Comsol values of dependent variables I believe it works to use either the "Interpolated" or "Manual" settings for parameter value in the Values of Dependent Variables section. In Study 2, Step 2 expand the "Values of dependent variables" submenu and set it as Alberto suggests. The name should not conflict with other auxiliary dependent variables. In comsol, how can we get this kind of integration? For f(x) from 0 to x, is it int(f(x) from 0 to x I use a separate "General form PDE" with a dependent variable intX on the domain of the function. 11. This factor will make convergence the "int() and dxdydz are "implicit" when you call up un integration operator or a post-processing "Derived Variable" operator. Select from the following built-in distributions: Study 2 takes the lam0-dependent fields from Study 1 and solves other fields, which are my solution. Posted 20. From the physics of the problem, I know that the value of u cannot exceed a certain value, say u_max. Manual scaling is some times required for solid contact physics or user defined equations and dependent variables. but nevertheless, there are three open questions left for me: 1) If I am using the "Inital values of variables solved for" option with the results from the previous study (let's say of solid1) In this case, there is no reason to have different names for Field name and Dependent variables. You can also add the same type of node to a physics interface as an auxiliary equation contribution. under the sub-node "initial values" give the initial value of your material density, don't forget this aspect rho_mat is your material density that is a function of temperature. The Dependent Variables node's Settings window. Posted Apr 5, 2012, 4:00 p. 6, Variable Name by Vdown and Variable Expression V[V]. (as used under Results Derived Values Global Evaluation) about the "global" scope of variables. The type of distribution can be selected using the Distribution function setting in the Initial Value of Auxiliary Dependent Variables section of all release features. Results While Solving. 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. Apart from that what I would like to do is the following: I would like to solve the problem with a certain initial condition for the variable which the time dependent study solves for, and that I would like to use the solution I obtained as the inital condition for the time dependent study, in order to see if the The Multiphysics column contains the names of all multiphysics couplings in the model. The software plots the dataset of the selected plot Select a Time unit from the list (default: s) to use a time unit that is convenient for the time span of the simulation. These scale factors are automatically determined by default, but sometimes need to be manually tuned. This node represents a special type of feature in the Model Builder that you get by default when you add a physics interface. When the solver finishes calculating, the results indicate no sings of the static solution as if the frequency domain was calculated independently from the static solution. . Anup Paul. Then the initial value expressions is evaluated without using the current or stored solution. m. The model setup for our example in the software, with the settings for the Inlet boundary condition displayed. EST. I was amusing that by using "Values of variables not solved for" I would get it work, but when I run a sweep of A I get always the same result for Step 2. When the Setting condition is satisfied, the plasticity variables are reset to the specified values. And you can create new variables from those. Scaling is often necessary for numerical purposes. Posted Nov 8, 2010, 9:02 a. Scaling is A Dependent Variable Declaration node declares a dependent variable (field variable) used by the physics interface. Initial value for the dependent variable. Best If you disable those nodes, the variables created in that node are no longer defined. Auxiliary dependent variable. The initial values can also be the solution from another study by adjusting the settings in the Values of Dependent Variables section of the study step. This node is available as a subnode for the Electrode Surface, Perforated Electrode Surface and Internal Electrode Surface. Bz in your case). 15 K, you can check out the Scaling of Variables and Equations and Dependent Variables sections in the COMSOL Multiphysics Reference Manual. Best regards, Magnus Ringh, COMSOL This setup requires that the Values of Dependent Variables section in the settings for the Time Dependent study step are set to refer to the results of the stationary study, as shown in the screenshot below. The default behavior of the COMSOL ® software is to assume a different scaling for each set of variables in your model. PNG; usual_solver_setup. The solver tab "Values of Dependent Variables" is there to set the initial values of one case to be used by the next-- You can switch to a segregated solver and use "lower limit" option provided. EDT Electromagnetics, Low-Frequency Electromagnetics, Charged Particle Tracing Hi Im trying to reproduce a simulation from a paper about the simulation of streamer discharge in comsol But in some parts I just dont follow what it says and how to do it I am using the Charged particle In time-dependent problems the variables are scaled when initializing the problem, and if wished, rescaled after consistent initialization. Expanding it gives the list of those. in the heat transfer T is the dependent variable so you solve for T that means that T=T(x,y,z,t) (T only if you are in a transient case, so if you select a boundary and use the variable T it will scan over the edge coordinates, whatever they are. Nancy regarding the time dependent solvers. I try to use the solution from study 1 (stationary heat transfer) as the initial temperature value for a second time dependent study. On This Page: In the Variables table or the fields under the table, enter variables by defining a variable name under Name, an expression that define the variable under Expression (see About Parameters, Variables, Variable Utilities, and Expressions), and (optionally) a description that explains the variable under Descriptions. In addition, the built-in differentiation operator d(<expr>, <var>) can always compute derivatives with respect to any set of coordinates, internally using the chain rule. The methods are applicable to the dependent variables present as Field subnodes ( ) under the Dependent How do I pass the solved value of the varibles into the equations that I try to solve subsequently? For example, I first solve a pair of question to get the Value of U and V, then I In this article, we discuss the importance of scaling for a model and how to manually set the scaling of dependent variables. I am wondering if there is either a way to get the evolution of these variables as the simulation converges, or at least if there is a way to get the final values of these variables at the end of the simulation. you can set two studies, first stationary and then time dependent. 3 0 Replies For the equation above, I get the warning "V is an unknown variable" even though it is defined as the dependent variable for the Electric Currents physics. This is useful, for example, when implementing material models with history The computation of boundary flux variables involves solving a system of equations to obtain a continuous field from nodal flux values. Sherif Lotfy Abdelaziz Do you have any idea how to use the coupling variables in COMSOL 4. 2019, 02:12 GMT-5 Interfacing, General, but in the setting of the "values of variables not solved for", I can only choose on study( and i actuallly want to add two study). Hi When solving the dependent variables, any numerical system must be scaled such that the matrix values are reasonnably close to 1, because if you want to mix i. Under the node "Laminar flow" you have the title "Dependent Variables". 3 0 Replies If the Add initial value as variable check box is selected, a variable will be added containing the initial value of the dependent variable. Hello COMSOL community, Attached is a bidomain model representing heart tissue that we are developing. If you clear the Solve for button, any equations and dependent variables that the multiphysics coupling adds are not I have created a lookup table for frequency dependent values of epsilon_r. I have sometimes been pondering what is the Comsol name of a variable (like 'spf. the solutions contains the values of all the variables given in the Dependent Variables section. Posted Mar 7, 2013, 12:45 p. The Dependent Variables node handles initial data and scaling for the dependent variables that you solve for as well as how to compute dependent variables not solved for. I need to define the dependent variable (u) to be the vector form electric field. t time at boundaries . Also see Physics I am using Electric Currents physics to solve for the voltage distribution over the electrode (dependent variable = V) and Transport of Diluted Species physics to solve the chemical reactions. Some special auxiliary interfaces, notably Optimization and Sensitivity, are not shown when their dependent variables are controlled in other ways. 5), which To overcome this problem, use an initial expression for the values of the dependent variables (see the Values of Dependent Variables section in the study step's Settings window). Thank you Ivar, I'm doing what you have suggested and it works well. I have read from another thread that the way to solve this is Enter a Field variable name. 2013, 15:45 GMT-5 Low-Frequency Electromagnetics, Fluid & Heat, Computational Fluid Dynamics (CFD) Version 4. 1,1. To enable these settings, select User defined from the Defined by study step list under General. mf interface output variable,), hoping that it would give me a set of B values only along that boundary. 