Latest Discussions - COMSOL Forums Most recent forum discussions Sun, 17 Jan 2021 19:15:02 +0000 COMSOL Forum: Latest Discussions Using the last eigenfrequency of the parametric study in 'search eigenfrequencies around' <p>The below post is related to an <a href="//">archived discussion</a></p> <hr /> <p>[start here]I suppose my calculations og photonic bands odf a 2D photic crystal would benefit from using the previous eigenfrequency of the parametric study to find a band as an estimate for 'search eigenfrequencies around. The question was already put but 8 yeras ago (see archived discussion above). Is this possible in 5.6?</p> <p>Thank you Margarida</p> Sun, 17 Jan 2021 19:15:02 +0000 4.2021-01-17 19:15:02.276621 Magnetic gears <p>Hello dears I am working on magnetic gears. I kept seeing the errors, while simulating the study. I started with the axial gears with altering the design. Comsol teams have posted the study of axial magnetic gears. Link: I wanted to change the design, firstly started with changing the number of magnetic pole pairs. Comsol team created 5 pole pairs for high speed, 2 pole pairs for low speed rotor and 7 steel bars between the rotors. I have changed those numbers to 4 pole pairs for both rotors and 8 steel bars. Everything was ok, it worked. Then, I tried to change the topology of these magnets. The boundaries of the magnets have straight face, but for the new design it has changed, they are curved. First problem appeared when I tried to mesh it. It refused to mesh one of the boundaries, then I added "free tetraherdral" for the "remaining" and it solved my problem, BUt I guess, It should not be solved in such a way. Then when I try to simulate it and it gives me some problems. Screenshot is given</p> Sun, 17 Jan 2021 14:21:04 +0000 4.2021-01-17 14:21:04.276611 pressure outlets <p>edit: figured ut out</p> <p>I am trying to create an oscillating flow case . for as a start, i tried to create a simple 2D case with two pressure outlets. one with an oscillating pressure of 20,000 pascals and the other with a constent pressure of 0 (gauge). For some reason the 0 pressure outlet refueses to stay at 0 pascals.</p> <p>I am enclosing some screen shots of the first cycle- the first half is as i expected- the left part oscilates and the right is maintained at 0 pascals. however, in the second half of the cycle the pressure at the right outlet drops.</p> <p>the case is attached as well, and the boundary condition defintion. happy to supply any required information</p> Sun, 17 Jan 2021 09:41:42 +0000 4.2021-01-17 09:41:42.276601 Fluid not flowing through nozzle <p>I have modeled an electrolyte within a nozzle surrounded by air. I have also modeled a separate electrolyte domain (a meniscus) at the outlet of the nozzle. The meniscus was drawn on a work plane and then revolved to make a 3D part, Basically, the fluid should diffuse at the meniscus / air interface and generate a convective flux within the electrolyte.</p> <p>I have defined all the necessary boundary conditions for laminar flow / transport of diluted species. However, the fluid is not flowing as when I plot the velocity it is zero throughout the nozzle.</p> <p>What could the issue be? This is a 3D model by the way. I have modeled the same system in 2D and 2D axisymmetric and obtain accurare results.</p> Sat, 16 Jan 2021 20:44:14 +0000 4.2021-01-16 20:44:14.276582 Plot of NormE <p>Hello. I am new at comsol. I am trying a very simple simulation. I want to see the propagation of the plane wave(TE polarized) in air medium at various incident angles. So when I model the problem, I am facing a problem while plotting the normE. The component of the electric field gives the expected result( wave like paatern) while normE looks a bit strange. Also the pattern of normE changes with change in inident angle. So can you help me understanding this behaviour. Why the normE is not appeared as a wave in the figures while the electric field appered as a wave. Here I am attaching the line plots for both norE and one of field componet and also .mph file for my model. Thank you. <img src="https://" alt="" /> <img src="https://" alt="" /></p> Sat, 16 Jan 2021 18:10:21 +0000 4.2021-01-16 18:10:21.276581 Sparging- Bubbly flow - Bubble composition <p>Hi all</p> <p>I'm trying to simultate sparging using bubbles with a certain vol% CO2 (80 vol% N2, 20 vol% CO2 for example).</p> <p>I found a really good example ( but I understand the example uses 100 % CO2. How can I change the composition od the bubble?