how to define variables in comsol

The only reference I found of this in the documentation is in the "Summary of Common Predefined Variables" where it is lumped with a bunch of other variables under "Mesh Information". if(dom==1,epsilonr_air,if(dom==2,epsilonr_container,epsilonr_ball) ) But now comes the tricky part, how do I write in Comsol that f(x+dest(x),y+dest(y)) = 1 only when x+dest(x),y+dest(y) \in dom 1 (else 0)? "dom" is one of these variables, even an internal variable that takes the entity "ID" be it Domains, Boundaries Edges or Points. 7 Replies, Please login with a confirmed email address before reporting spam. Hence since f is 1 on dom 1 we have Thanks. Then in integration you choose the boundaries , if it is domain or boundary you will see how you can pick up just the space between your lines. Hi Mohammed, In the manual, but what is the scope etc here? 1 This is probably too late but you could try using min (limit,function or variable). That is, you can define it without specifying the actual names of the arguments that you will use when calling it. 9 Replies, Please login with a confirmed email address before reporting spam. Under Component right-click Definitions and choose Variables, or click Local Variables in the Definitions toolbar (Windows users). Am I right on this one? Is there a better way to integrate over fixed boundaries? Then again T might well be T(x,y,z,) and so on Check the doc and test out the numerous examples, you will quickly learn. - For a variable defined under Variables, you can define an expression in a flexible way, but it must represent a scalar-valued function (that is, when called with its inputs, it returns a scalar value). I suppose you can define a new PDE module. How to make a variable of 3rd order derivatives? You can generate a report that displays within the software and includes this information by completing the following steps: Select and right-click the Report node Choose to generate a Complete Report Select the option in the settings to Preview All of the report How to find the in built functions such as integrate. Once the option is enabled, you'll see a Variable Utilities button within the Definitions ribbon, and a Variable Utilities submenu when you right-click the Component > Definitions branch within the model tree. For the record, if anyone else is having trouble with this, the way to do it is as follows: I figured out how to do it. In such a case, only damping coefficient and source term are non-zero. So physical parameters are entered on the domains principally. in an axisymmetric model where r is a spatial coordinate, for example. The boolean expression did the trick. For the function I tipped different solution in the variable expression: spf.sr e (n-1) or spf.sr*e (n-1) or exp (log (spf.sr) (n-1) Poissons ratio, nu I want to integrate a function f(x,y) from y=0 to y=1. Good luck I would appreciate your help in setting up this problem in COMSOL. Because the microrobot legs consists of several materials with different material properties, you have to define subdomain settings for each materials. What I want to do is that to define a variable that varies for continuous range of values like the range function does the same but with a step size(discontinuity). Note that while COMSOL employees may participate in the discussion forum, COMSOL software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team. I would be really happy if you help me, How and where from can i define the following variable for subdomain in comsol3.5a? -- For example, I hope to do write something like "(x,y) in domain1" that will return 1 if the coordinates (x,y) are in the domain and 0 otherwise. For the source term f I use: d (intX,x)-f (x,y). By doing so the problem is converted from an integration to a differentiation and therefore a boundary condition needs to be set. I know I could set up a "General projection" for this but I noticed that this is computationally very expensive. PHYSICS SETTINGS For f(x) from 0 to x, is it int(f(x),0,x)? (COMSOL version: 5.0) A Domain-ODE is needed to solve for variable Np. It is useful where you specify lists of values: In the Times field for the output times from a time-dependent study, for example. By doing so the problem is converted from an integration to a differentiation and therefore a boundary condition needs to be set. Ivar, integrate over the whole domain the function f(x)*(x>x0)*(xx0)*(x. In my model [H+] is calculated in mol/m^3 unit so, I converted the unit M (mol) for calculating pH. Posted Jan 18, 2020, 1:00 a.m. EST In this way COMSOL looks after the continuity on the "interiour boundaries" for you and you have only to deal specifically with the two overlapping points do define some variables to link them together the way you want (or to apply specific Boundary physics on them) I'm not sure what you want to do, but I can see a couple of issues here: It demonstrates how to define global parameters and variables. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version For the record, if anyone else is having trouble with this, the way to do it is as follows: You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Ivar. The heat capacity, C Is there a way to speed it up? Particularly when you need to think meshing, and how to ease the meshing procedure, which is easy or impossible simply by cutting up your geometry in a clever way with a few extra internal boundaries, but that is another story. you define your 4 segments in the geometry, you set the "Geometry FInish" node to "Assembly" then normally when you go to the "material" or the "physics" nodes and look at the "Entity list" page, you will see 4 domains and 8 boundary points wheres at the domain intersections you have 2 overlapping boundaries each time. Then you can multiply your exquation by a boolean (x. Is the nojac()-operator somehow useful? You can define a variable as With more than 30 add-on products to choose from, you can further expand the simulation What you can do is draw 2 lines exactly at the positions you want to carry on the integration. If you want to define pc=2sigma/r you can do it as a local variable of your 2d axisymmetrical geometry (comp1) but not as a global variable. Your internet explorer is in compatibility mode and may not be displaying the website correctly. C is obviously a spatio-temporal variable and at each time step the total value of C across the domain would be C_total. If you want to define *pc=2sigma/r* you can do it as a local variable of your 2d axisymmetrical geometry (comp1) but not as a global variable. Since it is important that all x,y values are considered in f(x+dest(x),y+dest(y)), I chose the second alternative II) above to procede. where r is the position vector from the differential element on the conductor to the point of measurement(x0,y0,z0). If you define it as analytic function, you can call it with "t" for time or any other input argument. Your internet explorer is in compatibility mode and may not be displaying the website correctly. In this way you will also end up with 4 domains, but only 6 boundaris (points) whereas 2 are overlapping at the common intersection of the two previous "objects". Note that while COMSOL employees may participate in the discussion forum, COMSOL software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team. How do I define Pc as something that varies for a range of 'r' values. Hi How to define region heat source with 3D variables using the If else condition? Regards, Hi circular shaped ones). - For a variable defined under Variables, you can define an expression in a flexible way, but it must represent a scalar-valued function (that is, when called with its inputs, it returns a scalar value). But I have another question related to this. COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH), Reverse proxy setup for Model Manager server, Integrals with Moving Limits and Solving Integro-Differential Equations, How to Activate Material in Simulations of Manufacturing Processes. This is how my variable look like: y^ (n-1). Discussion Closed This discussion was created more than 6 months ago and has been closed. The boolean expression did the trick. For example with dest(x)=2*dest(y)=1/4 the above example should give the answer G = 0.6563 (=21/32). To start a new discussion with a link back to this one, click here. Worked perfectly for me. listed if standards is not an option). (root.mod2.at2(x+dest(x),y+dest(y),dom) == 1 To start a new discussion with a link back to this one, click here. With COMSOL Multiphysics, you will be able to account for coupled or multiphysics phenomena. Try a search on the forum, I have discussed this several times here already ;) Note: This discussion is about an older version of the COMSOLMultiphysics software. e.g. I am trying to add this variable as a function of T in COMSOL>Model builder>definitions>parameters. Discussion Closed This discussion was created more than 6 months ago and has been closed. Ivar, Dear Comsol community, PHYSICS SETTINGS Define the following parameters for the materials: The thermal conductivity, k The heat capacity, C The density, rho Young's modulus, E Poisson's ratio, nu The thermal expansion coefficient, alpha and Tempereature Regards, Rashedul -- You can integrate power densities over surfaces to compute powers. I have problems to define a specific function G(x,y) involving an integral of the kind \int \int f(x+dest(x),y+dest(y))*f(x,y) dx dy. I hope this helps. Model Library path: Structural_Mechanics_Module/Thermal-Structure_Interaction/microrobot_3d COMSOL Employee Sweden The problem is the use of a Global Variable in the Analytic function. The homogenous, time harmonic case of the wave equation is simply the Helmholtz equation, which is already built in COMSOL. Note that while COMSOL employees may participate in the discussion forum, COMSOL software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team. One way I like evaluating my ranges is using normalized ranges, for example: Materials, Parameters, Variables, & Functions, COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH), How to Use State Variables in COMSOL Multiphysics, Mode Analysis for Electromagnetic Waveguides in COMSOL. Ali, Hi Excuse me if my explanation is not clear enough Good luck I stumbled upon the same problem. How to define a coordinate system along a customized direction. Hi How to use COMSOL functions (analytic) to define user-defined pressure force. and hare you sure you define these functions and use the variables in