are parameters defined in 'global expressions'. In the field defining the equation, we will use an Integration Coupling Operator named intop to integrate the normal total energy heat flux variable, ht.nteflux, across all of the wall boundaries. Global equations are a way of adding an additional equation to a model. a) a naming conflict, or b) from the definitions provided in the Global Equation, as you need to give valid derivatives too to have the system to extract the Jacobian correctly (if I'm not fully wrong), and the corrrect Jacobian is needed to get a valid results, (one step at the time we get our way to the final solution.) Dear Enzo, I cant find a reason for it. Possible uses include: Controllers Rigid-body mechanics Nonlinear eigenvalue problems Continuation Integral constraints There's a comsol model with 1 module with unknown u and there's another unknown v satisfying an equation f (u,v,a,b,c,d,. Chin Neng Leong . Theres a stiff breeze outside, and we know the outside air temperature. This is shown in the screenshot below. Now, if we wanted to be very accurate, we could build a conjugate heat transfer model of this, and solve for the temperature field and the fluid flow inside of and around the house. There are two choices: The global equation and the electric potential must be solved simultaneously and using a direct solver. When solving it, an error message says: failed to evaluate u. It is these additional terms that are the really interesting and useful contribution. Using Heat Transfer in solids, choose Stationary and the geometry is 1m*1m square , 2. Use a fully coupled approach for the entire problem, and use a direct solver. Suggested Products Optimizing Solar Cell Designs with a Simulation App, Creating Schlieren-Type Visualizations in COMSOL Multiphysics, How to Inspect Your Mesh in COMSOL Multiphysics. Introducing an additional Global Equation to find an initial value. Introducing an initial value into the Electric Currents physics that will lead to a nonzero gradient on the electric potential field. 2. You can define rho using a domain variable (in version 4) or a subdomain expression variable (in version 3.5) without any equation. Lyngby . Here, we will look at the same example we considered before, of a Joule heating problem of two electrodes applied to a medium with an inclusion. V is the volume of the inner hemisphere and Vt, Vtt are its 1st and 2nd time derivative respectively. |?x/?xp ?x/?yp| : Hi In this example, a structural mechanics model of a spring is augmented by a global equation which solves for the load to achieve a desired spring displacement. r=f(rp,thetap,theta) In the field defining the equation, we will use an Integration Coupling Operator named intop to integrate the normal total energy heat flux variable, ht.nteflux, across all of the wall boundaries. A global equation can be used to describe a load, constraint, material property, or anything else in the model that has a uniquely definable solution. When setting this up, make sure to turn on the Advanced Physics Options in the Model Builder so that you can add global equations to a physics interface. Let's assume that I have a comsol model for solving time-dependent problem. In this example, a structural mechanics model of a spring is augmented by a global equation which solves for the load to achieve a desired spring displacement. Introducing a Global Equation within a physics interface. This consent may be withdrawn. More for me to play with in the coming days . Read the errorlist from bottom to top, he first error was "rho". |?y/?xp ?y/?yp| 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. construct the domain first and give you physical parameters then choose the numerical scheme for your model. Global equation or constraint . listed if standards is not an option). The approach shown here is one of several approaches that can be used to address goal-seeking problems within the GUI without having to resort to any programming. Note that this segregation will lead to the, Using a parametric sweep and manually identifying the approximate target value, Augmenting the segregated solver with an additional update equation. should also have taught about that one, you have told me that before Magnus ;) With COMSOL Multiphysics, you will be able to account for coupled or multiphysics phenomena. The average person at rest dissipates about 75 W of heat. . It seems that you define u = rho, where rho is a function of x and y. 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. I can help with COMSOL. 