http://www.k-wave.org/forum/topic/dirichlet-condition-doesnt-work-as-expected Support for the k-Wave MATLAB toolbox en-US Wed, 13 May 2026 05:18:52 +0000 http://bbpress.org/?v=1.0.2 q http://www.k-wave.org/forum/search.php http://www.k-wave.org/forum/topic/dirichlet-condition-doesnt-work-as-expected#post-7212 Tue, 11 Feb 2020 12:00:44 +0000 Bradley Treeby 7212@http://www.k-wave.org/forum/ <p>Hi grabka,</p> <p>I haven't quite managed to get to the bottom of your problem yet. First, I don't think you're plotting the same point. So I changed <code>sensor.mask = source.u_mask;</code> and then plotted</p> <p><code>plot(kgrid.t_array, sensor_data.uz(1,:), kgrid.t_array, source.uz(1,:))</code></p> <p>If you set the shear sound speed to zero, everything works as expected. However, when the shear speed is non-zero, the input and output don't agree. I'll keep digging and come back to you. </p> <p>Brad. </p> http://www.k-wave.org/forum/topic/dirichlet-condition-doesnt-work-as-expected#post-7133 Thu, 21 Nov 2019 23:31:11 +0000 grabka 7133@http://www.k-wave.org/forum/ <p>Hello.<br /> I have set up a simulation with homogeneous viscoelastic material and excite by a Velocity Gauss impulse in the middle. I have noticed that the velocities at the source positions are not equal to the defined ones, although I have defined dirichlet conditions. Why is that?</p> <p>In the manual it states: ‘dirichlet’: at each time step, the input pressure and velocity values are used to replace the existing values</p> <p>Here my code:</p> <pre><code>%% variables f_max = 300; %[Hz] %% create the computational grid spacing = 5e-3; x_size = 0.15; %[m] total size x-direction y_size = 0.15; %[m] total size y-direction z_size = 0.014; %[m] total size z-direction dx = spacing; % grid point spacing in the x direction [m] dy = spacing; % grid point spacing in the y direction [m] dz = spacing; % grid point spacing in the z direction [m] Nx = ceil(x_size/dx)+2; % number of grid points in the x direction Ny = ceil(y_size/dy)+2; % number of grid points in the y direction Nz = ceil(z_size/dz)+2 % number of grid points in the z direction disp(&#39;Number of grid points: &#39;); disp(Nx*Ny*Nz); kgrid = kWaveGrid(Nx, dx, Ny, dy, Nz, dz); %% simulation time and step size dt = 0.1 * spacing / 1440.3; % CFL*dx/c_max CFL 0.3 default t_end = 0.5/300; % [s] kgrid.t_array = 0:dt:t_end; %% define the properties of the propagation medium medium.sound_speed_compression = ones(Nx,Ny,Nz) * 1440.3; % [m/s] medium.sound_speed_shear = ones(Nx,Ny,Nz) * 201.74; % [m/s] medium.alpha_coeff_compression = ones(Nx,Ny,Nz) * 0.5; % [10–3 m–1] medium.alpha_coeff_shear = ones(Nx,Ny,Nz) * 0.5; % [10–3 m–1] medium.density = ones(Nx,Ny,Nz) * 923.47; % [kg/m^3] %% define the source % define a square source element source_radius = 0.005/dx; % [grid points] source.u_mask = zeros(Nx,Ny,Nz); source.u_mask(Nx/2 - source_radius:Nx/2 + source_radius, Ny/2 - source_radius:Ny/2 + source_radius, Nz) = 1; nbr_of_sources = sum(source.u_mask,&quot;all&quot;); % define a gaussian impulse pos = gaussmf(kgrid.t_array, [t_end/20 t_end/6]); vel_gaussian = [0 diff(pos)/dt]; source.uz = repelem(vel_gaussian,nbr_of_sources, 1); source.u_mode= &#39;dirichlet&#39;; %% define sensor sensor.mask = ones(Nx, Ny, Nz); %% run the simulation sensor.record = {&#39;u&#39;} % u particle velocity PML_size=5; % size of the PML in grid points input_args = {&#39;PMLSize&#39;, PML_size, &#39;PlotPML&#39;, true, &#39;PMLInside&#39;, false}; sensor_data = pstdElastic3D(kgrid, medium, source, sensor, input_args{:});</code></pre> <p>plotting the input vs ouput at sensor position gives different plots:<br /> plot(kgrid.t_array, sensor_data.uz(4659,:), kgrid.t_array, source.uz(1,:)) </p>