Latest Discussions - COMSOL Forums

What is the meaning of (nitf1.qwf_u)?

Thu, 31 Jul 2025 01:00:13 +0000

I just know this formula for calculate the power of exchange but i do not know the exact formula contained in it. I will appreciate it, please help me.

Suppress recovery files writing from Matlab

Wed, 30 Jul 2025 12:28:23 +0000

Dear Support, I'm running Comsol 6.1, and doing simulations from Matlab. I am running a different Matlab/Comsol instance for each of the 32 cores of my workstation, and each is running a loop. The problem I have is that each is loading the hard drive with writing recovery files. Besides of the wasted space, I worry this is going to reduce its life, and I want to suppress all unnecessary writing. How can it be done? Looking at the names of the files, there seem to be geometry files, mesh files, etc. I got the impression that each Comsol server instance opened its own folder in the AppData/Local/Temp folder, and wrote recovery information for each loop step, which quickly amounted more than 100Gb of unneeded data.

Best regards, Javier

Quantification of Loss Due to Evanescent Phenomenon in Underground-to-Aboveground RF Communication

Tue, 29 Jul 2025 21:45:05 +0000

Hi everyone,

I am simulating underground-to-aboveground (UG-to-AG) RF communication using the RF Module in COMSOL. Specifically, I placed a dipole antenna underground and evaluated the power both just below and above the soil-air interface to study the evanescent wave phenomenon and quantify related losses.

As we know, evanescent waves occur when the incident angle exceeds the critical angle at a dielectric boundary (in this case, from soil to air), preventing the wave from propagating into the upper medium.

However, in the case of a dipole antenna, which emits a spherical radiation pattern, it is unclear how to define or compute a unique incident angle. I am wondering:

What is the correct way to verify the presence of evanescent waves in this scenario?

Can the incident angle be inferred from the phase of the field (e.g., arg(emw.Ez)) or perhaps by tracking the direction of the Poynting vector near the interface?

How do we quantify evanescent loss, and how can we distinguish it from reflection loss in COMSOL simulations?

Any guidance or references on how to confirm evanescent behavior and quantify associated losses in full-wave simulations like COMSOL would be highly appreciated.

Thanks in advance!

Simple model not converging

Tue, 29 Jul 2025 15:33:35 +0000

Hi all,

I am trying to model electric field shielding with a copper box that has some holes in it. I feel as though this should be a very simple simulation for COMSOL to run, but for some reason my convergence plot plateaus before the specified tolerance of the solver. I have tried doing very fine meshing, and this did not help.

Does anyone know what I can do about this?

Thanks

Importing "STEP file" into geometry of COMSOL showing no geometry?

Tue, 29 Jul 2025 09:30:04 +0000

Please if someone can help with this matter?

Error in Fluid Structure Interaction

Tue, 29 Jul 2025 09:14:53 +0000

Dear all, I am trying to simulate a closed rotating cylinder with a solid object like cube or ball which will be displaced due to the rotation of the cylinder (The cylinder is filled with water). Maximum no of newton iteration reached, i also tried direct solver which normally worked when i had convergence errors in other models i had done. Also what type of boundary condition should be given for the object?. I had given moving mesh to the fluid domain and also prescribed displacement for the solid body.

Thank you for your time

An Unexpected Error occurred while opening files.

Tue, 29 Jul 2025 07:33:38 +0000

2025-07-29T15:13:00.513+08:00 INFO Using locale: en_US
2025-07-29T15:13:00.686+08:00 INFO InitNativeRenderDevice with screenDpi:96
2025-07-29T15:13:00.687+08:00 INFO C:\Program Files\COMSOL\COMSOL62\Multiphysics\ext\graphicsmagick\win64;C:\Program Files\COMSOL\COMSOL62\Multiphysics\lib\win64;C:\Program Files\COMSOL\COMSOL62\Multiphysics\bin\win64;C:\Program Files\COMSOL\COMSOL62\Multiphysics\java\win64\jre\bin;C:\Program Files\COMSOL\COMSOL62\Multiphysics\ext\dcm\win64;C:\WINDOWS\system32;C:\WINDOWS;C:\WINDOWS\System32\Wbem;C:\WINDOWS\System32\WindowsPowerShell\v1.0\;C:\WINDOWS\System32\OpenSSH\;C:\Program Files (x86)\NVIDIA Corporation\PhysX\Common;C:\Program Files\NVIDIA Corporation\NVIDIA NvDLISR;C:\Program Files\MATLAB\R2022b\runtime\win64;C:\Program Files\MATLAB\R2022b\bin;C:\Program Files (x86)\Microsoft SQL Server\160\Tools\Binn\;C:\Program Files\Microsoft SQL Server\160\Tools\Binn\;C:\Program Files\Microsoft SQL Server\Client SDK\ODBC\170\Tools\Binn\;C:\Program Files\Microsoft SQL Server\160\DTS\Binn\;C:\Program Files (x86)\Windows Kits\8.1\Windows Performance Toolkit\;C:\Program Files\dotnet\;C:\Users\dell\AppData\Local\Microsoft\WindowsApps;
2025-07-29T15:32:18.494+08:00 ERROR Unexpected error. System.ArgumentException: Value does not fall within the expected range. at ComsolDesktop.Bridge.BridgeCommonDialogManager.HandleClientDialog(DialogViewWindow dialog, NDialogContent dialogContent, List`1 widgetChanges)
at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)

