Latest Discussions - COMSOL Forums Most recent forum discussions Sun, 17 Nov 2019 13:19:23 +0000 COMSOL Forum: Latest Discussions How to do add a constant magnetic field to a physical domain <p>I am a newcomer,and I want to ask how to add an upward magnetic field in the figure below ,Thank you</p> Sun, 17 Nov 2019 13:19:23 +0000 4.2019-11-17 13:19:23.246553 Postprocessing access to timespecific values <p>Hey there, I have a big issue with the following topic.</p> <p>I created an time dependent model which includes a few ODEs calculating the biochemical concentrations. I need a small step size to get adequat numerical values. Since I want to optimise some of my model parameters with matlab I try to generate a value to compare. There is already a STOP function implemented which stops the model if a concentration goes below a specific value.</p> <p>To generate the optimisation function I want to access the values of the concentrations in specific time points which are also dependend of the last time step of the simulation to compare those with manually imported datas.</p> <p>So is there a possibility to access ODE values at specific time points which are calculated with the time point of the end of the simulation?</p> <p>Thanks a lot!</p> Sun, 17 Nov 2019 11:58:14 +0000 4.2019-11-17 11:58:14.246551 Why the sound intensity "acpr.I_mag" in posting is nothing? <p>I used the comsol pressure acoustic interface to simulate an ultrasonic cleaner, but selected the sound intensity in the post-processing results, all areas are 0, why?</p> Sat, 16 Nov 2019 10:01:37 +0000 4.2019-11-16 10:01:37.246483 Applying constraint points for welding in assembly <p>I have searched info for welds, but only found info on modeling the welding process.</p> <p>I have a welded assembly for a water-cooled part, but not sure how to define constraints properly for the weld points. My goal is to simulate distortion from water pressure. My prior experience with AutoDesk Inventor is you could actually model the type of weld and weld material, but don't see this functionality here. If I added weld material in my Creo 5.0 assembly would that help?</p> <p>Frankly I would be happy with just getting the weld point constraints correct between the assembly components. Thanks. --m</p> Fri, 15 Nov 2019 15:55:25 +0000 4.2019-11-15 15:55:25.246462 Filling void space in assembly <p>I have a welded assembly that I have imported from Creo 5 that is a water-cooled part. I want to simulate the distortion from the internal space due to the water pressure. I've tried searching for this info without luck.</p> <p>Can I somehow fill this internal volume with a domain and apply a volume pressure constraint, or set the new domain to water and apply a pressure constraint? Or do I need to create a volume in Creo that represents the water cooling space and then assign material/constraints to it? Part of the reason I'm asking is I don't see how to select a domain that is internal to the assembly.</p> <p>Thanks. --m</p> Fri, 15 Nov 2019 15:45:56 +0000 4.2019-11-15 15:45:56.246452 Question About The Application Builder <p>Dear all,</p> <p>I am running a model about pm-motor with a 2D model. I want to change some parameters of the motor, for example, the air gap in the pm-motor. However, the model I import without the parameterization, while I defined the paramters in my model, I just use the size I need. After I changed the size in the picture. I press the button "plot Geometry", the Graphic with no changes. How can I make my model in a correct way. Does someone know about the application builder? Hope you share your idea with me.</p> <p>Regards</p> <p>Joey</p> Fri, 15 Nov 2019 13:39:03 +0000 4.2019-11-15 13:39:03.246443 weak form <p>whether the dweak form in comsol has been canceled, only the weak form can be set</p> Fri, 15 Nov 2019 10:12:07 +0000 4.2019-11-15 10:12:07.246433 Heat transfer surface to surface radiation <p>Hi, I've read the document provided for the topic Sun's Radiation Effect on Two Coolers Placed Under a Parasol at It has provide a formula " Tamb = Tavg+dT<em>cos(2</em>pi*(x-14)/24)." to define the ambient temperature for a simple 24 hour periodic sinusoidal distribution around an average temperature.</p> <p>May I know what is the theory behind the formula? why does it use x-14? Please help.