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Repeating a force vs time signal being applied to a piezo device and its steady state voltage

Posted Apr 22, 2012, 9:24 p.m. EDT Structural Mechanics Version 4.2a 7 Replies

Shriram Kulkarni
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Hi, I have a force vs time signal data for 3.3 seconds that I am importing as an interpolation function. Is there any way to apply this signal to a piezoelectric device for say, 200 seconds without having to modify the data itself. Can I do it using extrapolation option in the interpolation function tab? I see no option in this tab by which I can repeat the signal.
Also, I am running the piezo output through a bridge rectfier, a capacitor and a load resistor. The voltage across the load resistor should be the DC voltage output but is it the steady state voltage?
7 Replies Last Post May 7, 2012, 2:20 a.m. EDT
Edgar Kaiser
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Posted: 1 decade ago Apr 23, 2012, 6:07 a.m. EDT
Hi,

you could try to use the modulo operator. Use t modulo 3.3 as the argument of your function. This should repeat the signal.

Cheers
Edgar
Hi, you could try to use the modulo operator. Use t modulo 3.3 as the argument of your function. This should repeat the signal. Cheers Edgar
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Apr 23, 2012, 8:06 a.m. EDT
Hi

you can use a combination of step, or rectangle functions and an analytical function, there yu have also the possibility to make some of the function to repeat, check the advanced tab (if I remember right)

--
Good luck
Ivar
Hi you can use a combination of step, or rectangle functions and an analytical function, there yu have also the possibility to make some of the function to repeat, check the advanced tab (if I remember right) -- Good luck Ivar
Shriram Kulkarni
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Posted: 1 decade ago May 2, 2012, 7:46 a.m. EDT
Hello and thank you for your reply,
My function is too random. I have created an analytical curve out of it by curve fitting but for my work, I will prefer to use it as it is. I have made the analytical function periodic as you said. I am attaching an image of the analytical as well as raw function that I want to use. I apply these loads as boundary loads (Total force) on the surface of a piezo structure. I call the function as -an1(x) or -int1(x) (- sign as I want the force to be vertically downwards). But, as you can see in the attached point graph for a point on the surface (50,15,10) the output voltage is decreasing. Is it a mistake in the function calling? Also is there any way by which I can simultaneously see the amount of force being applied with the output voltage? (Currently I set the results while plotting option to voltage and I can see the voltage generated for each time step). Also how do I call the modulo function for this case. IF you can suggest me with a example for modulo function use in this case, it would be really helpful.
Hello and thank you for your reply, My function is too random. I have created an analytical curve out of it by curve fitting but for my work, I will prefer to use it as it is. I have made the analytical function periodic as you said. I am attaching an image of the analytical as well as raw function that I want to use. I apply these loads as boundary loads (Total force) on the surface of a piezo structure. I call the function as -an1(x) or -int1(x) (- sign as I want the force to be vertically downwards). But, as you can see in the attached point graph for a point on the surface (50,15,10) the output voltage is decreasing. Is it a mistake in the function calling? Also is there any way by which I can simultaneously see the amount of force being applied with the output voltage? (Currently I set the results while plotting option to voltage and I can see the voltage generated for each time step). Also how do I call the modulo function for this case. IF you can suggest me with a example for modulo function use in this case, it would be really helpful.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago May 2, 2012, 5:15 p.m. EDT
Hi

if you call your function with a myfunc(t[1/s]) then the numerical value of time, in seconds, should be well understood by COMSOL.
However with such random signals, have you set the solver node to "strict" time stepping (and not the default "automatic"), with a small predefined tme step to solve the signal details ?

Check also your log file, if you have several lines with" -out" without any solver steps, its COMSOL interpolating and probably skipping over the spikes of your signal

--
Good luck
Ivar
Hi if you call your function with a myfunc(t[1/s]) then the numerical value of time, in seconds, should be well understood by COMSOL. However with such random signals, have you set the solver node to "strict" time stepping (and not the default "automatic"), with a small predefined tme step to solve the signal details ? Check also your log file, if you have several lines with" -out" without any solver steps, its COMSOL interpolating and probably skipping over the spikes of your signal -- Good luck Ivar
Shriram Kulkarni
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Posted: 1 decade ago May 3, 2012, 3:42 a.m. EDT
HI, I am indeed getting '-out' in front of most of the time steps. What can be possible solution to this? I have switched the solver node to 'strict' time stepping method. Also, I am still confused about the function calling methods as calling the function as 'an1(x[1/s])' is giving an error about syntax. Thank you in advance.
HI, I am indeed getting '-out' in front of most of the time steps. What can be possible solution to this? I have switched the solver node to 'strict' time stepping method. Also, I am still confused about the function calling methods as calling the function as 'an1(x[1/s])' is giving an error about syntax. Thank you in advance.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago May 3, 2012, 5:59 a.m. EDT
Hi

sorry I was assuming "t" for time, if your function is "x" for position you need a x[1/m] or x[1/mm] all depends what your interpolation function input type you are using

--
Good luck
Ivar
Hi sorry I was assuming "t" for time, if your function is "x" for position you need a x[1/m] or x[1/mm] all depends what your interpolation function input type you are using -- Good luck Ivar
Shriram Kulkarni
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Posted: 1 decade ago May 7, 2012, 2:20 a.m. EDT
Hello Sir,

I am still getting 'out' in front of the solver steps even if I do the simulation with time steps as little as 0.0001. Is there any problem in the tolerance value? Current tolerance value is 0.001. As you said, the solver is probably skipping the spikes in the signal. Is there any way, by which I can see the force value being applied at the time instant and compare it with displacement and potential generated? Thank You in advance.
Hello Sir, I am still getting 'out' in front of the solver steps even if I do the simulation with time steps as little as 0.0001. Is there any problem in the tolerance value? Current tolerance value is 0.001. As you said, the solver is probably skipping the spikes in the signal. Is there any way, by which I can see the force value being applied at the time instant and compare it with displacement and potential generated? Thank You in advance.

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