How to create non-uniform geometry array in COMSOL

Tue, 29 Jul 2025 06:47:22 +0000

I want to create an array of ellipses ( i.e. a Nanobeam Cavity ) with each of them having major and minor radii and spacing defined by a function. I already tried Comsol with MATLAB, but that creates the ellipses but not parameterized, i want the parameters to be an comsol array which i can change to get the parameters of each ellipse in the and they will also change accordingly. For reference I have attached my scripts of MATLAB, but these dont parameterize the geometry instead each of the geometry is just separate entity and I cannot optimize them. My idea is to use a COMSOL vector as the the parameter for radii and lattice constant of the photonic crystal cavity and use the vectors indexing as a parameters for creating the array of geometries, but COMSOL only allow diplacement to be a vector not the geomtery parameters like radius and there is no for loop in COMSOL geomtery creation to get the indexing of vector and generating geometry array. Even using MATLAB I dont get how all the geometry of the array can be parameterize with just one vector.

Load vector extraction

Mon, 28 Jul 2025 08:23:06 +0000

I am using Livelink for MATLAB for research. I want to extract the load vector in the steady-state problem of solid mechanics. I use mphmatrix to extract according to the guidance document, but the result of the extraction is a field ' as1 ' rather than a specific vector. What should I do ?

X axis for Fourier Transform

Sun, 27 Jul 2025 04:27:20 +0000

So I am doing a RF simulation in the frequency domain. I want to look at the beam profile behind my launch port as there is a back scattering event happening.

I was dealing with other scattering events possibly interfering with my data so I though I could do a spatial fourier transform and filter out the other scattered waves by their wavenumber

My main question is the x axis data for my line graph showing the FFT, should i just make it the dataset space variable or should i have it as arc length to properly display the intensity vs wavenumber. The hierarchy of data is as follows I have a cut line 2d that samples the data directly behind my launch port I then have a spatial FFT that has its dataset from the cut line 2d

I then create a line graph from the spatial FFT with the following expression for Y

abs(fft(sqrt( (0.5real( emw.Exconj(emw.Hy) - emw.Eyconj(emw.Hx) ))^2 + (0.5real( emw.Eyconj(emw.Hz) - emw.Ezconj(emw.Hy) ))^2 + (0.5real( emw.Ezconj(emw.Hx) - emw.Ex*conj(emw.Hz) ))^2 )))

Im confused on this because the peak K when i have the x axis as dataset space variable is rather low

meanwhile if I choose arc length I get this where the peak is rather high compared to my vacuum wavenumber of my wave of 1467 1/m

I have attached the link to my mph file and the interpolation file used for my plasma data if that is of interest.

https://drive.google.com/drive/folders/19PSXzqse9gKx34wrRkHaxVEES8iZuziW?usp=sharing

inherent phase-Variable

Sat, 26 Jul 2025 12:47:13 +0000

With a workaround I can get the inherent phase variable and the phase-slider in Results to work effectively with Coefficient PDE Form and Frequency Domain study.

I add an extra frequency-domian-physics-modul like emw, but disable it in the solver. It even gets no domain assigend.

It just activates the phase slider (or Phase Section) in Results with changing values for Coefficient PDE Form values when using the slider.

How can I make the Phase Section appear in Results without this workaround?

Greetings

How to Model Shape Memory Polymer (SMP) Behavior in COMSOL

Sat, 26 Jul 2025 11:54:07 +0000

I am seeking to simulate the thermomechanical behavior of Shape Memory Polymers (SMPs) using COMSOL Multiphysics and would appreciate guidance on the most suitable approach.

