You find the variable in the list of predefined expressions but under Definitions (not Electrostatics). What is puzzling me is I have seen on some forum discussions, that other people who are plotting field intensity are discussing about a predefined expression "normE". I am only allowed to enter a constant or an expression. You can also make global variables here by i.e.
There is no support for grouping user-defined variables and declare them as components of a vector quantity. Do you mean the dependent variables in the physics tree under "dependent variables"? Download two of the examples featured in this blog post by clicking the button below. The State Variables functionality makes some of our modeling work a lot more convenient and easier to use. @ Lasse you said for diffusion you have two variable c1 and c2. If I replace "normE" by "sqrt(realdot(es.Ex,es.Ex)+realdot(es.Ey,es.Ey)+realdot(es.Ez,es.Ez))" in the expression field the plot works without error. its value. Lets start from the setting at the bottom of the window. Once the material becomes fully liquid, or fully solid, we will want to switch the function used to define the material properties. If this . In order to have access to the **Replace Expression** dialog, you must have some results. would you recommend to use a state domain variable as parameter? listed if standards is not an option). Please contact support@comsol.com and mention this, as we will address it. Excellent, this is exactly what I was looking for.
In order to have access to the Replace Expression . --
This, however assumes that the variable you are looking for is announced as a postprocessing variable. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. This enables you to: See how the variables are calculated by the software See the names of variables and the quantities each one defines Access and use the variables when formulating expressions listed if standards is not an option). its value. integrating over the spatial domain i.e. Your internet explorer is in compatibility mode and may not be displaying the website correctly. I cannot select the variable for plotting and if I write it in the expression field, it is not recognized. Giulio Remo Cupilari. A good example of this is the Laser Heating of a Silicon Wafer example from the Application Gallery. You also need to activate the **Equation View** from the **Show** menu in the Model Builder toolbar. In 4.0, you can define it yourself as a variable using the same expression as in 4.0a: sqrt (realdot (es.Ex,es.Ex)+realdot (es.Ey,es.Ey)+realdot (es.Ez,es.Ez)) The variable becomes available for plotting and evaluation after re-computing or updating the solution.
Example: I simulate diffusion in two domains that have variables c1 and c2.
Because It took me some time to sort this out with COMSOL. Would be nice Magnus Ringh, COMSOL, Magnus suggestion is the way to go for 'reverse engineering', but what if you were to set up that variable 'theta' without knowing that you were looking for mbd.hgj3.e1z? But there is still a problem. Finally, the State Components settings allow you to define several state variables, their initial conditions, and how they should be updated. Variables A variable 's expression can contain numbers, parameters, mathematical constants, physical constants, other variables, functions of variable expressions, spatial variables, time, unary operators, and binary operators. tst = eps => if I get a value then "eps" is a COMSOL defined name (this might not be sufficient, as certain variables are only defined by COMSOL ad hoc during the solving process or during the model tree analysis, once you have arrived further "down" in the tree structure
I have displacement intensity "normD" in my expression list but NOT normE! However, it is found that the solutions (such as stress and strain) at previous step cannot be accurately recorded for a model with heterogeneous material properties, no matter what Order you select. Really appreciated. Transforming variables with Jinja2 filters . an expression V = V0+V1* (x>1) works well for many cases meaning V=V0 for X<= 1 and V=V0+V1 above. Thanks for your help, really appreciate it. Would you agree with this? A model has certain independent variables with which you can define new ones, also applied only in certain domains. So how to solve this problem? Good luck
ExpressionBase. Hi
Comsol Trial For Student Code To DownIoad Can you tell me how can I have got a demo passcode to downIoad the comsol 5.1 for home windows (test version). Jinja2 filters let you transform the value of a variable within a template expression. - Function . I use the variables to define geometry, constants and to perform my preliminary checking analytical validations of the results. Run a **Get Initial Value** if there is no solution yet. How to Use Maximum Likelihood for Parameter Estimation in COMSOL, 3 Examples of Optimizing Loudspeaker Components, Designing the Sound Absorption of Microlattice Structures. 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. It does not seem to work. Run a Get Initial Value if there is no solution yet. COMSOL. Overview of Integration Methods in Space and Time, How to Join Solutions in COMSOL Multiphysics, How to Activate Material in Simulations of Manufacturing Processes.
At least it saves some typing. Good luck
Discussion Closed This discussion was created more than 6 months ago and has been closed. you can define a global variable "Length = intop1(1)", as the operator intop1 is defined over a given Domain or Boundary it will give back a volume, surface or respective length depending on your space dimension of the model, and will be defined by default on all entities in your model. The very first half of the work shop offers an summary of COMSOL Multiphysics Version 4.2a - its abilities, its brand-new abilities and efficiency enhancements, and.. "/> dns spoofing tool kali . 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 ), or other global variables.
