Latest Discussions - COMSOL Forums Most recent forum discussions Mon, 21 Oct 2019 12:36:29 +0000 COMSOL Forum: Latest Discussions What does Cauchy mean in Double Dogleg solver? <p>Hello all,</p> <p>Can anyone tell me what Cauchy stands for in the Double Dogleg solver for a stationary solver? I do not obtain convergence in my model, but am unsure as to what might be the reason because I do not know where to search as long as I do not know what Cauchy stands for (see attached PNG pictures). It seems to almost converge (value of 0.011 before ramping up with tolerance 0.01).</p> <p>Also, if anyone could pinpoint why my model might not be converging, I would love to know. The model functions well for steps up until the addition of an internal convection (study 1 and study 2 step 1 work, study 2 step 2 doesn't), so I assume my model is properly setup for the other variables. I do not understand why the model is unable to solve for the last step. Does anyone have any experience with internal convection models not working? Might it be due to sharp edges in the geometry? Or do I have to set some extra condition on the boundary between the 'Water' and the 'Air' domain before the program understands that these fluids have seperate internal convection, but heat transfer between the two? I included the model and a schematic of the problem. If anyone could take a look at it, that would be very much appreciated!</p> <p>Thank you in advance!</p> <p>Kind regards, Maarten Steggink</p> Mon, 21 Oct 2019 12:36:29 +0000 4.2019-10-21 12:36:29.244761 Modelling Pressure Drag using Acoustics Module <p>Hi,</p> <p>I have a model of oscillating structure and I would like to study the pressure drag effects due to the surrounding fluid. Is it possible to use the Acoustics module of comsol to model pressure drag. I know it has thermoviscous and pressure acoustics submodules however I am uncertain if it can help model pressure drag aswell. I would like to avoid full FSI to reduce computation time.</p> Mon, 21 Oct 2019 08:31:19 +0000 4.2019-10-21 08:31:19.244751 How to setup a periodic Boundary condition with automatic remeshing? <p>I have a laminar flow problem coupled with heat transfer. The domain is periodic in the lateral direction, so I use the periodic flow condition for laminar flow and the periodic flow condition for heat transfer in solid. I have the copy I node in the mesh generated by physics-controlled mesh setting.</p> <p>It works fine with I don't have automatic remeshing enabled. If I want to implement automatic remeshing (because the fluid interface deforms quite severely and the mesh quality becomes quite poor), then it gives an error when remeshing occurs. It says 'Failed to build feature 'Copy 1' in sequence 'Mesh 1'. Geometry object and mesh object are not compatible. Vertex coordinates differ.'.</p> <p>So it looks like there is some problem with the copy 1 node related to periodic boundary condition. What does it mean for vertex coordinates to differ? How to solve this problem?</p> Mon, 21 Oct 2019 01:39:18 +0000 4.2019-10-21 01:39:18.244722 No stored reaction force data <p>Hi, While I am computing capacitance by changing distance between plates as a parameter, I am getting a message like no reaction force data. How can I correct this? Regards Anand A ![]</p> Sun, 20 Oct 2019 12:25:29 +0000 4.2019-10-20 12:25:29.244721 Inverse Magnetostriction Effect <p>How to set the model of Inverse Magnetostriction Effect</p> Sun, 20 Oct 2019 11:50:52 +0000 4.2019-10-20 11:50:52.244713 Transmission voltage response, TVR <p>Hi,</p> <p>I'm simulating a piezo-discs vibrations under water. And, I have got stuck at implementation of the TVR. Getting the error message: "Unknown function or operator. -Name: comp1.pfar ..."</p> <p>Tried to add the specifik component (comp1), so that pfar should know what is meant, but still get the same error message.</p> <p>Do anyone known where I am going wrong?</p> <p>Best regards, Kim</p> Sun, 20 Oct 2019 07:39:46 +0000 4.2019-10-20 07:39:46.244711 Material Properties <p>How do I know the precise numerical value of a particular properties? For sound velocity it shows cs(T). But I want to know the precise numerical value .</p> Sun, 20 Oct 2019 04:43:16 +0000 4.2019-10-20 04:43:16.244703 3d and 2d structure of sillicon carbide mosfet <p>Any idea on how to build 2d and 3d structure of silicon carbide mosfet with heatsink in comsol 5.3a?</p> Sat, 19 Oct 2019 14:45:06 +0000 4.2019-10-19 14:45:06.244701 Band gap analysis of phononic crystals <p>I am performing band structure analysis using eigenfrequency domain in structural mechanics physics. Can anyone suggest the expressions for kx and ky, which will be used to sweep around the eigen frequencies.</p> <p>My unit cell shape is for both T and H shaped unit cell,</p> Sat, 19 Oct 2019 07:46:57 +0000 4.2019-10-19 07:46:57.244681 Variable for refractive index in Ray Optics <p>Hello I am using glasses from the Material Library and the dispersion model for each of these glasses. I wonder if it is possible to access the refractive index for a particular wavelength or a range of wavelengths that is actually used. What is the variable in those cases? Thank you Margarida</p> Sat, 19 Oct 2019 07:25:12 +0000 4.2019-10-19 07:25:12.244671 Initial values for Poisson's equation. <p>Hi I am trying to solve the following equation <img class="latexImg" src="data:image/png;base64,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" /> Where <img class="latexImg" src="data:image/png;base64,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" /> is the electric field in the y direction inside a capacitor and u at y=0 equals pi/60 and y=D equals -pi/60</p> <p>To solve the equation I am using the electrostatic module and the Poisson's equation.<br /> However I am getting the following error. "Failed to find a solution for the initial parameter. Maximum number of Newton iterations reached. Returned solution is not converged."