http://www.k-wave.org/forum/topic/question-about-discrete-k-space-equation-for-particle-velocity-force-source Support for the k-Wave MATLAB toolbox en-US Wed, 13 May 2026 15:49:54 +0000 http://bbpress.org/?v=1.0.2 q http://www.k-wave.org/forum/search.php http://www.k-wave.org/forum/topic/question-about-discrete-k-space-equation-for-particle-velocity-force-source#post-6111 Wed, 23 Aug 2017 19:42:28 +0000 Bradley Treeby 6111@http://www.k-wave.org/forum/ <p>Hi MA_student92,</p> <p>As these factors are constant, the source is multiplied by them before reaching the time loop. You will find the relevant code inside the sub-script <code>kspaceFirstOrder_scaleSourceTerms.m</code>. </p> <p>Hope that helps,</p> <p>Brad. </p> http://www.k-wave.org/forum/topic/question-about-discrete-k-space-equation-for-particle-velocity-force-source#post-6103 Thu, 10 Aug 2017 10:16:36 +0000 MA_student92 6103@http://www.k-wave.org/forum/ <p>Hi,<br /> i'm trying to get a fundamental understanding of the k-space equation implementation and i have a question about the discrete particle velocity equation (2.17b) of the k-Wave User Manual. I do understand the equation except for the last term "dt*S_F" that includes the Force Source Term. I simulated the acoustic wave propagation with kspaceFirstOrder3D using a transducer object as source and sensor input. I took a close look to the implementation of the discrete equations and finally got to the point where the transducer input signal (defined as a velocity signal) is added to the calculated particle velocity of the next simulation time step.<br /> The Implementation of equation 2.17b is split into two parts: First the particle velocity components (ux_sgx and uy_sgy) of the staggered grid are calculated based on the momentum conservation function:</p> <p>ux_sgx = bsxfun(@times, pml_x_sgx, ...<br /> bsxfun(@times, pml_x_sgx, ux_sgx) ...<br /> - dt./ rho0_sgx .* real(ifft2( bsxfun(@times, ddx_k_shift_pos, kappa .* p_k) )) ...<br /> );</p> <p>(uy_sgy in an analogous manner)</p> <p>This corresponds to the first part of equation 2.17b. After that the input signal is added (after beamforming and apodization modification of the signal):</p> <p>ux_sgx(u_source_index) = ux_sgx(u_source_index) + transducer_transmit_apodization.*transducer_input_signal(delay_mask);</p> <p>My question is:<br /> Why is the Fource Source Term in equation 2.17b multiplied by the simulationstep dt? This factor isn't used in the implementation and i actually see no reason for this factor... Furthermore the Fource Source Term S_Fx is described further in equation (2.18): </p> <p>S_Fx = source.ux*2c0/dx; (where source.ux is the transducer input signal)</p> <p>This equation isn't implemented either?</p> <p>I hope you guys understand my questions and can help me with that problem. Maybe i just have a wrong view on the subject right now </p>