stationary solver comsol

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. Improving Convergence of Nonlinear Stationary Models - Informazioni Repeat this for every nonlinearity of the model. They worked with me. The default solver for most 3D models is an iterative solver, which is more sensitive to ill-conditioned problems. The coupling terms between the different groups are thus neglected. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. To switch between these solver types, go to the Stationary Solver node within the Study sequence. 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. For example, if there is a temperature-dependent material property such as: Most multiphysics problems are nonlinear. 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. 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. Segregated approach and Direct vs. See Knowledge Base 1240: Manually Setting the Scaling of Variables. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). How can I use it? You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version 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. Any trademarks referenced in this document are the property of their respective owners. This information is presented in the context of a very simple 1D finite element problem, and builds upon our previous entry on Solving Linear Static Finite Element Models. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. listed if standards is not an option). 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. 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. The algorithm is, generally speaking, a Newton's method approach. - The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. Computational Fluid Dynamics (CFD), API If it does so, use a finer increment in that range. The default Initial Values for the unknowns in most physics interfaces are zero. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. Not assigning proper boundary conditions: Especially if you have ports. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. This case is generally difficult, or impossible, to solve since this material property is non-smooth. If your matrix is singular than no solver in the world can solve Ax=B. Wrong ordering of study steps. The other low-level default settings within the Stationary Solver are chosen for robustness. "I chose this print shop based off yelp reviews and was very happy with the outcome! listed if standards is not an option). The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. 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. 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. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). Repeat this for every nonlinearity of the model. Your internet explorer is in compatibility mode and may not be displaying the website correctly. 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. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. The settings controlling the predictor type. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. For example, if there is a temperature-dependent material property such as: Consult your product manuals for complete trademark details. Most multiphysics problems are nonlinear. 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. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) so many cute little stationary items , hair". What are people saying about cards & stationery in Brea, CA? Click the link in the email we sent to to verify your email address and activate your job alert. The other low-level default settings within the Stationary Solver are chosen for robustness. This can arise as a consequence of extreme variations in the material properties, or high aspect ratio geometry. 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. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. The segregated approach, on the other hand, solves sets of unknowns separately. 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. Multiphysics problems are often nonlinear. 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. With respect to any nonlinearities, replace them by a reasonable linearized term. That is, they are tuned to achieve convergence in as many cases as possible. 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. Troubleshooting for 3D trusses, if anyone's out there. : r/COMSOL - reddit Save this information to a file. 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 351 Stationary Engineer jobs in Brea, California, United States (15 new) The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. 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. This involves a systematic reduction in the model complexity. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) First, it is physically intuitive, often matching how one would perform an experiment. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Trying to understand how to get this basic Fourier Series. Discussion Closed This discussion was created more than 6 months ago and has been closed. However, if a lower-level change has been manually made to the solver settings, the software will not automatically use the correct default solver. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. This is a review for cards & stationery in Brea, CA: "Love this store!!! 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. 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. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. Again, introduce a Global Parameter that gets ramped from exactly zero to one. If you see this, right-click on the Solution feature and select Reset Solver to Default. By creating this job alert, you agree to the LinkedIn User Agreement and Privacy Policy. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) Linear solvers. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) Solve the stationary study then the time dependent study. Is there a way to use the stationary solution obtained in Comsol 4.2 as the initial conditions in a time dependent model? Such problems must solved in the time domain. COMSOL does not assume any legal liability for the accuracy of the data disclosed. I am trying to solve the coupling between a waveguide and a microring resonator. Does anyone know what should cause this problem? 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. What is the purpose of this D-shaped ring at the base of the tongue on my hiking boots? There will also be a red cross over the Materials branch icon. November 11, 2013. Repeat this for every nonlinearity of the model. If you are unsure if your problem is linear and stationary, look at the Log. 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. 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 Error for Initial Values(RF Module) Stationary (time-invariant) models with nonlinearities may converge very slowly. If it does so, use a finer increment in that range. It may also reveal that the model itself is ill-posed in some way. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. I want to conduct a simulation to find a solution (u) and its first derivative (ux) using a 3D stationary model. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. - Feature: Stationary Solver 1 (sol1/s1)Failed to find a solution. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. Not entering required material parameters. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. You can write the discrete form of the equations as f(U) = 0, where f(U) is the residual vector and U is the solution vector. Stationary Solver Iterative Direct . 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. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. 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. Hi Alexis, What are some highly rated cards & stationery in Brea, CA? 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. I am solving a linear stationary finite element model but the software is not solving. What is the purpose of non-series Shimano components? 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. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. Your internet explorer is in compatibility mode and may not be displaying the website correctly. - the incident has nothing to do with me; can I use this this way? 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. Connect and share knowledge within a single location that is structured and easy to search. Tutti i diritti sono riservati. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. It is also possible to manually refine the mesh. The advantages of the continuation method are two-fold. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. That is, start by first solving a model with a small, but non-zero, load. If the model is nonlinear, see: Improving Convergence of Nonlinear Stationary Models. How to solve "Undefined material property 'sigma - ResearchGate This is relatively expensive to do, but will lead to the most robust convergence. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. 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. Posted Sep 9, 2020, 1:44 p.m. EDT This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. 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. COMSOL Blog Series on COMSOL Multiphysics Solvers To learn more, see our tips on writing great answers. Iterative - COMSOL Multiphysics There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Posted 26 set 2019, 11:57 GMT-4 However, it is usually not possible to know this ahead of time. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. The algorithm is, generally speaking, a Newton's method approach. 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 highly rated cards & stationery in Brea, CA: What are some cards & stationery with a large number of reviews in Brea, CA? 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. (Frequency Domain should be the last step) Does ZnSO4 + H2 at high pressure reverses to Zn + H2SO4? Such a case would be better to address instead with the Shell physics interface, which is specially formulated for handling thin-walled structural parts. When you use an iterative solver, COMSOL Multiphysics estimates the error of the solution while solving. That is, they are tuned to achieve convergence in as many cases as possible. Consult your product manuals for complete trademark details. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. Some models are numerically ill-conditioned due to the setup. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. 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. Why doesn't iterative solver converge in COMSOL? - ResearchGate Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. 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. 0 Replies, Please login with a confirmed email address before reporting spam. The objective here is to simplify the model to a state where the model will solve, with linear approximations. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. COMSOL makes every reasonable effort to verify the information you view on this page. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. Cooling and Solidification of Metal. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. -Detail: NaN or Inf found when solving linear system using SOR. Consult your product manuals for complete trademark details. If you have both as steps in the same study, then solve that study. 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. Improving Convergence of Nonlinear Stationary Models - COMSOL This is relatively expensive to do, but will lead to the most robust convergence. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings.

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