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"Undefined" variable won't allow my study to execute

Posted 18 nov 2019, 16:06 GMT-5 Materials, Parameters, Variables, & Functions, Results & Visualization Version 5.4 1 Reply

Sonny Thakkar
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Hi all,

First off this this is my first real project in comsol. It was handed to me to fix, and I've gotten it this far. Now my defined variable shows up as undefined, causing the entire program to halt. If I could get any help I'd appreciate it. Thank you!

1 Reply Last Post 20 nov 2019, 09:35 GMT-5
Jeff Hiller COMSOL Employee

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Posted: 5 years ago 20 nov 2019, 09:35 GMT-5
Updated: 5 years ago 20 nov 2019, 09:08 GMT-5

Hi Sonny,

It's difficult to give you a definite answer without being able to click around your model, but from those three screenshots a couple of things jump at me as suspicious.

The first one is the use of c in a global expression. In one of the screenshots c seems to depend on T (temperature), which itself is generally a field, so that c will be spatially dependent: it doesn't a priori have a since global value.

The second issue is that it looks like the person who set up the file tried to equate a capacitance and the speed of sound in air. That raises red flags, if nothing else from the perspective of dimensions. Besides, there doesn't seem to be an independent variable in that Global ODE if c is the speed of sound in air and es.C11 is the capacitance coming from the Electrostatics physics.

Best,

Jeff

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Jeff Hiller
Hi Sonny, It's difficult to give you a definite answer without being able to click around your model, but from those three screenshots a couple of things jump at me as suspicious. The first one is the use of c in a global expression. In one of the screenshots c seems to depend on T (temperature), which itself is generally a field, so that c will be spatially dependent: it doesn't a priori have a since global value. The second issue is that it looks like the person who set up the file tried to equate a capacitance and the speed of sound in air. That raises red flags, if nothing else from the perspective of dimensions. Besides, there doesn't seem to be an independent variable in that Global ODE if c is the speed of sound in air and es.C11 is the capacitance coming from the Electrostatics physics. Best, Jeff

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