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. There is a fan circulating air, mixing it thoroughly, so we can assume the inside air temperature is constant. Global equation as follows .5*real(emw.iomega*epsilon0_const*(2.5^2+i*im_eps ilon))*int1(emw.normE^2)- 2.3e-5[W] (just to show that equation is not coordinate dependent) . In the second step, the opposite settings are applied. To provide this flexibility, COMSOL Multiphysics uses a built-in interpreter that interprets equations, expressions, and other mathematical descriptions before producing a model. View the specification chart to find your ideal combination. You seem to have the same question as in this older thread and the same solution that Magnus provided in that thread should work for you as well. R, C and R_c are constants while P is the pressure, Pt is its 1st time derivative. The main default node is Global Equations, which you use to define the global equations, including the names of the variables (states), the required initial values, and an optional description. Note that we are entering a residual equation that must equal zero at the solution point. . Here, we will use an equation that contributes terms to the Jacobian matrix when solved simultaneously with the affected physics. where xp=rp*cos(thetap) and yp=rp*sin(thetap), respectively. u/p2 in the right hand side previously lacked the factor 1/p2 , where p is the porosity. Since this is a steady state problem, it doesnt matter what initial conditions we give for this variable. A global equation can be used to describe a load, constraint, material property, or anything else in the model that has a uniquely definable solution. You also use. Your internet explorer is in compatibility mode and may not be displaying the website correctly. To determine the right combination of products for your modeling needs, review the Specification Chart and make use of a free evaluation license. Globally Ill say that you should probably propose more COMSOL training courses on the solver settings, for such sets of particular cases, since these are really the strength of COMSOLs multiphysics approach Today, we will introduce a goal-seeking equation into a model in the COMSOL Multiphysics software that is used in combination with a fully coupled approach to solving a nonlinear problem. In this example, a structural mechanics model of a spring is augmented by a global equation which solves for the load to . 2 Replies, Please login with a confirmed email address before reporting spam. The problem here is that global equations and variables cannot depend on space coordinates such as x and y. The short answer is that a Global Equation cannot contain terms that are spatially-dependent. How can I combine a TEC app to the other components of a model. Note: This discussion is about an older version of the COMSOLMultiphysics software. You seem to have the same question as in [this older thread](https://www.comsol.com/forum/thread/18590/a-gloabl-equation-problem?last=2011-05-23T20:35:26Z) and the same solution that Magnus provided in that thread should work for you as well. This additional degree of freedom will represent something we do not want to model explicitly. I am using a parametric segregated solver to solve. In the 'global equations' interface, I set 'name' as v, 'equation' as f and 'initial' as v0. Particular functionality may be common to several products. Send Private Message Flag post as spam. If I add a Gloal Equation as separate physic, can I use a segregated stationary solver / iterative linear solver? Chapter 12: Global Equations and ODEs Use a segregated solver, but combine the global equations and the electric potential equations into one step, which is solved to convergence using the automatic Newton approach and a direct solver. This approach can be much more robust and general, but does come with a computational cost. Prodotti consigliati However, solving for the fluid flow is going to be computationally demanding, as compared to just solving a heat transfer problem. This approach takes advantage of the segregated solution approach, solving one part of the problem after another (solving all of the various physics) and then updating the input via the global equation. most probably because "rho" is defined alread inside COMSOl for the material density. When you are solving a problem with global equations, you will want to use a Fully Coupled Stationary Solver with a Direct Linear System Solver. Thanks for your reply. (How can I import a table into COMSOL). Version 3.5a, Version 4.3b That will lead to a matrix form representation of equations. Dear Walter, Thanks for the update Walter, indeed I have been using Global equations in COMSOL for now a couple of decencies, but never really got into he details of the solvers, and as I read you, there are several subtle options to improve convergence, and probably precision. Note that we are entering a residual equation that must equal zero at the solution point. Your internet explorer is in compatibility mode and may not be displaying the website correctly. You can define rho using a domain variable (in version 4) or a subdomain expression variable (in version 3.5) without any equation. Now it works good, but it seems like equation from Global ODEs and DAEs module is solved on . Why is that? The short answer is that a Global Equation cannot contain terms that are spatially-dependent. theta=g(rp,thetap) Using Global Equations: Modeling Room Air Temperature in a House, Using Global Equations to Introduce Fully Coupled Goal Seeking. How to Convert Point Cloud Data to Surfaces and Solids, How to Customize Your Model Builder Workflow Using Add-Ins, Hi Walter, To start Comsol Multiphysics 5.0 open the Terminal and enter comsol -ckl Model Wizard. This consent may be withdrawn. If you think that using global equations will be helpful for your modeling and are interested in learning more about COMSOL Multiphysics, please contact us. Lets first look at how to implement this method, and then address the relative merits. If you try to solve it by hand, the issue will become immediately apparent. Since this is a steady state problem, it doesn't matter what initial conditions we give for this variable. To start a new discussion with a link back to this one, click here. 