Latest Discussions - COMSOL Forums

Problems with S-parameter calculation

Tue, 22 May 2012 21:01:36 +0000

I do not understand the behavior of the transmission parameter S21 in a rectangular wave guide excited with two Port, there are differences in behavior between S21 and dBS21, these are the following differences:

-S21 has peaks. Evident when exporting data and analyze it presents oscillation between 1 and -1

-dBS21 plot in COMSOL, the oscillatory beahavoir of S21 is not presente and what is more strange is when calculated
with the formula (dBS21 = 20 * log (abs (S21)), I get different values from those used in the graphic COMSOL dBS21 and the oscillatory beahavoir is present.

If Comsol used otherwise for caculation of dBS21 parameter please enlighten me, that the results did not close.

Please help me!

Which type of stress should i use

Tue, 22 May 2012 18:13:02 +0000

Hi everyone ,
In my model pressure is being applied to the top surface of a cube. ( say pressure is applied along z axis )
I want to study the the variation in stress perpendicular to the pressure ( x axis ). To make it clear , pressure is applied along z axis , to the face of the cube in xy plane . I am trying to find stress variations along x axis.
Now i don't understand which which how to find the stress along the x axis. The options available are First Principal stress , piola kirchoff stress , von mises stress etc.
Plz tell me which of these is applicable in the above case i have mentioned.

I have another basic doubt , wats the difference between surface stress plot and volume stress plot ? And to study variation of stress along x axis i have to use 'Cut line' in the surface stress plot or in the volume stress plot ?

Thanks in advance

Fixed Temperature Boundary Condition

Tue, 22 May 2012 13:31:03 +0000

Hello, I'm new to COMSOL and am trying to run a non-isothermal flow problem where I have basically a rectangular solid object immersed in a volume of air flowing across the object. I placed a fixed temperature boundary condition on one of the sides of the rectangle, a temperature and velocity boundary condition on the inlet and a pressure boundary condition on the outlet. What I'm trying to accomplish is to determine the heat loss from the object to the air (without radiation for the time being). After I run the scenario, I plot the temperature and to my surprise the temperature on the wall that I placed the fixed boundary condition on is somehow lower than the fixed value I applied. What have I done wrong, or is there something else I need to do to the model?

Thanks

Cotinuous Release in Particle Tracing Module

Tue, 22 May 2012 13:27:54 +0000

I would like to continuously release particles for a set amount of time using the new particle tracing module. Under hte Inlet settings there only seems to be the availability of step-wise release times. Is there any way to implement continuous release in this module? Or should I so a quasi-continuous release, ie: setting the interval time to a very small value?

Which port type to use with RF module

Tue, 22 May 2012 10:48:41 +0000

Hello everyone,

I am trying to simulate a CPW resonator in 3D. Can anyone help me with the chioce of the ports? In 'real life', the rf signal is fed in by several aluminum bond wires. I saw that the tutorial models cpw_bandpass_filter and coupled_line_filter (which are the closest to what I want to do) use lumped ports with the 'cable' option. However, when I do this I get errors, except when I define length and width of the lumped ports. Can anyone provide a short overview when to use lumped, rectangular or numeric ports...?

Best regards,
Diana

problem in meshing

Tue, 22 May 2012 09:54:39 +0000

Hi Ivar,

I am trying to solve a model where i get this error:
Failed to respect boundary element edge on geometry face.
although i mesh the geometry in parts and using finer mesh in critical areas but still it doesn't work? Do you know what is causing this error in meshing?

Thanks,
Rabia

How to increase the resolution of a geometry? (in my case a circle).

Tue, 22 May 2012 08:49:33 +0000

Hej,

I have a solid block where I want to substract a really small part from the top surface (tries to be a sagging of 20 um). I am using a the difference booelan operation to do it.

The volume to subract is a cylinder. My problem is that the cylinder is huge compared to the solid block. The circle (which I extrude to obtain the cylinder) is defined by a defined number of segments (or points).

In other software's there is the option to increase this number of points (segments) when defining a circle. I think it is called "resolution".

How can I do it in Comsol?

(I was also thinking about defining a parabolic curve and extrude it, will I have the same problem?

Thanks in advance.

How can I avoid the interference between the deflected structures

Sat, 19 May 2012 20:23:15 +0000

I'm using comsol to do static analysis for a cantilever beam. I used a relatively large force to press the beam toward the substrate, I expected the deformation of the beam tip would stop at the substrate, but according to the value I got, it already penetrated the substrate.
Has anybody had this problem before?
How can I avoid it?

