Some models are numerically ill-conditioned due to the setup. November 11, 2013. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. 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. Stationary (time-invariant) models with nonlinearities may converge very slowly. That is, start by first solving a model with a small, but non-zero, load. So far, weve learned how to mesh and solve linear and nonlinear single-physics finite element problems, but have not yet considered what happens when there are multiple different interdependent physics being solved within the same domain. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. This involves a systematic reduction in the model complexity. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) 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. Stationary Engineer Jobs in Brea, California, United States, $87,400.00 Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. Set initial conditions in the physics to the appropriate dependent model variable names rather than the default 0. listed if standards is not an option). That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. listed if standards is not an option). COMSOL makes every reasonable effort to verify the information you view on this page. The nature of simulating nature: A Q&A with IBM Quantum researcher Dr. Jamie We've added a "Necessary cookies only" option to the cookie consent popup. Feature: Stationary Solver 1 (sol1/s1) Attempt to evaluate nonintegral power of negative number. The technique of load ramping is not always reasonable for all problems. 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. Hello, The other low-level default settings within the Stationary Solver are chosen for robustness. I am solving a linear stationary finite element model but the software is not solving. Top 10 Best Stationary Stores in Brea, CA - December 2022 - Yelp . The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. 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. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. If the default iterative solver is not converging, try switching to a direct solver, as described here: Understanding the Fully Coupled vs. In such cases, see if one material (or the other) can be omitted from the analysis completely. Multiphysics problems are often nonlinear. Why? The following are possible reasons why a linear stationary model will fail to solve, along with resolutions: The combination of the constraints and boundary conditions must be sufficient to define a unique solution to the problem, in terms of the field variables being solved. Alternatively, delete and re-create the study. Solving for laminar flow using Comsol - YouTube Changes to these low-level settings from the defaults will usually be quite model- and case-specific. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. The Fully Coupled solution approach, with the Plot While Solving enabled. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. There will always already be either a Segregated or Fully Coupled feature beneath this. The technique of load ramping is not always reasonable for all problems. It is also possible to manually refine the mesh. - With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: 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. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. New Stationary Engineer jobs added daily. This can arise as a consequence of extreme variations in the material properties, or high aspect ratio geometry. 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,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. 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 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. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. 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. Different physics have different default solvers. Use this parameter to modify the nonlinearity expressions in the model. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. These are some cards & stationery with a large number of reviews in Brea, CA. First, it is physically intuitive, often matching how one would perform an experiment. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. One of the key concepts there was the idea of mesh convergence as you refine the mesh, the solution will become more accurate. Function: / Failed to evaluate expression. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. Click the link in the email we sent to to verify your email address and activate your job alert. Please dont hesitate to post comments below or send emails to us if you experience any other problems. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. 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. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. For example, if there is a temperature-dependent material property such as: An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: Hi Alexis, Does anyone know how to solve error in stationary solver in COMSOL 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. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. 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. 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. Office Supplies, Stationery, and Gift Retailers Companies in Brea The default solver for most 3D models is an iterative solver, which is more sensitive to ill-conditioned problems. Your internet explorer is in compatibility mode and may not be displaying the website correctly. The default Initial Values for the unknowns in most physics interfaces are zero. 3 Replies, Please login with a confirmed email address before reporting spam. Not entering required material parameters. That is, they are tuned to achieve convergence in as many cases as possible. COMSOL 22.9K subscribers Adding a study to your simulation is necessary in order to solve your problem. It is also possible to manually refine the mesh. 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. For example, in a Solid Mechanics (wherein the software is solving for the displacement field within the solid) applying two opposite and equal Boundary Load conditions on a part is not sufficient to define the displacement. When you use an iterative solver, COMSOL Multiphysics estimates the error of the solution while solving. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version See Knowledge Base 1240: Manually Setting the Scaling of Variables. 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. 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. Why doesn't iterative solver converge in COMSOL? - ResearchGate 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. Common Mistakes: Not assigning materials to all the domains. listed if standards is not an option). $140,000.00, $120,000.00 An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: Iterative , Direct . If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. The advantages of the continuation method are two-fold. This guide applies solely to nonlinear stationary models. 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. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. What sort of strategies would a medieval military use against a fantasy giant? What did people search for similar to stationary stores in Brea, CA? The settings controlling the predictor type. 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. 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. Cooling and Solidification of Metal. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. It can be useful while solving sequences of linear systems arising from, for example, nonlinear problems. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. 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. The Fully Coupled solution approach, with the Plot While Solving enabled. comp1.u2, comp1.v2, and comp1.w2 are usually variables associated with the x,y, and z component of deformation in COMSOL. The advantages of the continuation method are two-fold. Hi ! Stationary Solver Use the Stationary Solver () to find the solution to linear and nonlinear stationary problems (also called static or steady-state problems). First, it is physically intuitive, often matching how one would perform an experiment. if I want to do an adaptive mesh refinement, I get this error. The Iterative Solvers - COMSOL Multiphysics Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. Use this parameter to modify the nonlinearity expressions in the model. Perhaps this approach could be adapted to represent your model. Once the error estimate is small enough, as determined by the convergence criterion (20-16) the software terminates the computations and returns a solution. $125,000.00, Project Engineer (In-person/Hybrid/Remote), $100,000.00 Today's top 351 Stationary Engineer jobs in Brea, California, United States. The advantages of the continuation method are two-fold. 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. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. Repeat this for every nonlinearity of the model. There are also cases when an extremely poor quality mesh leads to an ill-conditioned problem, This issue often arises in combination with, and as a consequence of, geometries that have extreme aspect ratios. There will also be a red cross over the Materials branch icon. 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. Stationary (time-invariant) models with nonlinearities may converge very slowly. The algorithm is, generally speaking, a Newton's method approach. 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. Note: there is no way to couple this . Your internet explorer is in compatibility mode and may not be displaying the website correctly. Such problems must solved in the time domain. P&S: COMSOL Design Tool for Photonic Devices - ETH Z This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. 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. Stationary (time-invariant) models with nonlinearities may converge very slowly. The difference between the phonemes /p/ and /b/ in Japanese. Solving such models in a stationary sense should simply require solving a single (large) system of linear equations and should always be solvable, but there are cases when the software will fail to find a solution. 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. Not assigning proper boundary conditions: Especially if you have ports. She opened prepackaged 6-packs of Seegars to make ", All "stationary stores" results in Brea, CA, Search stationary stores in popular locations. Reply . How to Add a Study to Your Simulation in COMSOL Multiphysics 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. 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. 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. 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. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. Wish you all the best. As a second example, when solving for Electric Currents, do not model perfect electrical insulators as materials with zero conductivity, instead, omit the domain from the model and use the Electric Insulation boundary condition. Tutti i diritti sono riservati. An example would be a linear static structural model of an aluminum beverage can. Does ZnSO4 + H2 at high pressure reverses to Zn + H2SO4? 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. Any trademarks referenced in this document are the property of their respective owners. For example, if there is a temperature-dependent material property such as: Staging Ground Beta 1 Recap, and Reviewers needed for Beta 2, Simulation of effect of heated resistance on temperature distribution in laminar flow, COMSOL: Diffusion in Transport of Diluted Species Produces Unphysical Results.
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