Good afternoon All,
I’m a newer user of PrePoMax, and I’m now making some correlation tests with Solidworks Simulation (that I’m currently using in the company where I’m working).
I did a modal simulation on a fan made in alluminium; I setting up the simulation at the same way in PrePoMax and Sw Simulation (also tried to have the same mesh size in both cases). The geometry was fixed in the central hole, with no other loads applied.
When I checked the eigenvalues I found that the results found in Sw Simulation are different with the results found in PrePoMax. The modal shapes are similar, but the natural frequencies have a different of more of 200Hz (the results found in Sw are the correct one from my experience).
I tried to check the geometry, the material properties, etc. in PrePoMax (just to see if I did some mistakes) but in any cases I did not be able to have a results closer to the Sw’s results.
Did someone else have the same problem with PrePoMax using frequency analysis?
I was also thinking about a problem in the import phase (I imported the solid geometry in STEP format), but I did not found in PrePoMax a feature on the geometry that can permit, for example, to check the volume of the solid imported (in this way I can be sure that the solid imported is correct or not).
Thank you in advace.
Marco F.
difficult to answer you without any data; i’m thinking in many topics to explain it: units (are you consistent), type / order / size of the elements, fixing mode and so on.
I would suggest you to make a basic test case to compare both solversn, and to post it if you’ll encounter any trouble.
Make sure you are setting correct unit system in PrePoMax, measure the imported geometry (you can also do some measurements e.g. in FreeCAD with the imported STEP file but it would be better to do it in PrePoMax to make sure nothing changes) and double-check the material properties. For example, density is in t/mm^3 when using the SI(mm) unit system.
This are the results that I found in Sw:
and this the result found in PrePoMax:
I attach also the STEP file:
FAN_FEM.zip (180.6 KB)
I did try a lot but I’m still not able to find what was wrong in PrePoMax
it would be better to have the prepomax file to have informations on the material and so on
Here below the PrePoMax file that I did it:
Ventola ECO43 attuale.pmx (3.4 MB)
Main changes:
First run and it probablty can be improved
Super!!! Thank you very much for your help 
Just two questions (because I’m a new user):
- why you did a “compound” of the two element?
- you did not use “tie” feature because the two element was united?
Thank you again for your help!
Marco F.
Yes
You’ve to create a compound so that the mesh is coincident
In the geometry module, select the 2 parts, right click and create a compound
note you can easily create aimations in prepromax 
Compounding is super useful but it may not work in some cases: Deformation in 2 or more bodies - #10 by Matej
Mode shapes from frequency analysis are actually a great way to find disconnected regions. And if you still have some discrepancy, try refining the mesh in each software.
When working with SWS and assemblies, keep in mind a few key points:
First, SWS automatically creates “glued” contact pairs between components. However, if you export an assembly composed of two parts to a STEP file, they will become two separate bodies.
Second, regarding the mesh, SWS defaults to creating second-order elements (10-node tetrahedrons). If you try a “draft quality” mesh (bozza in italian), you’ll get a very different result, as SWS will then create 4-node tetrahedron elements, which are significantly stiffer.
Four-node tetrahedrons should generally be avoided. I also believe that SWS is an excellent FEA module, but it simplifies command names to make them more accessible to those unfamiliar with FEM techniques. For this reason, it’s always necessary to consult the manual to understand their true meaning and implications.
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Thank you very much for your feedback
I wanted to move to PrePoMax because SWS do not have a high level of control in terms of input/output; it’s a very good sw for the beginners but if you want to push more on the details it’s not the best.
