stationary solver comsol

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. Specify Material Properties in COMSOL Multiphysics (3/8) By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. 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. To switch between these solver types, go to the Stationary Solver node within the Study sequence. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) Multiscale Modeling in High-Frequency Electromagnetics. This can arise as a consequence of extreme variations in the material properties, or high aspect ratio geometry. 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. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. 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. . Iterative , Direct . What is \newluafunction? Repeat this for every nonlinearity of the model. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. Not meshing all the domains. With respect to any nonlinearities, replace them by a reasonable linearized term. 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. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. This case is generally difficult, or impossible, to solve since this material property is non-smooth. If you try to enter a variable that is undefined, the automatic syntax highlighting will identify this as you enter it, and it is best practice to resolve this immediately. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. Leverage your professional network, and get hired. The Fully Coupled solution approach, with the Plot While Solving enabled. Posted 26 set 2019, 11:57 GMT-4 The default solver for most 3D models is an iterative solver, which is more sensitive to ill-conditioned problems. 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. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Set initial conditions in the physics to the appropriate dependent model variable names rather than the default 0. Segregated approach and Direct vs. 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. If it does so, use a finer increment in that range. Please dont hesitate to post comments below or send emails to us if you experience any other problems. If the default iterative solver is not converging, try switching to a direct solver, as described here: Understanding the Fully Coupled vs. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. 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. Here we introduce the two classes of algorithms used to solve multiphysics finite element problems in COMSOL Multiphysics. If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base. Learn how your comment data is processed. Such problems must solved in the time domain. If so, see: Knowledgebase 1030: Error: "Out of memory". 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. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) 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. Consult your product manuals for complete trademark details. Again, introduce a Global Parameter that gets ramped from exactly zero to one. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. Solving for laminar flow using Comsol - YouTube Comsol help video number 2: Solving a laminar flow problem in a slit. Repeat this for every nonlinearity of the model. 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. 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. 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. Review the model setup to resolve these. Most multiphysics problems are nonlinear. 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. This guide applies solely to nonlinear stationary models. It is also possible to manually refine the mesh. This solver is automatically used when a Stationary or Frequency Domain study is added to the model. The other low-level default settings within the Stationary Solver are chosen for robustness. 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. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Stationary Solver Use the Stationary Solver () to find the solution to linear and nonlinear stationary problems (also called static or steady-state problems). Top 10 Best Stationary in Brea, CA - October 2022 - Yelp This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. ", "Absolutely the best place to shop for flowers and greenery, I spent an hour just looking around for fun prior to purchasing a bouquet, they have the best customer service people all over the place and it's a huge place", "Recently came in here to pick up 45 chocolate Seegars (cigars) for a dinner banquet in honor of my baby nephew. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. It is sometimes necessary to manually scale the dependent variables. It may also reveal that the model itself is ill-posed in some way. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) 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 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. Numerically ill-conditioned means that the system matrix is nearly singular and that it will be difficult to solve on a finite-precision computer. Making statements based on opinion; back them up with references or personal experience. 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. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. This guide applies solely to nonlinear stationary models. About the Stationary Solver - COMSOL Multiphysics 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. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. This approach is known as a Continuation Method with a Constant predictor. 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. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. What are people saying about cards & stationery in Brea, CA? 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. 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. 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, 2023 by COMSOL. How to solve "Feature: Stationary Solver 1 (sol1/s1) Attempt - COMSOL Then I stored the resulting solution, and used it to to solve the stationary solver again by using the solver manager. This is relatively expensive to do, but will lead to the most robust convergence. 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. See if these can be used instead of explicitly modeling parts with high-aspect ratio geometries. replace it with the expression: The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. 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. Save this information to a file. 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. [COMSOL_Users] output of stationary solver as input to time-dependent Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. I am trying to solve the coupling between a waveguide and a microring resonator. 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. - Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. 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. Such a case would be better to address instead with the Shell physics interface, which is specially formulated for handling thin-walled structural parts. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. Not assigning proper boundary conditions: Especially if you have ports. 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. Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the - COMSOL With respect to any nonlinearities, replace them by a reasonable linearized term. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. 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. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. Perhaps this approach could be adapted to represent your model. If your matrix is singular than no solver in the world can solve Ax=B. That is, they are tuned to achieve convergence in as many cases as possible. 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. New Stationary Engineer jobs added daily. Why doesn't iterative solver converge in COMSOL? - ResearchGate 0 Replies, Please login with a confirmed email address before reporting spam. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version The advantages of the continuation method are two-fold. 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. Stationary Solver Iterative Direct . The Fully Coupled solution approach, with the Plot While Solving enabled. The objective here is to simplify the model to a state where the model will solve, with linear approximations. The settings controlling the predictor type. Posted 26 set 2019, 17:57 CEST Mesh Version 5.3 0 Replies. 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. 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. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. P&S: COMSOL Design Tool for Photonic Devices. - A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). It is also possible to manually refine the mesh. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. When you use an iterative solver, COMSOL Multiphysics estimates the error of the solution while solving. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. Stationary Solver - COMSOL Multiphysics The default Initial Values for the unknowns in most physics interfaces are zero. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. $125,000.00, Project Engineer (In-person/Hybrid/Remote), $100,000.00 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. 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. This approach is known as a Continuation Method with a Constant predictor. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. The algorithm is, generally speaking, a Newton's method approach. They deal with COMSOL package and train users. They are usually called comp1.u, comp1.v, and comp1.w though. Version 5.3 Multiphysics problems are often nonlinear. COMSOL makes every reasonable effort to verify the information you view on this page. 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. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) The algorithm is, generally speaking, a Newton's method approach. If the model is very large, and if you do not have very much memory in your computer, you may get an error message regarding memory. comp1.u2, comp1.v2, and comp1.w2 are usually variables associated with the x,y, and z component of deformation in COMSOL. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Does ZnSO4 + H2 at high pressure reverses to Zn + H2SO4? Set "Values for dependent variables" in study step settings to User ControlledSolutionYour Stationary Study. Troubleshooting for 3D trusses, if anyone's out there. : r/COMSOL - reddit Your Discussion has gone 30 days without a reply. This involves a systematic reduction in the model complexity. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. 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. $130,000.00. Such problems must solved in the time domain. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. Name: actdep_int1, Your email address will not be published. rev2023.3.3.43278. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Wish you all the best. Have you taken a look at this [blog post](https://www.comsol.com/blogs/modeling-fluid-structure-interaction-in-multibody-mechanisms/)? This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. It is sometimes necessary to manually scale the dependent variables. 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. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. Use this parameter to modify the nonlinearity expressions in the model. 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. 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. The technique of load ramping is not always reasonable for all problems. "After the incident", I started to be more careful not to trip over things. Get notified about new Stationary Engineer jobs in Brea, California, United States. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. Such a large difference in the materials properties can be challenging. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Here, we begin an overview of the algorithms used for solving nonlinear static finite element problems. Feature: Stationary Solver 1 (sol1/s1)" . Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions.

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