You should use a nonzero step size for the range function. 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 listed if standards is not an option). 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. [QUOTE] For example with dest(x)=2*dest(y)=1/4 the above example should give the answer G = 0.6563 (=21/32). This tool enables you to document all the details of your entire model. You can define a variable as 2*pi*r^2 in an axisymmetric model where r is a spatial coordinate, for example. 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 fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Defining a function for a material enables the software to approximate. where we use a nested if statement to assign domain 1 the relative permitivity of espislonr_air, domain 2 epsilonr_container, and the remaining domain epsilonr_ball. This is done by adding a "constraint" to the boundary where x=0 with reaction term R=-intX. If the definition of myVar*t means "a constant times the time t" you can define it directly as Global Variable, where "t" is a predefined variable for time. Thanks for your reply. 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. 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". I wonder How can I define a variable or parameter which can access the voltage of these two coordinate in each step and change the conductivity of material for next other step? pH = -log ( [H+] [M]). listed if standards is not an option). Subdomain Expressions : Update: never mind, I figured out how to do it in COMSOL 5.2. 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. How to define region heat source with 3D variables using the If else condition? The case I am working on is a conductor of length 1m lying at 45 degrees with the x-axis. Ivar Kjelberg "Retired" but still part time CSEM SA (CH) 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. Best regards Michael Rembe ------------------- I am trying to add this variable as a. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version I hope this helps. Worked perfectly for me. Is the nojac()-operator somehow useful? This is done by adding a "constraint" to the boundary where x=0 with reaction term R=-intX. in an axisymmetric model where r is a spatial coordinate, for example. That is, you can define it without specifying the actual names of the arguments that you will use when calling it. To start a new discussion with a link back to this one, click here. Posted May 19, 2015, 3:04 a.m. EDT Best regards, I don't understand what you want to simulate! I want to integrate a function f(x,y) from y=0 to y=1. If I use the built-in integrate()-operator for this, I get an error-message. But I have another question related to this. 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". - Using a step size of 0 is not allowed. 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. 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 Good luck Also define a new variable, Temperature, to visualize the temperature in all domains in the postprocessing analysis. I'm not sure what you want to do, but I can see a couple of issues here: Do you know if it is possible to write such an expression for existing boundaries? How to find the in built functions such as integrate. where (a,a,0) is the position of differential elements. 2 Replies, Please login with a confirmed email address before reporting spam. If you define it as analytic function, you can call it with "t" for time or any other input argument. 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. 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 ) ? 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. 1 Reply, Please login with a confirmed email address before reporting spam. The source term (f) is -d(d(Pc,x),x). Posted Feb 10, 2011, 11:48 a.m. EST Hello Magnus, thanks for the reply. Good luck Note: This discussion is about an older version of the COMSOLMultiphysics software. First, for a 2-D problem, how can I use the x value and y value of a point evaluated? I know I could set up a "General projection" for this but I noticed that this is computationally very expensive. I hope this helps. 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. 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. This is done by adding a "constraint" to the boundary where x=0 with reaction term R=-intX. Thanks! How do I define Pc as something that varies for a range of 'r' values. The homogenous, time harmonic case of the wave equation is simply the Helmholtz equation, which is already built in COMSOL. Best regards Thank you so much! \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. Best regards Michael Rembe ------------------- In my model [H+] is calculated in mol/m^3 unit so, I converted the unit M (mol) for calculating pH. Using global parameters it is very easy to change geometry easily. 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. -- 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). 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. In the settings I set all coefficients of the PDE to zero exept for the source term f. For the source term f I use: d(intX,x)-f(x,y). This can be solved very nicely. 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 :) I would be really happy if you help me, 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). . -- You can integrate the normal-to-the-surface component of a power density vector over a surface, to compute the power flow through it. Discussion Closed This discussion was created more than 6 months ago and has been closed. 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. 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. 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))]. For the source term f I use: d (intX,x)-f (x,y). A continuous range of values takes infinitely long to evaluate. Trivially we also have for dest(x)=dest(y)=0, that G = intop((dom==1)*1)=1. I am working on the fault diagnosis of the grounding grid. While I am defining the variable as pH = -log ( [H+] [M]), it is showing. ), or other global variables. The information provided may be out of date. Hi The density, rho As a simple 2D example, assume I have a square domain [0,1]*[0,1] (here called dom 1). Your internet explorer is in compatibility mode and may not be displaying the website correctly. 