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Global ODE or General form PDE

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Hi everyone,

i need to input this equation into my model and i am very unsure as to how you go about doing it.

td * (du/dt) = T_avg > Td

td = time taken
T_avg = average temperature of the cell
Td = temperature needed for the cell to be destroyed.

could someone please help me out.

thanks in advance!

work with deformed geometry

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Dear Colleagues,

I have to perform nonlinear analysis on thin walled columns. Before performing this study I need to model geometric imperfections. I want to follow this procedure:

1) perform a stationary study where I model imperfections
2) export deformed geometry (because in nonlinear analysis I want to study my deformed geometry without stresses born from step (1))
3) perform nonlinear study

So, is it possible to do that? I have a solid model and I need to use a particular mesh (prismatic element, quadratic shape functions and only one finite element along the thickness).
I tried to use “Remesh Deformed Configuration”, but seems to work with tetrahedral elements only. I must use prismatic element because I have a better description of the problem with less, many many less, degrees of freedom.

Thanks for any suggestions (or for alternative methods to solve that problem).

Simone

Simulation error

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Hi ,

I am getting this type of error whey i am trying to start simulation.

"Variables property does not include all variables in Xmesh"

Could anybody can give me any solution/ suggestion.

Thank you
Sanjay

magnetic field gradient in 3D return zero!

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Hi everybody

If anybody knows that why the gradient of magnetic field in 3D models is always zero? I checked the different methods. for example I wrote d(Bx,x) or different component of B and H. Even d(d(Ax,x),x) is always zero! I am using the quadratic discretization. It is OK when I simulating in 2D or 2D axisymmetric, However the similar geometry in 3D give the zero for gradient of magnetic field.

could somebody help me?

Acoustic Band Structure of Metamaterials

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Hi folks,

I have been trying to find the band structure of an acoustic metamaterial. I have been attempting to adapt the "Bandgap analysis of Photonic Crystal" tutorial given for COMSOL 3.5a to 4.3. I am attaching the tutorial here. I was having some difficulties in implementing the same in 4.3.

1. The model says "Open the Solver Parameters dialog box from the Solve menu. Choose Harmonic propagation from the Analysis list." . However, I have not been able to find 'Harmonic Propogation' or an Analysis List in 4.3. How do I implement this?

2. The model says- "1From the Physics menu, choose Scalar Variables.
2In the dialog box that appears, enter the value freq for the nu_rfwe variable. Click OK.
3Click the Solve button on the Main toolbar. COMSOL Multiphysics uses the latest eigenvalue to calculate the initial guess for the ODE variable freq."

There is no 'Scalar Variables' options under the physics menu in 4.3 . Also, there is no 'nu_rfwe' variable. How do I get around this?

I would also appreciate any help in adapting the same for an acoustic metamaterial.

Coupled PDEs, Last time step is not converged

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Hi,
I am new to COMSOL, and what I encountered is about coupled PDEs. I have two coupled PDEs in one physics model in general form. One is about heat transfer (T), the other is an ODE used for the source term of the heat transfer (T). The ODE looks like du/dt=f(u,T), namely du/dt is a function of u and T.

When I ignore the T, like du/dt=f(u), COMSOL works. But it doesn't work when I consider the T. As follows.

Repeated error test failures. May have reached a singularity.
Time : 0.334945980028302
Last time step is not converged.

Thanks,
Du

DEP particle tracing for fluid flow COMSOL 4.3 simulation

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Hi,

I've tried to simulate dielectrophoresis by using the particle tracing for fluid flow module of COMSOL 4.3, but I' ve encountered some problems with the dielectrophoresis force.

I am trying to follow the simulation described in the powerpoint presentation, you can find here:

community.cmc.ca/servlet/JiveS...ling%20in%20COMSOL%204.2a.pptx

but my 3D model is only able to simulate drag force together with the gravity force. If I add the dielectrophoresis force, COMSOL shows me a message of error (Image1.png).

I've tried to simulate the electric field in the frequency domain in a separately Study: COMSOL outputted no errors, but particles remains in their initial position.

So, I choose to simulate in the same Study both the electric field and fluid flow contributions with a stationary solver, however dielectrophoresis force is not taken into account.

Could someone please help me fixing this problem, making my DEP model working?

