Latest Discussions - COMSOL Forums Most recent forum discussions Tue, 25 Jun 2019 18:30:28 +0000 COMSOL Forum: Latest Discussions Division by zero, Failed to evaluate variable, Failed to evaluate Jacobian of expression <p>Hello, I am using comsol to model conjugate heat transfer and fluid mechanics under turbulent flow regime. But I keep getting this error below:</p> <hr /> <p>Division by zero. - Function: / Failed to evaluate variable. - Variable: comp1.nitf1.vhNS_lin Failed to evaluate expression. - Expression: nojac((1.4142135623730951455^(1-shapeorder(comp1.u)))<em>max(comp1.nitf1.vhNS_lin-comp1.nitf1.vhNS_quad,0)) Failed to evaluate variable. - Variable: comp1.nitf1.vhNS Failed to evaluate temporary symbolic derivative variable. - Variable: comp1.nitf1.crosswindnitf@VDN${test@683} Failed to evaluate expression. - Expression: dvol_spatial</em>((((-comp1.spf.gijxx)<em>((comp1.nitf1.vhNS+comp1.nitf1.vhNS_prime)</em>(comp1.ux<em>comp1.nitf1.rho)))-(comp1.spf.gijxy</em>((comp1.nitf1.vhNS+comp1.nitf1.vhNS_prime)<em>(</em>comp1.nitf1.rho))))-(comp1.spf.gijxz<em>((comp1.nitf1.vhNS+comp1.nitf1.vhNS_prime)</em>(<em>comp1.nitf1.rho)))) Failed to evaluate Jacobian of expression. - Expression: (comp1.nitf1.crosswindnitf)</em>(dvol_spatial)</p> <hr /> <p>Can someone please help me.</p> <p>regards.</p> Tue, 25 Jun 2019 18:30:28 +0000 4.2019-06-25 18:30:28.237951 Parameter estimation + Parametric sweep <p>Hi,</p> <p>I am tring to perform Parameter Estimation on a set of measured data. I am using a Stationary Solution to solve the Helmholtz Eq and a Parametric Sweep to vary the width of a wire. As you may be already thinking, I am notified that the Parameter Estimation and the Parametric Sweep modules are not compatable. How can I get around this?</p> <p>Prevously, before I had measured data, I included the parameter I would like to determine in the Parametric Sweep. Now that I have the data I would like to fit it. Most of the literature on parameter estimation uses Time Dependent solvers, not sure how it would work with others.</p> <p>I am new to comsol so please forgive any naive remarks. Thanks for reading.</p> Tue, 25 Jun 2019 15:13:53 +0000 4.2019-06-25 15:13:53.237942 Electric switch in circuit <p>dear all, Hoping all is well with all of you.Kindly how to make a switch in electric circuit.. kindest regards samar akef</p> Tue, 25 Jun 2019 11:19:56 +0000 4.2019-06-25 11:19:56.237941 lock symbol in node <p>Can anyone explain what this lock symbol denote in comsol? Screenshot attached. Looking for a quick reply.</p> Tue, 25 Jun 2019 10:19:16 +0000 4.2019-06-25 10:19:16.237931 Boundary Condition <p>I am trying to insert a parabolic boundary condition in the inlet of my pipe flow model. The equation is like U=Umax(1-(R/Rmax)^2); I do know the value of Rmax &amp; Umax. But R is a variable one. How can I insert these in my boundary conditions?</p> Tue, 25 Jun 2019 07:04:28 +0000 4.2019-06-25 07:04:28.237921 changing air humidity <p>I am trying to simulate a model which consists of two electrodes. The electrode at the top is shaped as a cone and the one at the bottom is shaped as a plate. The plate is grounded and the cone is given -4V. The whole setup is enclosed in a box. The electrodes are made of copper and the box has air inside it. I would like to change the humidity of air in my model, and then i would like to observe the relation between the conductivity of air wrt humidity. Do i have to add another physics to my model? At present i have only added electric currents. I tried to find some emperical relation between conductivity of air and humidity, but couldn't.