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Electric Field Streamlines Inconsistent

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Hello

I am new to COMSOL and I am currently trying to create an electric field by using a block as a positive voltage terminal, which is inside of a sphere. The sphere itself is assigned the material of Air. Currently I am just using the physics controlled mesh and then after that clicking study. The issue is that the created streamlines for the Electric Field are bizzare and I can not make much sense of them. How do I correct this or make it better? For reference I am using the Electrostatic physics.



5 Replies Last Post Nov 19, 2023, 1:13 p.m. EST
Robert Koslover Certified Consultant

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Posted: 8 months ago Oct 13, 2023, 12:05 a.m. EDT
Updated: 8 months ago Oct 13, 2023, 12:05 a.m. EDT

I just opened your file. Your external boundary is set at zero charge density, which does not seem physical to me (since it will cause the radial component of E to be zero), considering how the rest of your model is configured. If you instead set the outer surface to an electric potential (such as with V=0,) you'll get nice radially outward looking streamlines. I hope that helps.

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Scientific Applications & Research Associates (SARA) Inc.
www.comsol.com/partners-consultants/certified-consultants/sara
I just opened your file. Your external boundary is set at zero charge density, which does not seem physical to me (since it will cause the radial component of E to be zero), considering how the rest of your model is configured. If you instead set the outer surface to an electric potential (such as with V=0,) you'll get nice radially outward looking streamlines. I hope that helps.

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Posted: 8 months ago Nov 1, 2023, 7:40 p.m. EDT
Updated: 8 months ago Nov 1, 2023, 7:59 p.m. EDT

That did resolve it, my issue now is that when I add Arrow Volume to try and view it. the Arrows are diffrent sizes. Is there a particular reason for that? I also have a question on how the strength of the electric field is computed. When the terminal voltage is raised, the electric fields strength is increased but the area is cover does not grow. Is that correct and I am just not understanding the equations. I am trying to view the strength of the electric feild at diffrent distances and with diffrent geometries for the voltage terminal. Is there anyway to accomplish this?

That did resolve it, my issue now is that when I add Arrow Volume to try and view it. the Arrows are diffrent sizes. Is there a particular reason for that? I also have a question on how the strength of the electric field is computed. When the terminal voltage is raised, the electric fields strength is increased but the area is cover does not grow. Is that correct and I am just not understanding the equations. I am trying to view the strength of the electric feild at diffrent distances and with diffrent geometries for the voltage terminal. Is there anyway to accomplish this?


Robert Koslover Certified Consultant

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Posted: 8 months ago Nov 2, 2023, 8:56 a.m. EDT
Updated: 8 months ago Nov 2, 2023, 8:56 a.m. EDT
  1. You have overlaid two kinds of arrow plots: streamline arrows and field volume arrows. 2. I'm not sure what you mean by "the area is cover does not grow." 3. If you want to view the strength of electric field quantitatively, create another type of plot. (E.g., plot the electric field along the x axis, or something like that. See attached.)
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Scientific Applications & Research Associates (SARA) Inc.
www.comsol.com/partners-consultants/certified-consultants/sara
1. You have overlaid two kinds of arrow plots: streamline arrows and field volume arrows. 2. I'm not sure what you mean by "the area is cover does not grow." 3. If you want to view the strength of electric field quantitatively, create another type of plot. (E.g., plot the electric field along the x axis, or something like that. See attached.)


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Posted: 7 months ago Nov 18, 2023, 10:08 p.m. EST
Updated: 7 months ago Nov 18, 2023, 10:07 p.m. EST

Is their any particular reason why the arrows used by the arrow volume are not uniform in size? Is this to demonstrate diffrent force values? I also have a question on why are the field lines not showing any curvature? Is that because there is no negative potential to be found?

Is their any particular reason why the arrows used by the arrow volume are not uniform in size? Is this to demonstrate diffrent force values? I also have a question on why are the field lines not showing any curvature? Is that because there is no negative potential to be found?


Robert Koslover Certified Consultant

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Posted: 7 months ago Nov 19, 2023, 1:13 p.m. EST
Updated: 7 months ago Nov 19, 2023, 1:06 p.m. EST

The arrows are plotted with different sizes because the field strength varies with position and the arrow sizes are intended to indicate that. There is no (or very little) curvature in the vector field because you have placed what is nearly a point charge in nearly the center (Note: you missed the center slightly, whether on purpose or accident) of a sphere. See, for example: https://photonics101.com/images/articles/pointcharge/pointcharge256.png

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Scientific Applications & Research Associates (SARA) Inc.
www.comsol.com/partners-consultants/certified-consultants/sara
The arrows are plotted with different sizes because the field strength varies with position and the arrow sizes are intended to indicate that. There is no (or very little) curvature in the vector field because you have placed what is *nearly* a point charge in *nearly* the center (Note: you missed the center slightly, whether on purpose or accident) of a sphere. See, for example: https://photonics101.com/images/articles/pointcharge/pointcharge256.png

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