6,0. So, if the Analysis (for the solver sequence) is altered or if a Hello COMSOL community, Attached is a bidomain model representing heart tissue that we are developing. EST Version 4. Plot total value of dependent variable. It is possible to assign a single initial value to an auxiliary dependent variable or to sample multiple values from a distribution. Define the name and properties of the auxiliary dependent variable. For a parametric sweep, it uses the first parameter value. In the Initial Values node you define the initial value for the dependent variable declared in the parent node. In rare cases, more than one Auxiliary Dependent Variable node can be used on subsets of the Weak Contribution node’s selection (to use different initial values, for example). For example I created a maximum operator (maxop1) and I calculated the position of the maximum value of the height1 (h1) in my domain by applying: maxop1(h1,x). ec. 1 2 Replies . In the same way as “Variables 2a”, “Variables 3a” was configured by selecting boundary No. Can anybody give me some help to realize that? This setup requires that the Values of Dependent Variables section in the settings for the Time Dependent study step are set to refer to the results of the stationary study, as shown in the screenshot below. The Physics interface column contains the names of all true physics interfaces in the model. In the next step, select a Time-Dependent study. These attributes are automatically created and updated by this feature. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for In other words, the key is what T is for COMSOL (I mean for COMSOL running your model). In the latest version of COMSOL Multiphysics, version 5. initial value for stationary and time dependent solver. The idea is that the scaling brings the variable to roughly 1 unit--Good luck The default behavior of the COMSOL ® software is to assume a different scaling for each set of variables in your model. If it's the Interpolated setting, then the expected input is the value of the parameter under "Values of Dependent Variables " ( see attached files) - Initial values of variables solved for - Values of variables not solved for Attachments: solver_uses_last_solution. The Initial values of variables solved for settings have no effect when using the eigenvalue solver. So, if the Analysis (for the solver sequence) Use user-controlled values of variables not solved for. Look at it as a programming function, any name within the Normally Comsol has a good internal algorithm to estimate the scaling values so 99% of the time I do not bother to use manual scaling. The beginning and end of the phases are controlled by the "event" physics and depend on the value of a variable. This can be used to allow other initial value expressions to depend on a dependent variable’s expression. Posted Mar 9, 2015, 9:35 a. By default this plots the initial values of the variables solved for as specified by the Field subnode under a Dependent Variables node for the first study step in the solver configuration. The exact distance, D, to the closest wall can be found by solving the Eikonal equation: |\nabla D|=1. Select the Plot check box to allow plotting of results while solving in the Graphics window. there you can force the lowest value the variable can get and if it goes below that value solver automatically overrides it with the limit you have defined. Enter the: Field variable name (the dependent variable). In the Equationsection, the mathematical equations applica See Values of Dependent Variables above for details about the settings for controlling the values of the dependent variables that you solve for or exclude from the solvers. Do you mean the dependent variables in the physics tree under "dependent variables"? If so, I was talking about the variables I can define under the definitions node. In Mode Analysis node, I check "initial values of variables solved for", then And under the frequency domain solver, the Values of Dependent variables were taken from the static solution, at least I think I am doing it so. All dependent variables in a physics interface must have a unique identifier (or reference tag) within an interface. EDT Materials, Modeling Tools & Definitions, Parameters, Variables, & Functions, Studies & Solvers 0 Replies . solid. Note that the Study Settings section is empty if there is no Include geometric nonlinearity check box or Parameter list method list. COMSOL Multiphysics solves for a modified version of the Eikonal equation, where the To make the initial values available for results evaluation and plotting, right-click the Study node (), and select Get Initial Value (). However, due to numerics, I obtain values larger than this maximum value which is unrealistic. (there is also the glossary on the main In more specific terms, I'm trying to implement the vector wave equation in 3D using the coefficient form PDE. If the window. This will remember the largest value of the material So i asume that a good solution wuould be to compute these predifined variables once and store its value in the stored solution with the tempreture field and the others dependent variables, but i haven't found a way to do this. something and mod2. The Model Builder tree appears as follows: 2)Values of dependent variables Initial values of variables solved for : Physics controlled Values of variables not solved for : Physics controlled Step 3 1) Model configuration for study step Bolt pretension : Enable Heat transfer-thermal expansion : Enable Service load : Disable 2)Values of dependent variables Initial values of variables I am trying to run a 1d stationary simulation of heat transfer through a slab and wish to define a value of thermal conductivity that is dependent on temperature. I need to get a value of dependent variable w. If this field is part of a physics for which a Model Reduction node is computing a reduced model that include reduction, Thank you Ivar, I'm doing what you have suggested and it works well. Bz values (i. If you are solving a heat problem, T is usually the name of the dependent variable (you can check that in the physics node, The default initial value for the Heat Transfer in Solids physics interface is 293. A screenshot of the COMSOL Multiphysics UI showing the settings for the sample model's Inlet boundary condition. 