the right environment (global definitions or local domain definitions. Ivar Kjelberg "Retired" but still part time CSEM SA (CH) listed if standards is not an option). COMSOL Multiphysics is a general-purpose software platform, based on advanced numerical methods, for modeling and simulating physics-based problems. I am trying to simulate a spontaneous fluid uptake process in a rock where capillary pressure is the driving force. I think I got the essentials from your explanations, such a simple geometry is good for the learning process (easier to go throuh all cases): its the same for "solid.rho" rho is depending on the "dom" of the domains as it might change from one material block to another material block (hence one should talk of "rho_i" for the "i" domains in a complex model. how to define variable. You need global. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version This can be solved very nicely. I don't understand what you want to simulate! When current I flows in the conductor the magnetic flux density produced at point (x0,y0,z0) will be If yo check your geometrical "Object" list you should end up with two Entities. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Defining a function for a material enables the software to approximate. Thank you so much! B=uI/(4pi)*[cos(45)*integrate((y0-a)/r^3,a,0,cos(45))-sin(45)*integrate((x0-a)/r^3,a,0,sin(45))]. Note that while COMSOL employees may participate in the discussion forum, COMSOL software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team. A nice thing about doing a 0 to 1 range is it's easy to modify the progression. How to Use the Find and Auto Completion Tools for Faster Model Setup, How to Use the Parameter Estimation Study Step for Inverse Modeling, Equation-Based Modeling with a Space-Time Discretization, Solving Models with Step Changes to Loads in Time. Using subdomain expression variables makes it easier to enter the subdomain properties of the model. The information provided may be out of date. there are a few concepts and implicit usage of references and variables that are essential to be able to use COMSOL efficiently. But I have another question related to this. I hope this helps. (dom==1)*alpha , the question is how could I know if this condition is evaluated for boundary 1 or domain 1 ? or both? To start a new discussion with a link back to this one, click here. \int \int f(x+dest(x),y+dest(y))*f(x,y) dx dy = \int \int f(x+dest(x),y+dest(y))*(dom==1) dx dy. [QUOTE] The necessity of functions, Gaussian Pulse, Ramp, Rectangle, Step, Triangle, Waveform, RandomGaussian Distribution Function: http://hyperphysics.phy-astr.gsu. I figured out how to do it. Usually the richard's equation (for example) is solved for the capillary pressure pc and the velocities u, v, w are results of d (Pc,x), d (Pc,y) and d (Pc,z). Now, the problem is that I want to vary the absorption coefficient "a" according to the material of the regions I define. 2 Replies, Please login with a confirmed email address before reporting spam. The density, rho Worked perfectly for me. Hi Roger, listed if standards is not an option). Best Then, try to change the pre-defined form to the form of your equation. Discussion Closed This discussion was created more than 6 months ago and has been closed. Because It took me some time to sort this out with COMSOL. Actually I want to define a variable in my variables(local) that will take the range of values but in my variables we can not use the range function so what other function we have in comsol to define a variable that takes a range of values and can be defined in my variables. . How and where from can i define the following variable for subdomain in comsol3.5a? I am trying to add this variable as a. John. do it with integrate(expr,var,lower,upper) operator defining some variable tempInt. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version PHYSICS SETTINGS Define the following parameters for the materials: The thermal conductivity, k The heat capacity, C The density, rho Young's modulus, E Poisson's ratio, nu The thermal expansion coefficient, alpha and Tempereature Regards, Rashedul -- If you master this you get away with many frustrating subjects, and you quickly learn how to design/build very efficient geometries for your models in the COMSOL CAD environment. Thanks! Once you've added this feature, you can define variables on any geometric entity level, including: Domains Boundaries Edges Points Posted May 19, 2015, 3:04 a.m. EDT Np depends on a field variable Vm ( Vm = a * (ec.normE/maximumOf (ec.normE)) where a can be any number b/w 0.5 to 3). Discussion Closed This discussion was created more than 6 months ago and has been closed. Now you apply again "Finish - Assembly mode". To start a new discussion with a link back to this one, click here. How to access a variable value at a particular time in COMSOL during simulation Question 5 answers Asked 27th Apr, 2017 Saad Pasha Hi I need to solve an equation like: a = b (at time=0.2s)*exp. As I inject the current, the magnetic flux density that is produced is to be measured. Best regards I don't understand what you want to simulate! in document, it was written, After reading this thread and the documentation, I used the''dom'' variable conveniently in my 1D simulation in 4.0a. Using global parameters it is very easy to change geometry easily. you select the two -three adjacent domains/lines that have continuity between them and you apply the "Geometry - Compose object" on them to "group" them into one "Geoemtrical Object" with an interiour boundary, if your fan is in the middle you need to do this operation twice for the two objects to the left and the two to the right. 