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. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. November 11, 2013. replace it with the expression: By creating this job alert, you agree to the LinkedIn User Agreement and Privacy Policy. I am solving a linear stationary finite element model but the software is not solving. COMSOL does not assume any legal liability for the accuracy of the data disclosed. Dr.S.Ravindran Cite 1 Recommendation Popular answers (1). An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: You can unsubscribe from these emails at any time. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. $140,000.00, $120,000.00 Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. To learn more, see our tips on writing great answers. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. Direct PARDISO Solver , PARDISO . What is the purpose of non-series Shimano components? If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. What is \newluafunction? Not the answer you're looking for? That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. 3 Replies, Please login with a confirmed email address before reporting spam. -Detail: NaN or Inf found when solving linear system using SOR. The default Initial Values for the unknowns in most physics interfaces are zero. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. 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 Wrong ordering of study steps. 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. 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. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. 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. Required fields are marked *. Connect and share knowledge within a single location that is structured and easy to search. The coupling terms between the different groups are thus neglected. Not meshing all the domains. 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. The other low-level default settings within the Stationary Solver are chosen for robustness. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. With respect to any nonlinearities, replace them by a reasonable linearized term. 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. What is the purpose of this D-shaped ring at the base of the tongue on my hiking boots? 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! 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. See if these can be used instead of explicitly modeling parts with high-aspect ratio geometries. 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. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version 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. The fully coupled and segregated approaches are discussed below. Perhaps this approach could be adapted to represent your model. Full text of the 'Sri Mahalakshmi Dhyanam & Stotram'. The fully coupled and segregated approaches are discussed below. 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. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. Discussion Closed This discussion was created more than 6 months ago and has been closed. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. COMSOL makes every reasonable effort to verify the information you view on this page. Here we introduce the two classes of algorithms used to solve multiphysics finite element problems in COMSOL Multiphysics. This case is generally difficult, or impossible, to solve since this material property is non-smooth. 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. It is also possible to manually refine the mesh. (Frequency Domain should be the last step). Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. COMSOL makes every reasonable effort to verify the information you view on this page. If the material properties entered are incorrect for the governing equation, the model will generate an error at runtime, usually a Singular Matrix error. Name: actdep_int1, Your email address will not be published. Is it possible to rotate a window 90 degrees if it has the same length and width? When you use an iterative solver, COMSOL Multiphysics estimates the error of the solution while solving. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. 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. Not assigning proper boundary conditions: Especially if you have ports. 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. Repeat this for every nonlinearity of the model. Your internet explorer is in compatibility mode and may not be displaying the website correctly. 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. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. What sort of strategies would a medieval military use against a fantasy giant? Iterative , Direct . "I chose this print shop based off yelp reviews and was very happy with the outcome! 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. This involves a systematic reduction in the model complexity. 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. Understanding the Fully Coupled vs. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. Use this parameter to modify the nonlinearity expressions in the model. - How do/should administrators estimate the cost of producing an online introductory mathematics class? In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. Alternatively, delete and re-create the study. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: 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. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. Under Initial values of variables solved for, the default value of the Settingslist is Physics controlled. Making statements based on opinion; back them up with references or personal experience. 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. Not assigning proper boundary conditions: Especially if you have ports. Segregated approach and Direct vs. The objective here is to simplify the model to a state where the model will solve, with linear approximations. This can arise as a consequence of extreme variations in the material properties, or high aspect ratio geometry. This approach is known as a Continuation Method with a Constant predictor. 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]+10[W/m/K]*(T>400[K]) In our previous blog entry, we introduced the Fully Coupled and the Segregated algorithms used for solving steady-state multiphysics problems in COMSOL. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. 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. Any trademarks referenced in this document are the property of their respective owners. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. thanks for reply 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. 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. Solving for laminar flow using Comsol - YouTube Comsol help video number 2: Solving a laminar flow problem in a slit. Here, we begin an overview of the algorithms used for solving nonlinear static finite element problems. First, it is physically intuitive, often matching how one would perform an experiment. Again, introduce a Global Parameter that gets ramped from exactly zero to one. There will also be a red cross over the Materials branch icon. 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 so, see: Knowledgebase 1030: Error: "Out of memory". Could you expand a little bit more why the coupling is impossible? It is sometimes necessary to manually scale the dependent variables. Segregated approach and Direct vs. Iterative linear solvers, About the time step setting of the solver, Introducing Goal Seeking into the Segregated Solver. Use this parameter to modify the nonlinearity expressions in the model. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. 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. 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. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) Then I stored the resulting solution, and used it to to solve the stationary solver again by using the solver manager. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. Reply . 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. The coupling terms between the different groups are thus neglected. Not assigning proper boundary conditions: Especially if you have ports. This is a review for cards & stationery in Brea, CA: "Love this store!!! If you try to enter a variable that is undefined, the automatic syntax highlighting will identify this as you enter it, and it is best practice to resolve this immediately. 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. Posted 26 set 2019, 17:57 CEST Mesh Version 5.3 0 Replies. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. 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. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Repeat this for every nonlinearity of the model. These are some cards & stationery with a large number of reviews in Brea, CA. See Knowledge Base 1240: Manually Setting the Scaling of Variables. 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. Improving Convergence of Nonlinear Stationary Models, Knowledgebase 1030: Error: "Out of memory", Knowledgebase 1030: Performing a Mesh Refinement Study, Understanding the Fully Coupled vs. Computational Fluid Dynamics (CFD), API The Fully Coupled solution approach, with the Plot While Solving enabled. It may also reveal that the model itself is ill-posed in some way. Why is there a voltage on my HDMI and coaxial cables? Consult your product manuals for complete trademark details. Cooling and Solidification of Metal. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. It is also possible to manually refine the mesh. Communication over the phone, in person, and through email was very easy. Your internet explorer is in compatibility mode and may not be displaying the website correctly. There will always already be either a Segregated or Fully Coupled feature beneath this. 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. 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.
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