex, 1, 200e3 mp , prxy, 1, 0.33 w = 0.1 ! single element (note nodal locations) n , 1, w, -w, -w n , 2, w, w, -w n , 3, -w, w, -w n , 4, -w, -w, -w n , 5, w, -w, w n , 6, w, w, w n , 7, -w, w, w n , 8, -w, -w, w e , 1, 2, 3, 4, 5, 6, 7, 8 /solu anty...

CMS circa 2019R3 Roughly a year ago, I wrote about how you could reuse CMS elements using APDL snippets within Ansys Mechanical. The new feature of Condensed Geometry in recent releases unfortunately does not completely solve the problem; but does get you half way there. To recap, the goal here is to have a part (A) that is complicated/ huge  but now condensed into a teeny-tiny Super-Element. Changes can be quickly made to other parts (B). When combined together (C/D), the model as a whole is smaller and faster to solve since A is reused. This blog post is an update to the earlier post that uses the same technique but takes advantage of two new tools:  Condensed Geometry & Mesh Numbering . To get started, download the Ansys 2019R3 archived file to follow along. Archived File with RST ( 177.0MB )    Link  or Archived File without RST ( 1.5MB )   Link The rough procedure: Create and mesh both Analysis A for CMS part and Analysis B fo...

Fig 1: Project Schematic With the release of Mechanical 19.2, substructuring is now available for Modal & Rigid Dynamics without scripting. That just made my  earlier post on CMS outdated! Note that there is still a key limitation where Generation and Expansion Pass must be performed on your local machine. To get ahead of the game a bit, here is a way to do Harmonic Analysis extending on previous work . (Please go through that before this post). Some points of note: The method of merging the CMS and non-CMS models together into System C is the same. All files related to the superelement has to be copied over to the solver file directory as before. Modal analysis need not be performed first as the example here uses Full Method instead of Modal Superposition for simplicity.  The script expands the responses the same way as Modal Analysis does so the script will look familiar. Command Snippet for Combined Analysis D !!!!! Save full model fini /filnam...

Figure 1: CMS Reuse Project Schematic In the previous two posts ( here and here ), the workflow requires another generation pass when reusing the model. This diminishes the advantage of using a component mode synthesis (CMS) superelement model. The difficulty is that when the model changes, the superelement node numbering no longer matches the new workbench (WB) model. Everything gets shuffled around. To reuse a superelement body, we need the  nodes to persist in the final Analysis for expansion. Strategy We start out with an original modal analysis ( Analysis A ) that would have worked on it's own. Next, the original modal analysis is duplicated (becoming Analysis B ). Analysis A will be modified to only have the superelement body while  Analysis B will be modified to have the geometry and mesh of non-superelement body. When both analysis are assembled into a new modal Analysis C , Analysis B 's element and nodes are automatically offset so that ...

Figure 1: Results from Full Model (Left) and CMS (Right) Background In a previous post on Component Mode Synthesis (CMS) in Ansys Workbench, the expansion of the results were omitted. This is remedied in this post. Figure 1 compares the results favorably between the full model to a model with the mid-section as a CMS part. Resources 1. The archived workbench file (R18) can be downloaded  here  (download icon at top-right). 2. Script that is used as solution snippet can be downloaded here . 3. A key resource is available in the help documentation . 4. Some fancy graphics describing the process here . General Setup Figure 2: Overall Geometry (Left) & CMS Part (Right) This example has a few prerequisites: 1. Multi-parts with shared topology  (Figure 2) 2. Named Selection of the CMS part (Body1 in example) 3. Named Selection of interface on CMS part (c1a & c2a in example) 4. Command snippet under solution does everything. Between steps, no sup...

In a previous post , the Craig -Bampton (CB) substructuring method was used in Ansys to simplify a part for reuse. To learn more about what Ansys does in the background, I did some reading up. Here are some good resources: Resources Original Paper link FEMCI general description:  link My Go-to Primer link Tom Irvine's tutorial papers and Matlab scripts link Octave/Matlab Scripts Inspired by Tom's Matlab script, I coded a script to condense two 'random' bodies, keep only 10 modes of each body with 3 nodal interface points between them. The 'random' bodies are positive definite matrix that is generated randomly for each run to represent two mass and stiffness matrices. Running the script again would generate a different system and different plots. Here are the links to the two Octave/Matlab scripts used to create the plots below: Main Script: Random2PartsCB.m   link   (run this one) Minion Script: CraigBampton.m   link A run of the script may yie...

Here is a basic example of how one may use CMS inside Workbench with APDL command snippets. These appropriately named superelements has the advantage of being quick to solve once the initial investment is put in. This saves time especially for multiple iteration of the same parts (condensed once with CMS) while changes are performed on a local full model part. The archived workbench file (R18) can be downloaded here   (download icon at top-right). Original Model in ANSYS Work Bench The model is rather simple with 3 parts. The bodies are in this case to be connected with CEINTF . The "MainBody" part will be condensed into a superelement (Craig-Bampton method) and will be used later when connected to "Leg1" and "Leg2". The system natural frequencies are then evaluated. The results are compared to the old fashion way of creating a full model for verification. Step 1 Suppress all other bodies except for the "MainBody" which a superelement...