Multiphysics problems are often nonlinear. 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. 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 nature of simulating nature: A Q&A with IBM Quantum researcher Dr. Jamie We've added a "Necessary cookies only" option to the cookie consent popup. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. Posted 26 set 2019, 17:57 CEST Mesh Version 5.3 0 Replies. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. Not assigning proper boundary conditions: Especially if you have ports. I am trying to solve the coupling between a waveguide and a microring resonator. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. To switch between these solver types, go to the Stationary Solver node within the Study sequence. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. This case is generally difficult, or impossible, to solve since this material property is non-smooth. Repeat this for every nonlinearity of the model. I personally liked emailing them the file, ", "This flower shop is the best! If the material properties entered are incorrect for the governing equation, the model will generate an error at runtime, usually a Singular Matrix error. That is, they are tuned to achieve convergence in as many cases as possible. If so, see: Knowledgebase 1030: Error: "Out of memory". The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. Why is there a voltage on my HDMI and coaxial cables? Stationary Engineer Jobs in Brea, California, United States, $87,400.00 I use comsol multiphysics 5.2a and . This information is presented in the context of a very simple 1D finite element problem, and builds upon our previous entry on Solving Linear Static Finite Element Models. The default Initial Values for the unknowns in most physics interfaces are zero. This consent may be withdrawn. This approach is known as a Continuation Method with a Constant predictor. 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. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). Asking for help, clarification, or responding to other answers. 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. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. Does anyone know what should cause this problem? Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. Different physics have different default solvers. 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. The settings controlling the predictor type. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. See Knowledge Base 1240: Manually Setting the Scaling of Variables. listed if standards is not an option). Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. Stationary (time-invariant) models with nonlinearities may converge very slowly. 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. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. This guide applies solely to nonlinear stationary models. 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. 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. Hi Jason, It is also possible to manually refine the mesh. Is there a way to use the stationary solution obtained in Comsol 4.2 as the initial conditions in a time dependent model? There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. If the default iterative solver is not converging, try switching to a direct solver, as described here: Understanding the Fully Coupled vs. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. The coupling terms between the different groups are thus neglected. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) (Frequency Domain should be the last step). Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. Set initial conditions in the physics to the appropriate dependent model variable names rather than the default 0. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. "After the incident", I started to be more careful not to trip over things. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. Find centralized, trusted content and collaborate around the technologies you use most. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. 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. Direct Iterative , Direct . Solving such models in a stationary sense should simply require solving a single (large) system of linear equations and should always be solvable, but there are cases when the software will fail to find a solution. An example would be a linear static structural model of an aluminum beverage can. What is \newluafunction? 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. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. As part of our solver blog series we have discussed solving nonlinear static finite element problems, load ramping for improving convergence of nonlinear problems, and nonlinearity ramping for improving convergence of nonlinear problems. 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. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. Most multiphysics problems are nonlinear. Multiscale Modeling in High-Frequency Electromagnetics. listed if standards is not an option). Multiphysics problems are often nonlinear. The problem is that when I run my model this message appear: Undefined value found. 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. So far, weve learned how to mesh and solve linear and nonlinear single-physics finite element problems, but have not yet considered what happens when there are multiple different interdependent physics being solved within the same domain. 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. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. 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. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. Review the model setup to resolve these. . 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. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Under Initial values of variables solved for, the default value of the Settingslist is Physics controlled. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. However, load ramping will not work in all cases, or may be inefficient. This guide applies solely to nonlinear stationary models. The settings controlling the predictor type. 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. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. Could you expand a little bit more why the coupling is impossible? If the model is nonlinear, see: Improving Convergence of Nonlinear Stationary Models. - 3. 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. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. 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! Hello guys. COMSOL makes every reasonable effort to verify the information you view on this page. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. What are people saying about cards & stationery in Brea, CA? Thanks, Andres. In particular, choosing an improper initial condition or setting up a problem without a solution will simply cause the nonlinear solver to continue iterating without converging. COMSOL does not assume any legal liability for the accuracy of the data disclosed. Your email address will not be published. Get notified about new Stationary Engineer jobs in Brea, California, United States. 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. The other low-level default settings within the Stationary Solver are chosen for robustness. The objective here is to simplify the model to a state where the model will solve, with linear approximations. The default solver for most 3D models is an iterative solver, which is more sensitive to ill-conditioned problems. Hello, 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. 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. - By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. 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. - Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. 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. 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. 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. Not assigning proper boundary conditions: Especially if you have ports. For the Nozomi from Shinagawa to Osaka, say on a Saturday afternoon, would tickets/seats typically be available - or would you need to book? Such a case would be better to address instead with the Shell physics interface, which is specially formulated for handling thin-walled structural parts. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Function: / Failed to evaluate expression. For example, if there is a temperature-dependent material property such as: