k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) Not meshing all the domains. Not assigning proper boundary conditions: Especially if you have ports. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. Why? Today's top 351 Stationary Engineer jobs in Brea, California, United States. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. This involves a systematic reduction in the model complexity. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. We are planning to continuously update this page throughout the semester and hopefully, this will become a reference during your projects as well. The coupling terms between the different groups are thus neglected. The fully coupled and segregated approaches are discussed below. See Knowledge Base 1240: Manually Setting the Scaling of Variables. The fully coupled and segregated approaches are discussed below. 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. There will also be a red cross over the Materials branch icon. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. 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. Use this parameter to modify the nonlinearity expressions in the model. replace it with the expression: COMSOL makes every reasonable effort to verify the information you view on this page. Building on these topics, we will now address how to prepare your mesh for efficiently solving nonlinear finite element problems. 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. If some, or all, of the needed materials properties needed by the physics interfaces are not defined, the model will generate an error at runtime. However, it is usually not possible to know this ahead of time. Here, we begin an overview of the algorithms used for solving nonlinear static finite element problems. Again, introduce a Global Parameter that gets ramped from exactly zero to one. 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 unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. Making statements based on opinion; back them up with references or personal experience. COMSOL does not assume any legal liability for the accuracy of the data disclosed. This approach is known as a Continuation Method with a Constant predictor. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. That is, they are tuned to achieve convergence in as many cases as possible. Using the first order optimality. This doesn't seem to me the most elegant of methods, since I am essentially solving a stationary solution using a time dependent Segregated approach and Direct vs. Iterative linear solvers, About the time step setting of the solver, Introducing Goal Seeking into the Segregated Solver. Posted 26 set 2019, 11:57 GMT-4 thanks for reply Such problems must solved in the time domain. When the difference in the computed solutions between successive iterations is sufficiently small, or when the residual is sufficiently small, the problem is considered converged to within the specified tolerance. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) 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. 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. Such problems must solved in the time domain. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Any trademarks referenced in this document are the property of their respective owners. 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. thanks for reply Do you also know how to solve this problem: using stationary solution as the initial conditions in time dependent model, How Intuit democratizes AI development across teams through reusability. This approach is known as a Continuation Method with a Constant predictor. 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. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. First, it is physically intuitive, often matching how one would perform an experiment. Is there a way to use the stationary solution obtained in Comsol 4.2 as the initial conditions in a time dependent model? Understanding the Fully Coupled vs. It can be useful while solving sequences of linear systems arising from, for example, nonlinear problems. 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. Multiphysics problems are often nonlinear. Not the answer you're looking for? 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. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. In this page, we will be sharing some common errors that might occur in Comsol and their solutions. 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. Connect and share knowledge within a single location that is structured and easy to search. listed if standards is not an option). The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. These can be used alone, or in combination with other interfaces. 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. What is \newluafunction? 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. The segregated approach, on the other hand, solves sets of unknowns separately. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. Use a manually defined mesh to avoid elements with extreme aspect ratios and perform a mesh refinement study, as described here: Performing a Mesh Refinement Study, For problems that are ill-conditioned, using a direct solver is often called for. However, it is usually not possible to know this ahead of time. It is sometimes necessary to manually scale the dependent variables. The solver settings are stored at Study > Solver Configurations > Solution. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. One of the key concepts there was the idea of mesh convergence as you refine the mesh, the solution will become more accurate. Hence Comsol solved for the stationary solution at different points of time. P&S: COMSOL Design Tool for Photonic Devices. Thanks, Andres. The Fully Coupled solution approach, with the Plot While Solving enabled. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. 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. Dr.S.Ravindran Cite 1 Recommendation Popular answers (1). Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. 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. Full text of the 'Sri Mahalakshmi Dhyanam & Stotram'. 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. See if these can be used instead of explicitly modeling parts with high-aspect ratio geometries. I am solving a linear stationary finite element model but the software is not solving. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. listed if standards is not an option). 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. 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. 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, 2023 by COMSOL. This case is generally difficult, or impossible, to solve since this material property is non-smooth. The algorithm is, generally speaking, a Newton's method approach. Note: there is no way to couple this field with the time dependent nature of this physics. In particular, choosing an improper initial condition or setting up a problem without a solution will simply cause the nonlinear solver to continue iterating without converging. - GCRO-DR is a method for Krylov subspace recycling. What is the purpose of non-series Shimano components? 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. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. The conditions on the geometric aspect ratio are relatively more strict. There will always already be either a Segregated or Fully Coupled feature beneath this. It is also possible to manually refine the mesh. 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. numeric (each ports needs their ownboundary mode analysis in the study if they are numerically defined)Wave excitation: on/off(input/output), - Feature: Stationary Solver 1 (sol1/s1) Division by zero. Your internet explorer is in compatibility mode and may not be displaying the website correctly. However, load ramping will not work in all cases, or may be inefficient. This can arise as a consequence of extreme variations in the material properties, or high aspect ratio geometry. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. With respect to any nonlinearities, replace them by a reasonable linearized term. The settings controlling the predictor type. Dun & Bradstreet gathers Office Supplies, Stationery, and Gift Retailers business information from trusted . 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. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. 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. This case is generally difficult, or impossible, to solve since this material property is non-smooth. Perhaps this approach could be adapted to represent your model. Not entering required material parameters. if I want to do an adaptive mesh refinement, I get this error. 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 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 memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. 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. With respect to any nonlinearities, replace them by a reasonable linearized term. A linear finite element model is one in which all of the material properties, loads, boundary conditions, etc are constant with respect to the solution, and the governing partial differential equations are themselves linear. 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. 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. This consent may be withdrawn. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version COMSOL makes every reasonable effort to verify the information you view on this page. 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. Here we introduce the two classes of algorithms used to solve multiphysics finite element problems in COMSOL Multiphysics. 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. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. Stationary (time-invariant) models with nonlinearities may converge very slowly. To switch between these solver types, go to the Stationary Solver node within the Study sequence. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. SGP handled 7 different prints for me at once and they all came out perfectly, in a timely manner. - If it does so, use a finer increment in that range. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. Understanding the Fully Coupled vs. 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. Any trademarks referenced in this document are the property of their respective owners. In that case, the continuation method will automatically backtrack and try to solve for intermediate values in the range of 0.6 through 0.8. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. Could you expand a little bit more why the coupling is impossible? The objective here is to simplify the model to a state where the model will solve, with linear approximations. 3. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) Why is there a voltage on my HDMI and coaxial cables? With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed.