Latest Discussions - COMSOL Forums

mesh of rigid plane in contact mechanics

Sun, 28 Apr 2024 03:33:35 +0000

As attached a rectangular plane is drawn. Though the rectangular plane is not specified by the user to be a rigid body, it is assumed by comsol to be a rigid body. Does the mesh of the rectangular plane affect the simulation at all?

About the 'Reuse Solution from Previous Step' in Parametric Sweep

Sun, 28 Apr 2024 03:03:37 +0000

Hi there, I am trying to modeling the buckling and post-buckling process using the parameteric sweep and time-dependent solver like in this presentation about psudo-dynamic approach. We may take the buckling of a compressed bar as an extremely simplified example. Suppose a bar measured $L$ is fixed at the left end and loaded through displacement control in terms of nominal compressive strain $ee$ at the right end (as shown by the graph below). Due to the strong nonlinearity of the original problem, the steady problem is passed to a time-dependent one like in this presentation. The modeling is based on the time-dependent solver with parameteric sweep over $ee$. In each time-dependent study step, initial conditions like $w_0=0.1(1-cos(16{\pi}x/L)), u_0=-eex$ are prescribed and then the system is allowed to evolve for a sufficiently long time period $T$, say, $T=5000s$.

During the trail run, I encounter several questions:

1) The system doesn't seem to start from the initial conditions. For example, the result of $w$ at $ee=0, t=0s$ (shown belown) is quite different from the prescribed initial condition. And the $w$ profile at $t=0$ changes as $ee$ varies, though the box of 'reuse solution from previous step' is unchecked under the node of 'parametric sweep'. This is important because the steady configuration can be sensitive to initial conditions when the system have multiple energetic minimum. 2) How to perturbe the solution of previous step when the box of 'resue solution from previous step' is checked? In modeling a system with strong nonlinearity, it's hard for the model to directly evolve from an arbitrary initial condition into the realistic final configuration in a single time-dependent study step, for the final configuration may depend on the intermediate process. So, I suppose the 'reuse solution from previous step' is needed. Neverthless, only reusing previous results can lead to another question. In the compressed bar example, with 'reuse solution from previous step', comsol keeps giving the trivial solution as $ee$ increases far beyond its critical value (shown below), maybe because the system only has trivial solution at small $ee$ and this trivial solution keeps being passed on to the next parametric sweep step as initial condition. As a result, the system is stucked in the trivial solution. Maybe a perturbation needs to be added into the previous solution before it is passed on to the next sweep step as initial condition. 3) How to suppress the storage of intermediate time solutions in each time-dependent study step? In the psudo-dynamic approach, only the final solution at $t=T$ is realistic in a time-dependent study step. The intermediate solution from $t=0$ can be dropped, so that the disk space can be released. Is it possible to evaluate and store the strain energy for each $t$, but drop the rest solution before $t$ reaches $T$?

Thank you so much for your reading. I would appreciate it if anyone could shed lights on these questions.

Best regards, HC L

Coupling semiconductor and electrostatics physics in different domains

Sat, 27 Apr 2024 14:12:38 +0000

Hi. I am trying to simulate MOSFET with ferroelectric gate using Semiconductor Module. I am using semiconductor physics to simulate semiconductor part, but I need to use my own electrostatics equations (created with General form PDE) to interface with LGD (Landau-Ginzburg-Devonshire) equation in ferroelectric (dielectric) insulator part. How do I interface or couple semi with electrostatics? I need to couple electric potential from ferroelectric domain (with electrostatics equation) with semiconductor domain (with semi equation).

I tried many different setups. I think its something trivial that I am just missing. Any boundary condition? Making the semi and electrostatics with the same dependant variable (field name)?

I am sending my mph file, if anyone wants to looks at my model. I am thankfull for everyone who tries to help.

Species adsorption in Electrocoagulation

Sat, 27 Apr 2024 13:20:44 +0000

I am trying to simulted the electrocoagulation. And I have added the laminar flow, Secondary current distribution and also the transport of diluted species. The aluminum is getting dissolved into the solvent. and the pollutant is also getting dissolved. concentration of both species are increasing with time. I want to know 2 things. 1). how to go forward with the electrolysis at the cathode 2). how to simulate the adsorption of pollutant by another species.

I want to know how to model langmuir isotherm if possible.

How to build a pyramid based on a dodecagon

Fri, 26 Apr 2024 21:18:45 +0000

Hello guys! I'm asking if it's possible to build a pyramid based on dodecagon in 3D geometry. I tried to draw polygons and then convert them first in surfaces and then in solid but it doesn't work. I'm wondering if it's possible or not. Hope you'll help me! Kind regards and have a nice weekend!

