stationary solver comsol stationary solver comsol

To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Why doesn't iterative solver converge in COMSOL? - ResearchGate 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. Again, introduce a Global Parameter that gets ramped from exactly zero to one. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. 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. Here we introduce the two classes of algorithms used to solve multiphysics finite element problems in COMSOL Multiphysics. However, it is usually not possible to know this ahead of time. listed if standards is not an option). This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. Hi ! 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. See Knowledge Base 1240: Manually Setting the Scaling of Variables. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. 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. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); This site uses Akismet to reduce spam. There will always already be either a Segregated or Fully Coupled feature beneath this. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. Hello, That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. P&S: COMSOL Design Tool for Photonic Devices - ETH Z Multiphysics problems are often nonlinear. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. Posted 26 set 2019, 17:57 CEST Mesh Version 5.3 0 Replies. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. That is, start by first solving a model with a small, but non-zero, load. 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. Such problems must solved in the time domain. It is also possible to manually refine the mesh. 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. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. The other low-level default settings within the Stationary Solver are chosen for robustness. COMSOL does not assume any legal liability for the accuracy of the data disclosed. This approach is known as a Continuation Method with a Constant predictor. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) The other low-level default settings within the Stationary Solver are chosen for robustness. 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, 2023 by COMSOL. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. Few days back i was also facing this problem in . This solver is automatically used when a Stationary or Frequency Domain study is added to the model. For the Nozomi from Shinagawa to Osaka, say on a Saturday afternoon, would tickets/seats typically be available - or would you need to book? Second, the continuation method will automatically take smaller load increments if a solution cannot be found. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. One of the key concepts there was the idea of mesh convergence as you refine the mesh, the solution will become more accurate. The settings controlling the predictor type. It can be useful while solving sequences of linear systems arising from, for example, nonlinear problems. COMSOL Blog Series on COMSOL Multiphysics Solvers comp1.u2, comp1.v2, and comp1.w2 are usually variables associated with the x,y, and z component of deformation in COMSOL. 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. Solving for laminar flow using Comsol - YouTube Comsol help video number 2: Solving a laminar flow problem in a slit. The coupling terms between the different groups are thus neglected. P&S: COMSOL Design Tool for Photonic Devices. The settings controlling the predictor type. 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. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. GCRO-DR is a method for Krylov subspace recycling. Stationary (time-invariant) models with nonlinearities may converge very slowly. rev2023.3.3.43278. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. ", "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. Your email address will not be published. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. (Frequency Domain should be the last step) Consult your product manuals for complete trademark details. The objective here is to simplify the model to a state where the model will solve, with linear approximations. 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. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. 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. However, if a lower-level change has been manually made to the solver settings, the software will not automatically use the correct default solver. This involves a systematic reduction in the model complexity. Stationary (time-invariant) models with nonlinearities may converge very slowly. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. 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. 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. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. 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. However, load ramping will not work in all cases, or may be inefficient. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: Have you taken a look at this [blog post](https://www.comsol.com/blogs/modeling-fluid-structure-interaction-in-multibody-mechanisms/)? Have you taken a look at this blog post? New Stationary Engineer jobs added daily. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. 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. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the - COMSOL You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version COMSOL makes every reasonable effort to verify the information you view on this page. 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 is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. Solver . 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. However, it is usually not possible to know this ahead of time. 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. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. Alternatively, delete and re-create the study. An example would be a linear static structural model of an aluminum beverage can. listed if standards is not an option). Not entering required material parameters. Stationary Solver Iterative Direct . You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version The technique of load ramping is not always reasonable for all problems. Your internet explorer is in compatibility mode and may not be displaying the website correctly. P&S Comsol Team: Arif Gngr , Yannik Horst , Stefano Valente. 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. The conditions on the geometric aspect ratio are relatively more strict. Perhaps this approach could be adapted to represent your model. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. 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. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. Not assigning proper boundary conditions: Especially if you have ports. 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. Any trademarks referenced in this document are the property of their respective owners. This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. 