how to define variables in comsol
After reading this thread and the documentation, I used the''dom'' variable conveniently in my 1D simulation in 4.0a. Youngs modulus, E
Is there a way to speed it up?
How to define a coordinate system along a customized direction. Is there a better way to integrate over fixed boundaries? The necessity of functions, Gaussian Pulse, Ramp, Rectangle, Step, Triangle, Waveform, RandomGaussian Distribution Function: http://hyperphysics.phy-astr.gsu. 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".
This would allow me to used more complicated boundaries (e.g. This is how my variable look like: y^ (n-1). 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. 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". Trivially we also have for dest(x)=dest(y)=0, that G = intop((dom==1)*1)=1. 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. I suppose you can define a new PDE module. but then afterwards C at each position is different than C_total. Once you've added this feature, you can define variables on any geometric entity level, including: Domains Boundaries Edges Points Ivar. 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. 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. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Data format of CSV file is as: nx3-matrix with first column as data values, and 2nd and 3rd as x and y-coordinates. 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. Best regards Michael Rembe ------------------- How to define region heat source with 3D variables using the If else condition? Hence since f is 1 on dom 1 we have
9 Replies, Please login with a confirmed email address before reporting spam. Hi Mohammed, Posted Jan 5, 2010, 7:56 a.m. EST Check out Chapter 5 of the COMSOL Multiphysics Reference Manual, version 5.2a. 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. Thanks for your reply. ):
The heat capacity, C
pH = -log ( [H+] [M]). listed if standards is not an option). However, the expression is marked red which means that there is an error, which I could not. Materials, Parameters, Variables, & Functions By doing so the problem is converted from an integration to a differentiation and therefore a boundary condition needs to be set. Defining a function for a material enables the software to approximate. Discussion Closed This discussion was created more than 6 months ago and has been closed. Here, I would like to define Pc as a variable under Global Definitions wherein for its expression I want to write 2*sigma/r. Include function as a variable. Thank you so much! how to define variable. Fluid & Heat, Computational Fluid Dynamics (CFD), Porous Media Flow Thanks for the reply Daniel. 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. 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) In comsol, how can we get this kind of integration? I don't understand what you want to simulate! Your internet explorer is in compatibility mode and may not be displaying the website correctly. 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. 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. Under Global Definitions>Parameters, define variable "freq" and assign the same numerical value of the frequency you are using in the Study Step. Posted May 19, 2015, 3:04 a.m. EDT I am working on the fault diagnosis of the grounding grid. In comsol 3.5a, i couldn't find any place in option or Physics tool to define these parameters. Regards
So physical parameters are entered on the domains principally. Discussion Closed This discussion was created more than 6 months ago and has been closed. How and where from can i define the following variable for subdomain in comsol3.5a? The thermal conductivity, k
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. Then, try to change the pre-defined form to the form of your equation. 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. But I have another question related to this.
This is done by adding a "constraint" to the boundary where x=0 with reaction term R=-intX. 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 do I define Pc as something that varies for a range of 'r' values. if(dom==1,epsilonr_air,if(dom==2,epsilonr_container,epsilonr_ball) )
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. 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.
How to find the in built functions such as integrate. 4 Replies Last Post 4 mai 2013, 13:13 UTC+2. You need global. 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). - 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). do it with integrate(expr,var,lower,upper) operator defining some variable tempInt. 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. variant b) the more rigurous:
listed if standards is not an option). Check out Chapter 5 of the COMSOL Multiphysics Reference Manual, version 5.2a. I'm not sure what you want to do, but I can see a couple of issues 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. 6 Replies, Please login with a confirmed email address before reporting spam. Now I want to put the formula for magnetic flux density B that is through Biot Savat law. How to use COMSOL functions (analytic) to define user-defined pressure force. By doing so the problem is converted from an integration to a differentiation and therefore a boundary condition needs to be set. listed if standards is not an option). This can be solved very nicely. Thanks, Hi,
John. where r is the position vector from the differential element on the conductor to the point of measurement(x0,y0,z0). I don't understand what you want to simulate! Model Library path: Structural_Mechanics_Module/Thermal-Structure_Interaction/microrobot_3d
Michael Rembe. Check the doc and test out the numerous examples, you will quickly learn. 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,)". . listed if standards is not an option). listed if standards is not an option). Cheers, Hans. 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. 5 + 7 * range(0, 0.01, 1)^2
So you probably don't want that.
