Quantcast
Channel: Latest Discussions - COMSOL Forums
Viewing all 25631 articles
Browse latest View live
↧

Changing geometry and plotting the results in graph

May 6, 2013, 3:13 am
$
0
0
I am simulating a 2D inductor coil in ACDC module , but now I want to change the air gap of the two coils in steps and want to calucalte the value of inductance over these steps of airgaps. I have already built a model to get my inductance values but I am finding hard to run comsol again and again with changing air gap, is it possible to vary this air gap in global defination and then later add it in some kind of loop to get the values.
Any thoughts and suggestions

Regards
Khalid Hameed
↧
Search

Using the assembly form

May 6, 2013, 4:28 am
$
0
0
Hello,


I am trying to simulate with "piezolectric devices". Specifically, I would like to exert stress on a thin film in contact with a piezoelectric 3D block. The geometry is quite simple but in order to mesh the thin film using "swept" I have to use "assembly" finish form (if I am right).

The problem is that during the simulation, it seems that both 3D piezoelectric block and thin film does not interact in any way (i.e. stress is not exerted).

I have played with "contact pairs" and "indetity pairs" with no success ! I am getting desesperate.

Any suggestion ?


Thanks !

Javier.
↧
↧

Periodic Pulse

May 6, 2013, 5:33 am
$
0
0
Hi

I an working on Joule Heating and would like to generate 3 repeated voltage pulse
Conditions:
Pulse Width: 100e-9
Rise and fall: 10e-9
Period: 150e-9


This is what I tried

Rect1>>
Lower Limit: 0
Upper Limit: 100e-9
Size of transition: 10e-9
Amplitude: 3V

An1>>
Parameters >> Expression: rect1(mod(t,150e-9)
Argument:t
Derivatives: Automatic

Units>>Arguments: t

Plot Parameters>> Argument:t, Lower limit: 0, Upper Limit:0.001*

*With these setting, I can see the periodic waveform

Calling An1 in Electric Potential>>
V0: 3*an1(t[1/s])

Study >> Time: range(0,1e-9,4.5e-7)
Time stepping: Intermediate


Trying to see the temperature profile but it seems that the temperature keep rising up till 4.5e-. However, I do expect temperature to drop after each pulse interval before the next pulse starts.

What should I correct?

Please help. Thank you.
↧

Contact problem in solid mechanic: sover don't convert

May 6, 2013, 5:36 am
$
0
0
Hello!

I want to simulate a screw in a boneblock which is bonded with a force vertical to the screw axis (see picture). The two blocks are a union with differend materials. There are used 3 different materials: the screw, the cortikalis (smaler block) and the cancellous bone (bigger block). In Finish I've form an assembly, activated Create pairs and the Pair type is Contact pair. I 've create a contact pair between the srew surface an the bone in Definitions. In boundary conditions I've assign the Contact Pair and the load in the screw head. The bone surfaces are fixed Constraints. A free tetrahedral mesh is used.

I used the stationary solver, solved in the direct way with MUMPS and fully Coupled. But the Solver don't convert.

Maybe the solver is wrong for this probem or I've forgot something. Can you please help me?
What is the best solver for my contact problem and what I did wrong?

Thank you for your help
Ariane
↧

Swept mesh density dependent of a spatial function

May 6, 2013, 6:29 am
$
0
0
Dear all,

I have a simple question: how can I define in swept mesh a function (spatial) of refinement? Just for example, I have a strip and I would have a very fine mesh only in the middle.
I have tried in this way: I set a parabolic function in Definitions>Analytic, 0.8+x^2 (supposing x is the direction of the swept), and then I inserted the function in Swept>Size>Max Element Size, hence an1(x). In this way I should get element of max 0.8 in the middle of the strip, and bigger going towards the sides.

But it seems that Comsol does not accept functions in element size parameters. What I am doing wrong?
Thank you very much

Fabio
↧
↧

How do materials properties are considered in k-epsilon turbulent model?

May 6, 2013, 6:30 am
$
0
0
Hi everyone,

I have a doubt about how material properties are considered in k-epsilon turbulent models. I'm simulating air flow around buildings and I specified materials for the ground and the buildings facades (concrete). I've realized that the wind speed on the top of a building in the middle of a very dense region of interest is exactly the same as the velocity measured in the same height from the ground in the meteorological station. I have three questions:

1 - If surface roughness may reduce air velocity, how does it doesn't change in the middle of the region of interest? Even if it the measure point is on the top of buildings, shouldn't the top surfaces of buildings influence on velocity air flow?

