k-Wave

1. huangchao
   

   Member
   Joined: Nov '10
   Posts: 57

   I did the following simulation:

   Nx=64;
   Ny=64;
   Nz=64;
   dx=1e-3;
   dy=1e-3;
   dz=1e-3;
   kgrid=makeGrid(Nx,dx,Ny,dy,Nx,dz);

   medium.sound_speed=1500*ones(Nx,Ny,Nz); % sound speed in water
   medium.density=1000*ones(Nx,Ny,Nz); % water density
   medium.sound_speed(:,:,50:64)=343; % sound speed in air
   medium.density(:,:,50:64)=1.2; % air density

   source.p0=makeBall(Nx,Ny,Nz,32,32,32,10);

   sensor.mask=[makeCartCircle(15e-3, 100);zeros(1,100)];

   input_args = {'Smooth', false,'CartInterp', 'nearest', 'DisplayMask','off', 'PMLInside', true, 'PMLSize', 10, 'PlotPML', false, 'PlotSim', false, 'DataCast', 'gsingle'};

   p=kspaceFirstOrder3D(kgrid,medium,source,sensor,input_args{:});

   Without smoothing the medium, the simulated pressure 'p' is blowing up, and if I smoothed the medium by setting the 'input_args' as

   input_args = {'Smooth', [false,true,true],'CartInterp', 'nearest', 'DisplayMask','off', 'PMLInside', true, 'PMLSize', 10, 'PlotPML', false, 'PlotSim', false, 'DataCast', 'gsingle'};

   Then 'p' looks reasonable. So I am wondering if this means that the medium needs to be smoothed if the variation of sound speed/density is very large.

   Posted 12 years ago #

2. bencox
   

   Developer
   Joined: Mar '10
   Posts: 292

   Hi Huangchao,

   k-Wave uses a spectral method for calculating the gradients of the field, so is based on a representation of the field as a finite sum of Fourier components, which works well when everything is nice and smooth (and the Fourier coefficients decay rapidly) but is less good when there are sharp gradients as Gibbs-type errors are introduced. Essentially, the finite number of Fourier components is unable to describe the sharp step accurately. See Section VB in our latest paper "Modeling nonlinear ultrasound propagation in heterogeneous media with power law absorption using a k-space pseudospectral method" for more explanation. (See the publications page).

   Kind regards,

   Ben

   Posted 12 years ago #

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