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)
Ivar, Dear Comsol community,
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. Right-click Global Definitions and choose Variables. In such a case, only damping coefficient and source term are non-zero. thanks in advance. Thanks in advance ! This tool enables you to document all the details of your entire model.
For the source term f I use: d (intX,x)-f (x,y). 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. Note: This discussion is about an older version of the COMSOL Multiphysics software.
What you can do is draw 2 lines exactly at the positions you want to carry on the integration. r=sqrt((xo-a)^2+(y0-a)^2+(z0-0)^). Hello everyone, I would like to define a variable suppose 'a' that starts from 0 to 1 with stepsize=0. As a simple 2D example, assume I have a square domain [0,1]*[0,1] (here called dom 1). in an axisymmetric model where r is a spatial coordinate, for example. Good luck
(dom==1)*alpha , the question is how could I know if this condition is evaluated for boundary 1 or domain 1 ? I am trying to add this variable as a function of T in COMSOL>Model builder>definitions>parameters.
If yo check your geometrical "Object" list you should end up with two Entities. Update: never mind, I figured out how to do it in COMSOL 5.2. is a range from 5 to 12 with 101 points. - Using a step size of 0 is not allowed. Now, the problem is that I want to vary the absorption coefficient "a" according to the material of the regions I define. Excuse me if my explanation is not clear enough
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. Note: This discussion is about an older version of the COMSOLMultiphysics software. I would appreciate your help in setting up this problem in COMSOL. Posted 9 apr 2018, 16:56 GMT-4 Fluid & Heat, Computational Fluid Dynamics (CFD), Parameters, Variables, & Functions 0 Replies. 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. For example, if I want to slowly increase the step size I can do:
To start a new discussion with a link back to this one, click here. 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). 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. 7 Replies, Please login with a confirmed email address before reporting spam. Here the excerpt from Comsol documentation :
However, Pc is different for different values of r. My question is how can I incorporate this in COMSOL?
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 With more than 30 add-on products to choose from, you can further expand the simulation The information provided may be out of date. Aref Shaikh. --
2*pi*r^2
I want to use these values as initial values of a variable in comsol. 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'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. Because the microrobot legs consists of several materials with different material properties, you have to define subdomain settings for each materials. I believe it is rather important to catch the concept of "Geometrical Objects" and "FEM Entities" in COMSOL. Best regards Michael Rembe ------------------- --
You can define probes, coupling variables, and can execute post-processing integrations as well, among other possibilities. You can define an Analytic, Interpolation, or Piecewise Function to describe any material property in COMSOL Multiphysics. You can define a variable as
For f(x) from 0 to x, is it int(f(x),0,x)?
For the source term f I use: d (intX,x)-f (x,y). 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. Try a search on the forum, I have discussed this several times here already ;)
This is a tutorial for COMSOL 4.2. Also define a new variable, Temperature, to visualize the temperature in all domains in the postprocessing analysis. If you define it as analytic function, you can call it with "t" for time or any other input argument. 1 This is probably too late but you could try using min (limit,function or variable). I think this is due to the fact that this operator is supposed to be used for postprocessing only but not for solving. You can integrate power densities over surfaces to compute powers. How to make a variable of 3rd order derivatives?
Using global parameters it is very easy to change geometry easily. So i don't know if a ''domain point probe'' would the trick
), or other global variables. 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)? You can define a variable as 2*pi*r^2 in an axisymmetric model where r is a spatial coordinate, for example. 5 + 7 * range(0, 0.01, 1)
The expressions for lower and upper limits do not have to be constants but are required to evaluate to real values. I am trying to add this variable as a. Best regards,
How can I see the equations COMSOL is defining? As I inject the current, the magnetic flux density that is produced is to be measured. 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. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Using subdomain expression variables makes it easier to enter the subdomain properties of the model. 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). 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 have to study the chapter of "Integration Coupling Variables" in the doc, there are different types, not only on a border or a subdomain (projection or extrusion items), in the worst case you add a few specific interiour subdomains, sometimes this is simpler. there are a few concepts and implicit usage of references and variables that are essential to be able to use COMSOL efficiently. Best,
Thanks! Ali, Hi
Subdomain Expressions :
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.
You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version
I have a problem to define a variable. 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. 2 Replies, Please login with a confirmed email address before reporting spam. If I use the built-in integrate()-operator for this, I get an error-message. Version 4.1 You should use a nonzero step size for the range 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 . where (a,a,0) is the position of differential elements. and hare you sure you define these functions and use the variables in the right environment (global definitions or local domain definitions. Worked perfectly for me. COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH), How to Use State Variables in COMSOL Multiphysics. I want to integrate a function f(x,y) from y=0 to y=1. COMSOL Multiphysics is a general-purpose software platform, based on advanced numerical methods, for modeling and simulating physics-based problems. Thanks for the reply Daniel. 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))]. Is the nojac()-operator somehow useful?
