Latest Discussions - COMSOL Forums https://www.comsol.com/forum/ Most recent forum discussions Wed, 19 Feb 2025 14:52:47 +0000 COMSOL Forum: Latest Discussions https://www.comsol.com/shared/images/logos/comsol_logo.gif https://www.comsol.com/forum/ Evaluation of a value at a specific point within a Cut Point 3D Grid Dataset https://www.comsol.com/forum/thread/349161/evaluation-of-a-value-at-a-specific-point-within-a-cut-point-3d-grid-dataset?last=2025-02-19T18:26:10Z <p>Hopefully a quick and easy one!</p> <p>I have created a 3D simulation of an arc magnet that moves around in space, and want to evaluate the z component of field at specific points within a 3D Cut Point dataset.</p> <p>Obviously if the dataset had 1 discrete point, I would just evaluate mfnc.Bz for the dataset.</p> <p>However, with a grid definition of the dataset (see attachment) I want to evaluate it at a specific point within that grid definition. I have customised the point number variable to be "chip_n" so clearly need to use that within my expression to evaluate, but I cannot determine what the correct syntax for this is!</p> <p>In my attached example there are 54 discreet points defined by my grid, and I would like (for example) to determine the difference in the z field at points 1 and 10.</p> <p>Thanks in advance for your guidance...</p> <p>Mark</p> Wed, 19 Feb 2025 14:52:47 +0000 4.2025-02-19 14:52:47.349161 Modelling Magnetostriction and defining bias point for AC simulation in Magnetoelectric Antenna Design. https://www.comsol.com/forum/thread/349151/modelling-magnetostriction-and-defining-bias-point-for-ac-simulation-in-magnetoelectric-antenna-design?last=2025-02-19T14:30:24Z <p><strong>I am designing a magnetoelectric antenna and need to apply a 20 mT background field to establish a bias point for AC simulation. However, the simulation will not converge in COMSOL 6.0 or 6.3, resulting in various errors and preventing me from achieving any meaningful solution. I don't realize any kind of magnetostriction as well.</strong></p> <p><em>A. DC SIMULATION The DC simulation is carried out by the Stationary solver, in which the magnetic physics and solid mechanic physics are coupled in the multiphysics branch in COMSOL. The result of the stationary solver defines the bias point for the magnetostrictive material. In addition, in order to consider the magnetic DC bias we have activated the uniform background magnetic flux density in Magnetic Field physics.</em></p> <p>Thank you.</p> Wed, 19 Feb 2025 14:30:24 +0000 4.2025-02-19 14:30:24.349151 Neumann BC at the outlet in laminar flow module https://www.comsol.com/forum/thread/349141/neumann-bc-at-the-outlet-in-laminar-flow-module?last=2025-02-19T13:59:27Z <p>I'm trying to solve a microfluidic flow problem where inlet BC is velocity (dirichlet BC) and outlet BC is velo flux (neumann BC). In the laminar flow module, i do not get option for neumann BC @ outlet.</p> <p>Comsol manual states that velocity @ inlet and outlet is not feasible. It has to be velo and pr or vice-versa.</p> <p>The solution converges fine with velo @ inlet and pr BC @ outlet but the axial pr gradient does not match solution in literature.</p> <p>Any help/advise is appreciated.</p> Wed, 19 Feb 2025 13:59:27 +0000 4.2025-02-19 13:59:27.349141 Delete https://www.comsol.com/forum/thread/349131/delete?last=2025-02-19T17:00:15Z <p>Delete</p> Wed, 19 Feb 2025 11:28:42 +0000 4.2025-02-19 11:28:42.349131 Can COMSOL Simulate Corona Discharges in 3D Models? https://www.comsol.com/forum/thread/349121/can-comsol-simulate-corona-discharges-in-3d-models?last=2025-02-19T07:20:26Z <p>Hello everyone, I have a question about the newly released Electric Discharge Module. Can we simulate corona discharges occurring in high-voltage switching components? Specifically, we can consider a circuit breaker or a load disconnect switch. The body, made of resin material, provides insulation depending on its wall thickness.</p> <p>I would like to simulate whether corona discharge occurs for different wall thicknesses. For example, let's assume that corona discharge occurs at 10 mm thickness. If I increase the thickness to 15 mm, to what extent will the corona discharges be reduced?</p> <p>Does COMSOL’s Electric Discharge Module provide a solution for this? Can this scenario be simulated in COMSOL?