Latest Discussions - COMSOL Forums Most recent forum discussions Thu, 19 Jul 2018 09:53:43 +0000 COMSOL Forum: Latest Discussions Failed to find a solution for the initial parameter. Stystem Matrix is 0 <p>Hi Experts,</p> <p>I'm trying to simulate an acoustic structure interaction. It's 2 rooms ( cylindre ) seperated by a window, and i want to calculate the Sound Transmission Loss between these rooms.</p> <p>After setting up materials and B.Cs , i used triangular mesh, then i tried to launch the simulaion eventhough i have 3 warnings for the mesh ( as far as i know, the simulation cannot be influenced by warnings )</p> <p>When i try to compute i receive this error message : - - Feature: Stationary Solver 1 (sol1/s1) Failed to find a solution for the initial parameter. Segregated Step 1 System matrix is zero. In Segregated Step 1: Returned solution is not converged. Not all parameter steps returned.</p> <p>I'm new to the field, so i'm really sory if my question isnt clear enough,</p> <p>Thank you for your time,</p> <p>Yasser</p> Thu, 19 Jul 2018 09:53:43 +0000 4.2018-07-19 09:53:43.182822 Magnetic fields in 1D <p>Hi,</p> <p>I wanted to know if it is possible to add mangnetic fields to a 1D study.</p> Thu, 19 Jul 2018 02:41:10 +0000 4.2018-07-19 02:41:10.182803 Working with parameterized datasets <p>Hi all,</p> <p>I have a problem where I am trying to optimize a parameterized geometery. So for a large number of parameter settings I have COMSOL output datasets (e.g. x vs y datasets) and I need to analyze these datasets to evaluate the "goodness" of my geometery - for example extracting a resonance frequency and a Q-factor for each parameterized solution.</p> <p>I think I have two questions:</p> <p>1) How do I automatically export datasets to a file for each parameter sweep so I can evaluate them externally (using Excel, Python, etc.)</p> <p>or barring this,</p> <p>2) How do I evaluate these datasets internally to COMSOL?</p> Wed, 18 Jul 2018 22:54:58 +0000 4.2018-07-18 22:54:58.182802 Passing post processing result to another study <p>Hi,</p> <p>I was wondering if its possible to do some calculations to results from a study then pass those to another study and run that? More specifically, I want to calculate the inductance of a finite element model that acts like an inductor, then pass that inductance value to an circuit model containing just a normal inductor, and measure the current through that circuit. I can't integrate the model with the circuit physics because of the AC/DC physics I'm using doesn't lend itself nicely to that formulation.</p> <p>Instead, I'd like to calculate the inductance by integrating the magnetic energy density in the inductor and the total current going through the inductor, finding the inductance that way (think W=1/2<em>L</em>I^2). Then send those calculated values for the inductance (and also voltage) of the finite element model to a normal circuit study. Conceivably I could do this in two separate COMSOL applications, but I'd like to do it in the same application.</p> <p>Best, Henry</p> Wed, 18 Jul 2018 20:58:01 +0000 4.2018-07-18 20:58:01.182792 Cavity Eigenmodes not Returned <p>Hello, I've been browsing the forum for a while and it has been very helpful in the past but I cannot seem to find an answer to the problem I'm currently having. Inside of my microwave cavity I have two conducting surfaces that create a capacitance because of an electric field. In previous versions of my cavity without the conductive surfaces, I was able to find eigenmodes that I could confirm as accurate. However, once I added the two conducting surfaces I get the following error:</p> <p>Maximum number of Arnoldi iterations reached. Increase the dimension of the Krylov subspace. Not all eigenfrequencies returned.</p> <p>I am not entirely sure what any of that means because I am pretty new to using COMSOL. Also, saying "not all eigenfrequencies returned" to me means that there were some that were returned. Is that correct to assume? If so, which ones and are they accurate?</p> <p>Any help I can get to understand this error would be greatly appreciated.