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Strange results in transient acoustics.

Posted Jan 16, 2012, 2:29 p.m. EST Acoustics & Vibrations, Structural Mechanics Version 4.2 3 Replies

Glenston Miranda
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Hi,

I found it rather strange while i was setting the flow point source .
The equation that it uses is the dS/dt to define the source.
When i define S=(1/(2*pi*1000000))*sin(2*pi*1000000[Hz]*t)*(t<=0.0000001) i should be getting
a cosine pulse when 0<t<0.000001 and zero otherwise. But it gives me a sine pulse of magnitude
0.5 as shown in Fig 1.

The second strange result that i observed was when i used S=-(1/(2*pi*1000000))*cos(2*pi*1000000[Hz]*t)*(t<=0.0000001) i should be getting a sine pulse when 0<t<0.0000001 and zero otherwise. But it gives me a srange result as shown in Fig 2.

Looks simple but im quite stumped at these results.
Thanks a lot for your time and effort!!


Regards
Glenston

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3 Replies Last Post Jan 17, 2012, 10:34 a.m. EST
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Jan 16, 2012, 5:33 p.m. EST
Hi

I suppose it depends if you plot S or dS/dt
And what you assume for the integration constants, if you are integrating
--
Good luck
Ivar
Hi I suppose it depends if you plot S or dS/dt And what you assume for the integration constants, if you are integrating -- Good luck Ivar

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Glenston Miranda
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Posted: 1 decade ago Jan 17, 2012, 9:36 a.m. EST

Hi

I suppose it depends if you plot S or dS/dt
And what you assume for the integration constants, if you are integrating
--
Good luck
Ivar

Hi Ivar,

Let me put it in a better way with a figure of my geometry.
I'm not checking these functions in the analytic section. But giving them as inputs to the problem.

When i define S=(1/(2*pi*1000000))*sin(2*pi*1000000[Hz]*t)*(t<=0.0000001) i should be getting
a cosine pulse when 0<t<0.000001 and zero otherwise. But it gives me a sine pulse of magnitude
0.5 as shown in Fig 1.

The second strange result that i observed was when i used S=-(1/(2*pi*1000000))*cos(2*pi*1000000[Hz]*t)*(t<=0.0000001) i should be getting a sine pulse when 0<t<0.0000001 and zero otherwise. But it gives me a srange result as shown in Fig 2.
It asks us to enter the S field but in the equation it uses dS/dt.

I use point graph to obtain Fig1 & 2 using the source point as the point to plot the graph for.

Thanks a lot for your time and effort.

Regards
Glenston
[QUOTE] Hi I suppose it depends if you plot S or dS/dt And what you assume for the integration constants, if you are integrating -- Good luck Ivar [/QUOTE] Hi Ivar, Let me put it in a better way with a figure of my geometry. I'm not checking these functions in the analytic section. But giving them as inputs to the problem. When i define S=(1/(2*pi*1000000))*sin(2*pi*1000000[Hz]*t)*(t

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Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Jan 17, 2012, 10:34 a.m. EST
Hi

sorry I cannot help more, acoustics is one of the modules I'm missing (it's on my list but it's my boss = my efficiency that might pay it) so I'm not sure how COMSOL handles "S" and if it was not adding a constant or changing the amplitude via some normalisation in the same process

--
Good luck
Ivar
Hi sorry I cannot help more, acoustics is one of the modules I'm missing (it's on my list but it's my boss = my efficiency that might pay it) so I'm not sure how COMSOL handles "S" and if it was not adding a constant or changing the amplitude via some normalisation in the same process -- Good luck Ivar

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