k-Wave User Forum » Topic: Defining the computational grid and acoustic absorption

k-Wave User Forum » Topic: Defining the computational grid and acoustic absorption http://www.k-wave.org/forum/topic/defining-the-computational-grid-and-acoustic-absorption Support for the k-Wave MATLAB toolbox en-US Wed, 13 May 2026 10:19:38 +0000 http://bbpress.org/?v=1.0.2 <![CDATA[Search]]> q http://www.k-wave.org/forum/search.php Ed Qu on "Defining the computational grid and acoustic absorption" http://www.k-wave.org/forum/topic/defining-the-computational-grid-and-acoustic-absorption#post-5430 Thu, 17 Mar 2016 23:43:17 +0000 Ed Qu 5430@http://www.k-wave.org/forum/ Hi Dr. Treeby We found the file according to your reply. We have fixed the problem in our code. Thanks for your help! Sincerely, Ed Bradley Treeby on "Defining the computational grid and acoustic absorption" http://www.k-wave.org/forum/topic/defining-the-computational-grid-and-acoustic-absorption#post-5429 Thu, 17 Mar 2016 15:02:55 +0000 Bradley Treeby 5429@http://www.k-wave.org/forum/ Hi Ed, Just to check - are using k-Wave for your simulations, or have you coded your own version? The absorption terms in k-Wave are defined in the function <code>/private/kspaceFirstOrder_createAbsorptionVariables.m</code>. The values for the absorption and dispersion terms are set to zero for k = 0. Keep in mind that when you add absorption, simulations using <code>kspaceFirstOrderND</code> are no longer unconditionally stable, even for a homogeneous medium. You will need to choose the time step to satisfy the appropriate stability criteria. In general, the time step will need to be reasonably small if the absorption values are very high. You can use the function <code>checkStability</code> to check the value of time step required. Hope that helps, Brad. Ed Qu on "Defining the computational grid and acoustic absorption" http://www.k-wave.org/forum/topic/defining-the-computational-grid-and-acoustic-absorption#post-5417 Mon, 14 Mar 2016 14:51:43 +0000 Ed Qu 5417@http://www.k-wave.org/forum/ Hi Our group wanted to integrate the algorithm for the acoustic dissipation and dispersion into our code for USCT simulation, but we encountered a problem during coding. The manual shows that the power index y can be defined between 0 and 3, except for 1; the grid (defined in 2.17e) includes the origin where k = 0. On the other hand, the first term on the right hand side of the equation (2.24) multiply the Fourier transform with k^(y-2). If we assume y < 2, this term will diverge at the origin. So far, we just simply define the value of Ld in (2.24) equal to 0 at the origin, but the stability of our program using this resolution is not good enough. The program will diverge in hundreds of steps if we define a large alpha and a y<2. Does anyone know how to resolve this problem? Thanks a lot. Sincerely, Ed