stationary solver comsol

- Feature: Stationary Solver 1 (sol1/s1) Again, introduce a Global Parameter that gets ramped from exactly zero to one. The other low-level default settings within the Stationary Solver are chosen for robustness. Discussion Closed This discussion was created more than 6 months ago and has been closed. 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. Again, introduce a Global Parameter that gets ramped from exactly zero to one. listed if standards is not an option). 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 is relatively expensive to do, but will lead to the most robust convergence. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. 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 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. Stationary Solver Use the Stationary Solver () to find the solution to linear and nonlinear stationary problems (also called static or steady-state problems). The conditions on the geometric aspect ratio are relatively more strict. 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. 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. Most multiphysics problems are nonlinear. (Frequency Domain should be the last step). 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. For example, if there is a temperature-dependent material property such as: Find centralized, trusted content and collaborate around the technologies you use most. This is relatively expensive to do, but will lead to the most robust convergence. November 11, 2013. $125,000.00, Project Engineer (In-person/Hybrid/Remote), $100,000.00 What did people search for similar to stationary stores in Brea, CA? Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. What is the purpose of non-series Shimano components? This approach is known as a Continuation Method with a Constant predictor. Thanks for contributing an answer to Stack Overflow! (I am begginer in comsol) Thank you. Segregated approach and Direct vs. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) 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. GCRO-DR is a method for Krylov subspace recycling. 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. rev2023.3.3.43278. The advantages of the continuation method are two-fold. Learn how your comment data is processed. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. 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. They worked with me. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. That is, start by first solving a model with a small, but non-zero, load. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: 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. Function: / Failed to evaluate expression. Once the error estimate is small enough, as determined by the convergence criterion (20-16) the software terminates the computations and returns a solution. Not assigning proper boundary conditions: Especially if you have ports. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. P&S: COMSOL Design Tool for Photonic Devices. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. 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. 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. 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. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. Save my name, email, and website in this browser for the next time I comment. . It is sometimes necessary to manually scale the dependent variables. Linear solvers. Multiscale Modeling in High-Frequency Electromagnetics. 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. My comment is perhaps a bit nave but it seems to me that you could simply deactivate the \frac{\partial \cdot}{\partial t} term of the background field equation but keep its connexion to the solid to get what you want. Making statements based on opinion; back them up with references or personal experience. Such problems must solved in the time domain. thanks for reply Contact COMSOL at Bangalore on their telephone: +9180 25323003. First, it is physically intuitive, often matching how one would perform an experiment. Leverage your professional network, and get hired. Could you expand a little bit more why the coupling is impossible? However, load ramping will not work in all cases, or may be inefficient. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. In many physics areas there exist alternative physics formulations specifically meant for solving cases where the geometry has an extreme aspect ratio. Linear solvers. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. With respect to any nonlinearities, replace them by a reasonable linearized term. Tutti i diritti sono riservati. This involves a systematic reduction in the model complexity. 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. Then I stored the resulting solution, and used it to to solve the stationary solver again by using the solver manager. if I want to do an adaptive mesh refinement, I get this error. Different physics have different default solvers. Your internet explorer is in compatibility mode and may not be displaying the website correctly. listed if standards is not an option). Then use this file to provide the initial conditions in time dependent model. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. 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. Here we introduce the two classes of algorithms used to solve multiphysics finite element problems in COMSOL Multiphysics. 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. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. The coupling terms between the different groups are thus neglected. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. New Stationary Engineer jobs added daily. This consent may be withdrawn. Set initial conditions in the physics to the appropriate dependent model variable names rather than the default 0. -Detail: NaN or Inf found when solving linear system using SOR. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Hi Jason, The objective here is to simplify the model to a state where the model will solve, with linear approximations. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. Improving Convergence of Nonlinear Stationary Models, Knowledgebase 1030: Error: "Out of memory", Knowledgebase 1030: Performing a Mesh Refinement Study, Understanding the Fully Coupled vs. Get email updates for new Stationary Engineer jobs in Brea, California, United States. listed if standards is not an option). To subscribe to this RSS feed, copy and paste this URL into your RSS reader. However, it is usually not possible to know this ahead of time. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. What are people saying about cards & stationery in Brea, CA? If the default iterative solver is not converging, try switching to a direct solver, as described here: Understanding the Fully Coupled vs. The other low-level default settings within the Stationary Solver are chosen for robustness. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. 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. For example, if there is a temperature-dependent material property such as: A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. If your matrix is singular than no solver in the world can solve Ax=B. Repeat this for every nonlinearity of the model. If these settings have been manually changed, you will see a small star symbol on the Solution feature, as shown in the screenshot below. Does anyone know what should cause this problem? Communication over the phone, in person, and through email was very easy. Why? k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. That is, start by first solving a model with a small, but non-zero, load. 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. Note: there is no way to couple this . listed if standards is not an option). Posted Sep 9, 2020, 1:44 p.m. EDT How do/should administrators estimate the cost of producing an online introductory mathematics class? Alternatively, delete and re-create the study. - 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: Manuel Kohli, Raphael Schwanninger, Feature: Stationary Solver 1 (sol1/s1) The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. (Frequency Domain should be the last step) 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. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. 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. That is, they are tuned to achieve convergence in as many cases as possible. My comment is perhaps a bit nave but it seems to me that you could simply deactivate the term of the background field equation but keep its connexion to the solid to get what you want. It's brand new in the hmart plaza and I wish it was open back when I would hangout in the plaza after school (although they would have taken all my allowance money! listed if standards is not an option). How can I check before my flight that the cloud separation requirements in VFR flight rules are met? The default Initial Values for the unknowns in most physics interfaces are zero. If the model is nonlinear, see: Improving Convergence of Nonlinear Stationary Models. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: Review the model setup to resolve these. Hi ! SGP handled 7 different prints for me at once and they all came out perfectly, in a timely manner. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) 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. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. Connect and share knowledge within a single location that is structured and easy to search. 140K views 8 years ago COMSOL Multiphysics Tutorial for Beginners Please note that an updated version of the content in this video can be found in the Modeling Workflow video in the COMSOL. 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. The default Initial Values for the unknowns in most physics interfaces are zero. Version 5.3 See Knowledge Base 1240: Manually Setting the Scaling of Variables. Stationary (time-invariant) models with nonlinearities may converge very slowly. It is also possible to manually refine the mesh. Computational Fluid Dynamics (CFD), API 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. Stationary Engineer Jobs in Brea, California, United States, $87,400.00 Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. 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. Not meshing all the domains. That is, start by first solving a model with a small, but non-zero, load. 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. 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. Have you taken a look at this [blog post](https://www.comsol.com/blogs/modeling-fluid-structure-interaction-in-multibody-mechanisms/)? In the extreme case, suppose one wants to model an instantaneous change in properties, such as: The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. See if these can be used instead of explicitly modeling parts with high-aspect ratio geometries. Solving for laminar flow using Comsol - YouTube Comsol help video number 2: Solving a laminar flow problem in a slit. It is sometimes necessary to manually scale the dependent variables. Your internet explorer is in compatibility mode and may not be displaying the website correctly. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. 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. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. Stationary (time-invariant) models with nonlinearities may converge very slowly. What is the purpose of this D-shaped ring at the base of the tongue on my hiking boots? If you are unsure if your problem is linear and stationary, look at the Log. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. Not the answer you're looking for? First, it is physically intuitive, often matching how one would perform an experiment. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Check the solver log to see if the continuation method is backtracking. 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. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. Posted 26 set 2019, 11:57 GMT-4 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. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well.

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