Nastran performance

[NigelHay]

We are considering changing our Inventor package when it comes up for renewal later this year & are using a trial copy of Nastran to see how it works. We are finding that it takes a long time to compute results, is that down to our PC spec or is that just how Nastran works?

PC is:

Intel core i7-3770K CPU at 3.5GHz

16Gb RAM

250Gb SSD hard drive

NVIDIA GeForce GTX 670 graphics

Windows 7 64bit.

[JDMather]

You have not given any indication of the complexity of your part/assembly or analysis?

[NigelHay]

At the moment my colleague who has some training on FEA & previous experience in ANSYS is playing with Nastran to see what it will do. We are looking at 3 axis vibration & shock as well as static loading & hope to move on to thermal. I've attached an image of a typical assembly.

[John_Holtz]

Hi Nigel,

I think we need a lot more information about the actual analysis, not a diagram of the model.

For example, for each model that has been analyzed:

1. How long is the analysis taking?
2. What analysis type?
3. How many mode shapes or load cases or steps in the analysis?
4. How many nodes?
5. How many elements? (The In-CAD model tree shows the number of solid and shell elements, but contact adds many more elements. The total count is in the log and output file.)
6. What types of elements?
7. Is there anything in the model that makes the analysis iterative or nonlinear? Iterative/nonlinear effects occur when the analysis includes separation contact (linear or nonlinear stress), nonlinear materials (rubber or yielding in a nonlinear analysis), large displacements (in a nonlinear analysis)?

There are usually different methods to setup an analysis: some may be more efficient than others. If you can provide any of your examples, someone can look at it and make some suggestions. (The model consists of all of the part file .ipt and assembly files .iam, preferably zipped together so that we only need to download one file.)

[NigelHay]

John, lots of questions & few answers I can provide.

1. Analysis taking around 1 hour.

2. Modal analysis.

3-6. Don't know, our 30 day trial has ended. We are talking to our reseller about ways of having an extended trial.

7. I don't think so, no 'soft' materials. Possibly the wedge type circlip?

Please bear in mind that we are absolute novices in this trying to assess if it is worth including Nastran at our next license renewal later this year &, if so, whether we would have to allow for an upgraded workstation.

[John_Holtz]

Thanks @NigelHay 

I looked at the model, but it was not setup for an analysis.

Not knowing specifically what you were intending, I tried to set it up for a modal analysis using any arbitrary constraint, but I was having some problems. (Part of the problems may have been that the parts are interfering in some locations. That may be throwing the mesher off or the contact. See the image below.)

A mesh size of around 0.5 mm looked reasonable to me. This resulted in about 1.5 million nodes and about 1 million elements. If you were solving for 10 to 20 modes, I can see how a runtime of 1 hour for a model this large would be reasonable. (I will have a better idea if you have a file that had been analyzed and can send the Inventor part and assembly files, just like you did for the 740-TUBE model. You can know if the model was analyzed by looking at the files in the folder. Go into the folder with the model name, then into Incad\FEA. If there are .LOG and .FNO files, the model has been analyzed.)

Your computer specs look to be good. The one thing that is not indicated is if it has multiple processors. (The Nastran solvers take advantage of multiple processors.)

Interferences between some parts in 740-TUBE..iam

[NigelHay]

John,

I have attached the files from the InCAD folder.

Where the model parts interfere is where we would perform a final machining operation to set the gaps we require between parts & to allow for variation in tolerance for individual parts.

Our PCs have 8 cores, you are saying that the performance looks OK which was really all I was asking for now. If we are going to invest in Nastran I needed to know if upgraded PCs needed to be part of the condideration.

[John_Holtz · Accepted solution]

Thanks @NigelHay 

I suppressed the parts that were interfering in the model 740-TUBE, and created a fine mesh that resulted in 6 million elements. The modal analysis solved for 16 modes in 0.8 hours on my desktop computer (using 8 processors). That runtime seems reasonable to be for a model of that size. Your computer specs are similar to mine, so you should not need a new computer to perform the analyses.

The new "FEA.zip" file that you provided showed the analysis solved in 20 seconds which seems good to me . (Obviously, those files are for a different model.)

We look forward to hearing from you in the future if you go forward with using In-CAD.

[NigelHay]

John,

Thanks for your helpful comments. We are currently having a look to see if we have a spare PC which would allow us have another 30 day Nastran trial (along with a 30 day Inventor trial). The only thing our reseller could offer was to convert one of our Inventor Product Design Suites to Product Design & Manufacturing Collection until our renewal in September but this will cost us about £1400.