Latest Discussions - COMSOL Forums Most recent forum discussions Sat, 24 Mar 2018 18:05:04 +0000 COMSOL Forum: Latest Discussions Meshing faces - A beginner's question <p>Hi everyone, apologies if this may seem trivial but I've been struggling to create a separate mesh for separate faces in my model.</p> <p>The geometry is a simple I-beam of length 4m but thicknesses of 6.7mm and 11.8mm along the web and flanges respectively, created from extruding the cross section. Clearly a much finer mesh is required for the faces with comparatively smaller thicknesses than the span, however whatever I try, when selecting the domain for the mesh it just selects the entire geometry. Tried to use domain partitioning via faces and mesh control faces but this did not do the trick. This probably has a really simple answer which I'll be banging my head over but would really appreciate some help here.</p> <p>Thanks!</p> Sat, 24 Mar 2018 18:05:04 +0000 4.2018-03-24 18:05:04.173041 Using Integration Operators To Calculate Volume To Use As A Stop Condition <p>Hi there,</p> <p>I have a multiphase (2 phase) flow of a droplet of a fluid in a flow (domain 2) that eventually leaves domain 1. I want to have the calculation stop when the fluid starts to leave the domain so I created a integration operator to calculate the volume and then a variable that is used in the stop conditions. As the droplet starts to leave the outlet the volume of the fraction of fluid (domain 2) will decrease and I will have the condition stating that when around half of this fluid has disappeared, the study will stop calculating.</p> <p>Problem is, I am having trouble with the integration operator.</p> <p>I want it to calculate the volume of fluid for every iteration, so I assume it is dependent upon time. My variable "Vdroplet" (volume of droplet) is defined as intop1(1) in the local variables section and then in the stop conditions stated as Vdroplet&lt;=(an size) then stop.</p> <p>Would the integration operator calculate the volume every iteration or should it be Vdroplet=intop1(t[1/s])?</p> <p>Please ask if you need more information and thanks for your help in advance.</p> <p>Oliver</p> Sat, 24 Mar 2018 16:26:23 +0000 4.2018-03-24 16:26:23.173031 Re-use time-dependent flow field outside of solved time window <p>Hi all,</p> <p>I'm trying to model a simple reactor with a stir bar and chemical reactions happening on the reactor surface. I can solve for both the time-dependent flow field and concentration gradients of key reactants and products as a function of time. However, the flow field calculation is relatively quite expensive (~5 minutes to solve for only a few seconds of stir bar rotation, as compared to ~10 seconds for concentration gradients).</p> <p>I want to model the concentration gradients over several hours, so I don't want to have to solve for the flow field over such a long time scale. The flow field is periodic (once the stir bar has completed one rotation, the flow field looks equivalent to t = 0). Is there a way repeatedly use these values in a study for the concentration gradient?</p> <p>I don't want to use the trick where I make a new study and use the final time concentration values as the initial condition for the next study, because that will require a ton of studies to get the full several hours window.</p> <p>I feel like i'm missing something simple.</p> <p>Thanks for the help!</p> Sat, 24 Mar 2018 01:15:48 +0000 4.2018-03-24 01:15:48.173012 Absolute vs Relative Tolerance <p>Hello there,</p> <p>I'm curious what the difference between absolute and relative tolerance is. Particularly when you are setting the absolute tolerance to a factor of the relative tolerance, it seems that the absolute tolerance is redundant.</p> <p>I'm sure I'm misunderstanding something.</p> <p>Thanks, Grant</p> Sat, 24 Mar 2018 00:47:44 +0000 4.2018-03-24 00:47:44.173002 Does anyone know how to assign spatial-dependent vectorial values to a Control variable field when using Sensitivity Analysis module? In the Sensitivity interface, I can only specify a scalar to the property "Initial value" <p>Hi,</p> <p>Does anyone know how to assign spatial-dependent vectorial values to a Control variable field when using Sensitivity Analysis module? In the Sensitivity interface, I can only specify a scalar to the property "Initial value."