Shape-memory polymers (SMPs) are polymeric smart materials that can return from a deformed state (temporary shape) to their original (permanent) shape induced by an external stimulus (trigger), such as temperature change. Their shape memory behavior is based on the thermo-viscoelasticity of polymer materials. The key SMP behaviors I am aiming to simulate include: -Shape fixity -Shape recovery -Thermo-mechanical coupling (interaction between temperature and mechanical loading

My specific questions are:

What is the recommended best method or approach for modeling SMP behavior in COMSOL? (e.g., built-in physics interfaces, user-defined material models, external C-code (External Material Model), etc.)
Considering the viscoelastic properties and temperature-dependent modulus changes of SMPs, what constitutive models should I use to integrate these behaviors into COMSOL, and which modules might I need for this purpose? (e.g., Arrhenius-type equations, Toll-Feng model).
Can you suggest a step-by-step simulation approach for a specific SMP model (e.g., thermally-triggered)?

Thank you in advance for your help and guidance.

Problem with secondary current distribution physics for modeling an electrolysis cell

Fri, 25 Jul 2025 14:41:56 +0000

Hello everyone! I have modeled an electrolysis cell using secondary current distribution physics. I have a porous anode and cathode and a separator (predefined not available, it's a geometry with electrolyte conductivity) in between in this model and electric potential and ground applied on cathode and anode respectively. when I run the model, I see discontinuity in the current distribution over the thickness of the cell. Current density jumps very high at the separator and opposed to what I expected for electrode and electrolyte current density (I expected electrolyte cd to decrease from current collector to separator in the cathode and opposite trend for the electrode cd), they are almost uniform. I really appreciate your help in this matter!

How to limit the initial length of the truss

Fri, 25 Jul 2025 03:51:45 +0000

After importing the Truss physics, I didn't know how to limit the initial length of the truss I defined, which caused me to be unable to determine where the point of the truss axial force was 0 in the subsequent legends about the axial force of the truss

Dynamic Parameter Sweeps

Thu, 24 Jul 2025 15:48:58 +0000

I've been simulating micro ring resonators in COMSOL for a while now, and wondered if there's anyway to implement a 'dynamic' parameter sweep when trying to characterise the resonators response.

As it is currently, the wavelength can be swept only by a fixed interval. This means that an interval value that is small enough to map a resonance in high detail also wastes lots of data (and computation) points plotting the response outside of the resonance where the change is minimal.

Is there a way that the sweep interval value can be calculated as a function of the transmission from the through port?

I.e. When the change in transmission relative to the last point in the sweep is low (non-resonant), the interval increases to speed up computation - Sweep gets more coarse

When delta is high (in resonance), the interval decreases to map notch with high resolution - sweep gets more fine

Any help on this would be appreciated, thanks!

Space Charge Density for Frozen and Stuck Charged Particles

Thu, 24 Jul 2025 04:14:56 +0000

When I used The Electric Particle Field Interaction multiphysics to compute potential, I found that space charged density is zero at the boundary where the particle interaction condition is stuck or frozen, but this is not correct considering more and more charges would accumulate at the boundary and contribute increasing space charge density to determine the resulted potential. Can anyone help to solve this problem?

Volume reference temperature and initial intrinsic stress

Wed, 23 Jul 2025 20:21:00 +0000

I am trying to model a film deposition process on a substrate where:

(1) the substrate is heated up from room temperature in such a way that surface temperature of the substrate is non-uniform. I can achieve this by using a spatially varying input heat flux and/or temperature boundary conditions etc... No issues here!

followed by

(2) a film of a different material is deposited on the surface such that the "Volume reference temperature" of different parts of the film matches the temperature of the substrate directly underneath the film. Would someone know how to do this? I do not know how to enter different volume reference temperatures for the substrate (which would be the room temperature) as well as the different parts of the film -- which would be the temperature of the substrate at the location directly underneath the film obtained from item #1 above.

and

(3) the film should have an intrinsic stress tensor that is spatially varying. This can be read from an external file. This intrinsic stress should be activated only when the film is deposited at the elevated temperature -- it cannot be present from the beginning. Would someone know how to do this?

followed by

(4) the whole substrate+film assembly cooled down to room temperature. This part is straightforward too.

Thank you for any pointers!

Circular variable dependency when using surface slope error model in axisymmetric coordinates

Wed, 23 Jul 2025 17:36:57 +0000

I have encountered a circular variable dependency error when using the Scattering Boundary's "Surface slope error" model in axisymmetric coordinates. I am not certain, but this appears to be an internal error. I would appreciate help in confirming the root cause and finding a resolution to the problem.

