[MBDyn-users] questions regarding to sky-engin.jp example 20

Louis Gagnon louis.gagnon at polimi.it
Mon May 29 09:37:58 CEST 2017


Dear Onur,
If you want to model a truck, you should start from the multibody model 
I have made freely available in the examples section, look for 
"semitrailer: 22 wheel vehicle model" on this page: 
https://www.mbdyn.org/?Documentation___Official_Documentation___Examples
I recommend disabling the rigid ring (module-wheel4) tire model and 
replacing it by a simple driver on the wheels until you better grasp the 
functioning of MBDyn as it can be a difficult tire model to use.
Best,
-Louis

On 27-May-2017 02:55 PM, Pierangelo Masarati wrote:
> On 05/25/2017 04:06 PM, onur akbas wrote:
>>
>> Hi everyone,
>>
>> I want to use mbdyn to model a truck. I started with the tutorials on 
>> this site then found sky-engin.jp
>>
> For issues about examples from sky-engin.jp you should definitely 
> contact them.
>
>> and continued from there. By the way I'm using version 1.5.6.
>>
>> At example 20:
>>
>> 1) I did not understand what do revolute rotation joint and total pin 
>> joints do.
>>
> "revolute rotation" constrains rotation (and only that) about two 
> axes.  Nodes connected by a revolute rotation joint are only allowed 
> relative rotation about a fixed axis (axis 3).  Relative displacement 
> is not constrained.
>
> "total pin joint" can constrain the absolute position and orientation 
> of a node in a component-wise manner, that is you can specify 
> component by component which are constrained and which are not.  
> Moreover, for the constrained ones you can prescribe the 
> displacement/rotation.
>
>> 2) I started to change it from 2d to 3d and got this error
>>
>>  ''Initial derivatives calculation 1 does not converge; aborting...
>>
>> (hint: try playing with the ''derivatives coefficient'')''
>>
> The model does not execute because two included files are missing.
>
> In general, to check whether such problem is critical or not, you 
> should set a very large "derivatives" tolerance (greater than the 
> error), to see if the analysis can continue past that.  If it can, it 
> will likely undergo an abrupt transient, but at least it tells you 
> there's nothing blatantly wrong with your model.
>
> Sincerely, p.
>
>> The code is attached.
>>
>> Thanks in advance
>>
>> Onur
>>
>>
>>
>> _______________________________________________
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>> MBDyn-users at mbdyn.org
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>
>
> -- 
> Pierangelo Masarati
> Professor
> Dipartimento di Scienze e Tecnologie Aerospaziali
> Politecnico di Milano
>
>
> _______________________________________________
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> MBDyn-users at mbdyn.org
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-- 
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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