k-Wave

1. Rola
   

   Member
   Joined: Nov '18
   Posts: 10

   Hi there,

   I'm running a simple simulation with two media air and water. The air interface is around 1mm and water is around 2.4cm. When I run the simulation (using an initial pressure dx= dy = 100 um) without considering alpha coefficients, the reflection coming from air has spurious oscillations. Introducing a coefficient attenuation for water and air the reflection coming from air does not have oscillations at all. Nevertheless, I have tried with random values for the alpha_coeff. So, if I perform a simulation with an initial pressure do I need to be precise with alpha_coeff? If yes, what is right way to introduce the attenuation coefficient for two media?

   Best.

   Posted 5 years ago #

2. Bradley Treeby
   

   Developer
   Joined: Mar '10
   Posts: 1,640

   Hi Rola,

   Adding attenuation will preferentially dampen the high frequencies, which in your case dampens the high-frequency oscillations in your simulation. Is the initial pressure distribution smoothed? If not, turning smoothing on could also help.

   If you want to the wave amplitude to be correct, then I'd suggest trying to be reasonably accurate for the attenuation in water. As the transmission into air is close to zero, I don't think the attenuation value for air matters.

   In general, modelling water-air interfaces is difficult with k-Wave due to the huge impedance mis-match. I normally recommend artificially increasing the density of air in the simulation to 10 or 100. The reflection coefficient will still be close to -1, but the simulation will converge for much lower points-per-wavelength.

   Brad.

   Posted 5 years ago #

3. Rola
   

   Member
   Joined: Nov '18
   Posts: 10

   Thank you.

   Posted 5 years ago #

4. babakkh
   

   Member
   Joined: Feb '17
   Posts: 10

   Hi,

   You might also include the pressure release acoustic boundary conditions in the source code.
   I have done in this paper:
   https://academic.oup.com/gji/article-abstract/216/1/545/5146453

   Best regards,

   Babak

   Posted 5 years ago #

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