http://www.k-wave.org/forum/topic/simulation-blows-up Support for the k-Wave MATLAB toolbox en-US Wed, 13 May 2026 01:26:43 +0000 http://bbpress.org/?v=1.0.2 q http://www.k-wave.org/forum/search.php http://www.k-wave.org/forum/topic/simulation-blows-up#post-3830 Fri, 26 Jul 2013 13:30:55 +0000 Civilian 3830@http://www.k-wave.org/forum/ <p>Thanks Brad!<br /> My simulation works fine with these values. I understand now that the frequency in the absorption model is meant to be the frequency at which the absorption coefficient is measured not the ultrasonic frequency I am using. Thank you for the clarification. </p> http://www.k-wave.org/forum/topic/simulation-blows-up#post-3816 Thu, 25 Jul 2013 10:39:12 +0000 Bradley Treeby 3816@http://www.k-wave.org/forum/ <p>Hi Civilian,</p> <p>The absorption coefficient pre-factor (<code>alpha_coeff</code>) is defined in units of dB/(MHz^y cm), where <code>alpha = alpha_coeff * f ^ alpha_power</code>. In your case, <code>alpha = 20</code>, so if you assume your absorption varies with y = 1.5, you would then set <code>alpha_coeff = 20 / 1^1.5 = 20</code>.</p> <p>With very high values of absorption, the stability criterion of the model used in k-Wave becomes more stringent. If you are still seeing instabilities with <code>alpha_coeff = 20</code>, try decreasing the size of the time step (you can do this by reducing the CFL number in <code>makeTime</code>).</p> <p>Brad. </p> http://www.k-wave.org/forum/topic/simulation-blows-up#post-3811 Wed, 24 Jul 2013 16:21:45 +0000 Civilian 3811@http://www.k-wave.org/forum/ <p>Hi k-Wave,</p> <p>I am trying to simulate ultrasound through a medium with a relatively high absorption coefficient (20 dB/cm at 1 MHz). The way I understand, please correct me if I am mistaken, the simulation parameters should be set is that alpha_coeff*freq^alpha_power should be equal to 20. So if the frequency I am using is 0.2 MHz and assume alpha_power is 1.5, then alpha_coeff should be 223.6.</p> <p>The problem is that when I provide these values the whole simulation will blow up! Am I doing anything wrong at all?</p> <p>Your help will be highly appreciated. </p>