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JonathanHodgson13-Aquamarine
13-Aquamarine
February 2, 2011
Solved

Pro/M optimisation: "invalid model or geometry"

  • February 2, 2011
  • 11 replies
  • 6564 views

I'm trying to run an optimisation study on a gear with a thin web and holes drilled through the web.

I've set up some relations to keep the web in the middle of the gear facewidth, and I've used the web thickness and the hole diameter as design variables in the study.

The .rpt file keeps giving the error:

** Warning: Changing the parameters has produced invalid
model or geometry for the following parameter
values:

Parameters:
d18 10.14 (this is the web thickness, which started at 10)
d28 20 (hole diameter, unchanged in this iteration)
Recovering from invalid parameter values by cutting
step size.

but if I go back to the model and enter the values it shows (which are only a small change from the start point) it regenerates fine.

What gives?

(Initially I used the number of holes as a variable, leaving the diameter fixed, but it recognised the unit as "mm" and then started trying to use non-integer values!)

Edit: I've tried it with both "Repeat P-Loop Convergence" and "Remesh after each shape update" selected, and now with neither selected. Same result either way.

Edit 2: It seems to be running, but for every iteration it has to go through about four 'invalid geometry' cycles, which is making it really slow...


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Best answer by StephenBerkeley

Hi Jonathan,

This issue is fixed in the currently shipping build of Creo 2.0. I would encourage you to upgrade if you can - aside from this problem, optimization and sensitivity studies run somewhat faster than they do in WF 4.0. PTC is no longer shipping regular maintenance builds of WF 4.0.

In Creo 2.0, your study from case C11549838 converges at the following dimension values, without reaching any invalid intermediate states:

d73 7.99501
d72 8.18416
d74 14.1397
d68 10.908

Regards,

Steve.

11 replies

R.Rabe1-Visitor
1-Visitor
January 24, 2012

Same problem here – more than once.

Sometime there is a true regenerating problem. For example changing the geometry makes the part to lose a reference – even for a small feature like a datum point. It can be tricky to spot it until the right combination of geometries that causes the problem is found and the problem isolated.

On the other hand there are cases where there is no explanation for such “invalid model or geometry”. A manual change does not produce any geometry or meshing problem at all.

And this can be a real problem. The optimization goes ahead but this problem slows really a lot the optimization speed. Especially if it cannot test long steps to get close to a solution. In this case to move the initial variables closer to a solution region may help a little as well as to combine it with “remesh after each update”.

Another side effect is that it forces ProMechanica to test only small changes. And if the changes results are keeping below a given optimization convergence level (ex.10%) it simple stops since “no better solution was found than the initial values”.

I tested the same model in WF4 and WF5 (Creo) and I got the same problem. What is common between my model and your description is that I also use relations, although they are very simple. “Remesh after each update” also does not work.

The optimization option in ProMechanica is far from be “clever” but yet very useful. I wish to use it more but sometimes – and especially when this “warning” message appears it is quicker to find a better solution “by hand”.

If someone can provide any other clue, welcome to share. Until now I had no feedback from PTC and by the lack of similar topics it may not be a common problem (or almost no one uses ProMechanica optimization).

JonathanHodgson13-AquamarineAuthor
13-Aquamarine
January 24, 2012

Well, thanks for the solidarity at least!

To be honest, I've given up running Optimisation studies. I use Sensitivity a lot, then use those results to guide my design - they're quicker and ultimately more useful, at the moment.

It's more difficult when you have several variables that interact, though. I still wish PTC could get Optimisation to work properly - until they do, I think almost no-one will use Optimisation.

echan1-Visitor
1-Visitor
January 24, 2012

Hi Jonathan:

Would you please contact PTC technical support and file an issue so that we can take a look at this problem? It's hard to determine what the issue is until we can take a look at the model.

Thanks

Eduardo

JonathanHodgson13-AquamarineAuthor
13-Aquamarine
June 4, 2013

Well, I thought it was worth marking this occasion: I've finally run a successful optimisation study!

After 7 iterations it started giving the usual "Recovering from invalid parameter values by cutting

step size" and, as usual, when I plugged the offending values into the model it regenerated with no problem; but after a few cycles of "cutting step size" it actually came to a conclusion!

Only two parameters on a relatively simple part, but hey, it's a start...

Oh, and I did have "remesh after update" selected - the difference in run time is usually trivial so I generally do.

JonathanHodgson13-AquamarineAuthor
13-Aquamarine
August 21, 2013

I've got another one: over 3.5 hours to reach iteration 5, on an assembly that runs a static analysis in two minutes.

Call C11549838 opened and model uploaded.

StephenBerkeley1-VisitorAnswer
1-Visitor
September 6, 2013

Hi Jonathan,

This issue is fixed in the currently shipping build of Creo 2.0. I would encourage you to upgrade if you can - aside from this problem, optimization and sensitivity studies run somewhat faster than they do in WF 4.0. PTC is no longer shipping regular maintenance builds of WF 4.0.

In Creo 2.0, your study from case C11549838 converges at the following dimension values, without reaching any invalid intermediate states:

d73 7.99501
d72 8.18416
d74 14.1397
d68 10.908

Regards,

Steve.

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