4 "global" meant non-adscribed particularly to any geometrical Hi, If you switch to a segregated solver (choose Segregated from a Stationary Solver node, for example, you can then add Lower Limit and Upper Limit subnodes to limit the values of field variables (dependent variables) in the model. The settings for the Time Dependent study step node, which uses the initial values computed from the previous stationary study. In this article, we discuss the importance of scaling for a model and how to manually set the scaling of dependent variables. I am an absolute beginner at COMSOL Multiphysics and I am trying to model the effect of the movement of soil on a steel pipeline buried in it. - Boundaries: 1,3,4,32 - I looked at other forums and tried to change boundary conditions, yet this didn't seem to change anything. + Electrostatics data is transferred into the same module via 'values of variables not solved for' option in transient solver. Then use the Method list to specify how to compute the initial values of In the solver configuration of the second study, solver configurations -- > solver 1 -- > dependent variables -- > initial values of variables solved for and values of variables not solved for: I set the Method to Solution, and solution field to : solution 1 (using the solution from study 1), then compute and get the final deformation 1. The correct approach is to modify the solver settings so that the state variable is not solved for in the second study, That is, deselect the Solve for this field checkbox for the state variable node under Dependent Variables. 03. 5, you can add Lower Limit and Upper Limit nodes to limit the values of the dependent variables when using a segregated solver. 5), which I've solved 2D PDE problem and I've got distribution field of the dependent variable (_u_). If you clear the Solve for check box, any equations and dependent variables To plot and evaluate the initial values for the dependent variables, right-click the Dependent Variables node and choose Compute to Selected or click the button on the toolbar (this is similar to the Get Initial Value option for the main Study nodes). Best regards, Magnus Ringh @Magnus Thank you very much for the prompt reply. In the uploaded images you can see information 1, information 2 . This setup requires that the Values of Dependent Variables section in the settings for the Time Dependent study step are set to refer to the results of the stationary study, as shown in the screenshot below. How to set the Values of dependent variables. Thank You In COMSOL Multiphysics, by convention, the force acting on the model or the flux into the model is specified. This worked for me When computing and plotting the gradients of two dependent variables (temperature and alpha) x time in a simulation of an axisymmetric geometry, the results show extremelly high values for both gradients in a very locallized region, around a boundary point (top-right), as shown in animations 1 and 2 attached, even though the surface maps of the Handle initial data and scaling for variables solved, as well as how variables not solved for are computed. I am choosing fields whose solutions depend on a specific lam0 value) for input as 'initial values' and 'values not solved for', under the Values of Dependent Variables menu. EDT Studies & Solvers Version 4. e. Submit feedback about this page or contact support here. My confusion also arises due to the fact that that I haven't added any dependent variables on the boundaries. 1, Version 4. 3a. I obtain results and they seem correct but I am not sure of my implementation. You can choose to not solve for one or more of the multiphysics couplings by clearing the check box in the Solve for column (by default, a study step solves for all coupling features that recognize the study type). You can choose to not solve for one or more of the multiphysics couplings by clicking the button in the Solve for column (by default, a study solves for all physics interfaces). Apart from that what I would like to do is the following: I would like to solve the problem with a certain initial condition for the variable which the time dependent study solves for, and that I would like to use the solution I obtained as the inital condition for the time dependent study, in order to see if the Select the Dependent variable quantity that defines the unit for the dependent variable u. I have to get the values of phi1 at boundary 1 with function of time. Since COMSOL needs an initial guess to determine a solution at the stationary solver (at least for How could I define a dependant variable in comsol a specific quantity like Displacment or displacment e. 2, if any? Sherif hello Duanhui, please check the mesh quality and initial values before computing. 