You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version I am specifically looking for summation as in Fourier and Taylor series. The case I am working on is a conductor of length 1m lying at 45 degrees with the x-axis. Thank you so much! How to find the in built functions such as integrate. To start a new discussion with a link back to this one, click here. Discussion Closed This discussion was created more than 6 months ago and has been closed.
In the manual, but what is the scope etc here? 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). Under Component right-click Definitions and choose Variables, or click Local Variables in the Definitions toolbar (Windows users). The information provided may be out of date. 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. PHYSICS SETTINGS
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) I am trying to simulate a spontaneous fluid uptake process in a rock where capillary pressure is the driving force. By doing so the problem is converted from an integration to a differentiation and therefore a boundary condition needs to be set. 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? Worked perfectly for me.
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 :)
Hi Ivar ,
To start a new discussion with a link back to this one, click here. I hope this helps. - 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). To start a new discussion with a link back to this one, click here. y is my shear rate and can also be written as "spf.sr" and n is a variable I defined already. Hi Mohammed,
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. Good luck
variant a) the lazy long path (? Then you can multiply your exquation by a boolean (x. :
So, you can use the calculated outcome as a variable in your boundary. How can we define? This way if the value of your variable goes above the limit, comsol will just use the value of the limit. How and where from can i define the following variable for subdomain in comsol3.5a? Simulating the Tunneling Current Across a Graded Heterojunction. The homogenous, time harmonic case of the wave equation is simply the Helmholtz equation, which is already built in COMSOL. 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. I figured out how to do it. I can calculate the area of dom 1 either as I) intop(1)=1 on dom 1, or as II) intop( (dom==1)*1)=1 on all domains. [QUOTE]
Hope this helps on the way
Hi Roger,
Posted Dec 8, 2010, 7:32 p.m. EST A nice thing about doing a 0 to 1 range is it's easy to modify the progression. One way I like evaluating my ranges is using normalized ranges, for example:
Note: This discussion is about an older version of the COMSOLMultiphysics software. where a ranges from 0 to 0.707. The information provided may be out of date.
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 hope this helps. But this variable could be either for a domain or for a boundary, as mentioned in the doc. Analytic functions take one or more argument that you define directly in the Settings window for the Analytic function. I am using Coefficient Form PDE physics. 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. 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 First, for a 2-D problem, how can I use the x value and y value of a point evaluated? Then again T might well be T(x,y,z,) and so on
That is, you can define it without specifying the actual names of the arguments that you will use when calling it. I am trying to solve the inhomogeneous wave equation on COMSOL. This is done by adding a "constraint" to the boundary where x=0 with reaction term R=-intX. 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 It demonstrates how to define global parameters and variables.
e.g. So you probably don't want that. A continuous range of values takes infinitely long to evaluate. It is useful where you specify lists of values: In the Times field for the output times from a time-dependent study, for example. 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). Am I right on this one? This is done by adding a "constraint" to the boundary where x=0 with reaction term R=-intX. Peter. Your internet explorer is in compatibility mode and may not be displaying the website correctly. In matlab, we can use int(f(x),x0,x1) which represents the integration of f(x) from x0 to x1? A continuous range of values takes infinitely long to evaluate. Regards, Hi
circular shaped ones). 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. or both? "dom" is one of these variables, even an internal variable that takes the entity "ID" be it Domains, Boundaries Edges or Points. Good luck
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 would be really happy if you help me,
At different Pc values, subsequent variables are also calculated such as Se, krw, etc. Best
While I am defining the variable as pH = -log ( [H+] [M]), it is showing. Use the Variables node to define expressions as user-defined variables. Share Improve this answer Follow answered Jan 7, 2021 at 1:01 Sameep Shah 11 1 Add a comment Your Answer Hi,
(root.mod2.at2(x+dest(x),y+dest(y),dom) == 1
Best regards
COMSOL Employee Sweden The problem is the use of a Global Variable in the Analytic function. Hi
Discussion Closed This discussion was created more than 6 months ago and has been closed. But I have another question related to this. Best regards, Magnus Ringh, COMSOL 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 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). Ivar, integrate over the whole domain the function f(x)*(x>x0)*(x
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