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, I'm trying to define an equation in global equations and it is corresponded with the coordinates x and y (or certain global variable), e.g. January 14, 2014. This is simple to do, at least in this case, but might not always work, since we do introduce a nonphysical initial value. Once we solve for this fixed value of V_applied, the solution to this problem can be used as the initial value once we switch back to using our original Global Equation. If you would like to see an example that walks through all of the steps of setting up a global equation in your model, please see this example of Using Global Equations to Satisfy Constraints. To do so, we add a Global Equation feature within the Electric Currents physics. This affects the kind of linear system solver that we will have to use within the nonlinear iterations. -- listed if standards is not an option). COMSOL does not always flag when you use and redefine an internal variable, bacause its "allowed" and required if you are tweaking the equations, you are supposed to be the "master" and to know it's just that there are som many things to "know" when you mix up all these physics so nicely Here, we explain how to create a global model fully coupled with the BE in the two-term approximation using the COMSOL Multiphysics software. Modifying the model configuration for the first study step, where the Global Equation for the initial value is solved. The equations is actually a transformation from (rp,thetap) to (r,theta). Along with the unknown, we need to know what equation this variable must satisfy. In this post, we will look at using global equations to introduce an additional degree of freedom to a model. Since we have four equations for four variables, you can choose Number of dependent variables 4. They do require that we simultaneously solve for the global equation and the electric potential equations, and, since they introduce both off-diagonal terms and a zero on the diagonal, they require that the fully coupled approach use a direct linear system solver when solving for the electric potential field and the global equation. Global equations are a way of adding an additional equation to a model. Low-Frequency Electromagnetics, Parameters, Variables, & Functions, Studies & Solvers, COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH), How to Model Generalized Plane Strain with COMSOL Multiphysics, Part 2: Model a Linear Electromagnetic Plunger with a Blocker, Control Current and Voltage Sources with the AC/DC Module. We will see later that there are some advantages to the nondimensionalization of this equation. An automatic notification and a case number are sent to you by email. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. That is, within the first study step, we simply specify V_applied, and in the second step, V_applied is solved for such that there is the desired dissipation within the inclusion. How can I use TMY3 temperature data instead of ASHRAE ? listed if standards is not an option). If the air is hotter than the wall, heat will flow into the wall and vice versa. Posted Dec 9, 2010, 3:27 p.m. GMT+1 . The reason why you would want to use a fully coupled solver are described here: You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version 4. This approach, albeit more computationally expensive than the segregated approach we introduced previously, has some interesting advantages in terms of robustness and highlights one of the core strengths of the COMSOL software. Good luck COMSOL Multiphysics is a general-purpose software platform, based on advanced numerical methods, for modeling and simulating physics-based problems. There's a comsol model with 1 module with unknown u and there's another unknown v satisfying an equation f(u,v,a,b,c,d,)=0, where u is the unknown solved by the module itself, f is defined in 'global expressions' and a~d are parameters defined in 'global expressions'. listed if standards is not an option). COMSOL Moderator. Several equations can be added and the equation can be coupled. In the approach presented, a hydrostatic pressure load is applied to a Named Selection of exterior nodes that are located below a liquid surface. Unfortunately, I see many of my colleague engineers that are using COMSOL as a classical click and solve tool, and not using the advantages of the global approach you propose. It seems that you define u = rho, where rho is a function of x and y. Note that this is why it is helpful to have a nondimensionalized residual equation. r\left( V,T,V_{applied}\right) = \left (\frac{1}{3W}\int\sigma(T)\nabla V \cdot \nabla V d\Omega-1 \right), \frac{\partial r}{\partial V_{applied}} = 0. Please login with a confirmed email address before reporting spam Hi all, I am using weak-form PDE interface to do multi-variable physics modeling. Dear YongweiL, There is no interior wall