Latest Discussions - COMSOL Forums Most recent forum discussions Wed, 22 Nov 2017 23:09:50 +0000 COMSOL Forum: Latest Discussions calculation of metal potential <p>Hi all,</p> <p>I want to simulate a metal-semiconductor solar cell. Unlike the demo in the software, I want the metal electrode from the metal side to be disconnected, creating sort of 'floating gate', but the electrode from silicon side still connected (say 0v). IN this case, I want to see the metal potential change under illumination due to photo carrier injection from semiconductor.</p> <p>I have tried using floating gate, but it doesn't work, because floating gate cannot attached to anything. I also tried Schottky junction demo in the software, but in the demo the metal electrode cannot be disconnected; in other words, the voltage has to be fixed.</p> <p>Can anyone please gieve some suggestions on how to probe the potential of 'floating metal' in a metal-semiconductor solar cell?</p> <p>Thanks!</p> Wed, 22 Nov 2017 23:09:50 +0000 4.2017-11-22 23:09:50.160532 Comsol creates more domains than that defined in mphtxt <p>I am trying to select the domains using matlab code.</p> <p>I create a mphtxt file which has 3 domains from external software but when I import this mphtxt file to COMSOL, I get 4 domains in the selection lists.</p> <p>Or are there any other methods could select the domians in Comsol consistent with the number of domains in mphtxt?</p> Wed, 22 Nov 2017 22:58:15 +0000 4.2017-11-22 22:58:15.160522 Convergence issues caused by sudden change in storage term, Two phase flow, Coupled HM model <p>Dear all,</p> <p>I am running a coupled HM model for the two phase flow in poroue media. What I want to achieve a gas breakthrough event which means the gas pressure at the upstream side would reach a peak value before declining to a certain value because of the fracture development. Thus, I have developed a permeability model which increases rapidly once a certain strain. As the storage term in the mass balance equation is a function of the permeability model, this term will also experience a significant change. This equation is shown as</p> <p>S×rho×dp/dt+div(rho×v)=Qm</p> <p>where S is the storage term, rho is density, v is Darcy's velocity, Qm is the mass source.</p> <p>Due to this rapid change in S, the whole model is hard to reach convergence. Could you please give me an idea how to solve such an issue?</p> <p>Thank you so much for your help.</p> Wed, 22 Nov 2017 19:48:14 +0000 4.2017-11-22 19:48:14.160502 Problem solving a flow with inlet pressure <p>Hi,</p> <p>I have to model a flow of Helium inside a micronozzle (inlet diameter = 5 mm and outlet diameter = 1mm) and all I am given is the inlet pressure (30 bars), and the pressure at the other side of the micronozzle is ambiant pressure. The tube is 23 mm. The issue I'm facing is that the solver can't find a solution if I just put an inlet and outlet with pressure, no viscous stress as BC. I tryied both laminar and turbulent flow.</p> <p>I know it has been discussed a few times in the forum but I wasn't able to find a thread resolving my problem. I don't know if I missed something in comsol or simply with the actual phenomena.</p> <p>If someone knows what I could do step by step, Thanks in advance!</p> Wed, 22 Nov 2017 14:16:01 +0000 4.2017-11-22 14:16:01.160501 Problem with 'Remesh Deformed Configuration' <p>Hi,</p> <p>I have modeled my design with a solid and a shell in structural mechanics module and then I've performed a buckling analysis. Now I want to export the final deformed model for further study in RF module. However, when I select 'Remesh Deformed Configuration' , an error appears which says this option just works for solids. So how can I export my final structure? I've even tried to replace the shell with another solid (very thin). In this way, I receive another error 'Multiple moving frame on the same selection'. Could you please help me?</p> <p>Thanks</p> Wed, 22 Nov 2017 14:02:57 +0000 4.2017-11-22 14:02:57.160491 Time dependent - steady state <p>Hello, I am doing a time dependent study of a nonlinear spring (its stiffness is deformation dependent). The simulation time to reach steady state is quite long. I wonder if there is a way in order to skip the transient state? Many thanks, Khaled HARMOUCH</p> Wed, 22 Nov 2017 13:34:36 +0000 4.2017-11-22 13:34:36.160472 Continuity Boundary Condition <p>How to use continuity boundary condition for electromagnetic wave propagation module and bio heat transfer module?</p> Wed, 22 Nov 2017 13:10:01 +0000 4.2017-11-22 13:10:01.160463 Copying physics to another geometry <p>Ciao tutti</p> <p>I am sure this has been discussed before, but is it possible to copy a model/physics to another geometry? Say, I have managed to do a 1D model and would like to expand it to 2D.