</p> Wed, 19 Feb 2025 07:20:26 +0000 4.2025-02-19 07:20:26.349121 Using a single Matlab function for electrical conductivity as tensor but COMSOL requires one function per tensor component https://www.comsol.com/forum/thread/349112/using-a-single-matlab-function-for-electrical-conductivity-as-tensor-but-comsol-requires-one-function-per-tensor-component?last=2025-02-19T00:50:57Z <p>Hi,</p> <p>I have a Matlab function that calculates the electrical conductivity of the material as a function of strain and other material constants. So I am using the Solid Mechanics and Electric Currents interfaces. I wrote a wrapper (Matlab) function that takes the strain components as vector inputs (solid.el11,solid.el22,solid.el33,solid.el12,solid.el13,solid.el23) so that my electrical conductivity function calculates the conductivity tensor. I am using this function within my Materials definition as the electrical conductivity. The issue is that my function calculates the full tensor, i.e., the 3x3 matrix for a given strain tensor (3x3 matrix) as input. In the vectorized version, it obtains a 3x3xN matrix if the solid.elxx variables are vectors of length N. However, I can't find the way to give the full tensor to COMSOL as, from the screenshot, each component of the electrical conductivity needs to be its own function. So what I had to do was to make the wrapper function to output the vectorized component of the electrical conductivity tensor for a given component. For instance, in the screenshot, the function sigma_wraper_c3 that is called for the (1,1) component takes as input 1,1 so that the function outputs only that component. Similarly for the other tensor components. This results in computing the full tensor for the whole model three times if using the diagonal form or nine times if using the full tensor, one per each component. This is why in the screenshot I am using the diagonal form to save time.</p> <p>So, is it possible to pass the full tensor to COMSOL so that the tensor is calculated only once?</p> <p>Additionally, I tried to use my Matlab function in "Current Conservation" within the "Electric Currents" interface. I tried this by selecting "User defined" for the electrical conductivity. But there not only I find the same issue, I see a message of "Unknown function or operator". How could this happen if my Matlab function is defined within Global Definitions?</p> <p>Whether in the Materials definition or the "Electric Currents" interface, I would like a way to pass the full tensor to COMSOL.</p> <p>Thanks.</p> Wed, 19 Feb 2025 00:50:57 +0000 4.2025-02-19 00:50:57.349112 How can I select a point as a source of my prescribed velocity in a 2D geometry? https://www.comsol.com/forum/thread/349102/how-can-i-select-a-point-as-a-source-of-my-prescribed-velocity-in-a-2d-geometry?last=2025-02-19T00:10:10Z <p>Hello. I'm using the Elastic Waves module and I'm trying to simulate the wave propagation with a point source, but I don't know how to select the point when I'm selecting a boundary in the Prescribed Velocity.</p> Tue, 18 Feb 2025 21:10:15 +0000 4.2025-02-18 21:10:15.349102 define crystal drug material https://www.comsol.com/forum/thread/349092/define-crystal-drug-material?last=2025-02-18T14:24:09Z <p>Hi, I am preparing a model including a thin layer of coating drug. The main component is urea as crystal. Could you please help me determine its properties or the closest material to it in the library?</p> Tue, 18 Feb 2025 14:24:09 +0000 4.2025-02-18 14:24:09.349092 Modelling CFRP (Carbon Fiber reinforced polymer) https://www.comsol.com/forum/thread/349071/modelling-cfrp-carbon-fiber-reinforced-polymer?last=2025-02-17T13:02:16Z <p>How to model CFRP material on a hollow cube structure? I could not find CFRP directly in the Material Library. I found Carbon fiber epoxy, but the values for Young's modulus, Poisson's ratio, Shear modulus were empty. Also, I wanted to assign the fiber direction for each wall so would it depend on the direction with highest Young's modulus?</p> Mon, 17 Feb 2025 13:02:16 +0000 4.2025-02-17 13:02:16.349071 Guidance Needed On How to Correctly Add Piezoelectricity? https://www.comsol.com/forum/thread/349062/guidance-needed-on-how-to-correctly-add-piezoelectricity?last=2025-02-17T17:33:03Z <p>Hello, I need help adding piezoelectricity to a MEMS simulation I made. I have the Solid Mechanics and the Electrostatics Physics options added, but when I go to add the Multiphysics it doesn't recognize the parts of the geometry with the electrostatics physics enabled. Essentially, everything is deselected and I cannot add anything to the piezoelectricity multiphysics tab.</p> <p>I've included a few photos of what I currently have set-up (current should run through the proof mass and the thin wire on top of the springs). I cannot seem to include my file because it's too big and I don't know how to compress it to 5 MB. I'm using the license my university has and it's version 6.2 of COMSOL.</p> Sun, 16 Feb 2025 22:54:58 +0000 4.2025-02-16 22:54:58.349062 The d-operator is not well defined in the current context, use dtang or mean and d operators instead. https://www.comsol.com/forum/thread/349061/the-d-operator-is-not-well-defined-in-the-current-context-use-dtang-or-mean-and-d-operators-instead?last=2025-02-16T10:25:49Z <p>I am working on COMSOL using the Mathematics module for a non-generic 2D problem. My setup involves three different physical phenomena, each implemented using separate mathematics modules with their respective governing equations.</p> <p>I am facing an issue with defining flux boundary conditions (Neuman) that are functions of dependent variables of all the modules. When I incorporate such boundary conditions, I encounter the following error:</p> <p>“The d-operator is not well defined in the current context. Use dtang or mean and operators instead.”</p> <p>However, when I assign a constant value as the boundary condition, the simulation runs successfully, and I obtain results. Unfortunately, my actual problem requires boundary conditions that are functions of the dependent variables.</p> <p>Could anyone kindly help me resolve this issue?</p> Sun, 16 Feb 2025 10:25:49 +0000 4.2025-02-16 10:25:49.349061 Guidance Needed for Designing a Coil https://www.comsol.com/forum/thread/349041/guidance-needed-for-designing-a-coil?last=2025-02-17T13:23:06Z <p>Dear COMSOL Community,</p> <p>I am currently working on designing a coil in COMSOL Multiphysics and would appreciate some guidance on how to proceed. My goal is to model a coil and simulate its electromagnetic behavior, but I am unsure about the steps involved in setting up the physics correctly. my coil design is so complicated for me. i upload image of my coil for you in real i have this coil.</p> <p>-What is the best way to design the coil geometry? Should I use a 2D or 3D model, and are there any specific tools or features in COMSOL that can help with this?</p> <p>-Which physics interfaces should I use for simulating the electromagnetic fields generated by the coil? Should I use the Magnetic Fields (mf) interface, Magnetic and Electric Fields (mef), or another option?</p> <p>-What boundary conditions are typically applied to such problems?</p> <p>If anyone has experience with similar simulations or could point me to relevant tutorials, documentation, or example models, I would greatly appreciate it.</p> Sat, 15 Feb 2025 09:44:02 +0000 4.2025-02-15 09:44:02.349041 Calculating heat generated during cell thermal runaway https://www.comsol.com/forum/thread/349031/calculating-heat-generated-during-cell-thermal-runaway?last=2025-02-14T15:14:31Z <p>Hello, I'd want to calculate the total heat released from a cell undergoing runaway. However when declaring the domain probe there are multiple heat released/heat rate/energy released options. Which probe selection is the most accurate for this case (to obtain the heat released in watts). Help is very much appreciated.</p> <p>Thank you.</p> Fri, 14 Feb 2025 15:14:31 +0000 4.2025-02-14 15:14:31.349031 Microwave drilling in COMSOL https://www.comsol.com/forum/thread/349021/microwave-drilling-in-comsol?last=2025-02-14T19:01:39Z <p>I'm completely new to COMSOL and I need help on How is microwave drilling process to be carried in COMSOL?</p> Fri, 14 Feb 2025 14:25:03 +0000 4.2025-02-14 14:25:03.349021 Bending of Clamped orthotropic rectangular plate due to uniform load https://www.comsol.com/forum/thread/349011/bending-of-clamped-orthotropic-rectangular-plate-due-to-uniform-load?last=2025-02-18T13:38:33Z <p>Hello, I am trying to model a very simple problem wherein a clamped orthotropic rectangular plate is bending due to a uniform load acting on it. I am modeling it as a <strong>Shell</strong> wherein Plane stress formulation will be implemented. I am solving it for the following Linear Elastic Material settings: 1. Solid Model: Orthotropic; 2. Material data ordering: Voigt; 3. Young's Modulus: E (User-defined) Ex=130GPa, Ey=130GPa, Ez=0; 4. Poisson's ratio: nu (User-defined) nu_xy=0.28, nu_yz=0, nu_xz=0; 5. Shear modulus: G (User-defined) Gyz=79.6GPa, Gxz=79.6GPa, Gxy=79.6GPa;</p> <p>Subsequently, the following are the settings in the Shell Local System node: 1. Coordinate System Selection: Global Coordinate System</p> <p>Extra information: I am using an orthotropic stiffness matrix for silicon with three axes at [100], [010], and[001]. Reference: Hopcroft et al. : What is the Young's Modulus of Silicon? Journal of Microelectromechanical Systems, Vol.19, No.2, April 2010.