stationary solver comsolstationary solver comsol

A nonlinearity can be introduced into the model either in the governing equation, or by making any of the material properties, loads, or boundary conditions dependent upon the solution. COMSOL does not assume any legal liability for the accuracy of the data disclosed. Dr.S.Ravindran Cite 1 Recommendation Popular answers (1). Most multiphysics problems are nonlinear. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. Not assigning proper boundary conditions: Especially if you have ports. The default Initial Values for the unknowns in most physics interfaces are zero. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). Do you also know how to solve this problem: using stationary solution as the initial conditions in time dependent model, How Intuit democratizes AI development across teams through reusability. See Knowledge Base 1240: Manually Setting the Scaling of Variables. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. One of the key concepts there was the idea of mesh convergence as you refine the mesh, the solution will become more accurate. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. There are also cases when an extremely poor quality mesh leads to an ill-conditioned problem, This issue often arises in combination with, and as a consequence of, geometries that have extreme aspect ratios. Why do many companies reject expired SSL certificates as bugs in bug bounties? November 11, 2013. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. With sufficient simplification, a model can be reduced to a linear problem, and if this simplified model does not converge, see: What to do when a linear stationary model is not solving. Common Mistakes: Not assigning materials to all the domains. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. Save my name, email, and website in this browser for the next time I comment. The conditions on the geometric aspect ratio are relatively more strict. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. Check the solver log to see if the continuation method is backtracking. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. It may also reveal that the model itself is ill-posed in some way. Different physics have different default solvers. Hi Jason, Dun & Bradstreet gathers Office Supplies, Stationery, and Gift Retailers business information from trusted . Any trademarks referenced in this document are the property of their respective owners. Why? That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. 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. Such problems must solved in the time domain. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. It is also possible to manually refine the mesh. To start a new discussion with a link back to this one, click here. The advantages of the continuation method are two-fold. At low flow speeds the flow solution will be time invariant, but at higher flow rates there will be vortex shedding, a time-varying change in the flow field behind the cylinder. - Function: ^ Failed to evaluate variable. replace it with the expression: What version of COMSOL are you using? 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. Perhaps this approach could be adapted to represent your model. The Iterative Solvers - COMSOL Multiphysics A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. Posted 26 set 2019, 17:57 CEST Mesh Version 5.3 0 Replies. COMSOL makes every reasonable effort to verify the information you view on this page. Then I stored the resulting solution, and used it to to solve the stationary solver again by using the solver manager. For the Nozomi from Shinagawa to Osaka, say on a Saturday afternoon, would tickets/seats typically be available - or would you need to book? Also, keep in mind that a linear stationary model should solve regardless of how coarse the mesh is (albeit to a low accuracy) so you can always start with as coarse a mesh as possible, and refine the mesh (See also: Knowledgebase 1030: Performing a Mesh Refinement Study. Thanks for contributing an answer to Stack Overflow! -Detail: NaN or Inf found when solving linear system using SOR. - See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. The following are possible reasons why a linear stationary model will fail to solve, along with resolutions: The combination of the constraints and boundary conditions must be sufficient to define a unique solution to the problem, in terms of the field variables being solved. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. numeric (each ports needs their ownboundary mode analysis in the study if they are numerically defined)Wave excitation: on/off(input/output), - Feature: Stationary Solver 1 (sol1/s1) Division by zero. Any trademarks referenced in this document are the property of their respective owners. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. Cooling and Solidification of Metal. Not entering required material parameters. if I want to do an adaptive mesh refinement, I get this error. That is, they are tuned to achieve convergence in as many cases as possible. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. For example, if there is a temperature-dependent material property such as: The latter method is known as the Continuation Method with a Linear predictor, and is controlled within the Study Configurations as shown in the screenshot below. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. Understanding the Fully Coupled vs. That is, they are tuned to achieve convergence in as many cases as possible. Discussion Closed This discussion was created more than 6 months ago and has been closed. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. How can I check before my flight that the cloud separation requirements in VFR flight rules are met? Your Discussion has gone 30 days without a reply. Most multiphysics problems are nonlinear. Find centralized, trusted content and collaborate around the technologies you use most. It is sometimes necessary to manually scale the dependent variables. Office Supplies, Stationery, and Gift Retailers Companies in Brea That is, start by first solving a model with a small, but non-zero, load. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. - If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. Hello guys. Reviews on Stationary Stores in Brea, CA - Typo, Mievic, Posh Paper, Morning Glory, Select Graphics & Printing, Daiso Japan, Urban Outfitters, Office Depot, Barnes & Noble With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. Multiphysics problems are often nonlinear. Few days back i was also facing this problem in . - Feature: Stationary Solver 1 (sol1/s1) 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. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. P&S Comsol Team: Arif Gngr , Yannik Horst , Stefano Valente. The advantages of the continuation method are two-fold. P&S Comsol Team: Manuel Kohli, Raphael Schwanninger, Feature: Stationary Solver 1 (sol1/s1) Staging Ground Beta 1 Recap, and Reviewers needed for Beta 2, Simulation of effect of heated resistance on temperature distribution in laminar flow, COMSOL: Diffusion in Transport of Diluted Species Produces Unphysical Results. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) Changes to these low-level settings from the defaults will usually be quite model- and case-specific. Use a manually defined mesh to avoid elements with extreme aspect ratios and perform a mesh refinement study, as described here: Performing a Mesh Refinement Study, For problems that are ill-conditioned, using a direct solver is often called for. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. Use this parameter to modify the nonlinearity expressions in the model. There will always already be either a Segregated or Fully Coupled feature beneath this. If it does so, use a finer increment in that range. This case is generally difficult, or impossible, to solve since this material property is non-smooth. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version First, it is physically intuitive, often matching how one would perform an experiment. Computational Fluid Dynamics (CFD), API The Fully Coupled solution approach, with the Plot While Solving enabled. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. To learn more, see our tips on writing great answers. P&S: COMSOL Design Tool for Photonic Devices - ETH Z Stationary (time-invariant) models with nonlinearities may converge very slowly. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. The default Initial Values for the unknowns in most physics interfaces are zero. Wish you all the best. 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. Repeat this for every nonlinearity of the model. Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the same mesh: adaptmesh1. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. In many physics areas there exist alternative physics formulations specifically meant for solving cases where the geometry has an extreme aspect ratio. 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. listed if standards is not an option). solving stationary solver after each time step - COMSOL Multiphysics If these settings have been manually changed, you will see a small star symbol on the Solution feature, as shown in the screenshot below. About the Stationary Solver - COMSOL Multiphysics Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. 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. Common Mistakes: Not assigning materials to all the domains. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. The latter method is known as the Continuation Method with a Linear predictor, and is controlled within the Study Configurations as shown in the screenshot below. Your internet explorer is in compatibility mode and may not be displaying the website correctly. listed if standards is not an option). Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. 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. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Alternatively, delete and re-create the study. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. These are some cards & stationery with a large number of reviews in Brea, CA. - Version 5.3 See if these can be used instead of explicitly modeling parts with high-aspect ratio geometries. L'objectif de notre prsent travail se repose sur l'tude par simulation numrique du comportement de bton au jeune ge sous des conditions svres de temprature pendant les premires 24h aprs. The settings controlling the predictor type. $131,100.00, Simplified Vehicle Operations Project Engineer, $115,000.00 The other low-level default settings within the Stationary Solver are chosen for robustness. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. Not entering required material parameters. 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. Not meshing all the domains. If you define this nonlinearity ramping such that the first case (P=0) is a purely linear problem, then you are guaranteed to get a solution for this first step in the ramping. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. Stationary (time-invariant) models with nonlinearities may converge very slowly. This approach is known as a Continuation Method with a Constant predictor. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. Asking for help, clarification, or responding to other answers. I am trying to solve the coupling between a waveguide and a microring resonator. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. The advantages of the continuation method are two-fold. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. In that case, the continuation method will automatically backtrack and try to solve for intermediate values in the range of 0.6 through 0.8. P&S Comsol Team: Yannik Horst, Manuel Kohli, Xinzhi Zhang. Reply . 3. Linear solvers. 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. We use COMSOL Multiphysics for solving distributed optimal control of un-steady Burgers equation without constraints and with pointwise control constraints. Hence Comsol solved for the stationary solution at different points of time. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. A linear finite element model is one in which all of the material properties, loads, boundary conditions, etc are constant with respect to the solution, and the governing partial differential equations are themselves linear. Again, introduce a Global Parameter that gets ramped from exactly zero to one. View the Settings window for the Materials branch to get a list of all domains with undefined materials and add a material to those domains. They are usually called comp1.u, comp1.v, and comp1.w though. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. Direct PARDISO Solver , PARDISO . By default, the COMSOL Multiphysics software determines these values heuristically depending on the physics as, for example, the specified initial values or a solution from an earlier study step. 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. Under Initial values of variables solved for, the default value of the Settingslist is Physics controlled. If the material properties entered are incorrect for the governing equation, the model will generate an error at runtime, usually a Singular Matrix error.
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