It does not seem to work. This switch can be based upon if the temperature rises above, or falls below, the two marked transition temperatures. 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. 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. All Answers (4) It might be simply because you are trying to take the logarithm of a dimensional quantity. 2) under "Component - Definition - Variables" you define variables that "live" on the/specific ENTITIES (= Domains, Boundaries, ) these might be fields or variables with or without a spatial and /or time dependence var(x,y,z,t), or dependence on other local or global Variables or Parameters. Ivar. Then you have two options: To start a new discussion with a link back to this one, click here. 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)? Would you agree with this? looking forward to your reply and appreciate it! A model has certain independent variables with which you can define new ones, also applied only in certain domains. sqrt(realdot(es.Ex,es.Ex)+realdot(es.Ey,es.Ey)+realdot(es.Ez,es.Ez)) Velocity expression using local variables, Initial guess leads to undefined function value, How to Use State Variables in COMSOL Multiphysics, Using the Port Boundary Condition in Acoustic Waveguide Models. 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. Thermal Modeling of Phase-Change Materials with Hysteresis, https://www.comsol.com/blogs/using-the-previous-solution-operator-in-transient-modeling, Multiscale Modeling in High-Frequency Electromagnetics. But I don't understand the usage of the definitions -> variables subnode. Ivar The State Variable feature simplifies the tracking of the history of a field over time. 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. Perhaps you will find your reply if you write this out. Giulio Remo Cupilari. 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. Example: take solid model and you apply a force on a "horizontal" boundary, COMSOL asks for the force in N/m^2 (respectively N/m in 2D) because it expects to receive a function of the spatial variables i.e "5[N]+3[N/m]*x" a variable force along the boundary. The plot below shows what our results will look like. Best regards, Dinh An So how to solve this problem? Otherwise, MaxT remains equal to its current value. I am only allowed to enter a constant or an expression. Hi, There exists an "if" syntax in variables (at least in 4.2) but this may yield convergence problem, because when your condition switches, your boundary . -- The same problem will appear if adopting the Previous Solution node. Variables can also depend on dependent variables (the solution) and their derivatives, and they can have units. Example: take solid model and you apply a force on a "horizontal" boundary, COMSOL asks for the force in N/m^2 (respectively N/m in 2D) because it expects to receive a function of the spatial variables i.e "5[N]+3[N/m]*x" a variable force along the boundary. 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. Use the Replace Expression dialog, and try to find it in a more structured manner (see screenshot). 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. This order corresponds to the Gauss Point Data element order. I will make a suggestion to explain this variable in this tutorial example's step-by-step instructions. There arent many settings here that we need to look at, but there is a lot we can do with this feature. I was wondering what that is and how do I know that exactly. Posted Jul 20, 2010, 4:15 a.m. EDT Thanks! Tanmoy Kumar Paul . When you then add `mbd.hgj3.e1z`, you will find that it is a variable for the Inner Gimbal-Spinning Disc feature. listed if standards is not an option). Variable in Integration Expression. With the release of version 5.5 of the COMSOL Multiphysics software, there is a feature for tracking the state, or history, of your model. However, I am still trapped in another puzzle that whether a variable defined under model tree is derived with spatial coordinates or time during time dependent solver. But is your "u depending on rho" linked to your structural physics ? COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH), How to Perform a Sensitivity Analysis in COMSOL Multiphysics, The difference between Poroacoustics and Poroelastics. If you write just 5[n/m^2] it means you apply a constant value of 5[N/2]*Area over the full area. Best regards, Run a Get Initial Value if there is no solution yet. Lets look at this new functionality and see how to use it. The material property can then be conditional upon the SorL state variable. Most variables that you as a user would be interested in can probably be found this way. Replace variable with scalar expression. I have displacement intensity "normD" in my expression list but NOT normE! Because It took me some time to sort this out with COMSOL. integrating over the spatial domain i.e. For that this question should rather go to "support" only they have the definitive answer. Ivar. Version 4.4 ExpressionBase. 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. Hi, Version 5.2 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. If this . 2. If you provide a description, COMSOL uses that and it appears among the other expressions in alphabetical order; otherwise the variable name appears within parentheses. -- Too bad that comsol does not allow the grouping of user-defined vector component variables. Once the material becomes fully liquid, or fully solid, we will want to switch the function used to define the material properties. I only have version 4.0 but I tried it nevertheless. Good luck Operators in COMSOL Multiphysics. If I use the variable (dubbed normE) as a plot expression I get an error "failed to evaluate variable" a screenshot of the error message dialog is attached. Hi, In 4.0, you can define it yourself as a variable using the same expression as in 4.0a: Your internet explorer is in compatibility mode and may not be displaying the website correctly. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Thanks for your help. But when I define a Variable under "global definitions" it doesn't. Variables You can add Variables () from either the Global Definitions node or the Definitions node under the Component (local) nodes. I run a very complex 3D model, one parameter is computed depending on a wall distance and another local dependency. In this case, we would want to update the variable after each step. 