</p> Tue, 25 Jun 2019 06:15:00 +0000 4.2019-06-25 06:15:00.237911 Evaluating Objective function from only part of a parametric sweep <p>Dear all,</p> <p>I am sweeping an electromagnetic problem in frequency domain. If I am investigating for example frequencies 1, 2, and 3, is there a way to create an objective function that is only evaluated for frequency 1, and another for frequency 2 and so on? I'm thinking something like the at() function but for general parametric sweep.</p> Mon, 24 Jun 2019 20:59:30 +0000 4.2019-06-24 20:59:30.237902 Why do Comsol and Ansys have different mode shapes? <p>Hi,</p> <p>I am doing coupling anaysis for structural vibration and acousitc pressure. I have compared the result from Comsol to that from Ansys, but they have different mode shapes. Since I do not use Acoustic-structure interactions, I totally understand eigenfrequencies should be slightly different, but the mode shapes should be same.</p> <p>Every condition such as bounday conditions, contact, or material properties is same in Ansys and Comsol, but they show some different mode shapes. Why do they result in that differece?</p> Mon, 24 Jun 2019 18:57:30 +0000 4.2019-06-24 18:57:30.237901 Electric field - electric potential - AC/DC Module <p>Hello,</p> <p>I'm trying to simulate a photonic crystal with the AC/DC module. Does someone know why i'm having no variaton on electric potential or electric field when i changed the currently work frequency ?</p> <p>Thank you in advance,</p> <p>Saúl</p> Mon, 24 Jun 2019 18:08:44 +0000 4.2019-06-24 18:08:44.237891 Plotting Coordinates for Specific Condition (Heat Transfer) <p>Is it possible to plot a graph of x,y coordinates for a specific temperature condition in COMSOL?</p> <p>I am taking a slice, similar to the one attached, out of a 3D model and looking to create a graph of the position coordinates for one tempearature. From the picture, the goal would to have the graph look like a parabola.</p> <p>I found that exporting the data and using python to get the coordinates wasn't sufficient since there wasn't enough data points in the temperature range I wanted.</p> <p>Thanks</p> Mon, 24 Jun 2019 15:30:48 +0000 4.2019-06-24 15:30:48.237882 Delete user defined material <p>Hello fellow COMSOLers,</p> <p>is there a way to remove materials from the user defined materials library. I already checked the forum and manual but cannot find anything.</p> <p>Any advice is greatly appreciated.</p> <p>Best regards, André</p> Mon, 24 Jun 2019 14:37:05 +0000 4.2019-06-24 14:37:05.237881 SAW Device with IDTs <p>I'm trying to create a finite-sized surface acoustic wave device (file attached) with gold electrodes for the IDTs.</p> <p>Essentially, I'm creating an IDT similar to but looking at what happens to the wave as it penetrates the piezoelectric substrate without the periodic boundary conditions (since the IDT I fabricate will be finite sized). There are a few simulations I wish to run:</p> <p>(1) Finite-sized (i.e. no periodic boundary conditions) surface acoustic wave device (2) 3D version of IDT -- i.e. extrude the entire setup along an axis (3) IDT with input and output ports, as in the paper linked.</p> <p>I cannot seem to get any of these three to work; I've attached files from (1), could someone take a look and see if I'm doing anything in my setup wrong? How would I set up an output port and get the resonance plot?</p> Mon, 24 Jun 2019 14:09:54 +0000 4.2019-06-24 14:09:54.237872 Deposited Ray Power <p>Hi all,</p> <p>I am modelling a Winston cone by using geometric optic engine. I'm sucessfull getting the ray trajectories but however when I computed the deposited ray power at the entrace aperture and the exit apeture of the cone, they are always zero. Attached is the screenshot from my simulation. Please help me to compute the power enterinng and exiting the cone.