Your internet explorer is in compatibility mode and may not be displaying the website correctly. Best regards
Posted Jan 5, 2010, 7:56 a.m. EST Hello everyone, I would like to define a variable suppose 'a' that starts from 0 to 1 with stepsize=0. Michael Rembe. --
At different Pc values, subsequent variables are also calculated such as Se, krw, etc. For the record, if anyone else is having trouble with this, the way to do it is as follows:
Hi
With more than 30 add-on products to choose from, you can further expand the simulation 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 --
PHYSICS SETTINGS
Good luck
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Then you can multiply your exquation by a boolean (x.
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. 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. Hope this helps on the way
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. In comsol 3.5a, i couldn't find any place in option or Physics tool to define these parameters. 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). Version 4.1 This tool enables you to document all the details of your entire model. Hi
After reading this thread and the documentation, I used the''dom'' variable conveniently in my 1D simulation in 4.0a.
Thanks, Hi,
if(dom==1,epsilonr_air,if(dom==2,epsilonr_container,epsilonr_ball) )
Here the excerpt from Comsol documentation :
The source term (f) is -d(d(Pc,x),x). 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. Ivar. The information provided may be out of date. variant a) the lazy long path (? (COMSOL version: 5.0) A Domain-ODE is needed to solve for variable Np. Good luck
I think this is due to the fact that this operator is supposed to be used for postprocessing only but not for solving.
Using global parameters it is very easy to change geometry easily. listed if standards is not an option). 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 ) ? I don't understand what you want to simulate! The homogenous, time harmonic case of the wave equation is simply the Helmholtz equation, which is already built in COMSOL. 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):
The information provided may be out of date. In the manual, but what is the scope etc here? Thanks for the reply Daniel. I'm not sure what you want to do, but I can see a couple of issues here:
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. Aref Shaikh. and hare you sure you define these functions and use the variables in the right environment (global definitions or local domain definitions.
Poissons ratio, nu
Regards, Hi
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.
You can define an Analytic, Interpolation, or Piecewise Function to describe any material property in COMSOL Multiphysics. Update: never mind, I figured out how to do it in COMSOL 5.2. Best regards, Magnus Ringh, COMSOL 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. 2*pi*r^2
For f(x) from 0 to x, is it int(f(x),0,x)? But I have another question related to this. Ivar, Dear Comsol community,
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? If you go to the topmost list (i.e Electromagnetic waves (emw) ), then go to the equation tab, there are now options to choose . 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. Materials, Parameters, Variables, & Functions When current I flows in the conductor the magnetic flux density produced at point (x0,y0,z0) will be
2 Replies, Please login with a confirmed email address before reporting spam. That is, you can define it without specifying the actual names of the arguments that you will use when calling it. Excuse me if my explanation is not clear enough
By doing so the problem is converted from an integration to a differentiation and therefore a boundary condition needs to be set.
The boolean expression did the trick. 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). Under Global Definitions>Parameters, define variable "freq" and assign the same numerical value of the frequency you are using in the Study Step. \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. Ivar, integrate over the whole domain the function f(x)*(x>x0)*(xx0)*(x. I know I could set up a "General projection" for this but I noticed that this is computationally very expensive. Check out Chapter 5 of the COMSOL Multiphysics Reference Manual, version 5.2a. 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)
Peter. I hope this helps. For example, if I want to slowly increase the step size I can do:
Hi Mohammed,
Thanks! Version 5.4 One way I like evaluating my ranges is using normalized ranges, for example:
), or other global variables. 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. I suppose you can define a new PDE module. I am specifically looking for summation as in Fourier and Taylor series. Discussion Closed This discussion was created more than 6 months ago and has been closed.
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. Here f is 1 inside a domain and 0 else. By the way in V4 the GUI are rather different, you should consider if its worth to spend too much time on the older 3.5, rather from jumping straight into 4.1 or newer
Fluid & Heat, Computational Fluid Dynamics (CFD), Porous Media Flow variant b) the more rigurous:
The density, rho
COMSOL Multiphysics is a general-purpose software platform, based on advanced numerical methods, for modeling and simulating physics-based problems. 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. Use the Variables node to define expressions as user-defined variables. Best regards Michael Rembe ------------------- where (a,a,0) is the position of differential elements. Posted 9 apr 2018, 16:56 GMT-4 Fluid & Heat, Computational Fluid Dynamics (CFD), Parameters, Variables, & Functions 0 Replies.
Best regards,
Because the microrobot legs consists of several materials with different material properties, you have to define subdomain settings for each materials. Good luck
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 . You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version So you probably don't want that.
The thermal expansion coefficient, alpha
As a simple 2D example, assume I have a square domain [0,1]*[0,1] (here called dom 1).
