Re: Shock wave refection

From: Edward Green (spamspamspam3_at_netzero.com)
Date: 06/21/04 

Date: 20 Jun 2004 17:26:26 -0700

"Franz Heymann" <notfranz.heymann@btopenworld.com> wrote in message news:<cb36n1$l1s$1@hercules.btinternet.com>...
> "heiko ackermann" <heiack@gmx.de> wrote in message
> news:cb22rf$n4v$04$1@news.t-online.com...
> > Hi,
> > I've a question about the reflection of a shock wave.
> > First I've a spherical shock wave which is in water. The acoustic
> > impedance of water is about 1,5 Million then the shock wave hits an
> > spherical bubble with a acoustic impedance of 0,375 million. If i
> can
> > use the classical caculation for reflection, transmisson etc. I know
> how
> > I can caculate the intensities. But there is a problem, the bubble
> has
> > nearly a diameter of 0,5 mikrometers, and the wavelength of the
> shock
> > wave is much greater. So I'am not sure if can use the classical
> > caculations, because I know if an object is much smaller than the
> wave
> > length of a wave, the wave is not recoignizign the object, this
> means in
> > my special case that the shock wave will completly tranmitted.
>
> In your case, the shock wave will go almost clean through the bubble,
> with only a minor amount of diffraction.
>
> Incidentally, are you sure that concepts like acoustic impedance apply
> to shock waves? Surely they are only valid in the linear region of
> pressures and amplitudes?

Perhaps one should also mention that "the classical calculations",
whatever they are, should not cease being valid merely because one
treats an object much smaller than a wavelength: rather they should
_predict_, validly, that certain effects are negligable.

As to what will happen to the bubble: surely you are right that
treating this as a problem in continuum mechanics with some fixed bulk
parameters for fluid and bubble will likely fail.