[MBDyn-users] Hints

masarati at aero.polimi.it masarati at aero.polimi.it
Mon Mar 15 11:22:56 CET 2010

> I would like to use "Hints", so I made an example : I would like to add a
> velocity to the current velocity of the node to a node from T2 to T3 :
> "
>         driven: TEST, string, "(Time-T2)*(Time-T3) <= 0",
>                 hint, "drive{Var = model::xvelocity(NODE); ",
>         joint: TEST, linear velocity,
>                 NODE,
>                         1., 0., 0.,
>                         double step, T2, T3, Pulsion+Var, Var;
> "
> I tried severals way to write the joint, but each time, it imposes a
> velocity of "Pulsion" instead of what I would like "Pulsion + actual
> velocity". Which is the correct way to write it?

Hi.  You can't do it like that for a simple reason: the "linear velocity"
joint does not support hints (yet).  You could work things around a little
bit by using a total joint that imposes the **displacement** in that

You'd need to use hints to build a linear imposed displacement (or a ramp)
whose slope is the current velocity of the node plus the "Pulsion" value
you want to impose, starting from the current position of the node. 
Something like


Please note that in this case you're imposing the **position** rather than
the **velocity**; so, if you look at the velocities, you'll see some
spikes related to numerical integration.  They can be smoothed out by
adding the additional velocity in a smoother manner, e.g. using a "ramp"
plus a "cosine" drive.

Cheers, p.

More information about the MBDyn-users mailing list