Latest Discussions - COMSOL Forums Most recent forum discussions Mon, 16 Jul 2018 19:28:47 +0000 COMSOL Forum: Latest Discussions 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 Simple plate acoustic radiation issues <p>Hi, I am struggling with the simulation results from a model which considers a 0.5x0.4 m^2 aluminium plate (with 0.004 m thickness). In particular, I am performing an eigenfrequency study through a pure FEM simulation. The plate is therefore sourrounded by a sphere with a spherical wave radiation condition. My issues are the following: -Imaginary part in the eigenfrequency computed values. Some eigenfrequenciers show an imaginary part. I understand that this come from some sort of damping which comes from considering the energy loss caused by the radiation of the sphere. What bothers me is that some frequencies remain purely real, and that there seems to be no logic in the mixture of real and complex frequency values. -Strange results for some eigenfrequencies. Some eigenfrequencies produce a completely unexpected (irregular) mode shape, associated with an unreal acoustic pressure fields which is zero above the plate and increases towards the sphere boundaries. - Different simulated modal shapes between a pure mechanical study and a coupled mechanical acoustics study. In the first case I am able to obtain only some of the frequencies I can obtain from the complete acoustic coupled system. I would expect some differences because of air coupling, but the coupled system find way more mode shapes than the pure mechanical study. I need to find which modes are correct and which are not, as I need to collect the correct shapes outside of comsol. I attach the model with the two studies for better understanding. Thank you to anyone would help me figuring out what is going on.</p> <p>Riccardo</p> Mon, 16 Jul 2018 08:41:18 +0000 4.2018-07-16 08:41:18.182591 Periodic structure with oblique incidenting circular polarized light <p>Dear All, I am writing to you all for help. These days i have been simulating a 3-D model of a periodic structure with oblique incidenting circular polarized light. But I have encountered some problems that have been solved for a long time. I want to define a circular polarized light with an angle of theta between the k and z axes, and k is on the z-x plane, that is the polar angle theta is not equal to 0°,the azimuthal angle phi is equal to 0°. My settings are as follows:I chose "periodic" in type of port and I defined the polarization of circular polarized light at both input and output port : cos (theta) in x direction, a* i in y direction, and -sin(theta) in z direction. Then, i chose "floquent periodicity" in x and y direction in periodic condition. And I chose "from periodic port" in k-vector for floquent periodicity. However, the charge map derived from the calculation results is not continuous on the right and left side of the structure in x direction. I don't know if my periodic conditions are wrong. If wrong, how should I revise. Any reply would be greatly appreciated. Sincerely yours, Zhimin Jing</p> Mon, 16 Jul 2018 03:13:40 +0000 4.2018-07-16 03:13:40.182573 Picosecond laser heat of solid-liquid system <p>Hello Users, I am modeling the heat transfer between a metal nanoparticle in an aqueous medium (water) when subject to a picosecond Gaussian pulse. At present, I am assuming classical heat diffusion under the heat transfer module. Later, I will switch to the 'two-temperature model' for accuracy.</p> <p>I want to compare the temperature v/s time plots (probe situated at the nanoparticle-water interface) for the cases - with and without 'thin film resistance'. On comparing the temperature plots, I find that the temperature at the nanoparticle surface from the 'perfect contact (zero thermal boundary resistance)' simulation to be higher than the simulation with a finite value of the thermal boundary resistance. This is not the correct behavior, as in the latter, there is resistance to the heat flow and hence the temperature of the surface should be higher than the perfect contact simulation.</p> <p>I have checked the quality of mesh and using very fine timesteps. Can anyone comment on this? Please note, this is not the case for 'ns' laser pulse heating and over there the results are consistent with the physics.