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If one particular material is missing one property, that material will also be highlighted with a red cross over that material icon in the Model Builder. "I chose this print shop based off yelp reviews and was very happy with the outcome! Improving Convergence of Nonlinear Stationary Models - Informazioni The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. 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. If the default iterative solver is not converging, try switching to a direct solver, as described here: Understanding the Fully Coupled vs. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. Wrong ordering of study steps. Not entering required material parameters. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the - COMSOL k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) Thanks for contributing an answer to Stack Overflow! The technique of load ramping is not always reasonable for all problems. What sort of strategies would a medieval military use against a fantasy giant? $130,000.00. For example, if there is a temperature-dependent material property such as: Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. To switch between these solver types, go to the Stationary Solver node within the Study sequence. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. 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. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Your internet explorer is in compatibility mode and may not be displaying the website correctly. 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. 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. Hi Jason, Reviews on Stationary Stores in Brea, CA - Typo, Mievic, Posh Paper, Morning Glory, Select Graphics & Printing, Daiso Japan, Urban Outfitters, Office Depot, Barnes & Noble In the extreme case, suppose one wants to model an instantaneous change in properties, such as: COMSOL does not assume any legal liability for the accuracy of the data disclosed. Repeat this for every nonlinearity of the model. 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. 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. Acidity of alcohols and basicity of amines. This algorithm was also useful for understanding what happens near a failure load. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. P&S: COMSOL Design Tool for Photonic Devices - ETH Z That is, start by first solving a model with a small, but non-zero, load. The segregated approach, on the other hand, solves sets of unknowns separately. Any trademarks referenced in this document are the property of their respective owners. Tutti i diritti sono riservati. 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. Any trademarks referenced in this document are the property of their respective owners. Does anyone know how to solve error in stationary solver in COMSOL listed if standards is not an option). Why is there a voltage on my HDMI and coaxial cables? replace it with the expression: 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. 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. Then I stored the resulting solution, and used it to to solve the stationary solver again by using the solver manager. If you are unsure if your problem is linear and stationary, look at the Log. Again, introduce a Global Parameter that gets ramped from exactly zero to one. 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. In this page, we will be sharing some common errors that might occur in Comsol and their solutions. Contact COMSOL at Bangalore on their telephone: +9180 25323003. The segregated approach, on the other hand, solves sets of unknowns separately. This consent may be withdrawn. 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. there is no defined multiphysics for it as I know, I have a standing accoustic wave and a flow in the background but I don't see their connection. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: This case is generally difficult, or impossible, to solve since this material property is non-smooth. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: First, it is physically intuitive, often matching how one would perform an experiment. If you see this, right-click on the Solution feature and select Reset Solver to Default. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. This is a review for cards & stationery in Brea, CA: "Love this store!!! - the incident has nothing to do with me; can I use this this way? 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. Wish you all the best. That is: Even if the forces on a part are opposite and equal, this is not sufficient information to say where the part is, so you must add some other condition, such as as Fixed Constraint to constrain displacement. Numerically ill-conditioned means that the system matrix is nearly singular and that it will be difficult to solve on a finite-precision computer. 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. Not meshing all the domains. Understanding the Fully Coupled vs. It is sometimes necessary to manually scale the dependent variables. P&S: COMSOL Design Tool for Photonic Devices. 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 approach is known as a Continuation Method with a Constant predictor. To start a new discussion with a link back to this one, click here. Solver . Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. Hi ! 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. Get notified about new Stationary Engineer jobs in Brea, California, United States. 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. Not the answer you're looking for? That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. I highly recommend this flower shop. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. When you use an iterative solver, COMSOL Multiphysics estimates the error of the solution while solving. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. Multiphysics problems are often nonlinear. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); This site uses Akismet to reduce spam. 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. (Frequency Domain should be the last step). Connect and share knowledge within a single location that is structured and easy to search. Consult your product manuals for complete trademark details. Making statements based on opinion; back them up with references or personal experience. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. 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. Screenshot showing a Solver Configuration that has been altered. 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. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. Solving for laminar flow using Comsol - YouTube comsol - using stationary solution as the initial conditions in time Direct PARDISO Solver , PARDISO . Improving Convergence of Nonlinear Stationary Models, Knowledgebase 1030: Error: "Out of memory", Knowledgebase 1030: Performing a Mesh Refinement Study, Understanding the Fully Coupled vs. If it does so, use a finer increment in that range. These are some cards & stationery with a large number of reviews in Brea, CA. The problem is that when I run my model this message appear: Undefined value found. 