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Segregated approach and Direct vs. Iterative linear solvers, About the time step setting of the solver, Introducing Goal Seeking into the Segregated Solver. Set initial conditions in the physics to the appropriate dependent model variable names rather than the default 0. 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. Full text of the 'Sri Mahalakshmi Dhyanam & Stotram'. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) If so, see: Knowledgebase 1030: Error: "Out of memory". This can arise as a consequence of extreme variations in the material properties, or high aspect ratio geometry. 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. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version 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. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Check the solver log to see if the continuation method is backtracking. 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. $130,000.00. 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. I highly recommend this flower shop. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. Wish you all the best. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Such a case would be better to address instead with the Shell physics interface, which is specially formulated for handling thin-walled structural parts. 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. $140,000.00, $120,000.00 Can I tell police to wait and call a lawyer when served with a search warrant? Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. Building on these topics, we will now address how to prepare your mesh for efficiently solving nonlinear finite element problems. 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. listed if standards is not an option). It is also possible to manually refine the mesh. Not entering required material parameters. P&S: COMSOL Design Tool for Photonic Devices. There will always already be either a Segregated or Fully Coupled feature beneath this. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. This is a review for cards & stationery in Brea, CA: "Love this store!!! To learn more, see our tips on writing great answers. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. I am trying to solve the coupling between a waveguide and a microring resonator. 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. Why is there a voltage on my HDMI and coaxial cables? COMSOL makes every reasonable effort to verify the information you view on this page. The Fully Coupled solution approach, with the Plot While Solving enabled. This is relatively expensive to do, but will lead to the most robust convergence. Any trademarks referenced in this document are the property of their respective owners. Feature: Stationary Solver 1 (sol1/s1) Attempt to evaluate nonintegral power of negative number. 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. See Knowledge Base 1240: Manually Setting the Scaling of Variables. Does anyone know what should cause this problem? The Fully Coupled solution approach, with the Plot While Solving enabled. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. 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. First, it is physically intuitive, often matching how one would perform an experiment. What is the purpose of this D-shaped ring at the base of the tongue on my hiking boots? 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. 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.) 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! Today's top 351 Stationary Engineer jobs in Brea, California, United States. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. Posted Sep 9, 2020, 1:44 p.m. EDT An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: When you use an iterative solver, COMSOL Multiphysics estimates the error of the solution while solving. 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. L'objectif de notre prsent travail se repose sur l'tude par simulation numrique du comportement de bton au jeune ge sous des conditions svres de temprature pendant les premires 24h aprs. The coupling terms between the different groups are thus neglected. 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. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. 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. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Does ZnSO4 + H2 at high pressure reverses to Zn + H2SO4? Again, introduce a Global Parameter that gets ramped from exactly zero to one. Understanding the Fully Coupled vs. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base. Consult your product manuals for complete trademark details. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version I am following the same model as Comsol provide us on the web. Hi ! From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. 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 objective here is to simplify the model to a state where the model will solve, with linear approximations. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. - In the extreme case, suppose one wants to model an instantaneous change in properties, such as: Therefore, an initial value of zero is almost always reasonable if a very small load is applied. Thanks, Andres. By creating this job alert, you agree to the LinkedIn User Agreement and Privacy Policy. GCRO-DR is a method for Krylov subspace recycling. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. As a rough rule of thumb, once the aspect ratio between the largest characteristic dimension to the smallest approaches 100:1, you might start to run into issues and should look to alternative ways of posing the problem, especially in a 3D model. 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. In many physics areas there exist alternative physics formulations specifically meant for solving cases where the geometry has an extreme aspect ratio. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. ", "Absolutely the best place to shop for flowers and greenery, I spent an hour just looking around for fun prior to purchasing a bouquet, they have the best customer service people all over the place and it's a huge place", "Recently came in here to pick up 45 chocolate Seegars (cigars) for a dinner banquet in honor of my baby nephew. - How do/should administrators estimate the cost of producing an online introductory mathematics class? If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. I am solving a linear stationary finite element model but the software is not solving. First, it is physically intuitive, often matching how one would perform an experiment. This involves a systematic reduction in the model complexity. Unknown function or operator. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. I use comsol multiphysics 5.2a and . An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. Your Discussion has gone 30 days without a reply. Few days back i was also facing this problem in . if I want to do an adaptive mesh refinement, I get this error. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. My comment is perhaps a bit nave but it seems to me that you could simply deactivate the term of the background field equation but keep its connexion to the solid to get what you want. Repeat this for every nonlinearity of the model. In our previous blog entry, we introduced the Fully Coupled and the Segregated algorithms used for solving steady-state multiphysics problems in COMSOL. Wrong ordering of study steps. One of the key concepts there was the idea of mesh convergence as you refine the mesh, the solution will become more accurate. Multiphysics problems are often nonlinear. 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. There will always already be either a Segregated or Fully Coupled feature beneath this. 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. 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. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. "After the incident", I started to be more careful not to trip over things. 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 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. Set "Values for dependent variables" in study step settings to User ControlledSolutionYour Stationary Study. The settings controlling the predictor type. That is: Even if the forces on a part are opposite and equal, this is not sufficient information to say where the part is, so you must add some other condition, such as as Fixed Constraint to constrain displacement. 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. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. 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. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Use this parameter to modify the nonlinearity expressions in the model. Contact COMSOL at Bangalore on their telephone: +9180 25323003. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) Direct Iterative , Direct . Multiphysics problems are often nonlinear. The algorithm is, generally speaking, a Newton's method approach. An example would be a linear static structural model of an aluminum beverage can. Not entering required material parameters. 3 Replies, Please login with a confirmed email address before reporting spam. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. Feature: Stationary Solver 1 (sol1/s1)" . If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. 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. Linear solvers. It may also reveal that the model itself is ill-posed in some way. The settings controlling the predictor type. 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. COMSOL does not assume any legal liability for the accuracy of the data disclosed. 0 Replies, Please login with a confirmed email address before reporting spam.