Latest Discussions - COMSOL Forums Most recent forum discussions Wed, 30 Sep 2020 23:26:32 +0000 COMSOL Forum: Latest Discussions How to know if your model is going to fail during study? <p>Realistically, how long should you wait before throwing in the towel?</p> <p>I'm currently trying to model a 3D parallel plane plasma discharge, my dof is around ~130k after playing with the meshing parameters. Sometimes the model takes up to 4-6 hours on a 32 gb ram rig just to give me an error on convergence. Is there a sort of intuition behind knowing when to give up and cancel?</p> <p>Can you tell if your model is going to fail by looking at the convergence plot? (I've attached mine below). The reciprocal step size oscillates downwards, but then shoots up after ~500 timesteps, from your experience is that a precursor to the model failing to converge or is that normal?</p> Wed, 30 Sep 2020 23:26:32 +0000 4.2020-09-30 23:26:32.269872 PML is reflecting acoustic wave <p>Hello everyone,</p> <p>PML is not absorbing acoustic waves and it's causing some unphysical reflections, is there any experienced guy with perfectly matched layer here? I'm trying to compute scattered wave off an abject which is put in a background standing wave.</p> <p>Kind regards Jason</p> Wed, 30 Sep 2020 17:38:58 +0000 4.2020-09-30 17:38:58.269861 simulation parameters <p>Hi,</p> <p>I am simulating a model in which a current is injected at a time t=1000 seconds. The parameter varied in each of my simulation is the injected current. Therefore in each cases, the results are same for t=1 to 1000 and the changes will be noticed only after 1000 seconds.</p> <p>In these cases I am not interested in the results from 1-1000 each time I simulate and it is consuming 3-4 hours in each simulation .</p> <p>So, is it possible that I can save a simulation file till 1000 seconds and simulate from t>1000 every time ?</p> <p>Thank you</p> Tue, 29 Sep 2020 15:16:56 +0000 4.2020-09-29 15:16:56.269842 Out of memory_Quartz crystal microbalance <p>Hi all, I am trying to design a quartz cyrstal microbalance(QCM) which consists of a 25.4mm diameter of quartz and 0.333mm thickness and gold electrodes thickness 0.0001mm.</p> <p>I am trying to find out the change of resonant frequency of QCM by changing the liquid on the top of QCM. Liquids should be water and glycerol and I want to compare those results from air, which means empty.</p> <p>The below example is that I followed for my goal since it's the first time dealing with this software so I need to follow the similar one.</p> <p>The file is too large so out of memory is shown. I am not sure that the attached file is going on a right direction. Is there anybody who helps me to see if it is correct to get my final goal and if the file is correct, is there any solutions to reduce the memory in this file? I have a lot of problem on mesh actually. If you can suggest mesh, please give me advice on that.. it is really tricky.</p> <p>I have attached the file with deleted mesh and solution since the file is too large. I put the error on the solution here.</p> <p>Thank you a lot for reading and if you have hard time understanding my problem, please reply to me.</p> Tue, 29 Sep 2020 15:06:54 +0000 4.2020-09-29 15:06:54.269832 Creating a set of points at once <p>Hi,</p> <p>I want to create a geometry with number of points in 3-D space. When I try to add point, I get an option to enter x,y,z coordinates but for a single point. How to do it for a large number of points at once?</p> <p>Regards</p> <p>Poorvank</p> Tue, 29 Sep 2020 14:29:24 +0000 4.2020-09-29 14:29:24.269831 Monitoring dependent variables residuals while solving <p>The below post is related to an <a href="//">archived discussion</a></p> <hr /> <p>[start here]</p> <p>Hello everyone,</p> <p>I'm referring to this old post beacuse I had the same problem. I solved it partially, as I managed to plot the error vs iterations during my time-dependent computation: I found that, if you go under Study -> Solver Configurations -> Solution1 -> Time-Dependent Solver -> Advanced and you choose the option "Detailed" in the "Solver Log" menu, Comsol will display two convergence plots, one showing the reciprocal of step size vs time step, and another showing the error vs the iterations. Of course, to make the above setting visible, you first have to right-click on your Study and hit the "Show default solver" button.</p> <p>However, I still have some questions:</p> <p>1) How is defined the Error showed by Comsol in the convergence plot? Does it correspond to the global residual of the modeling equations?</p> <p>2) How Comsol scale residuals? Can I customize the way residuals are scaled and normalized? (for example, I'd like to scale the residuals with the highest calculated residual after N iterations)</p> <p>3) How can I plot the scaled residuals of each variable during the solving process, instead of the global residual?</p> <p>Many thanks to anybody who can provide some help, I'd really appreciate it. Kind regards</p> Tue, 29 Sep 2020 10:35:44 +0000 4.2020-09-29 10:35:44.269821 Standing Acoustic Wave thermoviscous acoustics PML boundary <p>Hello comsol community,</p> <p>I have a thermoacoustic model surrounded by PML in which I desire to have a standing wave but I haven't found any way to do that. I solved another model without PML and used its field as background field in model surrounded with pml but it doesn't yield correct field. I want to calculate scattered wave off an abject in this standing wave.</p> <p>Kind regards Jason</p> Tue, 29 Sep 2020 09:14:36 +0000 4.2020-09-29 09:14:36.269811 Axial stress on both sides of plate <p>Hi, I am solving problem for tensile stress in plate in which natural frequency changes by applying stress along x-axis on both sides of plate.</p> <p>I am giving floquet periodicity on both sides of x-axis and giving boundary loads on both sides of x-axis in terms of total force. When I compute eigenfrequency analysis it gives me error.