The attached picture shows another structure. A load is added at the upper surface in the middle, the deflection will cause the upper inner surface of the channel touch the bottom when the force is large enough, but in my simulation, it goes beyond the bottom, how can I solve this problem?

time dependent boundary conditions

Sat, 19 May 2012 19:46:11 +0000

hello all..

i am solving a time dependent heat transfer problem..

at the start ,for a rectangular domain boundaries 1 and 2 are insulated and 3 and 4 are assigned with constant temperature..
after some time t>100 my BC changes to all 1 2 3 and 4 boundaries insulated..
how can i do that

thanks in advance
pavan

Temperature decline in autoclave model while rise expected

Sat, 19 May 2012 18:53:59 +0000

Hi there,

I've made a model for an autoclave with 2 blocks in it that should heat up during time. They however first cool down to like 200K and after they start to heat up again. That's not what i suspect and what is realistic. Since the model with results is to big i will upload only the model. It isnt that big so should be computable in short time;). (comsol 4.2a)

See the attachted image.

hope all is clear.

Thanks in advance!

the domain of fluid

Fri, 18 May 2012 21:35:07 +0000

Hi,
I am using the Conjugate Heat Transfer Model to model a structure with water cooling. I imported the solidworks drawing file to COMSOL. My question is what is the easiest way to define the domain of the fluid for the structure? The fluid region wasn't previously defined and the shape of the cooling pipe is very complicated.
Please help. Thanks a lot.

Define PH

Fri, 18 May 2012 16:38:10 +0000

Hi

Anyone has any idea how I can define PH of my solution in ACDC module?

Best
Bahar

Coplanar Waveguide Resonator with RF Module

Wed, 16 May 2012 08:45:06 +0000

I have only little experience with COMSOL and consequently I appreciate any kind of advice:

Eventually I would like to simulate a metallic sample on top of the resonator, separated by a slab of dielectric. Right now I am trying to get the S-parameters for the empty resonator (my model is attached, I am using COMSOL 4.2). I tried to keep close to the Coplanar Waveguide Bandpass Filter Example, just using my dimensions. However I am not sure what kind of ports to use (in 'reality', the signal comes in through a bonded aluminum wire) and also how to optimize the mesh in order to save resources. Also when I try computing the model with the current mesh, the program crashes after a while without any error message.

Determining the residence time of a massless particle in microfluidic channel

Thu, 10 May 2012 13:18:19 +0000

Hi all!

I have a question regarding determination of a residence time for a masless particle in microfluidic channel.

I have modeled steady fluid flow with 'Laminar Flow' physics in Comsol 4.2 through some channel geometry and now i would like to make an investigation on how long does a particle (masless or with really small dimensions) flow through the geometry. Thus measuring residence time for a particle.

Can anybody help me with this - maybe guide me to a tutorial on this subject?

Every help would be very much appreciated!

Thanks in advance and best regards,
Izidor

Hiding geometry boundaries in graphics window?

Tue, 08 May 2012 12:46:42 +0000

Hi,

I have a model geometry that includes some sub-domains. I want to show the results from these domains, but I don't want their boundaries to be visible in the graphics window, so visually the model looks like only one domian. Does anyone know if and how this can be done?

Acoustic Module Simulation

Thu, 12 Apr 2012 16:49:08 +0000

I am just wondering what would cause the damping effect on fluid-structure interaction simulation based on Acoustic and Structure modules. For instance if you run two simulations, one on air and the other on water. You'd see the higher damping effect from frequency response. You can even calculate the damping using Half Power Bandwidth Mehtod. When I run fluid-structure interaction simulation using Acoustic module without adding any damping, I could still see the extra damping effect of water compared to that of air. What caused this? Thanks!

pulse and heat flow

Wed, 14 Mar 2012 06:04:17 +0000

Dear Sir

I need urgent help !!!

i have to apply pulse train voltage with( 13kv and 1khz) on cable termination to get its effect on temp. after 3 hours.

i can not solve by time dependent solver (take very long time)

i can solve for 10 pluses and get the heat produced Q(W/m3) after 10 pluses then i can get the total energy produced by multiply (Q* (time of 10 pulses =0.01 sec). afterthat , how can i use the value of Q or the value of the energy to get the temperature after 4 hours

Variable material properties

Mon, 21 Nov 2011 13:49:08 +0000

Is it possible to make my material properties temperature dependend? I'm talking about a Cp value for example. Also do I have a MATLAB license, so if that has to be incoorporated; that's not a problem. Thanks in advance.

voltage induction due to changing magnetic field

Tue, 24 May 2011 12:14:58 +0000

hello,

I'm a relative newbie to comsol. what I'm trying to do is (I think) relatively easy, but I have no idea how to tackle it. what I need to do is model voltage induction in a coil due to a changing magnetic field. I know how to how to create a coil in a fixed magnetic field, but I don't know how to set up time varying field. but, more importantly, I don't know how to measure the induced voltage. should the coil be open and then specify two points where the voltage would be measured? thanks for any suggestions.

r.

Comsol 4.2

Wed, 18 May 2011 14:34:09 +0000

For your informations,

I just received an email for a free workshop on COMSOL Multiphysics Version 4.2 at montreal in one week. We should receive the cd soon!