</p> <p>-DS</p> Mon, 16 Jul 2018 02:03:05 +0000 4.2018-07-16 02:03:05.182572 Comsol in Ubuntu 18.04 always crashes after clicking Compute button in Study. <p>The issue happens even with very simple models, for example <a href="">Heat Transfer by Free Convection</a>. I can open files files, look at the results, but if I choose click Study, then click Compute, Comsol after few seconds crashes with the following error:</p> <blockquote> <p>A fatal error has been detected by the Java Runtime Environment:</p> <p>SIGSEGV (0xb) at pc=0x00007f41883939e9, pid=32753, tid=0x00007f40cabef700</p> <p>JRE version: Java(TM) SE Runtime Environment (8.0_112-b15) (build 1.8.0_112-b15) Java VM: Java HotSpot(TM) 64-Bit Server VM (25.112-b15 mixed mode linux-amd64 compressed oops)</p> <p>Problematic frame: C [] NodeMaker::reset(bool)+0x89 ...</p> </blockquote> <p>5.2a also crashes in similar way, but problematic frame is different ("C []").</p> <p>I have NVidia GTX 770, 32 GiB RAM and CPU Intel Xeon X3460.</p> <p>Did Comsol work for someone in earlier version of Ubuntu? Did anyone was able to run Comsol in Ubuntu 18.04?</p> Sun, 15 Jul 2018 14:51:47 +0000 4.2018-07-15 14:51:47.182571 How to add the periodic boundary conditions into Darcy module ? <p>In COMSOL 5.2, there is no periodic boundary conditions in Darcy module,however, periodic boundary conditions are needed in the problems of my research ,so I should like to express my appreciation to anyone to solve my problems.</p> Sun, 15 Jul 2018 12:57:13 +0000 4.2018-07-15 12:57:13.182563 Calculation of effective refractive index/propagation constant 3D <p>Hello everyone! I am looking for a way to extract the effective refractive index of a 3D geometry in the optics module (or the complex wavenumber). The thing is that the simulated geometry is not a waveguide, neither is it symmetric so as to perform a 2D mode analysis or eigenfrequency. Is there any possible way to do it? Thank you in advance.</p> Sun, 15 Jul 2018 11:12:35 +0000 4.2018-07-15 11:12:35.182561 How to see the temperature values in Celsius along with the temperature field on COMSOL? <p>Is there a way to view the temperature values in Celsius along with the temperature field in the Tecplot or in another post-view tool?</p> <p>I appreciate the help. My email is</p> Sat, 14 Jul 2018 20:05:53 +0000 4.2018-07-14 20:05:53.182552 Implementation of Topology Optimization in Comsol <p>I am trying to implement this paper "Topology Optimization by a time-dependent diffusion equation" in Comsol (See my attached Comsol model). The author implemented everything in Comsol (Page 812-816 of the attached paper). But I have some challenges. I could not locate where to specify <strong>shape</strong> (page 813), <strong>dweak</strong> (page 814). Also, I specified the "Global expressions" (Table A.2, page 814) and "Subdomain integration coupling variables" (Table A.3, page 814) in <em>Parameters</em> but some of them came up in red. Please, can someone helped me take a look at my model and page 812-816 of the paper, kindly help me make necessary corrections or let me know what I need to correct? Thank you so much</p> Fri, 13 Jul 2018 21:48:57 +0000 4.2018-07-13 21:48:57.182542 *Friday, July 20th* Abstract Submission Deadline for COMSOL Conference 2018 <p>Hello COMSOL Community!</p> <p>The final abstract submission deadline for the COMSOL Conference 2018 Boston is coming up on <em>Friday, July 20</em>.</p> <p>Presenting at the conference is a great opportunity to get recognition for your work from researchers and scientists at the forefront of mathematical modeling and numerical simulation. Papers, posters, and presentations from the conference will also be published online to maximize exposure worldwide.</p> <p>Submit an abstract (500 words or less) at Accepted abstracts may be considered for Best Paper or Best Poster awards. All presenters and coauthors will receive a reduced registration rate.</p> <p>For suggested topics, deadlines, and to submit an abstract, visit:</p> <hr /> <p>Dates &amp; Locations:</p> <p>COMSOL Conference 2018 Boston - October 3-5 (</p> <h2>COMSOL Conference 2018 Lausanne - October 22-24 (</h2> Fri, 13 Jul 2018 18:23:25 +0000 4.2018-07-13 18:23:25.182532 Electric Current Transient Equation <p>Hi,</p> <p>Does any one know what the governing equation is for a transient simulation in the electrical currents package? For some reason, every time I click to see it, it freezes and I need the equation for a homework report. I know for steady state, it's \del \cdot \sigma \del U = 0 where U is the voltage and \del is the nabla operator. Ie \del U is the gradient of U</p> <p>Thanks! Nick</p> Fri, 13 Jul 2018 17:15:03 +0000 4.2018-07-13 17:15:03.182522 Sinusoidal pipe in 2D axisymmetric model <p>How to draw a wavy pipe (sinusoidal curve) in 2D axisymmetric Model?