Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. We have also introduced meshing considerations for linear static problems, as well as how to identify singularities and what to do about them when meshing. However, it is usually not possible to know this ahead of time. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. They deal with COMSOL package and train users. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. Any trademarks referenced in this document are the property of their respective owners. November 11, 2013. This doesn't seem to me the most elegant of methods, since I am essentially solving a stationary solution using a time dependent This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. 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. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. Cecilia M. came from the backroom to help me and went out of her way to help me even though I had not called before going into the store. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. However, it is usually not possible to know this ahead of time. Most multiphysics problems are nonlinear. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Create the time-dependent step or study. Leverage your professional network, and get hired. We are planning to continuously update this page throughout the semester and hopefully, this will become a reference during your projects as well. COMSOL makes every reasonable effort to verify the information you view on this page. 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 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 the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. These can be used alone, or in combination with other interfaces. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Stationary (time-invariant) models with nonlinearities may converge very slowly. Common Mistakes: Not assigning materials to all the domains. At a value of P=0 the above expression is linear, and at a value of P=1 the expression is equal to the original nonlinear expression. Stationary (time-invariant) models with nonlinearities may converge very slowly. Hello guys. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. 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. 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. Minimising the environmental effects of my dyson brain. If the material properties entered are incorrect for the governing equation, the model will generate an error at runtime, usually a Singular Matrix error. However, it is usually not possible to know this ahead of time. COMSOL makes every reasonable effort to verify the information you view on this page. 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. If you have both as steps in the same study, then solve that study. There will always already be either a Segregated or Fully Coupled feature beneath this. The solver settings are stored at Study > Solver Configurations > Solution. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. 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. Multiphysics problems are often nonlinear. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. First, it is physically intuitive, often matching how one would perform an experiment. The default Initial Values for the unknowns in most physics interfaces are zero. About the Stationary Solver The following background information about the Stationary Solver discusses these topics: Damped Newton Methods, Termination Criterion for the Fully Coupled and Segregated Attribute Nodes, Linear Solvers versus Nonlinear Solvers, and Pseudo Time Stepping. 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. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. 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. That is, start by first solving a model with a small, but non-zero, load. The Fully Coupled solution approach, with the Plot While Solving enabled. 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. Click the link in the email we sent to to verify your email address and activate your job alert. If it does so, use a finer increment in that range. 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. My comment is perhaps a bit nave but it seems to me that you could simply deactivate the term of the background field equation but keep its connexion to the solid to get what you want. Not the answer you're looking for? Check the solver log to see if the continuation method is backtracking. It can be useful while solving sequences of linear systems arising from, for example, nonlinear problems. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. 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. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) Note: there is no way to couple this . In many physics areas there exist alternative physics formulations specifically meant for solving cases where the geometry has an extreme aspect ratio. Different physics have different default solvers. This is relatively expensive to do, but will lead to the most robust convergence. There will also be a red cross over the Materials branch icon. 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. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); This site uses Akismet to reduce spam. - Variable: B1 - Defined as: 1/ ( ( (comp1.cH2 (unit_m_cf^3))/unit_mol_cf)^2.5) Failed to evaluate variable. replace it with the expression: It is also possible to manually refine the mesh. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. This guide applies solely to nonlinear stationary models. 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. The other low-level default settings within the Stationary Solver are chosen for robustness. This solver is automatically used when a Stationary or Frequency Domain study is added to the model. The coupling terms between the different groups are thus neglected. Screenshot showing a Solver Configuration that has been altered. By creating this job alert, you agree to the LinkedIn User Agreement and Privacy Policy. Linear solvers. 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 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. Again, introduce a Global Parameter that gets ramped from exactly zero to one. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. The objective here is to simplify the model to a state where the model will solve, with linear approximations. Comsol help video number 2: Solving a laminar flow problem in a slit..