stationary solver comsol

Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. Again, introduce a Global Parameter that gets ramped from exactly zero to one. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. Hence Comsol solved for the stationary solution at different points of time. 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. The algorithm is, generally speaking, a Newton's method approach. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. comsol - using stationary solution as the initial conditions in time 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. 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. 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. If the material properties entered are incorrect for the governing equation, the model will generate an error at runtime, usually a Singular Matrix error. 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. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. Specify Material Properties in COMSOL Multiphysics (3/8) 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. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. Then I stored the resulting solution, and used it to to solve the stationary solver again by using the solver manager. Not entering required material parameters. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. 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. - Feature: Stationary Solver 1 (sol1/s1)Failed to find a solution. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. Use a manually defined mesh to avoid elements with extreme aspect ratios and perform a mesh refinement study, as described here: Performing a Mesh Refinement Study, For problems that are ill-conditioned, using a direct solver is often called for. This is relatively expensive to do, but will lead to the most robust convergence. 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. 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. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. It may also reveal that the model itself is ill-posed in some way. 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. 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. COMSOL makes every reasonable effort to verify the information you view on this page. Trying to understand how to get this basic Fourier Series. 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. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. I am trying to solve the coupling between a waveguide and a microring resonator. What are some highly rated cards & stationery in Brea, CA? Check the solver log to see if the continuation method is backtracking. 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. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. Note: there is no way to couple this field with the time dependent nature of this 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. COMSOL makes every reasonable effort to verify the information you view on this page. Most multiphysics problems are nonlinear. COMSOL does not assume any legal liability for the accuracy of the data disclosed. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. However, it is usually not possible to know this ahead of time. - Variable: B1 - Defined as: 1/ ( ( (comp1.cH2 (unit_m_cf^3))/unit_mol_cf)^2.5) Failed to evaluate variable. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. 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. These are some highly rated cards & stationery in Brea, CA: What are some cards & stationery with a large number of reviews in Brea, CA? She opened prepackaged 6-packs of Seegars to make ", All "stationary stores" results in Brea, CA, Search stationary stores in popular locations. This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. It may also reveal that the model itself is ill-posed in some way. Posted 26 set 2019, 17:57 CEST Mesh Version 5.3 0 Replies. Click the link in the email we sent to to verify your email address and activate your job alert. . If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. For example, if there is a temperature-dependent material property such as: The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). It is also possible to manually refine the mesh. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. $125,000.00, Project Engineer (In-person/Hybrid/Remote), $100,000.00 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 that case, the continuation method will automatically backtrack and try to solve for intermediate values in the range of 0.6 through 0.8. 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. 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. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. This solver is automatically used when a Stationary or Frequency Domain study is added to the model. 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. The segregated approach, on the other hand, solves sets of unknowns separately. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: Today's top 351 Stationary Engineer jobs in Brea, California, United States. Popular answers (1) This problem generally occurs when there is some mistake in the physics or study section or wrong selection of the mesh size. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. I am following the same model as Comsol provide us on the web. 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. 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. Unknown function or operator. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: Again, introduce a Global Parameter that gets ramped from exactly zero to one. This guide applies solely to nonlinear stationary models. That is, start by first solving a model with a small, but non-zero, load. This involves a systematic reduction in the model complexity. 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. 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. 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. Here we introduce the two classes of algorithms used to solve multiphysics finite element problems in COMSOL Multiphysics. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. 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. replace it with the expression: 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. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. P&S Comsol Team: Arif Gngr , Yannik Horst , Stefano Valente. COMSOL makes every reasonable effort to verify the information you view on this page. The difference between the phonemes /p/ and /b/ in Japanese. 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.