[MBDyn-users] slide crank problem

MBDyn users list mbdyn-users at mbdyn.org
Sun Oct 11 19:01:09 CEST 2020


Luis,

Your suggestion helped.  I found the inline joint 4 needed an offset for
the second node.  I tried that earlier; maybe something else was wrong
with the earlier model.

I am including the working input file.

Thanks,

Matt

> Matt,
>
> you can find out which "point" doesn't match by adding these lines in
> the initial value section of your input file:
>
> begin: initial value;
> .
> .
> .
>         output: iterations;
>         output: residual;
> .
> .
> .
> end: initial value;
>
> you will then see a possibly very long output where directly after this
> line "Residual(0:0) t=0 dt=0" you will get a hint towards which point is
> misaligned in your initial assembly (ie: the one(s) that are bigger than
> zero).
>
> I'm eager to see what your FreeCAD preprocessor brings.
>
> Kind regards,
>
>
> -Louis
>
> On 09.10.20 14:14, MBDyn users list wrote:
>> I will check to see if a point doesn't match. Is there an lower bound of
>> the
>>   mismatch that will be acceptable?
>>
>> The repository for the FreeCAD workbench is below.
>> https://github.com/mfasano727/MBDynFCwb
>>
>> Thanks,
>>
>> Matt
>>
>>> Hi Matt,
>>>
>>> the error simply means that some point does not match at initial
>>> assembly. So far I don't know what. I have never used Euler angles, I
>>> prefer coordinate systems defined by vectors. Maybe I find the error.
>>>
>>> Do you have a public repository with the FreeCAD workbench?
>>>
>>> Cheers,
>>> Torsten
>>>
>>> Am Mittwoch, den 07.10.2020, 05:09 -0500 schrieb MBDyn users list:
>>>> Hello;
>>>>
>>>> I am working on a pre-processor for MBDyn with FreeCAD.  I am trying
>>>> to
>>>> create a side crank model similar to the one from Sky Engineering's
>>>> tutorial.  My model works when it there is no offset unlike there is
>>>> in
>>>> Sky Engineering's example.  The error I get when there is an offset
>>>> says
>>>> "Initial assembly iterations reached maximum number 1".
>>>>
>>>> I am including the MBDyn input files and drawings of the slide crank
>>>> with
>>>> no offset and with the connecting rod at a 5 degree angle. The global
>>>> origin is at the crank pivot marked on the drawing.  The +x direction
>>>> is
>>>> up, +y direction is left and +z direction is out of the page. each
>>>> body is
>>>> 5mm thick and are offset from the xy plane by either 2.5mm or -2.5mm
>>>>
>>>> Let me know if you will need more information.
>>>>
>>>> Thanks,
>>>>
>>>> Matt
>>>>
>>>>
>>>> _______________________________________________
>>>> MBDyn-users mailing list
>>>> MBDyn-users at mbdyn.org
>>>> https://mail.mbdyn.org/cgi-bin/mailman/listinfo/mbdyn-users
>>>
>>>
>>>
>>
>>
>> _______________________________________________
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>> MBDyn-users at mbdyn.org
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>>
>
> --
> Dr.-Ing. Louis Gagnon, Ph.D.
> Humboldt Postdoctoral Research Fellow
> Institut für Aerodynamik und Gasdynamik
> Universität Stuttgart
> Pfaffenwaldring 21 (Rm 0.011 ), 70569, Stuttgart
> GERMANY
> +49 711 685 64278
> http://louisgagnon.com/research/
> gagnon at iag.uni-stuttgart.de
>
>
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