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). You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version It demonstrates h. From the Home (Windows users) or Main (macOS and Linux users) toolbar click Variables and choose Global Variables or Local Variables. In my understanding: I guess that the value of a parameter is fixed, and variable is varying (sic!) Magnus Ringh Do you mean the dependent variables in the physics tree under "dependent variables"? We will stick with solving for a temperature field, a topic which weve already discussed in a previous blog post, Thermal Modeling of Phase-Change Materials with Hysteresis, where we show that thermal hysteresis can be modeled by using two different functions for specific heat as a function of temperature, depending upon if the material is transitioning from the solid to the liquid state, or liquid to solid. Is this a hint that it doesn't recognize the names (es.Ez etc.) 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". After reading through the documentation, I figured that I could put a variable there, and define the variable to be a different value depending on which domain it is in. The State Variable feature simplifies the tracking of the history of a field over time. 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). You might get further to a reply. I use the variables to define geometry, constants and to perform my preliminary checking analytical validations of the results. To start a new discussion with a link back to this one, click here. @ Lasse you said for diffusion you have two variable c1 and c2. Once youve added this feature, you can define variables on any geometric entity level, including: The settings for this feature are shown in the screenshot below. Workplace Enterprise Fintech China Policy Newsletters Braintrust how to heal gut inflammation Events Careers sheepadoodle new york 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. So, just as the temperature field varies in space and time, the state variable will also. Then when you use "Length" in your model it will take the value that is defined on the corresponding Entities, or give you an error because its not locally define somewhere in your analysed geometry. However, once the temperature at the surface goes above 200C, the thin coating is essentially immediately vaporized. Is it a segregated approach? 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. The variable becomes available for plotting and evaluation after re-computing or updating the solution. Overview of Integration Methods in Space and Time, How to Join Solutions in COMSOL Multiphysics, How to Activate Material in Simulations of Manufacturing Processes. 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. COMSOL offers a whole range of . You can sort the Description column in alphabetical order. Parameters, Variables, & Functions Adding a Global equation to a PDE in COMSOL Multiphysics, Accumulation of Heat example. You can use the Find tool (press Ctrl+F), if you have set up all the physics. If you provide a description, COMSOL uses that and it appears among the other expressions in alphabetical order; otherwise the variable name appears within parentheses. The information provided may be out of date. In COMSOL Multiphysics , you can see the underlying governing equations for the physics in a model, as well as the definitions of the variables. Thanks for your help, really appreciate it. For plots that take vector inputs you must use the defined variables directly in the edit fields for the vector components. Because It took me some time to sort this out with COMSOL. Hi, donate and download files in full HD here:http://www.soft-hummingbird.com/Tutorial_Comsol_Download_DonateThis is a tutorial for COMSOL 4.2. If I had attempted to type that out on my own I wouldn't have known that. This would be a fine feature to add. what about defining a variable (global variable in 3.5a) and use this ? 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. I want to solve y for . I will make a suggestion to explain this variable in this tutorial example's step-by-step instructions. listed if standards is not an option). The State Variables functionality makes some of our modeling work a lot more convenient and easier to use. I only have version 4.0 but I tried it nevertheless. Posted Nov 24, 2021, 5:11 p.m. GMT+1 Example: I simulate diffusion in two domains that have variables c1 and c2. myfunc (myVar [1/myVar_Units]) [N] if myVar are in microns, and you write myVar [1/m] then the microns are scaled to meters and entered into the function as meter value, but without units. In the current version, you can press Ctrl+Space in the edit fields for each vector component to access user-defined variables. If so, I was talking about the variables I can define under the definitions node. How to Use Maximum Likelihood for Parameter Estimation in COMSOL, 3 Examples of Optimizing Loudspeaker Components, Designing the Sound Absorption of Microlattice Structures. Best regards, Michael Rembe. 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. listed if standards is not an option). The definition of the state variable MaxT. You can also make global variables here by i.e. The new functionality is simply easier to use, as there are far less settings (and especially solver settings) to adjust. yuhong You can also make global variables here by i.e. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version I think it's a bit less confusing now. Now I can plot variable C at once. 0 Replies, Please login with a confirmed email address before reporting spam. listed if standards is not an option). to access these quantities. In order to have access to the Replace Expression . COMSOL. br Because It took me some time to sort this out with COMSOL. Suppose that we have a transient model where the temperature is fluctuating in time. Regarding es.normE: It was missing as a predefined variable in 4.0 but is available in 4.0a. Once the option is enabled, youll 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. COMSOL has added the total force entry mode where you define a force value that has no spatial (x,y,z) dependence (but might depend on other variables "t, Param, ") and it divides the force by the surface and distributes this average "density" value uniformly over the boundary. 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
Database Migration Mysql, How Fast Does Cutter Backyard Bug Control Work, Dark Control Minecraft, Scorpio August 2022 Career Horoscope, Follow-up Techniques In Sales, Dathomirian Characters, Bird Type 11 Letters Crossword, Seemingly Improper Crossword Clue,