Frequency analysis - Helmholtz

[legris]

Dear all,

I am slowly discovering all the great features of this program and would firstly like to thank all people that took part in this.

At the moment I am running the Helmholtz Solver and am looking into running this at a number of different frequencies. I did have a browse through the available documentation but am not sure on how to go about doing this. If someone could put me in the right direction that would be much appreciated.

Thanking you in advance,

legris

[raback]

The appropriate analysis type for frequency scan is "scanning". Then the time goes as 1,2,3,... but the equations themselves are treated as steady state. Now you can simply have Frequency (or material parameters) depend on time using, for example, a MATC dependece.

Code: Select all

Frequency = Variable time
  Real MATC "100*tx"

Would give you frequencies 100,200,300...

Now to take some meaningful results out of each frequency, you can perhaps use the SaveScalars solver. For example, it may be used to compute the maximum pressure, or mean pressure over boundary etc. of the result field. This information is saved to an ascii file and provides thereby easy way of visualizing frequency dependent data using Matlab, Exel, or some other plotting tool. Of course the results of the scan will be available also in the .ep file but many times this is not of primary interest.

-Peter

[legris]

Peter,

Many thanks for your swift reply, much appreciated. Will carry on exploring this program.

legris

[Juha]

Hi,

just a small hint when using the 'scanning' mode: you could have arbitrary pregiven
values for the parameters by inserting, e..g.

$ freq = 51 7 20 40 951

to the sif-file and using the running 'time' as an index to the array:

Frequency = Variable time
Real MATC "freq(tx)"

or even using something like:

Frequency = Variable time
Real MATC "freq=51 7 20 40 951; freq(tx)"

Regards, Juha

[legris]

Juha,

Thank you for this addition, will come in very handy,

Regards,
legris

[Supituki]

Hi all,

after reading this post, i was wondering if it is possible to introduce an array of Values at the "Frequency = ---" at the solver part of the ".sif", instead of using the scanning mode. It would be much easier to implement.

If it can be done, how are arrays introduced in Elmer? I tried with "Frequency = 10 100 200" but it does not detect the second and the thirds values.

Thanks in advance

Supituki

[Juha]

Hi,

You can enter arrays using array syntax like this:

Code: Select all

arr(4) = Real 1 2 3 4

However, the frequency for Helmholtz solver is a scalar property and can't be
entered as an array.

Regards, Juha