</p> <p>My question here is what is coordinate system that COMSOL will use for defining the material properties?</p> Fri, 14 Feb 2025 11:34:23 +0000 4.2025-02-14 11:34:23.349011 PEM water electrolyzer https://www.comsol.com/forum/thread/349001/pem-water-electrolyzer?last=2025-02-14T11:10:52Z <p>Hello everyone,</p> <p>I am a student conducting research on PEMWE. I have been learning about fuel cell and electrolyzer systems through the examples provided on the official website.</p> <p>Since I couldn't find a specific example for PEMWE, I have been referring to a PEMFC example instead. I assumed that by swapping the values of the anode and cathode in the PEMFC model, I could build a system that operates as a PEMWE.</p> <p>However, I am currently encountering an error, as shown in the attached image. Would anyone be able to help me with this issue?</p> <p>To aid in understanding, I have attached the MPH file and the image.</p> <p>Any opinions or questions are welcome! ?</p> Fri, 14 Feb 2025 11:10:52 +0000 4.2025-02-14 11:10:52.349001 Conductivity gradient error https://www.comsol.com/forum/thread/348992/conductivity-gradient-error?last=2025-02-14T07:48:21Z <p>Hello everyone,</p> <p>I am working on a simulation in COMSOL to check how the electric current moves in the system where I model a box with three layers: insulator, conductor, and insulator. The layers have micrometer-scale thickness, and I am studying how current flows through the system.</p> <p>I am using the Electric Currents physics interface in the Frequency Domain. However, when I assign a conductivity of 10^7 S/m or higher to the metal layer, the solver fails to converge. I have tried various solvers, but none of them successfully solved the problem.</p> <p>After doing some changes, I found that COMSOL struggles with large conductivity gradients, which seems to be causing the issue. Interestingly, the simulation works fine if I reduce the conductivity to 10^1 or 10^2, use Stationary Study and also when I use a frequency higher than 1 MHz. However, for frequencies between 1 Hz and 1 MHz, the solver fails to converge.</p> <p>I would really appreciate any guidance on how to address this issue. Has anyone encountered a similar problem?</p> <p>Thank you in advance</p> Fri, 14 Feb 2025 05:10:39 +0000 4.2025-02-14 05:10:39.348992 How to introduce AC voltage excitation into a circular coil in a transient situation https://www.comsol.com/forum/thread/348983/how-to-introduce-ac-voltage-excitation-into-a-circular-coil-in-a-transient-situation?last=2025-02-14T01:45:40Z <p>In the transient case, it is possible to introduce an alternating current into the coil, but when the current excitation is changed to voltage excitation, the model will not run. I would appreciate it if someone could help me with this.</p> Fri, 14 Feb 2025 01:45:40 +0000 4.2025-02-14 01:45:40.348983 How to find an expression for the gradient of pressure? https://www.comsol.com/forum/thread/348982/how-to-find-an-expression-for-the-gradient-of-pressure?last=2025-02-14T13:20:44Z <p>Hello,</p> <p>I was wondering how to find the expression of the gradient of pressure. So \nabla^2 * p in the acoustics domain. Would it just simply be d(laginterp(2,p),x) + d(laginterp(2,p),y) in 2D? Or is there another way?</p> <p>Thanks!</p> Thu, 13 Feb 2025 19:27:35 +0000 4.2025-02-13 19:27:35.348982 Adding an constant external B-field in the "mf." module https://www.comsol.com/forum/thread/348981/adding-an-constant-external-b-field-in-the-mf-module?last=2025-02-13T10:14:00Z <p>Hello,</p> <p>I am working with a model that combines the "ec." and "mf." modules. The idea is the following: 1) The "ec." module takes a current "I" as input and computes the current density "J" that distributes according to the electrical conductivity. 2) "J" serves as input for the ".mf" module, which computes the rest.</p> <p><strong>Question</strong>: How can I add-up an external B-field, like a permanent magnet acting on my model ?</p> <p>I tried adding a boundary condition for "B", but I actually don't know the total B-field there... I also tried using the following option: "Magnetic fields (mf) -> Background field -> Solve for: Reduced field ". But this second idea does not seem to model what I need (when I plot "mf.By", I do not see the contribution of the external field along "y").</p> <p>Any help would be greatly appreciated :)</p> <p>Pierre</p> Thu, 13 Feb 2025 10:09:59 +0000 4.2025-02-13 10:09:59.348981