Your internet explorer is in compatibility mode and may not be displaying the website correctly. Does ZnSO4 + H2 at high pressure reverses to Zn + H2SO4? Trying to understand how to get this basic Fourier Series. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. See if these can be used instead of explicitly modeling parts with high-aspect ratio geometries. COMSOL 22.9K subscribers Adding a study to your simulation is necessary in order to solve your problem. 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) = 10[W/m/K]+10[W/m/K]*(T>400[K]) There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. $140,000.00, $120,000.00 Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. Stationary Solver Use the Stationary Solver () to find the solution to linear and nonlinear stationary problems (also called static or steady-state problems). COMSOL makes every reasonable effort to verify the information you view on this page. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. 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. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. The technique of load ramping is not always reasonable for all problems. Building on these topics, we will now address how to prepare your mesh for efficiently solving nonlinear finite element problems. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. I want to conduct a simulation to find a solution (u) and its first derivative (ux) using a 3D stationary model. Not entering required material parameters. How can I check before my flight that the cloud separation requirements in VFR flight rules are met? Repeat this for every nonlinearity of the model. rev2023.3.3.43278. COMSOL does not assume any legal liability for the accuracy of the data disclosed. The coupling terms between the different groups are thus neglected. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. This case is generally difficult, or impossible, to solve since this material property is non-smooth. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. 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. 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. Linear solvers. Stationary Solver Iterative Direct . 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. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. 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. Check the solver log to see if the continuation method is backtracking. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. Save my name, email, and website in this browser for the next time I comment. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. 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. Stationary (time-invariant) models with nonlinearities may converge very slowly. Comsol help video number 2: Solving a laminar flow problem in a slit.. Use this parameter to modify the nonlinearity expressions in the model. Hello guys. 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. You can unsubscribe from these emails at any time. If you are unsure if your problem is linear and stationary, look at the Log. 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. - Feature: Stationary Solver 1 (sol1/s1)Failed to find a solution. I am following the same model as Comsol provide us on the web. In a previous blog entry, we introduced meshing considerations for linear static problems. With respect to any nonlinearities, replace them by a reasonable linearized term. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. What version of COMSOL are you using? If it does so, use a finer increment in that range. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. 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. Cooling and Solidification of Metal. Hi Jason, Common Mistakes: Not assigning materials to all the domains. Check the solver log to see if the continuation method is backtracking. Hello, There will always already be either a Segregated or Fully Coupled feature beneath this. The problem is that when I run my model this message appear: Undefined value found. The difference between the phonemes /p/ and /b/ in Japanese. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Most multiphysics problems are nonlinear. 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. In the COMSOL Multiphysics software, this step of the modeling workflow is made. 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. What are people saying about cards & stationery in Brea, CA? - Not entering required material parameters. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. The technique of load ramping is not always reasonable for all problems. If the model is nonlinear, see: Improving Convergence of Nonlinear Stationary Models. They worked with me. See Knowledge Base 1240: Manually Setting the Scaling of Variables. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. How can I use it? P&S: COMSOL Design Tool for Photonic Devices. If so, see: Knowledgebase 1030: Error: "Out of memory". 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. Could you expand a little bit more why the coupling is impossible? That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. 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. Here, we begin an overview of the algorithms used for solving nonlinear static finite element problems. This approach is known as a Continuation Method with a Constant predictor. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. "After the incident", I started to be more careful not to trip over things. if I want to do an adaptive mesh refinement, I get this error. This is relatively expensive to do, but will lead to the most robust convergence. I am trying to solve the coupling between a waveguide and a microring resonator. 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. Posted 26 set 2019, 11:57 GMT-4 This solver is automatically used when a Stationary or Frequency Domain study is added to the model. If it does so, use a finer increment in that range. My comment is perhaps a bit nave but it seems to me that you could simply deactivate the \frac{\partial \cdot}{\partial t} term of the background field equation but keep its connexion to the solid to get what you want. The other low-level default settings within the Stationary Solver are chosen for robustness. In this posting, we introduce the idea of ramping the nonlinearities in the problem to improve convergence. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version This involves a systematic reduction in the model complexity. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. There will also be a red cross over the Materials branch icon. Have you taken a look at this blog post? 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. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. Function: / Failed to evaluate expression. This is relatively expensive to do, but will lead to the most robust convergence. 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. 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. 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.) Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. Full text of the 'Sri Mahalakshmi Dhyanam & Stotram'. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: 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. Wrong ordering of study steps. listed if standards is not an option). With respect to any nonlinearities, replace them by a reasonable linearized term. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. Name: actdep_int1, Your email address will not be published.

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