. It can be useful while solving sequences of linear systems arising from, for example, nonlinear problems. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. This is a review for cards & stationery in Brea, CA: "Love this store!!! Trying to understand how to get this basic Fourier Series. Check the solver log to see if the continuation method is backtracking. The Fully Coupled solution approach, with the Plot While Solving enabled. In a previous blog entry, we introduced meshing considerations for linear static problems. 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. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. Hi Jason, 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. Name: actdep_int1, Your email address will not be published. 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. What to do when a linear stationary model is not solving - COMSOL The coupling terms between the different groups are thus neglected. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Is there a way to use the stationary solution obtained in Comsol 4.2 as the initial conditions in a time dependent model? Your Discussion has gone 30 days without a reply. 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. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. Hi Alexis, The fully coupled and segregated approaches are discussed below. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. 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. Understanding the Fully Coupled vs. 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. I use comsol multiphysics 5.2a and . 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. The Fully Coupled solution approach, with the Plot While Solving enabled. 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. If all of the above approaches have been tried and you are certain that the problem itself is well-posed, consider that the nonlinear problem may not, in fact, have a stationary (time-invariant) solution. Some models are numerically ill-conditioned due to the setup. They are usually called comp1.u, comp1.v, and comp1.w though. This approach is known as a Continuation Method with a Constant predictor. 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. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. 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. This guide applies solely to nonlinear stationary models. This is relatively expensive to do, but will lead to the most robust convergence. In the COMSOL Multiphysics software, this step of the modeling workflow is made. Wrong ordering of study steps. 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. Tutti i diritti sono riservati. Wrong ordering of study steps. . 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. Posted 26 set 2019, 17:57 CEST Mesh Version 5.3 0 Replies. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. It is quite rare that changing these settings is superior to using a combination of the other techniques in this Knowledgebase, although it is possible to tune these settings to reduce solution time and memory requirements, once a model is already converging. 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. 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. 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. Here, we will examine techniques for accelerating the convergence of these two methods. This is relatively expensive to do, but will lead to the most robust convergence. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. 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. Common Mistakes: Not assigning materials to all the domains. Solve the stationary study then the time dependent study. For example, in a Solid Mechanics (wherein the software is solving for the displacement field within the solid) applying two opposite and equal Boundary Load conditions on a part is not sufficient to define the displacement. so many cute little stationary items , hair". k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) 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. Thanks, Andres. Perhaps this approach could be adapted to represent your model. Tutti i diritti sono riservati. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. Such a case would be better to address instead with the Shell physics interface, which is specially formulated for handling thin-walled structural parts. Set "Values for dependent variables" in study step settings to User ControlledSolutionYour Stationary Study. If you try to solve such a model, there will be an error at runtime that will provide information about the variable name and where it is being called. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: Can someone help me fix the COMSOL error below? | ResearchGate Consult your product manuals for complete trademark details. Singular matrix., Make sure you defined your ports correctly:Boundary selectionType of port: e.g. listed if standards is not an option). 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. However, it is usually not possible to know this ahead of time. As we saw previously in the blog entry on Solving Nonlinear Static Finite Element Problems, not all nonlinear problems will be solvable via the damped Newton-Raphson method. 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. If the model is very large, and if you do not have very much memory in your computer, you may get an error message regarding memory. 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. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. 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. The default solver for most 3D models is an iterative solver, which is more sensitive to ill-conditioned problems. Asking for help, clarification, or responding to other answers. To learn more, see our tips on writing great answers. Computational Fluid Dynamics (CFD), API 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. Consult your product manuals for complete trademark details. See Knowledge Base 1240: Manually Setting the Scaling of Variables. The solver settings are stored at Study > Solver Configurations > Solution. listed if standards is not an option). It may also reveal that the model itself is ill-posed in some way. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Can I tell police to wait and call a lawyer when served with a search warrant? What is the purpose of this D-shaped ring at the base of the tongue on my hiking boots? - To switch between these solver types, go to the Stationary Solver node within the Study sequence. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. Acidity of alcohols and basicity of amines. COMSOL Error for Initial Values(RF Module) The continuation method will again backtrack and try intermediate values of the ramping parameter, thus giving you the nearest approximation to the abrupt transition that is solvable. 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. 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. 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. (Frequency Domain should be the last step) What are some highly rated cards & stationery in Brea, CA? For example, if there is a temperature-dependent material property such as: If all of the above approaches have been tried and you are certain that the problem itself is well-posed, consider that the nonlinear problem may not, in fact, have a stationary (time-invariant) solution. Dun & Bradstreet gathers Office Supplies, Stationery, and Gift Retailers business information from trusted . Segregated approach and Direct vs. Iterative linear solvers, Time dependent function and stationary study, Combining Adaptive Mesh Refinement with Data Filtering, What to do when a linear stationary model is not solving, Galleria dei Modelli e delle App di Simulazione, 2023 da COMSOL. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. Top 10 Best Stationary Stores in Brea, CA - December 2022 - Yelp Again, introduce a Global Parameter that gets ramped from exactly zero to one. The default Initial Values for the unknowns in most physics interfaces are zero. thanks for reply Hello guys. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); This site uses Akismet to reduce spam. Discussion Closed This discussion was created more than 6 months ago and has been closed. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. Direct PARDISO Solver , PARDISO . Review the model setup to resolve these. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. 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. Consult your product manuals for complete trademark details. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) COMSOL makes every reasonable effort to verify the information you view on this page. Cecilia M. came from the backroom to help me and went out of her way to help me even though I had not called before going into the store. 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. Save my name, email, and website in this browser for the next time I comment. Different physics have different default solvers. Sign in to create your job alert for Stationary Engineer jobs in Brea, California, United States. [COMSOL_Users] output of stationary solver as input to time-dependent COMSOL does not assume any legal liability for the accuracy of the data disclosed.
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