Simulation frequency

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Simulation frequency

Postby lancelot » Tue Jun 18, 2013 5:55 am

Just a couple of observations on the simulation frequency.

The code from this post: http://www.algodoo.com/forum/viewtopic.php?f=16&t=10066 seems to be an example that doesn't work at all with frequency 60 but works fine with frequency 100.

This code requires frequency around 10000 to get an approximation to the closed trajectory (I know that it can be simulated using the attraction property):

Code: Select all
Scene.Clear;
Sim.gravitySwitch=false;
Sim.airSwitch=false;

Scene.my.atan2=(v)=>{
  v(0)==0?
    {math.pi*(v(1)>0?(.5):(-.5))}:
    {math.atan(v(1)/v(0))+(v(0)>0?0:math.pi)}};

Scene.my.sun=Scene.addCircle({pos=[0,0];radius=.1;geomID=1});
Scene.addFixJoint({geom0=1;geom1=0;geom0pos=[0,0]});
Scene.my.earth=Scene.addCircle({pos=[2,0];radius=.1;density=1/(.01*math.pi);vel=[0,1];geomID=2});
Scene.addThruster({geom=2;relPoint=[0,0];followGeometry=false;
  _r = {Scene.my.sun.pos-Scene.my.earth.pos};
  rotation={Scene.my.atan2(_r)};
  force={5/(_r(0)^2+_r(1)^2)}});
Scene.addPen({geom=2;relPoint=[0,0];size=.01;fadeTime=30})


Also, it's difficult to model a conservative system that involves a wheel rolling without slipping or a solid swinging on a hinge. If I just have a rectangle on a hinge, turn off the air friction, let the rectangle swing freely and plot its total energy, it shows a linearly decreasing trend. A higher frequency makes the linear decrease coefficient smaller.
lancelot
 
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Re: Simulation frequency

Postby jon_joy_1999 » Thu Jul 18, 2013 5:29 am

lancelot wrote:Also, it's difficult to model a conservative system that involves a wheel rolling without slipping or a solid swinging on a hinge. If I just have a rectangle on a hinge, turn off the air friction, let the rectangle swing freely and plot its total energy, it shows a linearly decreasing trend. A higher frequency makes the linear decrease coefficient smaller.
energy is lost in the stretching of the hinge as it swings, a higher sim frequency reduces the amount of stretch required to hold the object to the hinge
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