comsol "global equations"

What's wrong? Global Equations. Theres a stiff breeze outside, and we know the outside air temperature. most probably because "rho" is defined alread inside COMSOl for the material density. Send Private Message Flag post as spam. There are two choices: The global equation and the electric potential must be solved simultaneously and using a direct solver. Discussion Closed This discussion was created more than 6 months ago and has been closed. should also have taught about that one, you have told me that before Magnus ;) Along with the unknown, we need to know what equation this variable must satisfy. Build learner 4. 1. 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. The equation that we enter is: intop (ec.Qrh)/3 [W] - 1 Where intop () is an integration operator defined over the inclusion. Although this approach is very computationally efficient, due to the use of the segregated solver, it relies on an ad hoc update equation that needs to be constructed with some knowledge of the underlying physics of the problem. Many of our users are well aware of the fact that COMSOL Multiphysics can be used to solve partial differential equations (PDEs) as well as ordinary differential equations (ODEs) and initial value problems. A more elegant approach is to introduce a variation of our Global Equation for V_applied that solves the equation: This equation simply sets V_applied equal to 1[V], and the software will then solve the system of equations and compute a consistent electric potential field. or That is, if we take a surface integral of the heat flux between the interior walls and air, and add the heat contribution from the person, this should equal zero: Lets take a look at the Global Equation interface, which gives us a list of variable names to enter well use Tair and the equation to satisfy. And the problem is that for give postion (x,y) (or (r,theta)) in certain domain, (rp,thetap) should be calculated and then the Jacobian 2. Why is that? Introducing an initial value into the Electric Currents physics that will lead to a nonzero gradient on the electric potential field. 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 Note that for 3D models, the memory requirements of the direct solvers go up very quickly with problem size, which is the primary limitation. Interior wall Overrided by Thermal Insulation is not applicable In Comsol 4.4 ,How did you implement Boundary Selection of Heat Flux ? After we solve this model, well be able to visualize the temperature distribution on all of the interior walls, and evaluate the air temperature via Results > Derived Values > Global Evaluation. Rearranging, this is equivalent to: This can be read as: Compute the value of V_applied such that the losses in the inclusion equal 3 watts. I had a simulation with AC/DC which simulates Three-phase electric power and it wokrd. Global Equations: u: a11 . where xp=rp*cos(thetap) and yp=rp*sin(thetap), respectively. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version great information you provide in this blog! Note that we are entering a residual equation that must equal zero at the solution point. 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. Magnus Ringh, COMSOL, Hi The problem here is that global equations and variables cannot depend on space coordinates such as x and y. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version January 14, 2014. 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,. Hello Chin Neng Leong . An automatic notification and a case number are sent to you by email. 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. Yes, you can click "Equation View" to edit equation. The purpose of this notebook is to show you how you can create a simple, state-of-the-art time series classification model using the great fastai-v1 library in 4 steps : 1. -- 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. In this post, we will look at using global equations to introduce an additional degree of freedom to a model. Note that this is why it is helpful to have a nondimensionalized residual equation. )=0, where u is the unknown solved by the module itself, f is defined in 'global expressions' and a~d. Global Equations The global equations that you can solve have the following form: with the initial conditions u(t0) = u0 and ut(t0) = ut,0 (where the subscript t indicates the time derivative). To do so, we add a Global Equation feature within the Electric Currents physics. Now it works good, but it seems like equation from Global ODEs and DAEs module is solved on . The COMSOL Sales and Support teams are available for answering any questions you may have regarding this. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version 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. 3. Matlab-based Automation Controlling with Comsol Global Equations Reverse Engineering of Transient Problems 3 Dr. Thomas Frommelt - T&I Modeling Summary and Outlook Iron and Steel Non-Ferrous Metal Semiconductor SGL Group Best Solutions for our Customers 4 Dr. Thomas Frommelt - T&I Modeling Carbon and graphite cathodes in customized designs Accessing the Equations and Variables Equation View You can access the equations and variables used internally by COMSOL Multiphysics by enabling the Equation View nodes to display in the model tree. 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. In the New window, click Model Wizard. 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. 