</p> <p>I believe that this is due to because my intial values are too off from the solution. However, if I change the voltage applied to the capactior I need to use another intial values. Futhermore depending on what inital values I give it I get different results.</p> <p>Do you guys have any idea what are some good initial values to give it?</p> Sat, 19 Oct 2019 02:32:56 +0000 4.2019-10-19 02:32:56.244662 Simulation of a gear pump with intermeshing sprockets <p>simulation of a gear pump with intermeshing sprockets</p> <p>I have been trying to simulate flow in a gear pump with two intermeshing sprockets ( see the model model). I have created two rotating domains for sprockets and one channel. I searched through the literature and people have done this type of simulation using overset mesh in other software. I am not sure how to use those methods in COMSOL. Your thoughts/suggestions are highly appreciated.</p> <p>Sohan Birla</p> Fri, 18 Oct 2019 21:20:47 +0000 4.2019-10-18 21:20:47.244652 Required Time to Reach A Specific Solution Value <p>Dear all,</p> <p>I am running a 1D time-dependent diffusion simulation. Is there an automated way to find the required time for a point in the domain to reach a specific concentration value? For example, I would like to know the time required for x = 0.5 m to have a concentration of 0.2 mol/m^3. I could manually find by various ways but I need an automated approach so that I can use in the Application Builder as an analysis result.</p> <p>P.S: I am not interested in stopping the simulation.</p> <p>Thanks in advance.</p> Fri, 18 Oct 2019 13:44:16 +0000 4.2019-10-18 13:44:16.244642 saw gas sensor <p>The below post is related to an <a href="//">archived discussion</a></p> <hr /> <p>how to identify resonance nad anti-resonance frequency of saw gas sensor and resonant frequency shift before and after exposure of the gas</p> Fri, 18 Oct 2019 13:08:00 +0000 4.2019-10-18 13:08:00.244641 surface Acoustic Wave Gas Sensor <p>Sir, Iam working on MEMS based Surface Acosutic Wave gas sensor.Since this works on Mass-loading effect to know the sensor performance like sensitivity etc "resonant frequency shift" is to be calculated. I request you to mention the process that is available to assess the resonance frequency shoft in comsol multiphysics tool.</p> Fri, 18 Oct 2019 10:31:06 +0000 4.2019-10-18 10:31:06.244621 Strange mechanical behavior in FSI <p>Hello,</p> <p>I am a student, new to COMSOL, and I'm trying to compute a fluid-structure interaction study where the sinusoidal body load applied to the mechanism induces a motion in the fluid. Everything seems to run smoothly but when I observe the results, something odd is displayed. While the solid body is deformed (cf attached file), it seems the the motion in the fluid is computed taking into account a not deformed solid(cf attached file).</p> <p>It is problematic since the fluid solution is antiisymetric, while the solid behavior is not, and I'm not sure the results are right. Do any of you happen to know where the problem might come from? Is it a PEBKAC?</p> <p>Regards</p> Thu, 17 Oct 2019 21:38:08 +0000 4.2019-10-17 21:38:08.244601 What is a Pressure Point Constraint? When is it used? <p>My solution is not converging. The model consists of inlet and outlet pressures. I read online in such cases you can use Pressure Point constraint. But I don't know much about it. Can someone help me out in this.</p> Thu, 17 Oct 2019 16:18:12 +0000 4.2019-10-17 16:18:12.244582 Negative & irregular concentration with an applied concentration flux <p>Hi,</p> <p>I want to study the mass transport of diluted species under convection and diffusion. My simulations yielded a significant amount of negative concentration. Therefore I created a model for testing purposes:</p> <ol> <li>Only diffusion</li> <li>Geometry (see geometry.png) -> a defined flux is applied at the surface. This flux was originally defined by a square pulse (for testing purposes the flux is constant)</li> <li>Time-dependent study</li> </ol> <p>The results show that:</p> <ul> <li>There is a zone of negative concentration above the surface where the flux is set</li> <li>The concentration on the surface where the flux is applied has not a uniform concentration.</li> </ul> <p>What did I try to resolve this:</p> <ul> <li>Change the mesh. I used the standard mesh from comsol and two custom quad meshes different accuracy. Concentration profiles from the quad-meshes are attached. It seems that the mesh quality only compresses/shifts the negative concentration zone.</li> <li>Ramping up the pulse and removing the pulse (constant flux)</li> <li>change time-steps (smaller steps)</li> <li>change the stabilization methods</li> <li>change the magnitude of the flux</li> </ul> <p>Nothing of the above methods did help. I have also attached my test model.</p> <p>TLDR: Transient study using diffusion of a concentration applied via a flux results in significant regions of negative concentration as well as concentration "hot-spots".</p> <p>Thanks Claus</p> Thu, 17 Oct 2019 15:06:01 +0000 4.2019-10-17 15:06:01.244571 Sanity Question <p>Hi,</p> <p>I've been working on some simulations in the RF module and just need a quick sanity question answered. In order to "prepare" my simulations I first try to simulate a Air -> Dielectric substrate interface. My question is, for each domain in the simulation, is there an ideal amount of wavelengths which should propagate in the domain. For example, if I have a 14 um wavelength incident on a air column and I want to measure the transmission, what would be considered an appropriate width / height of the air domain? In this proposed simulation, the air would be surrounded by PMLs too.</p> Thu, 17 Oct 2019 15:02:35 +0000 4.2019-10-17 15:02:35.244562 modelling of moving laser heat source <p>Hi, I want to model a moving laser heat source for heating a hemispherical cavity. I want to define a helical path inside the cavity for the laser heat source but i am having difficulty in defining the path. So, please help me regarding this.</p> Thu, 17 Oct 2019 11:17:42 +0000 4.2019-10-17 11:17:42.244551