http://www.k-wave.org/forum/topic/surface-wave-between-two-media Support for the k-Wave MATLAB toolbox en-US Wed, 13 May 2026 09:02:44 +0000 http://bbpress.org/?v=1.0.2 q http://www.k-wave.org/forum/search.php http://www.k-wave.org/forum/topic/surface-wave-between-two-media#post-7462 Fri, 01 May 2020 09:14:50 +0000 Bradley Treeby 7462@http://www.k-wave.org/forum/ <p>Hi jinyoung,</p> <p>A few problems:</p> <p>- Your PML absorption is too high. Higher isn't always better as this can create a sharp absorption profile which causes reflections. I'd stick to the defaults.<br /> - Your plot scale is off. Try setting to the approximate value of the pressure by setting <code>&#39;PlotScale&#39;, [-1, 1] * Z</code>, where Z is the impedance in the medium where your source is located.<br /> - To increase speed, try and make your grid size have small prime factors. If you set <code>&#39;PMLSize&#39;, &#39;auto&#39;</code>, k-Wave will do this for you.<br /> - k-Wave can struggle with sharp impedance discontinuities between concrete and air. A work around is discussed in <a href="http://www.k-wave.org/forum/topic/simulation-of-ultrasonic-testing-borehole-in-solid#post-6473">this post</a>.</p> <p>Brad </p> http://www.k-wave.org/forum/topic/surface-wave-between-two-media#post-7434 Fri, 24 Apr 2020 11:13:00 +0000 jinyoung 7434@http://www.k-wave.org/forum/ <p>Hello,<br /> I'm trying to model a simulation to measure surface waves in two different media. At this time, a wave with strange straight line shape is generated in the unset position. what is this problem?<br /> Thank you.</p> <p>code:<br /> clear all;<br /> close all;<br /> clc;</p> <p>%% create the computational grid<br /> Nx = 300; % [grid points]<br /> Ny = 400; % [grid points]<br /> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%<br /> dx = 0.001; % [m] %% See changes.<br /> dy = 0.001; % [m] %% See changes.<br /> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%<br /> kgrid = makeGrid(Nx, dx, Ny, dy);</p> <p>%% define the compressional sound speed [m/s]<br /> medium.sound_speed_compression = 343*ones(Nx, Ny); % P-wave velocity of air<br /> medium.sound_speed_compression(200:300, :) = 4000; % P-wave velocity of concrete</p> <p>%% define the shear sound speed [m/s]<br /> medium.sound_speed_shear = 0*ones(Nx, Ny); % S-wave velocity of air<br /> medium.sound_speed_shear(200:300, :) = 2500; % S-wave velocity of concrete</p> <p>%% define the mass density [kg/m^3]<br /> medium.density = 1.2754*ones(Nx, Ny); % air density<br /> medium.density(200:300,:) = 2350; % concrete density</p> <p>%% define the absorption coefficients [dB/(MHz?2 cm)]<br /> % medium.alpha_coeff_compression = 0.9;<br /> % medium.alpha_coeff_shear = 0;</p> <p>%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%<br /> %%% Create the time array (Refer to Manual Page 31)<br /> kgrid.t_array = makeTime(kgrid, medium.sound_speed_compression, 0.1,10e-4); </p> <p>%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%</p> <p>% define u_mask<br /> source.u_mask = zeros(Nx,Ny);<br /> source.u_mask(160,70:100) = 1;<br /> source.u_mode = 'additive';</p> <p>%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%<br /> dt = kgrid.t_array(2)-kgrid.t_array(1) ; %[s] %%%%<br /> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%<br /> sampling_freq = 1/dt; % [Hz]<br /> tone_burst_freq = 5e4; % [Hz]<br /> tone_burst_cycles = 10;<br /> source.ux = 1*toneBurst(sampling_freq, tone_burst_freq, tone_burst_cycles);<br /> source.uy = 1*toneBurst(sampling_freq, tone_burst_freq, tone_burst_cycles);</p> <p>% define sensor<br /> sensor.mask = zeros(Nx, Ny);<br /> sensor.mask(160, 300:400) = 1;</p> <p>input_args = {'PlotPML', true, 'PMLInside', false, 'PMLSize', [40, 40], 'PMLAlpha',100, 'DataCast', 'single'};</p> <p>% run the simulation<br /> sensor_data = pstdElastic2D(kgrid, medium, source, sensor, input_args{:}); </p>