http://www.k-wave.org/forum/topic/apply-absorption-on-particle-velocity Support for the k-Wave MATLAB toolbox en-US Wed, 13 May 2026 00:13:01 +0000 http://bbpress.org/?v=1.0.2 q http://www.k-wave.org/forum/search.php http://www.k-wave.org/forum/topic/apply-absorption-on-particle-velocity#post-1249 Fri, 15 Feb 2013 12:25:08 +0000 bencox 1249@http://www.k-wave.org/forum/ <p>Hi Chao,</p> <p>Yes, carry on with kgrid.k. When Fourier transforming from the spatial to the wavenumber domain you don't retain any spatial information, so the fact you are on a shifted grid won't make any difference. </p> <p>Ben </p> http://www.k-wave.org/forum/topic/apply-absorption-on-particle-velocity#post-1248 Thu, 14 Feb 2013 19:16:31 +0000 huangchao 1248@http://www.k-wave.org/forum/ <p>Hi Dr. Cox and Dr. Treeby,</p> <p>When you incorporated the absorption and dispersion, you modified the equation of state, which has the form p = c^2*{\rho - \tau*F^(-1){k^(y-2)F{d/dt \rho}} - \eta*F^(-1){k^(y-1)F{\rho}} }.</p> <p>In the code, the dispersion term, for example, was implemented as absorb_eta.*real(ifft2( absorb_nabla2.*fft2(rhox + rhoy))), where absorb_nabla2 was computed by the following statements</p> <p>absorb_nabla2 = (kgrid.k).^(medium.alpha_power-1);<br /> absorb_nabla2(isinf(absorb_nabla2)) = 0;<br /> absorb_nabla2 = ifftshift(absorb_nabla2); </p> <p>Now I want to incorporate the absorption and dispersion through the particle velocity u as<br /> u_i' = {u_i - \tau*F^(-1){k^(y-2)F{d/dt u_i}} - \eta*F^(-1){k^(y-1)F{u_i}} }, i = x,y,z, and let's first put the correctness of this aside. In this case, the corresponding dispersion term will be absorb_eta.*real(ifft2( absorb_nabla2.*fft2(u_i))). My question is: can absorb_nabla2 be computed in the same way as above since now u is on the staggered grid? Specifically, can kgrid.k still be used to compute absorb_nabla2 in this case, or some staggered kgrid.k is needed?</p> <p>Thanks,<br /> Chao </p>