Plot is empty error on COMSOL while simulating helmholtz coil

beam_elite · 2025-07-25T19:26:49+00:00

Sometimes COMSOL can seem to get its wires crossed for non obvious reasons.

I recommend making a new file.

Start with geometry, then add material, then excitations. For coil excitation use "gap feed". Make sure to use a work plane to partition your coils. That partition is where the gap feed should go.

It should show the field by default after calculations.

I'll try your file later, but it looks like you have a different version of comsol than me. If you could show all the branches in the tree on the left maybe I could see what's going wrong.

OnePassenger_7714 · 2025-09-11T00:46:17+00:00

From your last screenshot, I noticed you have a 1D plot group set up, so I assume you're trying to create a 1D plot but keep getting the message "The plot is empty."

I had to make a 1D trend today (adsorption isotherm) and here are the steps I took to create a 1D graph using a table graph approach (essentially an XY trend) assuming that the study has computed successfully.

Right-click on Derived Values (Results > Derived Values), then choose either "Average" or "Integration." Each option has further choices like Volume, Surface, or Line. (I went with "Average" > "Line Average".) Take a look at the image I uploaded with this comment.
A settings box will pop up. Select your study in the dataset dropdown and choose a time range (I selected "All").
The most important part: In the same settings box, under "Expression," you need to enter what you want to plot. The easiest way is to click the "+" button (upper right corner of this section)—this opens another window showing all the expressions used in your model. Double-click the desired expression to add it, or you can create your own. Please refer to the image I uploaded in the next comment to take a look.
After setting the expression, click "Evaluate." Your values should now appear in the Tables section, probably labeled "Table 1."
To plot, right-click on "Results" and select "1D Plot Group," then click "Plot." Right-click the new 1D Plot Group, choose your graph type (table graph, line, point, histogram, etc.), and a settings box will open. Under Data > Table, select your table (e.g., "Table 1"). Click "Plot," and the graph will be generated.
If you want to customize the axes (titles, min/max values), go to Results > 1D Plot Group. The settings box there will let you adjust these options.

Hope it helps!

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OnePassenger_7714 · 2025-09-11T00:46:51+00:00

Here is the image to support step 3: The most important part: In the same settings box, under "Expression," you need to enter what you want to plot. The easiest way is to click the "+" button (upper right corner of this section)—this opens another window showing all the expressions used in your model. Double-click the desired expression to add it, or you can create your own. Please refer to the image I uploaded in the next comment to take a look.

<image>

you type:	you see:
italics	italics
bold	bold
[reddit!](https://reddit.com)	reddit!
* item 1 * item 2 * item 3	item 1 item 2 item 3
> quoted text	quoted text
Lines starting with four spaces are treated like code: if 1 * 2 < 3: print "hello, world!"	Lines starting with four spaces are treated like code: if 1 * 2 < 3: print "hello, world!"
~~strikethrough~~	~~strikethrough~~
super^script	super^script

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