stationary solver comsol

By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. Cooling and Solidification of Metal. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. Segregated approach and Direct vs. Comsol help video number 2: Solving a laminar flow problem in a slit.. $130,000.00. listed if standards is not an option). 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. 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. Consult your product manuals for complete trademark details. This is relatively expensive to do, but will lead to the most robust convergence. Feature: Stationary Solver 1 (sol1/s1) Attempt to evaluate nonintegral power of negative number. 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. The fully coupled and segregated approaches are discussed below. With respect to any nonlinearities, replace them by a reasonable linearized term. An example would be a linear static structural model of an aluminum beverage can. The other low-level default settings within the Stationary Solver are chosen for robustness. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. 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. Such problems must solved in the time domain. Get email updates for new Stationary Engineer jobs in Brea, California, United States. Note the star symbol on the Solution feature. Dun & Bradstreet gathers Office Supplies, Stationery, and Gift Retailers business information from trusted . 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. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. replace it with the expression: Posted Sep 9, 2020, 1:44 p.m. EDT This involves a systematic reduction in the model complexity. The default Initial Values for the unknowns in most physics interfaces are zero. 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 the COMSOL Multiphysics software, this step of the modeling workflow is made. Alle Rechte vorbehalten. 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. In this case, it would likely be reasonable to treat the insulative material as a perfect insulator, omit it from the analysis, and use the Electric Insulation boundary condition instead of modeling those domains. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Function: / Failed to evaluate expression. 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. Posted 26 set 2019, 17:57 CEST Mesh Version 5.3 0 Replies. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. Again, introduce a Global Parameter that gets ramped from exactly zero to one. Computational Fluid Dynamics (CFD), API This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. Then use this file to provide the initial conditions in time dependent model. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. Then I stored the resulting solution, and used it to to solve the stationary solver again by using the solver manager. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. We use COMSOL Multiphysics for solving distributed optimal control of un-steady Burgers equation without constraints and with pointwise control constraints. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) The settings controlling the predictor type. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. 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. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. What is the purpose of non-series Shimano components? 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. The technique of load ramping is not always reasonable for all problems. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: It is sometimes necessary to manually scale the dependent variables. 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. Does ZnSO4 + H2 at high pressure reverses to Zn + H2SO4? 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. Segregated approach and Direct vs. Iterative linear solvers, About the time step setting of the solver, Introducing Goal Seeking into the Segregated Solver. It is also possible to manually refine the mesh. About the Stationary Solver The following background information about the Stationary Solver discusses these topics: Damped Newton Methods, Termination Criterion for the Fully Coupled and Segregated Attribute Nodes, Linear Solvers versus Nonlinear Solvers, and Pseudo Time Stepping. 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. Stationary Solver Use the Stationary Solver () to find the solution to linear and nonlinear stationary problems (also called static or steady-state problems). k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) Making statements based on opinion; back them up with references or personal experience. The segregated approach, on the other hand, solves sets of unknowns separately. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. Does anyone know what should cause this problem? 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! 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. Full text of the 'Sri Mahalakshmi Dhyanam & Stotram'. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. To switch between these solver types, go to the Stationary Solver node within the Study sequence. 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. Wish you all the best. 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. Numerically ill-conditioned means that the system matrix is nearly singular and that it will be difficult to solve on a finite-precision computer. 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. That is, start by first solving a model with a small, but non-zero, load. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. Most multiphysics problems are nonlinear. 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. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. 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. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) 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. 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. Different physics have different default solvers. Get notified about new Stationary Engineer jobs in Brea, California, United States. Thanks, Andres. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. 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. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. rev2023.3.3.43278. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. 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. 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. Use this parameter to modify the nonlinearity expressions in the model. This case is generally difficult, or impossible, to solve since this material property is non-smooth. 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. Tutti i diritti sono riservati. What are some highly rated cards & stationery in Brea, CA? The advantages of the continuation method are two-fold. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. Stationary (time-invariant) models with nonlinearities may converge very slowly. This case is generally difficult, or impossible, to solve since this material property is non-smooth. The advantages of the continuation method are two-fold. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. 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. Set "Values for dependent variables" in study step settings to User ControlledSolutionYour Stationary Study. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. The other low-level default settings within the Stationary Solver are chosen for robustness. In a previous blog entry, we introduced meshing considerations for linear static problems. Communication over the phone, in person, and through email was very easy. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. Click the link in the email we sent to to verify your email address and activate your job alert. - This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. 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. Review the model setup to resolve these. Common Mistakes: Not assigning materials to all the domains. Here we introduce a more robust approach to solving nonlinear problems. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. However, it is usually not possible to know this ahead of time. If the material properties entered are incorrect for the governing equation, the model will generate an error at runtime, usually a Singular Matrix error. There will also be a red cross over the Materials branch icon. The algorithm is, generally speaking, a Newton's method approach. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. 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. P&S Comsol Team: Yannik Horst, Manuel Kohli, Xinzhi Zhang. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. If it does so, use a finer increment in that range. . Direct PARDISO Solver , PARDISO . Acidity of alcohols and basicity of amines. 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. 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. 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. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). Studysteps might be listed in wrong order: Not assigning materials to all the domains. The objective here is to simplify the model to a state where the model will solve, with linear approximations. - the incident has nothing to do with me; can I use this this way? Understanding the Fully Coupled vs. 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. In such cases, see if one material (or the other) can be omitted from the analysis completely. 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 will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). These can be used alone, or in combination with other interfaces. Your email address will not be published. Not meshing all the domains. 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. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. Perhaps this approach could be adapted to represent your model. It is also possible to manually refine the mesh. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. 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. 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. Stationary in the COMSOL Multiphysics Programming Reference Manual Damped Newton Methods The nonlinear solver uses an affine invariant form of the damped Newton method as described in Ref. Consult your product manuals for complete trademark details. The conditions on the geometric aspect ratio are relatively more strict. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) Stationary Solver Iterative Direct . If you try to enter a variable that is undefined, the automatic syntax highlighting will identify this as you enter it, and it is best practice to resolve this immediately. Is it possible to rotate a window 90 degrees if it has the same length and width? Check the solver log to see if the continuation method is backtracking. Hello guys. If these settings have been manually changed, you will see a small star symbol on the Solution feature, as shown in the screenshot below. 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. 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. It may also reveal that the model itself is ill-posed in some way. COMSOL does not assume any legal liability for the accuracy of the data disclosed. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. Have you taken a look at this blog post? From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. GCRO-DR is a method for Krylov subspace recycling. 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. (I am begginer in comsol) Thank you. Leverage your professional network, and get hired. The Fully Coupled solution approach, with the Plot While Solving enabled. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. Not assigning proper boundary conditions: Especially if you have ports. Hi Jason, Singular matrix., Make sure you defined your ports correctly:Boundary selectionType of port: e.g. Your Discussion has gone 30 days without a reply. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. Repeat this for every nonlinearity of the model. 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 default solver for most 3D models is an iterative solver, which is more sensitive to ill-conditioned problems. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. 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. Cooling and Solidification of Metal. To switch between these solver types, go to the Stationary Solver node within the Study sequence. Note: there is no way to couple this field with the time dependent nature of this physics. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. First, it is physically intuitive, often matching how one would perform an experiment. This is a review for cards & stationery in Brea, CA: "Love this store!!! It is sometimes necessary to manually scale the dependent variables. See Knowledge Base 1240: Manually Setting the Scaling of Variables. 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. Your internet explorer is in compatibility mode and may not be displaying the website correctly. (Frequency Domain should be the last step). I want to conduct a simulation to find a solution (u) and its first derivative (ux) using a 3D stationary model. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. It is sometimes necessary to manually scale the dependent variables. I highly recommend this flower shop. Any trademarks referenced in this document are the property of their respective owners. When you use an iterative solver, COMSOL Multiphysics estimates the error of the solution while solving. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. 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. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. 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. Therefore, it is recommended to use Adaptive Mesh Refinement which will automatically refine the mesh only in regions where it is needed, and coarsen the mesh elsewhere. This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. If the default iterative solver is not converging, try switching to a direct solver, as described here: Understanding the Fully Coupled vs. 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. 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. 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 solver settings are stored at Study > Solver Configurations > Solution. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. Reviews on Stationary Stores in Brea, CA - Typo, Mievic, Posh Paper, Morning Glory, Select Graphics & Printing, Daiso Japan, Urban Outfitters, Office Depot, Barnes & Noble 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. There will always already be either a Segregated or Fully Coupled feature beneath this. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: In this post, we will delve deeper into how to choose an appropriate mesh to start your mesh convergence studies for linear static finite element problems. Therefore, it is recommended to use Adaptive Mesh Refinement which will automatically refine the mesh only in regions where it is needed, and coarsen the mesh elsewhere. They worked with me. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. Not the answer you're looking for? COMSOL does not assume any legal liability for the accuracy of the data disclosed. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. COMSOL does not assume any legal liability for the accuracy of the data disclosed. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. 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. COMSOL makes every reasonable effort to verify the information you view on this page. . Segregated approach and Direct vs. 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. Consult your product manuals for complete trademark details. listed if standards is not an option). Solving for laminar flow using Comsol - YouTube Comsol help video number 2: Solving a laminar flow problem in a slit.

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