[MBDyn-users] questions on 'relative orientation matrix' in MBDyn

xiaoli zhang zhangxl.bitase at yahoo.com
Thu Sep 14 11:03:58 CEST 2017


Dear MBDyners, I have some puzzles on the relative orientation matrix in MBDyn:
such as the joint card:

    <joint_type> ::= axial rotation
    <joint_arglist> ::=
    <node_1> ,
    [ position , ] (Vec3) <relative_offset_1> ,
    [ orientation , (OrientationMatrix) <relative_orientation_matrix_1> , ]
    <node_2> ,
    [ position , ] (Vec3) <relative_offset_2> ,
    [ orientation , (OrientationMatrix) <relative_orientation_matrix_2> , ]
    (DriveCaller) <angular_velocity>

In order to illustrate my puzzles, put forward a simple example: a rotating plate amounted on tip of a rigid cantilever beam(connect to ground by a torsion spring) :

---------------------------------------------------------
                   \     /     | z
                    \   /      |
 |ground  beam       \ /       |
 O---------O----------O  plate |______x
 |                   / \
                    /   \
                   /     \
O---Stands for structural node;
----------------------------------------------------------
the main model described by mbdyn is as follows, my questions are:

1. Does the relative_orientation_matrix_1 means a transformation matrix that makes z axis of node 1 reference coincide with hinge's axis?
 
2. how about the relative_orientation_matrix in the deformable hinge since it has more than one rotation axis?

3. in this model, when i run MBDyn, it could not pass the initial assembly, 
the residual of axial rotation joints did not converge:'Eq        67:              355.867 AxialRotationJoint(50): orientation constraint derivative wy'what wrong with this definition of axis rotation joint or deformable joint? 

Thank you in advanve!
-------------------------------------------------------------------------
#Here is the rotating plate model:

reference: RF_ground,
    reference, global, null,
    reference, global, eye,
    reference, global, null,
    reference, global, null;

reference: RF_beam,
    reference, RF_ground, l/2,0.,0.,
    reference, RF_ground, eye,
    reference, RF_ground, null,
    reference, RF_ground, null;

reference: RF_plate,
    reference, RF_beam, l/2,0.,0.,
    reference, RF_beam, eye,
    reference, RF_beam, null,
    reference, RF_beam, omega, 0., 0.;


begin: nodes;
    structural: ground, static,
        reference, RF_ground, null,
        reference, RF_ground, eye,
        reference, RF_ground, null,
        reference, RF_ground, null;

    structural: beam, dynamic,
        reference, RF_beam, null,
        reference, RF_beam, eye,
        reference, RF_beam, null,
        reference, RF_beam, null;

    structural: plate, dynamic,
        reference, RF_plate, null,
        reference, RF_plate, eye,
        reference, RF_plate, null,
        reference, RF_plate, null;
end: nodes;

begin: elements;
    joint: ground, clamp, ground, node, node;
    
    joint: torsion_spring, deformable hinge,
        ground, position, reference, RF_ground, null,
                orientation, reference, RF_ground, eye,
        beam, position, reference, RF_ground, null,
                 orientation, reference, RF_ground, eye,
    linear elastic generic,
        sym, -kx, 0., 0.,
                 -ky, 0.,
                     -kz; 
    joint: plate, axial rotation,
        beam, position, reference, RF_beam, l/2.0, 0., 0.,
                 orientation, reference, RF_beam,
                        1, 0., 0., -1.,
                        3, 1., 0., 0.,
        plate, position, reference, RF_plate, null,
                   orientation, reference, RF_plate,
                        1, 0., 0., -1.,
                        3, 1., 0., 0.,
        const, omega;
    body: beam, beam,
            m, 
            reference, RF_beam, null,
            diag,
                1,
                1,
                1;
    body: plate, plate,
            m,
            reference, RF_plate, null,
            diag,
                1,
                1,
                1;
end: elements;
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