</p> Wed, 18 Jul 2018 20:33:33 +0000 4.2018-07-18 20:33:33.182782 Composite domains <p>Hi everybody, is it possible to compose domains which initially are distant each other, but then one moves towards the other? If not, anybody has some ideas on how to change boundaries conditions on a moving mesh? Thank you in advance!</p> Wed, 18 Jul 2018 14:50:26 +0000 4.2018-07-18 14:50:26.182781 Moving-Mesh <p>The below post is related to an <a href="//">archived discussion</a></p> <hr /> <p>[start here] Hi evreybody I need some examples about moving-mesh I want to apply it on my simulation for piezoelectric fan in electronic cooling ,, and can you advise me to sutible methods in my simulation I will be greatful thanks in advance</p> Wed, 18 Jul 2018 13:41:09 +0000 4.2018-07-18 13:41:09.182771 Modelling of potential field and redox reactions from electrodes in agar containing NaCl and Ferrocyanide(FCN) and pyocyanin(PCN) <p>Hello,</p> <p>As part of a student project, we are trying to model the potential field in a block agar. Four electrodes pierce into the agar, as can be seen in the uploaded model. The agar will contain NaCl at a concentration of 10mg/ml. The agar also contains FCN and PCN at defined concentrations. FCN and PCN oxidize and reduce and ultimately what we want to find out is the reduced/oxidised state of these molecules.</p> <p>We have done the modelling of the potential field from the electrodes but we now are having trouble at integrating: * Transport of diluted Na+ and Cl- ions in the agar * Redox reactions</p> <p>What modules should we use to solve these problems? Any help is very welcome.</p> Wed, 18 Jul 2018 11:35:52 +0000 4.2018-07-18 11:35:52.182761 Compressibility in Fluid-Structure Interaction <p>Hi Everyone,</p> <p>I am performing a simulation using the FSI interface in Comsol 5.3. In the settings of the FSI under the physical model where we select the compressibility option, there two options are listed: - Compressible (Ma&lt;0.3). - Incompressible.</p> <p>As far as I understand it should be the other way around (at least for air); incompressible for Mach numbers below 0.3, and compressible for Mach numbers above 0.3.</p> <p>I did a density plot, but since I was using water as fluid with relatively small velocity it wouldn't be of much help.</p> <p>Am I misunderstanding here or is this a mistake?</p> <p>Many Thanks,</p> Tue, 17 Jul 2018 21:07:58 +0000 4.2018-07-17 21:07:58.182742 Building Of Helical Fins On Circular Pipe <p>Hi, I want to build helical fins on circular pipe in COMSOL version 5.3. So ,i am facing a problem to generate SWEEP. Below i am attaching a typically JPG file. Please prvode me idea about this.</p> Tue, 17 Jul 2018 13:08:24 +0000 4.2018-07-17 13:08:24.182741 How can I edit boundaries in a moving mesh? <p>Hi everybody, I have got an expanding cylindrical domain and I want to create a hole at a certain length (in order to set pressure at 0 at that boundary), which is not present in the initial geometry. Any suggestions?</p> Tue, 17 Jul 2018 11:34:19 +0000 4.2018-07-17 11:34:19.182731 Heat and moisture transfer in building material <p>Hi, I have simulated a wall and floor (2D) under staitionary situation. results shows relative humidity of more than 100% in some part of my model! 1- is this relative humidity for material or for the air inside it? 2- how the amount of relative humidity goes over 100%? thanks</p> Tue, 17 Jul 2018 10:41:03 +0000 4.2018-07-17 10:41:03.182711 Sign convention in weak form pde expression <p>The below post is related to an <a href="//">archived discussion</a></p> <hr /> <p>Hi all,</p> <p>JM Buchot had earlier posted a model which solves for flow over cylinder using weak form PDE. Weak form expressions of Navier Stokes equations were given as input. But in the expressions he had used, I feel like the signs are reversed for second and third terms in x &amp; y momentum equations (First module in attached .mph file). I get convergence error when the signs are changed.</p> <p>The actual PDE are as shown in the below link, <img src="" alt="" /></p> <p>Please can someone clarify on this.