Questions tagged [comsol]

Formerly FEMLAB, COMSOL is a finite element analysis software package for various engineering and physics applications, with special emphasis on coupled phenomena (multiphysics).

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Conceptual doubt regarding 2D conjugate heat transfer modelling (COMSOL and Mathemtica)

I have been dealing with some conceptual flaws in my understanding of modelling, which I will elaborate herein. I am modelling conjugate heat transfer of a reciprocating fluid, which flows with ...
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What is the difference between non-linear elastic simulation and linear elastic simulation with plasticity?

I'm learning how to do Finite Element calculations using Comsol Multiphysics. In Comsol, Linear Elastic Material and Nonlinear Elastic Material are available as material models: Using Linear Elastic ...
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switching boundary conditions to simulate a reciprocating flow in COMSOL

This is a re-posted question which was poorly defined earlier I have been trying to simulate reciprocating flow of a convective fluid through a heated channel in COMSOL-Multiphysics. The schematic of ...
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Weird "oscillatory" modes appearing in FEM simulations

I am using COMSOL to solve a mathematical model involving thermoelectric hydrodynamic (TEMHD) flow. I am running a very large parameter sweep and using the solutions obtained to make some plots. ...
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Why does COMSOL treat a well as a rectangular cube?

I'm trying to learn COMSOL for a graduate research project and am struggling through a flow and transport in 3D tutorial. As such I'm walking through my boundary conditions and trying to figure out if ...
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How to connect two cylinders to form a knee in Comsol Multiphysics?

I have this I want it to be single bended wire. How to accomplish?
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Writing a single PDE from a gradient equation

I have a differential system like this, where $\Phi$ is a scalar valued unknown function: $$\nabla\Phi = \left(f_1(x, y), f_2(x,y)\right)^T$$ I'm trying to solve it in a FEM solver (COMSOL ...
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COMSOL Circularl polarization

I'm having some problems trying to implement circularly polarized light in COMSOL Muliphysics. For a isotropic homogenous media, I've obtained without problems the TE and TM reflectance curves. ...
2 votes
1 answer
197 views

Does mass balance hold in convective diffusion

I'm trying to understand how convection-diffusion equations are solved in pipe flow modules available in CFD solvers. $$ \frac{\partial C}{\partial t} + \nabla \cdot (\mathbf{v} C) = \nabla \cdot (D \...
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A lot of identical staff in Comsol material database?

I got a lot of elements in Material Browser of Comsol Multiphysics of Optics section. ...
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Fitting a multivariate PDE (using Java)

I'm doing simulations of 2 coupled PDE's with Comsol Multiphysics. I want to fit some data (using the Application method, whose language is Java) to those simulations. In order to answer my question ...
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Simulating flow in a branched pipe

I am trying to simulate 1D advection and convection of a solute in the following blood vessel segment. I would like to know if this system can be simulated in COMSOL or MATLAB. I have used pdepe ...
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For a determined (known) Space charge density, what are the conditions to obtain the Electric potential/field distribution? (COMSOL, MATLAB)

Theoretic part From the theory, in Electrostatics inside a real dielectric material between real conductors, in a simple 1D plane geometry between points $P1$ and $P2$, according to the current ...
2 votes
1 answer
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Derivatives over a Finite Element mesh

I have a data extracted from Comsol on some node points and I know the coordinates of each node. Does anyone know how Comsol calculate the partial derivative from the values at each node and also ...
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How to set an initial guess for the iterative solver in Comsol?

How to set the initial guess for the iterative solver GMRES or FGMRES for linear problems (Helmholtz equation of RF module) in Comsol?
3 votes
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Strain propagation from surface to bulk in COMSOL

I am trying to simulate strain propagation from the surface into the bulk. I have a rectangular semiconductor block (~2 μm thick) on top of which metal gates (~25 nm thick) are deposited as seen in ...
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364 views

Changing geometry scale breaks simulation

I'm trying to find the capacitance matrix for a small array of metal boxes in air using Comsol 5.4. The geometry presented here is a simple geometry that recreates the problem I'm experiencing. ...
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How to simulate water, falling under gravity, and impinging on a curved surface, which is kept/present in a domain, containing air?

