Thanks. This can be solved very nicely. 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. 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. 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 expressions for lower and upper limits do not have to be constants but are required to evaluate to real values. Ivar, Dear Comsol community,
Once you've added this feature, you can define variables on any geometric entity level, including: Domains Boundaries Edges Points r=sqrt((xo-a)^2+(y0-a)^2+(z0-0)^). Thanks! In comsol 3.5a, i couldn't find any place in option or Physics tool to define these parameters. Note: This discussion is about an older version of the COMSOLMultiphysics software. y is my shear rate and can also be written as "spf.sr" and n is a variable I defined already. 7 Replies, Please login with a confirmed email address before reporting spam. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version For the source term f I use: d (intX,x)-f (x,y). 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. Use the Variables node to define expressions as user-defined variables. Discussion Closed This discussion was created more than 6 months ago and has been closed. Right-click Global Definitions and choose Variables. Thanks, Hi,
), or other global variables. Jeff. --
(dom==1)*alpha , the question is how could I know if this condition is evaluated for boundary 1 or domain 1 ? 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. 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). Define the following parameters for the materials:
Your internet explorer is in compatibility mode and may not be displaying the website correctly. Magnus Ringh, COMSOL. Ali, Hi
- Using a step size of 0 is not allowed. Share Improve this answer Follow answered Jan 7, 2021 at 1:01 Sameep Shah 11 1 Add a comment Your Answer Under Global Definitions>Parameters, define variable "freq" and assign the same numerical value of the frequency you are using in the Study Step. 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. [QUOTE]
Your internet explorer is in compatibility mode and may not be displaying the website correctly. I am working on the fault diagnosis of the grounding grid. Good luck
As a simple 2D example, assume I have a square domain [0,1]*[0,1] (here called dom 1). Hi Mohammed,
To start a new discussion with a link back to this one, click here. Peter. or both? Discussion Closed This discussion was created more than 6 months ago and has been closed. Fluid & Heat, Computational Fluid Dynamics (CFD), Porous Media Flow Your internet explorer is in compatibility mode and may not be displaying the website correctly. You can define an Analytic, Interpolation, or Piecewise Function to describe any material property in COMSOL Multiphysics.
Now you apply again "Finish - Assembly mode". Then again T might well be T(x,y,z,) and so on
Try a search on the forum, I have discussed this several times here already ;)
(root.mod2.at2(x+dest(x),y+dest(y),dom) == 1
Your internet explorer is in compatibility mode and may not be displaying the website correctly. where a ranges from 0 to 0.707. I don't understand what you want to simulate! It is useful where you specify lists of values: In the Times field for the output times from a time-dependent study, for example. 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)
This would allow me to used more complicated boundaries (e.g. 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 am specifically looking for summation as in Fourier and Taylor series. 2*pi*r^2
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. How to define a coordinate system along a customized direction. in an axisymmetric model where r is a spatial coordinate, for example. --
You should use a nonzero step size for the range function. By doing so the problem is converted from an integration to a differentiation and therefore a boundary condition needs to be set. How and where from can i define the following variable for subdomain in comsol3.5a? I am using Coefficient Form PDE physics. 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). 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. Here, I would like to define Pc as a variable under Global Definitions wherein for its expression I want to write 2*sigma/r. The boolean expression did the trick. circular shaped ones). 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 a tutorial for COMSOL 4.2. Version 4.1 there are a few concepts and implicit usage of references and variables that are essential to be able to use COMSOL efficiently. Posted May 19, 2015, 3:04 a.m. EDT Worked perfectly for me. Am I right on this one? 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.
This is done by adding a "constraint" to the boundary where x=0 with reaction term R=-intX. 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). if(dom==1,epsilonr_air,if(dom==2,epsilonr_container,epsilonr_ball) )
To start a new discussion with a link back to this one, click here. The case I am working on is a conductor of length 1m lying at 45 degrees with the x-axis. Good luck
You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Youngs modulus, E
For the diagnosis I am using electromagnetic Induction Method. Hence since f is 1 on dom 1 we have
How and where from can i define the following variable for subdomain in comsol3.5a? 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 .