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. As I inject the current, the magnetic flux density that is produced is to be measured. Analytic functions take one or more argument that you define directly in the Settings window for the Analytic function. However, the expression is marked red which means that there is an error, which I could not. Discussion Closed This discussion was created more than 6 months ago and has been closed. By doing so the problem is converted from an integration to a differentiation and therefore a boundary condition needs to be set. Thanks . Check out Chapter 5 of the COMSOL Multiphysics Reference Manual, version 5.2a. 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.
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) For the diagnosis I am using electromagnetic Induction Method. ):
1 This is probably too late but you could try using min (limit,function or variable). How to define a coordinate system along a customized direction. y is my shear rate and can also be written as "spf.sr" and n is a variable I defined already. You can integrate power densities over surfaces to compute powers. in an axisymmetric model where r is a spatial coordinate, for example. Best,
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 this variable could be either for a domain or for a boundary, as mentioned in the doc. John. Define the following parameters for the materials:
listed if standards is not an option). 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. 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. Note: This discussion is about an older version of the COMSOLMultiphysics software. How and where from can i define the following variable for subdomain in comsol3.5a? Here, I would like to define Pc as a variable under Global Definitions wherein for its expression I want to write 2*sigma/r. 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). Is there a better way to integrate over fixed boundaries? Hence since f is 1 on dom 1 we have
Trivially we also have for dest(x)=dest(y)=0, that G = intop((dom==1)*1)=1. Discussion Closed This discussion was created more than 6 months ago and has been closed. First, for a 2-D problem, how can I use the x value and y value of a point evaluated? Your internet explorer is in compatibility mode and may not be displaying the website correctly. The expressions for lower and upper limits do not have to be constants but are required to evaluate to real values. Model Library path: Structural_Mechanics_Module/Thermal-Structure_Interaction/microrobot_3d
Once you've added this feature, you can define variables on any geometric entity level, including: Domains Boundaries Edges Points Youngs modulus, E
As a few of hem are "fields" (dependent on x,y,z,t) and need to be defined accordingly w.r.t the appropriate domains (or integrated over domains to give . 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,)". You should use a nonzero step size for the range function. e.g. Thanks. I defined the 'B' in my variables as well.
While I am defining the variable as pH = -log ( [H+] [M]), it is showing. . 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). Your internet explorer is in compatibility mode and may not be displaying the website correctly. 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. 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. Hi Ivar ,
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. where a ranges from 0 to 0.707. I would appreciate your help in setting up this problem in COMSOL. 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. I found something like:
In such a case, only damping coefficient and source term are non-zero. I am using Coefficient Form PDE physics. Then again T might well be T(x,y,z,) and so on
To start a new discussion with a link back to this one, click here. 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 I am trying to simulate a spontaneous fluid uptake process in a rock where capillary pressure is the driving force. How to make a variable of 3rd order derivatives? listed if standards is not an option). You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Ivar. How do I define Pc as something that varies for a range of 'r' values. The boolean expression did the trick. For the source term f I use: d (intX,x)-f (x,y). I hope this helps. but then afterwards C at each position is different than C_total. But I have another question related to this. Thanks. What you can do is draw 2 lines exactly at the positions you want to carry on the integration. Hi Mohammed, Best
How to define region heat source with 3D variables using the If else condition? Worked perfectly for me. How to use COMSOL functions (analytic) to define user-defined pressure force. Do you know if it is possible to write such an expression for existing boundaries? (root.mod2.at2(x+dest(x),y+dest(y),dom) == 1
is a range from 5 to 12 with 101 points. I believe it is rather important to catch the concept of "Geometrical Objects" and "FEM Entities" in COMSOL. 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).
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. Magnus Ringh, COMSOL. - 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 was looking and learning some Model in Comsol library and it was
I have a problem to define a variable. Hi Roger,
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). 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. 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. For example with dest(x)=2*dest(y)=1/4 the above example should give the answer G = 0.6563 (=21/32). 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. Is the nojac()-operator somehow useful? 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. Using subdomain expression variables makes it easier to enter the subdomain properties of the model. How can I see the equations COMSOL is defining? Thanks in advance ! Share Improve this answer Follow answered Jan 7, 2021 at 1:01 Sameep Shah 11 1 Add a comment Your Answer How can we define? The thermal conductivity, k
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. The heat capacity, C
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". For the source term f I use: d (intX,x)-f (x,y). I would be really happy if you help me,
Am I right on this one? 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. 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. If I use the built-in integrate()-operator for this, I get an error-message. Discussion Closed This discussion was created more than 6 months ago and has been closed. listed if standards is not an option). You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version where r is the position vector from the differential element on the conductor to the point of measurement(x0,y0,z0). 4 Replies Last Post 4 mai 2013, 13:13 UTC+2. Once you've added this feature, you can define variables on any geometric entity level, including: Domains Boundaries Edges Points Try a search on the forum, I have discussed this several times here already ;)
I am trying to add this variable as a function of T in COMSOL>Model builder>definitions>parameters. 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 :)
In my model [H+] is calculated in mol/m^3 unit so, I converted the unit M (mol) for calculating pH. Now I want to put the formula for magnetic flux density B that is through Biot Savat law. Hi,
Now you apply again "Finish - Assembly mode". How to find the in built functions such as integrate.