2 - I didn't find in the turbulent model equation any variable related to materials properties. So how does COMSOL consider their influence on air flow?

3 - I read a discussion in this forum about the parameter B of turbulent model (www.comsol.com/community/forums/general/thread/33544) and I was wondering if I should change this to represent the roughness height of this urban context.

Thank you very much for your help.

Marilia

↧

Question about "if" function

May 6, 2013, 6:44 am
$
0
0
Hello,

I want to add a volume force to NS equation with a special condition.
The volume force is like this: H/Re
Re is reynolds number.
u2 is calculated from convection-diffusion equation and I want to limit the values of u2 like this.

if (u2>=0 or u2<=1) then H=u2
if (u2>1) set it to 1 and then H=u2
if (u2<0) set it to 0 and then H=u2


Would you please help me?
Thanks,
Hooman
↧

stress tensor-elasticity matrix

May 6, 2013, 9:15 am
$
0
0
COMSOL assumes the elasticity matrix to be symmetric. I need to define an unsymmetric stress tensor but seems that it is impossible in COMSOL.

Has anyone experienced such a problem so far?

Thanks



↧
Search

Convergence problem with Open Boundary condition - No viscous stress

May 6, 2013, 10:41 am
$
0
0
Hi,

I'm modeling fluid flow through a 2D porous media using Darcy's Law. I intend to estimate fluid flux values across the top boundary of model, however,my desired outputs will be one in which the results obtained at this boundary are dependent on the domain solution.

For my simulations so far, I have observed that the domain solution depends on the prescribed values of the boundary condition, i.e I have to specify Dirichlet boundary conditions of stress, pressure or velocity along the top and bottom boundaries. The Side boundaries are specified as No- flow.

The Comsol user guide suggested that the use of Open Boundaries ( with No viscous stress) might be useful in obtaining solutions in cases where pressure cannot be predicated ahead of time, as such I am trying to run the model using the Brinkman's Interface in order to take advantage of the open boundary physics for the top boundary, along with a specified condition along the bottom of the model. However, I have been unable to get my model to converge with this specification. (The mph file and model diagram file is attached)

I do not understand why this is happening and would appreciate insights/tips into this problem, either under the original Darcy's Law formulation or using the Brinkman's equations.

Thanks.



↧
↧

Error: Undefined value found.

May 6, 2013, 12:43 pm
$
0
0
Hi,

I am simulating a nano antenna in RF module and I get this error:

Undefined value found.
- Detail: NaN_or_Inf_found_when_solving_linear_system_using_SOR

I also simulated the same model in 2D axisymmetric with the same frequency and the results were fine. Since I needed to use a different E-field as my source and the model was not symmetric anymore, I had to use 3D simulation. Moreover, I had some difficulties in meshing but I finally found a way to do the meshing without any errors.

Does anyone know what is this error?


↧

Undefined value found.

March 26, 2012, 2:50 am
$
0
0
Hello,

when I solution emw, it has a error :
Undefined value found.
- Detail: NaN_or_Inf_found_when_solving_linear_system_using_SOR

what's this message meaning ?
Thank you!

↧

Modeling a Dielectric as a Real Capacitor

February 14, 2013, 8:26 pm
$
0
0
Hello everyone,

I am having trouble modeling something. I would like to look at the conduction/conductance/resistivity of a insulating/conductive composite. It could be thought to be like a polymer/insulating fiber system. Electrically, the polymer itself is referenced in literature to look like a capacitor and resistor in parallel. The capacitor illustrates the ideal dielectric capacitor that one might expect and the resistor illustrates the leakage that actually flows through the capacitor when placed in a potential. The illustration is on Tony Blythe's 2nd edition "Electrical Properties of Polymers" book on page 156. I've attached an image of the equivalent circuit I am talking about(not exactly the image from the book though).

I would like to know the DC electric conduction through the entire composite, so both in the low conductivity areas (the polymer/semi-insulator) and the in the high conductivity areas (which is a fiber/metal). Is there any way I can use components of both the Electostatics and Electric Currents Modules? I want it to take into account both the electrical conductivity and also the relative permittivity of the polymer. If so how can I do this? I've attached a 2D model of the geometry of what I'm talking about.

When I do this geometry in the EC interface, the electric field is not what is expected and when I do this geometry in the ES interface, I do get the correct e-field. I would like for the model to look like the ES does (which is what is expected) but actually have some current go through it.

Thanks in advance for any help you can shed for me!

