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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12
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3answers
15k views

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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4answers
342 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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2answers
562 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 ...
6
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1answer
4k views

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; ...
4
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2answers
746 views

COMSOL on Ubuntu (10.04 LTS and 11.04)

I am running into a problem with COMSOL 4.2.0.187 on Ubuntu (both 10.04 LTS and 11.04). When using the option -np x with x > 1, ...
4
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1answer
3k views

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 ...
3
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3answers
2k views

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 ...
3
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2answers
604 views

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 ...
3
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2answers
8k views

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 ...
3
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1answer
5k views

In Comsol Multiphysics, is there a way to change parameter values when something happens in the solution?

I'm beginning to learn Comsol Multiphysics as part of a modelling course in my masters degree. Currently, we are modelling a circuit with a spark gap, which presents some problems for me. I'm using ...
3
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0answers
67 views

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 ...
2
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1answer
627 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 ...
2
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1answer
3k 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 ...
2
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1answer
107 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 \...
2
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1answer
151 views

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} = \...
2
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0answers
711 views

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
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0answers
3k views

COMSOL - Implementing Perfectly Matched Layers (3D)

If there are any COMSOL gurus here, I want to simulate a 3D RF system infinite in 1 direction. I realize I need to use PML's, but am unsure how to configure them. it seems that simply scaling them by ...
1
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2answers
106 views

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 ...
1
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1answer
766 views

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 ...
1
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1answer
158 views

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 ...
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1answer
1k views

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
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1answer
879 views

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?
1
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1answer
2k views

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)$...
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0answers
23 views

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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0answers
66 views

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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0answers
157 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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0answers
131 views

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 ...
1
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0answers
749 views

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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0answers
53 views

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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0answers
80 views

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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0answers
87 views

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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0answers
368 views

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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0answers
1k views

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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0answers
63 views

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 ...
1
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1answer
808 views

How to include parameters in plot title in comsol? [closed]

I have a comsol model. I want to draw a few plots for different values of a global parameter called plot_z, e.g. if plot_z can ...
0
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1answer
117 views

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 ...
0
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1answer
66 views

A lot of identical staff in Comsol material database?

I got a lot of elements in Material Browser of Comsol Multiphysics of Optics section. ...
0
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2answers
605 views

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 ...
0
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1answer
189 views

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?
0
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1answer
1k views

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 ...
0
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1answer
50 views

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 ...
0
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1answer
2k views

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}\...
0
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2answers
274 views

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 ...
0
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1answer
3k views

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, ...
0
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0answers
9 views

COMSOL Cannot evaluate expression

I'm working on a 2D model to simulate groundwater flow through pores using the Darcy's law interface. I'd like to eventually tie in flow and transport of diluted species. The domain is defined as a 0....
0
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0answers
29 views

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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0answers
22 views

Show deformed mesh in Comsol

I am using COMSOL Multiphysics 5.2a in order to do thermal, mechanical and thermo-mechanical simulations. Due to a boundary load, my components get deformed which I can simulate very well. However, ...
0
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0answers
29 views

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. ...
0
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0answers
24 views

Boundary conditions for triangular lattice in comsol

I am trying to simulate an infinite 2D triangular lattice in Comsol but I am confused that how should I use periodic floquet boundary conditions on the unit-cell. A unit cell that I am using is given ...
0
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0answers
46 views

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 ...