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C/++/# How to Implement Damping in Particle Simulation

  1. Mar 21, 2016 #1

    TheDemx27

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    Gold Member

    So I made this simulation of charged particles: https://github.com/TheDemx27/Charge-Simulator
    My goal is to be able to put the charges on a line, as I've done, and see them tend toward a final state where there is more charge at the ends of the line and less towards the center. The problem is, the simulation runs like an elastically no matter what I try. At the moment, I've tried adding an acceleration in the opposing direction of motion, proportional to the velocity. This is the main loop for calculating the acceleration and setting the velocity:

    Code (Text):

                for (int i = 0; i < charges.Count; i++) {
                    for (int j = i + 1; j < charges.Count; j++) {

                        distance = GetDistVec(charges[i], charges[j]);
                        f = charges[i].q * charges[j].q * k / (distance.Magnitude * distance.Magnitude);

                        acceleration1.Magnitude = Math.Abs(f / charges[i].m);
                        acceleration2.Magnitude = Math.Abs(f / charges[j].m);
                        acceleration1.Direction = distance.Direction;
                        acceleration2.Direction = distance.Direction += Math.PI;

                        // DAMPENING
                        double c = 10;

                        accel1 = PolarToComponent(acceleration1);
                        accel2 = PolarToComponent(acceleration2);

                        accel1.x -= c * charges[i].x;
                        accel1.y -= c * charges[i].y;
                        accel2.x -= c * charges[j].x;
                        accel2.y -= c * charges[j].y;
                        // DAMPENING

                        SetVelVec(charges[i], accel1);
                        SetVelVec(charges[j], accel2);
                    }
                }
     
    This doesn't seem to do anything. If I make c large enough, the oscillations get bigger, the sim eventually spirals out of control, and I get null values for the positions.
     
  2. jcsd
  3. Mar 21, 2016 #2

    Henryk

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    Hi,I'm not quite certain but it looks like you are adding a spring, not damping, variable charges.x is an x position, not velocity. Change this to charges.vx

    Hope this helps.
     
  4. Mar 21, 2016 #3

    TheDemx27

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    Haha, yes that helped! Wow... ok then.
    Thankyou!
     
  5. Mar 21, 2016 #4

    TheDemx27

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    https://media.giphy.com/media/xThuWlHZT7zEPGyYP6/giphy.gif
    ~success~
     
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