</p> <p>Because I am now using the Livelink Matlab to manipulate the Sensitivity module to compute the partial derivative of a scalar objective(OBJ) function with respect to a control variable field ("rho", which is spatial-dependent) defined over a domain, I'd like to get the derivative of the OBJ with respect to an arbitrary control variable field "rho", which should be coordinate(x, y) dependent. However, it seems like in the Sensitivity interface the only way to assign a value to the "rho" is through the "Initial value," which only supports scalar input.</p> <p>Thanks, Bryant</p> Fri, 23 Mar 2018 22:41:56 +0000 4.2018-03-23 22:41:56.172992 Limitations of the Plasma Module <p>Dear COMSOL Employees,</p> <p>My question is about COMSOL and Space Thrusters. I'm a scientist in the field of Plasma Thrusters and I need to modelling some type of Electric Rocket Propulsion (space thruster). I read many thing about COMSOL and still I am trying to find information how it works! In the COMSOL Documentation I found the next info:</p> <ul> <li>Limitations of the Plasma Module. The Plasma Module cannot currently model magnetrons and space thrusters due to the fact that the perpendicular versus cross field electron mobility and diffusivity can be on the order of 108. This poses severe numerical challenges and inevitably there is unphysical numerical diffusion across the magnetic field lines. As such, a truly self consistent model of a Hall thruster or magnetron is not currently possible, although it is still possible to gain valuable insight into the physics. * </li> </ul> <p>But when i searched the "space thruster" in the the COMSOL website, i found some articles about using COMSOL for space thrusters solution. Somebody can explain me what in fact can and can not be done in a COMSOL?</p> <p>THANKS AND REGARDS</p> Fri, 23 Mar 2018 21:23:38 +0000 4.2018-03-23 21:23:38.172991 Unable to Save model. "Error: Content not allowed in prolog." <p>I keep receiving the attached error "Content is not allowed in prolog." when I try to save a certain model file. I've tried clearing all solutions and meshes, resetting the solvers, compacting the history, deleting unused nodes, parameters, functions, etc...</p> <p>It won't let me save the model; I'm not sure if it's related but I've had another error message pop up every time I compact my history that reads "Unkown Frame. -Tag: ".</p> <p>Any help with these errors would be great, thank you.</p> Fri, 23 Mar 2018 21:21:39 +0000 4.2018-03-23 21:21:39.172982 capillary <p>I'm looking for anything that could help me. My task is only to describe the capillaries, which are usually in a heat pipe. I found a tutorial that is not my case, even though "Capillary Filling - Phase Field Method" is called. I try to simulate a pipe with capillary on the walls. The pipe is vertical and the water is below. it is to expect that the water goes up by the capillary(porous media) on the walls and the low pressure by itself. I have seen all the tutorial in this regard. Nothing helped</p> Fri, 23 Mar 2018 19:43:43 +0000 4.2018-03-23 19:43:43.172921 Creating limited contact geometry <p>I am currently working on simulating conduction within a small packed bed of uniformly sized spheres but having problems with building the geometry and meshing. If I try to form a union, some of the domains become unselectable. And while the alternitive option of forming an assembly doesn't have this problem, it introduces other issues and still refuses to mesh. The file I have attached is has 11 of the 60 spheres I use in my model enabled. 2 of these 11 spheres refuse to be selected if Form Union is used, and show weird things between them in the case of Form an Assembly. The goal is to be able to implement thermal contact BC's at the faces of contacts and either insulated/diffuse surface BC pretty much every where else. Preferably without haveing to manually use the GUI to go through and specify each of the 240+ contact locations manually. Ivar, if you can hear me, I am fully willing to sacrifice an undergrad from our lab upon an alter to you in exchange for your help.</p> Fri, 23 Mar 2018 19:12:28 +0000 4.2018-03-23 19:12:28.172912 Hydrocyclone <p>Hi,</p> <p>I am curently working on hydrocyclone, and i have follows all notes in the attached file, unfortunetly, it is dosn't work.