</p> <p>Lasse</p> Wed, 22 Nov 2017 10:44:56 +0000 4.2017-11-22 10:44:56.160441 The question about the calculate of magnetic <p>Hello everyone, I to expressions to calculate the magnetic field, using the transient solver, when setting a small time steps, and only when calculating a cycle, the magnetic induction intensity is much larger than the steps I use big time steps, setting calculation for a long time calculation of magnetic induction intensity . What reason is this</p> Wed, 22 Nov 2017 08:21:16 +0000 4.2017-11-22 08:21:16.160433 "Clear and Evaluate All" for Derived Values <p>Hello, I'm using Comsol with MATLAB to generate a very large number of iterations.</p> <p>I'm using MATLAB to generate the input paramters, prompt COMSOL to run, then extract the resultant table values generated in COMSOL, but I cannot seem to find a way to get the table values to be automatically evaluated at each iteration (old values are kept in the tables).</p> <p>The only way I could find was to go to the derived values and manually click "clear and evaluate all"</p> <p>Is there a way to get COMSOL to automatically clear and evaluate all derived values per run, or a way to get MATLAB to prompt it at each iteration?</p> Wed, 22 Nov 2017 02:55:23 +0000 4.2017-11-22 02:55:23.160432 stress tensor in nonlinear elastic material <p>Hi all Could you please tell me how can I enter the prestress tensor in the case of nonlinear elastic material. Since in this case, there is no initial stress and strain option available.</p> <p>Thanks</p> Tue, 21 Nov 2017 17:18:53 +0000 4.2017-11-21 17:18:53.160401 Interaction between objects in contact with set magnetisations <p>Hi all, I am a new user and have been trying to simulate two objects that are in contact with each other that will have a magnetisation related to each of them using the magnetic fields, no currents (mfnc) physics module. Both objects are located in a larger block of air.</p> <p>I've noticed that when I set the magnetix flux conservation, magnetic field to magnetisation for both of them, there seems to be no interaction between either (using the stationary solver). Conversely, if only one is set for the magnetic field to be reliant upon magnetisation, and the other relative permeability, there is some interaction observed. Is it possible for a user to set the initial magnetisation for both and have them interact with one another as well?</p> <p>And if so, are there any tutorials out there that I may refer to? Many thanks.</p> Tue, 21 Nov 2017 16:58:58 +0000 4.2017-11-21 16:58:58.160391 Rickwer Wavelet as an edge boundary load <p>I am analysing the wave propagation on a 2D elastic medium.</p> <p>I used as imput a force dependent on time having the form of a ricker wavelet on an edge boundary. I expect no residual deformations since everything is elastic, however when I plot the deformation on time, I get a considerable residual displacement. Can anyone see if I am missing something?</p> <p>The domain is a rectangle (2x16) having periodic conditions on the sides. At the bottom a boundary load and at the top absorbing conditions.</p> Tue, 21 Nov 2017 15:25:28 +0000 4.2017-11-21 15:25:28.160381 Maximum over time - at operator, point/line evaluation <p>Hi all</p> <p>I've done a Parametric Sweep and I'm trying to Evaluate a Line or set of Points at a time instant corresponding to a maximum of a variable, <em>mfh.By</em>. This time instant is dependent on the solution.</p> <p>When I evaluate (Point Evaluation) the expression "<em>at(attimemax(0, 0.25, mfh.By,t),mfh.By)</em>" it gives me this error:</p> <p>The solution specification is nonscalar or out of range. - Operator: at - Geometry: geom2 - Domain: 2 Failed to evaluate expression. - Expression: at(attimemax(0,0.25,comp1.mfh.By,t),comp1.mfh.By) Failed to evaluate expression. - Expression: at(attimemax(0,0.25,comp1.mfh.By,t),comp1.mfh.By)</p> <p>Also, I find "<em>Geometry: geom2</em>" weird because I only have Geometry 1.</p> <p>However when I evaluate the arguments of the "<em>at</em>" operator separately, they are evaluated with no problem. The same if I put them on an expression in a Point Graph.</p> <p>Also, I have a Cut Point 2D Data Set over which I'm evaluating, which has more than one point (five) in a line with different x-coordinates. When I evaluate, the different points are different columns. Is there anyway I can put them in rows, so than I can plot the Table Graph in as a function of x? Or another way to do this?