</p> <p>With thanks &amp; regards, Alwar Samy R</p> Tue, 17 Jul 2018 09:56:29 +0000 4.2018-07-17 09:56:29.182701 Oblique incidence For Scattering of 2D cylinder <p>Dear all, I am simulating the scattering from a 2D PEC cylinder. The E field is along the z axis of the cylinder. Under normal incidence I write the background E field as follows.</p> <p>Ex=0 Ey=0 Ez=exp(1i<em>k0</em>x)</p> <p>For oblique incidence: Ex=sin (Φ) exp (1i<em>k0</em>(x cos (Φ)-z sin (Φ))) Ey=0 Ez= cos (Φ) exp (1i<em>k0</em>(x cos (Φ)-z sin (Φ)))</p> <p>z=0 Φ: Angle of incidence</p> <p>However the results that I am getting are wrong as for a PEC cylinder whatever be the incidence angle, the scattering must be that the. With the above descibed configurations, the results are different.</p> <p>Any suggestions would be of great help. Thanks</p> Tue, 17 Jul 2018 08:46:34 +0000 4.2018-07-17 08:46:34.182681 Charge discharge cycle for LFP cell thermal management <p>In comsol , for thermal management of battery it is running in charge and dischage cycles , but I want to just discharge the battery from some initial temperature . how it can be done in COMSOL 5.3</p> Tue, 17 Jul 2018 07:20:25 +0000 4.2018-07-17 07:20:25.182671 Import model domain selection <p>Hi, I am facing a problem in domain selection of import file .how can i select domain of import file accordinly. I imported a helical fin pipe .I want to select pipe and helical fins as a different things.</p> Tue, 17 Jul 2018 05:17:12 +0000 4.2018-07-17 05:17:12.182661 Dynamic tip bending <p>Hello,</p> <p>I have a circular tube that is approximately 150 mm long and the last 15 mm of the tube (the tip) will deflect 30 degrees to -30 degrees. I have a velocity inlet and a pressure outlet. I want to simulate a fluid flowing through the bending tip. The tip motion is to be defined from an external device and is not due to fluid forces. I would like to examine the effect of tip angle on the exit flow rate as well as examine the exit flow velocity distribution. I have attached a picture detailing how the tip will displace during one oscillation. The red dotted lines indicate where the bending will take place. I believe I would need to define a moving mesh with a prescribed deformation for the bending region. Any suggestions or advice on how I may go about this would be greatly appreciated. I am using COMSOL 5.3a.</p> <p>Regards, Will McKinney</p> Tue, 17 Jul 2018 04:58:45 +0000 4.2018-07-17 04:58:45.182652 Particle Tracing Will Not Let Me Select Inlet <p>Hi,</p> <p>I hope someone can help. When I run a computation, I get the message:</p> <p>The release or inlet features have no selection. Add a selection to at least one of the release or inlet features.</p> <p>When I attempt to add an inlet and specify a wall as the inlet, nothing happens. Is there something else I have to do beforehand? Thanks in advance.</p> Mon, 16 Jul 2018 19:28:47 +0000 4.2018-07-16 19:28:47.182642 How to set the integration variable <p>Hi, I build a model in electrostatics, AC/DC model. I define a angle named 'thita' in global definition which equals to atan(r/z) of the geometry. Now i have simulated the potential of geometry, and i want to calculate the dipole moment by using line integration. the expression of integration part includes the extention of potential I modelled and angle I defined. the expression is like Vsin(thita). My problem is, when I choose the line of what I want to integrate, what is the integration variable of the function(...dx, what x is). The equation I want to calculate is ∫Vsin(thita) d(thita). How can I set the thita as the integration variable</p> Mon, 16 Jul 2018 15:22:34 +0000 4.2018-07-16 15:22:34.182631 Model a closing mold <p>Hello, I want to optimize the cooling of a non-newtonian fluid while the mold is closing, so the fluid is beeing compressed. Can I model the closing mold? Or should I just model the compression with a not changing mold? how can I model such a continuous compression? Thanks in advance, Christian</p> Mon, 16 Jul 2018 11:01:38 +0000 4.2018-07-16 11:01:38.182611