TL;DR: How do I simulate a hole, at the bottom of a (full) water tank? I am attempting to simulate water, flowing out of a hole/slit, at the bottom of a tank (Water Domain) (under the influence of ...
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Simulation of a complicated projectile motion

I'm trying to model a projectile motion, considering every detail such as projectile aerodynamics, effects of wind, air temperature etc. What is a good software to model it in with good graphics? I ...
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temperature profile on axial direction of a chamber

I have a task to plot average temperature profile at each cross-section in the axial direction of a combustion chamber. I have $x$, $y$, $z$ coordinates data in excel as well as the corresponding ...
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3D visualization of the results of a 2D simulation in COMSOL

Considering that COMSOL forum is dead and CFD-online is not responsive, I'm gonna try asking my question here: I have done a 2D simulation in COMSOL multiphysics. I have two independent variables x ...
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Computing dilogarithm

I'm measuring the integral of a quantity which, mathematically, requires the computation of a dilogarithm function. $$\operatorname{Li}_2(be^{ax})$$ where $b$ and $a$ (are real and) can be positive ...
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2 answers
683 views

Mesh ordering algorithms used by COMSOL Multiphysics

Ordering of elements in an unstructured mesh is undoubtedly very important for the performance of computations. For example, it determines the structure of sparse matrices arising from PDE ...
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Modelling fracture flow in stress field in COMSOL [closed]

I am new to COMSOL and I want to model fluid flow in stress field. As starting point I want a simple 2D box having a fracture from right to left while pressure gradient vertically. I want to know the ...
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1 answer
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Flux boundary condition in solute transport

I have a pretty naive question, though important to me. Usually when solving the following PDE in solute transport: $\frac{{\partial C}}{\partial t } = \nabla. (D\nabla C -vC )=0,$ one can be asked to ...
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Why FEM electric analysis gives only access to current density?

A Comsol study using frequency sweep on electric current physics yields only current density as accessible variables. I understand the underlying equation used is Ohm's law, i.e. $$\mathbf{J} = \...
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How does rigid body rotation affect resuts in a simulation?

I have been running a finite-element simulation where, for the sake of convergence, I chose to stay in small deformation hypothesis (in comsol, include non-linear geometry box not checked for who that ...
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3 answers
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Understanding Finite-Element Modal Analysis

I am teaching a basic course on computational physics and for the last part of the course I will introduce freshman physics undergraduates to finite-element modelling methods. I am preparing a COMSOL ...
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COMSOL: get list of eigenfrequencies [closed]

In COMSOL, is there a way to get it to export a txt file with all the eigenfrequencies found during an eigenfrequency analysis? I suppose that it could be done through the MATLAB interface or through ...
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Different Meshes Different Maximum velocities

I am working on a model in COMSOL and I am usin different meshes from coarse to fine keeping the other parameters constant. And, I got different maximum velocities for all the meshes. What can I do ...
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Representing a 3D system in 2D (Electromagnetic modelling)

Ok so I'm a complete beginner in computational modelling (I use analytical methods of physics typically) but I would like to model an anisotropic, aperiodic (but not random) finite array of metallic ...
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Solving coupled PDE in COMSOL [closed]

I have the system of equations \begin{align} &A \frac{\partial u_1}{\partial t} = 1 - u_1 B \frac{\partial u_2}{\partial y}\\ &\frac{\partial u_2}{\partial t} = \frac{\partial}{\partial y}\...
10 votes
4 answers
364 views

How to make a good mesh in a biologically accurate model with very small domains

I have been trying to make a biologically accurate 2D spatial model of tissue layers, where different physiological processes happen. This includes mainly chemical reactions, diffusion and fluxes over ...
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3D Divergence-free Stokes equations

