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Stationary (time-invariant) models with nonlinearities may converge very slowly. 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. Not entering required material parameters. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version 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. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) Hi ! The objective here is to simplify the model to a state where the model will solve, with linear approximations. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) Could you expand a little bit more why the coupling is impossible? They deal with COMSOL package and train users. Such a large difference in the materials properties can be challenging. Here, we begin an overview of the algorithms used for solving nonlinear static finite element problems. The Fully Coupled solution approach, with the Plot While Solving enabled. Not meshing all the domains. I am solving a linear stationary finite element model but the software is not solving. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. The default Initial Values for the unknowns in most physics interfaces are zero. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. There will always already be either a Segregated or Fully Coupled feature beneath this. 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. This guide applies solely to nonlinear stationary models. 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. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); This site uses Akismet to reduce spam. With respect to any nonlinearities, replace them by a reasonable linearized term. If you see this, right-click on the Solution feature and select Reset Solver to Default. 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. To switch between these solver types, go to the Stationary Solver node within the Study sequence. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. Does anyone know what should cause this problem? 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. One can say that, in general, if the loads on a nonlinear system are zero, the system will be at rest; that is, the solution will be zero. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. The prices are good, and when I needed something delivered, same day, they were able to do it, and it looked beautiful!! This case is generally difficult, or impossible, to solve since this material property is non-smooth. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. 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. Here, we will examine techniques for accelerating the convergence of these two methods. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. This is relatively expensive to do, but will lead to the most robust convergence. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. The segregated approach, on the other hand, solves sets of unknowns separately. Set "Values for dependent variables" in study step settings to User ControlledSolutionYour Stationary Study. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. Solving for laminar flow using Comsol - YouTube Comsol help video number 2: Solving a laminar flow problem in a slit. 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. 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. replace it with the expression: 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. The algorithm is, generally speaking, a Newton's method approach. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. However, it is usually not possible to know this ahead of time. This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. It may also reveal that the model itself is ill-posed in some way. Consult your product manuals for complete trademark details. 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 . Singular matrix., Make sure you defined your ports correctly:Boundary selectionType of port: e.g. This is relatively expensive to do, but will lead to the most robust convergence. Different physics have different default solvers. Asking for help, clarification, or responding to other answers. The nature of simulating nature: A Q&A with IBM Quantum researcher Dr. Jamie We've added a "Necessary cookies only" option to the cookie consent popup. (Frequency Domain should be the last step) Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). See if these can be used instead of explicitly modeling parts with high-aspect ratio geometries. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. Find detailed information on Office Supplies, Stationery, and Gift Retailers companies in Brea, California, United States of America, including financial statements, sales and marketing contacts, top competitors, and firmographic insights. The settings controlling the predictor type. The objective here is to simplify the model to a state where the model will solve, with linear approximations. Use this parameter to modify the nonlinearity expressions in the model. Stationary (time-invariant) models with nonlinearities may converge very slowly. 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. 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. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. The other low-level default settings within the Stationary Solver are chosen for robustness. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. Repeat this for every nonlinearity of the model. listed if standards is not an option). Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Common Mistakes: Not assigning materials to all the domains. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) Hello guys. $130,000.00. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. 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. (Frequency Domain should be the last step) Changes to these low-level settings from the defaults will usually be quite model- and case-specific. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Wrong ordering of study steps. $131,100.00, Simplified Vehicle Operations Project Engineer, $115,000.00 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. This can arise as a consequence of extreme variations in the material properties, or high aspect ratio geometry. They worked with me. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. Leverage your professional network, and get hired. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. - Function: ^ Failed to evaluate variable. - Feature: Stationary Solver 1 (sol1/s1) In many physics areas there exist alternative physics formulations specifically meant for solving cases where the geometry has an extreme aspect ratio. 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. If this was solved using the Solid Mechanics physics interface the thin walls of the container would need to be explicitly modeled, but the wall thickness is much smaller than the overall can dimensions.

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