The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). 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. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. 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. To learn more, see our tips on writing great answers. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base. I am trying to solve the coupling between a waveguide and a microring resonator. 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. 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. She opened prepackaged 6-packs of Seegars to make ", All "stationary stores" results in Brea, CA, Search stationary stores in popular locations. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. Is it possible to rotate a window 90 degrees if it has the same length and width? It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. They are usually called comp1.u, comp1.v, and comp1.w though. - 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. 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. The default Initial Values for the unknowns in most physics interfaces are zero. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. Learn how your comment data is processed. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. Your internet explorer is in compatibility mode and may not be displaying the website correctly. We use COMSOL Multiphysics for solving distributed optimal control of un-steady Burgers equation without constraints and with pointwise control constraints. 3 Replies, Please login with a confirmed email address before reporting spam. 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.) Therefore, an initial value of zero is almost always reasonable if a very small load is applied. Not entering required material parameters. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. What is \newluafunction? The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. comp1.u2, comp1.v2, and comp1.w2 are usually variables associated with the x,y, and z component of deformation in COMSOL. How do/should administrators estimate the cost of producing an online introductory mathematics class? Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. 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. This approach is known as a Continuation Method with a Constant predictor. Most multiphysics problems are nonlinear. Please dont hesitate to post comments below or send emails to us if you experience any other problems. Minimising the environmental effects of my dyson brain. 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. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. Not assigning proper boundary conditions: Especially if you have ports. I use comsol multiphysics 5.2a and . However, if a lower-level change has been manually made to the solver settings, the software will not automatically use the correct default solver. 3. Under Initial values of variables solved for, the default value of the Settingslist is Physics controlled. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. This consent may be withdrawn. 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. For example, if there is a temperature-dependent material property such as: If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. 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 instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. 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. 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. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Create the time-dependent step or study. That is, they are tuned to achieve convergence in as many cases as possible. Cooling and Solidification of Metal. With respect to any nonlinearities, replace them by a reasonable linearized term. 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. This is relatively expensive to do, but will lead to the most robust convergence. The settings controlling the predictor type. 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. Here, we will examine techniques for accelerating the convergence of these two methods. - Feature: Stationary Solver 1 (sol1/s1)Failed to find a solution. First, it is physically intuitive, often matching how one would perform an experiment. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version If the default iterative solver is not converging, try switching to a direct solver, as described here: Understanding the Fully Coupled vs. The other low-level default settings within the Stationary Solver are chosen for robustness. Reviews on Stationary Stores in Brea, CA - Typo, Mievic, Posh Paper, Morning Glory, Select Graphics & Printing, Daiso Japan, Urban Outfitters, Office Depot, Barnes & Noble rev2023.3.3.43278. Consult your product manuals for complete trademark details. Then use this file to provide the initial conditions in time dependent model. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. 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. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. 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. Common Mistakes: Not assigning materials to all the domains. Alle Rechte vorbehalten. Unknown function or operator. If it does so, use a finer increment in that range. That is, they are tuned to achieve convergence in as many cases as possible. Set initial conditions in the physics to the appropriate dependent model variable names rather than the default 0. It can be useful while solving sequences of linear systems arising from, for example, nonlinear problems. This is a review for cards & stationery in Brea, CA: "Love this store!!! 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. If so, see: Knowledgebase 1030: Error: "Out of memory". That is, start by first solving a model with a small, but non-zero, load. However, it is usually not possible to know this ahead of time. The segregated approach, on the other hand, solves sets of unknowns separately. 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. In such cases, see if one material (or the other) can be omitted from the analysis completely. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. 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. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. Any trademarks referenced in this document are the property of their respective owners. One of the key concepts there was the idea of mesh convergence as you refine the mesh, the solution will become more accurate. 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. listed if standards is not an option). 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. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. The advantages of the continuation method are two-fold. Your internet explorer is in compatibility mode and may not be displaying the website correctly. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. Wrong ordering of study steps. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). 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]) replace it with the expression: The issue here has do with the iterative algorithm used to solve nonlinear stationary models. An example would be a linear static structural model of an aluminum beverage can. Multiphysics problems are often nonlinear. The coupling terms between the different groups are thus neglected. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. However, it is usually not possible to know this ahead of time.
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