</p> <p>Thank you beforehand</p> Sat, 16 Jan 2021 16:21:16 +0000 4.2021-01-16 16:21:16.276571 Droplet in microchannel: Nonlinear solver did not converge <p>I am simulating a droplet flow in a microchannel using ALE moving mesh module. But it always comes with 'No convergence, even when using the minimum damping factor' and 'Failed to find consistent initial values.' I have tried different solvers, e.g direct, segerated, fully coupled, and I also using a step function at the inlet to aviod suddent change in flow field. But all of these attampts turn out to be failures. Someone could help me?</p> Sat, 16 Jan 2021 00:49:49 +0000 4.2021-01-16 00:49:49.276563 How to plot a power-temperature curve in COMSOL <p>I did a microwave heating simulation to get the temperature distribution cloud diagram of the model under a certain power condition. Now I want to plot the change of the maximum temperature at different power levels. How can I achieve this,thanks!</p> Sat, 16 Jan 2021 00:24:16 +0000 4.2021-01-16 00:24:16.276553 can't reproduce the capacitance value of the submarine cable example <p>Hi,</p> <p>I am trying to reproduce the following Comsol example on submarine cable simulation: Specifically, I am working on the models.acdc.submarine_cable_02_capacitive_effects example in the tutorial series. Because my Comsol version is 5.1, I can't open the example .mph file, so I am trying to make the model myself in Comsol 5.1 following the tutorial ( I followed most of the steps in the tutorial, but since in comsol 5.1 there is no "terminal" domain condition, I used "terminal" boundary condition on one surface of the conductors. By far I am able to reproduce most of the results in the example. But somehow, when I use global evaluation to calculate the capacitance value of the three phases , the results (0.13, 2.1, 1.1 uF/km) are totally different from the example (0.14 uF/km). I attached my model in this post, can anyone help me to have a look and tell me why the capacitance I calculated for each phases are different from each other, and why they are not close to the tutorial?</p> Fri, 15 Jan 2021 17:42:02 +0000 4.2021-01-15 17:42:02.276551 How to add point loads on an irregular surface? <p>I have scanned a geometry and now want to simulate the 3 or 4 points flexural test on it (See the image) <img src="" alt=" " /> I am still working on how to import the file correctly into COMSOL (It shows some wired edges on the geometry!). Let's say I can figure that out!</p> <p>How can I add point loads on an irregular surface while I don't have any vertex/point on that specific spot on the geometry? <img src="" alt="" /></p> Fri, 15 Jan 2021 16:39:36 +0000 4.2021-01-15 16:39:36.276542 2D laminar flow: use shallow channel approximation <p>At the moment I do laminar flow simulations in 2D. I was wondering, if the shallow channel approximation is useful for me. The Navier-Stokes equation from laminar flow to laminar flow with shallow channel approximation differs by the summand "-12viscosity(kinematic)velocity vector/diameter^2". The diameter indicates the channel height. I didn't found any further documentations about this shallow channel approximation in the comsol documentations, blog etc. The additional term obviously takes the channel height into account, while the simple 2D laminar flow does not. But where does the term come from? What geometrical properties the geomery should be fullfilled to use the shallow channel approximation (aspect ratio or length scale µm or mm)? Thank you for your help!</p> Fri, 15 Jan 2021 14:08:33 +0000 4.2021-01-15 14:08:33.276541 Entities needing a material <p>The below post is related to an <a href="//">archived discussion</a></p> <hr /> <p>I have a silicon wafer with a nickel nanostructure on top of it. I have assigned the material accordingly and still for the top and bottom surface, there is an error of Entities needing a material. I have tried closing and reopening. Didn't work!. Can anyone help me with this issue?</p> <p>I m attaching the .mph file.</p> Fri, 15 Jan 2021 06:12:10 +0000 4.2021-01-15 06:12:10.276521 remanent flux density vs surface flux density. <p>I want to design a permanent magnet. On the comsol, the remanent flux density is the value to input the intrinsic value of the actual permanent magnet. However, I can check the surface flux density through the actual measured results. Therefore, I would like to ask if it is correct to make the actual measured surface magnetic flux density value by adjusting the residual magnetic flux density.