search

phetsims / circuit-construction-kit-common

"Circuit Construction Kit: Basics" is an educational simulation in HTML5, by PhET Interactive Simulations.
GNU General Public License v3.0
10 stars 10 forks source link

Oscillatory spiking in capacitors #788

Open samreid opened 2 years ago

samreid commented 2 years ago

From https://github.com/phetsims/circuit-construction-kit-common/issues/784#issuecomment-976717775

First, in this video (the resistance is 0.0 ohm), you will see the capacitors not appearing to reach a steady state solution when connected across a battery.

In my testing in dev.52, I do see a steady state solution reached soon. I'm not sure if I had the same battery voltage or capacitances in your test, since they were not reported. I'm using default values for capacitance, and a 120V battery in this test.

Kapture 2021-11-23 at 08 21 35

However, notice the oscillation in the voltage graph. That is new in dev.52 (not present in dev.48) and looks buggy.

And then when the capacitors are shorted, they should fully discharge, but appear to retain charge and have a voltage across them

I saw it go to 0.0V but still showed some charge.

Kapture 2021-11-23 at 08 25 00

Likely this could be solved with a different tolerance in the voltage-to-charge mapping, but we should understand the oscillation behavior first.

For the 2nd video, I'm seeing all the same behaviors in dev.48 (the first QA dev test, before we changed any signs), so presumably that buggy behavior predates any sign changes in this issue. So perhaps I'll move that aspect to a new issue.

So this issue will be about correcting the buggy oscillation behavior in the capacitors. Or, we have the option of reverting the changes in this issue and going back to a dev.48 behavior which did not have the buggy oscillation.

samreid commented 2 years ago

Or, we have the option of reverting the changes in this issue and going back to a dev.48 behavior which did not have the buggy oscillation.

I am seeing the same spiking oscillatory behavior in dev.48:

image

samreid commented 2 years ago

In yesterday's meeting, we wondered if this issue relates to #787 .

In Java, I'm seeing a spike but no oscillation. Could this be why we require the initial bias calculation?

Java has different values for wire resistance and default capacitances, maybe that explains it?

samreid commented 2 years ago

@arouinfar and I discussed that shorting capacitors is somewhat nonphysical, and that the behavior is as expected as soon as the resistance is 0.1 ohms or higher. Therefore this doesn't need to be addressed for RC.1. @arouinfar confirmed this is already documented in the teacher tips. We may not ever fix this ourselves with our hand-written model, but maybe leave this open in case we explore spice or another model implementation.