Posted Jul 20, 2010, 4:15 a.m. EDT Operators in COMSOL Multiphysics. I guess that the value of a parameter is fixed, and variable is varying (sic!) used in defining the variable? Perhaps you could clarify better by adding the dependent variables: i.e "rho" is a field (not just a variable ) it's formally rho(x,y,z,t), "w" if this is the displacement along Z is also a field w(x,y,z,t). Regarding es.normE: It was missing as a predefined variable in 4.0 but is available in 4.0a. 0 Replies, Please login with a confirmed email address before reporting spam. You can use the Find tool (press Ctrl+F), if you have set up all the physics. This, however assumes that the variable you are looking for is announced as a postprocessing variable. Another use is to verify that the Parameter or Variable name I want to use is not already defined by COMSOL, by making i.e. Magnus Ringh
To start a new discussion with a link back to this one, click here. In this scenario you know that you are looking for the orientation of the axis of Inner Gimbal-Spinning Disc, but not what its variable is called. For a simple rule of 2 variables x and y: if x<a then y=c1 else y=c2 In Comsol: y= if (x<a,c1,c2) Furthermore, i don't know how to link 2 rules with 3 variables x,y,z: if x<a then y=c1 else if z<b then y=c2 else y=c3 I will appreciate if anyone know the solution. Hi
I was wondering what that is and how do I know that exactly. Good luck
Lets look at this new functionality and see how to use it. What ist the difference between the new state variable and the old previous solution operator, you explained some years ago in a blog post (https://www.comsol.com/blogs/using-the-previous-solution-operator-in-transient-modeling)? In one of the tutorials I come across, the modelling gyroscopic effect tutorial, there is a section where a variable is defined in the definition section of the model tree, and the expression reads mbd.hgj3.e1z, and I am expected to type this out. Hello Dirk,
The use of variables and fields in COMSOL are somewhat tricky/confusing in the beginning, because of the implicit suppression of the (x,y,z,t) writing, these spatial variables are defined by your Entity selection higher up in the nodes. I cannot select the variable for plotting and if I write it in the expression field, it is not recognized. In this scenario you know that you are looking for the orientation of the axis of **Inner Gimbal-Spinning Disc**, but not what its variable is called. However, some variables might only be used in the post-processing and be of no specific use in the solving process, unfortunately these are also defined "high" up in the tree, and not under a (logical for me) "Definition node" at the "Results" or "Data Set" level, hence clearly defined as post-processing variables to work on the resulting Data Sets
Sincerely Regarding grouping of vector components: That is something that we will look into. Ivar
To implement such a model, we need to introduce a switching state variable to decide if we should be following the lower or the upper branch. You might get further to a reply. looking forward to your reply and appreciate it! Adding a Global equation to a PDE in COMSOL Multiphysics, Accumulation of Heat example.
2 Replies, Please login with a confirmed email address before reporting spam. After running a simulation for a 3D structure with a magnetic field going in the z (vertical) direction, COMSOL returns the following error: Division by zero. Hi Walter, Most variables that you as a user would be interested in can probably be found this way. It's the same for node fields where you fill in values or expressions, these are mostly expressed as "densities" to be understood as what applies directly to a dx*dy*dz volume of the Domain entity (respective surface for boundaries) and we humans mostly work in "total field/flux" mode, that is the integration over the selected entities of any density value. now if you are in the time domain a F = F0* (t>1) to turn on the force F after 1 second is a "hard" way to go for your solver, try the heaviside functions to smoothen the turn on/off (search for heaviside in the doc good luck Ivar Use the Replace Expression dialog, and try to find it in a more structured manner (see screenshot). It looks like you are gently getting COMSOL to accept full tensor notations and have the GUI to fill in the details while we may write high level equations and not need to develop everything at component level Posted Mar 19, 2015, 9:05 a.m. GMT+1 Our laser heating model already defines a Global Parameter called emissivity, which is a constant value of 0.8 and is used within the model to define both the absorbed and radiated heat. These variables can also be used to affect other fields, such as material properties, and can thus be used to implement hysteresis into your model. Furthermore, by asking the question: what is the difference between a time series solving process and a parametric sweep of stationary steps of variable "t" tending to "0". - Function: / Failed to evaluate . You probably didn't think of it, but in the expression I just mentioned, sqrt, ^, and even + are all examples of operators. You can also define "Length" locally on only the same Domains or Boundaries as for the inop1 operator, and then define another intop2 operator on another Domain or Boundary and define the same "Length" variable (same name) only on this new Domain or boundary. 9 Replies, Please login with a confirmed email address before reporting spam. An order of 0 would mean that, over each element, there is only a single state variable defined. By providing your email address, you consent to receive emails from COMSOL AB and its affiliates about the COMSOL Blog, and agree that COMSOL may process your information according to its Privacy Policy.
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