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. 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. 0 Replies, Please login with a confirmed email address before reporting spam. By creating this job alert, you agree to the LinkedIn User Agreement and Privacy Policy. One of the key concepts there was the idea of mesh convergence as you refine the mesh, the solution will become more accurate. 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. What version of COMSOL are you using? 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. Thanks for contributing an answer to Stack Overflow! That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. "I chose this print shop based off yelp reviews and was very happy with the outcome! An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: P&S Comsol Team: Manuel Kohli, Raphael Schwanninger, Feature: Stationary Solver 1 (sol1/s1) Consult your product manuals for complete trademark details. When you use an iterative solver, COMSOL Multiphysics estimates the error of the solution while solving. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. However, load ramping will not work in all cases, or may be inefficient. 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. Again, introduce a Global Parameter that gets ramped from exactly zero to one. Name: actdep_int1, Your email address will not be published. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. Discussion Closed This discussion was created more than 6 months ago and has been closed. Numerically ill-conditioned means that the system matrix is nearly singular and that it will be difficult to solve on a finite-precision computer. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. The prices are good, and when I needed something delivered, same day, they were able to do it, and it looked beautiful!! listed if standards is not an option). The objective here is to simplify the model to a state where the model will solve, with linear approximations. This guide applies solely to nonlinear stationary models. 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. Feature: Stationary Solver 1 (sol1/s1)" . In this blog post we introduce the two classes of algorithms that are used in COMSOL to solve systems of linear equations that arise when solving any finite element problem. Perhaps this approach could be adapted to represent your model. Hello guys. The objective here is to simplify the model to a state where the model will solve, with linear approximations. My comment is perhaps a bit nave but it seems to me that you could simply deactivate the \frac{\partial \cdot}{\partial t} term of the background field equation but keep its connexion to the solid to get what you want. The default Initial Values for the unknowns in most physics interfaces are zero. Wrong ordering of study steps. - 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. Hi ! The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. 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. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. For the Nozomi from Shinagawa to Osaka, say on a Saturday afternoon, would tickets/seats typically be available - or would you need to book? Your internet explorer is in compatibility mode and may not be displaying the website correctly. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. 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. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. Multiphysics problems are often nonlinear. Wrong ordering of study steps. The default Initial Values for the unknowns in most physics interfaces are zero. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. 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. 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. 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. 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. listed if standards is not an option). As we saw previously in the blog entry on Solving Nonlinear Static Finite Element Problems, not all nonlinear problems will be solvable via the damped Newton-Raphson method. COMSOL does not assume any legal liability for the accuracy of the data disclosed. It may also reveal that the model itself is ill-posed in some way. Not meshing all the domains. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. The settings controlling the predictor type. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. They deal with COMSOL package and train users. As we saw in Load Ramping of Nonlinear Problems, we can use the continuation method to ramp the loads on a problem up from an unloaded case where we know the solution. See Knowledge Base 1240: Manually Setting the Scaling of Variables. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. The coupling terms between the different groups are thus neglected. This case is generally difficult, or impossible, to solve since this material property is non-smooth. There will always already be either a Segregated or Fully Coupled feature beneath this. If you have both as steps in the same study, then solve that study. 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. New Stationary Engineer jobs added daily. 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. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. I am following the same model as Comsol provide us on the web. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. - Function: ^ Failed to evaluate variable. Comsol help video number 2: Solving a laminar flow problem in a slit.. Use this parameter to modify the nonlinearity expressions in the model. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. This approach is known as a Continuation Method with a Constant predictor. 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. . To learn more, see our tips on writing great answers. There will also be a red cross over the Materials branch icon. Can I tell police to wait and call a lawyer when served with a search warrant? How can I check before my flight that the cloud separation requirements in VFR flight rules are met? Get email updates for new Stationary Engineer jobs in Brea, California, United States. What is the purpose of this D-shaped ring at the base of the tongue on my hiking boots? 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. If so, see: Knowledgebase 1030: Error: "Out of memory". Repeat this for every nonlinearity of the model. Understanding the Fully Coupled vs. The advantages of the continuation method are two-fold. It may also reveal that the model itself is ill-posed in some way. Different physics have different default solvers. Have you taken a look at this [blog post](https://www.comsol.com/blogs/modeling-fluid-structure-interaction-in-multibody-mechanisms/)? k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) 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. This can arise as a consequence of extreme variations in the material properties, or high aspect ratio geometry. That is, they are tuned to achieve convergence in as many cases as possible. Check the solver log to see if the continuation method is backtracking. Find centralized, trusted content and collaborate around the technologies you use most. 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. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. COMSOL makes every reasonable effort to verify the information you view on this page. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. What are some highly rated cards & stationery in Brea, CA? Your internet explorer is in compatibility mode and may not be displaying the website correctly. listed if standards is not an option). The technique of load ramping is not always reasonable for all problems. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. Multiphysics problems are often nonlinear. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. Stationary Solver Iterative Direct . The technique of load ramping is not always reasonable for all problems. Again, introduce a Global Parameter that gets ramped from exactly zero to one. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. 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. I have searched all over comsol forum to fix this stationary solver configuration and still doesn't work because I don't know the logic behind the solver system. An example would be a linear static structural model of an aluminum beverage can. If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base. 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. 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 Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. 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. Review the model setup to resolve these. Not assigning proper boundary conditions: Especially if you have ports. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: To start a new discussion with a link back to this one, click here. Your email address will not be published. If the material properties entered are incorrect for the governing equation, the model will generate an error at runtime, usually a Singular Matrix error. Then use this file to provide the initial conditions in time dependent model. Any trademarks referenced in this document are the property of their respective owners. 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. If it does so, use a finer increment in that range. Then I stored the resulting solution, and used it to to solve the stationary solver again by using the solver manager. if I want to do an adaptive mesh refinement, I get this error. 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, 2023 by COMSOL. 3 Replies, Please login with a confirmed email address before reporting spam. Trying to understand how to get this basic Fourier Series. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. 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. Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the same mesh: adaptmesh1. -Detail: NaN or Inf found when solving linear system using SOR. (I am begginer in comsol) Thank you. replace it with the expression: k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) In the extreme case, suppose one wants to model an instantaneous change in properties, such as: Dr.S.Ravindran Cite 1 Recommendation Popular answers (1). $125,000.00, Project Engineer (In-person/Hybrid/Remote), $100,000.00 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. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. These are some cards & stationery with a large number of reviews in Brea, CA. The settings controlling the predictor type. Not entering required material parameters.
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