</p> Fri, 15 Nov 2019 08:07:05 +0000 4.2019-11-15 08:07:05.246423 how to model spring with variable stiffness in tension and compression <p>Hi . I am working on buckling of beams resting on springs.I found the spring foundation node in beams but it enables a constant stiffness. But in my case the spring has stiffness 30N/m in tension and 100 N/m in compression. How may i model it? I tried the (force vs extension node but results do not converge) Can some one help out.</p> <p>Suresh kumar</p> Thu, 14 Nov 2019 14:40:01 +0000 4.2019-11-14 14:40:01.246401 Form union & form assembly = multiple geometries? <p>Hi,</p> <p>I am trying to use "form union" to some parts of my geometry, while I want to use "form assembly" to other parts of it. Is this possible within the same geometry, or one geometry can take only one of the two options? If that is the case, how do I create another geometry?</p> <p>Thanks in advance, Darko</p> Thu, 14 Nov 2019 09:43:05 +0000 4.2019-11-14 09:43:05.246371 Moving wall on outer boundary - specifying rotation <p>Hi everyone,</p> <p>I'm actually struggling to find out what's the proper way to model a 'moving wall' at a fluid-structure boundary that is in fact a rotational movement. For example, imagine a tubular geometry filled with a fluid, where the geometry is continuously rotating. The main physical effect here is the transmission of the boundary velocity to the fluid (resulting flow depending on fluid properties like viscosity).</p> <p>There are numerous examples that show this when demonstrating couette flow (but here only for planar boundaries with quasi-infinity movement directions) or when simulating rotating machinery (like stirrer elements within domains).</p> <p>I tried to start with the simplest case possible (after failing with ALE/FSI setups for this) imho: A fully filled geometry, describing the boundary movement on the wall property by checking "sliding wall". However, COMSOL expects cartesian velocity components here and as far as I can see, positional variables (to just work with cos/sin math) do not seem to be supported here, hence I don't know how to tell COMSOL about the continuous rpm speed.</p> <p>Note: I'm doing this in 3D space because I definitely will have to in the end (here I'm just trying to accomplish what I seem to misunderstand, however this model will be extended to phasefield within the geometry, thus symmetry will vanish)</p> <p>Thanks in advance!</p> Thu, 14 Nov 2019 08:25:18 +0000 4.2019-11-14 08:25:18.246361 COMSOL with matlab always stop looping <p>DERA All, I use COMSOL with matlab to run my model with a for-loop (change some parameters every time) . But, when the loop time achieved about 15, it will be ended, and says my computer's memory is not enough. What from where it ends, and after about 15 times loop, it comes again. And, the problem described by COMSOL is bellow:</p> <pre><code> Java exception occurred: Exception: com.comsol.util.exceptions.FlException: The following feature has encountered a problem Messages: 以下特征遇到问题: - 特征: 稳态求解器 1 (sol1/s1) 找不到解。 执行稀疏矩阵操作时内存不足。 返回的解不收敛。 没有返回所有参数步长。 Stack trace: at com.comsol.solver.SolverOperation.execute(SourceFile:284) at com.comsol.solver.SolverOperation.addError(SourceFile:442) at com.comsol.solver.SolverOperation.execute(SourceFile:292) at com.comsol.model.method.SolverSequenceMethod.doRun(SourceFile:2168) at com.comsol.model.method.SolverSequenceMethod.doRun(SourceFile:2710) at at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke( at sun.reflect.DelegatingMethodAccessorImpl.invoke( at java.lang.reflect.Method.invoke( at com.comsol.bridge.command.b.a(SourceFile:145) at at com.comsol.bridge.command.i.execute(SourceFile:45) at com.comsol.bridge.command.j.d(SourceFile:711) at com.comsol.bridge.command.j.a(SourceFile:699) at com.comsol.bridge.command.j$3.a(SourceFile:600) at com.comsol.bridge.command.j$ at at java.util.concurrent.ThreadPoolExecutor.runWorker( at java.util.concurrent.ThreadPoolExecutor$ at </code></pre> <p>Can somebody help me ? Thanks!