stationary solver comsol

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. Why do many companies reject expired SSL certificates as bugs in bug bounties? However, it is usually not possible to know this ahead of time. This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. 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. 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. Wrong ordering of study steps. That is, start by first solving a model with a small, but non-zero, load. Communication over the phone, in person, and through email was very easy. 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. Consult your product manuals for complete trademark details. Hi Alexis, 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 am trying to solve the coupling between a waveguide and a microring resonator. 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. 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. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. 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. 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. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. I personally liked emailing them the file, ", "This flower shop is the best! There will always already be either a Segregated or Fully Coupled feature beneath this. You can write the discrete form of the equations as f(U) = 0, where f(U) is the residual vector and U is the solution vector. Set "Values for dependent variables" in study step settings to User ControlledSolutionYour Stationary Study. listed if standards is not an option). If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. The settings controlling the predictor type. Here, we begin an overview of the algorithms used for solving nonlinear static finite element problems. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. listed if standards is not an option). A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. It may also reveal that the model itself is ill-posed in some way. rev2023.3.3.43278. Reply . 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. However, load ramping will not work in all cases, or may be inefficient. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. 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 are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. 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. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Multiphysics problems are often nonlinear. 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. In such cases, use the same continuation method, but instead ramp the nonlinearities in 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. listed if standards is not an option). Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. 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. Stationary (time-invariant) models with nonlinearities may converge very slowly. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. 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. See Knowledge Base 1240: Manually Setting the Scaling of Variables. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: Studysteps might be listed in wrong order: Not assigning materials to all the domains. Building on these topics, we will now address how to prepare your mesh for efficiently solving nonlinear finite element problems. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Save my name, email, and website in this browser for the next time I comment. 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 a previous blog entry, we introduced meshing considerations for linear static problems. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) Some models are numerically ill-conditioned due to the setup. - Singular matrix., Make sure you defined your ports correctly:Boundary selectionType of port: e.g. 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. These are some cards & stationery with a large number of reviews in Brea, CA. This case is generally difficult, or impossible, to solve since this material property is non-smooth. P&S Comsol Team: Manuel Kohli, Raphael Schwanninger, Feature: Stationary Solver 1 (sol1/s1) The advantages of the continuation method are two-fold. The algorithm is, generally speaking, a Newton's method approach. What did people search for similar to stationary stores in Brea, CA? Using the first order optimality. Posted Sep 9, 2020, 1:44 p.m. EDT For example, in Solid Mechanics, if the Poisson Ratio set to 0.5, then the model will not solve, as this value in incompatible with the theory of linear elasticity. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Find centralized, trusted content and collaborate around the technologies you use most. Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the same mesh: adaptmesh1. Minimising the environmental effects of my dyson brain. Posted 26 set 2019, 11:57 GMT-4 Linear solvers. Your internet explorer is in compatibility mode and may not be displaying the website correctly. To start a new discussion with a link back to this one, click here. 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. For example, in a Solid Mechanics (wherein the software is solving for the displacement field within the solid) applying two opposite and equal Boundary Load conditions on a part is not sufficient to define the displacement. COMSOL makes every reasonable effort to verify the information you view on this page. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version That is, they are tuned to achieve convergence in as many cases as possible. Click the link in the email we sent to to verify your email address and activate your job alert. Not the answer you're looking for? Second, the continuation method will automatically take smaller load increments if a solution cannot be found. Feature: Stationary Solver 1 (sol1/s1)" . See Knowledge Base 1240: Manually Setting the Scaling of Variables. There will always already be either a Segregated or Fully Coupled feature beneath this. 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. She opened prepackaged 6-packs of Seegars to make ", All "stationary stores" results in Brea, CA, Search stationary stores in popular locations. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. If so, see: Knowledgebase 1030: Error: "Out of memory". Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. 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. If you are unsure if your problem is linear and stationary, look at the Log. Again, introduce a Global Parameter that gets ramped from exactly zero to one. It can be useful while solving sequences of linear systems arising from, for example, nonlinear problems. What is the purpose of this D-shaped ring at the base of the tongue on my hiking boots? Then use this file to provide the initial conditions in time dependent model. If it does so, use a finer increment in that range. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. COMSOL does not assume any legal liability for the accuracy of the data disclosed. If the default iterative solver is not converging, try switching to a direct solver, as described here: Understanding the Fully Coupled vs. Asking for help, clarification, or responding to other answers. 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. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. Consult your product manuals for complete trademark details. $125,000.00, Project Engineer (In-person/Hybrid/Remote), $100,000.00 Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Not entering required material parameters. Such a case would be better to address instead with the Shell physics interface, which is specially formulated for handling thin-walled structural parts. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. COMSOL makes every reasonable effort to verify the information you view on this page. 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. 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. k(T) = 10[W/m/K]*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. Not meshing all the domains. 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. Numerically ill-conditioned means that the system matrix is nearly singular and that it will be difficult to solve on a finite-precision computer. Your email address will not be published. 3. 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. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). Leverage your professional network, and get hired. COMSOL makes every reasonable effort to verify the information you view on this page. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. In such cases, see if one material (or the other) can be omitted from the analysis completely. Alternatively, delete and re-create the study. 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. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. 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. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. It is sometimes necessary to manually scale the dependent variables.