</p> <p>Thank you,</p> Mon, 24 Jun 2019 13:49:38 +0000 4.2019-06-24 13:49:38.237862 In the acoustic module, how to set the parameters of anisotropic materials <p>In the acoustic module, how to set the parameters of a material when the density of mass or the bulk modulus of elasticity is anistropic i.e. the density of mass or the bulk modulus of elasticity of the material is a martrix?</p> Mon, 24 Jun 2019 13:39:06 +0000 4.2019-06-24 13:39:06.237853 Difference between available Hydrogen gas models <p>What is the difference between the following?</p> <ul> <li>Liquids and Gases > Gases > Hydrogen</li> <li>Material Library > Elements > Hydrogen > Hydrogen [gas] > Hydrogen [gas, H2]</li> </ul> <p>Specifically with respect to equations for density (the second one has density independent of pressure).</p> Mon, 24 Jun 2019 10:48:32 +0000 4.2019-06-24 10:48:32.237833 Training courses <p>Hello, I was interested in learning how to use comsol for simulation of penetration of drugs in spheroids in peritoneal cavity tumors Is there any training courses given by comsol or textbook that can help me in this issue</p> Mon, 24 Jun 2019 07:14:46 +0000 4.2019-06-24 07:14:46.237832 Ground Temperature Profile <p>I need to set boundary condition as Ground Temperature profile given by Kasuda function<img class="latexImg" 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/> however i am not getting desired plot, is the cos function in Redian or in degree ? Tmean 18.5 mean surface temperature Tamp 21 apmlitude of surface temeprature depth 1 1 Depth of the Ground a 0.1728 Thermal Diffusivity tshift 35 minimum surface temp O 3.14/365 omega</p> Mon, 24 Jun 2019 06:11:47 +0000 4.2019-06-24 06:11:47.237821 Sin function in COMSOL <p>Dear , how to put sin function at boundary condition.</p> Mon, 24 Jun 2019 06:04:53 +0000 4.2019-06-24 06:04:53.237811 modeling heat transfer in LiNb at 10**-2 K and with a heat source, power of heat source 10**-3 W <p>Hi,</p> <p>I am traying to model heat transfer in a lithium noibate resonator at E-2 K tempreture. So I defined heat conductivity k=4T<strong>3 and heat capacity 0.000234T</strong>3 at E -2 K with a heating source which has a power of E-3 W (a laser source 1550 nm wavelenght). The problem is when my power is less than E-8 It gives me a solution which I attached here but when I put my actuall power E-3 W it gives me this error:</p> <p>Feature: Time-Dependent Solver 1 (sol1/t1) Failed to find consistent initial values. Error in user-defined function. Function: comp1.mat9.def.K Failed to evaluate variable. Variable: comp1.mat9.def.k33, Defined as: (comp1.mat9.def.K(comp1.T/unit K cf)<em>unit W cf)/(unit K cf</em>unit m cf) Failed to evaluate variable. Variable:, Defined as: comp1.mat9.def.k33 Failed to evaluate variable. Variable: effzz, Defined as: Failed to evaluate variable. Variable:, Defined as: ( effzz)<em>comp1.Tz Failed to evaluate expression. Expression: d((2</em>(<em>test(comp1.Tr)</em>test(comp1.Tz))<em></em>pi<em>r)</em>(dvol spatial),{test1}) Failed to evaluate Jacobian of expression. Expression: (2<em>(</em>test(comp1.Tr)<em>test(comp1.Tz))</em><em>pi</em>r)*(dvol spatial) Last time step is not converged.</p> Sun, 23 Jun 2019 08:29:36 +0000 4.2019-06-23 08:29:36.237792 Angled Waveguide 2D <p>Dear All</p> <p>I have problem in Geometry. I am trying to Draw an angled waveguide with 60 degrees bend. Help will be appreciated</p> <p>Thanks in Advance</p> Sat, 22 Jun 2019 17:16:52 +0000 4.2019-06-22 17:16:52.237791