4 Replies Last Post Mar 10, 2011, 5:41 a. For example, for the original dependent variable phi_PDE=mpheval(model,'phi','dataset','dset1','Edim','domain','Selection','sel1'); The result is 3) Now set these settings => Study 1 > Solver Configurations > Dependent Variables: Initial Values of Variables Solved For > Method: Initial Expression, Solution: Solver 1, Time: Automatic Initial Values of Variables Not Solved For > Method: Initial Expression, Solution: Solver 1, Time: Automatic 4) Solve your model. EDT Battery Design, Parameters, Variables, & Functions Version 4. There is also detailed information in the Physics and Variables Selection and Values of Dependent Variables sections. goo luck, Mohammad I can plot in terms of the simulation's dependent variables, but not in terms of variables that are defined in terms of the dependent variables. The Multiphysics couplings column contains the names of all multiphysics couplings in the model. The default is to use results from the previous study as initial conditions. I have tried calling the last value of the dependent variable through prev(u2(dx1),1) but haven't been successful. The expressions for lower and upper limits do not have to be constants but are required to evaluate to real values. If you start using parametric sweeps, you should look at the setval I tried defining a local variable, B_surf, along the boundary I am interested using the mf. If scaling is choosen "automatic", comsol will not know anything about high temperatures in the time-domain and will probably set the scaling factor at around 300K. Click the Update Variables button in the toolbar to refresh the dependent variable list, which might be useful if you need to manually The Dependent Variables node handles initial data and scaling for the dependent variables that you solve for as well as how to compute dependent variables not solved for. How can I write the expression for it? for example, in 1D phi1 and phi2 are dependent variables and function of both(x,t) in subdomain 1 containing 2 boundaries. For example, the first component of the spatial, material, and geometry frame gradients of u are, respectively d(u The following dependent variables are not coupled to all degrees of freedoms in the model: comp1. Then select what to plot from the Plot group list and, for time dependent simulations, at which time steps to update the plot: the output times or the time steps taken by the solver. I need to pass one neff from one iteration to the next as an initial value. I typically use the COMSOL default value for a model that I do not But I need to confine the value of the dependent variable into a range, which can be defined by a piecewise function. This node is available as a subnode for the Internal Electrode Surface and Electrode-Electrolyte Boundary Interface . 8 was selected. If they are from 2 different models, you must add mod1. something. Ivar KJELBERG COMSOL Multiphysics(r) fan If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. Send Private Message The comsol doesn't let me have same variable in both of them. When I select User controlled for the initial values in Step 1, Comsol complains that the solution is not calculated yet. First, This will evaluate expr using the results from the solution with tag sol_tag for the values of the dependent variables (such as mfnc. Posted Oct 24, 2013, 9:28 p. 2011, 11:55 UTC−4 Battery Design, Parameters, Variables, & Functions Version 4. Value of dependent variable at a point as boundary condition at another edge. The only difference is how the node is treated in study step settings: a node under Definitions can be Hello, I am currently dealing withabout the storage of time steps in time-dependent simulations. 002,0. The default initial value for the Heat Transfer in Solids physics interface is 293. -----Henrik Sönnerlind Hello COMSOL community, Attached is a bidomain model representing heart tissue that we are developing. The node is not available if no adsorbing-desorbing species are present in the parent node. The methods are In this article, we discuss the importance of scaling for a model and how to manually set the scaling of dependent variables. Thank you . The variable will get a “physics scope” although the dependent variable itself has a “component scope”. That helped. A dependent variable needs an initial value for nonlinear and transient simulations. Then the concentration is a dependent field variable so when you write "c" you write in fact c(x,y,z) or even c(x,y,z,t) over the defined Boundary (surface in 3D) or Domain (volume in 3D) Hello COMSOL community, Attached is a bidomain model representing heart tissue that we are developing. Each DOF is given a unique name, which can be used anywhere in equations and variable definitions. But be sure you take global values, or that they can point back to a identical