</p> <p>any one can help me please ?</p> <p>Regards O.S.L</p> Fri, 23 Mar 2018 17:08:38 +0000 4.2018-03-23 17:08:38.172911 Map vector field from 2D axisymmetric component (r-z coordinate) to 3D component (x-y-z coordinate) <p>Hi COMSOL community,</p> <p>I am encountering an obstacle that the results from 2D axisymmetric component are mapped to 3D component as the initial values. The General Extrusion coupling is used in the 2D axisymmetric component (e.g. r=sqrt(x^2+y^2), z=z), and in the 3D component, this operator is utilized to generate initial values for, like, Solid Mechanics interface with this kind of form, e.g. comp1.genext1(withsol('sol1',u)). I found the scalar value can be directly mapped from 2D (r-z coordinate) to 3D (x-y-z coordinate), but for the vector fields, it is not straightforward since the revolving angle (phi) is unknown. Unlike the Revolution 2D data set in the postprocessing stage where we know the revolution ange (rev1phi) helping transform from 2D r-z coordinate to 3D Cartesian coordinate, the General Extrusion operator will not offer the information of revolving angle in the model set-up stage.</p> <p>I also attached a simple testing model with two components in 2D axisymmetric and 3D Cartesian coordinate, respectively. The general extrusion coupling is set in the 2D component, and the initial values are expressed with this general extrusion operator in 3D component. However, the initial values are not correctly calulcated in the 3D Cartesian cooordinate.</p> <p>Please any thoughts or solutions to this problem.</p> <p>Thanks.</p> Fri, 23 Mar 2018 16:18:40 +0000 4.2018-03-23 16:18:40.172892 Problem regarding eddy current calculation with impedance boundary condition <p>Hello everybody,</p> <p>I'm having trouble calculating the eddy current losses in an aluminium frame of a high frequency (92000Hz) transformer.</p> <p>I'm following the instructions in the "<a href="">Eddy current</a>" library model which sets the boundaries of the metal plate to the impedance boundary condition. I've got several problems with this appoach:</p> <ol> <li><p>This boundary condition only works in the frequency domain. However, I wish to model a triangular current in the coils, which is possible only in the time domain. I made a compromise and set only the fundamental harmonic as the coil current.</p></li> <li><p>Again because of this boundary condition, I have to form an assembly instead of a union, otherwise the boundary condition is shown as not applicable. I understand that this migh happen because of the contacting aluminium plates, but it also happens when I build only one plate. The library model uses a union. I'm not sure how this affects my model.</p></li> <li><p>Even when considering only the fundamental harmonic and forming an assembly, the calculated surface loss density is exactly zero, even with an extremely fine mesh.</p></li> </ol> <p>Any suggestions or corrections are welcome. I attach my model for anyone willing to help.</p> <p>Thanks a lot in advance.</p> Fri, 23 Mar 2018 16:16:44 +0000 4.2018-03-23 16:16:44.172891 Solver questions regarding a COMSOL tutorial: "Pull-in of an RF MEMS Switch" <p>Hi Everyone</p> <p>I have done the "Pull-In of an RF MEMS Switch" tutorial:</p> <p>It is a nice tutorial, but I don't understand the choices made regarding the solvers used. Therefore, I am listing my questions here together with the original instructions of the tutorial. Hopefully someone can help me or guide me to a good reference.</p> <blockquote> <p>1 In the Settings window for Time Dependent, locate the Study Settings section.</p> <p>2 In the Times text field, type range(0,5e-7,5e-5).</p> <p>3 Locate the Physics and Variables Selection section. Select the Modify physics tree and variables for study step check box.</p> <p>4 In the Physics and variables selection tree, select Component 1 (comp1)>Electromechanics (emi)>Terminal 3.</p> <p>5 Click Disable.</p> </blockquote> <ol> <li>What is the aim of these steps?</li> <li>Why do we have to disable terminal 3 ?</li> </ol> <blockquote> <p>Change the default solver to a Fully CoupledDirect solver and use BDF time stepping 3. Why do we have to change the default settings to BDF time stepping and Fully Coupled Direct?