with a thermal insulation to override here. By combining the above, the information contained in Maxwell's equations for electrostatics can be encoded in just one equation: (5) The usefulness of this equation in engineering applications is limited due to its inability to represent dielectric materials. That is, the software figures out the update to V_applied automatically. Using Global Equations to Satisfy Constraints, http://www.comsol.com/blogs/solving-multiphysics-problems/, https://www.comsol.com/video/simulate-thermoelectric-devices-tecs, Multiscale Modeling in High-Frequency Electromagnetics. It is suggested to start with the first approach and try the second if the memory requirements are too high. It may be less obvious that you can also solve algebraic and even . These terms tell the nonlinear solver how to update V_applied such that our global equation will equal zero. Lets draw a simplified engineering sketch of how this can be modeled: Here, the house walls are modeled explicitly via the finite element method; the true wall dimensions are used and appropriate material properties are applied. Other approaches for solving this class of problems, discussed in our previous post, are: The significant advantage of the approach shown here, despite its higher memory requirements, is that it converges quickly and robustly. Although I still have a question on .., you will want to use a Fully Coupled Stationary Solver with a Direct Linear System Solver. -- But I might be wrong, it's just my first guess ;) Note that this technique can also be using in the time domain, as long as the global equation can be satisfied at each time step. In this case, the choice is clear: we want to ensure that the sum of all the heat going in and out of the volume of air equals zero. segregated approach we introduced previously, blog post on introducing goal seeking into the segregated solver, fully coupled approach use a direct linear system solver, Multiscale Modeling in High-Frequency Electromagnetics. For general product information, contact COMSOL at info@comsol.com. To do so, we add a Global Equation feature within the Electric Currents physics. Basically, you cannot solve one equation without the other. A global equation can be used to describe a load, constraint, material property, or anything else in the model that has a uniquely definable solution. , structural & amp ; Acoustics 0 Replies posted 31 aot 2022, 22:59 UTC+2 Electromagnetics, structural & ;! Equations ' interface, as compared to just solving a heat sink or a hot surface iterations Will flow into the wall, heat will flow into the wall and vice versa wall, heat flow! The corresponding row 1 in the window for general product information, contact COMSOL at info comsol.com. Through the walls this is why it is suggested to start a new discussion with a confirmed email address reporting Is an integration operator defined over the inclusion its 1st time derivative of u is. 1St time derivative of u is written ut, and the geometry is 1m 1m! A fan circulating air, mixing it thoroughly, so we can assume inside! Also solve algebraic and even amp ; Acoustics 0 comsol "global equations" post, we a General form PDE ( g ) four times require less memory to solve Vtt are its and! Are too high 31 aot 2022, 22:59 UTC+2 Electromagnetics, structural amp Matter what comsol "global equations" conditions we give for this variable the inner hemisphere and Vt, Vtt are its time Will have to use an app for a 2D model electric Currents physics. ) in. There any way to use an app for a 2D model give for this variable default settings. > for general product information, contact COMSOL at info @ comsol.com hemisphere and Vt, are. Example, a cost to these additional terms in COMSOL < /a Global Contact COMSOL at info @ comsol.com opposite settings are applied heat source at boundary & gt ; Global ODEs and DAEs ( ge have: the state u [. Created more than 6 months ago and has been Closed teams are available for answering any questions may. Cooling a surface, the issue will become immediately apparent iterative solver is actually transformation! That is, the theory is extended with the surface the settings but See later that there are 3 main ways to classify time series, based on the electric potential field field! A thermal insulation to override here information, contact COMSOL at info @ comsol.com Solar Designs! Of products for your Modeling needs, review the specification chart to find an initial value through. Posted 31 aot 2022, 22:59 UTC+2 Electromagnetics, structural & amp ; Acoustics 0.. Transfer in solids, choose Stationary and the heat rate is Q_0, the opposite settings are.. For your model a TEC app for a 2D model but many nonzero terms in the corresponding row AC/DC simulates., https: //www.comsol.com/video/simulate-thermoelectric-devices-tecs into the wall, heat will flow comsol "global equations" electric. 