Latest Discussions - COMSOL Forums Most recent forum discussions Wed, 22 May 2019 14:25:05 +0000 COMSOL Forum: Latest Discussions Contraction of a cell on a gel <p>Hi!</p> <p>I created a 2D axisymmetrical model to examine the deformation of a (stem) cell on a (polyacrylamide) gel after contraction.</p> <p>In order to do so, I should define a prestress over a part of the cell (the cytoplasm). However, since the cytoplasm is made up of a hyperelastic Neo-Hookean material, it is not possible to define a prestress -I used "Initial stress"- in a way it is possible for a linear elastic material (also, when applying linear elastic materials, the model does only converge for a positive prestress, so radially outward, instead of radially inward as in a contraction).</p> <p>What could cause the model to not converge for a radially inward prestress?</p> <p>And is there any other way to define a prestress for a Hyperelastic Material, to imitate contraction?</p> <p>Thank you in advance!</p> Wed, 22 May 2019 14:25:05 +0000 4.2019-05-22 14:25:05.235881 Different S11 values for the same frequency <p>Hi all,</p> <p>I simulate a pin-fed patch antenna at 3.5 GHz. When I set Frequency to <strong>3.5&#91;GHz]</strong>, The S11 value is -28.474 dB. But if I enter <strong>range(3.3&#91;GHz],0.1&#91;GHz],3.7&#91;GHz])</strong> phrase into the frequencies text box. I get the following results, which is -23.569 dB at 3.5 GHz.</p> <pre><code>3.3000 -3.9214 3.4000 -8.0754 3.5000 -23.569 3.6000 -10.408 3.7000 -5.3938 </code></pre> <p>Why are two S11 values different at the same frequency (3.5 GHz) even I don't change anything else?</p> <p>Thanks.</p> Wed, 22 May 2019 09:50:48 +0000 4.2019-05-22 09:50:48.235751 Computing transmittance and reflectance of glass for different wavelengths <p>Hello everyone, I'm a beginner user of COMSOL, and I'm stuck on a little problem. I'm using the "<em>Electromagnetic Waves, Frequency Domain</em>" interface to model an incident wave on a smooth surface, in order to calculate the transmittance and the reflectance of an <strong>N-BK7 glass</strong>. I followed the instructions of the "Plasmonic Wire Grating" tutorial, but my purpose is to compute the aforementioned quantities for different wavelengths. For this reason, I don't want the <strong>refractive index</strong> of my material to be constant: it must vary with the wavelength. Therefore, I created an analytic expression for the real part of the refractive index (which I named "<em>n_NBK7</em>"), as well as an interpolation function for the imaginary one (which I named "<em>k_NBK7</em>"). As concerns the air above my sample, I did the same thing with the real component (naming the function "<em>n_air</em>"), while I set the extinction coefficient to 0. I took all these relations from this <a href="">link</a>. My questions are the following: <strong>1)</strong> In the study settings, I can make the wavelength sweep within the range of interest: how can I tell the software that the wavelength must be the <em>input variable</em> for my interpolation/analytic functions (i.e.: <em>n_NBK7</em>, <em>k_NBK7</em> and <em>n_air</em>)? <strong>2)</strong> In the <strong>Port boundary conditions</strong>, the ewfd interface needs to know the refractive index of the air (Port 1) and of the N-BK7 glass (Port 2), in order to compute the diffraction orders. Provided that I don't have a constant value for them (they depend on the wavelength), I want to <em>call</em> here the functions <em>n_air</em> and <em>n_NBK7</em>, respectively: is this feasible? Which is the correct syntax to do it? <strong>3)</strong> If I understood correctly, the software computes the number of <strong>diffraction orders</strong> as a function of three parameters: the angle of incidence, the refractive index of the material (in my case, the N-BK7 glass) and the wavelength itself. This means that, during the sweep study that I'd like to run, the software should be able to adjust the number of Ports in order to compute the different diffraction orders: I mean, without requiring me to click manually on the "<em>Compute Diffraction Orders</em>" button (provided that it is disabled while the solver is running!). Am I reasoning right? Is there a way to automate the computation of diffraction orders?