Thanks in advance,
Selina

Error while simulating Trussed Leg

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I am currently doing a simulation on both Cylindrical and Trussed Leg for Jackup Units. I have ended the simulations for Cylindrical Legs using Comsol 4.3b. Sadly, I am getting an error while using 4.4 for the Trussed Legs. I am using the same parameters and I get:
Failed to find consistent initial values.
System matrix is zero.
Last time step is not converged.
- Feature: Time-Dependent Solver 1 (sol1/t1).

And in the Error Tab it says:
Failed to find consistent initial values.
System matrix is zero.
Last time step is not converged

Can anyone help?

Auxiliary problem on different domain

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Good afternoon!

I am simulating the reaction-diffusion problem in 2 domains separated by a membrane with transmission conditions on this membrane.

I have 3 reaction-diffusion equations for 3 functions: u, u2, u3.
u (t, x, y) and u2 (t, x, y):
- are defined on 2 2d domains (which are squares actually) with the adjacent boundary (= membrane = S = (x, 0))
- on the S each has Neumann condition defined by the integral of u3

u3 (t, x, y, z):
- is defined on 3d domain ([0, 1] x [0, 1] x [-1, 1])
- has Dirichlet boundary condition on 2 (out of 6) boundaries defined by the functions u and u2 (u3(t, x, y, 1) = u (t, x, 0); u3(t, x, y, -1) = u2(t, x, 0))

I define 2 different components: one for 2d problems, another - for auxiliary 3d problem.

I receive the following problem: Failed to evaluate variable Jacobian. Under variable u and u2 are understood in the part where they enter boundary conditions for u3.

I think that maybe the problem is related to the fact that the functions are defined on different domains and in different components, but I do not know the way to define the equations in one component.

Could you give me a piece of advice how to overcome this error?

Another problem which I have is the abortion when I try to switch to the tab with the second (3d) geometry. It is displayed on the other tabs (e.g. on the Convection-Diffusion Equation tab), but when I try to switch to the Geometry Comsol shuts down.

I would appreciate any help you could provide.
Thank you in advance!

COMSOL help needed. (RF module - Heating of water using waveguide)

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Hello there,
I am a relatively new COMSOL user who is in the process of validating a paper, to be able to get a better grasp at COMSOL.
The paper I am trying to validate using my simulation can be found here:
dspace.library.tu.ac.th/bitstr....pdf?origin=publication_detail
On page 547.

I want to use a wave guide to send microwaves in the TE 10 mode to the water body in an air container.
The water body exhibits dielectric loss, The equations are found in table 1 page 550.

I have followed the microwave over(potato) model and feel like I've set up everything appropriately, however when I conduct the study the results indicate that the water body is not heating, perhaps there is a mistake in the way I defined the physics.
I've been trying to crack my head around this, but have had no luck.

In the attachment I've included my model. The paper also describes the boundary conditions in page 547.
The result I wish to achieve is the graph in page 553( Fig. 11 )

Any help or words on this matter will be greatly appreciated.

Kind regards,
Mohammed

Failed to find consistent initial values

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I am fairly new to COMSOL and I realize this topic has been covered in the discussion forum, and one of the major problems seem to be that the initial conditions are too far from the final solution.
However, I'm working on a two phase flow problem using the Darcy flow module and I want to start with a 2-D box completely saturated with water (the wetting fluid) into which I introduce a second fluid (non-wetting, with greater density) at a known velocity. The only way I've been able to get the model to converge is to give the model unrealistic initial conditions. Any suggestions would be greatly appreciated.

about MUMPS allocaion factor increased

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When I use MUMPS solver, the warning is MUMPS allocaion factor increases to 1.44. What is the mean? Although the warning is exist, I can also get the result, then the result is right? What is the reason? grid, time step, or other Settings? What should I do?

thank you!

Strange issue with laminar flow level set method

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Hi, I recently started using the laminar flow level set method to simulate the motion of water in a partially filled channel as air flows above it. The simulation runs well when the distance scales are large (50 m model width for example) running for a full 15 seconds time range or longer, but when I drop this to smaller scales (such as 5m) the simulation just blows up a few seconds in (or less) with water appearing from the outlet boundary for no reason. Anyone know what could be causing such an error?


Hoping for a match.