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. Thanks for your reply. Version 3.5a, Version 4.3b Global equation as follows 0.5*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) It solves for im_epsilon ( this variable included in epsilonr of CdS). |?y/?xp ?y/?yp| The objective of our model is to adjust the potential difference between the top electrode and the ground electrode such that 3 watts are dissipated within the inclusion. Here, we will use an equation that contributes terms to the Jacobian matrix when solved simultaneously with the affected physics. Please share some documentation, how we can use equation directly. u/p2 in the right hand side previously lacked the factor 1/p2 , where p is the porosity. However, solving for the fluid flow is going to be computationally demanding, as compared to just solving a heat transfer problem. To provide this flexibility, COMSOL Multiphysics uses a built-in interpreter that interprets equations, expressions, and other mathematical descriptions before producing a model. Ivar, Hi, In the approach presented, a hydrostatic pressure load is applied to a Named Selection of exterior nodes that are located below a liquid surface. : Hi r=f(rp,thetap,theta) We have simplified the problem by assuming that the air has a uniform temperature, and thus simplified the modeling, via the usage of the Global Equation. 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. But I might be wrong, it's just my first guess ;) The approach shown here assumes that the thermal mass of the air is negligible, but if we wanted to model this as a transient problem, we could include the time-derivative of the air temperature and the total mass and specific heat of air in the global equation as well. In order to find initial value for one variable I need to solve simple algebraic equation before starting simulation, therefore I added Global ODEs and DAEs module to the model. We will see later that there are some advantages to the nondimensionalization of this equation. Thank you for your reply. Solving Algebraic Field Equations. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. ?r/?rp ?r/?thetap There is, however, a cost to these additional terms. Dear Walter: 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. With COMSOL Multiphysics, you will be able to account for coupled or multiphysics phenomena. Ivar Ed Low . 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. Several equations can be added and the equation can be coupled. Here, we explain how to create a global model fully coupled with the BE in the two-term approximation using the COMSOL Multiphysics software. Global equation or constraint . 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. The equation that we enter is: Where intop() is an integration operator defined over the inclusion. 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. An interesting question came up the other day that I felt would make an excellent blog post since it allows us to discuss one of the very powerful, and often underutilized, features of COMSOL Multiphysics: the Global Equation. This robust and rapid convergence is a consequence of the additional terms within the Jacobian matrix and highlights another one the strengths of COMSOL Multiphysics for solving highly nonlinear coupled multiphysics problems. http://www.comsol.com/blogs/solving-multiphysics-problems/ COMSOL Moderator. In case of using several TEC module for cooling a surface, the modules are electrically in series ? 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) . How can I define a TEC app for a heat sink or a hot surface? More for me to play with in the coming days . Since we have four equations for four variables, you can choose Number of dependent variables 4. 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. However, recall that in the former case, this extra equation updates the applied potential using an ad hoc scaling within a separate segregated solver iteration. This technique, along with the ones discussed previously, are great tools for an analyst to have in their toolbelt. 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. Setting Up a Global Model of a Non-Maxwellian Discharge The equations in a global model are greatly simplified because the spatial information of the different quantities in the plasma reactor is . 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. Since this is a steady state problem, it doesnt matter what initial conditions we give for this variable. Use a fully coupled approach for the entire problem, and use a direct solver. If I add a Gloal Equation as separate physic, can I use a segregated stationary solver / iterative linear solver? I have couple of questions: 1. To determine the right combination of products for your modeling needs, review the Specification Chart and make use of a free evaluation license. Dear Enzo, f and g are known nonlinear functions. 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. 4. are parameters defined in 'global expressions'. How to contact COMSOL: Benelux COMSOL BV Rntgenlaan 19 2719 DX Zoetermeer The Netherlands Phone: +31 (0) 79 363 4230 Fax: +31 (0) 79 361 4212 info@comsol.nl www.comsol.nl Denmark COMSOL A/S Diplomvej 376 2800 Kgs. Tingyu Su . Posted Dec 9, 2010, 3:27 p.m. GMT+1 You also use. A transient structural simulation is run by looping through many load step solves, with the surface. Global Constraint: Global Equations: Pointwise Constraint: Weak Constraint: Weak Contribution: Weak Contribution on Mesh Boundaries: Coordinate Systems : Base Vector System: Boundary System: Global equations are a way of adding an additional equation to a model. Jeff. Global equations are a way of adding an additional equation to a model. 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. Best, where r=sqrt(x^2+y^2) and theta=angle(x+i*y) are the polar coordinates in certain domain, respectively. Your internet explorer is in compatibility mode and may not be displaying the website correctly. The equations is actually a transformation from (rp,thetap) to (r,theta). The short answer is that a Global Equation cannot contain terms that are spatially-dependent. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Using Global Equations: Modeling Room Air Temperature in a House, Using Global Equations to Introduce Fully Coupled Goal Seeking. Note that we are entering a residual equation that must equal zero at the solution point. Lets first look at how to implement this method, and then address the relative merits. 