listed if standards is not an option). Common Errors in Comsol - P&S: COMSOL Design Tool for Photonic Devices 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. They worked with me. 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 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. There will always already be either a Segregated or Fully Coupled feature beneath this. How to solve "Undefined material property 'sigma - ResearchGate However, it is usually not possible to know this ahead of time. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: It's brand new in the hmart plaza and I wish it was open back when I would hangout in the plaza after school (although they would have taken all my allowance money! Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) 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. See Knowledge Base 1240: Manually Setting the Scaling of Variables. The fully coupled and segregated approaches are discussed below. For example, if ramping P over values of: 0.2,0.4,0.6,0.8,1.0 the nonlinear solver may fail to converge for a value of 0.8. If your matrix is singular than no solver in the world can solve Ax=B. Trying to understand how to get this basic Fourier Series. If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base. If the model is nonlinear, see: Improving Convergence of Nonlinear Stationary Models. 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. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the same mesh: adaptmesh1. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. Your Discussion has gone 30 days without a reply. 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. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version First, it is physically intuitive, often matching how one would perform an experiment. The Fully Coupled solution approach, with the Plot While Solving enabled. The algorithm is, generally speaking, a Newton's method approach. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. 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. Not entering required material parameters. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) 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. Here, we will examine techniques for accelerating the convergence of these two methods. Reviews on Stationary Stores in Brea, CA - Typo, Mievic, Posh Paper, Morning Glory, Select Graphics & Printing, Daiso Japan, Urban Outfitters, Office Depot, Barnes & Noble Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. Wish you all the best. 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. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. The coupling terms between the different groups are thus neglected. 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. COMSOL makes every reasonable effort to verify the information you view on this page. COMSOL does not assume any legal liability for the accuracy of the data disclosed. 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 former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. Feature: Stationary Solver 1 (sol1/s1) Attempt to evaluate nonintegral power of negative number. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Create the time-dependent step or study. - Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. Stationary (time-invariant) models with nonlinearities may converge very slowly. 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. 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. Then use this file to provide the initial conditions in time dependent model. Have you taken a look at this blog post? Such problems must solved in the time domain. The idea behind the GCRO-DR method is to retain the subspace determined while solving previous systems and use it to reduce the cost of solving the next system. With respect to any nonlinearities, replace them by a reasonable linearized term. Once the error estimate is small enough, as determined by the convergence criterion (20-16) the software terminates the computations and returns a solution. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Understanding stationary and time dependent solver COMSOL Multiphysics Solve the stationary study then the time dependent study. Function: / Failed to evaluate 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. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. 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. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. 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. 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. Get notified about new Stationary Engineer jobs in Brea, California, United States. These are some highly rated cards & stationery in Brea, CA: What are some cards & stationery with a large number of reviews in Brea, CA? Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. Consult your product manuals for complete trademark details. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). At low flow speeds the flow solution will be time invariant, but at higher flow rates there will be vortex shedding, a time-varying change in the flow field behind the cylinder. 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. 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. Dr.S.Ravindran Cite 1 Recommendation Popular answers (1). Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. Review the model setup to resolve these. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. Numerically ill-conditioned means that the system matrix is nearly singular and that it will be difficult to solve on a finite-precision computer. 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. 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. 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. They are usually called comp1.u, comp1.v, and comp1.w though. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: 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. Stationary (time-invariant) models with nonlinearities may converge very slowly. I am following the same model as Comsol provide us on the web. 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. Studysteps might be listed in wrong order: Not assigning materials to all the domains. Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the - COMSOL The coupling terms between the different groups are thus neglected. Again, introduce a Global Parameter that gets ramped from exactly zero to one. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Not entering required material parameters. 0 Replies, Please login with a confirmed email address before reporting spam. If it does so, use a finer increment in that range. Stationary Solver Iterative Direct . 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. The segregated approach, on the other hand, solves sets of unknowns separately. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. The objective here is to simplify the model to a state where the model will solve, with linear approximations. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. 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. 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. 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. This is a review for cards & stationery in Brea, CA: "Love this store!!! The fully coupled and segregated approaches are discussed below. I'm trying to model a solid that's moving through a steady background field in a background flow, I want to take into account the effect of movement of the solid after each time step so I have to use stationary solver after each time step in order to see how field has changed after solid moved. Posted Sep 9, 2020, 1:44 p.m. EDT If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. Segregated approach and Direct vs. 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. Consult your product manuals for complete trademark details. The objective here is to simplify the model to a state where the model will solve, with linear approximations. Required fields are marked *. This can arise as a consequence of extreme variations in the material properties, or high aspect ratio geometry. I am solving a linear stationary finite element model but the software is not solving. Use this parameter to modify the nonlinearity expressions in the model. If it does so, use a finer increment in that range. (Frequency Domain should be the last step) In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. Hi Alexis, Note the star symbol on the Solution feature. Feature: Stationary Solver 1 (sol1/s1)" . This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. replace it with the expression: COMSOL does not assume any legal liability for the accuracy of the data disclosed. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) 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. Reviews on Stationary in Brea, CA - Mievic, Typo, Tokyo Japanese Lifestyle, Fancy, Posh Paper, Morning Glory, Velvet Fox Designs, Barnes & Noble, Michaels, Select Graphics & Printing 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. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. rev2023.3.3.43278. 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. Full text of the 'Sri Mahalakshmi Dhyanam & Stotram'. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. In the COMSOL Multiphysics software, this step of the modeling workflow is made. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. Few days back i was also facing this problem in . An example would be a linear static structural model of an aluminum beverage can. Thanks for contributing an answer to Stack Overflow! This is relatively expensive to do, but will lead to the most robust convergence. What is the purpose of non-series Shimano components? By default, the COMSOL Multiphysics software determines these values heuristically depending on the physics as, for example, the specified initial values or a solution from an earlier study step. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. P&S: COMSOL Design Tool for Photonic Devices. Also, keep in mind that a linear stationary model should solve regardless of how coarse the mesh is (albeit to a low accuracy) so you can always start with as coarse a mesh as possible, and refine the mesh (See also: Knowledgebase 1030: Performing a Mesh Refinement Study. To learn more, see our tips on writing great answers. This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. For example, if there is a temperature-dependent material property such as: Computational Fluid Dynamics (CFD), API . Any trademarks referenced in this document are the property of their respective owners. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. Top 10 Best Stationary in Brea, CA - October 2022 - Yelp Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Consult your product manuals for complete trademark details. Not assigning proper boundary conditions: Especially if you have ports. Improving Convergence of Nonlinear Stationary Models - COMSOL comp1.u2, comp1.v2, and comp1.w2 are usually variables associated with the x,y, and z component of deformation in COMSOL. 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