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Hello everyone,

Before starting simulating tensile tests on defective steel bars, I want to make sure that the software behaves properly : I define the behavior of my material by interpolating some points (true strain/true stress) of an experimental hardening function, then I run the software for a simple cylindric bar without defects.
The software should normally return a behavior curve similar to the one I submitted. Unfortunately, this is not the case. One can see the difference on the file attached (xlsx).
I took care to choose the best interpolated points that reproduce the experimental behavior curve as faithfully as possible, and I verified that my points are ok by plotting the interpolated hardening function on the software interface before running the computing. I also tried to change my points (choose more points at the end of the curve to insist on that part for instance) but the numerical behavior curve has always the same shape, the one shown on the attached file. I really don't understand why it does not behave properly through all the strain interval. May be it's the type of extrapolating that I selected (linear) ?

If you have any idea or comment, feel free to share it ;)

Regards.

error: may have reached singularity

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Hi
what is meant by this error"repeated error test failures, may have reached singularity" and at what place does the error come from? from mesh, geometry, or what? i try to model DC Discharge plasma jet model

Error in DEP simulation-Help

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Hi All,
I m getting simulation error while simulating DEP based separation.I choose particle tracing with time dependent study, I m able to simulate for laminar-starionary, electric field-stationary..
i have following error when simulating particle tracing - time dependent study
Complex number encountered in real expression.
- Expression: (mod1.fpt.Ftx-d(mod1.qx,t)*d(mod1.fpt.mp,t))/mod1.fpt.mp
- Geometry: 2
- Boundary: 1

If anybody can help, i will be highly oblige

Random relative error for identical compute run

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I have just spent... don't ask.... a long time doing dozens of runs of the attached 2 plate capacitor driven in EC by a CIR current source single pulse.

* CONVERGES fine. Identical every time.

BUT
I get a Relative error in, say 10 repeats of the exact same mesh, exact same everything.
Erel = 7.9, 11.0, 8.6, 7, 3.8, 3.2, 1.9, 5.3, 7.1 ...

I have tried multiple runs where I "Delete solutions" each time.
I have tried multiple runs where I "Delete history" each time.
I have tried multiple runs where I "reload a whole new save, solution-emptied .MPH" each time.
I have tried multiple runs where I "reload a whole new save, solution-emptied .MPH + restarting COMSOL each time" each time.

The data it produces is the same. Except once, where a DELETE SOLUTION radically altered the solution from one solution to another that was then consistent.

Increasingly fine meshes do nothing. It just takes longer. Everything else stays the same, except the solution (max voltage in a potential slice) changes slightly.

Q1. Why? What do I have to do to get a consistent behaviour out of it?
Q2. I am told that these values for Erel are awful and I should not trust the data. Yet all I get is a 'warning' and no clue what to do about it. All the graphs look OK.

I am in need of some wisdom.
Please.... anyone out there got any pointers?
Offending .MPH is attached. It's small and takes 3 mins ish to run with mesh 2.

regards

Colin

switch off saving of recovery files in Matlab code

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Hello community,

I am running Comsol through the Matlab interface. My problem is that the directory assigned to the recovery files is to small to save them which terminates my calculations.

I would like to know how I can change that. I know that I can just uncheck the button on the COMSOL interface but I need the matlab command.

I tried relocating the recovery folder when starting up comsol in the terminal ( I use LINUX) with

comsol matlab -prefsdir /path
and
comsol server matlab -prefsdir /path

but both didn't work. I tried to relocate the folder in my home file
/voglerd/.comsol/v42/recoveries
by changing the file prefs.dir that was under /voglerd/.comsol/v42/
by rewriting the line
general.recovery.recoverydir=/<path/voglerd/.comsol/v42/recoveries>
to
general.recovery.recoverydir=/<newpath>

All that didn't work. Is there a command that you can write into your code before the solver configurations that switches off the saving of recovery files???

Any help would be much appreciated.

Best,

Daniel

Java Runtime Environment error

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Getting following error,

A fatal error has been detected by the Java Runtime Environment:
#
# SIGSEGV (0xb) at pc=0x0000003da3efbc6c, pid=6909, tid=46912497239488
#
# JRE version: 6.0_20-b02
# Java VM: Java HotSpot(TM) 64-Bit Server VM (16.3-b01 mixed mode linux-amd64 )
# Problematic frame:
# C [libgtk-x11-2.0.so.0+0xfbc6c] gtk_icon_set_render_icon+0x58c

Does anyone know how to resolve it...

Regards

how to use the "Previous solution" as initial value for new analysis

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Any idea how to use the "Previous solution" as initial value for new analysis, for the sake of solution convergence??
Preferably, step-by-step procedure!

Thanks,
Hina
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