2*pi*r^2 for example at the beginning of the process C_total is let's say 10, which is the same as C values across the domain. 1 Reply, Please login with a confirmed email address before reporting spam. Hi, listed if standards is not an option). You make an "identity pair" for all "pairs" for which you want to apply "continuity" under "Definitions - identity pair", under your "Physics" you add a "Pair - Continuity" and select in the list the identity pair. So you must ALWAYS check that when "dom" appears in a formula field are any entity clearly defined (by a selection such that of the Boundary conditions ) ? The range function returns a list (vector) of values, and it is therefore not applicable in the Variables definitions, so it should not work in any of the cases you describe. For example, if I want to slowly increase the step size I can do: You can define probes, coupling variables, and can execute post-processing integrations as well, among other possibilities. Note: This discussion is about an older version of the COMSOL Multiphysics software. y is my shear rate and can also be written as "spf.sr" and n is a variable I defined already. This is done by adding a "constraint" to the boundary where x=0 with reaction term R=-intX. Thanks, Hi, Hi If you want to define pc=2sigma/r you can do it as a local variable of your 2d axisymmetrical geometry (comp1) but not as a global variable. This is done by adding a "constraint" to the boundary where x=0 with reaction term R=-intX. Use the Variables node to define expressions as user-defined variables. Define the following parameters for the materials: Do you know if it is possible to write such an expression for existing boundaries? Simulating the Tunneling Current Across a Graded Heterojunction. COMSOL is different from many other FEM tools, these physical parameters are defined on the geometric "elements" and not into the mesh, the mesh elments are mapped on the domains and boundary , and the mesh heritate the physical properties from the domains respective boundaries. I am specifically looking for summation as in Fourier and Taylor series. Thanks Dr. Ivar for your interesting reply that sheds light on a matter that we can't find by reading the docs, but only through experience. Discussion Closed This discussion was created more than 6 months ago and has been closed. I believe it is rather important to catch the concept of "Geometrical Objects" and "FEM Entities" in COMSOL. Regards Check out Chapter 5 of the COMSOL Multiphysics Reference Manual, version 5.2a. Jeff. you can get material data by pointing directly to them with a mat1.rho or somethin like that, the difficulty is to identify the 1,2,3 and which material it is (check the tag number). I think this is due to the fact that this operator is supposed to be used for postprocessing only but not for solving. Discussion Closed This discussion was created more than 6 months ago and has been closed. 4 Replies Last Post 4 mai 2013, 13:13 UTC+2. 6 Replies, Please login with a confirmed email address before reporting spam. Under Global Definitions>Parameters, define variable "freq" and assign the same numerical value of the frequency you are using in the Study Step. Aref Shaikh. How to find the in built functions such as integrate. The information provided may be out of date. Here the excerpt from Comsol documentation : This is a tutorial for COMSOL 4.2. Once you've added this feature, you can define variables on any geometric entity level, including: Domains Boundaries Edges Points Youngs modulus, E Your internet explorer is in compatibility mode and may not be displaying the website correctly. Cheers, Hans. A continuous range of values takes infinitely long to evaluate. Thanks Dr. Ivar for your interesting reply that sheds light on a matter that we can't find by reading the docs, but only through experience. Data format of CSV file is as: nx3-matrix with first column as data values, and 2nd and 3rd as x and y-coordinates. Posted Jan 5, 2010, 7:56 a.m. EST Usually the richard's equation (for example) is solved for the capillary pressure pc and the velocities u, v, w are results of d(Pc,x), d(Pc,y) and d(Pc,z). To start a new discussion with a link back to this one, click here. I strongly suspect that the RF module can do this, but my license does not include it and I don't intend to waste any more of my advisor's funds. You can define a variable as 2*pi*r^2 in an axisymmetric model where r is a spatial coordinate, for example. Now I want to put the formula for magnetic flux density B that is through Biot Savat law. Note that while COMSOL employees may participate in the discussion forum, COMSOL software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team. I find that these could be better explained, as it took me very long before I started to feel confortable, so I do understand your