geometry & topology if you mix models and connect fields. Use the Set Variables subnode to Plasticity, Pressure-Dependent Plasticity, Porous Plasticity, Soil Plasticity, Concrete, Rocks, or Elastoplastic Soil Material, in order to reset plasticity variables according to a Setting condition that you define. Select a Time unit from the list (default: s) to use a time unit that is convenient for the time span of the simulation. Add a Global Dependent Variables node ()under Global Definitions > Equation Contributions to declare one or more global scalar degrees of freedom, or DOFs. I tried setting "Parameter value (A)" to "All" or "Automatic" but it seems that in both cases only the results of the last value of A You can switch to a segregated solver and use "lower limit" option provided. You can see the equation for any physics node in your model by selecting the respective node and in the Settings window, expanding the Equationsection. Posted 07. g suppose we have dependent variable u(x,y,t) and I want this dependant variable to be displacment. The new value of an auxiliary dependent variable may be defined To plot and evaluate the initial values for the dependent variables, right-click the Dependent Variables node and choose Compute to Selected or click the button in the toolbar (this is similar to the Get Initial Value option for the main Study nodes). so, How can I solve this?! how can I relate the T2 to T?! Thanks a lot Select a Time unit from the list (default: s) to use a time unit that is convenient for the time span of the simulation. Variables can also depend on dependent variables (the solution) and their derivatives, and they can have units. So following the built in tutorial, I I am using the values of a dependent variable 'phi' and its derivative in Matlab. Then in Variables name Vup and in Expression field V[V] were inserted. The default is 0. I am using variables that change during simulation and are used as input for forces on the mechanical part. I am trying to use the Soil Plasticity Criterion but as the tutorial describes, It needs to be given Initial values. Thanks, Waranatha. To achieve this, choose User controlled under Initial values of variables solved for, then choose Solution for the Method option, and then choose the best solution from the Study list, as shown The Multiphysics couplings column contains the names of all multiphysics couplings in the model. When solving for some physical quantity, u, COMSOL Multiphysics always stores the solution for a fixed set of mesh nodes. The methods are applied for the dependent variables present as Field or State subattributes. The default is Dimensionless (with 1 in the Unit column). Please login with a confirmed email address But in many cases both sets of derivative variables exist even if they are not used by the physics interface. The Settings window for the Current Conservation node, wherein the Equation section has been expanded. This is referred to as inconsistent initial values. I am using this in my problem for continously decreasing unreal concentration values and it is working pretty fine. So, is it possible to change the value of the dependent variable (defined using a function) at the end of each time step, so that the variable remains in the desired range? How do I implement this in comsol?. If you choose Property dependent, you can choose to zero out some components for specific values of some property values. where D=0 on selected walls and \nabla D\cdot n=0 on other boundaries. PST Low-Frequency Electromagnetics, Fluid & Heat, Computational Fluid Dynamics (CFD) Version 4. The methods are applicable to the dependent variables present as Field subnodes () under the Dependent Variables node. For each row in the table of property values, choose Zero out-of-plane , Zero in-plane , Keep all components or Explicit from the list under Components to zero out for the corresponding property value under Property value . In my model, charging and uncharging processes occur. Use state variables to, for example, store the previous-step value of some expression. This will also help me ploting predefined variables as they take a lot more time than the dependent variables to plot Initial Values for Dissolving-Depositing Species The node sets the initial values for the dissolving-depositing surface concentrations dependent variables. Table 6-74: Valid Variable Subattribute Field/State Properties. For some reason, the numbers of nodes are different between the original dependent variable and its derivative. It seems that prior to COMSOL v. therefore COMSOL scales all variables (check the solver log) before starting to mix the matrixes and to I believe Ivar refers to: study -> step 1 -> "values of dependent variables". I attempted to define the thermal conductivity as a global variable, but the expression is in orange and is coming up as an "Unknown function or operator" when assigned to the material, as shown in the attachments. To make the initial values available for results evaluation and plotting, right-click the Study node (), and select Get Initial Value (). States are dependent variables in the model and stored as such in