topic Re: How to get rid of "Spikes" - inaccurate VM stress calculations in Simulate? in Analysis

How to get rid of "Spikes" - inaccurate VM stress calculations in Simulate?

JS_9824412 — Mon, 07 Mar 2022 21:27:32 GMT

See above screenshot, the spikes of stress calculations among shell elements. Does anyone see this before?! The stresses should be less than 20ksi, however, these spikes are around 2.0e+7 ksi. I am using Simulate 6.

Re: How to get rid of "Spikes" - inaccurate VM stress calculations in Simulate?

SweetPeasHub — Tue, 08 Mar 2022 13:53:03 GMT

Please give us more information. If you can attach a zip file that would help greatly. My only comment on the images is that the elements look strangely shaped.

Re: How to get rid of "Spikes" - inaccurate VM stress calculations in Simulate?

JS_9824412 — Tue, 08 Mar 2022 14:43:29 GMT

The image on the left side shows the shell elements of a metal bracket of thickness 0.1". The image on the right side shows the von Mises stress distribution in the latest simulation just now. There is no more "spikes" shown in yesterday's post.

It never happened before according to my limited memory.

On yesterday afternoon, when the "spikes" showed up, Simulate popped up a message "Fatal error encountered", then quitted.

Today, this is no error message.

Re: How to get rid of "Spikes" - inaccurate VM stress calculations in Simulate?

JS_9824412 — Tue, 08 Mar 2022 14:46:20 GMT

The traceback.log about yesterday's incidence is attached here.

Re: How to get rid of "Spikes" - inaccurate VM stress calculations in Simulate?

JS_9824412 — Tue, 08 Mar 2022 14:59:05 GMT

Simulate allowed the Total Effective Mass to be greater than 100%!??

Re: How to get rid of "Spikes" - inaccurate VM stress calculations in Simulate?

JS_9824412 — Wed, 09 Mar 2022 17:14:15 GMT

NEVER HAPPENED BEFORE! Numerical errors in 1-sigma von Mises (ksi) calculations are absurd!

Total Effective Mass should be approaching 100%, not 351,854%! Creo Simulate should not allow this happen.

Re: How to get rid of "Spikes" - inaccurate VM stress calculations in Simulate?

JXBWk — Tue, 15 Mar 2022 08:55:45 GMT

Can the mesh (nodes /element ) and the data in the result (file) be for a different mesh? I have seen such issue in some tools as long as there is a node with say the same id then the tool will try to plot something. Is the plot for disp & rms stress ? looks like simulate is plotting rms disp hence the "spikes". You pointed to total MEFFMASS > 100% in another post so clearly something's not right

Re: How to get rid of "Spikes" - inaccurate VM stress calculations in Simulate?

JS_9824412 — Tue, 15 Mar 2022 12:18:36 GMT

The plot is for rms stress.

This is caused by some software bug. Because it can work sometimes, i.e., without changing anything, sometimes Simulate can produce normal results, at some other time it can't.

Re: How to get rid of "Spikes" - inaccurate VM stress calculations in Simulate?

pausob — Wed, 16 Mar 2022 06:37:05 GMT

I don't have an answer but point out that it is very possible that there are bugs in any software...

However, this thread and your examples do make me remember an old discussion from few years ago. In it, (in no small part due to how PTC handled it), I developed severe mistrust in Creo Simulate FEA capabilities:

Non-symmetric results for symmetric model and load?

Disclaimer: I don't have maintenance, so I can't track if the SPR 2258467 has been closed. I have to say that it seems to me that PTC has gotten better lately, so I'd be curious if there was a resolution to a very basic issue that somehow got past PTC QA and made it to a released product costing $$$

Re: How to get rid of "Spikes" - inaccurate VM stress calculations in Simulate?

JXBWk — Wed, 16 Mar 2022 07:16:27 GMT

Fully agree with you. And possibly compounded by the click-the-button and black-box approach

Re: How to get rid of "Spikes" - inaccurate VM stress calculations in Simulate?

TomU — Wed, 16 Mar 2022 12:28:39 GMT

@pausob wrote:

I don't have maintenance, so I can't track if the SPR 2258467 has been closed. I have to say that it seems to me that PTC has gotten better lately, so I'd be curious if there was a resolution to a very basic issue that somehow got past PTC QA and made it to a released product costing $$$

No.

Re: How to get rid of "Spikes" - inaccurate VM stress calculations in Simulate?

