Manually fix bodies :: OpenModelica

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Manually fix bodies

Manually fix bodies

Mar-21-18 12:25:38

In order to build more complex models, I need to understand why a so simple project is failing because of equations>variables.

It's a simple free-falling object that is fixed in two different ways: the first using MultiBody "Fixed", the second one by manually fixing a frame, using the exact same equations.
The only difference is where the equations reside.

First script:

Code:


model freefalling



  inner Modelica.Mechanics.MultiBody.World world(enableAnimation = false, n = {0, 0, -1});

  Modelica.Mechanics.MultiBody.Parts.Body body1(m = 10, r_CM = {0, 0, 0}) ;

  Modelica.Mechanics.MultiBody.Parts.Fixed fixed1;



equation

  connect(fixed1.frame_b, body1.frame_a);

  

  annotation(

    uses(Modelica(version = "3.2.2")));



end freefalling;

The second

Code:


model freefalling2

  

  inner Modelica.Mechanics.MultiBody.World world(enableAnimation = false, n = {0, 0, -1});

  Modelica.Mechanics.MultiBody.Parts.Body body1;

  Modelica.Mechanics.MultiBody.Interfaces.Frame_b frame_b;

  

equation

  connect(frame_b, body1.frame_a);

  

  Connections.root(frame_b.R);

  frame_b.r_0 = zeros(3);

  frame_b.R = Modelica.Mechanics.MultiBody.Frames.nullRotation();

  

  annotation(

    uses(Modelica(version = "3.2.2")));



end freefalling2;

In the second script I just replicated the same equations as script 1: however, at the end there are 6 more equations! Namely

Code:


frame_b.t[...] =0

frame_b.f[...] =0

that I didn't actually write and I don't know where they come from.

Why that happens? What am I doing wrong?

Edited by: DarioMangoni - Mar-22-18 11:21:01

DarioMangoni: 45 Posts; Thank you [ 7 ]

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