Raffaella

adding two different materials

Fri, 26 Apr 2024 07:37:52 +0000

Hello,

I am working on a piezoelectric model of the main domain (quartz) and I want to add another material (Aluminume), but this message appears to me, I need help what is wrong have done "Undefined variable. - Variable: comp1.solid.epsilonrmZX - Geometry: geom1 - Domain: 2 Failed to evaluate Jacobian of expression. - Expression: dvol(comp1.es.DZcomp1.es.d) Failed to evaluate Jacobian of expression. - Expression: ((comp1.es.DXtest(comp1.es.EX)+comp1.es.DYtest(comp1.es.EY)+comp1.es.DZtest(comp1.es.EZ))comp1.es.d)*(dvol)"

How to Add AC Voltage

Fri, 26 Apr 2024 02:10:57 +0000

Hi all, I encountered some problems while using the current component in the AC/DC module, and I hope you can help me answer them. After adding an AC voltage with an amplitude of 5V to the model, the actual simulation result shows that the voltage amplitude is only 10^-7 power. I want to know what's going on. Or if you know how to add AC voltage, please let me know.

Thanks a lot.

How to use moving mesh to simulate an Electromechanics problem

Thu, 25 Apr 2024 14:47:32 +0000

Hi all

I meet a problem when want to solve a multiphysics problem when using solid mechanics and electrostatics.

I use 2D structure. And I have two parallel electrode, and there have two separate dielectrtic layer attached to each electrode, and the air is between them. If we apply the voltage to the electrode, then the two parallel electrode and dielectric layer will attach to each other until contact to contact to each other. I use moving mesh to simulate the moving of air between the electrode, because the electrostatic force have a relationship with volume of air. But I meet a problem, which is with the moving of two electrodes, the gap between two electrode is small, then the moving mesh of air domain cannot remesh, then the simulation is shut down. I want to know whether have a way to solve this problem? Or, whether there has a method to set the Contact criteria, if the gap reach a small value, then the software will assume this two plate have contact each other, stop the remshing and contract process.

Thanks a lot.

Best wishes, Jingcheng

FLow electrode capacitive deionization (FCDI) modeling, coupling of flow and electric fields

Thu, 25 Apr 2024 12:38:41 +0000

Hi all. I've been teaching myself COMSOL recently, and I'm trying to model flow electrode capacitive deionization, where a graphite collector plate on both sides applies a transverse DC voltage perpendicular to the graphite plate, and ions in the intermediate solution channel move directionally through ion exchange membranes on both sides to the flow electrode (a mixture of sodium chloride solution and activated carbon particles) in the presence of an electric field. I tried to simulate the flowing electrode (a mixture of sodium chloride solution and activated carbon particles) with a mixture model, and at the same time, following the example of electrodialysis in this case library, I used a cubic current distribution physical field to simulate the distribution of the electric field or the distribution of the degree of polarisation of the graphite collector plate in the case where the graphite collector is energised on both sides. The flow field simulation was successful, but unfortunately the electric field simulation calculations never converged. I wonder if I am overlooking some details or if I am choosing the right physical field. Any input on the above would be appreciated!

Failed initialization during second study step

Thu, 25 Apr 2024 12:34:27 +0000

Hi,

My model consists of two study steps. First, I apply certain boundary conditions in a stationary step. Then, I maintain these boundary conditions and apply an additional time-dependent load in a time-dependent study step. This used to work fine when modelling in 2D.

In 3D, both steps converge when run individually (i.e., a stationary study encompassing the boundary conditions and a time-dependent study without those boundary conditions but including the time-dependent load). However, when combining both study steps (i.e., applying the time-dependent load on the model that includes specific boundary conditions), I get the error during the initialization of the second step: * - Feature: Time-Dependent Solver 1 (sol1/t1) Failed to find consistent initial values. Last time step is not converged.*

I get the same error even when I don't change anything of the model during the time-dependent study step. It seems that the second study step is not (correctly) using the results of the stationary solver as initial values. Does someone know why this is the case and how I can solve the issue?

Thank you.

Using simultaneously a Parametric and a Function sweep

Thu, 25 Apr 2024 11:34:05 +0000

Hi, I am currently working on a model that I need to upload to a Cluster that has no MATLAB nor Javascript functioning, so everything must be contained in a .mph that i can run from CMD. I need to do several studies where a function and some parameters switch. If I have in my Study a parameter sweep and a Function sweep, the computation takes all possible combination beween these two sweeps. What I want instead, is to have studies done one to one.

As an example, if I have a parametric sweep with a parameter A taking the values (1,2) and a function sweep with (fun1(t),fun2(t)), what I want to be done is only 2 studies. One that takes [A=1,fun1(t)] and another one that takes [A=2,fun2(t)].

Thanks.

mass flux from rock matrix to fracture

Thu, 25 Apr 2024 07:30:45 +0000

Hello, everyone

I'm now doing TH coupling for a fractured geothermal reservoir. My model is very simple where a 2D surface (fracture) is emdedded in a 3D rock. What I want to do is to add a source term on the fracture (an interior boundary) indicating the mass flux from rock matrix to fracture. However I have no idea how to solve it.

Output in the result section

Wed, 24 Apr 2024 14:57:00 +0000

Hello Friends, I have a question. I would be grateful if anyone could help me I want to get an output, but I encountered a problem and I don't know how it is... In the data set section, I defined the maximum and minimum values and connected these two using join according to the formula I had (i.e. take the difference between the maximum and minimum temperature, divide it by the maximum value and give the percentage (data1-data2) )/data1*100 )) But I don't know how to get this output and show it now I would be grateful if any of my friends know how to guide me step by step. Thank you

Cohesive Zone Modeling only mode I

Wed, 24 Apr 2024 03:34:21 +0000

Hello,

I am modeling the connection of two objects using CZM (Cohesive Zone Modeling). I only want to utilize Mode I (tension) instead of Mixed Mode. Does anyone have any suggestions or tips?

Thank you.

heat transfer time transient analysis results are not smooth.

Wed, 24 Apr 2024 01:52:09 +0000

hello.

I am using COMSOL to perform a time dependent analysis and I am facing a situation where the resulting values over time do not converge (smooth continuous values).

The analysis is to calculate the temperature through Joule heating in a simple structure and I need to get a continuous and smooth value with respect to time. Even with a very small time interval, a few microseconds, the calculation shows a discontinuous change in slope at certain points as follows.

Is there any way to prevent this from happening with the time dependent solver option?

Thanks.

i uploaded (mash-deleted) model file. and you may check the graph image of transient temperature image from : ,,,

https://drive.google.com/file/d/1-1vwWjPE7z24-BxKagzqldwba9j11e3r/view?usp=sharing

,,,,

https://drive.google.com/file/d/1IhpdtN4fqCT-1m8jhsnLi8Z9ysAX_iRD/view?usp=sharing

Failed to find a solution

Tue, 23 Apr 2024 21:42:31 +0000

Hello Comsol,

I am trying to compute a model in electromagnetic waves, frequency domain. So, I have to find out two results, one with time modulation and other with without time modulation. When I simulated for without time modulation, I got the correct result and simulation working well. But, when I added time modulated equation in variables definition, I started getting errors. Initially, I got an error that the model is not converging, after I increased the number to iterations but as soon as I did that I get stuck in new error of singular matrix and returned is not converged. not all parameter steps returned.

I am attatching the model file with this message. Please let me know how can I reslove this issue.

Coupling Physics

Tue, 23 Apr 2024 16:58:13 +0000

Hi everyone,

How to couple the heat transfer in solids with the heat transfer in Porous media, as there are no options of multiphysic coupling. The interface between them is deined in the thermal insulation, however I want to simulate the heat transfer through this contact. I thought to define a heat source at the boundaries but I do not want to define a specific value, as I need to define the heat transfer from and to the heat transfer in solid in different scineraios.

If you have an idea, just say it. Thanks for your support

gear pumps

Tue, 23 Apr 2024 12:54:53 +0000

I am looking for anyone to share their experience with emulating gear pumps in COMSOL. I am looking for feedback on the modules used, the problem setup including. Boundary conditions, and solver configuration.

Coupling the Deformed Geometry (dg) interface with the Laminar Flow interface

Tue, 23 Apr 2024 11:01:36 +0000

Hi Could you please suggest a way for me of how to couple the Deformed Geometry (dg) interface with the Laminar Flow interface in 3D model?

Transient Simulation in COMSOL

Tue, 23 Apr 2024 10:35:08 +0000

Hello,

Is it possible to the transient simulation in COMSOL just by changing the source signal with different period? Without using the "Events" could we do transient?

Challenge: I am getting same rise and fall time for three different material in a single device. Lets's say in Silicon on Insulator, I am getting same transient effect for silicon as well as silicon dioxide.

Thanks