Latest Discussions - COMSOL Forums Most recent forum discussions Wed, 16 Jan 2019 13:38:50 +0000 COMSOL Forum: Latest Discussions Tesla coil in comsol <p>hello, please I'm investigating how to transmit electrical power in the form of radio frequency from one coil to another, something like the tesla coil. radioactive and noninductive coupling. can you help me? (multi-turn coil, Bifilar coils, etc.)</p> Wed, 16 Jan 2019 13:38:50 +0000 4.2019-01-16 13:38:50.225802 using Prev operator <p>hello all,</p> <p>I am trying to create a condition were the solution of a present formula gets automatically added with the solution of the same formula from the previous time step. for this i used <em>Prev(exp,1)</em> operator but i am getting and error "Previous time step not stored". Any idea how to reslve this</p> <p>Thank you so much..:-)</p> <p>With regards Hari</p> Wed, 16 Jan 2019 11:47:29 +0000 4.2019-01-16 11:47:29.225771 Meshing techniques in comsol <p>I want to know if any there are any meshing techinques that can solve a complex domain consisting of extremely small and sensitive domain elements. (finer than extremely fine). I am using COMSOL Multiphysics with AC/DC module 5.3(a).</p> Wed, 16 Jan 2019 11:41:48 +0000 4.2019-01-16 11:41:48.225761 Can I use de Pipe Acoustics Module to study a pressure wave that came from explosion in a combustion motor <p>I want to study how a pressure wave travel a long a pipe. That pressure wave came from explosion in a combustion motor. I'm using the pipe acoustic module, but the results in my simulations were different of the results measured in real motor. So I'm in doubt if this pressure wave is a acoustic wave and if I can use the pipe acoustic module.</p> Wed, 16 Jan 2019 10:49:21 +0000 4.2019-01-16 10:49:21.225752 Heat source simulation <p>Hi, I'm a complete comsol newbie. I'm trying to run a simulation that seems to be quite simple yet somehow I keep getting errors upon computing (usually the error is "The Relative Residual (x) Is Greater Than The Relative Tolerance"). Basically I'm trying to get the temp on a simplified transformer model (which I'v imported from an .stp file if it matters), which consists of a ferrite core, copper windings and a surrounding block of air I've added, and calculate it based on known losses. I created a steady-state project with the heat transfer in solids physic. Each relevant component was assigned as a heat source with a total power of the given losses. I left all other settings as default. I also assigned each component with its material and added missing properties as instructed by the software. Your assistance would be highly appreciated as I keep feeling as if I'm missing some basic consepts, given the fact that I'm failing to do some things that seem quite trivial. I'm attaching my model here.</p> <p>Thank you</p> Wed, 16 Jan 2019 10:37:30 +0000 4.2019-01-16 10:37:30.225751 modelling of metal hydride reactor <p>How can i use the heat transfer in porous media interfaces for modelling of metal hydride reactor (MgH2)? i need step wise procedure.</p> Wed, 16 Jan 2019 09:29:51 +0000 4.2019-01-16 09:29:51.225732 Have problem with Particle Tracing for fluid flow! <p>Hi everyone! When I simulation with Particle Tracing for fluid flow! I met one warning like this: "Some particles have been removed from the simulation because maximal number of wall interactions within one time step has been reached." We need to use wall condition: bounce. I don't have problem with another wall conditions. However, I need to use bounce condition since I need particle can move on wall Could you help me to solve this problem?</p> Wed, 16 Jan 2019 05:36:17 +0000 4.2019-01-16 05:36:17.225671 how to use step function? <p>I want to apply a current in electrochemistry model. However, if I set a step fuction to the current, where do I use the step fuction?</p> Wed, 16 Jan 2019 02:11:18 +0000 4.2019-01-16 02:11:18.225662 Help For Studying current distribution in a grounding grid <p>I'm studying current distribution in a grounding grid buried at depth h=100 m below the earth surface . I am using magnetic and electric field interface in AC/DC module.</p> <p>Normally when current flows in a grounding conductor part of the current leaks into soil.</p> <p>Could anyone help me??</p> <p>Kindest Regards Samar</p> Tue, 15 Jan 2019 15:31:00 +0000 4.2019-01-15 15:31:00.225641 Step function in a time-dependent problem <p>Hello everyone,</p> <p>I am trying to implement a step function in my time-dependent problem where I want to lower the temperature of a constant temperature boundary from 40°C to 20°C after 10min (600s) of running the model. However, I always get the error "Failed to find consistent initial values. Last time step is not converged." Running the model without the step function works.