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Trouble plotting dielectrophoretic forces as a result of particle tracing simulation

Posted Feb 20, 2014, 10:45 a.m. EST Microfluidics, Results & Visualization Version 4.4 3 Replies

Alisha Schor
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Hello all,

I am simulating the motion of particles under a dielectrophoretic force in a microfluidic channel. There are two study steps: one that calculated the E-field and fluid flow field and one that calculates the time-dependent particle trajectories, using the Particle Tracing for Fluid Flow module. My model seems to run fine, and the behavior is what I would expect. However, when trying to plot an arrow surface or arrow volume of the DEP force, I always get the same error:

Failed to evaluate variable.
- Variable: comp1.fpt.Fdpx_deff1
- Geometry: 1
- Domain: 1
Failed to evaluate expression.
- Expression: comp1.fpt.Fdpx_deff1
- Plot: arws1 (Arrow surface)

Does anyone else get this or have any insight as to what the issue is? I don't understand how it can fail to evaluate the variable if it's using it to calculate the particle trajectory...

Thanks, Alisha
3 Replies Last Post Jul 17, 2014, 11:06 p.m. EDT
COMSOL Moderator

Hello Alisha Schor

Your Discussion has gone 30 days without a reply. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help.

If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base.

Saeid Movahed
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Posted: 10 years ago Jul 16, 2014, 11:31 p.m. EDT
Hello Alisha

Unfortunately I have exactly the same problem you mentioned.
I use fluid flow and DC modules and I get an accurate result for electroosmotic flow, but when I use a transient study for particle tracing module, I get same error that you wrote.
I am totally confused with this problem.
Please let me know if you have found a result.

I would appreciate if any one helps me.
Thanks in advance.
Hello Alisha Unfortunately I have exactly the same problem you mentioned. I use fluid flow and DC modules and I get an accurate result for electroosmotic flow, but when I use a transient study for particle tracing module, I get same error that you wrote. I am totally confused with this problem. Please let me know if you have found a result. I would appreciate if any one helps me. Thanks in advance.
Daniel Smith COMSOL Employee

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Posted: 10 years ago Jul 17, 2014, 8:36 a.m. EDT
Hi, the DEP force depends on properties of the individual particles, and so it only exists at the location of the particles, not in the geometric domain itself. This is why you get an error when trying to plot the force on the domain. The only way to visualize it is to set the color expression to be a component of the DEP force in the Particle Trajectories plot. To visualize the direction of the force, you can set the Point type to Comet and the expression to the DEP force.

Dan
Hi, the DEP force depends on properties of the individual particles, and so it only exists at the location of the particles, not in the geometric domain itself. This is why you get an error when trying to plot the force on the domain. The only way to visualize it is to set the color expression to be a component of the DEP force in the Particle Trajectories plot. To visualize the direction of the force, you can set the Point type to Comet and the expression to the DEP force. Dan
Saeid Movahed
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Posted: 10 years ago Jul 17, 2014, 11:06 p.m. EDT
Thank you dear Dan for your guide.

It worked.
Thank you dear Dan for your guide. It worked.

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