Applying a sinusoidal voltage in a time dependent study

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Hi,

I am trying to apply a sinusoidal voltage on the boundary of a rectangular transducer. I am using the equation: V=Asin(2pift) for which I define the variables on the global definitions section. However, I am not sure as to what 't' represents. Isn't the simulation time/variable? How am I going to define it at the global definitions section since it changes for different simulations?


7 Replies Last Post Feb 25, 2021, 6:19 AM EST

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Posted: 2 weeks ago Feb 23, 2021, 3:21 PM EST

Hi,

I tried to help even if I am not an expert. If you want to apply a time-dependent voltage, you have to select electric potential in "electrostatic interface", and you can define directly the voltage writing the expression that you need : V= Asin(2pift). "t" represents the time and you don't need to define it in the global defintions I think. I hope this helps.

Hi, I tried to help even if I am not an expert. If you want to apply a time-dependent voltage, you have to select electric potential in "electrostatic interface", and you can define directly the voltage writing the expression that you need : V= A*sin(2*pi*f*t). "t" represents the time and you don't need to define it in the global defintions I think. I hope this helps.

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Posted: 2 weeks ago Feb 24, 2021, 9:42 AM EST

Hi,

Thank you for your reply.

It worked and I don't get an error. However, I can't see a sinusoidal wave formed and I get a constant output similar to when I was applying a constant DC voltage. Do you happen to know why is that the case?

Hi, Thank you for your reply. It worked and I don't get an error. However, I can't see a sinusoidal wave formed and I get a constant output similar to when I was applying a constant DC voltage. Do you happen to know why is that the case?

Magnus Ringh COMSOL Employee

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Posted: 2 weeks ago Feb 24, 2021, 10:52 AM EST
Updated: 2 weeks ago Feb 24, 2021, 10:54 AM EST

Hi,

Just some basic checks:

  • Are you using a time-dependent study?
  • If you defined the sinusoidal wave as a function, are you calling it from the physics with the time t as the input?
  • You may also check that the dynamics of the physics and the sinusoidal match so that you can expect a sinusoidal output.

Best regards,

Magnus Ringh

Hi, Just some basic checks: * Are you using a time-dependent study? * If you defined the sinusoidal wave as a function, are you calling it from the physics with the time t as the input? * You may also check that the dynamics of the physics and the sinusoidal match so that you can expect a sinusoidal output. Best regards, Magnus Ringh

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Posted: 2 weeks ago Feb 24, 2021, 12:29 PM EST

Hi Magnus,

Thank you for your reply.

Yes, I am using a time-dependent study and I have included the V=A* (2pif*t) in the electric potential tab under Electrostatics. I have attached the .mph file.

Hi Magnus, Thank you for your reply. Yes, I am using a time-dependent study and I have included the V=A* (2*pi*f*t) in the electric potential tab under Electrostatics. I have attached the .mph file.


Dave Greve Certified Consultant

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Posted: 2 weeks ago Feb 24, 2021, 3:06 PM EST

Some thoughts

  • are you sure you want a time-dependent study? Most of the time people are interested in the sinusoidal steady state response, and that is much more easily determined in a frequency dependent study.
  • pdms should probably be a linear elastic solid with the pressure formulation checked.
Some thoughts - are you sure you want a time-dependent study? Most of the time people are interested in the sinusoidal steady state response, and that is much more easily determined in a frequency dependent study. - pdms should probably be a linear elastic solid with the pressure formulation checked.

Magnus Ringh COMSOL Employee

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Posted: 2 weeks ago Feb 25, 2021, 2:36 AM EST
Updated: 2 weeks ago Feb 25, 2021, 7:07 AM EST

Hi,

I had a brief look at the model. You are using a very high frequency when compared to the simulated time span, and with the output times and default time stepping you will get aliasing effects, etc. Try starting with a shorter simulation time span (just a few periods) and check the time stepping options in the Time-Dependent Solver subnode: with a strict time stepping and a tight tolerance, you will see a sinusoidal electric potential at the boundaries where you applied it.

That said, perhaps this modeling approach isn't the best for this type of physics (see the comment above by Dave Greve). I'm no expert in that part, so I cannot really say.

Best regards, Magnus Ringh

Hi, I had a brief look at the model. You are using a very high frequency when compared to the simulated time span, and with the output times and default time stepping you will get aliasing effects, etc. Try starting with a shorter simulation time span (just a few periods) and check the time stepping options in the Time-Dependent Solver subnode: with a strict time stepping and a tight tolerance, you will see a sinusoidal electric potential at the boundaries where you applied it. That said, perhaps this modeling approach isn't the best for this type of physics (see the comment above by Dave Greve). I'm no expert in that part, so I cannot really say. Best regards, Magnus Ringh

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Posted: 2 weeks ago Feb 25, 2021, 6:19 AM EST

Hi Dave and Magnus,

Thank you both for your replies, they are realy helpful!

I need a time-dependent study to understand the formation of standing waves in a water channel since in the frequency domain, the type of wave is not very clear.

I think the issue is with the frequency and the time-step as Magnus pointed out.

I will give this a go and see if it is working.

Hi Dave and Magnus, Thank you both for your replies, they are realy helpful! I need a time-dependent study to understand the formation of standing waves in a water channel since in the frequency domain, the type of wave is not very clear. I think the issue is with the frequency and the time-step as Magnus pointed out. I will give this a go and see if it is working.

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