</p> <p>The details of my step function are: Location 600, From 0, To 1. Implemented into the constant temperature boundary like this: T0 = 40 - (20*step1(t)) [degC]</p> <p>Thanks for your help!</p> Tue, 15 Jan 2019 14:55:23 +0000 4.2019-01-15 14:55:23.225632 How to apply two or more interpolation schemes when using Topology Optimization node with COMSOL 5.4 <p>Dear Mr./Mrs.,</p> <p>The latest COMSOL 5.4 version has integrated the Topolgy optimization node in "definition". The filter as well as the projection can be accessed more conveniently compared with previous versions.</p> <p>My question is: <em>How to apply two or more interpolation schemes when using Topology Optimization node with COMSOL 5.4?</em></p> <p>That is because in some fluidic-thermal topology optimization problems, I need to use different interpolation schemes for different physical properties. For example, I want to use Darcy penalization for body force terma, and to use RAMP penalization for thermal conductivity.</p> <p>On the other hand, is it possible to self-define the interpolation scheme by using the built-in topology optimization node?</p> <p>Hope to hear from you guys soon.</p> <p>Kindly regards, Hao LI</p> Tue, 15 Jan 2019 11:47:45 +0000 4.2019-01-15 11:47:45.225623 A problem about the well boundary condition in the Darcy's law module <p>There seems to be a problem with well boundary conditions when simulating reservoir production processes by the Darcy’s law module. I assigned Neumanna boundary conditions (constant mass flow) to the injection and production wells, and then the calculation was perfomed smoothly. In post-processing, I used the Darcy’s velocity to solve the mass flux of the production well, but I found that the mass flux calculated by the integral was inconsistent with the pre-prescribed mass flux. So, when I simulate the production process using the well boundary conditions with the specified production pressure, is it suitble to calculate the productivity by the the Darcy's velocity? Can someone give me some advice?</p> <p>Thanks!</p> Tue, 15 Jan 2019 07:35:31 +0000 4.2019-01-15 07:35:31.225613 Integration operator on element level? <p>Dear all,</p> <p>I want to integrate the independent variable on each element, rather than on the whole geometry. But there is no corresponding operater in COMSOL. Does anyone have experience about that? Would you mind sharing some ideas with me? Thank you so much.</p> <p>Yu</p> Tue, 15 Jan 2019 01:22:33 +0000 4.2019-01-15 01:22:33.225602 both shells and solids <p>Hi How i can model the viscoelastic sandwich plate (top and bottom layers are elastic, and core is viscoelastic) using both shells and solids.</p> Mon, 14 Jan 2019 20:14:07 +0000 4.2019-01-14 20:14:07.225582 Saving file between runs in a parameter sweep? <p>The IT department where I work is a stone wall that will not budge. I run a simulation over the weekend, come in to find my computer had been restarted by automatic updates and now I have to start over. We're talking fluid dynamics, so these things will run for days on their own.</p> <p>If there was a way to pause between parameter runs in a sweep and save the file, I could at least pick up where I left off. Is there something like that in COMSOL? If not, is it something I can implement with java? I've used COMSOL with java before, so I know it can be very powerful, but I don't know the details enough...</p> <p>Thanks!</p> Mon, 14 Jan 2019 17:21:11 +0000 4.2019-01-14 17:21:11.225572 Equivalent to Conductive Media DC model version 3.4 in Comsol 5.3a <p>Hi, I have an issue for calculating the current in ground and i want to know the equivalent for the old model Conductive Media DC model version 3.4 in Comsol 5.3a..</p> <p>Kindest Regards Samar</p> Mon, 14 Jan 2019 17:20:33 +0000 4.2019-01-14 17:20:33.225571 How to simulate water falling under gravity and impinging on a curved surface, which is kept/present in a domain, containing air? <p>Hello,</p> <p>I am attempting to <strong>simulate water, flowing out of a hole/slit, at the bottom of a tank (under the influence of gravity); entering into a domain (vertically downward), that contains air, and impinging on a curved surface.</strong> The idea is to simulate (<em>in 2D</em>) and obtain data on:</p> <p><em>1. The distribution of water, as it flows along the surface, on two sides of the surface (for a 2D Simulation), for different initial points of impingement.</em></p> <p><em>2. The (distribution of) stress produced, due to the impinging water, on the (different points of the) curved surface.</em></p> <p>I have looked through a plethora of papers, as well as tutorials and none of them include, <strong>liquid/gas, flowing out, under gravity, into another domain, containing a different liquid/gas</strong>. I am assuming <em>Laminar Flow</em> and <em>No Slip Boundary Condition</em>, at the walls and the curved surface.