</p> Thu, 14 Nov 2019 07:48:31 +0000 4.2019-11-14 07:48:31.246353 simulation of a reacting pipe <p>Hi friends I wanna simluate a pipe that contains a crude oil in it and we inject a high pressure air. Then they react and produce heat. But i dunno how to start, i will be happy if anyone could help me. It's an urgent project for me. Thanks you! It's my email for contact</p> Thu, 14 Nov 2019 07:26:40 +0000 4.2019-11-14 07:26:40.246351 rate coefficient import feature in plasma module?? <p>Hi,</p> <p>I was wondering how I can efficiently import a large rate coefficient data for gaseous species (including ions and neutral species). In plasma module, it seems that I can only specify each reactions manually one by one? For instance, I can easily import a large electron impact cross section data using 'cross section import' feature but I couldn't find an equivalent feature for reaction rate coefficients. I have more than 50 reactions I would like to include so I would like to avoid manaul data entry if possible. 'Chlorine global model' seems like a relevant sample model but the manual does not indicate whether import option is available for chemical reactions....</p> <p>I appreciate your comments!</p> Wed, 13 Nov 2019 19:41:34 +0000 4.2019-11-13 19:41:34.246322 Calculate impedance variation <p>Hi,</p> <p>I would like to calculate impedance variation on a specified boundary based on time dependent study. The way of finding the impedance variation is to calculate elecrtical potential variation and divided this results by terminal current. I am not sure this is the correct way and also model give singularity problem. The model was attached Can you please guide me regaridng that?</p> <p>Thank you in advance</p> <p>Enver</p> Wed, 13 Nov 2019 17:13:11 +0000 4.2019-11-13 17:13:11.246321 heat source location <p>I am modling moving laser heat source having guassian profile on flat plate of 5mm<em>3mm</em>200microns. I have two queries 1. I am getting moving laser sorce but it moving on corner of plate. However i want to move it on centre of plate. How to locate heat source for it. 2. As i want to implement guassian profile. For that i have defined heat flux as 2<em>(1-R)</em>P/A<em>exp(-2</em>r_focus^2/rad^2). which having guassian profile. however in function tab there is local/global guassian pulse availiable. I am cunfused which way is correct. If guassian function can be use than how to implement it.</p> <p>Thanks in advance. Have a great day ahead.</p> Wed, 13 Nov 2019 16:26:22 +0000 4.2019-11-13 16:26:22.246311 Boundary conditions don't seem to hold throughout simulation <p>Hello!</p> <p>I am currently working with the microfluidics module and using the laminar two phase flow, phase-field work. For my particular case, I want to use an outlet flow (e.g. 5 μL/min) while leaving the two inlets I have in the module at a certain pressure.</p> <p>My issue lies on the boundary condition. I computed the surface integral of the velocity at the outlet boundary and, whereas in the beginning there is not a significant difference in the theoretical value (the one I used as input) and the calculated one (i.e. the integral on COMSOL), but after some time, the calculation becomes around 4 times bigger than want I have inputed (refer to annex figure, it represents the relative difference between the two values).</p> <p>Does anyone have any suggestion to why this happens and how to make this right?</p> <p>Thanks in advance!!</p> Wed, 13 Nov 2019 14:59:10 +0000 4.2019-11-13 14:59:10.246301 How to input a field variable from matlab to comsol <p>I am doing a structual optimization, and I can not find a way to transfer the design variable (a field variable) to the comsol from matlab. Can someone shed a light on it, please!!!</p> Wed, 13 Nov 2019 14:57:23 +0000 4.2019-11-13 14:57:23.246293 transformer vibration <p>Now I need to simulate the acceleration of transformer winding, where can I find a reference case?</p> Wed, 13 Nov 2019 13:47:15 +0000 4.2019-11-13 13:47:15.246283 Failed to find consistent initial values. Singular matrix. Last time step is not converged. <p>I used partical tracing for fluid flow(fpt) and spf from Laminar flow to simulate my design, I set inlet(including velocity field) and outlet for spf and fpt and release number and walls. It always tells me Failed to find consistent initial values. Singular matrix. Last time step is not converged.</p> <p>Which step needs improvments?</p> <p>Thank you</p> Wed, 13 Nov 2019 13:21:11 +0000 4.2019-11-13 13:21:11.246281