However, it is usually not possible to know this ahead of time. Perhaps this approach could be adapted to represent your model. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. Linear solvers. Click the link in the email we sent to to verify your email address and activate your job alert. 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. Your internet explorer is in compatibility mode and may not be displaying the website correctly. replace it with the expression: For example, in an Electric Currents problem, you may want to consider a system of materials including a good conductor such as copper (with an electric conductivity of ~6e7 S/m) and an insulative material such as glass (which can have electric conductivity of ~1e-14 S/m.) As we saw in Load Ramping of Nonlinear Problems, we can use the continuation method to ramp the loads on a problem up from an unloaded case where we know the solution. You can unsubscribe from these emails at any time. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. Check the solver log to see if the continuation method is backtracking. Once the error estimate is small enough, as determined by the convergence criterion (20-16) the software terminates the computations and returns a solution. 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. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. It may also reveal that the model itself is ill-posed in some way. thanks for reply Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. Hi Jason,
Feature: Stationary Solver 1 (sol1/s1) Attempt to evaluate nonintegral power of negative number. - Use this parameter to modify the nonlinearity expressions in the model. Could you expand a little bit more why the coupling is impossible? An example would be a linear static structural model of an aluminum beverage can. 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. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. Not assigning proper boundary conditions: Especially if you have ports. See Knowledge Base 1240: Manually Setting the Scaling of Variables. However, it is usually not possible to know this ahead of time. Some models are numerically ill-conditioned due to the setup. 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. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. 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. Hello, Dr.S.Ravindran Cite 1 Recommendation Popular answers (1). Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. 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. 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. If the material properties entered are incorrect for the governing equation, the model will generate an error at runtime, usually a Singular Matrix error. 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. Consult your product manuals for complete trademark details. Multiphysics problems are often nonlinear. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. Not entering required material parameters. COMSOL does not assume any legal liability for the accuracy of the data disclosed. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. Not assigning proper boundary conditions: Especially if you have ports. Not entering required material parameters. This algorithm was also useful for understanding what happens near a failure load. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. For example, if there is a temperature-dependent material property such as: To learn more, see our tips on writing great answers. 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. It is sometimes necessary to manually scale the dependent variables. Any trademarks referenced in this document are the property of their respective owners. The objective here is to simplify the model to a state where the model will solve, with linear approximations. For example, in Solid Mechanics, if the Poisson Ratio set to 0.5, then the model will not solve, as this value in incompatible with the theory of linear elasticity. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. 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. SGP handled 7 different prints for me at once and they all came out perfectly, in a timely manner. 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. The segregated approach, on the other hand, solves sets of unknowns separately. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. Use this parameter to modify the nonlinearity expressions in the model. Multiphysics problems are often nonlinear. 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. Asking for help, clarification, or responding to other answers. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. Again, introduce a Global Parameter that gets ramped from exactly zero to one. That is, they are tuned to achieve convergence in as many cases as possible. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) 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. The following are possible reasons why a linear stationary model will fail to solve, along with resolutions: The combination of the constraints and boundary conditions must be sufficient to define a unique solution to the problem, in terms of the field variables being solved. COMSOL does not assume any legal liability for the accuracy of the data disclosed. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Wrong ordering of study steps. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. Discussion Closed This discussion was created more than 6 months ago and has been closed. Find detailed information on Office Supplies, Stationery, and Gift Retailers companies in Brea, California, United States of America, including financial statements, sales and marketing contacts, top competitors, and firmographic insights. First, it is physically intuitive, often matching how one would perform an experiment. The settings controlling the predictor type. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. 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. It may also reveal that the model itself is ill-posed in some way. The difference between the phonemes /p/ and /b/ in Japanese. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. Get email updates for new Stationary Engineer jobs in Brea, California, United States. listed if standards is not an option). Acidity of alcohols and basicity of amines. Hi Alexis,
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. 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. 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. The solver settings are stored at Study > Solver Configurations > Solution. The coupling terms between the different groups are thus neglected. There will always already be either a Segregated or Fully Coupled feature beneath this. Check the solver log to see if the continuation method is backtracking.
If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. Get notified about new Stationary Engineer jobs in Brea, California, United States. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. With respect to any nonlinearities, replace them by a reasonable linearized term. Not meshing all the domains. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. 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. If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base. Check the solver log to see if the continuation method is backtracking. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. This is a review for cards & stationery in Brea, CA: "Love this store!!! You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version If this was solved using the Solid Mechanics physics interface the thin walls of the container would need to be explicitly modeled, but the wall thickness is much smaller than the overall can dimensions.