</p> <p>Any help is very much appreciated! Thank you</p> <p><strong>PS</strong>: I'm going to attach the .mph file of my model, it could be useful to better understand my problem</p> Wed, 22 May 2019 08:50:15 +0000 4.2019-05-22 08:50:15.235741 How to Define Poisson Boltzmann equation in Cylindrical coordinates <p>Hi, I want to define poisson Boltzmann equation in cylindrical coordinates in comsol, can some one please help me. The equation is dsqrU/dRsqr + (1/R)*dU/dR + dsqr U/dZsqr = (kh)^2 * sinh(U)</p> Tue, 21 May 2019 16:18:50 +0000 4.2019-05-21 16:18:50.235721 Maximum concentration in the domain (transport of diluted species in Pouros Media) <p>I'm working on simulating a mass transfer in porous media. I am having difficulty setting the maximum concentration in the domain. The stream has a higher concentration that my domain can adsorb.</p> <p>Any help will be welcome!</p> <p>Att. Mirian</p> Tue, 21 May 2019 13:46:16 +0000 4.2019-05-21 13:46:16.235712 Deformation of an agar surface <p>Hello alll,</p> <p>I'm new to comsol and i am wanting to use it to model the deformation of a disk of agar by a small force being applied to the underside of the disk by a piece of plastic. The plastic is a square in shape and is smaller in diameter than the disk of agar.</p> <p>So far i've identified that i can set the material parameters for both the plastic and the agar and also that i can place them in space so that they are initally directly touching, with the plastic being below the agar and they are boith centered around x,y,z=0. I've also read about making the two structures into an assembly with contact regions (but i'm not sure exactly if this is needed for my simulation).</p> <p>I was wondering if anyone can help me with any advice about how to progress next with this simulation. I now need to input that 1. the square of plastic is moved in the postive z direction by 3mm as so the impose a force on the agar and deform it and 2. i need to put in boundary conditions so that the sides of the agar remain fixed at z=0 so that only the middle regions of the agar is moved by the square of plastic.</p> <p>Sorry if this all sounds a bit confusing and hopefully someone can help!</p> <p>Cheers</p> <p>Paul</p> Tue, 21 May 2019 11:59:55 +0000 4.2019-05-21 11:59:55.235701 Simulate voids in soil <p>Hi, I want to know if someone have already built a model of propagation of EM waves in soil. If yes how? Thanks for your answers!</p> Tue, 21 May 2019 10:41:51 +0000 4.2019-05-21 10:41:51.235692 2D FSI Failed to evaluate reaction forces <p>Hi I'm performing a microfluidic FSI: 4us analysis</p> <p>Error: Failed to evaluate reaction forces</p> <p>COMSOL version 5.3</p> <p>(See attached geometry and input)</p> <p>This is what comes out from my time dependent analysis of a layered vibrating membrane, with prescribed displacement of 0.5um, over a fluid chamber, following a rectangle wave. I'm using Generalized alpha solver, 0.001 relative tollerace +0.1 tolerance factor, fully coupled + Automatic Newton, strict time stepping:</p> <p>range(0,1e-7,7e-7)range(7.4e-7,1e-9,3.4e-6)range(3.5e-6,1e-8,4e-6)</p> <p>The error comes out after the first ramp, around 1.7 us ( i tried a lot of configurations, at most I reached 1.9 us).</p> <p>Any suggestions? Thanks in advance.</p> Tue, 21 May 2019 09:45:34 +0000 4.2019-05-21 09:45:34.235671 crash test for batteries <p>What is the equation to be used for solid mechanics module for crash test of batteries?</p> Tue, 21 May 2019 08:57:20 +0000 4.2019-05-21 08:57:20.235661 Element's Data <p>There are a simple duct and just laminar flow, Is it possible to extract the velocity of each element at outlet boundary in Time-dependent study at output times without using "excel", I mean using internal COMSOL's functions?</p> Tue, 21 May 2019 07:40:22 +0000 4.2019-05-21 07:40:22.235652 triboelectric pressure sensor. electrical fluid solid mechanic <p>Hi, I am currently working on the development of triboelectric pressure sensor. I am now facing with the simulation of the flowing of the fluid driviive by pressure, interaction of PDMS and my fluid, and lastly the physics that i had to applied on each boundaries. i had working on this for three month plus already and feeling quite exhausted. Anyone here can help me to solve my problem?</p> Tue, 21 May 2019 07:23:04 +0000 4.2019-05-21 07:23:04.235651 Effective thermal conductivity of alloy <p>Hi all,</p> <p>I am trying to model a thermal crystal made up of Si-Ge alloy and airholes in comsol 5.4, for which i am using linear elastic materials in solid mechanics module. I have already modeled the band structure of unit cell by applying floquet boundary conditions and eigen solver analysis. Now i want to find effective thermal conductivity v/s eigen frequency graph of alloy used in same geometry. As COMSOL solves the heat equation in each part of the geometry using its own thermal properties. How can i extract the effective properties?</p> <p>Thanks in advance</p> Tue, 21 May 2019 07:09:41 +0000 4.2019-05-21 07:09:41.235643 Selection of physics <p>What physics needs to be used to analyse the stress/strain experienced by a pipe due to fluid flow?</p> Tue, 21 May 2019 01:40:22 +0000 4.2019-05-21 01:40:22.235642 convective heat flux boundary condition <p>Hi,</p> <p>I'm confused by the result I got by using convective heat flux boundary condition. Hope I can find the answer here. Thanks a lot.</p> <p>I'm working on a time dependent heat transfer model, one of the boundaries is defined as convective heat flux, q0=h<em>(Text-T). Based on the definition of heat flux, q0=-k(dT/dx), I checked my result after running a few time steps. I plotted ht.q0 line graph along the boundary, as well as -material.k_iso</em>Tx along the boundary, they are not the same.</p> <p>I also plot integration(q0) and integration(-k*Tx) along the boundary with respect to time, they are getting closer as time, but I'm still confused about this, is it because my mesh is not good enough? I'm checking all these because I didn't get a good result for my model and trying to find out the reason.</p> <p>Really appreciate your help. Thanks a lot.</p> <p>Jing</p> Tue, 21 May 2019 01:31:58 +0000 4.2019-05-21 01:31:58.235632 How to use the result of each time-step as input to next time-step? <p>Basically this is how I would do it in hand calculation:</p> <p>T_out_0 = 22 [degC] %% Guessed initial value.</p> <p>%% at t=1:</p> <p>COP(1) = 5[1/K] * <strong>T_out_0</strong></p> <p>T_out(1) = T_avg_Domain(1) - COP(1)/7[1/K]</p> <p>%% at t=2:</p> <p>COP(2) = 5[1/K] * T_out(<strong>1</strong>)</p> <p>T_out(2) = T_avg_Domain(2) - COP(2)/7[1/K]</p> <p>and so on ..</p> <p>My problem is how to calculate COP from the <strong>previous</strong> T_out? When I define this in Variables node (As shown below), I got this warning: "circular variable dependencies".</p> <p>COP : 5[1/K] * T_out</p> <p>T_out : T_avg_Domain - COP/7[1/K]</p> Mon, 20 May 2019 20:06:26 +0000 4.2019-05-20 20:06:26.235612 How to simulate AC Multi-turn coil numeric <p>Hi,</p> <p>I want to simulate the result as changing inductace of coil in an active eddy current sensor with different material target. The Multi-turn coil numeric fuction is selected to simulate regtangular coil geometry. I use two steps in simulaiton; step1 Coil Geometry Analysis and step2 Frequency Domain. However, I cannot find the coil inductance parameter in results. There are only coil current and coil resistance DC.</p> <p>Can anyone guide me to solve this problem?</p> <p>Note that I follow the example of using Multi-turn coil numeric with Alternative Current in However, there is only DC simulation case in that example.</p> <p>Thank</p> Mon, 20 May 2019 17:09:33 +0000 4.2019-05-20 17:09:33.235601 How to set user defined Boundary Conditions in poisson equation <p>Hi, I want to define n ˙∇U = (e2/εε0kBT)σsh as my boundary condition in the Poisson boltzman equation, can some please guide me how to do this. Thank you.</p> Mon, 20 May 2019 16:26:01 +0000 4.2019-05-20 16:26:01.235591 Different results of S11 parameter for different mesh element sizes <p>Hi,</p> <p>I have achieved two very different S11 parameter plots for the same patch antenna simulation at "extremelly coars" and "normal" element sizes of mesh. I attached these two results as image files to this question. "normal" one is more similar to the measurement results. But how can I be sure which element size is enough for me. Because, the finer element sizes are very heavy for my computer.</p> <p>Thank you</p> Mon, 20 May 2019 12:04:25 +0000 4.2019-05-20 12:04:25.235581 How to apply frequency shift in acoustic module <p>Hi all, I am doing research in acoustics module on transducers.Please tell me how to apply frequency shift in acoustics module.</p> <p>Thank u.</p> Mon, 20 May 2019 09:14:48 +0000 4.2019-05-20 09:14:48.235561 Light propagation in waveguide <p><em>Can we simulate light propagation in plane tiO2/SiO2 waveguide on silicon substrate? Please help regarding the problem. Thank you.</em></p> Mon, 20 May 2019 08:34:10 +0000 4.2019-05-20 08:34:10.235551