JS_9824412 — Wed, 16 Mar 2022 14:12:26 GMT

Now they are trying to sell ANSYS to Simulate users. On 9/16/2021, when my Simulate simulation encountered a serious weird issue, ANSYS sales agent called me out of a sky. What a coincidence. Most of my time were spent on creating manufacturing drawings in CREO. How could they know I was using Simulate? Might be just a coincidence.

If they are focusing on ANSYS sales, there would be less funding and manpower on improving Simulate. Just a guess.

Re: How to get rid of "Spikes" - inaccurate VM stress calculations in Simulate?

pausob — Wed, 16 Mar 2022 16:59:01 GMT

Well, if you want accurate results, then ANSYS might be the way to go. By the outcome of the SPR 2258467, it seems that PTC feels that they would spend too much effort on fixing Creo Simulate and since it gives "almost right" answers most of the time, that is good enough.

I would not be surprised if there is no one left at PTC (be it product manager, software developer, mathematician) that knows about this closed issue. And since it was filed away under Creo Elements Direct - Drafting (???), most FEA users won't come to know that they are using sub-standard solution.

But then again, I kind of doubt that Creo Simulate is used in any serious, mission critical type of projects.

Re: How to get rid of "Spikes" - inaccurate VM stress calculations in Simulate?

JXBWk — Thu, 17 Mar 2022 07:50:43 GMT

Very good points.

On the last statement. “… mission critical type of projects”

With the move or incorporation of ANSYS capabilities (I’ll admit I have not read any flyers/marketing glossy brochures on it) how does one know how far one can push the tool? Short of doing huge amount of testing and comparison?

Re: How to get rid of "Spikes" - inaccurate VM stress calculations in Simulate?

JS_9824412 — Thu, 17 Mar 2022 12:39:00 GMT

Hopefully NASA can explicitly ban some FEA software tools with sub-standard solutions. Soon they will ban Simulate as an analysis tool used by their contractors.

Re: How to get rid of "Spikes" - inaccurate VM stress calculations in Simulate?

pausob — Thu, 17 Mar 2022 21:24:00 GMT

I'd think any NASA mission-critical designs would have to be validated in a real life test.

Personally, I don't fully trust FEA results because... well, I'm just ignorant about the limitations of computer modeling and always have doubts about high stresses being an artefact of improper mesh element size, eg.

FEA is being used with great success. I'm just under the impression that FEA experts use software that is just better.

Anyway, I thought ANSYS was already integrated into Creo somehow - for the PTC simulate "live" technology? So maybe the inherent flaw I pointed out in the other thread is simply gone and this discussion which basically involves me ranting about quality of PTC software is moot.

But I'd be curious to know what FEA experts think of latest Creo Simulate?

Re: How to get rid of "Spikes" - inaccurate VM stress calculations in Simulate?

skunks — Fri, 18 Mar 2022 12:14:26 GMT

for amusement device: https://www.youtube.com/watch?v=Fllzv_mkRwQ

Mechanism Dynamics Option, Simulate and Fatigue (Creo 2.0 M080)

I don't have a subscription

Re: How to get rid of "Spikes" - inaccurate VM stress calculations in Simulate?

pausob — Fri, 18 Mar 2022 20:17:52 GMT

Thanks for the example and an amusing break to my day @skunks !

So what do you think of that whole SPR 2258467 affair chronicled in the thread Non-symmetric results for symmetric model and load? ?

I guess I still can't get over how PTC handled this, despite clear demonstration of the issue and how other software (Solidworks, Abaqus) didn't require any "mesh refinement" mentioned as a work-around. Also, it seemed that some knowledgeable users pointed out the root cause. Yet PTC didn't seem to fix it. My impression: they don't care enough, or they can't. Either way, kills my confidence. It's like using a spreadsheet application and accepting that, with value in cell A1 = 2.000 and one in A2 = 2.000, then formula "=A1+A2" in cell B1 will, in some cases, display 4.010

Re: How to get rid of "Spikes" - inaccurate VM stress calculations in Simulate?

skunks — Mon, 21 Mar 2022 08:26:11 GMT

I think: PTC will direction toward Ansys

Re: How to get rid of "Spikes" - inaccurate VM stress calculations in Simulate?

skunks — Wed, 23 Mar 2022 09:27:01 GMT

"...So what do you think of that whole SPR 2258467 affair chronicled in the thread Non-symmetric results for symmetric model and load? ?..."

example att.