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. For example, if there is a temperature-dependent material property such as: If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. It is also possible to manually refine the mesh. Common Mistakes: Not assigning materials to all the domains. Understanding the Fully Coupled vs. Screenshot showing a Solver Configuration that has been altered. If the model is nonlinear, see: Improving Convergence of Nonlinear Stationary Models. Again, introduce a Global Parameter that gets ramped from exactly zero to one. 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.) 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. 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. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. 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. November 11, 2013. 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. See if these can be used instead of explicitly modeling parts with high-aspect ratio geometries. 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. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. Making statements based on opinion; back them up with references or personal experience. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. It is also possible to manually refine the mesh. It is sometimes necessary to manually scale the dependent variables. Mesh If you are unsure if your problem is linear and stationary, look at the Log. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. Different physics have different default solvers. Any trademarks referenced in this document are the property of their respective owners. The problem is that when I run my model this message appear: Undefined value found. This involves a systematic reduction in the model complexity. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version The default solver for most 3D models is an iterative solver, which is more sensitive to ill-conditioned problems. Not entering required material parameters. 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. Could you expand a little bit more why the coupling is impossible? The Fully Coupled solution approach, with the Plot While Solving enabled. Using the first order optimality. COMSOL makes every reasonable effort to verify the information you view on this page. If the default iterative solver is not converging, try switching to a direct solver, as described here: Understanding the Fully Coupled vs. listed if standards is not an option). A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. 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. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. 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. The Iterative Solvers - COMSOL Multiphysics Then use this file to provide the initial conditions in time dependent model. 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. 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. 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. Find centralized, trusted content and collaborate around the technologies you use most. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. P&S Comsol Team: Manuel Kohli, Raphael Schwanninger, Feature: Stationary Solver 1 (sol1/s1) Communication over the phone, in person, and through email was very easy. With respect to any nonlinearities, replace them by a reasonable linearized term. COMSOL Error for Initial Values(RF Module) Sign in to create your job alert for Stationary Engineer jobs in Brea, California, United States. if I want to do an adaptive mesh refinement, I get this error. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: (Frequency Domain should be the last step). Not meshing all the domains. listed if standards is not an option). In particular, choosing an improper initial condition or setting up a problem without a solution will simply cause the nonlinear solver to continue iterating without converging. If your matrix is singular than no solver in the world can solve Ax=B. Feature: Stationary Solver 1 (sol1/s1) Attempt to evaluate nonintegral power of negative number. I personally liked emailing them the file, ", "This flower shop is the best! Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) Posted 26 set 2019, 11:57 GMT-4 COMSOL makes every reasonable effort to verify the information you view on this page. 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. Improving Convergence of Nonlinear Stationary Models - COMSOL Hence Comsol solved for the stationary solution at different points of time. Check the solver log to see if the continuation method is backtracking. The advantages of the continuation method are two-fold. What version of COMSOL are you using? This involves a systematic reduction in the model complexity. Why? Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. Is it possible to rotate a window 90 degrees if it has the same length and width? Multiphysics problems are often nonlinear. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. Hi Alexis, 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. 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. Dr.S.Ravindran Cite 1 Recommendation Popular answers (1). Not entering required material parameters. Perhaps this approach could be adapted to represent your model. 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. 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. 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. Check the solver log to see if the continuation method is backtracking. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. 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. 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. Full text of the 'Sri Mahalakshmi Dhyanam & Stotram'. Any trademarks referenced in this document are the property of their respective owners. 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. 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. How can I use it? 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. Contact COMSOL at Bangalore on their telephone: +9180 25323003. If it does so, use a finer increment in that range. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. The algorithm is, generally speaking, a Newton's method approach. This consent may be withdrawn. Such a large difference in the materials properties can be challenging. Posted Sep 9, 2020, 1:44 p.m. EDT With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. Linear solvers. - Function: ^ Failed to evaluate variable. Reviews on Stationary in Brea, CA - Mievic, Typo, Tokyo Japanese Lifestyle, Fancy, Posh Paper, Morning Glory, Velvet Fox Designs, Barnes & Noble, Michaels, Select Graphics & Printing 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. COMSOL does not assume any legal liability for the accuracy of the data disclosed. Feature: Stationary Solver 1 (sol1/s1)" . 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. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. This algorithm was also useful for understanding what happens near a failure load. replace it with the expression: That is, they are tuned to achieve convergence in as many cases as possible. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. 3. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates.