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Piezoelectric Coupled With A Shunt Circuit For Vibration Damping

May 6, 2019, 12:22 pm
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Hi, I have been using comsol to study topics related to piezoelectric materials. I'm modelling a beam with a piezo attached on the top, and an electrical circuit attached to the patch: to do so I used the solid mechanics (solid), electrostatic (es) and circuit (cir) modules. I want to perform the eigenvalue analysis (I want to extract the dispersion using my model as a periodic cell...) it doesn't work and it says that one equation is missing ("Singular matrix. - Detail: There are 1 void equations (empty rows in matrix) for the variable comp1.es.term1.Q0_ode. at coordinates: (0,0), ... "). The implementation is ok for time domain study. Do you have any ideas?

The piezo-shunt is implemented as follows: the bottom face of the piezoelectric patch (attached to the beam) is grounded (es.ground), the upper one is connected to a circuit terminal (es.terminal 1 - type circuit), then a resistor and a inductor (in cir) is connected in series from node 0 (ground) to node 1 which is in turn connected to the terminal (in es) through a "External I - Terminal" connection (selecting terminal 1 for the electric potential).

Please see the attached file for details.

Thanks, Yongchen

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Mesh size changes results with dipole

May 6, 2019, 7:02 pm
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I've been working to model NIR waveguiding of a thin film on silicon. To implement this, I've created 2D models of an air gap followed by a thin dielectric film on a silicon wafer in the wave optics module and the RF module. I've placed an electric dipole point source in the thin dielectric film.

As I change the meshing, the magnitude of the electric field in the device changes significantly. Playing around with meshing, it seems to exclusivley change due to the meshing around the dipole. Currently, the meshing is much less than the wavelength of light in any media (~50x less), so I don't believe that the mesh frequency is the problem. Indeed, the problem continues to get worse the finer I mesh my system.

I've tried using a PML and perfect electrical conductor layers as boundary conditions and implemented the model in wave optics and RF modules.

Is there something obvious that I'm missing?

Edit: For whatever reason, using an out-of-plane line sources seemed to significanlty fix my problems. When I used an electric field dipole, there were wild reflections in the PML layer and I'm not entirely sure why. Does anybody have advice? If possible, I'd like to use the electric field dipole so that I can test different polarizations.

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Phase of S-Parameters

May 6, 2019, 11:31 pm
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What exactly are the S-Parameters in Comsol? In my opinion, the S-Parameters (S11, S21, etc.) are normally defined as S11=reflected field over incident field and S21=transmitted field over incident field.

In Comsol this seems to be different since the S-Parameters depend on the size of the simulation box (ports at top and bottom) filled with vacuum (periodic conditions left and right). Is there a phase in the definition of the S-Parameters?

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Calorimeter Method

May 7, 2019, 1:40 am
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Hello everyone, I'm in need of some help with my project task regarding the calorimeter method where I have to create some sort of example in COMSOL program before creating one piece by piece. If you can help me out with some suggestions/tutorials about the way to create one in this program would be great.

The calorimeter represent a copper hall in which is gonna be another cylindrical hall inside of the first one with heat transfer between them, cooled by water. In this application I have to calculate the temperature inside of it in rapport with the exterior temperature and the efficiency.

Thanks!

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Phase Change - liquid to vapor

May 7, 2019, 2:48 am
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Hi,

I am interested in studying to model the phase change of liquid water to vapor by heating the downside of a cup (in 2D), like it is shown in the attachment.

To model this, I selected two materials: Water and Air. For the Physics Interfaces I selected 'Nonisothermal Laminar Flow', which combines 'Heat Transfer in Fluids & Laminar Flow'. For the phase change you could choose the Domain 'Phase Change Material'. I am not really sure, how you have to model it with the right settings to simulate the phase change from liquid water, which will heated up, to vapor.

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Flattened Lens based on quasi-conformal mapping

May 7, 2019, 7:30 am
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I want to obtain the 2D flattened lens similar to the following link. I applied the boundary conditions, but the obtained meshes are not orthogonal. Is there someone know about it? Thanks.

https://www.comsol.com/paper/3d-modeling-of-transformation-optics-based-flattened-luneburg-lens-using-the-com-63462

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fluid simulation post processing

May 7, 2019, 8:04 am
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I would like to ask a simple waterway model, such as in the picture, how to get along the pipeline, a one-dimensional curve of pressure and velocity changes from the inlet to the outlet, or the average of the cross-section along the pipeline.

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Thermal Analysis of an actuator

May 7, 2019, 9:25 am
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To whom it may concern, I am trying to model and analysis EC 90 Maxonmotor actuator, I am modeling the actuator based on the CAD file and datasheet. For heat transfer part, I am making the winding as a heat source (P = (1-efficiency)IV) and then between the surface of winding and inside of the case I am defining surface to surface radiation with emissivity of 0.5. Based on the maxon motor manual, they are analyzing the motor when it is mounted to a plastic so, on one of the surface I am defining the heat convection coefficient around 1 and for rest of it, I am trying to get it based on the winding and housing tempreature. Based on the maxonmotor thermal analysis, Difference between the winding tempreature and housing tempreature can be calculated based on given thermal resistances: delT_housing = (R_housing/(R_housing + R_winding))*delT_winding. Based on this formula, we should have 30 degreeC (+/- 10% ) tempreature differences between winding and housing, however, what I am getting does not exceed 15 degC. I would be very grateful if someone can have some handful advice for fixing this issue, My project is stuck in first step at correct modeling and I do not know really what should I do to fix it. Comsol file can be provided upon a request. Sincerely, Ali.

