[MBDyn-users] what the force element format should be

Pierangelo Masarati pierangelo.masarati at polimi.it
Thu Mar 27 16:44:15 CET 2014

On 03/27/2014 04:10 PM, 邹栋 wrote:
> hello Reinhard and every one
> 1.   i am simulate a free rigid body taken by a 10N force at y
> direction,and the gravity is  ignored.
> the force element in my input file is like this:
>             force: 11,absolute, 1,0,1,0,null,const,10.
> the case is simple, but when i run it, the log file tells out :
>            Force(11):"position" keyword expected at line 45,file
> <freeRigidBody>;still using deprecated syntax?
>            ...
>            Initial derivatives calculation 1 does not converge; aborting...
> so, what 's the problem?

Section 8.8.4 Structural force: The message is self-explanatory, the 
syntax requires the keyword "position" before the offset of the force 
application point with respect to the node.

> 2.  from the input manual  , there is a description about the
> Derivatives Data  : "The system is solved with the kinematic unknowns
> constrained, in order to properly determine the dynamic unknowns, namely
> momenta and constraint reactions" , my question is ,in  an simple free
> rigid body case, what 's the "solved system" as mentioned up..
> thanks for your reply. best regards.

You likely need to allow more than one iteration during the 
"derivatives" phase for convergence.  Section 4.1.2 Derivatives Data: 
set "derivatives max iterations" to > 1.

Cheers, p.

> At 2014-03-26 20:11:09,"Resch Reinhard" <R.RESCH at secop.com> wrote:
>     Hello,
>     I'm not sure ifI understand what you reallyneed.
>     If you needa force asa function oftime or some other scalarparameter, you could usea structural force witha drivecaller.
>     In that case you can use the examplein the attachedfile (piecewiselinear
>     interpolation of a function of time).
>     If you need inter
>     processcommunication, then you have to use the external forcein
>     order to communicate with the peersoftware.
>     Best regards,
>     Reinhard Resch
>     ------------------------------------------------------------------------
>     *Von:* MBDyn-users [mbdyn-users-bounces at mbdyn.org
>     <mailto:mbdyn-users-bounces at mbdyn.org>]" im Auftrag von "邹栋
>     [zdong_hn at 163.com <mailto:zdong_hn at 163.com>]
>     *Gesendet:* Dienstag, 25. März 2014 15:53
>     *An:* mbydnEmailList
>     *Betreff:* [MBDyn-users] what the format of the external force file
>     should be
>                 Hello, every one, i am a new guy to  mbdyn, except the
>     official mannual, i realy can not find any thing that could help me
>     with the external force element.
>                 in the mbdyn-input-1.5.5.pdf , it's said that:
>     "input_file_name is the name of the file MBDyn expects to find with
>     the values of the force. The content depends on the purpose it is
>     used for."
>                  i am confused about this descrbtion, and failed to
>     prepare the input file.could you any one give me some advice or send
>     me some tutorial  which contain the using of external force
>     communicator "file" .
>     best wish for you , thanks so much.
>     abbott
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Pierangelo Masarati
Associate Professor
Dipartimento di Scienze e Tecnologie Aerospaziali
Politecnico di Milano

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