issue there :) COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH), How to Use State Variables in COMSOL Multiphysics. Best regards Michael Rembe ------------------- Analytic functions take one or more argument that you define directly in the Settings window for the Analytic function. In my understanding: 1) under "Global - Definition - Variables" you define variables that are INDEPENDENT of the spatial dimension (x,y,z) but these variables might be dependent on time or any other (sweeping) parameter "t, Param, freq . For integration of f(x,y) from 0 to x I use a separate "General form PDE" with a dependent variable intX on the domain of the function. I want to use these values as initial values of a variable in comsol. The case I am working on is a conductor of length 1m lying at 45 degrees with the x-axis. Once the option is enabled, you'll see a Variable Utilities button within the Definitions ribbon, and a Variable Utilities submenu when you right-click the Component > Definitions branch within the model tree. Peter. As a simple 2D example, assume I have a square domain [0,1]*[0,1] (here called dom 1). ), or other global variables. I'm trying to define a new variable in two different materials (water S=1 and glass S=1.8), and to put it in an equation as, ht.S, so I expect Comsol to pick the data while calculating in glass or water, however it's not reading the new defined variable, it keeps giving error, but when I put the properties of material which was defined automatically, it doesn't have the same problem. Update: never mind, I figured out how to do it in COMSOL 5.2. Also define a new variable, Temperature, to visualize the temperature in all domains in the postprocessing analysis. Good luck The expressions for lower and upper limits do not have to be constants but are required to evaluate to real values. Posted Dec 8, 2010, 7:32 p.m. EST Hello Dr Ivan, Check out Chapter 5 of the COMSOL Multiphysics Reference Manual, version 5.2a. Now I want to define this 'a' in my variables(local) because it takes range of values. In comsol 3.5a, i couldn't find any place in option or Physics tool to define these parameters. integrate(expr,var,lower,upper) computes the integral of expr for the integration variable var over an interval specified by expressions lower for the lower limit and upper for the upper limit. variant b) the more rigurous: In this way COMSOL looks after the continuity on the "interiour boundaries" for you and you have only to deal specifically with the two overlapping points do define some variables to link them together the way you want (or to apply specific Boundary physics on them) The thermal conductivity, k variant a) the lazy long path (? Thank you so much! The thermal expansion coefficient, alpha Subdomain Expressions : Thanks for your reply. Fluid & Heat, Computational Fluid Dynamics (CFD), Porous Media Flow, Sampling Random Numbers from Probability Distribution Functions, Time-dependent results are different with different time-range, Getting the Stats: Computing Standard Deviations and Other Statistical Quantities, Range of temperature and pressure for initial condition. 5 + 7 * range(0, 0.01, 1) Hello Magnus, thanks for the reply. You can integrate the normal-to-the-surface component of a power density vector over a surface, to compute the power flow through it. I am trying to solve the inhomogeneous wave equation on COMSOL. Share Improve this answer Follow answered Jan 7, 2021 at 1:01 Sameep Shah 11 1 Add a comment Your Answer If I use the built-in integrate()-operator for this, I get an error-message. Then I get small steps at the beginning but larger steps at the end but I don't need to do any math to figure out how to adjust the function. In matlab, we can use int(f(x),x0,x1) which represents the integration of f(x) from x0 to x1? Actually I want to define a variable in my variables(local) that will take the range of values but in my variables we can not use the range function so what other function we have in comsol to define a variable that takes a range of values and can be defined in my variables. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version This tool enables you to document all the details of your entire model. Ivar. Magnus Ringh, COMSOL. However, the expression is marked red which means that there is an error, which I could not. Best regards Michael Rembe ------------------- Note: This discussion is about an older version of the COMSOLMultiphysics software. So i don't know if a ''domain point probe'' would the trick r=sqrt((xo-a)^2+(y0-a)^2+(z0-0)^). The information provided may be out of date. Thanks for the reply Daniel. Usually the richard's equation (for example) is solved for the capillary pressure pc and the velocities u, v, w are results of d(Pc,x), d(Pc,y) and d(Pc,z). Good luck Your internet explorer is in compatibility mode and may not be displaying the website correctly. where a ranges from 0 to 0.707. i was looking and learning some Model in Comsol library and it was basically most variable depend on their context, such as spatial dimensions x,y,z or r,phi and the Entities (Domains, Boundaries, Edges or Points).

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how to define variables in comsol

how to define variables in comsol