stationary solver comsol

Mesh The segregated approach, on the other hand, solves sets of unknowns separately. Understanding the Fully Coupled vs. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. That is, they are tuned to achieve convergence in as many cases as possible. 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. - the incident has nothing to do with me; can I use this this way? 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. Leverage your professional network, and get hired. 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. 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. The settings controlling the predictor type. COMSOL makes every reasonable effort to verify the information you view on this page. 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. Wrong ordering of study steps. The algorithm is, generally speaking, a Newton's method approach. Connect and share knowledge within a single location that is structured and easy to search. The prices are good, and when I needed something delivered, same day, they were able to do it, and it looked beautiful!! 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. First, it is physically intuitive, often matching how one would perform an experiment. Multiphysics problems are often nonlinear. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. P&S Comsol Team: Arif Gngr , Yannik Horst , Stefano Valente. 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. These are some cards & stationery with a large number of reviews in Brea, CA. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. There will always already be either a Segregated or Fully Coupled feature beneath this. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. 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. $140,000.00, $120,000.00 The coupling terms between the different groups are thus neglected. 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. Using the first order optimality. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. The technique of load ramping is not always reasonable for all problems. Making statements based on opinion; back them up with references or personal experience. P&S: COMSOL Design Tool for Photonic Devices. - Feature: Stationary Solver 1 (sol1/s1)Failed to find a solution. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. You can unsubscribe from these emails at any time. Hi Alexis, From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. They worked with me. - Function: ^ Failed to evaluate variable. 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. The difference between the phonemes /p/ and /b/ in Japanese. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. This involves a systematic reduction in the model complexity. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. This is relatively expensive to do, but will lead to the most robust convergence. Once the error estimate is small enough, as determined by the convergence criterion (20-16) the software terminates the computations and returns a solution. The objective here is to simplify the model to a state where the model will solve, with linear approximations. The advantages of the continuation method are two-fold. Set "Values for dependent variables" in study step settings to User ControlledSolutionYour Stationary Study. To learn more, see our tips on writing great answers. replace it with the expression: Note: there is no way to couple this . Your internet explorer is in compatibility mode and may not be displaying the website correctly. Perhaps this approach could be adapted to represent your model. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. I personally liked emailing them the file, ", "This flower shop is the best! See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. Not assigning proper boundary conditions: Especially if you have ports. The algorithm is, generally speaking, a Newton's method approach. 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. The other low-level default settings within the Stationary Solver are chosen for robustness. Could you expand a little bit more why the coupling is impossible? Stationary (time-invariant) models with nonlinearities may converge very slowly. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. What version of COMSOL are you using? 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. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. -Detail: NaN or Inf found when solving linear system using SOR. November 11, 2013. 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. The segregated approach, on the other hand, solves sets of unknowns separately. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. 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. The fully coupled and segregated approaches are discussed below. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. What are people saying about cards & stationery in Brea, CA? This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. 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. 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 also possible to manually refine the mesh. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. Not entering required material parameters. Trying to understand how to get this basic Fourier Series. 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. 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. rev2023.3.3.43278. To switch between these solver types, go to the Stationary Solver node within the Study sequence. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Building on these topics, we will now address how to prepare your mesh for efficiently solving nonlinear finite element problems. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. Here, we begin an overview of the algorithms used for solving nonlinear static finite element problems. Hi Jason, If it does so, use a finer increment in that range. If you have both as steps in the same study, then solve that study. 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. Create the time-dependent step or study. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. 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 one particular material is missing one property, that material will also be highlighted with a red cross over that material icon in the Model Builder. However, it is usually not possible to know this ahead of time. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. Most multiphysics problems are nonlinear. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. Comsol help video number 2: Solving a laminar flow problem in a slit.. Function: / Failed to evaluate expression. 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. This guide applies solely to nonlinear stationary models. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. Click the link in the email we sent to to verify your email address and activate your job alert. We are planning to continuously update this page throughout the semester and hopefully, this will become a reference during your projects as well. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. if I want to do an adaptive mesh refinement, I get this error. 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. Such problems must solved in the time domain. Segregated approach and Direct vs. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. COMSOL does not assume any legal liability for the accuracy of the data disclosed. The objective here is to simplify the model to a state where the model will solve, with linear approximations. Contact COMSOL at Bangalore on their telephone: +9180 25323003. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. 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. 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. 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 nature of simulating nature: A Q&A with IBM Quantum researcher Dr. Jamie We've added a "Necessary cookies only" option to the cookie consent popup. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. 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. Discussion Closed This discussion was created more than 6 months ago and has been closed. Hello,

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