Hello guys. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) 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. 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. This can arise as a consequence of extreme variations in the material properties, or high aspect ratio geometry. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. Note: there is no way to couple this field with the time dependent nature of this physics. As part of our solver blog series we have discussed solving nonlinear static finite element problems, load ramping for improving convergence of nonlinear problems, and nonlinearity ramping for improving convergence of nonlinear problems. Posted 26 set 2019, 11:57 GMT-4 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. Unknown function or operator. This is relatively expensive to do, but will lead to the most robust convergence. Using the first order optimality. How to solve "Undefined material property 'sigma - ResearchGate Second, the continuation method will automatically take smaller load increments if a solution cannot be found. Most multiphysics problems are nonlinear. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version $140,000.00, $120,000.00 However, it is usually not possible to know this ahead of time. 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 This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. $130,000.00. Consult your product manuals for complete trademark details. 140K views 8 years ago COMSOL Multiphysics Tutorial for Beginners Please note that an updated version of the content in this video can be found in the Modeling Workflow video in the COMSOL. 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. 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. 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. Create the time-dependent step or study. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. It may also reveal that the model itself is ill-posed in some way. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. - Feature: Stationary Solver 1 (sol1/s1) Different physics have different default solvers. COMSOL does not assume any legal liability for the accuracy of the data disclosed. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. 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. If these settings have been manually changed, you will see a small star symbol on the Solution feature, as shown in the screenshot below. Your Discussion has gone 30 days without a reply. Here we introduce the two classes of algorithms used to solve multiphysics finite element problems in COMSOL Multiphysics. 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. We are planning to continuously update this page throughout the semester and hopefully, this will become a reference during your projects as well. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: 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. The prices are good, and when I needed something delivered, same day, they were able to do it, and it looked beautiful!! Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. By creating this job alert, you agree to the LinkedIn User Agreement and Privacy Policy. 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. Under Initial values of variables solved for, the default value of the Settingslist is Physics controlled. This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. 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. Cooling and Solidification of Metal. 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. In this post, we will delve deeper into how to choose an appropriate mesh to start your mesh convergence studies for linear static finite element problems. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version 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. Note: there is no way to couple this . That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. What version of COMSOL are you using? 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. 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. These can be used alone, or in combination with other interfaces. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. It is also possible to manually refine the mesh. Your email address will not be published. Multiphysics problems are often nonlinear. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. thanks for reply In this case, it would likely be reasonable to treat the insulative material as a perfect insulator, omit it from the analysis, and use the Electric Insulation boundary condition instead of modeling those domains. comsol - using stationary solution as the initial conditions in time That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. Why doesn't iterative solver converge in COMSOL? - ResearchGate This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. That is: It is also possible to compute the derivative of the solution with respect to the continuation parameter and use that derivative (evaluated at the iteration) to compute a new initial value: where is the stepsize of the continuation parameter. 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. Use this parameter to modify the nonlinearity expressions in the model. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. (I am begginer in comsol) Thank you. (COMSOL Multiphysics) : Then I stored the resulting solution, and used it to to solve the stationary solver again by using the solver manager. That is, start by first solving a model with a small, but non-zero, load. 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. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) Linear solvers. Your internet explorer is in compatibility mode and may not be displaying the website correctly. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. With sufficient simplification, a model can be reduced to a linear problem, and if this simplified model does not converge, see: What to do when a linear stationary model is not solving. Such a case would be better to address instead with the Shell physics interface, which is specially formulated for handling thin-walled structural parts. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. Save my name, email, and website in this browser for the next time I comment. How can I check before my flight that the cloud separation requirements in VFR flight rules are met? What did people search for similar to stationary stores in Brea, CA? Solve the stationary study then the time dependent study. 351 Stationary Engineer jobs in Brea, California, United States (15 new) Perhaps this approach could be adapted to represent your model. 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. Does ZnSO4 + H2 at high pressure reverses to Zn + H2SO4? It is sometimes necessary to manually scale the dependent variables. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version In many physics areas there exist alternative physics formulations specifically meant for solving cases where the geometry has an extreme aspect ratio. replace it with the expression: 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. See if these can be used instead of explicitly modeling parts with high-aspect ratio geometries. listed if standards is not an option). The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. Such problems must solved in the time domain. That is, start by first solving a model with a small, but non-zero, load. If it does so, use a finer increment in that range. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. Not entering required material parameters. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Connect and share knowledge within a single location that is structured and easy to search. Segregated approach and Direct vs. It may also reveal that the model itself is ill-posed in some way. First, it is physically intuitive, often matching how one would perform an experiment. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. 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. Stationary Solver Use the Stationary Solver () to find the solution to linear and nonlinear stationary problems (also called static or steady-state problems). If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. 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. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. 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. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. They are usually called comp1.u, comp1.v, and comp1.w though. This doesn't seem to me the most elegant of methods, since I am essentially solving a stationary solution using a time dependent thanks for reply 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. Top 10 Best Stationary Stores in Brea, CA - December 2022 - Yelp The issue here has do with the iterative algorithm used to solve nonlinear stationary models. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. The default solver for most 3D models is an iterative solver, which is more sensitive to ill-conditioned problems. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. If the model is nonlinear, see: Improving Convergence of Nonlinear Stationary Models. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. This algorithm was also useful for understanding what happens near a failure load. Improving Convergence of Nonlinear Stationary Models - COMSOL It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. The settings controlling the predictor type. The solver settings are stored at Study > Solver Configurations > Solution. Making statements based on opinion; back them up with references or personal experience. 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. Use this parameter to modify the nonlinearity expressions in the model. When you use an iterative solver, COMSOL Multiphysics estimates the error of the solution while solving. For example, if there is a temperature-dependent material property such as: 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. Again, introduce a Global Parameter that gets ramped from exactly zero to one. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. Dun & Bradstreet gathers Office Supplies, Stationery, and Gift Retailers business information from trusted . 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. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. In this page, we will be sharing some common errors that might occur in Comsol and their solutions. so many cute little stationary items , hair". There will always already be either a Segregated or Fully Coupled feature beneath this. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. Communication over the phone, in person, and through email was very easy. Stationary Solver Iterative Direct . Your internet explorer is in compatibility mode and may not be displaying the website correctly. The other low-level default settings within the Stationary Solver are chosen for robustness. replace it with the expression: The fully coupled and segregated approaches are discussed below. This approach is known as a Continuation Method with a Constant predictor. 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. If you try to solve such a model, there will be an error at runtime that will provide information about the variable name and where it is being called. 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. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. This consent may be withdrawn. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: Improving Convergence of Nonlinear Stationary Models, Knowledgebase 1030: Error: "Out of memory", Knowledgebase 1030: Performing a Mesh Refinement Study, Understanding the Fully Coupled vs. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt.
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