Non smooth plot, undesired points in chart.

Carlos Fondevila
Carlos Fondevila Altair Community Member
edited September 17 in Community Q&A

Hello collegues,

I have a modell in motionview, and I locate an output of the torque applied in a rotational motion. The motion follows the next expression: 

 

`STEP5(TIME,0,0,0.5,(185*3*(2*PI/40)))+STEP5(TIME,0.5,0,1,(-185*3*(2*PI/40)))+STEP5(TIME,1,0,1.5,(185*3*(2*PI/40)))+STEP5(TIME,1.5,0,2,(-185*3*(2*PI/40)))+STEP5(TIME,2,0,2.5,(185*3*(2*PI/40)))+STEP5(TIME,2.5,0,2.75,(-185*3*(2*PI/80)))`

When I plot the results of the torque, I obtain the attached chart, very irregular.

image

Do you know the root cause, and if it's possible to solve this undesirable result?

Thanks!

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Best Answer

  • Chris Coker_20903
    Chris Coker_20903 Altair Community Member
    edited September 17 Answer ✓

    In addition to Adam's excellent suggestions, I'd also recommend you verify your model has "reasonable" mass and inertia properties.  If you have a lot of massless parts in your model, that can also lead to the kinds of numerical instabilities shown.

Answers

  • GTT Adam
    GTT Adam
    Altair Employee
    edited September 17

    Hi Carlos,

    A Motion is a constraint that you apply to a certain Joint, so the applied/plotted torque is the amount of torque required to force the system to complete the prescribed Motion.

    Those spikes usually point to integrator error settings being too coarse (allowing too much error), your output step size being too small (not plotting enough data), or the Motion has to overcome imperfect kinematics to assert the desired movement on the Joint. 

     

    Hope this helps!

    Adam Reid

  • Chris Coker_20903
    Chris Coker_20903 Altair Community Member
    edited September 17 Answer ✓

    In addition to Adam's excellent suggestions, I'd also recommend you verify your model has "reasonable" mass and inertia properties.  If you have a lot of massless parts in your model, that can also lead to the kinds of numerical instabilities shown.

  • Carlos Fondevila
    Carlos Fondevila Altair Community Member
    edited September 13

    Thanks! T triyed to modify the Maximum step size, and integrator tolerance, and the plots has been drawed fine.

  • GTT Adam
    GTT Adam
    Altair Employee
    edited September 13
    Carlos Fondevila said:

    Thanks! T triyed to modify the Maximum step size, and integrator tolerance, and the plots has been drawed fine.

    Hi Carlos,

    That's great to hear. Please make sure you mark the reply as correct so other Users can quickly find the same answer as well. 

    Thanks,

    Adam Reid

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