k-Wave

1. tomk2006
   

   Member
   Joined: Nov '15
   Posts: 4

   I'm trying to simulate sound propegation inside a metal tube filled with air, with a rectangle source, and a point source (speaker and a microphone). I know that boundery conditions are not possible in K-wave, so I created a series of spherical sections that makes the tube, then placed the source and sensor in the tube.
   In the slit example provided in the package, you have created an object with higher density and speed of sound (times 20), to simulate the slit.
   I try to use the same method to simulate the increased density of the tube, and the speed of sound in it. A few question that I have regarding that topic:

   1)Is this the best way to simulate the conditions mentioned above using k-wave?

   2)If so, taking into account that sound speed is ~ 18 time in steel than in air, the calculation time length will be multipled by ~ 18 (since dt is propertional to max speed of sound). Since i'm not intrested in the way the sound propegated through the tube, I only care that the refrections and absorption stay the same, is there a way to go around this?

   3)in a later stage I would like to include the harmonic of my frequency. can I do this simply by setting sensor.p =sin(w_1*t_grid) +sin(2w*t_grid)?

   4) To make the spectral analysis I'm using FFT. is the rate of sample for the detector 1/dt?

   Posted 8 years ago #

2. tomk2006
   

   Member
   Joined: Nov '15
   Posts: 4

   Fix: I meant a point sensor, and a rectangular source

   Posted 8 years ago #

3. Bradley Treeby
   

   Developer
   Joined: Mar '10
   Posts: 1,640

   Hi tomk2006,

   Is the wavelength much larger than the dimensions of the tube such that the wave propagation could be assumed to be planar? If so, you could run the simulations in 1D, which would significantly improve the computation time.

   Otherwise, the only option at the moment is to use different material properties as you have done. Something to keep in mind is that if you try to define a circle on a discrete Cartesian grid, you will get staircasing errors. To minimise this, you might need to use a reasonable number of grid points per wavelength. If you want to simulate perfectly hard or soft boundaries, you could also look at this post.

   Regarding your other questions: (2) For the time step, you can define this yourself by setting kgrid.t_array (see Section 3.2 in the k-Wave manual). Keep in mind the stability conditions (see Section 2.7 in the manual). (3) Yes, you can create more complicated signals by adding them. (4) Yes, the sample rate of the recorded signal is 1/kgrid.dt.

   Something else to consider is that the correction factor used in the k-space scheme in k-Wave defaults to the maximum sound speed. I would override this using the medium.sound_speed_ref input and set it to the sound speed in the tube. This will minimise the numerical dispersion.

   Hope that helps,

   Brad.

   Posted 8 years ago #

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