FEA Chassis Analysis - Ansys Workbench

[eklipse]

I have some questions for frequent users of Ansys Workbench. I typically use Ansys Classic for my analyses, however, I am switching over to Ansys Workbench and am having difficulties achieving the same results.

I've modeled my frame in Solidworks with suspension and various mounting brackets and exported the assembly as an IGES file (Manifold Solid B-Rep Object, Type 186). The exported IGES file contains only a 3D line sketch of the frame and the mounting brackets as Solids floating in their relative places.

I have imported the file into an Ansys Workbench geometry file where it generated Line Bodies for the 3D line sketch and the Solids Bodies for the mounting brackets. I have assigned appropriate cross section attributes to each line-body in the Geometry File and have meshed the elements in the Simulation File.

This is where I have problems.
1) When I apply loads and constraints, it appears that all the individual beams are floating in space and will deform independently from the other beam members, as if nothing was connected. I have seen other beam analyses where the frame was merged into one single part, however I get an error when I try to solve the Solution that says "An internal solution magnitude limit was exceeded. Please check your Environment for inappropriate load values or insufficient supports. Also check that your mesh has more than 1 element in at least 2 directions if solid brick elements are present...". I will try to verify that my model is correct, but I can't seem to avoid getting this error.

2) Connections/Contacts. I cannot make any contacts or joint connections between the mounting brackets and the line-body beam elements. The Connection tool won't let me select lines or line bodies. Any suggestions?

3) Driver weight. I wanted to add a Point Mass to simulate the inertial forces of the driver sitting inside the vehicle, however, the Point Mass Feature seems to only apply to faces, whereas I have mentioned before, I only have line-bodies for the frame. Any ideas on how I can apply these loads? I suppose I could model a seat as a surface but that leads me back to Problem #2 where I can't seem to make any connections between line-bodies and anything else.

Any suggestions would be much appreciated.

Thanks,

Adam

[FormulaJuan]

My experience with ansys is pretty elementary, but i'll try and relate my knowledge to help you..


For beam type structures (space frame), we always use Ansys "classic". In ansys we define the analysis to a beam type analysis. From what i understand, if you import something as an iges into workbench, it will analyze it as a solid. This is much more time consuming and less accurate than the traditional beam type algorithms within ansys.

I would just input all the keypoints into ansys, define your lines, define the mesh, yadda yadda yadda, then analyze that. Just make sure your material props and whatnot are the ones you should be using.

[FormulaJuan]

For the record, thats how we analyze our frame.

[frenzy]

can anybody give me a clue how I could "easily" import keypoints from a solidworks 3d-sketch into ansys?
it's a pain in the a** to type them in manually ..

[DonMolina]

You know, you could use COSMOSWorks.

Works just great, and integration with Solidworks enables you to chage anything you wan on the fly so that you can do a lot of studies without having to go back and forth with ANSYS.

Is ANSYS so much better to be worth the hassle?

[fixitmattman]

I've never had any good luck importing any models from the usual CAD packages into Ansys. I don't use the program an extensive amount like I do the CAD packages so maybe I'm just doing it wrong. But even when I did get models to import my confidence in them wasn't there. Generally I just build my truss model from scratch in Ansys and work from there.

Cosmos is quite handy for general analysis and is not significantly less accurate, but as far as I'm aware Ansys is still for the most part the standard.

[DonMolina]

Originally posted by fixitmattman:

Cosmos is quite handy for general analysis and is not significantly less accurate, but as far as I'm aware Ansys is still for the most part the standard.

Well, ANSYS is undoubtedly one of the best solutions (if not THE best) for FEA.

But solving the frame is not something worth the trouble.

With Cosmos, you lose a totally insignificant amount of precision and you gain soooooo much in ease and speed and productivity that for me at least (and all of our team for that matter) there's not even a discussion on what package to use.

Being able to change your designs in a jiffy and have the results of a new study as fast, is what makes designs better imho. Trying to get the best of 2 designs never beats trying to take the best of 10 designs.

However, turns out that software is just like ladies (yes we engineers are THAT geeky unfortunately). Some of us like blondes, some of us go with the brunettes' option etc...

[Wes Burk]

I agree with the COSMOSWorks beam-element study being ridiculously easy. It is my first year using the program and I can set up from scratch a study and solve it in a few minutes.

HOWEVER, last year we used ANSYS (i forget what beam element type) and the study matched our physical testing within a couple percent. Then when I studied the same frame model in COSMOSWorks it output consistnant torsional stiffness values 30-40% higher. We used a conversion factor to equate the ANSYS and COSMOS values because the ANSYS values matched our physical testing. Will be able to get to the bottom of it when we complete this years physical testing and do an ANSYS model of the new frame, but I was wondering if anyone knows how to manipulate the beam element tests in COSMOSWorks like how you can choose a different beam type in ANSYS.

[eklipse]

I still didn't seem to get an answer to my questions over the weekend.

Regardless, Ansys is a very powerful package and I have seen model iterations done in a matter of seconds with DesignExplorer - Design of Experiments. I would like to continue working with Ansys considering it is an industry standard and for its reliability.

Back to the purpose of the thread. Can anyone with experience in Workbench offer any useful advice on the questions that I have asked.

Somebody asked about an easy method for entering keypoints automatically in Ansys Workbench. Yes, you can make a table in excel and export it as a Comma Separated Values (CSV) file and import them. Take a look at this tutorial http://www.padtinc.com/epubs/f...1006/TheFocus_52.pdf. If you look carefully you will find an FTP link to download the sample files.

Ansys workbench does analyze as solids however it automatically chooses your element types whereas you have to option to choose in Ansys Classic. If you click on FE Modeler you can view the element types if you look carefully. Typically, using Ansys classic, 2 point beam 188 elements will suffice. I would like to solve my analysis using lines and surfaces but I can't seem to change this option in Ansys Workbench, if anyone knows how to, it would be very helpful.

I still need to know how to constrain my beam lines to solid surfaces. I tried using a bonded connection however I can't seem to pick lines or keypoints, only surfaces. Can anyone help with this?

[RBbugBITme]

#1) It seems your nodes between beams are not attached even though they are at the same coordinate. There should be a merge function that will allow you to enter in a distance where all nodes within that distance will become one node and your beams will connect to each other.

Oh and any panels I wanted connected between tubes were modeled as shell elements. I would keep it simple and forget the solid model stuff you're doing in Ansys, at least during the initial testing to ball park your design.