Dear all, I do not know how to use "contact" to simulation the situation that when edge load is aplied in, the geometry is deformed, but the geometry shows self-intersection. I do not whether I express clearly or not, I do not know how to upload picture. Thank you very much!
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solid mechanics-How to avoid geometry self-intersection?
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Simple MEMS Cantilever - No Electrodes
Dear All,
I am new here and I would like to model a simple cantilever with no electrodes to figure out its fundamental resonance peak, and its frequency response. Please advice: what module(s) and physics (more than one may be?) may I use? How simple of an approach can I start with? How may I start making it (the model still with no electrodes) more sophisticated? If I import the geometry, could I still make use of Comsol's work plane features? Would I be able to add an applied force (or pressure) to just a specific part (surface) of the cantilever (say the tip)? Should I choose that force to be of harmonic type so I can make use of it at the time of frequency response? Would I be able to see the peak amplitude at the resonance frequency (the actual graph)? My apologies for the long text and multiple questions, but I would appreciate any help with any part of it.
Sincerely,
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Coupling between silicon waveguides
Dear everyone , I am new to comsol and need your help! I would like to ask a question regarding one of the problem i am facing in the simulation of my current project. I want to see coupling of em wave between two silicone waveguides. There are two silicone waveguide of cross section 640[nm] × 480[nm] and of length 10 [um] . Both are placed horizontally 100[nm] apart such that the total length from one end to other end is 20.1 [um] . The light source is of 1550 [nm] wavelength. I would like to know what boundary condition should i set for the waveguide and also should i add a block of air in that 100 [nm] space or not. Please let me know. Thanks in advance.
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Interconnect delay with respect to temperature
I would like to see the effect of temperature causing signal propagation delay through the interconnects. How should I model my physics?
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1D and 2D phononic crystals
Note: I am doing this project as my "learn-something-new-during-lockdown" affort. So, you are free to suggest me whatever could be interesting. However, I am planning to get a good publication in this field after learning COMSOL, sooner or later.
I want to study 1D and 2D phononic crystals (acoustic wave interaction), and simulate two things:
Study: 1) calculate band structure diagram
Study: 2) make real-space wave propogation animations (for examples, animations given here: https://www.comsol.com/blogs/modeling-phononic-band-gap-materials-and-structures/)
Both 1D and 2D cases have further 3 type of crystals:
a) both periodic materials are solids
b) both periodic materials are fluids
c) one material is fluid and other is a solid
My first question is that what kind of models should I use for solid-solid, fluid-fluid, and fluid-solid interaction? I understand that for solid-solid Solid Mechanics is an option. What about other two types? Also, please suggest what kind of solids and fluids could be interesting to study in these crystals?
My second question is about making real-space animations. What kind of study/model can I use to make animations which shows that how a wave comes and interact with a periodic structure and then either reflects back (if in stop-band) or transmits (if in allow-band). This kind of animations are given on the webpage that I have mentioned above.
Thank you very much for your time.
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Progress window not showing up during Matlab Livelink (COMSOL 5.5)
Using the ModelUtil.showProgress(true) command is not showing the progress window when I'm running COMSOL models from Matlab through Livelink on my Windows 10 system. I'm interested to know if anyone else has been having this issue and if there is any fix for this.
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how to deal with penestration during contact
Hi, coworkers! I have modeled a capacitance sensor with 1 top electrode and 4 bottom electrodes (Fig 1). The sensor is placed on a substrate, and a stick is going to contact and press it from the top. I have used to Solid Mechanics interface to do the stationary study.
I set a contact pair between stick and top electrode, and fix the position of the substrate. However, the dielectric material, which is between top and bottom electrode, will be squeezed into the interval of bottom electrodes and 'penestrate through the substrate'(Fig 2). This penestration won't happen in real world and is unwanted in the simulation.
As I know, the contact pair can define a pair of boundaries which can not penestrate each other, and I have tried to create a pair between dielectric and substrate. However, after many trials, the penestration still remains to be solved.
Could someone tell me how should i do with this situation? Sincerely thanks!
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Problem with gradients, wetted wall
Hello to all! I have a problem with gradients. My goal is to simulate wetting of a cylinder (1st picture). The red wall is the wetted wall. The dotted line is the axis of symmetry. Unfortunately, I can't upload the mph files because I don't have an access to my university PC now, but I remember almost everything about the model and have some graphics to show the problem. The equations I use are similar to the COMSOL equations for wetting (phase field), but my boundary condition is different.
It looks like this:
Pt = k*(A-B),
where P is the phase field variable, B = nr*Pr, Pt is the time-derivative of P, Pr is the r-derivative of P.
I'm using COMSOL 4.3.
At the start, A is bigger than B, but at equilibrium state they should become equal A=B which means Pt = 0.
The problem is... the left part [ Pt ] and the right part [ k*(A-B) ] are similiar, but not equal. (2nd picture)
This slight difference accumulates, and the system can't reach equilibrium.
My assumption is that Pr isn't calculated correctly (3rd picture) because it's should look like a parabola and in my calculation it only resembles parabola.
What can be the root of this problem? At first I thought of making the mesh finer, but this wasn't effective. I'm using rectangular elements.
I'm almost sure it has to do with my solver/numerical settings because I'm not strong at COMSOL yet.
Thanks in advance!
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Pressure attenuation in cylindrical pipes problem
Hello to all!
I am trying to simulate the pressure attenuation in cylindical pipes. I was expecting to get results similar to the analytical expression, but they are way too different.
The analytical expression for the attenuation coefficient is
,
where 
is the angular frequency of the wave, 
and are the viscosity and density of the fluid inside the pipe, 
is the speed of sound in the fluid, 
is the specific heat ratio and 
denotes the Prandtl number.
