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. Again, introduce a Global Parameter that gets ramped from exactly zero to one. 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. This involves a systematic reduction in the model complexity. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. $131,100.00, Simplified Vehicle Operations Project Engineer, $115,000.00 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. For example, if there is a temperature-dependent material property such as: This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. Multiphysics problems are often nonlinear. Mesh 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. To learn more, see our tips on writing great answers. Does anyone know how to solve error in stationary solver in COMSOL If the material properties entered are incorrect for the governing equation, the model will generate an error at runtime, usually a Singular Matrix error. Such a case would be better to address instead with the Shell physics interface, which is specially formulated for handling thin-walled structural parts. For example, if there is a temperature-dependent material property such as: The other low-level default settings within the Stationary Solver are chosen for robustness. Not assigning proper boundary conditions: Especially if you have ports. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. These are some cards & stationery with a large number of reviews in Brea, CA. This guide applies solely to nonlinear stationary models. Cecilia M. came from the backroom to help me and went out of her way to help me even though I had not called before going into the store. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. 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 algorithm is, generally speaking, a Newton's method approach. -Detail: NaN or Inf found when solving linear system using SOR. Check the solver log to see if the continuation method is backtracking. 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. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. In the COMSOL Multiphysics software, this step of the modeling workflow is made. 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. listed if standards is not an option). Solving for laminar flow using Comsol - YouTube The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. 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. "After the incident", I started to be more careful not to trip over things. Such problems must solved in the time domain. Posted 26 set 2019, 11:57 GMT-4 Such a large difference in the materials properties can be challenging. Why doesn't iterative solver converge in COMSOL? - ResearchGate COMSOL does not assume any legal liability for the accuracy of the data disclosed. listed if standards is not an option). The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. With respect to any nonlinearities, replace them by a reasonable linearized term. Reply . There will always already be either a Segregated or Fully Coupled feature beneath this. It may also reveal that the model itself is ill-posed in some way. Top 10 Best Stationary in Brea, CA - October 2022 - Yelp Here, we begin an overview of the algorithms used for solving nonlinear static finite element problems. This involves a systematic reduction in the model complexity. If you have both as steps in the same study, then solve that study. Not meshing all the domains. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. Iterative - COMSOL Multiphysics 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. However, if a lower-level change has been manually made to the solver settings, the software will not automatically use the correct default solver. Note the star symbol on the Solution feature. Function: / Failed to evaluate expression. - Feature: Stationary Solver 1 (sol1/s1)Failed to find a solution. 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. Cooling and Solidification of Metal. This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. $140,000.00, $120,000.00 COMSOL makes every reasonable effort to verify the information you view on this page. What is the purpose of non-series Shimano components? 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. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. Acidity of alcohols and basicity of amines. 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. Today's top 351 Stationary Engineer jobs in Brea, California, United States. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. so many cute little stationary items , hair". This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. Get email updates for new Stationary Engineer jobs in Brea, California, United States. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. Once the error estimate is small enough, as determined by the convergence criterion (20-16) the software terminates the computations and returns a solution. I personally liked emailing them the file, ", "This flower shop is the best! What did people search for similar to stationary stores in Brea, CA? - I want to conduct a simulation to find a solution (u) and its first derivative (ux) using a 3D stationary model. P&S Comsol Team: Arif Gngr , Yannik Horst , Stefano Valente. 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. By default, the COMSOL Multiphysics software determines these values heuristically depending on the physics as, for example, the specified initial values or a solution from an earlier study step. thanks for reply Thanks, Andres. The coupling terms between the different groups are thus neglected. Your internet explorer is in compatibility mode and may not be displaying the website correctly. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. To switch between these solver types, go to the Stationary Solver node within the Study sequence. 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. P&S Comsol Team: Yannik Horst, Manuel Kohli, Xinzhi Zhang. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Connect and share knowledge within a single location that is structured and easy to search. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. 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. . Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. The advantages of the continuation method are two-fold. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: To switch between these solver types, go to the Stationary Solver node within the Study sequence. Alternatively, delete and re-create the study. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. This case is generally difficult, or impossible, to solve since this material property is non-smooth. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. Version 5.3 How can I check before my flight that the cloud separation requirements in VFR flight rules are met? 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. 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. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. 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. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: 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. 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. Using the first order optimality. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. Tutti i diritti sono riservati. Stationary (time-invariant) models with nonlinearities may converge very slowly. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. See if these can be used instead of explicitly modeling parts with high-aspect ratio geometries. 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. Common Mistakes: Not assigning materials to all the domains. 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. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. If you see this, right-click on the Solution feature and select Reset Solver to Default. 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. P&S: COMSOL Design Tool for Photonic Devices. 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. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. Discussion Closed This discussion was created more than 6 months ago and has been closed. What are some highly rated cards & stationery in Brea, CA? 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. In such cases, see if one material (or the other) can be omitted from the analysis completely. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. Troubleshooting for 3D trusses, if anyone's out there. : r/COMSOL - reddit - By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) (COMSOL Multiphysics) : 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. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. Direct Iterative , Direct . That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. That is, start by first solving a model with a small, but non-zero, load. 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. Such problems must solved in the time domain. I am solving a linear stationary finite element model but the software is not solving. Repeat this for every nonlinearity of the model. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. 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 entering required material parameters. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. To start a new discussion with a link back to this one, click here. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Improving Convergence of Nonlinear Stationary Models - COMSOL Stationary Engineer Jobs in Brea, California, United States, $87,400.00 listed if standards is not an option). However, it is usually not possible to know this ahead of time. Wrong ordering of study steps. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. 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. That is, they are tuned to achieve convergence in as many cases as possible. This is relatively expensive to do, but will lead to the most robust convergence. This case is generally difficult, or impossible, to solve since this material property is non-smooth. Use this parameter to modify the nonlinearity expressions in the model. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. The default Initial Values for the unknowns in most physics interfaces are zero. Understanding the Fully Coupled vs. 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. The algorithm is, generally speaking, a Newton's method approach. The conditions on the geometric aspect ratio are relatively more strict. COMSOL makes every reasonable effort to verify the information you view on this page. comsol - using stationary solution as the initial conditions in time How to solve "Feature: Stationary Solver 1 (sol1/s1) Attempt - COMSOL Note: there is no way to couple this field with the time dependent nature of this physics. 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, start by first solving a model with a small, but non-zero, load. Could you expand a little bit more why the coupling is impossible? The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. 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. replace it with the expression: However, it is usually not possible to know this ahead of time. Why is there a voltage on my HDMI and coaxial cables? It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. Save this information to a file. You can unsubscribe from these emails at any time. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. The solver settings are stored at Study > Solver Configurations > Solution. 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. 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. Your internet explorer is in compatibility mode and may not be displaying the website correctly. The algorithm is, generally speaking, a Newton's method approach. If it does so, use a finer increment in that range. This solver is automatically used when a Stationary or Frequency Domain study is added to the model. 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. What is the purpose of this D-shaped ring at the base of the tongue on my hiking boots? Cooling and Solidification of Metal. These are some highly rated cards & stationery in Brea, CA: What are some cards & stationery with a large number of reviews in Brea, CA? In this page, we will be sharing some common errors that might occur in Comsol and their solutions. There will always already be either a Segregated or Fully Coupled feature beneath this. 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. How to solve "Undefined material property 'sigma - ResearchGate Learn how your comment data is processed. Use this parameter to modify the nonlinearity expressions in the model. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. The segregated approach, on the other hand, solves sets of unknowns separately. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the - COMSOL Common Mistakes: Not assigning materials to all the domains. 351 Stationary Engineer jobs in Brea, California, United States (15 new)