</p> <p>Here, as far as I know, I cannot define Inlet at the interface of the two domains. I have tried Multiphase (Phase Field), with no inlet and 1 outlet in the Air Domain (situated vertically downwards), but it did not converge. A Surface Plot of Fluid Velocity showed water, entering the Air Domain, but after a few more time steps, COMSOL threw a <strong>Did not converge</strong> error, thereby preventing the water from reaching the curved surface. I have tried making the hole into a nozzle (of sorts), with a smooth downward curve, but that did not change the outcome. Any help or hint is much appreciated.</p> <p>Regards, JS</p> <p>TL;DR: How do I simulate a hole, at the bottom of a (full) water tank?</p> Mon, 14 Jan 2019 15:38:47 +0000 4.2019-01-14 15:38:47.225561 Eigenfrequency, frequency domain, frequency domain modal and mode analysis studies <p>Hi,</p> <p>Could someone please explain to me what's the difference between eigenfrequency, frequency domain, frequency domain modal and mode analysis studies?</p> <p>I'm preparing a setup and I'm not sure which option to use.</p> <p>Thanks,</p> <p>Ana Luisa</p> Mon, 14 Jan 2019 15:00:49 +0000 4.2019-01-14 15:00:49.225551 How to solve "Feature: Stationary Solver 1 (sol1/s1) Attempt to evaluate nonintegral power of negative number." <p>Hello everybody, I’m working on a simulation of a tubular reactor for secondary reforming. Since my 3D simulation run resulted in error, I decided to face the same situation with a 1D model, but the error is the same. I have to define a temperature-dependent kynetic, so I attached to the simulation 2 physics, which are “transport of diluted species in porous media” and “heat transfer in porous media”. I checked that all the empty sections were filled out, but I didn’t find anything wrong. The kinetics for steam reforming are quite difficult, so I tried to check them, but I could not have seen some error in the variables. The error after "compute" is:</p> <p>Feature: Stationary Solver 1 (sol1/s1) Attempt to evaluate nonintegral power of negative number. - Function: ^ Failed to evaluate variable. - Variable: B1 - Defined as: 1/(((comp1.cH2<em>(unit_m_cf^3))/unit_mol_cf)^2.5) Failed to evaluate variable. - Variable: cost1 - Defined as: ((A1</em>B1)<em>(unit_m_cf^6))/((unit_kg_cf</em>unit_h_cf)<em>unit_mol_cf) Failed to evaluate variable. - Variable: cost1_1 - Defined as: cost1/(DEN^2) Failed to evaluate variable. - Variable: r1_ - Defined as: cost1_1</em>((comp1.cCH4<em>comp1.cH2O)-(((comp1.cCO</em>(comp1.cH2^3))<em>((comp1.T</em>R)^2))/Keq1)) Failed to evaluate variable. - Variable: r1 - Defined as: r1_<em>rhocat Failed to evaluate variable. - Variable: comp1.tds.rpb1.reac1.R_cCH4 - Defined as: (-r1)-r3 Failed to evaluate variable. - Variable: comp1.tds.rpb1.R_cCH4 - Defined as: comp1.tds.rpb1.reac1.R_cCH4 Failed to evaluate expression. - Expression: d(((4</em>pi<em>comp1.tds.rpb1.Npe</em>comp1.tds.rpb1.rpe<em>rpb1_r^2</em>(-(comp1.tds.rpb1.rpe/unit_m_cf)^2<em>comp1.tds.rpb1.epsilon_pe</em>d(comp1.tds.rpb1.cpe_cCH4,t)<em>test(comp1.tds.rpb1.cpe_cCH4)-comp1.tds.rpb1.Dpeff_cCH4</em>d(comp1.tds.rpb1.cpe_cCH4,rpb1_r)<em>test(d(comp1.tds.rpb1.cpe_cCH4,rpb1_r))+(comp1.tds.rpb1.rpe/unit_m_cf)^2</em>comp1.tds.rpb1.R_cCH4<em>test(comp1.tds.rpb1.cpe_cCH4)))</em>(tds_rpb1_xdim.atonly(dvol)))<em>(dvol_spatial),{test@0}) Failed to evaluate Jacobian of expression. - Expression: ((4</em>pi<em>comp1.tds.rpb1.Npe</em>comp1.tds.rpb1.rpe<em>rpb1_r^2</em>(-(comp1.tds.rpb1.rpe/unit_m_cf)^2<em>comp1.tds.rpb1.epsilon_pe</em>d(comp1.tds.rpb1.cpe_cCH4,t)<em>test(comp1.tds.rpb1.cpe_cCH4)-comp1.tds.rpb1.Dpeff_cCH4</em>d(comp1.tds.rpb1.cpe_cCH4,rpb1_r)<em>test(d(comp1.tds.rpb1.cpe_cCH4,rpb1_r))+(comp1.tds.rpb1.rpe/unit_m_cf)^2</em>comp1.tds.rpb1.R_cCH4<em>test(comp1.tds.rpb1.cpe_cCH4)))</em>(tds_rpb1_xdim.atonly(dvol)))*(dvol_spatial)</p> <p>I also changed the initial values, because in some forums I have read that values equal to 0 sometimes give rise to errors, but my error is persistent. I attach my file in order to let you understand better my study and my errors. Thank you in advance for your help, your help could be really important!</p> Mon, 14 Jan 2019 13:22:26 +0000 4.2019-01-14 13:22:26.225541 How to save data from parameters to a .txt file? <p>Hello! I have very simple comsol application with two input fields. I want to save this data to a .txt file. I have tried to use JFileChooser from javax.swing but in my case comsol has displayed an error:</p> <blockquote> <ul> <li>Resource specification not allowed here for source level below 1.7*</li> </ul> </blockquote> <p><strong>Question:</strong> how to save two field to a txt file?</p> Mon, 14 Jan 2019 12:14:43 +0000 4.2019-01-14 12:14:43.225531