To calculate the value of the final pressure, it is used the analytical expression
,
where 
is the attenuation coefficient, 
is the lenght of the pipe in which the pressure is wanted to be calculated and 
is the reference pressure.
I ran the simulations using 4 different interfaces with 2D Axyssimetric geometry in COMSOL 5.5
- Pressure acoustics, Transient (with viscous fluid model)
- Pressure acoustics, Transient (with thermally conducting and viscous model)
- Linearized Navier-Stokes, Transient
- Thermoviscous Acoustics, Transient
For a pipe filled with air (at atmospheric pressure) with a diameter 
excited with a single gaussian pressure pulse with a peak of 
and a standard deviation of 
, the analytical pressure, in 
is 
.
The results in the simulations were
- Pressure acoustics, Transient (with viscous fluid model) -
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- Pressure acoustics, Transient (with thermally conducting and viscous model) -
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- Linearized Navier-Stokes, Transient -
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- Thermoviscous Acoustics, Transient -
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I do not know why the numerical results are so different from the analytical. The mesh is already very fine.
Does someone have any idea of what can be causing this difference, or if I am missing something?
Sincerely thanks,
Bruno
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Perfect Electrical Conductor Problem
I'm having a problem where when I draw a geometry all of the boundaries are automatically selected as perfect electrical conductors and I can't change this. I've been trying to follow along with the RF power transfer example and I can't because it makes everything a PEC. What's going on?
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Induction heating, Solver gets stuck in middle. Does not converge. Can someone help me please?
Hello I am trying to Induction heating and basically I gave a coil which is straight with a current applied to the coil to heat up a tool below. But the solver does not converge. I have attached the following image below. Does anyone have an idea how to deal with this problem? please help me.
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The optimal load and voltage value are too large
I want to study how the voltage changes as the load increases. But the result I got is very different from the actual value, the voltage value is much larger than the value obtained during the experiment, and the external load value is also very large. I want to know what caused this, can someone help me?
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Multi turn numeric coil
Hi,
I'm trying to calculate the magnetic field due to two pairs of orthogonal coils one pair is circular and there are no issues. the other is a rectangular pair and I'm not able to get the homogonized multi turn, numeric coil option to run.
I'm not sure if the issue is not adding the input face correctly, not running the coil geometry step correctly or something else.
I've looked at other threads on the forum, but it seems like my problem is different, and more basic than other questions already posted.
thanks for any help!
Gal
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Combining Electric currents and Electrostatics
My Problem:
I have a condensator with a small non-conducting dielectric wire in between.
I try to get out how a conductive shell around the wire shields the electric field in the wire.
I tried electric current model, but the results don't make much sense, for example the epsilon (permittivity) of 12 in the wire is totally ignored. Also the ratio between conductivity of air (cant be set to 0) and the shell is important.
So I tried to combine electric current AND electrostatic model by giving the same name for the both potentials (V). It seemed to work, but if the conductivity gets around 1e-10 S/m it doesn't make sense any more. Suddenly the field in this shell is higher than outside and for smaller conductivities smaller again. Then it is the same result as in an electrostatic model only.
So my question: Is my thought of combining the two physics generally wrong or do I just use it in the wrong way?
Thanks for answers!
PS: My version is 4.2. Sorry, in my model some things are german.
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How are the data points chose in a Line Plot?
Hello!
Checking the reference for the Line Markes in a Line Plot, I found that the setting "In data points" under Coloring and Style ->Line Markers would give me the values at the mesh nodes. However, in the Line Plot I find many more data points than I would anticipate.
How are the data points generated in a Line Plot?
Best regards, Yao
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COMSOL plots with wrong time step
Hello.
I have written 0.025 s as time step but comsol plots every 0.1 s. How can i fix it? The study has been running more than 24 hours i can't re-do it easily.
While solving I had a probe ploting solutions and time step was right but when the study finished time step changed.
Thanks.
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Implementing periodic BC to moving mesh method
Dear friends, hi, I have a two phase flow problem including a bubble and I am using moving mesh method. I want to apply periodic BC to the top and bottom of my computational domain. Every thing is Ok till for example when the bubble reaches the bottom of the domain. What expected is that the bubble continues to fall and begins falling again from the top boundary, but this does not happen. When my bubble reaches the bottom boundary, I get an error and Comsol stops computing. First, Is there any way to solve the problem? Second, if periodic boundary condition does not work with moving mesh method, why is it includend in the boundary conditions?!!!
Thank you very much Hamid
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Set starting point for stationary study comsol
I am using ht in solids and fluids coupled with laminar flow. I started stationary study, and i saw that in first iteration Temperature of probe 1 and probe 2 are 215 degC and 205degC. I knew that they should be around 135degC and 125degC.
How can i speed up simulation by defining some initial values for solver to take?
Frist Comsol solve stationary study. Than i change my model a little. That change is not new geometry or new mesh or something like that. Its same model with some constants changed in model (heat flux coefficient, emissivity, etc). I expect that the final results does not change drastically. How can i start simulation of changed model from starting point which is final result of previous model simulation?
Is it possible for solver to take some part of the results from previous simulation? Lets say if i change inlet boundary condition to open boundary, i want that my solver at least takes all the temperatures from last solution.
Thanks.
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two mirror cavity by simulating one mirror, cavity length?
Hi everybody,
I am trying to simulate an open microwave cavity with two mirrors and get the eigenmodes and q-factors similar to the "Fabry-Perot application". I ve seen in publications that people usually just simulate one mirror surrounder by air and PMLS with the appropriate BCS. But how do you determine the cavity length and tha path of the beam this way?
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Simulate polarization and depolarization current (PDC) test in COMSOL
I want to simulate PDC test using Comsol for my final project. But I didn't find any tutorial or reference on how to do that. Anyone can help me?
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