[MBDyn-users] Input mistake

Romuald NORET romuald.noret at cdr.hutchinson.fr
Thu Aug 6 12:22:50 CEST 2009


Hello,

Thanks a lot for your answer and your time.
Indeed, I want to impose displacement on axis 2, so I wrote :
"position constraint,
        inactive, active, inactive, 
        0., 1., 0.,
        ramp, 5., 0., 10.0, 0.0, "

But now, I have the problem I had before : the solver fail and I have a 
warning "matrix is singular". I didn't find references to explain warnings 
so I am not sure where I made error. But in this case, I believe it comes 
from under or overconstrained system so I add a new joint (dubbed 
"JOINT_CREMAILLIERE") to regularize with but I didn't suceed.
I enclose updated files.

Best regards,
Romuald Noret








Pierangelo Masarati <masarati at aero.polimi.it> 
05/08/2009 17:33

A
Romuald NORET <romuald.noret at cdr.hutchinson.fr>
cc
mbdyn-users at mbdyn.org
Objet
Re: [MBDyn-users] Input mistake






Romuald NORET wrote:
> Hello,
> 
> I am trying  to modelize a car steering (very simplified one) and to 
> monitor kinetic by appling a displacement (last joint into the input 
> file). But I had to make a mistake somewhere because computation runs 
> without crashing but no movement happen. You can find enclosed the input 

> file "steer" (which requires 2 others files "steer.id" and "steer.ref").
> I will be very grateful if someone could explain where my mistake is.


Dear Romuald,

in joint JOINT_DISP (the total joint) you define the position constraint 
as "active" (which means "constrained") only in direction 1, but the 
vector of the imposed motion is zero in direction 1, and non-zero in 
direction 2.

Probably, you either meant to impose motion in direction 1, and thus you 
need to change the vector from 0., 1., 0. to 1., 0., 0., or you meant to 
impose motion in direction 2, and thus you need to change constraint 
equation activation to "inactive, active, inactive".

Hope this helps.

Cheers, p.

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