[MBDyn-users] Initial derivatives calculation 1 does not converge

Richard Crozier r.crozier at ed.ac.uk
Fri Mar 31 17:17:14 CEST 2017


Sorry, which lines?
Thanks,
Richard

On 31/03/17 16:15, Louis Gagnon wrote:
> Hi Richard,
> To see exactly what is going wrong try adding these lines
>
>
> On 31-Mar-2017 05:12 PM, Richard Crozier wrote:
>>
>> Well, absolutely sure is strong, but sure enough to be willing to
>> embarrass myself on a public forum if I haven't!
>>
>> The system is very simple, just two bodies, a revolute pin and a
>> revolute hinge. My matlab preprocessing tool (which I am sharing, but
>> plan to discuss in another post) has a visualisation tool, and in it
>> it looks like the attached image. Black block is the pin, green block
>> is the hinge, blue blocks are bodies and crosses are the nodes.
>>
>> Regards,
>>
>> Richard
>>
>>
>>
>> On 31/03/17 16:00, Andrea Zanoni wrote:
>>> Hi Richard,
>>>
>>> normally, that message can indicate that the initial state you are
>>> providing for the simulation is not compatible with the constraints.
>>> It might surface also if at assembly time your model is not in
>>> equilibrium.
>>>
>>> Are you absolutely sure that the system is assembled in the correct way?
>>>
>>> Cheers
>>> Andrea
>>>
>>> Il 31/03/2017 16:40, Richard Crozier ha scritto:
>>>> Hello,
>>>>
>>>> I have created the attached mbd file for a simple double pendulum,
>>>> identical to the example provided here:
>>>>
>>>> http://www.sky-engin.jp/en/MBDynTutorial/chap15/chap15.html
>>>>
>>>> I actually generated this file using a matlab preprocessor I have/am
>>>> developing for mbdyn.
>>>>
>>>> However, the file fails in mbdyn with the error:
>>>>
>>>> Initial derivatives calculation 1 does not converge
>>>>
>>>> and I cannot figure out why. Increasing "derivatives max iterations"
>>>> does not help. If I change "derivatives tolerance" to a very large
>>>> number it runs, but the motion is all wrong. I also tried playing with
>>>> the "derivatives coefficient" as suggested in the error, but it did
>>>> not help.
>>>>
>>>> Is there something obviously wrong with the file which I have not
>>>> spotted? I'm pretty sure all my positions and orientations are correct?
>>>>
>>>> Best regards,
>>>>
>>>> Richard
>>>>
>>>>
>>>>
>>>> _______________________________________________
>>>> MBDyn-users mailing list
>>>> MBDyn-users at mbdyn.org
>>>> https://mail.mbdyn.org/cgi-bin/mailman/listinfo/mbdyn-users
>>>
>>> --
>>> ---
>>> Andrea Zanoni
>>> Dipartimento di Scienze e Tecnologie Aerospaziali
>>> Politecnico di Milano
>>> Ph. (+39) 02 2399 8035
>>>
>>
>>
>>
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>> MBDyn-users mailing list
>> MBDyn-users at mbdyn.org
>> https://mail.mbdyn.org/cgi-bin/mailman/listinfo/mbdyn-users
>
> --
> Louis Gagnon, Ph.D.
> Postdoctoral fellow
> Dipartimento di Scienze e Tecnologie Aerospaziali
> Politecnico di Milano
> +39 02 2399 8642
> http://louisgagnon.com/research/
>

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