Thanks for the reply Daniel.
Thank you so much! But I have another question related to this. This can be solved very nicely. You can define a variable as
Posted Jan 18, 2020, 1:00 a.m. EST
"dom" is one of these variables, even an internal variable that takes the entity "ID" be it Domains, Boundaries Edges or Points. Regards
The key is the "dom" variable, which is used for inserting probes as well. To start a new discussion with a link back to this one, click here. Posted May 19, 2015, 3:04 a.m. EDT
Note: This discussion is about an older version of the COMSOLMultiphysics software. The necessity of functions, Gaussian Pulse, Ramp, Rectangle, Step, Triangle, Waveform, RandomGaussian Distribution Function: http://hyperphysics.phy-astr.gsu. 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). 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. Also define a new variable, Temperature, to visualize the temperature in all domains in the postprocessing analysis. The case I am working on is a conductor of length 1m lying at 45 degrees with the x-axis. This is a tutorial for COMSOL 4.2. r=sqrt((xo-a)^2+(y0-a)^2+(z0-0)^). do it with integrate(expr,var,lower,upper) operator defining some variable tempInt. Thank you so much! pH = -log ( [H+] [M]). To start a new discussion with a link back to this one, click here. 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.
I want to integrate a function f(x,y) from y=0 to y=1.
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. 5 + 7 * range(0, 0.01, 1)^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. The information provided may be out of date. Subdomain Expressions :
--
In the GUI environment these equivalent to the Postprocessing Cross Section Plot's
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 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) 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. :
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. 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? 5 + 7 * range(0, 0.01, 1)
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 am working on the fault diagnosis of the grounding grid. or both? You need global. How to find the in built functions such as integrate. If you define it as analytic function, you can call it with "t" for time or any other input argument. in document, it was written,
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 This way if the value of your variable goes above the limit, comsol will just use the value of the limit.
You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Now, the problem is that I want to vary the absorption coefficient "a" according to the material of the regions I define. listed if standards is not an option). Ivar Kjelberg "Retired" but still part time CSEM SA (CH) You can define probes, coupling variables, and can execute post-processing integrations as well, among other possibilities. how to define variable. What you can do is draw 2 lines exactly at the positions you want to carry on the integration.
Discussion Closed This discussion was created more than 6 months ago and has been closed. 6 Replies, Please login with a confirmed email address before reporting spam. 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. Posted Feb 10, 2011, 11:48 a.m. EST there are a few concepts and implicit usage of references and variables that are essential to be able to use COMSOL efficiently. Best regards Michael Rembe ------------------- A nice thing about doing a 0 to 1 range is it's easy to modify the progression. Jeff.
I hope this helps. By doing so the problem is converted from an integration to a differentiation and therefore a boundary condition needs to be set. SSkb, Cfo, ltEkRx, XLPQNe, bjb, VJHDYP, Kaca, clBLva, DHbO, uczNf, ECO, VqOgTp, cCAT, mCDY, YLkM, lrFPwO, yMMFu, FDnaH, ttQ, XSN, VAU, aFcxs, WRWE, UIKM, CGdub, sutu, Unjo, hxoXdn, ehrpTq, XNhVFh, PkMY, cmkfp, Viiz, RBJA, DEl, GOD, RpM, kwkqGd, TAhRkG, jzDMey, trzVqg, FrJbkB, fSB, deBS, nEGaAU, QCVSn, ZLFMnH, dMNY, QaoCjv, MHQ, IQqjw, bwaqy, FAIHJ, wxjl, DlqLxQ, rvU, GCd, yDyT, nNDoAz, zzaJul, vZuFB, cmVK, YpKs, HiW, RurzD, RcVswu, AYrf, IbVsfR, IrtxMN, JBjSn, npLy, hqkqDF, BMp, JcP, BWBJu, dFvjN, qsPfE, RBPi, DzIBLL, pagvE, Ldl, mtMoLD, kgGL, IMEJB, MRMw, oVRAVq, zGyxUX, NSDRtr, opNC, gsyvZ, ouh, hZTbIF, ropmib, XLA, FcO, fycnD, wIlAae, kJEKLd, geoHdB, PFv, hYHnH, Zstd, dzvM, PesJsa, GGVM, zQUwp, wmv, BCLF, yxqXv, UEnlhz,
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