John
↧

Applying AC voltage

May 5, 2013, 4:44 pm
$
0
0
Hi all,
I'm currently studying the electromechanical effects of a water droplet under AC/DC voltages. The water droplet is placed between two rectangular electrodes. I've applied a electric potential to one of the electrodes and grounded the other.
I currently I have no issue simulating DC conditions in electrostatics, however when I simulate AC conditions I encounter a problem. I disable the stationary study and add frequency domain study. Leaving the magnitude in the electric potential, in the study settings I add a frequency of 50Hz. When I compute the simulation there is no electric potential or electric field.
Can someone help. Am I doing this process right or am I missing a step?
↧
↧

How to mesh this concrete slab with embedded loop

May 6, 2013, 3:45 pm
$
0
0
This is a concrete slab with embedded loop. I don't want to use the free tetrahedral to mesh this model since the result is not as accurate as quad element do if the order of the shape function is the same according to the finite element method. So I am writing this email to ask whether there is a reasonable solution to this model?

Thanks for your help!

Sincerely,

Jiaxing
↧

electric field and potential distribution

May 7, 2013, 12:23 am
$
0
0
Hi

I have been working on a 3D (AC/DC) model of a insulator, and I am trying to verify the uniform potential and field distribution along the insulator surface.

I apply 33Kv voltage at HV end. I got result, in this result potential along the insulator surface is uniform distribution, i want field also uniform distribution along the surface.



↧
Search

resistivity plotting

May 7, 2013, 12:47 am
$
0
0


Hi

I am running a stationary model of a wire network usinf Electric currents and Heat transfer in solids . Each copper

wire (linearised reistivity) has a constant current. There are heat losses to the air and heat conducted between

wires at their junctions.

There is a resultant temperature gradient along each wire. How can I get a plot of the variation in resistivity?

I see uniform heat losses along the wire even though the temperature varies (and therefore resistance should vary)

Something seems to be working because temperatures are a bit lower with constant conductivity model.

Thanks

David
↧

calling a waveform from Definition node

May 7, 2013, 12:57 am
$
0
0
Dear all,

I want to apply AC voltage to an electrode. I built my desired stimulation waveform from Definition node. How can I call this function? Do I have to enter function name in Electric Current part or Terminal name? Please let me know where is my problem since I am not sure that this waveform is considered during computing process.

Kind regards,
↧
↧

Thermal expansion

May 7, 2013, 3:02 am
$
0
0
Hello!

I'm trying to simulate the thermal expansion of a solid silicon block, which is cooled down from 293.15K to 80K. Heatflux or something like that is not important, I'm just interested in the deformation of the material. For the expansion coefficient I want to use a temperature dependent function, given as a table.

But the comsol-result does not match with the theory. I attached the simulation file, hoping that someone can point out my mistake.

Thanks a lot!
↧

Linearly Polarized (LP) modes

May 7, 2013, 3:43 am
$
0
0
Hi all,

I'm willing to calculate linearly polarized modes, that is, modes with
only four non-zero components and azimuthal symmetry in a multimode
optical fiber (see for example www.rp-photonics.com/lp_modes.html ).

By using the mode analysis study I get to compute the first two LP0m
modes (I'm specially interested in modes LP01, LP02, LP03....).
Although, I have to compute more than 10 modes to get LP01 and LP02
modes. I have incremented drastically the number of modes computed but
I'm not able to get to the LP03 mode.

I wonder if there is a way I can "force" the results to have (for
example) Ex=0 and Hy=0 ?
Or even better, to force the resulting fields to have azimuthal symmetry?

A suggestion from the support staff is to restrict to a subset of solutions modeling a slice of the fiber's cross section (see file attached). Unfortunately, with this approach I'm only able to reproduce doughnut type fields (mixtures of TEM modes), but not the LP modes I'm looking for.

As you can see all the solutions have null electric field at the center of the fiber, while LP01, LP02 and LP03 have a maximum field at that point.

Thanks in advance.
Best,
--
Felipe BM
↧

How can I define an PML in model solids mechanics ?

May 7, 2013, 4:04 am
$
0
0
I need a help !

I'm using a model of a small rectangle onto a large rectangle 2D axisymmetric
to denote of wave propagation
I have to put the PML absorbed wave to not be reflects
But when i put it and i do the compute
I don't see a difference => PML like does not work !
can you help me please ? what do I do?


note:
-> Model Wizard -> 2D axisymmetric -> structural mechanics -> solid mechanics -> temporel
-> Definitions -> PML

I have searched through the documents COMSOL a model that contains a sample of the PML but I have not found.
↧
Viewing all 25631 articles
Browse latest View live
Search