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. 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. Stationary Solver Iterative Direct . A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. The Fully Coupled solution approach, with the Plot While Solving enabled. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. The coupling terms between the different groups are thus neglected. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. Communication over the phone, in person, and through email was very easy. Perhaps this approach could be adapted to represent your model. listed if standards is not an option). 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. 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. Such problems must solved in the time domain. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. (Frequency Domain should be the last step) 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. Most multiphysics problems are nonlinear. 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. This is relatively expensive to do, but will lead to the most robust convergence. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. That is, start by first solving a model with a small, but non-zero, load. What is the purpose of non-series Shimano components? In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. Dun & Bradstreet gathers Office Supplies, Stationery, and Gift Retailers business information from trusted . The objective here is to simplify the model to a state where the model will solve, with linear approximations. It may also reveal that the model itself is ill-posed in some way. Not assigning proper boundary conditions: Especially if you have ports. P&S Comsol Team: Arif Gngr , Yannik Horst , Stefano Valente. rev2023.3.3.43278. This guide applies solely to nonlinear stationary models. listed if standards is not an option). Your internet explorer is in compatibility mode and may not be displaying the website correctly. With respect to any nonlinearities, replace them by a reasonable linearized term. Have you taken a look at this blog post? Under Initial values of variables solved for, the default value of the Settingslist is Physics controlled. Feature: Stationary Solver 1 (sol1/s1)" . From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. Stationary Solver Use the Stationary Solver () to find the solution to linear and nonlinear stationary problems (also called static or steady-state problems). Not meshing all the domains. The algorithm is, generally speaking, a Newton's method approach. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. The fully coupled and segregated approaches are discussed below. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. - Function: ^ Failed to evaluate variable. If so, see: Knowledgebase 1030: Error: "Out of memory". Therefore, an initial value of zero is almost always reasonable if a very small load is applied. That is, they are tuned to achieve convergence in as many cases as possible. This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. About the Stationary Solver - COMSOL Multiphysics Here we introduce the two classes of algorithms used to solve multiphysics finite element problems in COMSOL Multiphysics. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. Direct Iterative , Direct . Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. COMSOL Blog Series on COMSOL Multiphysics Solvers 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]) Not assigning proper boundary conditions: Especially if you have ports. - Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the same mesh: adaptmesh1. Have you taken a look at this [blog post](https://www.comsol.com/blogs/modeling-fluid-structure-interaction-in-multibody-mechanisms/)? However, it is usually not possible to know this ahead of time. Use this parameter to modify the nonlinearity expressions in the model. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. Top 10 Best Stationary in Brea, CA - October 2022 - Yelp Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. Segregated approach and Direct vs. Iterative linear solvers, About the time step setting of the solver, Introducing Goal Seeking into the Segregated Solver. there is no defined multiphysics for it as I know, I have a standing accoustic wave and a flow in the background but I don't see their connection. Multiphysics problems are often nonlinear. Your internet explorer is in compatibility mode and may not be displaying the website correctly. It is sometimes necessary to manually scale the dependent variables. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. This case is generally difficult, or impossible, to solve since this material property is non-smooth. I have searched all over comsol forum to fix this stationary solver configuration and still doesn't work because I don't know the logic behind the solver system. There will always already be either a Segregated or Fully Coupled feature beneath this. This guide applies solely to nonlinear stationary models. 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. Common Study Step Settings - COMSOL Multiphysics k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) 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. It may also reveal that the model itself is ill-posed in some way. I'm trying to model a solid that's moving through a steady background field in a background flow, I want to take into account the effect of movement of the solid after each time step so I have to use stationary solver after each time step in order to see how field has changed after solid moved. If the model is nonlinear, see: Improving Convergence of Nonlinear Stationary Models. In our previous blog entry, we introduced the Fully Coupled and the Segregated algorithms used for solving steady-state multiphysics problems in COMSOL. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. 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. It may also reveal that the model itself is ill-posed in some way. Review the model setup to resolve these. Multiphysics problems are often nonlinear. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). Common Mistakes: Not assigning materials to all the domains. 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. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. GCRO-DR is a method for Krylov subspace recycling. solving stationary solver after each time step - COMSOL Multiphysics This is relatively expensive to do, but will lead to the most robust convergence. COMSOL makes every reasonable effort to verify the information you view on this page. Check the solver log to see if the continuation method is backtracking. An example would be a linear static structural model of an aluminum beverage can. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. - As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. 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.