[MBDyn-users] total pin joint with angular velocity constraint

MBDyn users list mbdyn-users at mbdyn.org
Sat May 30 07:35:12 CEST 2020


Your model is overconstrained.  You are using 3 nodes (3 x 6 = 18 
degrees of freedom), 3 revolute joints (two of them remove 5 degrees of 
freedom; the crank one removes 6) and a slider (which removes 5 degrees 
of freedom), so you're left with 18 - 21 = -3 degrees of freedom.

You can remove some of the duplicate constraints (e.g., in the slider 
joint all you need to constrain is the component of displacement in the 
model's plane that is normal to the sliding axis, and rotation about the 
axis normal to the model's plane), or use "joint regularization" to 
allow some compliance, or model (at least some of) the parts as flexible.

p.

Il 27/05/20 23:32, MBDyn users list ha scritto:
> Hello;
>
> I am writing code for an MBDyn preprocessor for FreeCAD.  I am trying to
> make a simulation for a slide crank usng total joints.  A picture of it is
> here.
>
>   https://github.com/mfasano727/MBDynFCwb/blob/media/screenshots/slidecrank.JPG
>
> the input text is below. The error I get is
>
> "Initial derivative failed because no pivot element could be found for
> column 42 (TotalPinJoint(1): dof(6) Mz) aborting..."
>
> Total pin joint 1 is for the crank.  I was trying to get it to revolve.  I
> guess I am not applying the angular velocity keyword in the constraint
> properly.  I hope you can help.
>
> Thanks.
>
>
> begin: data;
>          problem: initial value;
> end: data;
>
> begin: initial value;
>          initial time: 0.0;
>          final time: 40.0;
>          time step: 0.25;
>          tolerance: 0.001;
>          max iterations: 10;
>          derivatives tolerance: 0.0;
> end: initial value;
>
> begin: control data;
>          structural nodes: 3;
>          joints: 4;
>          rigid bodies: 3;
> end: control data;
>
> begin: nodes;
>          structural: 1, dynamic,
>                  21.0, 9e-16, 2.6e-15,
>                  euler321, 0.0, 0.0,0.0,
>                  null,
>                  null;
>          structural: 2, dynamic,
>                  88.0, -9e-16, 1.9e-15,
>                  euler321, 0.0, 0.0,0.0,
>                  null,
>                  null;
>          structural: 3, dynamic,
>                  143.132543069545, -2.7e-15, 5.4e-15,
>                  euler321, 0.0, 0.0,0.0,
>                  null,
>                  null;
> end: nodes;
>
> begin: elements;
>          body: 1, 1,
>                  23.036504591506368,
>                  null,
>                  diag, 253.25808965653337, 4544.629268369435,
> 4387.356614510845;
>          body: 2, 2,
>                  48.036504591506336,
>                  null,
>                  diag, 513.6747563231997, 37922.441125809266,
> 37608.91847195068;
>          body: 3, 3,
>                  44.91150459150636,
>                  null,
>                  diag, 1857.8165377775254, 3084.0319584803906,
> 3190.171919409456;
>          joint: 1, total pin joint,
>                  1,
>                          position, -21.0, -9e-16, -2.6e-15,
>                          position orientation, 1, 1.0, 0.0, 0.0,  2, 0.0,
> 1.0, 0.0,
>                          rotation orientation, 1, 1.0, 0.0, 0.0,  2, 0.0,
> 1.0, 0.0,
>                      position, null,
>                      position orientation, 1, 1.0, 0.0, 0.0,  2, 0.0, 1.0,
> 0.0,
>                      rotation orientation, 1, 1.0, 0.0, 0.0,  2, 0.0, 1.0,
> 0.0,
>                  position constraint,  active, active, active, null,
>                  orientation constraint,  active, angular velocity, active,
> 0., 1., 0., const, 1.;
>
>          joint: 2, total joint,
>                  1,
>                          position, 21.0, -9e-16, -2.6e-15,
>                          position orientation, 1, 1.0, 0.0, 0.0,  2, 0.0,
> 1.0, 0.0,
>                          rotation orientation, 1, 1.0, 0.0, 0.0,  2, 0.0,
> 1.0, 0.0,
>                  2,
>                          position, -46.0, 9e-16, -1.9e-15,
>                          position orientation, 1, 1.0, 0.0, 0.0,  2, 0.0,
> 1.0, 0.0,
>                          rotation orientation, 1, 1.0, 0.0, 0.0,  2, 0.0,
> 1.0, 0.0,
>                  position constraint,  active, active, active, null,
>                  orientation constraint,  active, inactive, active, null;
>
>          joint: 3, total joint,
>                  2,
>                          position, 46.0, 9e-16, -1.9e-15,
>                          position orientation, 1, 1.0, 0.0, 0.0,  2, 0.0,
> 1.0, 0.0,
>                          rotation orientation, 1, 1.0, 0.0, 0.0,  2, 0.0,
> 1.0, 0.0,
>                  3,
>                          position, -9.132543069544994, 2.7e-15, -5.4e-15,
>                          position orientation, 1, 1.0, 0.0, 0.0,  2, 0.0,
> 1.0, 0.0,
>                          rotation orientation, 1, 1.0, 0.0, 0.0,  2, 0.0,
> 1.0, 0.0,
>                  position constraint,  active, active, active, null,
>                  orientation constraint,  active, inactive, active, null;
>
>          joint: 4, total pin joint,
>                  3,
>                          position, -9.132543069544994, 2.7e-15, -5.4e-15,
>                          position orientation, 1, 1.0, 0.0, 0.0,  2, 0.0,
> 1.0, 0.0,
>                          rotation orientation, 1, 1.0, 0.0, 0.0,  2, 0.0,
> 1.0, 0.0,
>                      position, null,
>                      position orientation, 1, 1.0, 0.0, 0.0,  2, 0.0, 1.0,
> 0.0,
>                      rotation orientation, 1, 1.0, 0.0, 0.0,  2, 0.0, 1.0,
> 0.0,
>                  position constraint,  inactive, active, active, null,
>                  orientation constraint,  active, active, active, null;
>
> end: elements;
>
>
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-- 
Pierangelo Masarati
Professore Ordinario di Costruzioni e Strutture Aerospaziali
Dipartimento di Scienze e Tecnologie Aerospaziali
Politecnico di Milano



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