solutions, but they are explicitly updated by the solver after each converged time or parameter step rather than solved for in the usual sense. I am obtaining neff of a waveguide at different frequencies say 10 or 20 frequencies (dispersion graph) . here step 1 is where you define the overall setting of the solver like "stationary", "time dependent", etc Maybe you have another comsol version than I do? if Similarly, to specify the values of dependent variables that you do not solve for, select User controlled from the Settings list under Values of variables not solved for. nu'). By default, the COMSOL Multiphysics software determines these values heuristically depending on the physics as, To specify the initial values of the dependent variables that you solve for, select User controlled from the Settings list. These initial values are handled in the same way as for other dependent variables, depending on study and solver settings. The Field node name matches the name of the variable. Initial time Step 1: Time Dependent 1 In the Settings window for Time Dependent, locate the Study Settings section. 1E9 [Pa] sized items with 1E-6 [m] sizes you might easily get numerical overflows/underflows. However, if we create a vector-valued system of equations, then we can use Field name as a reference for a vector of dependent variables. PNG I am wondering if COMSOL allow us to calculate the value of a dependent variable at a point at which I calculated the maximum value of another variable. Alternately, you can import variable definitions from a text file. If you still need help with COMSOL and have an on-subscription license, please visit our Support Add a Dependent Variable Field node under Definitions > Equation Contributions in a model component to declare a scalar or vector dependent variable field on a selection. How to define a maximum value for a dependent variable? Posted 11 avr. From a physical point of view, the absolute value of the dependent variables are often of less interest, but the existence of a single, unique, solution is essential for some solvers. 2a 0 Replies . 5), which The value will be small when the object is far away from the respective walls and larger when closer. How to assign different values to dependent variables. Is this the right syntax If you still need help with COMSOL and have an on-subscription Dear COMSOL users, I'm a student and attempting a RF system in combination with a DC magnetic field. You need to take initial values from User Controlled-> Initial Expression in the second study. r. In Variables 2a, Boundary level was chosen and boundary No. Send Private Message Flag post as spam. I tried setting "Parameter value (A)" to "All" or "Automatic" but it seems that in both cases only the results of the last value of A If the variable is not solved for, its value is determined by the settings in the Values of Variables Not Solved For section of the parent Dependent Variables node. Ertan Agar Note that while COMSOL employees may participate in the discussion forum, Check the solver node: Dependent variables and the associated Help and/or DOC "Initial variables Solved For" Try using some of the COMSOL internal combined solver cases as shown herebelow for solid There is NO restriction that both solver cases must be under the SAME study--Good luck Ivar Hello Everybody. That is, the dependent variable u is treated internally as a function of the mesh coordinates and possibly time, u (X m, Y m, t). 2 2 Replies . I am using the General Form PDE mode to solve for a dependent variable, u. If you clear the Solve for check box, any equations and dependent variables Note: This discussion is about an older version of the COMSOL Multiphysics How to define a maximum value for a dependent variable? Posted 11 avr. This node does not make the interface add any shape functions for this variable, it just declares that a dependent variable exists. It is also possible to change the value of an auxiliary dependent variable discontinuously when a particle interacts with a boundary by entering an expression for the new value in the New Value of Auxiliary Dependent Variables section of the settings window for the Wall node. After every 6s of execution I need to reset the dependent variables to their initial values. Further a new geometry interval with new initial value and BC has to be added to the model for to the second study. Now I need global function that should use solution _u_ as a function of boundary, edges, points) and geometrical Objects (volume surfaces lines vertex/points) in the COMSOL doc or on theforum. I’m using comsol 4. A. Please login with a confirmed email address P1/S2 should start with the dependent variables at the last time-point of P1/S1 as initial values, and carry over the values at each frequency step, P2/S1 should carry over the end values of P1/S2 and so on. 15 K, For more information on the scaling of variables, you can check out the Scaling of Variables and Equations and Dependent Variables sections in the COMSOL Multiphysics Reference Manual. 