Discussion Forum

Hi

I do not have any Comsol running, as I'm off on holidays, but I thought that the rnd function could be called as a

rnd(t)

(now I might be wrong) if its a fuction from 0 to 1 then you set your F=F0*rnd(t) and you should get a new value for each time step t (I understand the variable given to the rnd() as a seed value)

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Good luck
Ivar

Ivar...if you're on holydays: don't answer my questions. I want you on september at 100%.
Well, I'm not saying that the values of the function are going from 0 to 1. I meant the random vector had a given size (a size I can not change as I want) and when ploting it, the x axis goes from 1 to 0. I don't know if I'm explaining it good, sorry for my english.
Anyway, I had tried putting t as an argument for the rn1 function but it must be a natural number, so I'd try to multiply the time t by a big number, and then take the number without decimals...something like that.
I'll brief you on that.
Have a good holydays!!
Miquel

Hi

Well do not expect 100% from me, because I'm a user as you (not linked to Comsol ;) apart that I'm a fan of the software tool.

So as most employee I'm 100% available for my boss (and pls do not tell him I'm here ;), but I use 10-20% of my free time to answer the forum so long I believe I have a usefull answer, also because I learn a lot and how to use the tool by exercicing me on the examples out here, you should try too

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Good luck
Ivar

Hi,

Ivar is right: If you define a uniform random function rn1 with 1 input argument, you can call it as

rn1(t)

where t is the time to create a random load. Regarding the range, you can change both the mean value and the range of the random function directly in its Settings window, or you can use the default mean of 0 and range 1 and instead use an expression for the body load like k*rn(t)+c, where k and c are parameters.

You can plot the random function directly from its Settings window and also by creating a Function 1D data set under Results, where you have more options for the plot and the range for the input argument, which defaults to a 0 to 1 range in the Random function's built-in plot.

Best regards,
Magnus Ringh
COMSOL

Hi,

Ivar is right: If you define a uniform random function rn1 with 1 input argument, you can call it as

rn1(t)

where t is the time to create a random load. Regarding the range, you can change both the mean value and the range of the random function directly in its Settings window, or you can use the default mean of 0 and range 1 and instead use an expression for the body load like k*rn(t)+c, where k and c are parameters.

You can plot the random function directly from its Settings window and also by creating a Function 1D data set under Results, where you have more options for the plot and the range for the input argument, which defaults to a 0 to 1 range in the Random function's built-in plot.

Best regards,
Magnus Ringh
COMSOL

Hi,
How to create a Function 1D data set under Results? I cannot find corresponding options, could you write it step by step? I use comsol4
and, can I change the range for the input argument ? I cannot find corresponding setting in the Random function definition interface.
Thank you!

Hi

I'm not sure I understand you, but if you create a random function in v4 "rn1()", then in the Result section you choose what you want to apply the random function to:

i.e. an edge/boundary in 2D, and you select line integration, you select i.e. a horizontal line and type the integrand rn1(x)
Then you will get a value out that is the the sum of the different rn1(x) taken over each x defined by the mesh (+ shape function interpolation). If you have selected a standard rn1() you should get about "0" out. The example is probably not very useful, but it illustrates the use of a function and how COMSOL implicitly refers to the variables of the mesh when you select Element item(s) (such as Domains,boundaries, edges or Points).

If you have a time series (transient analysis) or a parametric sweep and you select a point and type Results Derived Values Point Evaluation and if you use rn1(t) in the expression you will get a column of random numbers Again I'm not sure how useful these random number might be.

For me rn1() should typically be used to input some "noise" for a BC

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Good luck
Ivar

hi..
i am very new to the comsol (any FEA software) and i want to generate lamb waves in aluminum plate using piezoelectric transducers i have followed following steps

2D=>Structural Mechanics=>piezoelectric devices=>time dependant=>finish

=>parameters (Frequency,Voltage,Hanning window parameter)=>Geometry(created two rectangles)

=>materials(Al,PZT-5H)=>piezoelectric devices=>Linear Elastic material(selected Al plate)

=>Ground(1 edge grounded)=>Electric potential (applied vo/2*(1-cos(2*pi*fo*t/no))*cos(2*pi*fo*t) where vo=voltage,fo=frequency, no=hanning window size)

=>Mesh=>Time dependent(selected step size)=>Compute

1. Have i missed something?
2. I want to apply voltage as given by function only up to the time t<=no/fo otherwise zero, How can i do that?
3. If anyone has done similar simple simulation please send me .mph file so that i can learn.
4. Are there any tutorials on creating lamb waves i coudnt find anything simple related to lambwave please tell me the URL of the same if you have it

Thanks in advance.