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Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the same mesh: adaptmesh1. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. At a value of P=0 the above expression is linear, and at a value of P=1 the expression is equal to the original nonlinear expression. Have you taken a look at this blog post? The problem is that when I run my model this message appear: Undefined value found. Within either of these features, it can also be helpful to enable the Results While Solving option, as shown in the screenshot below, to visualize the iterations being taken during the solution. This solver is automatically used when a Stationary or Frequency Domain study is added to the model. Save this information to a file. The technique of load ramping is not always reasonable for all problems. My comment is perhaps a bit nave but it seems to me that you could simply deactivate the \frac{\partial \cdot}{\partial t} term of the background field equation but keep its connexion to the solid to get what you want. The settings controlling the predictor type. With respect to multiphysics couplings, rather than solving the problem using a fully coupled approach (the default) solve the problem sequentially, with one physics being solved after another. This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. It can be useful while solving sequences of linear systems arising from, for example, nonlinear problems. For example, if there is a temperature-dependent material property such as: Repeat this for every nonlinearity of the model. Solving such models in a stationary sense should simply require solving a single (large) system of linear equations and should always be solvable, but there are cases when the software will fail to find a solution. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. The technique of load ramping is not always reasonable for all problems. For example, in an Electric Currents problem, you may want to consider a system of materials including a good conductor such as copper (with an electric conductivity of ~6e7 S/m) and an insulative material such as glass (which can have electric conductivity of ~1e-14 S/m.) Cooling and Solidification of Metal. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. To switch between these solver types, go to the Stationary Solver node within the Study sequence. Extending this logic, if one wants to solve for any arbitrary load on a nonlinear system, it makes sense to solve a sequence of intermediate problems with gradually increasing load values and using the solutions from each previous step as the initial condition for the next step. Wrong ordering of study steps. How can I check before my flight that the cloud separation requirements in VFR flight rules are met? listed if standards is not an option). Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. Your email address will not be published. We use COMSOL Multiphysics for solving distributed optimal control of un-steady Burgers equation without constraints and with pointwise control constraints. Connect and share knowledge within a single location that is structured and easy to search. For example, in Solid Mechanics, if the Poisson Ratio set to 0.5, then the model will not solve, as this value in incompatible with the theory of linear elasticity. Sometimes, reducing the model complexity can be quite challenging and it can be better to start from as simple a case as possible and gradually increase the complexity. First, it is physically intuitive, often matching how one would perform an experiment. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. Communication over the phone, in person, and through email was very easy. The Automatic predictor setting will use the constant predictor when a segregated solution approach is being used, and use the linear predictor when the fully coupled approach is used. Find centralized, trusted content and collaborate around the technologies you use most. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. The software then computes an initial solution and from there it iteratively re-computes the solution, taking into account how these intermediate solutions affect the nonlinearities. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. It is also possible to manually refine the mesh. The objective here is to simplify the model to a state where the model will solve, with linear approximations. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. GCRO-DR is a method for Krylov subspace recycling. The objective here is to simplify the model to a state where the model will solve, with linear approximations. Extending this logic, if one wants to solve for any arbitrary load on a nonlinear system, it makes sense to solve a sequence of intermediate problems with gradually increasing load values and using the solutions from each previous step as the initial condition for the next step. Load ramping and nonlinearity ramping can be used in combination, but start with only one or a few of the loads or nonlinearities being ramped. The algorithm is, generally speaking, a Newton's method approach. 0 Replies, Please login with a confirmed email address before reporting spam. However, it is usually not possible to know this ahead of time. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) ", "Absolutely the best place to shop for flowers and greenery, I spent an hour just looking around for fun prior to purchasing a bouquet, they have the best customer service people all over the place and it's a huge place", "Recently came in here to pick up 45 chocolate Seegars (cigars) for a dinner banquet in honor of my baby nephew. In many physics areas there exist alternative physics formulations specifically meant for solving cases where the geometry has an extreme aspect ratio. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. The Automatic predictor setting will use the constant predictor when a segregated solution approach is being used, and use the linear predictor when the fully coupled approach is used. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. It is sometimes necessary to manually scale the dependent variables. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. Dun & Bradstreet gathers Office Supplies, Stationery, and Gift Retailers business information from trusted . The fully coupled and segregated approaches are discussed below. One of the key concepts there was the idea of mesh convergence as you refine the mesh, the solution will become more accurate. You can unsubscribe from these emails at any time. Note the star symbol on the Solution feature. This information is presented in the context of a very simple 1D finite element problem, and builds upon our previous entry on Solving Linear Static Finite Element Models. Solve the stationary study then the time dependent study. We have also introduced meshing considerations for linear static problems, as well as how to identify singularities and what to do about them when meshing. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. This approach is known as a Continuation Method with a Constant predictor. If it does so, use a finer increment in that range. I'm trying to model a solid that's moving through a steady background field in a background flow, I want to take into account the effect of movement of the solid after each time step so I have to use stationary solver after each time step in order to see how field has changed after solid moved. Could you expand a little bit more why the coupling is impossible? As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. The advantages of the continuation method are two-fold. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. This involves a systematic reduction in the model complexity. November 11, 2013. (I am begginer in comsol) Thank you. That is, they are tuned to achieve convergence in as many cases as possible. Not entering required material parameters. An example would be a linear static structural model of an aluminum beverage can. See Knowledge Base 1240: Manually Setting the Scaling of Variables. That is: It is also possible to compute the derivative of the solution with respect to the continuation parameter and use that derivative (evaluated at the iteration) to compute a new initial value: where is the stepsize of the continuation parameter. Save my name, email, and website in this browser for the next time I comment. This involves a systematic reduction in the model complexity. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. so many cute little stationary items , hair". The coupling terms between the different groups are thus neglected. The default solver for most 3D models is an iterative solver, which is more sensitive to ill-conditioned problems. Such a large difference in the materials properties can be challenging. . This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. P&S Comsol Team: Arif Gngr , Yannik Horst , Stefano Valente. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Unknown function or operator. $140,000.00, $120,000.00 k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) Alternatively, delete and re-create the study. The fully coupled and segregated approaches are discussed below. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. Asking for help, clarification, or responding to other answers. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. Popular answers (1) This problem generally occurs when there is some mistake in the physics or study section or wrong selection of the mesh size. Name: actdep_int1, Your email address will not be published. Assuming a well-posed problem, the solver may converge slowly (or not at all) if the initial values are poor, if the nonlinear solver is not able to approach the solution via repeated iterations, or if the mesh is not fine enough to resolve the spatial variations in the solution. Improving Convergence of Nonlinear Stationary Models - COMSOL Consult your product manuals for complete trademark details. Your internet explorer is in compatibility mode and may not be displaying the website correctly. New Stationary Engineer jobs added daily. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. Why is there a voltage on my HDMI and coaxial cables? The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. replace it with the expression: Hi Jason, Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. There will also be a red cross over the Materials branch icon. Required fields are marked *. About the Stationary Solver - COMSOL Multiphysics It is also possible to manually refine the mesh. Here, we begin an overview of the algorithms used for solving nonlinear static finite element problems. This is relatively expensive to do, but will lead to the most robust convergence. For example, if ramping P over values of: 0.2,0.4,0.6,0.8,1.0 the nonlinear solver may fail to converge for a value of 0.8. Making statements based on opinion; back them up with references or personal experience. Top 10 Best Stationary in Brea, CA - October 2022 - Yelp There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. Minimising the environmental effects of my dyson brain. Iterative , Direct . Consult your product manuals for complete trademark details. It is sometimes necessary to manually scale the dependent variables. My comment is perhaps a bit nave but it seems to me that you could simply deactivate the term of the background field equation but keep its connexion to the solid to get what you want. Consult your product manuals for complete trademark details. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. That is: It is also possible to compute the derivative of the solution with respect to the continuation parameter and use that derivative (evaluated at the iteration) to compute a new initial value: where is the stepsize of the continuation parameter. About the Stationary Solver - COMSOL Multiphysics This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). Contact COMSOL at Bangalore on their telephone: +9180 25323003. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). Understanding stationary and time dependent solver COMSOL Multiphysics This algorithm was also useful for understanding what happens near a failure load. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. Improving Convergence of Nonlinear Stationary Models - Informazioni For the Nozomi from Shinagawa to Osaka, say on a Saturday afternoon, would tickets/seats typically be available - or would you need to book? That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. If so, see: Knowledgebase 1030: Error: "Out of memory". If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. What are people saying about cards & stationery in Brea, CA? There will always already be either a Segregated or Fully Coupled feature beneath this. The segregated approach, on the other hand, solves sets of unknowns separately. I am following the same model as Comsol provide us on the web. COMSOL Blog Series on COMSOL Multiphysics Solvers thanks for reply The conditions on the geometric aspect ratio are relatively more strict. COMSOL makes every reasonable effort to verify the information you view on this page. Such problems must solved in the time domain. If it is not clear that any of the above strategies are working, it is useful to take a more general approach to verifying the general validity of the model. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the - COMSOL The other low-level default settings within the Stationary Solver are chosen for robustness. The Iterative Solvers - COMSOL Multiphysics Here, we will examine techniques for accelerating the convergence of these two methods. - Feature: Stationary Solver 1 (sol1/s1) That is, start by first solving a model with a small, but non-zero, load. listed if standards is not an option). Thanks for contributing an answer to Stack Overflow! Is it possible to rotate a window 90 degrees if it has the same length and width? The idea behind the GCRO-DR method is to retain the subspace determined while solving previous systems and use it to reduce the cost of solving the next system. Improving Convergence of Nonlinear Stationary Models - COMSOL As part of our solver blog series we have discussed solving nonlinear static finite element problems, load ramping for improving convergence of nonlinear problems, and nonlinearity ramping for improving convergence of nonlinear problems. Posted 26 set 2019, 17:57 CEST Mesh Version 5.3 0 Replies. Stationary (time-invariant) models with nonlinearities may converge very slowly. How to Add a Study to Your Simulation in COMSOL Multiphysics By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. The coupling terms between the different groups are thus neglected. Segregated approach and Direct vs. Iterative linear solvers, About the time step setting of the solver, Introducing Goal Seeking into the Segregated Solver. Solving for laminar flow using Comsol - YouTube Solver . In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. The coupling terms between the different groups are thus neglected. It is also possible to manually refine the mesh. For more details, see: Performing a Mesh Refinement Study, Mesh refinement may often need to be combined with load or nonlinearity ramping and may require a set of studies, first starting with a relatively coarse mesh for nonlinearity ramping, refining the mesh, and the ramping further on the refined mesh. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Your Discussion has gone 30 days without a reply. Hi Alexis, If some, or all, of the needed materials properties needed by the physics interfaces are not defined, the model will generate an error at runtime. This guide applies solely to nonlinear stationary models. This case is generally difficult, or impossible, to solve since this material property is non-smooth. Not assigning proper boundary conditions: Especially if you have ports. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. Could you expand a little bit more why the coupling is impossible? The difference between the phonemes /p/ and /b/ in Japanese. Review the model setup to resolve these. Trying to understand how to get this basic Fourier Series. Does ZnSO4 + H2 at high pressure reverses to Zn + H2SO4? In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. Knowledgebase 1260: What to do when a linear stationary model is not solving, Knowledge Base 1240: Manually Setting the Scaling of Variables, What to do when a linear stationary model is not solving, Knowledge Base 1254: Controlling the Time Dependent solver timesteps, Galleria dei Modelli e delle App di Simulazione, 2023 da COMSOL. At a value of P=0 the above expression is linear, and at a value of P=1 the expression is equal to the original nonlinear expression. Check the solver log to see if the continuation method is backtracking. Multiphysics problems are often nonlinear. Stationary Solver Use the Stationary Solver () to find the solution to linear and nonlinear stationary problems (also called static or steady-state problems). Load ramping and nonlinearity ramping can be used in combination, but start with only one or a few of the loads or nonlinearities being ramped. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. Stationary Engineer Jobs in Brea, California, United States, $87,400.00 Use this parameter to modify the nonlinearity expressions in the model. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. With respect to multiphysics couplings, rather than solving the problem using a fully coupled approach (the default) solve the problem sequentially, with one physics being solved after another. First, it is physically intuitive, often matching how one would perform an experiment. The default Initial Values for the unknowns in most physics interfaces are zero. Leverage your professional network, and get hired. As a second example, when solving for Electric Currents, do not model perfect electrical insulators as materials with zero conductivity, instead, omit the domain from the model and use the Electric Insulation boundary condition. Any trademarks referenced in this document are the property of their respective owners. 140K views 8 years ago COMSOL Multiphysics Tutorial for Beginners Please note that an updated version of the content in this video can be found in the Modeling Workflow video in the COMSOL. In a previous blog entry, we introduced meshing considerations for linear static problems. Your internet explorer is in compatibility mode and may not be displaying the website correctly. To start a new discussion with a link back to this one, click here. Cooling and Solidification of Metal. Office Supplies, Stationery, and Gift Retailers Companies in Brea When the difference in the computed solutions between successive iterations is sufficiently small, or when the residual is sufficiently small, the problem is considered converged to within the specified tolerance. For more details, see: Performing a Mesh Refinement Study, Mesh refinement may often need to be combined with load or nonlinearity ramping and may require a set of studies, first starting with a relatively coarse mesh for nonlinearity ramping, refining the mesh, and the ramping further on the refined mesh. In this blog post we introduce the two classes of algorithms that are used in COMSOL to solve systems of linear equations that arise when solving any finite element problem.

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