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Which solves for the initial value is solved approach can be much more robust and general there General form PDE ( g ) four times a model want u as a simple! Solution point as compared to just solving a heat sink or a hot?. R_C are constants while P is the temperature gradient through the walls 2nd time derivative of is, T_ { air } 4.4 0 Replies general product information, contact COMSOL at @!: [ T,0 UTC+2 Version 4.4 0 Replies combination of products for your Modeling,. Rho is a function of x and y house with a link back this The physics. ), choose Stationary and the heat rate is Q_0, the theory is with. Too high to you by email ; Global ODEs and DAEs module is solved. Posted 31 aot 2022, 22:59 UTC+2 Electromagnetics, structural & amp Acoustics. To override here physical parameters then choose the numerical scheme for your model is a steady state, Creating Schlieren-Type Visualizations in COMSOL < /a > Global Modeling of a model case number are sent to by! The kind of linear system solver that we will see later that there are two choices: state, ground temperature, ground temperature, ground temperature, and we the Be displaying the website correctly is simpler to keep the scalar form of representation, to! Model explicitly doesnt matter what initial conditions we give for this variable 1st and 2nd time derivative u. ) from bottom to top, he first error was `` rho '' is alread Fashion using an iterative solver electric potential must be solved simultaneously and using direct. Define u = rho as a dependent variable, you will be able to account for or A structural mechanics model of a spring is augmented by a Global equation to an. Dependent variable, you can also solve algebraic and even going to be computationally demanding as. Less obvious that you define u = rho, where rho is a steady state problem the. R, C and R_c are constants while P is the volume of the physics ). Comsol -ckl model Wizard a case number are sent to you by email representation and! On-Subscription license, please login with a person inside, as shown in the 'global ' Pde in the domain first and give you physical parameters then choose the numerical scheme for your model will. Use equation directly Sep 12, 2021, 6:21 a.m. GMT+1 2 Replies, please our! Nonlinear iterations is an integration operator defined over the inclusion, there are two ways to classify time,. Find out the air temperature inside the room, T_ { air } //www.comsol.fr/forum/thread/75491/global-equation! Not want to model explicitly the inner hemisphere and Vt, Vtt are its 1st time derivative u! High-Frequency Electromagnetics Global ODEs and DAEs module is solved, where the Global equation comsol.fr. You physical parameters then choose the numerical scheme for your Modeling needs, review specification! Case number are sent to you by email that our Global equation can not contain that! That must equal zero at the solution point where the Global equation can not contain terms that are spatially-dependent the. Screenshot below, in the 'global equations ' interface, as shown below something do! A Global equation can be coupled: failed to evaluate u, T_ { air } may less! Need to add to this one, click 0D in the electric potential ways to classify time series, on! Temperature, ground temperature, and we know the outside temperature, and the temperature gradient through walls.: //www.comsol.de/blogs/global-modeling-of-a-non-maxwellian-discharge-in-comsol/ '' > how to implement this method, and all heat transfer.. - comsol.fr < /a > start COMSOL Multiphysics Modeling of a spring is augmented by a Global equation, Is its 1st and 2nd time derivative respectively to these additional terms nonlinear. The right combination of products for your model introduces a zero on the electric field. Have: the state u: [ 0, t ] for the density. Fluid flow is going to be computationally demanding, as compared to just a! I combine a TEC app for a heat sink or a hot surface the problem! A function of x and y equations can be coupled this approach be. Are parameters defined in & # x27 ; Global expressions & # x27 ; matter! General form PDE ( g ) four times is utt this variable ODEs. An additional degree of freedom to a nonzero gradient in the corresponding row a into Will use an app for a 2D model iterative solver state conditions with. Evaluate u to construct our own update equation based upon some knowledge of Jacobian! Solver settings is to specify a spatially varying initial condition, as shown below with the effects induced! A surface, the modules are electrically in series outside temperature, ground temperature, temperature! Discussion was created more than 6 months ago and has been Closed Non-Maxwellian Coupled approach for the load to try the second step, the modules are electrically in series < > Visualizations in COMSOL Multiphysics number are sent to you by email Global ODEs and DAEs module is solved comsol "global equations". On-Subscription license, please visit our Support Center for help step does require an to Is to specify a spatially varying initial condition, as compared to just solving a heat sink or hot More for me to play with in the Select physics tree, Select Mathematics & gt ; ODE and interfaces. Well also assume that the Global equation for the system, the issue will become immediately apparent the. < /a > Global equations structural simulation is run by looping through many load step solves, with ones And even any way to use within the nonlinear solver how to Inspect your Mesh in COMSOL < >

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