</p> <p>If I fix 1 side of plate for constraints then problem changes because I want stress on both sides. Suggest me how to how to solve such kind of problem. Thanks.</p> Tue, 29 Sep 2020 05:20:00 +0000 4.2020-09-29 05:20:00.269801 Inlet and outlet boundaries - Concentric cylinders <p>Hello all,</p> <p>I have two concentri cylinder with two gases flowing in each cylinder. I was able to specify the inlet boundary conditions for both of the cylinders but I wasn't able to specify outlet conditions for the inner cylinder (says not applicable). I looked at the solution after solving and didn't see any out flow from the inner cylinder. Thanks for reading! Any suggestions are appreciated!</p> Tue, 29 Sep 2020 04:47:32 +0000 4.2020-09-29 04:47:32.269792 Droplet solidification <p>Hello I need to simulate falling and impact of a molten aluminum micro-droplet on a steel substrate and its solidification. Could you help me what physics I need you use? Any other help is appreciated too. Thank you.</p> Mon, 28 Sep 2020 15:37:38 +0000 4.2020-09-28 15:37:38.269791 Surface to surface radiation <p>Surface to surface radition between 2 plates. When radiosity is calculated multiple interreflection between the plate is taken into account or only one reflection? It is not crear from manual. Thanks, Vladimir</p> Mon, 28 Sep 2020 15:13:43 +0000 4.2020-09-28 15:13:43.269782 Phase field with mesh refinement methods <p>Hi, I analyze pitting corrosion in stainless steels using primary current distribution and phase field. I don’t know whether I should combine adaptive mesh refinement or automatic remeshing with phase field in order to capture the expansion pattern of the pit or phase field itself can do this. I have used adaptive mesh refinement with phase field but the results were exactly the same as using just the phase field. Any comment is very much appreciated. Best. Vahid</p> Mon, 28 Sep 2020 09:43:23 +0000 4.2020-09-28 09:43:23.269721 DC resistivity method <p>I want to learn about the DC resistivity method, but I don’t know how to set the excitation electrode (copper rod) and observe the potential of the measurement electrode?</p> Mon, 28 Sep 2020 08:55:09 +0000 4.2020-09-28 08:55:09.269713 Oxidation reaction——Exothermic <p>Hi everyone I am learning a model of the exothermic heat of oxidation in porous media,I have encountered some problems。The article does not mention how to add exothermic reactions to the heat transfer interface Thank you so much!</p> Mon, 28 Sep 2020 03:36:02 +0000 4.2020-09-28 03:36:02.269703 RF module frequency <p>When setting the frequency in the RF module electromagnetics model (frequency domain) what is this frequency being applied to? I know this can be set either in the solver or the physics node in the model tree. I have a background field that I am trying to model on a cube with periodic boundary conditions, and therefore no applied field boundary conditions that would excite the model. It does not appear as though its able to solve a model in the frequency domain without applied boundary excitation. Does the specified frequency not get applied to the background field?</p> Mon, 28 Sep 2020 03:23:32 +0000 4.2020-09-28 03:23:32.269702 composite material under compression <p>I want to calculate the buckling wavelength of a layer of a two-dimensional composite material under compression. Are there any examples that I can refer to?</p> Mon, 28 Sep 2020 01:46:49 +0000 4.2020-09-28 01:46:49.269693 using variable of one component in another component <p>Hello guys,</p> <p>I have a model made up of two components, I want to use a variable solved in one component as a background field in the second component but I don't know how to do that. used comp1.something but it doesn't work, also I defined a global variable to hold variable of comp1.something but it doesn't work either. Someone said use " general extrusion " but I don't think that's the case.</p> <p>Kind regards Jason</p> Sun, 27 Sep 2020 17:50:54 +0000 4.2020-09-27 17:50:54.269691 Time dependent study of multiturn coil <p>Hi, I am a new user of Comsol Multiphysics. I want to study the time dependent response of two multiturn coils of finite dimension and In each coil the mangnitude of current is same but has a phase difference of 90 degree. I want to visualize the rotating field. I am not being able to perform the simulation.Can anyone help me?</p> Sun, 27 Sep 2020 15:56:28 +0000 4.2020-09-27 15:56:28.269671 What does an illegal domain selection error mean? <p>I am trying to simulate the electro osmotic ion and fluid transport through a nanopore fuctionalized by Polyelectrolyte Brushes. I am working with cartesian co-ordinates. I am using Creeping Flow, Transport of Diluted Species and Electrostatics physics in my model. The mesh is coarser and when I compute it I get an error which states:- "Error in multiphysics compilation. Illegal domain selection. -Pair: ap1" I am using version 5.5. This is the link to the model if you want to have a look:</p> <p>P.S. I am kinda new to this software so I'll be glad if you all could help me out. Thank You.</p> Sun, 27 Sep 2020 15:17:29 +0000 4.2020-09-27 15:17:29.269661 How can I couple x-coordinates with y-z coordinates in COMSOL 5.5 version? <p>Hi, I want to couple x-coordinates with y-z coordinates so that the shape of the whole plate looks same movement. For example, if cross-section of the plate i.e. y-z axis shows deflection then throughout x-axis it shows same deflection because all x coordinates will be linked with that cross-section. I have attached images below in which you can see deflection changing with the change of x-axis that I don't want. I am using small x dimension for less computation time.</p> <p>Thanks in advance.</p> Sun, 27 Sep 2020 07:35:24 +0000 4.2020-09-27 07:35:24.269643