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Find Potential by using Poisson equation

May 7, 2019, 10:09 am
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I want to calculate charge distribution due to the geometry and potential due to geometry of a trap in PDMS. Can you please guide me how can I do this using the poisson equation. I am also new to comsol and have just started using it.

I am attaching the geometry profile with this message.

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Point load in 2D

May 7, 2019, 9:13 pm
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I have a simple 2D model, with a bezier open curve (linear segments) defining my beam structure. All beams are same and define some rigid truss (where I want to take into account torques so I am modeling all segments as beams). Now I want all vertices to be supported somehow, so I specify "spring foundation" in my beam section. That should hopefully (if I understand correctly) make all vertices spring-coupled to some rigid reference. And finally, I want to apply a point load to one of the vertices to see how much the beam structure deforms. This last part does not work for me. I can add point load to my beam section but it does not seem to act on the structure. I have seen prior discussions about how point loads are singularities and so on but in my case all geometry is just 2D lines (although there is material and cross-section defined but the structure geometry is lines in 2D). So I have no choice but to apply a point load. Any help?

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Motor in rmm Physics, Moving mesh,

May 8, 2019, 6:51 am
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Dear all I am simulating a pm_motor in comsol with rmm physics. While I added study in comsol, in time dependent step.I define the rotor with moving mesh.The result reached, but, while I export the amination of the motor, playing the file, the part of moving mesh that I defined became empty and disappeared. The video stopped and the rotor appeared. I feel so confused. Can you give me some advice to solve the problem.

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Proper Module/geometry to model fiber optic cable in comsol in soil layers

May 8, 2019, 10:03 am
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Hi,

I am new to comsol and I want to model a vertical Fiber Optic distributed temperature sensing (DTS) cable in soil layers, and then use the heat transfer module to get the temperature in different soil layers. I have started the modeling by simulating the DTS cable using a cylinder geometry. As you can imagine, the radius of the cable is very small (0.125 mm) as expected and the length is about 10 m. My question is: Is this the proper way to do this small scale modeling in comsol? Also, I don't have any electricity in my cable, a laser sends a pulse of light into the fiber to measure the temperature along the cable based on the difference in intensity of different scattered light in the cable.

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Induction heating with single conductor coil

May 8, 2019, 11:00 am
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Hi! I am a new COMSOL user and I am trying to model induction heating with a 3D single-turn single conductor coil (please see attached model). I get an error message to "solve [the coil] in a Coil Geometry Analysis step. The simulation works with a multi-turn coil but I am unable to solve it for a single conductor. Any help would be greatly appreciated!

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How to ensure convergence

May 8, 2019, 11:25 pm
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Hi, I am new in Comsol. I encountered a problem ,the computing remain 93% for a long time, and the convergence curve always fluctuated. The figure is attached. Anyone konw how to solve this problem, and accelerate the convergence.

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Analysis of Brick masonry wall

May 8, 2019, 11:29 pm
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Hello all,

I am analyzing a brick masonry wall under Structural Mechanics Module. I applied load diagonally at both ends. The study completed but stresses are shown only at the ends. I need individual stress values for each element like mortar and brick. Is there any way that I can get the stress in each element?. I am attaching my file

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The same definition but different results in different physics

May 9, 2019, 2:43 am
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Dear all Have you met the question that the same definitions but different rusults? I am simulating a pm_motor. While I used the same definitions to define the magnets in my motor, the result of magnetic flux density norm are completely different. Is that the reason of different physics? Plz help me.

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Beam Uncurling

May 9, 2019, 1:58 pm
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I have a curved beam that I am attempting to uncurl by keeping one end in place with a prescribed displacement) and applying a prescribed displacement on one point on the other end which should move it into an uncurled configuration. However, the model will not complete the full displacement (several millimeters in the x and y directions) and stops after about 0.2 mm displacement. Any suggestions are appreciated.

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set rotating boundary condition in 3D annulus flow

May 9, 2019, 2:02 pm
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Dear all, I'm kind of new user of Comsol. Any suggestion will be appreciated regarding to my question. I want to model fluid flow in annulus (between two cylinders) with the inter cyliner rotating with a given speed. The 2 ends of the annulus are the inlet and outlet. With either 5.4 or 5.3, I cannot find where to set that wall condition. The options under "moving wall" include "sliding wall" and "moving wall", but no "rotating wall". Somebody can point me to the right direction? thank you very much.

Chunlou

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Laser Heating of a Silicon Wafer

May 10, 2019, 12:24 am
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Hello, I am a novice in COMSOL. I have designed my own model based on "laser heating of a silicon wafer tutorial" https://www.comsol.com/model/laser-heating-of-a-silicon-wafer-13835

Can someone tell me why the maximum temperature in the above mentioned tutorial has fluctuation? What should I do to obtain a smooth profile for the maximum temperature?

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Loop Variable Correlation Was Detected

May 10, 2019, 12:56 am
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Hello!I meet a problem,when i click the study,it shows a error:Loop variable correlation was detected.If you have met this problem before,could you teach me how to solve it,please................. the error it shows like this: Loop variable correlation was detected. - Variable: comp1.taue - - Geometry: geom1 - - Border: 6

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