Transcendental functions such as logarithms operate on dimensionless arguments. This order corresponds to the Gauss Point Data element order. First of all how COMSOL is really considering this "inside, or under the hood" is not known for me. The State Variable feature simplifies the tracking of the history of a field over time. Thanks in advance. donate and download files in full HD here:http://www.soft-hummingbird.com/Tutorial_Comsol_Download_DonateThis is a tutorial for COMSOL 4.2. 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. Henrik. Discussion Closed This discussion was created more than 6 months ago and has been closed. You can check your entries by being systematic with the units, this helps to understand which value to put where. The default order of 4 corresponds to the Gaussian integration points that are used by the quadratic element order used by most physics, but if you use different element orders, adjust this setting to be twice the order of the element. The material property can then be conditional upon the SorL state variable. 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. Most variables that you as a user would be interested in can probably be found this way. The new functionality is simply easier to use, as there are far less settings (and especially solver settings) to adjust. Magnus Ringh To start a new discussion with a link back to this one, click here. It is possible, but then you need the syntax mod1.es.Ex etc. 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. For example, I define a physical property like density rho which is only a function of dependent variable w. the time derivative of rho is employed to solve another dependent variable u. I want to solve y for . listed if standards is not an option). Hi If that's true, how to solve these type of problems in COMSOL? You can sort the Description column in alphabetical order. Hi, Send Private Message Flag post as spam. Download two of the examples featured in this blog post by clicking the button below. 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. Jinja2 filters let you transform the value of a variable within a template expression. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version For that this question should rather go to "support" only they have the definitive answer. Excellent, this is exactly what I was looking for. 2. Too bad that comsol does not allow the grouping of user-defined vector component variables. Thank you Magnus!! ExpressionBase. its value. Your Discussion has gone 30 days without a reply. The variable becomes available for plotting and evaluation after re-computing or updating the solution. Ivar, Thanks for the help. You also need to activate the **Equation View** from the **Show** menu in the Model Builder toolbar. Parameters, Variables, & Functions We would want to update this variable before each step. If so, I was talking about the variables I can define under the definitions node. Variables You can add Variables () from either the Global Definitions node or the Definitions node under the Component (local) nodes. Discussion Closed This discussion was created more than 6 months ago and has been closed. This consent may be withdrawn. Regards, listed if standards is not an option). what about defining a variable (global variable in 3.5a) and use this ? -- looking forward to your reply and appreciate it! That is an interesting question, but likely not one which can be addressed here. If you expect complex-valued numbers, enable the Allow complex values option. 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 State Variable feature simplifies the tracking of the history of a field over time. Really appreciated. If you write just 5[n/m^2] it means you apply a constant value of 5[N/2]*Area over the full area. @ Lasse you said for diffusion you have two variable 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. Thank you. Suppose that we have a transient model where the temperature is fluctuating in time. . You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Operators in COMSOL Multiphysics. Once you've added this feature, you can define variables on any geometric entity level, including: Domains Boundaries Edges Points You can check your entries by being systematic with the units, this helps to understand which value to put where. 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 Nov 24, 2021, 11:11 a.m. EST Version 5.2 0 Replies . 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). Your detailed explaination about the variables relieves my confusion about them a lot. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Run a **Get Initial Value** if there is no solution yet. You can then find it in the Variables list in the Inner Gimbal-Spinning Disc node's Equation View subnode, where it is described as the z component of the joint axis. 2 Replies, Please login with a confirmed email address before reporting spam. used in defining the variable? Note: This discussion is about an older version of the COMSOLMultiphysics software. 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. You find the variable in the list of predefined expressions but under Definitions . If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. At least it saves some typing. 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 . cole des Mines d'Albi-Carmaux. 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. integrating over the spatial domain i.e. You might get further to a reply. Magnus Ringh Ivar. So, introduce a state variable, SorL, with initial value of 1 (presuming the material is initially solid) and with the update expression: This nested if statement will switch the value of SorL to 0 if the temperature rises above the upper threshold, and only switch it back to 1 if the temperature drops back below the lower threshold. How to enable the Variable Utilities option. Overview of Integration Methods in Space and Time, How to Join Solutions in COMSOL Multiphysics, How to Activate Material in Simulations of Manufacturing Processes. Regarding grouping of vector components: That is something that we will look into. The parameter should be computed only once at initialization. -- In order to have access to the Replace Expression . You also need to activate the Equation View from the Show menu in the Model Builder toolbar. 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". You can also make global variables here by i.e. If I had only known this before, it would have saved me countless hors. We can track the maximum temperature that the part gets to by defining a state variable MaxT, with an initial value of 0 (or any value lower than or equal to the initial temperature field) and use this variable to store the maximum temperature via the update expression: This if statement evaluates to true whenever, and wherever in space, the temperature field, T, is greater than MaxT, and then MaxT will take on the value of the temperature. You probably didn't think of it, but in the expression I just mentioned, sqrt, ^, and even + are all examples of operators. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Happy modeling! Thank you. Because It took me some time to sort this out with COMSOL. You can use the Find tool (press Ctrl+F), if you have set up all the physics. 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. Using subdomain expression variables makes it easier to enter the subdomain properties of the model. 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? 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. Hi The definition of the state variable MaxT. listed if standards is not an option). Thanks for your help. Your internet explorer is in compatibility mode and may not be displaying the website correctly. sqrt(realdot(es.Ex,es.Ex)+realdot(es.Ey,es.Ey)+realdot(es.Ez,es.Ez)) hence if you wanf to use myFunc (myVar) as a force input in Newtons, you should write: 1 [N]*myfunc (myVar [1/myVar_Units]) or just. 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)? Allow me to elaborate: let's say that I want to replace the turbulent dissipation (ep) with the following expression ep=eptil+D. where SolidtoLiquid(T) and LiquidToSolid(T) are two different functions of temperature associated with the two different branches. You can use the Find tool (press Ctrl+F), if you have set up all the physics. If I input the Young's modulus of the channel to about 1 [GPa], the . An order of 0 would mean that, over each element, there is only a single state variable defined. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version All Answers (4) It might be simply because you are trying to take the logarithm of a dimensional quantity. I am attaching the COMSOL image. 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. Ivar. But I still think I didn't understand it right. Because It took me some time to sort this out with COMSOL. Interesting question, and I do not have the answer like that. But when I define a Variable under "global definitions" it doesn't. 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. Perhaps you will find your reply if you write this out. Variable in Integration Expression. I assume, that the parameter is recomputed every iteration step, but this is not necessary. If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base. I cannot select the variable for plotting and if I write it in the expression field, it is not recognized. 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. Thanks! 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.
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