2 In the Output times text field, type range(0. Then specify the time interval for the output from the simulation in the Times field using the selected time unit. Any advice would be greatly appreciated. The Moving Mesh interface itself is also excluded, but instead there is a special entry with the same name for controlling the mesh Note: This discussion is about an older version of the COMSOL Multiphysics How to define a maximum value for a dependent variable? Posted Apr 11, 2011, 11:55 a. But I'm struggling to set this up in COMSOL. Generally I know that a parameter is a fixed value and a variable can change. How to Evaluate Dependent Variable at Different Position ? Posted Jan and with offset {0+dx1,L-dx2}, respectively. Variables representing the first and second time derivatives of the DOFs are optionally generated by appending t and Hello COMSOL community, Attached is a bidomain model representing heart tissue that we are developing. That is correct. the variable names in COMSOL functions are dummy names, and not linked to the main physics, as interpolation functions was one time set up for time signals, "t" was used, but you can call it with any variable. Click the Select Dependent Variable Quantity button to open the Physical Quantity dialog box to browse to find a physical quantity to use. Dear COMSOL Users, I am trying to use results of a stationary study as initial values for a time-dependent one. Then specify an Update expression for each state variable, if Update is not set to Only initialization. I'm new to the comsol environment and still haven't found this method in the user guide. please check those and for your reference i have attached the image where it says "Failed to find consistent initial values". Click the Update Variables button on the toolbar to refresh the dependent variable list, which might be useful if you need to manually In COMSOL Multiphysics ®, you can see the underlying governing equations for the physics in a model, as well as the definitions of the variables. If I do this in MATLAB using euler method, I can easily add an if statement and change the values of x and y used for the next step. Then in such a case, the solution of the current step has nothing to do with the solution of the preceding step under the same study? This is referred to as inconsistent initial values. 3 Click to expand the The Dependent Variables node handles initial data and scaling for the dependent variables that you solve for as well as how to compute dependent variables not solved for. The formula applies to an element of size dx,dy,dz (in 3D). Ertan Agar . 7). As in the uploaded mph file the mesh quality is not good enough. + Electrostatics data is employed in an auxiliary dependent variable to define particle charging. This setup requires that the Values of Dependent Variables section The node sets the initial values for the surface coverage of adsorbing-desorbing species dependent variables. This enables you to: See how the variables are calculated by the software; See the names A Dependent Variable Declaration node declares a dependent variable (field variable) used by the physics interface. Right now, I am manually choosing fields from Study 1 (ie. You can type a monotonically increasing list of individual values, for example, 0 1 2 5 10 20; use the range operator, for example, range(0,0. You can also type a search string in the text field at the top of the dialog box and then click the While I agree that the scaling value does not affect the final result, I have also found that a good scaling value can dramatically affect the convergence rate, and in come cases, whether you can get a solution at all due to divergence of the solution for bad scaling values. On This Page: Reference Files for Download: Enter state variable names in the State column and corresponding initialization expressions in the Initial value column. And that would bring my second question, regarding the time dependent solvers. choose solver at the time dependent solver, afterwards select dependent variables, u can set the input parameters from another solver. The model setup for our example in the software, with the settings The Dependent Variables node handles initial data and scaling for the dependent variables that you solve for as well as how to compute dependent variables not solved for. The chemical reaction rates Define the name and properties of the auxiliary dependent variable. I have attached the model file with this post. For example, a variable can be defined as @ Lasse you said for diffusion you have two variable c1 and c2. Since COMSOL needs an initial guess to determine a solution at the stationary solver (at least for the iterative solver), I suppose that it would require an initial guess for every time step, in case we are using a time-dependent solver. The default is rp and can be changed to anything provided it does not conflict with the name of the variables for the position or momentum degrees of freedom. Then I have configured my material as: However I'm confused on how to introduce the reset equations to the system when the condition is satisfied. Property + Fluid flow data is transferred into particle tracking module using an interpolation function. leaja cflno xji burht pxomd nxsyec mhekt hfrbhxhv befqbu roostj