Briefly, the error can be replicated by:

Using the Ray Optics module
Choosing the axisymmetric coordinate system
Creating a cylindrical domain
Applying a Release from Boundary boundary condition to the lower boundary, with only a z-component
Applying a Scattering Boundary boundary condition with the "Surface slope error" model selected to the upper boundary
Attempting to compute a solution

I have attached two virtually identical .mph files where the only major difference is the coordinate system. The cartesian version (denoted by the suffix 'cart') runs successfully. The axisymmetric version fails with the following error:

Circular variable dependency detected. - Variable: comp1.gop.bsca1.nsr - Geometry: Rays Failed to evaluate variable. - Variable: comp1.gop.bsca1.nspr - Defined as: (comp1.gop.bsca1.t1rmcomp1.gop.bsca1.deltat1)+(comp1.gop.bsca1.nsrcomp1.gop.bsca1.deltan) Failed to evaluate variable. - Variable: comp1.gop.bsca1.costhetai - Defined as: (comp1.gop.bsca1.nsprcomp1.gop.nir)+(comp1.gop.bsca1.nspzcomp1.gop.niz) Failed to evaluate variable. - Variable: comp1.gop.bsca1.tir - Defined as: (comp1.gop.bsca1.nref_insqrt(1-(comp1.gop.bsca1.costhetai^2)))>comp1.gop.bsca1.nref_out Failed to evaluate operator. - Operator: if - Argument: comp1.gop.bsca1.tir Failed to evaluate expression. - Expression: if(comp1.gop.bsca1.tir,0,1) Failed to evaluate variable. - Variable: comp1.gop.bsca1.nsr - Defined as: if(comp1.gop.bsca1.tir,0,1) Failed to evaluate variable. - Variable: comp1.gop.bsca1.nspr - Defined as: (comp1.gop.bsca1.t1rmcomp1.gop.bsca1.deltat1)+(comp1.gop.bsca1.nsrcomp1.gop.bsca1.deltan) Failed to evaluate variable. - Variable: comp1.gop.bsca1.costhetai - Defined as: (comp1.gop.bsca1.nsprcomp1.gop.nir)+(comp1.gop.bsca1.nspzcomp1.gop.niz) Failed to evaluate variable. - Variable: comp1.gop.bsca1.tir - Defined as: (comp1.gop.bsca1.nref_insqrt(1-(comp1.gop.bsca1.costhetai^2)))>comp1.gop.bsca1.nref_out Failed to evaluate operator. - Operator: if - Argument: comp1.gop.bsca1.tir Failed to evaluate expression. - Expression: if(comp1.gop.bsca1.tir,0,1) Failed to evaluate variable. - Variable: comp1.gop.bsca1.nsr - Defined as: if(comp1.gop.bsca1.tir,0,1) Failed to evaluate variable. - Variable: comp1.gop.bsca1.nspr - Defined as: (comp1.gop.bsca1.t1rmcomp1.gop.bsca1.deltat1)+(comp1.gop.bsca1.nsrcomp1.gop.bsca1.deltan) Failed to evaluate variable. - Variable: comp1.gop.bsca1.costhetai - Defined as: (comp1.gop.bsca1.nsprcomp1.gop.nir)+(comp1.gop.bsca1.nspzcomp1.gop.niz) Failed to evaluate variable. - Variable: comp1.gop.bsca1.tir - Defined as: (comp1.gop.bsca1.nref_in*sqrt(1-(comp1.gop.bsca1.costhetai^2)))>comp1.gop.bsca1.nref_out Failed to evaluate expression. - Expression: !comp1.gop.bsca1.tir

How to define synchronized parameter sweeps for multiple variable lists (with repeating values for one group)

Wed, 23 Jul 2025 10:24:05 +0000

Hello,

I am trying to perform a parametric sweep in COMSOL with four synchronized lists: n, lc, la, and G. Each list is divided into 6 ranges, with the following sizes:

n: [1–183], [184–367], [368–454], [455–543], [544–622], [623–692]

Each range has sizes: 183, 184, 87, 89, 79, 70

The variables lc and la are defined using range(start, step, stop) with specific values, and la includes a shift using lambda (lambda1, lambda2, etc.). For each block, I want to assign a constant value of parameter G (G1, G2, ..., G6) that repeats across the size of the block. So:

G1 should apply to the first 183 values,

G2 to the next 184 values,

… up to G6 applied to the last 70 values.

How can I define this synchronized parametric sweep so that n, lc, la, and G are swept together, with G repeated properly per block?

Thank you!

Simulation of the dispersion curve of microspheres

Tue, 22 Jul 2025 13:04:12 +0000

I want to simulate the dispersion curve of the WGM mode of the microsphere, with the x-axis being neff/β and the y-axis being λ/E. How can I do this simulation? If I use the mode analysis research module, I can't find the WGM mode of the microsphere in the obtained results, even if I set the mode number to 100. Is the effective refractive index corresponding to this wavelength accurate at this time? Can I use the boundary mode analysis + port method, set a port at the bottom of the side far from the microsphere, add a light source, select the surface of the microsphere as the listener port, extract its neff or β, and perform a parameterized scan of the wavelength to finally draw the dispersion curve? Also, I want to know what principle is used to calculate the neff and β of the port?