When you use an iterative solver, COMSOL Multiphysics estimates the error of the solution while solving. Does anyone know what should cause this problem? Posted 26 set 2019, 11:57 GMT-4 Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. Any trademarks referenced in this document are the property of their respective owners. Segregated approach and Direct vs. Name: actdep_int1, Your email address will not be published. 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. 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. 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. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) 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. Repeat this for every nonlinearity of the model. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version The Auxiliary Sweep can be used to implement ramping of any Global Parameter. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). This is a review for cards & stationery in Brea, CA: "Love this store!!! Changes to these low-level settings from the defaults will usually be quite model- and case-specific. She opened prepackaged 6-packs of Seegars to make ", All "stationary stores" results in Brea, CA, Search stationary stores in popular locations. These are some cards & stationery with a large number of reviews in Brea, CA. Tutti i diritti sono riservati. Such problems must solved in the time domain. Trying to understand how to get this basic Fourier Series. Your email address will not be published. Studysteps might be listed in wrong order: Not assigning materials to all the domains. Stationary Engineer Jobs in Brea, California, United States, $87,400.00 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. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. Iterative , Direct . In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. 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. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) 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. If it does so, use a finer increment in that range. Reply . How do/should administrators estimate the cost of producing an online introductory mathematics class? . However, it is usually not possible to know this ahead of time. Full text of the 'Sri Mahalakshmi Dhyanam & Stotram'. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. 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. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the same mesh: adaptmesh1. It is sometimes necessary to manually scale the dependent variables. Solver . A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. They worked with me. 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. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) 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. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the 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. 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. SGP handled 7 different prints for me at once and they all came out perfectly, in a timely manner. 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. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. Acidity of alcohols and basicity of amines. 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. 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. $125,000.00, Project Engineer (In-person/Hybrid/Remote), $100,000.00 Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. These are some highly rated cards & stationery in Brea, CA: What are some cards & stationery with a large number of reviews in Brea, CA? "After the incident", I started to be more careful not to trip over things. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. This involves a systematic reduction in the model complexity. This solver is automatically used when a Stationary or Frequency Domain study is added to the model. Here, we will examine techniques for accelerating the convergence of these two methods. The conditions on the geometric aspect ratio are relatively more strict. - 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. In such cases, see if one material (or the other) can be omitted from the analysis completely. Have you taken a look at this blog post? 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. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. This approach is known as a Continuation Method with a Constant predictor. $140,000.00, $120,000.00 Your internet explorer is in compatibility mode and may not be displaying the website correctly. 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. To switch between these solver types, go to the Stationary Solver node within the Study sequence. Solving for laminar flow using Comsol - YouTube Comsol help video number 2: Solving a laminar flow problem in a slit. Using the first order optimality. Your internet explorer is in compatibility mode and may not be displaying the website correctly. 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. See if these can be used instead of explicitly modeling parts with high-aspect ratio geometries. The Fully Coupled solution approach, with the Plot While Solving enabled. "I chose this print shop based off yelp reviews and was very happy with the outcome! Stationary Solver Iterative Direct . If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base. Check the solver log to see if the continuation method is backtracking. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. The other low-level default settings within the Stationary Solver are chosen for robustness. The segregated approach, on the other hand, solves sets of unknowns separately. The segregated approach, on the other hand, solves sets of unknowns separately. Singular matrix., Make sure you defined your ports correctly:Boundary selectionType of port: e.g. That is, they are tuned to achieve convergence in as many cases as possible. 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. Any trademarks referenced in this document are the property of their respective owners. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. They are usually called comp1.u, comp1.v, and comp1.w though. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. Not entering required material parameters. It is also possible to manually refine the mesh. Under Initial values of variables solved for, the default value of the Settingslist is Physics controlled. Solve the stationary study then the time dependent study. Hence Comsol solved for the stationary solution at different points of time. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) Please dont hesitate to post comments below or send emails to us if you experience any other problems. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Feature: Stationary Solver 1 (sol1/s1)" . Improving Convergence of Nonlinear Stationary Models, Knowledgebase 1030: Error: "Out of memory", Knowledgebase 1030: Performing a Mesh Refinement Study, Understanding the Fully Coupled vs. Use this parameter to modify the nonlinearity expressions in the model. 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. I want to conduct a simulation to find a solution (u) and its first derivative (ux) using a 3D stationary 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. This guide applies solely to nonlinear stationary models. 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. Then use this file to provide the initial conditions in time dependent model. However, it is usually not possible to know this ahead of time. This is relatively expensive to do, but will lead to the most robust convergence. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. (I am begginer in comsol) Thank you. To learn more, see our tips on writing great answers. P&S Comsol Team: Arif Gngr , Yannik Horst , Stefano Valente. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Such problems must solved in the time domain. Any trademarks referenced in this document are the property of their respective owners. Reviews on Stationary Stores in Brea, CA - Typo, Mievic, Posh Paper, Morning Glory, Select Graphics & Printing, Daiso Japan, Urban Outfitters, Office Depot, Barnes & Noble If it does so, use a finer increment in that range. listed if standards is not an option). 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. Numerically ill-conditioned means that the system matrix is nearly singular and that it will be difficult to solve on a finite-precision computer. Your internet explorer is in compatibility mode and may not be displaying the website correctly. COMSOL makes every reasonable effort to verify the information you view on this page. $130,000.00. The segregated approach, on the other hand, solves sets of unknowns separately. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) What did people search for similar to stationary stores in Brea, CA? Hi Alexis, 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. 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. Multiphysics problems are often nonlinear. 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. P&S Comsol Team: Yannik Horst, Manuel Kohli, Xinzhi Zhang. Linear solvers. 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. 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. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. COMSOL 22.9K subscribers Adding a study to your simulation is necessary in order to solve your problem. This guide applies solely to nonlinear stationary models. 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. First, it is physically intuitive, often matching how one would perform an experiment. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. The algorithm is, generally speaking, a Newton's method approach. Hi ! Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. The default Initial Values for the unknowns in most physics interfaces are zero. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. Hi Jason, With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. P&S: COMSOL Design Tool for Photonic Devices. 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. 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. The prices are good, and when I needed something delivered, same day, they were able to do it, and it looked beautiful!! listed if standards is not an option). This algorithm was also useful for understanding what happens near a failure load. Consult your product manuals for complete trademark details. The coupling terms between the different groups are thus neglected. 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. Alternatively, delete and re-create the study. What are people saying about cards & stationery in Brea, CA? 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. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). 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. It is sometimes necessary to manually scale the dependent variables. listed if standards is not an option). Use this parameter to modify the nonlinearity expressions in the model. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. So far, weve learned how to mesh and solve linear and nonlinear single-physics finite element problems, but have not yet considered what happens when there are multiple different interdependent physics being solved within the same domain. The problem is that when I run my model this message appear: Undefined value found. listed if standards is not an option). Stationary Solver Use the Stationary Solver () to find the solution to linear and nonlinear stationary problems (also called static or steady-state problems). Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. 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. It is also possible to manually refine the mesh. To start a new discussion with a link back to this one, click here. This case is generally difficult, or impossible, to solve since this material property is non-smooth. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. 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. 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. Direct Iterative , Direct . The objective here is to simplify the model to a state where the model will solve, with linear approximations. As a rough rule of thumb, once the aspect ratio between the largest characteristic dimension to the smallest approaches 100:1, you might start to run into issues and should look to alternative ways of posing the problem, especially in a 3D model. P&S Comsol Team: Manuel Kohli, Raphael Schwanninger, Feature: Stationary Solver 1 (sol1/s1) This approach is known as a Continuation Method with a Constant predictor. Dr.S.Ravindran Cite 1 Recommendation Popular answers (1). You can unsubscribe from these emails at any time.

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