http://www.k-wave.org/forum/topic/simulating-ultrasonic-reflection-from-a-cylinder-liner-oil-piston-ring-system Support for the k-Wave MATLAB toolbox en-US Wed, 13 May 2026 05:21:22 +0000 http://bbpress.org/?v=1.0.2 q http://www.k-wave.org/forum/search.php http://www.k-wave.org/forum/topic/simulating-ultrasonic-reflection-from-a-cylinder-liner-oil-piston-ring-system#post-7949 Thu, 26 Nov 2020 12:55:08 +0000 Bradley Treeby 7949@http://www.k-wave.org/forum/ <p>I ran a scaled down version of your simulation and didn't spot anything obvious. Note, your source frequency is set to 1 MHz, not 5 MHz. Have you looked at the frequency dependent transmission / reflection coefficients in 1D for a three layered medium (you can find these in e.g., the ultrasound book by Cobbold)? There is a resonance behaviour depending on frequency that might be worth considering. </p> http://www.k-wave.org/forum/topic/simulating-ultrasonic-reflection-from-a-cylinder-liner-oil-piston-ring-system#post-7921 Thu, 12 Nov 2020 12:16:33 +0000 jo-rooke 7921@http://www.k-wave.org/forum/ <p>Hi, I have been using this toolbox for a few months and have had little problems although I am now a bit stuck. I have worked through the toolbox manual and I am still unsure. As I have had it working in the past, I feel like I am missing something obvious but I just can't figure it out.</p> <p>I am using the toolbox to simulate an ultrasonic transducer measuring the film thickness between a piston ring and cylinder liner, for example see the linked paper. (Piezoelectric sensors to monitor lubricant film thickness at piston–cylinder contacts in a fired engine, Mills 2012 <a href="https://www.researchgate.net/publication/258178367_Piezoelectric_sensors_to_monitor_lubricant_film_thickness_at_piston-cylinder_contacts_in_a_fired_engine)" rel="nofollow">https://www.researchgate.net/publication/258178367_Piezoelectric_sensors_to_monitor_lubricant_film_thickness_at_piston-cylinder_contacts_in_a_fired_engine)</a>. </p> <p>So this involves running the simulation a series of times whilst moving the "piston ring" across the domain. Within each simulation the transducer pulses a 5MHz wave, which then reflects from the far side of the liner and is recorded by the same transducer, see Figure 5 in the refered paper. The simulation runs ~1000 times for the piston ring to move across the domain, which is quite computationally expensive but I have access to a supercomputer and so that aspect isn't a problem.</p> <p>Previous simulations I have run have worked fine and produced results like those I expected, (a decrease in reflected signal for the piston ring being aligned with the transducer) although I noticed an error in my input signal, so the actual input was close to 100MHz instead of 5MHz. After correcting this, I have been getting incorrect trends in results, e.g. when the piston ring is over the transducer I am getting a greater reflection when I should be getting less. The only part of the code that has been changed is the input and I am struggling to figure out why this has led to this.</p> <p>Due to this I have a few questions that I am hoping you can help me with:<br /> 1. Is there any reason why this toolbox should not be able to simulate systems that have thin oil films in? (~up to 30um).<br /> 2. Is there any reason why changing the input frequency would cause might output to produce the opposite trend that it was previously producing?<br /> 3. From looking at my code, are there any clear alterations to improve my code? </p> <p>Hopefully I have explained myself clearly, if not please let me know and I will try to clarify myself. Thank you in advance for the help!</p> <p>Below is a copy of the code:</p> <pre><code>function [ascan_output] = TwoD_5_Test1mhz(input_argument) if(ischar(input_argument)) j = str2double(input_argument); end %Above this line is set up for the supercomputer %% % create the computational grid Nx = 2560; % number of grid points in the x (row) direction Ny = 2560; % number of grid points in the y (column) direction dx = 7.8125e-6; % grid point spacing in the x direction [m] dy = 7.8125e-6; % grid point spacing in the y direction [m] kgrid = kWaveGrid(Nx, dx, Ny, dy); A=zeros(2560, 2560); for i = 1:1888 A(i,:)=5000; end for i = 1889:2560 A(i,:)=781; end for k=j:j+511 A(1892:2560,k)=5000; end B=zeros(1280, 2560); for i = 1:1888 B(i,:)=7300; end for i = 1889:2560 B(i,:)=781; end for k=j:j+511 B(1892:2560,k)=7300; end %% % define the properties of the propagation medium based on above medium.sound_speed = A; % [m/s] medium.density = B; % [kg/m^3] medium.alpha_coeff = 2.56e-7; % [dB/(MHz^y cm)] medium.alpha_power = 1.1; %are these right?? t_end = 16e-6; % [s] kgrid.makeTime(medium.sound_speed, [], t_end); t_end = 16e-6; % define the source mask to be a line across the top of the grid source.p_mask = zeros(Nx, Ny); source.p_mask(100, 1024:1536) = 1; %I think the error must be arising from this, as this is the section that has changed? % define a tone burst and assign it to the x-direction particle velocity SampleFreq=1/kgrid.dt; source.p = toneBurst(SampleFreq,1e6, 5, &#39;Plot&#39;, true); %% % define a linear sensor along edge of grid sensor.mask = zeros(Nx, Ny); sensor.mask(100, 1024:1536) = 1; sensor.record={&#39;p&#39;, &#39;p_max&#39;, &#39;u&#39;}; % run the simulation with optional inputs for plotting the simulation % layout in addition to removing the PML from the display sensor_data = kspaceFirstOrder2D(kgrid, medium, source, sensor, ... &#39;PMLInside&#39;, true, &#39;PlotLayout&#39;, false, &#39;PlotPML&#39;, false,... &#39;PlotSim&#39;, false, &#39;DataCast&#39;, &#39;single&#39;); %gpuArray-single / single / double avddatap=mean(sensor_data.p); timelength=length(avddatap); time=(1:1:timelength); time=time*kgrid.dt; %Below this line is to only save important variables from each simulation %on supercomputer clearvars -except avddatap time j save(sprintf([&#39;TwoD_Test_5_1mhz-&#39;,num2str(j)], &#39;avddatap&#39;)); end</code></pre>