The thermal conductivity, k
listed if standards is not an option). 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 boolean expression did the trick. variant a) the lazy long path (? But I have another question related to this. 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. Ivar. How to use COMSOL functions (analytic) to define user-defined pressure force. where r is the position vector from the differential element on the conductor to the point of measurement(x0,y0,z0). To start a new discussion with a link back to this one, click here. I want to integrate a function f(x,y) from y=0 to y=1. Worked perfectly for me. 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.
In matlab, we can use int(f(x),x0,x1) which represents the integration of f(x) from x0 to x1? 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))]. Model Library path: Structural_Mechanics_Module/Thermal-Structure_Interaction/microrobot_3d
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 Component right-click Definitions and choose Variables, or click Local Variables in the Definitions toolbar (Windows users). do it with integrate(expr,var,lower,upper) operator defining some variable tempInt. Your internet explorer is in compatibility mode and may not be displaying the website correctly. but then afterwards C at each position is different than C_total. I found something like:
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. What you can do is draw 2 lines exactly at the positions you want to carry on the integration. So i don't know if a ''domain point probe'' would the trick
In the manual, but what is the scope etc here? Regards, Hi
listed if standards is not an option). Posted Jan 5, 2010, 7:56 a.m. EST Discussion Closed This discussion was created more than 6 months ago and has been closed. 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. Simulating the Tunneling Current Across a Graded Heterojunction. 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.
While I am defining the variable as pH = -log ( [H+] [M]), it is showing. 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. Discussion Closed This discussion was created more than 6 months ago and has been closed. 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.
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. Once you've added this feature, you can define variables on any geometric entity level, including: Domains Boundaries Edges Points
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. How to find the in built functions such as integrate. 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. The density, rho
in document, it was written,
COMSOL Multiphysics is a general-purpose software platform, based on advanced numerical methods, for modeling and simulating physics-based problems. 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 5 + 7 * range(0, 0.01, 1)^2
For f(x) from 0 to x, is it int(f(x),0,x)? But this variable could be either for a domain or for a boundary, as mentioned in the doc. \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. I hope this helps. The information provided may be out of date. 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. Ivar Kjelberg "Retired" but still part time CSEM SA (CH) You can integrate the normal-to-the-surface component of a power density vector over a surface, to compute the power flow through it. So you probably don't want that. A continuous range of values takes infinitely long to evaluate. 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. (COMSOL version: 5.0) A Domain-ODE is needed to solve for variable Np.
I stumbled upon the same problem. Posted Jan 18, 2020, 1:00 a.m. EST i was looking and learning some Model in Comsol library and it was
Check out Chapter 5 of the COMSOL Multiphysics Reference Manual, version 5.2a. Do you know if it is possible to write such an expression for existing boundaries? 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. Thank you so much! Discussion Closed This discussion was created more than 6 months ago and has been closed. Here f is 1 inside a domain and 0 else. ):
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. Because the microrobot legs consists of several materials with different material properties, you have to define subdomain settings for each materials. Hi
I am trying to solve the inhomogeneous wave equation on COMSOL. e.g. How do I define Pc as something that varies for a range of 'r' values. First, for a 2-D problem, how can I use the x value and y value of a point evaluated? With COMSOL Multiphysics, you will be able to account for coupled or multiphysics phenomena. 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. I have a problem to define a variable. Aref Shaikh. COMSOL Employee Sweden The problem is the use of a Global Variable in the Analytic function. With more than 30 add-on products to choose from, you can further expand the simulation You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version To start a new discussion with a link back to this one, click here. Thanks. Thanks for the reply Daniel. Because It took me some time to sort this out with COMSOL. 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. The thermal expansion coefficient, alpha
Ivar, integrate over the whole domain the function f(x)*(x>x0)*(x
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