Basic acoustic transient project.

[Nick4]

Hello.

I've been trying to set up a basic, transient, type of situation as shown in the MPEGs on page "http://www.csc.fi/english/pages/elmer/e ... /Helmholtz".

If I use the Helmholtz equation then it seems to work OK except, when I open the Elmer Post Processing and load all the timesteps, only Pressure.wave.1 animates (which is normal to the direction of the sound). Pressure.wave.2 only has the same frame throughout. All I really want is "pressure".

Can anyone tell me how I get my simple Helmholtz example to animate like the "Acoustic scattering" videos? What variable is being output here? I must have tried every combination of setting and will soon have the complete works of Shakespeare but still no nice waves.

Regards to you : )

Nick.

Please see my attached project if you like - it's very simple.

[raback]

Hi

The Helmholtz equation is not actually transient. It is by default harmonic and no setting will change that. So it only has real and complex parts and to get animation follow the instructions "Animations of harmonic solution" in http://www.elmerfem.org/wiki/index.php/ ... Animations

-Peter

[Nick4]

Thank you Peter,

I'm really sorry for my stupidity. I will follow the link and spend some time playing.
If I produce something pretty I'll upload it to the Cases forum.

Have a nice evening.
Nick.

[Nick4]

Hi...
I have amended my project to be Steady State and I've tried to carry out the steps outlined in the above link but cannot get it to work for several reasons.
I did the following in ElmerPost:-

Code: Select all

math n=nodes
do i 1 50 { math phi=2*pi*$i/50; math nodes=n+Displacement*sin(phi)*3.3e-3; 
math pres=Pressure.wave.1*cos(phi)-Pressure.wave.2*sin(phi); display }

There was no variable '"Displacement", so I added Displacement to my list of exported variables in the solver control for the Helmholtz equation.

Adding Displacement

Solver Control.jpg (49.68 KiB) Viewed 5546 times

Then, when I open ElmerPost all the Graphics plots are "weird".

Weird Graphics

Elmer Post Graphics.jpg (82.53 KiB) Viewed 5546 times

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Also, I tried yesterday to use the "savempg" feature. Perhaps it because I'm using Windows 7, but I couldn't get any playable movie O/P. I'm quite sure I followed the procedure correctly for this at least. None of the Codec radio button choices produce any sizeable file except the YUV4 option but this would not play for me.
[Also, the JPG features create only black O/Ps for me]
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I will probably give up on trying to animate harmonic solutions. Honestly, I don't think it is well enough documented for me to follow
It does produce an animation but it's not right.

Thanks,
Nick.

[raback]

Hi Nick

The original equation was for displacement which were added to original nodal coordinates. In the case of pressure just skip that part and visualize for the computed absolut pressure.

-Peter

[teofilBitron]

Hello Elmer community,

I'm trying to solve a transient dynamic coupled with an Acoustic analisy.
Is it possibles?
Is the Helmholtz solver a transient one?
My workflow is more or less like this:
1) perform a Dynamic transient analisys
2) follow an Acoustic analisys taken as input the boundary displacements from the dynamic one
Anyone know in the web some examples from which I could take some suggest?

[iczajka]

Hello teofil,
as you can read before in this thread, Helmholtz equation is steady state. It is not transient. So, only if you can obtain result from dynamic harmonic analysis, it is possible to use it in helmholtz solution (for each frequency). Maybe some kind of modal superposition?

BR
Irek