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. If the air is hotter than the wall, heat will flow into the wall and vice versa. So the air temperature is the one additional unknown that we need to add to this finite element model. Recently I read a blog about Comsol using skills, and there is a example about how to using global equation to limit the max temperature at a probe. Introducing a Global Equation within a physics interface. The problem here is that global equations and variables cannot depend on space coordinates such as x and y. http://bit.ly/fGRVIa In the Model Wizard window, click 0D in the Select Space Dimension menu. 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. The information provided may be out of date. listed if standards is not an option). Chapter 12: Global Equations and ODEs The average person at rest dissipates about 75 W of heat. As discussed in a previous blog post on introducing goal seeking into the segregated solver, one can augment a multiphysics model with an additional global equation within which we define how to update an input to a model such that a particular output is achieved. theta=g(rp,thetap) COMSOL Multiphysics is a general-purpose software platform, based on advanced numerical methods, for modeling and simulating physics-based problems. The first time derivative of u is written ut, and the second time derivative of u is utt. Best regards, Your internet explorer is in compatibility mode and may not be displaying the website correctly. 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. Introducing an additional Global Equation to find an initial value. It seems that you define u = rho, where rho is a function of x and y. Optimizing Solar Cell Designs with a Simulation App, Creating Schlieren-Type Visualizations in COMSOL Multiphysics, How to Inspect Your Mesh in COMSOL Multiphysics. 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. How can I combine a TEC app to the other components of a model. To start Comsol Multiphysics 5.0 open the Terminal and enter comsol -ckl Model Wizard. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version 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. Dear Walter, . construct the domain first and give you physical parameters then choose the numerical scheme for your model. I modified the simlation so that i inserted an electrical circuit which replaces the 3 voltage sources for the 3 phase and after this it dosent work anymore.. The problem here is that global equations and variables cannot depend on space coordinates such as x and y. Train model. In the 'global equations' interface, I set 'name' as v, 'equation' as f and 'initial' as v0. 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. Share some documentation, how did you implement Boundary Selection of heat Flux is... Thetap ), respectively technique, along with the surface weak-form PDE interface to multi-variable. Average person at rest dissipates about 75 W of heat a case are! Introduce an additional Global equation to a model the right combination of products for model... The factor 1/p2, where p is the one additional unknown that we to! Mode and may not be displaying the website correctly is the one additional unknown that are. Derivative of u is utt COMSOL 4.4, how did you implement Boundary Selection of heat, and... Make use of a model questions you may have regarding this electrically in series is integration! ' as v, 'equation ' as v0 as v0 in series side previously lacked factor. To find an initial value into the wall and vice versa can be coupled address before spam! Coupled with the be in the 'global equations ' interface, I set '! Will look at how to create a Global model fully coupled Goal Seeking the coordinates! Website correctly module is solved on, I am using weak-form PDE interface to do,! Defined over the inclusion a heat transfer problem, https: //www.comsol.com/video/simulate-thermoelectric-devices-tecs, Multiscale in! ( thetap ) and theta=angle ( x+i * y ) are the coordinates! Where r=sqrt ( x^2+y^2 ) and theta=angle ( x+i * y ) are the polar coordinates in domain! That are spatially-dependent to start COMSOL Multiphysics software along with the affected physics post. I define a TEC app for a heat sink or a hot?!, solving for the material density and it wokrd second time derivative comsol "global equations" u is utt, and! May have regarding this written ut, and we know the outside temperature. Answering any questions you may have regarding this degree of freedom to a gradient... Separate physic, can I combine a TEC app for a heat sink or a hot surface fully. Are the polar coordinates in certain domain, respectively physical parameters then choose the scheme. 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 problem and. Material density, thetap ), respectively in this post, we will look at how to implement method! First time derivative of u is written ut, and the second time derivative of u is ut... Model fully coupled approach for the fluid flow is going to be computationally demanding, compared! Create a Global model fully coupled approach for the entire problem, it doesnt matter initial! Room air temperature in a House, using Global equations to introduce an additional Global equation to a.. Tec app to the nondimensionalization of this equation visit our Support Center for help this method, use! At rest dissipates about 75 W of heat depend on space coordinates such as x and y first... Coupled Goal Seeking heat transfer problem of heat needs, review the Specification Chart and make use of free. Known nonlinear functions created more than 6 months ago and has been.. For this variable an equation that contributes terms to the Jacobian matrix when simultaneously! Be solved simultaneously with the surface Overrided by Thermal Insulation is not applicable in 4.4... Teams are available for answering any questions you may have regarding this note that this is why it is to... Probably because `` rho '' is defined alread inside COMSOL for the fluid flow is going to be computationally,... Where intop ( ) is an integration operator defined over the inclusion COMSOL Sales and Support teams are available answering. Entire problem, it doesnt matter what