</p> Fri, 13 Jul 2018 17:03:25 +0000 4.2018-07-13 17:03:25.182521 Heat transfer in Fluid Flow <p>Hi,</p> <p>I'm trying to model a viscous fluid flow which is heated by a heat source. I want to set a temperature profile to the fluid, and then simulate the flow. For some reason I can't use the non-isothermal flow multiphysics.</p> Fri, 13 Jul 2018 16:36:15 +0000 4.2018-07-13 16:36:15.182512 3D Coil Magnetic field generated and maximum current density <p>Hello everybody,</p> <p>I'm new to comsol and I'm trying to model a small coil. I'm able to obtain the stationary study without problems. However, I would like to simulate the power dissipation and magnetic field generated by using a pulsed current, a sequence of a positive and negative pulse. I'm using the Time Dependent study to do that. When I start the computation of the study I get the following error:</p> <blockquote> <p>Failed to find consistent initial values. Matrix has zero on diagonal. Last time step is not converged. - Feature: Time-Dependent Solver 1 (sol4/t1)</p> </blockquote> <p>The model can be download from here: <a href="http://"></a></p> <p>Thanks in advance</p> Fri, 13 Jul 2018 14:23:59 +0000 4.2018-07-13 14:23:59.182511 Strainrate to find Viscosity <p>In the non-isothermal fluid physics, I prescribe certain velocity field boundary conditions and solve for the velocity field as a function of time. I would like to use the strain rate of the velocity field to also calculate the viscosity of the fluid during each iteration of the simulation. The strain rate depends on the partial spacial derivatives of the velocity components, i.e. ux, uy, uz, vx, etc. However, when I try to define the strain rate/viscosity as a function of these variables either within the Component or within the Material node, ux, uv, uz, etc. are considered undefined, and the function is not allowed. Any suggestions/solutions on how I can/should approach this issue would be greatly appreciated. Thank you!</p> <p>Carter</p> Fri, 13 Jul 2018 13:25:55 +0000 4.2018-07-13 13:25:55.182501 Help with scattering task <p>Hi I need help with scattering from curved PEC, somone can help me please? Thanks</p> Fri, 13 Jul 2018 12:40:47 +0000 4.2018-07-13 12:40:47.182491 Persisting errors after renaming a parameter <p>Hello, I have renamed a global parameter (originally D_beam_hole), which caused a few features using this parameter in the geometry structure to fail. After I have corrected all of these features, the geometry can be built now. However, I can not save the file, I get the informative message "An unexpected error occured". The log file is attached. I managed to save the file as java, and in the java code I discovered that the original parameter is still there. I have compacted the history and saved it again as Java, the old parameter name now disappeared. I can not find it anywhere in the .java file, meaning that no feature is using it. Very good. However, I still can not save the file, I get the same error message, and the important part of the log file is this: The following feature has encountered a problem:</p> <pre><code>Unknown model parameter. - Property: posx (x) - Name: D_beam_hole Error in multiphysics compilation. - Feature: Compile Equations: Stationary (sol1/st1) </code></pre> <p>Can one give me a tip how to remove this from comsol's memory? I can not save the file, and I would be extremely unhappy if I had to do these changes again, with probably the same result.</p> <p>Thank you Daniel</p> Fri, 13 Jul 2018 12:19:20 +0000 4.2018-07-13 12:19:20.182481 Gas mixture (2 immiscible fluid) One inlet - Is it avaliable with multiphase physics <p>Hey, I am trying to solve gas mixture problem in comsol. I need to start inflow with one inlet, and I have gas mixture, two immiscible gas. And flow must be on one inlet through to one outlet. I looked for 2 phase models but I could not find any supporting tutorial. After that, I tried to solve this problem with multiphysics coupling. Laminar flow and transport concentrated species(TCS). But I dont guess that, It can help. Because I couldnt add two gasses into one domain. Also, TCS has 2 component but I have mixture velocity so how can I do this study ?</p> Fri, 13 Jul 2018 09:43:59 +0000 4.2018-07-13 09:43:59.182471