</p> <p>Thank you</p> Tue, 21 Nov 2017 13:56:36 +0000 4.2017-11-21 13:56:36.160371 photonic crystal Qfactor <p>I use the eigenfrequency to calculate the 2D photonic crystal slab. I found a very good mode, but when I increase the number of air holes, I found qfactor decreasing. This is obviously wrong.</p> Tue, 21 Nov 2017 08:32:46 +0000 4.2017-11-21 08:32:46.160362 Pulsatile Flow in a Circular Pipe <p>How do you make fluid flow through a circular pipe pulsatile? I've been trying different fluid flow physics, but I am unsure which one represents pulsatile flow.</p> Tue, 21 Nov 2017 00:07:51 +0000 4.2017-11-21 00:07:51.160352 CFD Postdoctoral Fellow Opening, University of Connecticut, USA <p>Job Title: Postdoctoral Research Fellow – Rheological Modeling Department of Chemical &amp; Biomolecular Engineering/ Institute of Materials Science University of Connecticut, Storrs, CT, United States</p> <p>Application Deadline: Open until filled Position Start Date: January 2018</p> <p>Applications are invited for a postdoctoral research fellow opening with Prof. Anson Ma of the Chemical and Biomolecular Engineering Department and the Institute of Materials Science (IMS) at the University of Connecticut (UConn). For current research activities at Ma’s laboratory, please visit:</p> <p>Main Responsibilities: (1) To perform rheological modeling for industry-funded projects involving additive manufacturing (3D printing) and multi-phase flows; (2) Train and supervise graduate and undergraduate students; (3) Assist with proposal preparation, industry engagement, and new project launches.</p> <p>Required Qualifications: PhD in chemical engineering, mechanical engineering, physics, applied mathematics, or a related discipline. Prior research experience with COMSOL for complex fluid flow modeling.</p> <p>Compensation commensurate with experience. Exceptional candidates will also be considered for the Anton Paar Research Fellowship.</p> <p>Interested applicants should send a C.V., contact information of three referees, and a cover letter outlining research experience to Prof. Anson Ma at:</p> <p>Position Term: 12 months, renewable based on performance and funding availability</p> Mon, 20 Nov 2017 19:44:34 +0000 4.2017-11-20 19:44:34.160332 Total force generated in a pneumatic cylinder-piston with known clerance <p>I want to have a rough understanding of how the clearance between a pneumatic piston-cylinder affects the total drag/force generated on the position. I have elaborated the problem <a href="">here in this link</a> with details. Not finding any relevant studies, I would like to perform some simulations in COMSOL. Consider the 2D axisymeteric geometry below:</p> <p><img src="" alt="" /></p> <p>P1 is the inlet with constant pressure and P0 is the ambient pressure. I have implemented a very premitive model in COMSOL (attachment). How can I calculate the total force applied on the pistone?</p> Mon, 20 Nov 2017 18:31:23 +0000 4.2017-11-20 18:31:23.160331 Ferrofluid B-H curve and material properites <p>Does COMSOL materials library has a B-H curve for Ferrofluids or is it modelled as a linear paramagnetic material?</p> Mon, 20 Nov 2017 16:29:25 +0000 4.2017-11-20 16:29:25.160322 How to implement the Bingham-Papanastasiou model <p>Dear people,</p> <p>I've recently started using COMSOL (v5.2a), and I was wondering if somebody could help me. At the moment I'm trying the simulate a flow of a <strong>Non</strong>-Newtonian fluid, a magnetorheological fluid. This means that the dynamic viscosity of it isn't constant, and therefore I want to implement the Bingham-Papanastasiou model for this dynamic viscosity.</p> <p>An already predifined model in COMSOL for Non-Newtonian fluids is the Carreau model, and here the dynamic viscosity is defined as a function with definitions for the shear rate and strain rate tensor. My main purpose is actually to alter the expression for the dynamics viscosity, because the definitions for the shear rate and the strain rate tensor I will use also.</p> <p>Nevertheless I don't know how to do this. I was looking at the section where you can define your own parameters and functions, but I don't know how to implement the tensors and vectors for example.</p> <p>The Bingham-Papanastasiou model is defined as the following: <a href="http://"></a></p> <p>n = n0 +[ tauy/shearrate] * [1 - exp(-m*shearrate)]</p> <p>Here n is the dynamic viscosity, n0 is the plastic viscosity, tauy is the yield stress and m is the regularizing parameter. The shear rate and strain tensor D are defined as following, just as in COMSOL for the Carreau model.</p> <p>shearrate = [2trace(D)^2]^0.5, D = 0.5[div(u) + div(u)^T]</p> <p>This model I want to implement in COMSOL, any tips on how to do this? Thanks in advance!</p> <p>Regards,</p> <p>Marc</p> Mon, 20 Nov 2017 14:41:38 +0000 4.2017-11-20 14:41:38.160321