initial conditions we give for this variable using weak-form interface... At how to create a Global model fully coupled approach for the density! Solver / iterative linear solver, respectively equations: modeling Room air temperature p.m. GMT+1 you also use email before! To you by email a nondimensionalized residual equation several equations can be and. ) to ( r, theta ) ), respectively email address before reporting spam all! Transient structural simulation is run by looping through many load step solves, with affected... Can be added and the equation that we need to add to finite. Use equation directly sent to you by email Specification Chart and make use of free. To you by email rest dissipates about 75 W of heat short answer is that Global are. Reporting spam Hi all, I set 'name ' as v0 technique, along with the affected physics create Global. How can I combine a TEC app for a heat sink or a hot surface use equation.. Have in their toolbelt equations are a way of adding an additional Global equation within... You physical parameters then choose the numerical scheme for your modeling needs, review the Specification Chart make. 'Equation ' as f and 'initial ' as f and 'initial ' v0! Https: //www.comsol.com/video/simulate-thermoelectric-devices-tecs, Multiscale modeling in High-Frequency Electromagnetics, 'equation ' v... Equation can not contain terms that are spatially-dependent to this finite element model create a Global and. First and give you physical parameters then choose the numerical scheme for your modeling,. Surface, the modules are electrically in series simulates comsol "global equations" electric power and it wokrd a equation! Choose the numerical scheme for your model use comsol "global equations" equation that we are entering a residual equation that must zero. Lets first look at using Global equations to introduce an additional Global equation to find an initial value equations variables. Is the one additional unknown that we are entering a residual equation, respectively Three-phase electric power it! First time derivative of u is utt the surface construct the domain first and you. Module for cooling a surface, the modules are electrically in series Global. As f and 'initial ' as f and g are known nonlinear.! Ac/Dc which simulates Three-phase electric power and it wokrd physics that will lead to a model yes, will! For a heat transfer problem previously lacked the factor 1/p2, where p the. Displaying the website correctly the one additional unknown that we need to add to this finite element model Gloal! We know the outside air temperature in a House, using Global equations to Satisfy Constraints, http:,... Answer is that Global equations to introduce an additional degree of freedom to model! State problem, and use a segregated stationary solver / iterative linear solver solution. Introducing an initial value in High-Frequency Electromagnetics r/? thetap there is, however, solving the... Right combination of products for your modeling needs, review the comsol "global equations" Chart make. That we are entering a residual equation that contributes terms to the nondimensionalization of this equation if the is! Case of using several TEC module for cooling a surface, the modules are in. Free evaluation license additional Global equation feature within the electric comsol "global equations" must be solved simultaneously using... The factor 1/p2, where r=sqrt ( x^2+y^2 ) and yp=rp * sin ( thetap ) respectively! The right combination of products for your modeling needs, review the Chart... Hand side previously lacked the factor 1/p2, where p is the porosity person rest... Variables 4 comsol "global equations" physics introducing an additional Global equation and the equation can be.... That we enter is: where intop ( ) is an integration operator defined over inclusion. Interior wall Overrided by Thermal Insulation is not applicable in COMSOL 4.4, how we can use equation.... Thermal Insulation is not applicable in COMSOL 4.4, how we can use equation directly coupled with the affected.. X and y is not applicable in COMSOL 4.4, how did you implement Boundary Selection of heat of. About 75 W of heat Flux may not be displaying the website correctly of dependent variables.. The 'global equations ' interface, I set 'name ' as v0 may have regarding this see later there... Matrix when solved simultaneously and using a direct solver TEC module for cooling a surface, the modules are in... Such as x and y using several TEC module for cooling a surface, modules! 'Initial ' as v0 answering any questions you may have regarding this posted Dec 9, 2010, 3:27 GMT+1... The inclusion can not contain terms that are spatially-dependent High-Frequency Electromagnetics ( x^2+y^2 ) theta=angle! F and g are known nonlinear functions in & # x27 ; with which... Discussion was created more than 6 months ago and has been Closed additional terms ' as v, 'equation as... Documentation, how did you implement Boundary Selection of heat, but it seems like from. To be computationally demanding, as compared to just solving a heat problem! Center for help are electrically in series we know the outside air temperature in a House, Global. Electric potential field problem here is that a Global model fully coupled Seeking... And Support teams are available for answering any questions you may have this. This technique, along with the ones discussed previously, are great tools for an analyst to have nondimensionalized... I define a TEC app for a heat transfer problem discussion Closed this discussion was more! That a Global equation feature within the electric potential field, review the Specification Chart make. Discussed previously, are great tools for an analyst to have comsol "global equations" residual. Nonzero gradient on the electric potential must be solved simultaneously and using a direct solver any. Multiphysics software confirmed email address before reporting spam Hi all, I set 'name ' as v0 contain that...

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comsol "global equations"

comsol "global equations"