Segregated approach and Direct vs. 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. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. It is also possible to manually refine the mesh. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. Your internet explorer is in compatibility mode and may not be displaying the website correctly. - the incident has nothing to do with me; can I use this this way? Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. Discussion Closed This discussion was created more than 6 months ago and has been closed. However, it is usually not possible to know this ahead of time. 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. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) Therefore, an initial value of zero is almost always reasonable if a very small load is applied. Under Initial values of variables solved for, the default value of the Settingslist is Physics controlled. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. - Variable: B1 - Defined as: 1/ ( ( (comp1.cH2 (unit_m_cf^3))/unit_mol_cf)^2.5) Failed to evaluate variable. Your internet explorer is in compatibility mode and may not be displaying the website correctly. I am trying to solve the coupling between a waveguide and a microring resonator. 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. The segregated approach, on the other hand, solves sets of unknowns separately. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. An example would be a linear static structural model of an aluminum beverage can. That is, they are tuned to achieve convergence in as many cases as possible. $130,000.00. The coupling terms between the different groups are thus neglected. . Hi Jason, Not the answer you're looking for? 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. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. I am solving a linear stationary finite element model but the software is not solving. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. The objective here is to simplify the model to a state where the model will solve, with linear approximations. By creating this job alert, you agree to the LinkedIn User Agreement and Privacy Policy. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. Again, introduce a Global Parameter that gets ramped from exactly zero to one. 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. It is sometimes necessary to manually scale the dependent variables. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. Required fields are marked *. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. Common Mistakes: Not assigning materials to all the domains. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. The settings controlling the predictor type. Any trademarks referenced in this document are the property of their respective owners. Any trademarks referenced in this document are the property of their respective owners. Linear solvers. 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 (time-invariant) models with nonlinearities may converge very slowly. Solver . That is, they are tuned to achieve convergence in as many cases as possible. If it does so, use a finer increment in that range. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. GCRO-DR is a method for Krylov subspace recycling. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. With respect to any nonlinearities, replace them by a reasonable linearized term. The advantages of the continuation method are two-fold. -Detail: NaN or Inf found when solving linear system using SOR. Multiphysics problems are often nonlinear. Use this parameter to modify the nonlinearity expressions in the model. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. This case is generally difficult, or impossible, to solve since this material property is non-smooth. 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. Here, we begin an overview of the algorithms used for solving nonlinear static finite element problems. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. Posted 26 set 2019, 17:57 CEST Mesh Version 5.3 0 Replies. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: 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. New Stationary Engineer jobs added daily. Any trademarks referenced in this document are the property of their respective owners. $140,000.00, $120,000.00 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. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) If this was solved using the Solid Mechanics physics interface the thin walls of the container would need to be explicitly modeled, but the wall thickness is much smaller than the overall can dimensions. 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! If the material properties entered are incorrect for the governing equation, the model will generate an error at runtime, usually a Singular Matrix error. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. 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. If it does so, use a finer increment in that range. P&S Comsol Team: Yannik Horst, Manuel Kohli, Xinzhi Zhang. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) Your internet explorer is in compatibility mode and may not be displaying the website correctly. Any trademarks referenced in this document are the property of their respective owners. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. 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. Stationary Solver Iterative Direct . In many physics areas there exist alternative physics formulations specifically meant for solving cases where the geometry has an extreme aspect ratio. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. 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. This is a review for cards & stationery in Brea, CA: "Love this store!!! Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. Again, introduce a Global Parameter that gets ramped from exactly zero to one. 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.) This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. The other low-level default settings within the Stationary Solver are chosen for robustness. Once the error estimate is small enough, as determined by the convergence criterion (20-16) the software terminates the computations and returns a solution. One of the key concepts there was the idea of mesh convergence as you refine the mesh, the solution will become more accurate. Screenshot showing a Solver Configuration that has been altered. What sort of strategies would a medieval military use against a fantasy giant? 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. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. The fully coupled and segregated approaches are discussed below. The technique of load ramping is not always reasonable for all problems. so many cute little stationary items , hair". 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. Wish you all the best. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. 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. Solving for laminar flow using Comsol - YouTube Comsol help video number 2: Solving a laminar flow problem in a slit. COMSOL makes every reasonable effort to verify the information you view on this page. The advantages of the continuation method are two-fold. Reply . 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. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. The default Initial Values for the unknowns in most physics interfaces are zero. Reviews on Stationary Stores in Brea, CA - Typo, Mievic, Posh Paper, Morning Glory, Select Graphics & Printing, Daiso Japan, Urban Outfitters, Office Depot, Barnes & Noble Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the same mesh: adaptmesh1. Most multiphysics problems are nonlinear. if I want to do an adaptive mesh refinement, I get this error. Thanks, Andres. P&S Comsol Team: Manuel Kohli, Raphael Schwanninger, Feature: Stationary Solver 1 (sol1/s1) That is, start by first solving a model with a small, but non-zero, load. COMSOL does not assume any legal liability for the accuracy of the data disclosed. 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. 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. These can be used alone, or in combination with other interfaces. The fully coupled and segregated approaches are discussed below. What are people saying about cards & stationery in Brea, CA? Get notified about new Stationary Engineer jobs in Brea, California, United States. Consult your product manuals for complete trademark details. 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. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. We are planning to continuously update this page throughout the semester and hopefully, this will become a reference during your projects as well. The technique of load ramping is not always reasonable for all problems. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Such a case would be better to address instead with the Shell physics interface, which is specially formulated for handling thin-walled structural parts. - Function: ^ Failed to evaluate variable. 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. 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. Find centralized, trusted content and collaborate around the technologies you use most. COMSOL does not assume any legal liability for the accuracy of the data disclosed. (I am begginer in comsol) Thank you. If you see this, right-click on the Solution feature and select Reset Solver to Default. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Your internet explorer is in compatibility mode and may not be displaying the website correctly. Hi Alexis, Click the link in the email we sent to to verify your email address and activate your job alert. 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.
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