Latest Discussions - COMSOL Forums

State variables

Thu, 20 Feb 2025 16:41:32 +0000

Hi,

I am currently using State Variables to model the permanent change in boundary conditions (BCs). In the global parameters, I have defined Switch = 1 and utilized the following expression in State Variables definition to model the permanent change:

State: Switch Initial Value: 0 Update Expression: if(ps > pt, 1, Switch)

Additionally, I have set up the following condition for the BC transition:

Name: E_a Expression: if(Switch == 1, Ea, Ec)

The model converges. However, when I plot the Switch parameter, it displays values between 0 and 1 instead of just 0 or 1. This has caused me to question whether the BC switch is functioning correctly and if the results are accurate. I would appreciate any insights or advice you could provide.

Thank you in advance for your help!

Best regards,

Kedar

Understanding electrical continuity

Thu, 20 Feb 2025 14:41:04 +0000

I would kindly like to understand how COMSOL 'mf' physics interprets conduction continuity through different geometric domains that has physical contact. In the attached example model, I have a simple bus bar with two cylindrical tabs, to represent an input and output. I want to apply a current excitation to the input tab (Coil 1), conduct through the bus bar and then look at the current coming out of the output tab (Coil 3). I tried applying 'Passive Conductor' condition for the bus bar, but I cannot get any current flowing through it in a stationary study. I even tried a 'Coil' model for the bus bar and set it to 0[V] but still doesn't work.

The reason why I want to keep them as separate coils because I have a more complex bus bar model where there are more than one in, out and filter tabs attached to them that I want to link to an electric circuit, and see all the different conditions acting together on the bus bar. Could you please help me understand how I can resolve this in the simple model?

weak contribution implementation

Thu, 20 Feb 2025 11:35:31 +0000

Hello,

I have some questions regarding implementing the weak contribution in different physics. Let's assume we want to implement the weak contribution for a specific current/concentration equation in the battery module on a domain or boundary region. Since the dependent variables are electric potential and concentration field in this physics, please help me to get clarified about the following questions:

1- by applying the weak contribution to the domain region, will the weak expression be added to the governing equation? if yes, would it be added to the potential or concentration field equations?

2- is test() operator determining the corresponding governing equation?

3- when applying the weak contribution in the boundary region, how would it be included in the equations?

Kind Regards

Ahmad

Objective function

Thu, 20 Feb 2025 05:21:42 +0000

Respected Faculty

Please suggest, what is syntax error in this objective function for heat transfer through radial object ? I am using Comsol multiphysics version 6.0

(1-q)*comp1.intop1(k_simp*ht.gradTmag^2)+q*h0*hmax_design/A*comp1.intop1(sqrt(d(comp1.dtopo1.theta,x)^2+d(comp1.dtopo1.theta,y)^2)^2

Thank you sir

Evaluation of a value at a specific point within a Cut Point 3D Grid Dataset

Wed, 19 Feb 2025 14:52:47 +0000

Hopefully a quick and easy one!

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.

Obviously if the dataset had 1 discrete point, I would just evaluate mfnc.Bz for the dataset.

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!

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.

Thanks in advance for your guidance...

Mark

Modelling Magnetostriction and defining bias point for AC simulation in Magnetoelectric Antenna Design.

Wed, 19 Feb 2025 14:30:24 +0000

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.

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.

Thank you.

Neumann BC at the outlet in laminar flow module

Wed, 19 Feb 2025 13:59:27 +0000

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.

Comsol manual states that velocity @ inlet and outlet is not feasible. It has to be velo and pr or vice-versa.

The solution converges fine with velo @ inlet and pr BC @ outlet but the axial pr gradient does not match solution in literature.

Any help/advise is appreciated.

Can COMSOL Simulate Corona Discharges in 3D Models?

Wed, 19 Feb 2025 07:20:26 +0000

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.

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?

Does COMSOL’s Electric Discharge Module provide a solution for this? Can this scenario be simulated in COMSOL?

Using a single Matlab function for electrical conductivity as tensor but COMSOL requires one function per tensor component

Wed, 19 Feb 2025 00:50:57 +0000

Hi,

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.

So, is it possible to pass the full tensor to COMSOL so that the tensor is calculated only once?

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?

Whether in the Materials definition or the "Electric Currents" interface, I would like a way to pass the full tensor to COMSOL.

Thanks.

How can I select a point as a source of my prescribed velocity in a 2D geometry?

Tue, 18 Feb 2025 21:10:15 +0000

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.

define crystal drug material

Tue, 18 Feb 2025 14:24:09 +0000

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?

Modelling CFRP (Carbon Fiber reinforced polymer)

Mon, 17 Feb 2025 13:02:16 +0000

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?

Guidance Needed On How to Correctly Add Piezoelectricity?

Sun, 16 Feb 2025 22:54:58 +0000

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.

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.

The d-operator is not well defined in the current context, use dtang or mean and d operators instead.

Sun, 16 Feb 2025 10:25:49 +0000

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.

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:

“The d-operator is not well defined in the current context. Use dtang or mean and operators instead.”

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.

Could anyone kindly help me resolve this issue?

Guidance Needed for Designing a Coil

Sat, 15 Feb 2025 09:44:02 +0000

Dear COMSOL Community,

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.

-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?

-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?

-What boundary conditions are typically applied to such problems?

If anyone has experience with similar simulations or could point me to relevant tutorials, documentation, or example models, I would greatly appreciate it.

Calculating heat generated during cell thermal runaway

Fri, 14 Feb 2025 15:14:31 +0000

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.

Thank you.

Microwave drilling in COMSOL

Fri, 14 Feb 2025 14:25:03 +0000

I'm completely new to COMSOL and I need help on How is microwave drilling process to be carried in COMSOL?

Bending of Clamped orthotropic rectangular plate due to uniform load

Fri, 14 Feb 2025 11:34:23 +0000

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 Shell 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;

Subsequently, the following are the settings in the Shell Local System node: 1. Coordinate System Selection: Global Coordinate System

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.

My question here is what is coordinate system that COMSOL will use for defining the material properties?

PEM water electrolyzer

Fri, 14 Feb 2025 11:10:52 +0000

Hello everyone,

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.

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.

However, I am currently encountering an error, as shown in the attached image. Would anyone be able to help me with this issue?

To aid in understanding, I have attached the MPH file and the image.

Any opinions or questions are welcome! ?

Conductivity gradient error

Fri, 14 Feb 2025 05:10:39 +0000

Hello everyone,

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.

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.

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.

I would really appreciate any guidance on how to address this issue. Has anyone encountered a similar problem?

Thank you in advance