I would like to have a divergence-free formulation of the Navier-Stokes equations for creeping flow (a.k.a. Stokes equation, N.-S. without the inertial terms) in 3D, for purposes of tracking particle ...
14 votes
3 answers
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Alternatives to Comsol Multiphysics

This might be a question better suited for the Software Recommendations side of S.E., however I do believe that people who frequent this part of S.E. are more likely to be able to answer this question....
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infinite but non-periodic space with PMLs in Comsol [closed]

I have a problem with implementing proper boundary conditions on sides of my simulation (in RF or WaveOptics module of Comsol). I want to obtain an infinite but not periodic space (beacuse then I will ...
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What is numerical damping in the context of time-dependent FEM solvers?

Comsol Multiphysics (a popular FEM package) includes two time-stepping algorithms (IDA aka BDF, and Generalized-alpha), described in their documentation as follows (quoted here under Fair Use; ...
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1 answer
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boundary condition in COMSOL

I deal with PDE module in COMSOL and I would like to simulate Poisson's equation. Actually I need to simulate the distribution of the electric filed created by the spherical probe in the material, ...
1 vote
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COMSOL - 2D box - get for every x an average value over y (line average apply for more lines) [closed]

I would like to ask you for your help. I have 2D box. I know how to do an 2D cut line and compute an average value of someting over this line. (in Results -> Data Sets -> Cut Line 2D and then Results-...
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Integrating an Ordinary Differential Equation over a domain in Finite Element Methods

I'm trying to get a deeper understanding of the Finite Element Method (FEM) to better understand what I do in COMSOL and FEniCS. The sketch below shows the problem that I want to solve in FEM. The ...
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1 answer
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Calculating Divergence in COMSOL

Is it computationally safe and accurate to use the following equation in COMSOL to compute the divergence of the vector quantity J (instead of using its general built-in equations that have $\nabla$ ...
1 vote
1 answer
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How can I define Poisson’s equation in general and weak form in comsol

I want to simulate capacitor with Comsol by using Poisson's equation in genaral and weak form. How can I specify boundary condition for this case?
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How to solve global equation in Comsol only once? [closed]

Let's assume that I have a comsol model for solving time-dependent problem. In order to find initial value for one variable I need to solve simple algebraic equation before starting simulation, ...
2 votes
1 answer
674 views

Basic Finite Element Method (FEM) question: assembly and re-assembly

I'm reading up on the Finite Element Method (Zienkiewicz's Book), so I understand better what I'm doing in FEniCS and COMSOL. Currently, I'm wondering about this: Using FEM to solve fluid flow ...
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1 answer
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Divergence in COMSOL

I'm trying to calculate the divergence of a vector quantity $L(L_x, L_y, L_z)$ in COMSOL. I calculate it using the built-in differentiation operator as follow: $$\nabla L = d(L_x,x)+d(L_y,y)+d(L_z,z)$...
4 votes
1 answer
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Stress due to the mismatch of thermal expansion coefficients of two different attached materials in COMSOL

I'm simulating the thermo-electro-mechanical behavior of a copper wire which is surrounded by silicon dioxide. In other words, the wire segments is under mechanical and thermal loads and at the same ...
2 votes
1 answer
4k views

PDEs in their weak form in Comsol

If a physical model is not listed in the wizard, we can use Comsol's weak form to enter PDE's (governing equations of a system) in their weak form. How can it be done ? for example: 2 equations of ...
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Time stepping in comsol multiphysics

I would like to know which is the algorithm Comsol uses in order to correct the time step it uses. For example, when you try to solve an equation you've written in the PDE coefficient interface, and ...
1 vote
0 answers
4k views

Stationary solution converge but time dependent doesn't

I've coupled a COMSOL model for fluid dynamics with a very simple pde that model the transport of humidity in air. When I solve it for the stationary case, the solution converge easily, but when I ...
1 vote
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Can I use RANS to see the effect of mixed convection?

my question is: can I use a RANS simulation to see the effect of mixed/natural convection? Actually I have also a second question: I would like to do this in Comsol multiphysics, but it seems that it ...