</p> Fri, 15 Jan 2021 03:33:22 +0000 4.2021-01-15 03:33:22.276513 Saving data before completion and if statement in time dependent step? <p>I keep getting Comsol errors but still want to see and analyze the data before the crash is there some way for me to do this? Would it be possible to put a stop condition in the time dependent stop and not just solve for a final stop time? I am using the battery module and need the model to stop if the voltage gets too high or too low as it crashes the model. I have tried multiplying my stop time by <em>(phis&lt;0.7)</em>(phis>4.8) where phis is the cell potential but it doesnt read the variable. I am running a parameter estimation step with this so its kind of a necessity i do this auto not manual.</p> Fri, 15 Jan 2021 02:46:14 +0000 4.2021-01-15 02:46:14.276512 2D axial symmetry - remeshing due to prescribed displacement fails close to axis? <p>Hello everyone,</p> <p><strong>Short version:</strong> FSI 2D axially symmetric time-dependent simulation with solid moving along symmetry axis fails presumably because of remeshing failure on the solid-liquid boundary close to the symmetry axis. <strong>See image for full explanation.</strong></p> <p><strong>Long version:</strong> I am doing a fluid-solid interaction simulation. It is an axially symmetric 3D simulation, where a solid plate moves parallel to the symmetry axis within a pipe filled with fluid. I am using a prescribed displacement for the moving solid domain and all its edges/vertices, and a deforming Yeon mesh to accomodate for the distortion of the fluid with automatic remeshing. The solid moves fine, but the simulation fails because there is an inversion on the solid-fluid boundary close to the axis symmetry. I tried several conditions, but I am showing you a clear example where no matter how sensitive to distortion the remeshing is, the simulation fails. The less sensitive simulation shows the inversion issue very well.</p> <p>Any suggestions? Is what I am trying to do not possible on comsol? Thank you very much for your help!</p> <p>Christos</p> Fri, 15 Jan 2021 01:38:32 +0000 4.2021-01-15 01:38:32.276502 How to do definite integral of user defined function <p>Hi Everyone,</p> <p>I am new to comsol (version 4.2) and running into a problem: I defined a global function called generic_pulse_shape_func and I'm trying to evaluate the definite integral of this function (from t=0 to t=50E-9 seconds) and set the value as a global parameter. In global parameters I type in this:</p> <p>integrate(generic_pulse_shape_func(t),t,0,50E-9)</p> <p>but the result is not calculated and the text I typed apears orange with a warning: "Unexpected unit of input". Can anyone help me figure out what is going on or how to get around this problem?</p> <p>Thank you!</p> Thu, 14 Jan 2021 19:50:33 +0000 4.2021-01-14 19:50:33.276492 laminar flow <p>Hello I am trying to run my comsol program for transport of diluted species and I cannot choose laminar flow in Brinkman equation. Does anyone has any suggestions?</p> Thu, 14 Jan 2021 18:35:55 +0000 4.2021-01-14 18:35:55.276482 One dimension heat transfer model <p>Hi everyone, I am trying to simulate a 1D heat transfer model but my output seems different from I expected. I don't why I got a straight line as my output. Can someone explain the adjustment I need to make? I have attached the images of what I got and what I am expecting. Thank you.</p> Thu, 14 Jan 2021 15:44:23 +0000 4.2021-01-14 15:44:23.276472 How do I extract the external impedance of a piezo device? <p>I've simulated a piezoelectric device that is actuated by a boundary load and frequency of 10 Hz. I need to extract the external impedance seen by the disk. How do I go about this? Thanks.</p> Thu, 14 Jan 2021 15:17:59 +0000 4.2021-01-14 15:17:59.276471 How do I add edges to the circumference of a disk? <p>Basically I've modelled a tiny piezo disk and I need to provide in-plane stress and I'm doing that by making one boundary a fixed constraint and providing boundary load to the opposite boundary. Using the cylinder, I already got 4 edges along the circumference but this makes the boundaries too large. Can I create new edges somehow? I tried virtual operations but couldn't do it that way. I'd appreciate any help. Thanks!</p> Thu, 14 Jan 2021 15:14:56 +0000 4.2021-01-14 15:14:56.276461