[MBDyn-users] Initial derivatives calculation 1 does not converge

Richard Crozier r.crozier at ed.ac.uk
Fri Mar 31 16:40:14 CEST 2017


Hello,

I have created the attached mbd file for a simple double pendulum, 
identical to the example provided here:

http://www.sky-engin.jp/en/MBDynTutorial/chap15/chap15.html

I actually generated this file using a matlab preprocessor I have/am 
developing for mbdyn.

However, the file fails in mbdyn with the error:

Initial derivatives calculation 1 does not converge

and I cannot figure out why. Increasing "derivatives max iterations" 
does not help. If I change "derivatives tolerance" to a very large 
number it runs, but the motion is all wrong. I also tried playing with 
the "derivatives coefficient" as suggested in the error, but it did not 
help.

Is there something obviously wrong with the file which I have not 
spotted? I'm pretty sure all my positions and orientations are correct?

Best regards,

Richard

-- 
The University of Edinburgh is a charitable body, registered in
Scotland, with registration number SC005336.

-------------- next part --------------

begin: data;
    problem: initial value;
end: data;

# initial value problem
begin: initial value;
    initial time: 0.0;
    final time: 10.0;
    time step: 0.001;
    max iterations: 20;
    tolerance: 1.000000e-03;
end: initial value;


begin: control data;
    structural nodes: 2;
    rigid bodies: 2;
    joints: 2;
    gravity;
    default orientation: orientation matrix;
end: control data;

begin: nodes;

    # 6 DOF structural node
    structural : 1, dynamic, # label, type
        0.35355339059327, 0.0, 0.35355339059327, # absolute position
        matr, 0.70710678118655, 0.0, 0.70710678118655, 0.0, 1.0, 0.0, -0.70710678118655, 0.0, 0.70710678118655, # absolute orientation
        0.0, 0.0, 0.0, # absolute velocity
        0.0, 0.0, 0.0 # absolute angular velocity
    ; # end structural node

    # 6 DOF structural node
    structural : 2, dynamic, # label, type
        1.06066017177982, 0.0, 1.06066017177982, # absolute position
        matr, 0.70710678118655, 0.0, 0.70710678118655, 0.0, 1.0, 0.0, -0.70710678118655, 0.0, 0.70710678118655, # absolute orientation
        0.0, 0.0, 0.0, # absolute velocity
        0.0, 0.0, 0.0 # absolute angular velocity
    ; # end structural node

end: nodes;

begin: elements;

    # one-mass body
    body : 3, 1, # label, node label
        1.0, # mass
        null, # relative centre of mass
        matr, 0.0, 0.0, 0.0, 0.0, 0.08333333333333, 0.0, 0.0, 0.0, 0.08333333333333 # inertia matrix
    ; # end one-mass body

    # one-mass body
    body : 4, 2, # label, node label
        1.0, # mass
        null, # relative centre of mass
        matr, 0.0, 0.0, 0.0, 0.0, 0.08333333333333, 0.0, 0.0, 0.0, 0.08333333333333 # inertia matrix
    ; # end one-mass body

    joint : 5, revolute pin,
        1, # node label
            position, reference, global, 0.0, 0.0, 0.0, # node relative position
            orientation, reference, global, matr, 0.70710678118655, 0.0, 0.70710678118655, -0.70710678118655, 0.0, 0.70710678118655, 0.0, -1.0, 0.0, # node relative orientation
        position, 0.0, 0.0, 0.0, # pin absolute position
        orientation, matr, 0.70710678118655, 0.0, 0.70710678118655, -0.70710678118655, 0.0, 0.70710678118655, 0.0, -1.0, 0.0 # pin absolute orientation
    ; # end revolute pin

    joint : 6, revolute hinge,
        1, # node 1 label
            position, reference, node, 0.5, 0.0, 0.0,
            orientation, reference, global, matr, 0.70710678118655, 0.0, 0.70710678118655, -0.70710678118655, 0.0, 0.70710678118655, 0.0, -1.0, 0.0,
        2, # node 2 label
            position, reference, other node, 0.5, 0.0, 0.0,
            orientation, reference, global, matr, 0.70710678118655, 0.0, 0.70710678118655, -0.70710678118655, 0.0, 0.70710678118655, 0.0, -1.0, 0.0
    ; # end revolute hinge

    gravity : uniform, single, 0.0, 0.0, -1.0, const, 9.81;

end: elements;


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