</p> </blockquote> <p>Thank you very much.</p> <p>I actaully have a bit more questions regarding this tutorial. Please have a look at the attached file.</p> <p>Thank you very much for your time!</p> Fri, 23 Mar 2018 15:20:24 +0000 4.2018-03-23 15:20:24.172881 Material gradient <p>Dear Comsolers,</p> <p>I need to define nonlinear material where the gradient of the Young's modulus of elasticity changes between values depending of the position along one of the axis. Also I have trouble finding the expression of the position in order to define the function I need. Can anyone help me?</p> <p>All the best,</p> <p>Jovana Jovanova</p> Fri, 23 Mar 2018 15:01:14 +0000 4.2018-03-23 15:01:14.172871 Location of dEeqdT_int1(SOC) Function: Batteries & Fuel Cell Materials Library <p>Hi Everyone,</p> <p>The relationship between the electrode potential and temperature <img class="latexImg" src="data:image/png;base64,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" /> is defined by default for the graphite electrode material in the Materials Library of the Batteries and Fuel Cells Module. It is written as dEeqdT_int1(SOC). I would like to view the equation and/or graph of this predefined relationship. However, I cannot find a way of doing so, nor can I find where this function is defined. Can you please advise?</p> <p>Thank you for your time.</p> Fri, 23 Mar 2018 14:50:57 +0000 4.2018-03-23 14:50:57.172861 HOW TO FIND REFRACTIVE INDEX OF CLADDING IN PCF OF CAMSOL DESIGN <p>i can find neff. of pcf from camsol but how we know the index of cladding please help</p> Fri, 23 Mar 2018 13:34:06 +0000 4.2018-03-23 13:34:06.172851 Base motion <p>Hi,</p> <p>There is an option in comsol as base motion (Multi body dynamics). I want to know what will be considered as base.</p> <p>Regards, Varsha</p> Fri, 23 Mar 2018 11:04:48 +0000 4.2018-03-23 11:04:48.172841 Issues of continuously transposed conductor (CTC) modelling <p>Dear COMSOL Community, I am using COMSOL for some time and this is the first time I have encountered a problem. So, this is my first post in this forum. I am trying to investigating frequency dependent inductance due non-uniform current distribution and skin/proximity effect in solid and continuously transposed conductor (CTC) at high frequency upto 3 MHz. For this purpose, I have developed very simple 3D circular coil models of solid condutor and CTC with 5 strands. (Previously, I have also worked with 2D axisemmetry models to observe the effect of frequency on inductance of the coil and everything worked).</p> <p>And now I have simulated the 3D solid conductor coil model and it also works fine. But I have issues with the simulation of CTC coil model. I have tried to use different solvers but it is not working and solution does not converges. Can someone in the community help me in this regard? I have attached the model of simple 5-strand CTC.</p> <p>Secondly, as if we increase the no. of strands in the coil the geomatry becomes complex to build mannually. So, Is there any tool or code in COMSOL to create the geomatry of CTC with many strands?</p> <p>I would really appreciate your help in this regard.</p> <p>Thank you, Mehran</p> Fri, 23 Mar 2018 10:20:55 +0000 4.2018-03-23 10:20:55.172831 Time and voltage value setting <p>Hello everyone,</p> <p>Iam designing piezoelectric energy harvester and Iam using fem modelling technique for determining voltage using comsol 5.3. Iam getting the voltage value in 3d plot but iam not getting in 1d plot group for time dependant study. How to plot it?? I have attached my model below. Please help me to complete this work and correct my error.</p> Fri, 23 Mar 2018 09:42:17 +0000 4.2018-03-23 09:42:17.172821 Laminar Flow and Heat Transfer <p>The below post is related to an <a href="//">archived discussion</a></p> <hr /> <p>Hello!</p> <p>I am trying to model 3D laminar flow with heat transfer in a rectangular channel. I have coupled both the physics through the Multiphysics node. When I set the reference pressure pref as zero, I get the error message "Division by zero". As my model is not open to atmosphere, I do not want to keep the pref as 1[atm] (default value). Kindly provide your suggestions in this regard.</p> <p>Thanks in advance.</p> Fri, 23 Mar 2018 07:47:10 +0000 4.2018-03-23 07:47:10.172811