Stationary Solver Use the Stationary Solver () to find the solution to linear and nonlinear stationary problems (also called static or steady-state problems). Not entering required material parameters. Does ZnSO4 + H2 at high pressure reverses to Zn + H2SO4? listed if standards is not an option). The default solver for most 3D models is an iterative solver, which is more sensitive to ill-conditioned problems. Linear solvers. Linear solvers. Could you expand a little bit more why the coupling is impossible? 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. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. Again, introduce a Global Parameter that gets ramped from exactly zero to one. The Fully Coupled solution approach, with the Plot While Solving enabled. 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 am solving a linear stationary finite element model but the software is not solving. Find detailed information on Office Supplies, Stationery, and Gift Retailers companies in Brea, California, United States of America, including financial statements, sales and marketing contacts, top competitors, and firmographic insights. In this post, we will delve deeper into how to choose an appropriate mesh to start your mesh convergence studies for linear static finite element problems. Studysteps might be listed in wrong order: Not assigning materials to all the domains. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. 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. 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. Save my name, email, and website in this browser for the next time I comment. Singular matrix., Make sure you defined your ports correctly:Boundary selectionType of port: e.g. Wrong ordering of study steps. Perhaps this approach could be adapted to represent your model. With respect to any nonlinearities, replace them by a reasonable linearized term. . With respect to any nonlinearities, replace them by a reasonable linearized term. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. However, it is usually not possible to know this ahead of time. 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. Iterative , Direct . If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. 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. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: This can arise as a consequence of extreme variations in the material properties, or high aspect ratio geometry. Not assigning proper boundary conditions: Especially if you have ports. What are people saying about cards & stationery in Brea, CA? There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. 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. 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 both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. This is a review for cards & stationery in Brea, CA: "Love this store!!! Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the same mesh: adaptmesh1. 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. This solver is automatically used when a Stationary or Frequency Domain study is added to the model. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. 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. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. The solver settings are stored at Study > Solver Configurations > Solution. Alle Rechte vorbehalten. I am trying to solve the coupling between a waveguide and a microring resonator. Here we introduce a more robust approach to solving nonlinear problems. Under Initial values of variables solved for, the default value of the Settingslist is Physics controlled. - Feature: Stationary Solver 1 (sol1/s1)Failed to find a solution. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. It may also reveal that the model itself is ill-posed in some way. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. The segregated approach, on the other hand, solves sets of unknowns separately. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. Alternatively, delete and re-create the study. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. If your matrix is singular than no solver in the world can solve Ax=B. - Variable: B1 - Defined as: 1/ ( ( (comp1.cH2 (unit_m_cf^3))/unit_mol_cf)^2.5) Failed to evaluate variable. In a previous blog entry, we introduced meshing considerations for linear static problems. Can I tell police to wait and call a lawyer when served with a search warrant? Second, the continuation method will automatically take smaller load increments if a solution cannot be found. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. P&S Comsol Team: Yannik Horst, Manuel Kohli, Xinzhi Zhang. "After the incident", I started to be more careful not to trip over things. To switch between these solver types, go to the Stationary Solver node within the Study sequence. 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. 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. Building on these topics, we will now address how to prepare your mesh for efficiently solving nonlinear finite element problems. First, it is physically intuitive, often matching how one would perform an experiment. 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! Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. What is the purpose of non-series Shimano components? . Set "Values for dependent variables" in study step settings to User ControlledSolutionYour Stationary Study. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. 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. To learn more, see our tips on writing great answers. 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. 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. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version When you use an iterative solver, COMSOL Multiphysics estimates the error of the solution while solving. We are planning to continuously update this page throughout the semester and hopefully, this will become a reference during your projects as well. Set initial conditions in the physics to the appropriate dependent model variable names rather than the default 0. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Please dont hesitate to post comments below or send emails to us if you experience any other problems. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. Note: there is no way to couple this . If it does so, use a finer increment in that range. If you see this, right-click on the Solution feature and select Reset Solver to Default. 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 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. 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. 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. There will always already be either a Segregated or Fully Coupled feature beneath this. 3 Replies, Please login with a confirmed email address before reporting spam. 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. 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. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. Solve the stationary study then the time dependent study. Segregated approach and Direct vs. The technique of load ramping is not always reasonable for all problems. Why is there a voltage on my HDMI and coaxial cables? An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: COMSOL makes every reasonable effort to verify the information you view on this page. Understanding the Fully Coupled vs. Hi Jason, Cooling and Solidification of Metal. Is there a way to use the stationary solution obtained in Comsol 4.2 as the initial conditions in a time dependent model? Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. listed if standards is not an option). 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. 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. However, load ramping will not work in all cases, or may be inefficient. See Knowledge Base 1240: Manually Setting the Scaling of Variables. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. The technique of load ramping is not always reasonable for all problems. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). Such problems must solved in the time domain. Could you expand a little bit more why the coupling is impossible? An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: $125,000.00, Project Engineer (In-person/Hybrid/Remote), $100,000.00 The prices are good, and when I needed something delivered, same day, they were able to do it, and it looked beautiful!! Here, we begin an overview of the algorithms used for solving nonlinear static finite element problems. Most multiphysics problems are nonlinear. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. What sort of strategies would a medieval military use against a fantasy giant? The algorithm is, generally speaking, a Newton's method approach. Also, keep in mind that a linear stationary model should solve regardless of how coarse the mesh is (albeit to a low accuracy) so you can always start with as coarse a mesh as possible, and refine the mesh (See also: Knowledgebase 1030: Performing a Mesh Refinement Study. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. See Knowledge Base 1240: Manually Setting the Scaling of Variables. Use this parameter to modify the nonlinearity expressions in the model. SGP handled 7 different prints for me at once and they all came out perfectly, in a timely manner. Get email updates for new Stationary Engineer jobs in Brea, California, United States. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. 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.
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