Not the answer you're looking for? The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: If you see this, right-click on the Solution feature and select Reset Solver to Default. Name: actdep_int1, Your email address will not be published. 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. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. 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. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. Does anyone know what should cause this problem? Leverage your professional network, and get hired. By creating this job alert, you agree to the LinkedIn User Agreement and Privacy Policy. Here, we will examine techniques for accelerating the convergence of these two methods. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. The segregated approach, on the other hand, solves sets of unknowns separately. COMSOL does not assume any legal liability for the accuracy of the data disclosed. Create the time-dependent step or study. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. Hello, Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. Different physics have different default solvers. 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. Segregated approach and Direct vs. Iterative linear solvers, About the time step setting of the solver, Introducing Goal Seeking into the Segregated Solver. Is there a way to use the stationary solution obtained in Comsol 4.2 as the initial conditions in a time dependent model? Your internet explorer is in compatibility mode and may not be displaying the website correctly. Use this parameter to modify the nonlinearity expressions in the model. How do/should administrators estimate the cost of producing an online introductory mathematics class? Staging Ground Beta 1 Recap, and Reviewers needed for Beta 2, Simulation of effect of heated resistance on temperature distribution in laminar flow, COMSOL: Diffusion in Transport of Diluted Species Produces Unphysical Results. Trying to understand how to get this basic Fourier Series. This is relatively expensive to do, but will lead to the most robust convergence. (Frequency Domain should be the last step) Stationary (time-invariant) models with nonlinearities may converge very slowly. That is, they are tuned to achieve convergence in as many cases as possible. When you use an iterative solver, COMSOL Multiphysics estimates the error of the solution while solving. 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. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. - the incident has nothing to do with me; can I use this this way? 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. 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. First, it is physically intuitive, often matching how one would perform an experiment. numeric (each ports needs their ownboundary mode analysis in the study if they are numerically defined)Wave excitation: on/off(input/output), - Feature: Stationary Solver 1 (sol1/s1) Division by zero. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. About the Stationary Solver The following background information about the Stationary Solver discusses these topics: Damped Newton Methods, Termination Criterion for the Fully Coupled and Segregated Attribute Nodes, Linear Solvers versus Nonlinear Solvers, and Pseudo Time Stepping. Stationary (time-invariant) models with nonlinearities may converge very slowly. See Knowledge Base 1240: Manually Setting the Scaling of Variables. Stationary Solver Iterative Direct . 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. How can I use it? This algorithm was also useful for understanding what happens near a failure load. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. I use comsol multiphysics 5.2a and . What is \newluafunction? Such problems must solved in the time domain. About the Stationary Solver - COMSOL Multiphysics Mesh This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. 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. There will always already be either a Segregated or Fully Coupled feature beneath this. 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.) Function: / Failed to evaluate expression. How to solve "Undefined material property 'sigma - ResearchGate The conditions on the geometric aspect ratio are relatively more strict. Reply . If these settings have been manually changed, you will see a small star symbol on the Solution feature, as shown in the screenshot below. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. It is sometimes necessary to manually scale the dependent variables. When the difference in the computed solutions between successive iterations is sufficiently small, or when the residual is sufficiently small, the problem is considered converged to within the specified tolerance. (I am begginer in comsol) Thank you. This approach is known as a Continuation Method with a Constant predictor. 3 Replies, Please login with a confirmed email address before reporting spam. I am trying to solve the coupling between a waveguide and a microring resonator. I am following the same model as Comsol provide us on the web. P&S Comsol Team: Manuel Kohli, Raphael Schwanninger, Feature: Stationary Solver 1 (sol1/s1) 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. The default Initial Values for the unknowns in most physics interfaces are zero. This case is generally difficult, or impossible, to solve since this material property is non-smooth. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: For the Nozomi from Shinagawa to Osaka, say on a Saturday afternoon, would tickets/seats typically be available - or would you need to book? 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. The continuation method will again backtrack and try intermediate values of the ramping parameter, thus giving you the nearest approximation to the abrupt transition that is solvable. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. listed if standards is not an option). Segregated approach and Direct vs. Iterative linear solvers, Time dependent function and stationary study, Combining Adaptive Mesh Refinement with Data Filtering, What to do when a linear stationary model is not solving, Galleria dei Modelli e delle App di Simulazione, 2023 da COMSOL. For example, if there is a temperature-dependent material property such as: To switch between these solver types, go to the Stationary Solver node within the Study sequence. Stationary in the COMSOL Multiphysics Programming Reference Manual Damped Newton Methods The nonlinear solver uses an affine invariant form of the damped Newton method as described in Ref. 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. Again, introduce a Global Parameter that gets ramped from exactly zero to one. - How to solve "Feature: Stationary Solver 1 (sol1/s1) Attempt - COMSOL That is, start by first solving a model with a small, but non-zero, load. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. She opened prepackaged 6-packs of Seegars to make ", All "stationary stores" results in Brea, CA, Search stationary stores in popular locations. COMSOL does not assume any legal liability for the accuracy of the data disclosed. Not entering required material parameters. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) 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. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. thanks for reply You can unsubscribe from these emails at any time. 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. Hello guys. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version - As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. 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 algorithm is, generally speaking, a Newton's method approach. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. The settings controlling the predictor type.