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. 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. Discussion Closed This discussion was created more than 6 months ago and has been closed. With COMSOL Multiphysics, you will be able to account for coupled or multiphysics phenomena. 5 + 7 * range(0, 0.01, 1)^2 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. But rho might also change with position within a given material block (i.e.due to extreme pressures), or it changes with temperature hence in all generality one should write "solid.rho_i(x,y,z,T,)". Hi, How and where from can i define the following variable for subdomain in comsol3.5a? So you probably don't want that. This would allow me to used more complicated boundaries (e.g. So i don't know if a ''domain point probe'' would the trick If you go to the topmost list (i.e Electromagnetic waves (emw) ), then go to the equation tab, there are now options to choose . The necessity of functions, Gaussian Pulse, Ramp, Rectangle, Step, Triangle, Waveform, RandomGaussian Distribution Function: http://hyperphysics.phy-astr.gsu. It is useful where you specify lists of values: In the Times field for the output times from a time-dependent study, for example. Model Library path: Structural_Mechanics_Module/Thermal-Structure_Interaction/microrobot_3d How to find the in built functions such as integrate. (dom==1)*alpha , the question is how could I know if this condition is evaluated for boundary 1 or domain 1 ? To start a new discussion with a link back to this one, click here. Thanks for the reply Daniel. The key is the "dom" variable, which is used for inserting probes as well. if(dom==1,epsilonr_air,if(dom==2,epsilonr_container,epsilonr_ball) ) listed if standards is not an option). How to define a coordinate system along a customized direction. At different Pc values, subsequent variables are also calculated such as Se, krw, etc. Here f is 1 inside a domain and 0 else. I don't understand what you want to simulate! You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version 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. 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 was looking and learning some Model in Comsol library and it was Cheers, Hans. The expressions for lower and upper limits do not have to be constants but are required to evaluate to real values. or both? Thanks. there are a few concepts and implicit usage of references and variables that are essential to be able to use COMSOL efficiently. 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. Hi Mohammed, 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. Ivar, Dear Comsol community, Posted 9 apr 2018, 16:56 GMT-4 Fluid & Heat, Computational Fluid Dynamics (CFD), Parameters, Variables, & Functions 0 Replies. Now I want to put the formula for magnetic flux density B that is through Biot Savat law. Hence since f is 1 on dom 1 we have John. Discussion Closed This discussion was created more than 6 months ago and has been closed. You can define probes, coupling variables, and can execute post-processing integrations as well, among other possibilities. 4 Replies Last Post 4 mai 2013, 13:13 UTC+2. The information provided may be out of date. variant a) the lazy long path (? Because It took me some time to sort this out with COMSOL. Analytic functions take one or more argument that you define directly in the Settings window for the Analytic function. Poissons ratio, nu Under Component right-click Definitions and choose Variables, or click Local Variables in the Definitions toolbar (Windows users). [/QUOTE] Worked perfectly for me. How to make a variable of 3rd order derivatives? 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. I am specifically looking for summation as in Fourier and Taylor series. This way if the value of your variable goes above the limit, comsol will just use the value of the limit. Now I want to define this 'a' in my variables(local) because it takes range of values. -- I am trying to add this variable as a function of T in COMSOL>Model builder>definitions>parameters. 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. C is obviously a spatio-temporal variable and at each time step the total value of C across the domain would be C_total. "dom" is one of these variables, even an internal variable that takes the entity "ID" be it Domains, Boundaries Edges or Points. A nice thing about doing a 0 to 1 range is it's easy to modify the progression. I figured out how to do it. Data format of CSV file is as: nx3-matrix with first column as data values, and 2nd and 3rd as x and y-coordinates. It demonstrates how to define global parameters and variables. COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH), How to Use State Variables in COMSOL Multiphysics. Define the following parameters for the materials: For the diagnosis I am using electromagnetic Induction Method. Version 4.4 is a range from 5 to 12 with 101 points. I hope this helps. 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. in document, it was written, I have a problem to define a variable. Thanks for the reply Daniel. For the source term f I use: d (intX,x)-f (x,y). You should then remain with two boundaries, overlapping) where you apply your "fan effect" or equations to link velocity or whatever variable discontinuity you need. Good luck PHYSICS SETTINGS Is there a better way to integrate over fixed boundaries? Simulating the Tunneling Current Across a Graded Heterojunction. 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): : 9 Replies, Please login with a confirmed email address before reporting spam. For example, if I want to slowly increase the step size I can do: Am I right on this one? You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version In the manual, but what is the scope etc here? 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 how my variable look like: y^ (n-1). Ivar, integrate over the whole domain the function f(x)*(x>x0)*(xx0)*(x.

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