[MBDyn-users] Conditional activation of constraints in a Total joint.

MBDyn users list mbdyn-users at mbdyn.org
Sun Jun 18 16:50:22 CEST 2023


This worked.

Thank you.



On Sun, Jun 18, 2023 at 12:22 AM MBDyn users list <mbdyn-users at mbdyn.org>
wrote:

> You have two options:
>
>    - 2tot.mbd: you start with 5 constraints (free rotation about z axis),
>    then when appropriate replace it with 4 constraints (add free displacement
>    along z)
>    - 2tot2.mbd: you have one total joint with the constraints that do not
>    change, plus a driven one with the constraints that are going to disappear,
>    and switch the latter off when appropriate
>
> Sincerely, p.
>
> On 17/06/23 23:24, MBDyn users list wrote:
>
> Dejar Pierangelo.
>
> So I will need 2 joints?
>
> Would you please provide an example? What I need is to keep one component
> of the position or rotation active up to a certain time, and then
> deactivate it for the rest of the simulation. No need to activate it again
> after it has been disabled.
>
>  Kind regards.
>
>
>
> El sáb., 17 jun. 2023 14:11, MBDyn users list <mbdyn-users at mbdyn.org>
> escribió:
>
>> On 17/06/23 18:52, MBDyn users list wrote:
>>
>> Dear MBDyn users.
>>
>> I am trying to activate/deactivate components of the constraints of a
>> Total joint, as explained in the manual:
>>
>> "a boolean can be provided in status to indicate that the degree of
>> constraint is
>> either inactive (0) or active (1); this may be useful, for instance, to
>> make constraint activation conditional in parametric input files."
>>
>> So I have a drive:
>>
>> drive caller: 1, name,"drive:1", step, 1.0, 0.0, 1.0;
>>
>>
>> and I thought I would be able to use this drive to deactivate the Z
>> orientation constraint of a total joint, after one second of simulation
>> time, by doing:
>>
>>
>> orientation constraint,
>>
>> inactive, inactive, string, "model::drive(1, Time)",
>>
>> single, 0., 0., 1., string, "model::sf::function:20(Time)";
>> #<imposed_rotation> [rad]
>>
>>
>> But I get an error: "name expected after type in declaration".
>>
>>
>> Please, what am I getting wrong? Is this because I am using the wrong
>> drive?
>>
>> It doesn't work like that.  You can use a boolean, but it is only
>> evaluated at parse time, so no drive caller is allowed there.
>>
>> To have a joint change by switching off (or on, but that's much trickier)
>> one component, you need to define two "driven" elements, identical except
>> for the active components, and have one switched off and the other
>> simultaneously switched on.
>>
>> Sincerely, p.
>>
>>
>>
>> Thanks in advance.
>>
>> _______________________________________________
>> MBDyn-users mailing listMBDyn-users at mbdyn.orghttps://mail.mbdyn.org/cgi-bin/mailman/listinfo/mbdyn-users
>>
>>
>> --
>> Pierangelo Masarati
>> Professore Ordinario di Costruzioni e Strutture Aerospaziali
>> Dipartimento di Scienze e Tecnologie Aerospaziali
>> Politecnico di Milanohttps://www.dona.polimi.it/
>>
>> _______________________________________________
>> MBDyn-users mailing list
>> MBDyn-users at mbdyn.org
>> https://mail.mbdyn.org/cgi-bin/mailman/listinfo/mbdyn-users
>
>
> _______________________________________________
> MBDyn-users mailing listMBDyn-users at mbdyn.orghttps://mail.mbdyn.org/cgi-bin/mailman/listinfo/mbdyn-users
>
>
> --
> Pierangelo Masarati
> Professore Ordinario di Costruzioni e Strutture Aerospaziali
> Dipartimento di Scienze e Tecnologie Aerospaziali
> Politecnico di Milanohttps://www.dona.polimi.it/
>
> _______________________________________________
> MBDyn-users mailing list
> MBDyn-users at mbdyn.org
> https://mail.mbdyn.org/cgi-bin/mailman/listinfo/mbdyn-users
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