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Strange behavior for a simple mecanism model
Strange behavior for a simple mecanism model
I'm modeling a motor: as a torque source, a bearing friction (rotational), an ideal gear and an inertia. The torque source is control with a sinus source.
By looking the result of the simulation in OMEdit, i was skeptic, in fact at the begining of the simulation, the sinus source is positif and rises to 2 (is maximal amplitude) but the rotational speed and the position of the inertia are, during the transition phase, Negatives !
Then I try with 20sim, wich is an other physical modeling software. With the same parameters and same components, the simulation results are differents. In 20sim the results are corrects because there is no negative values for the rotationnal speed and position.
Parameters :
- sinus : freq 1Hz, Amp : 2 (if =1 : problem)
- bearing friction : [0,1], peak : 0.5
- ideal gear : ratio = 10
- inertia = 0.001
Here are screenshots from my models and their respective results.
OpenModelica model :
imagik.fr
20sim model :
imagik.fr
OpenModelica simulation results :
imagik.fr
20sim simulation results :
imagik.fr
could anyone explain me why is there a différence ? what need i do to avoid that ?
Is there any problems with OMC ?
I've got other problems :
- if the torque source is not enough "powered" (amplitud from the sinus source = 1 ), OMEdit stay in a loop : ...\OpenModelica\tmp\OMEdit\ NameOfMyModel_res becomes bigger but i never get my results... Is there no watch dog for this kind of issue?
that the results with 20sim for sinus.Amplitude = 1
imagik.fr
I forget to say, I m working with OpenModelica 1.7.0 on a windows XP pro 64bits
kind regards
Thomas
Thank you
Re: Strange behavior for a simple mecanism model
Hello Thomas,
I can't say much to the physics of the model, but as far as I can see our results are ok, at least they are the same as the results of Dymola.
Maybe the models between sim20 and Modelica differ a bit.
so long.
Willi
- wbraun
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- 75 Posts
Re: Strange behavior for a simple mecanism model
Did you mean that in Dymola, when you try to move a Inertia with a positif Torque, at the beginning of the movement the speed is negative as well as the position ?
I m sorry but i dont consider this result as normal...
Try to move a pen clockwise with your finger, and look if it s go countercloclwise... i don't think it will.
Re: Strange behavior for a simple mecanism model
Which version of the omc do you use?
Since for me neither the position of the inertia nor the speed of the inertia negative at the beginning of the movement.
Please consider me results.
Please note that I have changed some of the parameters to have one scaling for the results.
Sorry but your result images are so small to recognise something.
- wbraun
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- 75 Posts
Re: Strange behavior for a simple mecanism model
sorry, I didn't check the images.
For the OMC version, I just download this release : OpenModelica-1.7.0-revision-8711.msi
OpenMolica model : (plz take a look at the begining of the movement of the inertia)
20sim model:
OM simulation results :
20sim simulation results :
Re: Strange behavior for a simple mecanism model
ah, sorry I have set the peak parameter of the bearingfriction not on the same values as you, so I get other results.
But the Modelica model for the bearingfriction say that the minimum value for the peak is = 1, so you maybe break the model if you set if to =0.5.
Actually the compiler or at least the simulation has to come up with an assertion. That's a bug in openmodelica.
so long.
Willi
- wbraun
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- 75 Posts
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