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Member
benoitj
Posts: 5
Registered: ‎05-08-2012

Feature Matching of Surface Models

459 Views, 8 Replies
09-25-2012 07:34 AM

I have tried various times with various modelling software (Inventor, Autocad) to create surface models to run FEAs on. I keep having problems with feature matching that sometimes render my results useless. I have tried different file types to export or import, again issues. I have been forced to run FEAs on thin walled pressure vessel components with solid elements.  The pressure vessel program is simply not what I need for the custom booms and other geometries I deal with. Is there a way that simulation can handle surface models that are imported? The boss boasts having spent 30K on top notch FEA software. Surely it should be able to do this. Has anyone found a way to get imported surface geometry WITHOUT feature matching errors. The geometry I work with is not typically simple.

We run Autodesk Algor Simulation MES 2011 & we have Autodesk Simulation Mechanical 2012

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Valued Mentor
AstroJohnPE
Posts: 494
Registered: ‎08-30-2012

Re: Feature Matching of Surface Models

09-25-2012 09:05 AM in reply to: benoitj

If you could, please attach a CAD surface model. It is hard to give advice without knowing the specific problems.

 

Since you are more familiar with the models and issues than we are, a few images showing where the problems occur would be helpful -- unless the issues are very obvious.

 

John Holtz, PE
Mechanical Engineer
Pittsburgh, PA

16 years experience with Simulation Mechanical
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Member
benoitj
Posts: 5
Registered: ‎05-08-2012

Re: Feature Matching of Surface Models

09-25-2012 03:19 PM in reply to: AstroJohnPE

Here is an example. The Nozzle could be done with the pressure vessel utility in Autodesk Simulation Mechanical 2012. However, If I make the model using inventor or autocad, I get feature matching issues. I tried running the fea on this thing and ended up with large gaps between the nozzle and the repad. I could not use the results as they were exteremely hign and had to do a solid model. Unfortunately, most of the feas we need to do are not as simple as this one. In another study I did a simple bumper for fea. All the faces were normal. It still had a dozen or so feature matching errors. The fea did proceed to completion, however I question its accuracy.

 

Thank you for your input on this. Processing time is through the roof trying to do these thin walled vessels using cubic elements.

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Active Member
lesmfunk
Posts: 6
Registered: ‎09-26-2012

Re: Feature Matching of Surface Models

09-28-2012 08:34 AM in reply to: benoitj

For the nozzle, have you tried splitting the surface of the nozzle at the repad using the repad geometry? This creates an edge along the joint.

 

Also, I have been getting feature matching "warnings" from several parts in an assembly. When I zoom in on the mesh, it appears that they actually are matched, and when I run the analysis, the parts do not pull apart.

 

I don't know why there is a warning.

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Member
benoitj
Posts: 5
Registered: ‎05-08-2012

Re: Feature Matching of Surface Models

10-01-2012 07:15 AM in reply to: benoitj

What exactly are these feature matching errors. From my research there could be nodes that won't be connected properly accross the parts. I agree with you, I did not find any errors other then the warning with the bumper. The nozzle however, It gave me much grief as elements did not connect together at the intersection of the nozzle and repad. I was left with large gaps that pulled apartd during the analysis. Is this a software issue? I have done many of the tutorials and it does not cover mush on imported geometry. Especially of surfaces.Feature Matching Error Screenshot.jpg

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Active Member
lesmfunk
Posts: 6
Registered: ‎09-26-2012

Re: Feature Matching of Surface Models

10-01-2012 08:52 AM in reply to: benoitj

I always import geometry (from SolidWorks) and am now using Algor Simulation Multiphysics 2012.

 

I tried your nozzle.ipt file and although I got the warnings, the mesh appears to match at every node. I even pulled on the nozzle to try to get them to pull apart, and there was no separation. I also split the nozzle face at the repad (In Inventor Fusion and saved as a .stp) and got similar results, although the analysis seemed quicker.

 

I have tried a few things with your nozzle.ipt and get perfect mesh/node matching every time. I am using plate/shell elements. I cannot replicate your problem.

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Valued Mentor
AstroJohnPE
Posts: 494
Registered: ‎08-30-2012

Re: Feature Matching of Surface Models

10-01-2012 11:02 AM in reply to: lesmfunk

Hi Everyone,

 

Let me start by clarifying two concepts. One is "feature matching" which indicates whether the edge of a surface matches with one other edge, more than one (multi-match), or no other edges (unmatched). The terms original from CAD solid models in which each edge (feature) will meet up (match) with only one other edge (feature) in a valid solid. See this page in the documentation for more details.

 

The other concept is mesh matching. In order to transfer a load from one part to another, the nodes need to be connected together; that is, the mesh must match. (The exception is "smart bonding". See "Types of Contact" in the documentation.)

 

For surface models, I think the software may not have the intelligence to know that unmatched edges are not a problem, so you can normally ignore the feature matching warnings if they occur. The mesh does need to match, though. The construction vertices that are shown in benoitj's image may be causing some problems with the mesh not matching. These points (the blue dots) may have been imported as work points from the Inventor drawing. Unless they are needed for simulation purposes, it is better to not import the work points in my opinion.

 

I was able to mesh both models without a problem using Simulation Mechanical 2013 SP1. I analyzed the nozzle model to confirm that the nodes were connected together -- no problem. I did a visual inspection of the bumper model to confirm the nodes were connected -- at least 99% if not 100% of the nodes were connected.

 

John Holtz, PE
Mechanical Engineer
Pittsburgh, PA

16 years experience with Simulation Mechanical
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Member
benoitj
Posts: 5
Registered: ‎05-08-2012

Re: Feature Matching of Surface Models

10-03-2012 07:01 AM in reply to: AstroJohnPE

The model does not contain any work points. I simply highlighted the bad geometry. Now what can you do if the nodes don't match up or if features don't match up right? Is there a way to make them? I've looked into contacts a bit. I know these apply to solid models, can they be used to match up surface models? When I made up the model, I was very careful to make sure that the geometry is clean of small gaps. Thank you for your time and input in this matter.

 

Benoit Jolin

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Valued Mentor
AstroJohnPE
Posts: 494
Registered: ‎08-30-2012

Re: Feature Matching of Surface Models

10-03-2012 12:44 PM in reply to: benoitj

Hi Benoit,

 

I think the best solution for you is to update your software to version 2013. As can be seen from the Release Notes, there are a lot of enhancements in general, but the big change that helps you is the switch from a third party CAD kernel to the Autodesk CAD kernel, so models come in much cleaner.

 

Otherwise, this option may help to remove the gaps and achieve a matched mesh: "Mesh > Model Mesh Settings > Options > Model" (2011) or "Mesh > 3D Mesh Settings > Options > Model" (2012 and newer) and change the "Mesh matching" tolerance to a value larger than the gaps created.

 

The other way to repair the mesh is "Geometry > Tools > Point Move" (2011), "Draw > Modify > Point Move" (2012) and "Geometry > Add > Line"/"Draw > Draw > Line" (2012). What you see in the FEA Editor is just a bunch of lines, so you can do anything you want to do by using standard "CAD drawing" concepts to adjust the "elements".

 

John Holtz, PE
Mechanical Engineer
Pittsburgh, PA

16 years experience with Simulation Mechanical
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