stationary solver comsol

The segregated approach, on the other hand, solves sets of unknowns separately. 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]) (Frequency Domain should be the last step). Cooling and Solidification of Metal. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. Check the solver log to see if the continuation method is backtracking. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. 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. Understanding the Fully Coupled vs. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. 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. Common Mistakes: Not assigning materials to all the domains. rev2023.3.3.43278. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. Then use this file to provide the initial conditions in time dependent model. 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 involves a systematic reduction in the model complexity. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. Hi Jason, Does anyone know what should cause this problem? The default Initial Values for the unknowns in most physics interfaces are zero. That is, start by first solving a model with a small, but non-zero, load. The objective here is to simplify the model to a state where the model will solve, with linear approximations. COMSOL does not assume any legal liability for the accuracy of the data disclosed. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) There will also be a red cross over the Materials branch icon. The other low-level default settings within the Stationary Solver are chosen for robustness. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) 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! The issue here has do with the iterative algorithm used to solve nonlinear stationary models. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. If you are unsure if your problem is linear and stationary, look at the Log. COMSOL does not assume any legal liability for the accuracy of the data disclosed. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. If you have both as steps in the same study, then solve that study. Create the time-dependent step or study. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. The fully coupled and segregated approaches are discussed 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. Use this parameter to modify the nonlinearity expressions in the model. 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. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. The coupling terms between the different groups are thus neglected. If the model is nonlinear, see: Improving Convergence of Nonlinear Stationary Models. Consult your product manuals for complete trademark details. 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. Repeat this for every nonlinearity of the model. Such a large difference in the materials properties can be challenging. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. Why do many companies reject expired SSL certificates as bugs in bug bounties? This doesn't seem to me the most elegant of methods, since I am essentially solving a stationary solution using a time dependent replace it with the expression: Solver . - Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the 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. The segregated approach, on the other hand, solves sets of unknowns separately. The technique of load ramping is not always reasonable for all problems. - 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. However, it is usually not possible to know this ahead of time. For example, if there is a temperature-dependent material property such as: (Frequency Domain should be the last step) 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. With respect to any nonlinearities, replace them by a reasonable linearized term. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. I personally liked emailing them the file, ", "This flower shop is the best! Dr.S.Ravindran Cite 1 Recommendation Popular answers (1). 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. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. - Reply . What version of COMSOL are you using? 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. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. There will always already be either a Segregated or Fully Coupled feature beneath this. 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. Here, we will examine techniques for accelerating the convergence of these two methods. This guide applies solely to nonlinear stationary models. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. 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. A nonlinearity can be introduced into the model either in the governing equation, or by making any of the material properties, loads, or boundary conditions dependent upon the solution. Your internet explorer is in compatibility mode and may not be displaying the website correctly. 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. if I want to do an adaptive mesh refinement, I get this error. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. With respect to any nonlinearities, replace them by a reasonable linearized term. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. There will always already be either a Segregated or Fully Coupled feature beneath this. 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. 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. Most multiphysics problems are nonlinear. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. comp1.u2, comp1.v2, and comp1.w2 are usually variables associated with the x,y, and z component of deformation in COMSOL. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. Discussion Closed This discussion was created more than 6 months ago and has been closed. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. Thanks, Andres. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. What is the purpose of non-series Shimano components? We are planning to continuously update this page throughout the semester and hopefully, this will become a reference during your projects as well. Any trademarks referenced in this document are the property of their respective owners. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. We use COMSOL Multiphysics for solving distributed optimal control of un-steady Burgers equation without constraints and with pointwise control constraints. It is also possible to manually refine the mesh. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. 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