Here, we will examine techniques for accelerating the convergence of these two methods. The prices are good, and when I needed something delivered, same day, they were able to do it, and it looked beautiful!! With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. $131,100.00, Simplified Vehicle Operations Project Engineer, $115,000.00 From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. 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. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. The fully coupled and segregated approaches are discussed below. The objective here is to simplify the model to a state where the model will solve, with linear approximations. Direct PARDISO Solver , PARDISO . The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). Does anyone know what should cause this problem? That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. listed if standards is not an option). This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. November 11, 2013. Then I stored the resulting solution, and used it to to solve the stationary solver again by using the solver manager. Could you expand a little bit more why the coupling is impossible? 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. The Fully Coupled solution approach, with the Plot While Solving enabled. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. Such a large difference in the materials properties can be challenging. Repeat this for every nonlinearity of the model. The coupling terms between the different groups are thus neglected. Create the time-dependent step or study. 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. Most multiphysics problems are nonlinear. P&S: COMSOL Design Tool for Photonic Devices. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. Get notified about new Stationary Engineer jobs in Brea, California, United States. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. Under Initial values of variables solved for, the default value of the Settingslist is Physics controlled. - She opened prepackaged 6-packs of Seegars to make ", All "stationary stores" results in Brea, CA, Search stationary stores in popular locations. 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. 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. However, it is usually not possible to know this ahead of time. Stationary Solver Use the Stationary Solver () to find the solution to linear and nonlinear stationary problems (also called static or steady-state problems). They worked with me. Few days back i was also facing this problem in . Use this parameter to modify the nonlinearity expressions in the model. Hello guys. Connect and share knowledge within a single location that is structured and easy to search. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. It is also possible to manually refine the mesh. Why? You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base. What version of COMSOL are you using? 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. New Stationary Engineer jobs added daily. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. If so, see: Knowledgebase 1030: Error: "Out of memory". Not entering required material parameters. Here, we begin an overview of the algorithms used for solving nonlinear static finite element problems. - Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. comp1.u2, comp1.v2, and comp1.w2 are usually variables associated with the x,y, and z component of deformation in COMSOL. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. Common Mistakes: Not assigning materials to all the domains. 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 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. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. so many cute little stationary items , hair". Therefore, an initial value of zero is almost always reasonable if a very small load is applied. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: 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. 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 such cases, use the same continuation method, but instead ramp the nonlinearities in the model. 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. Stationary (time-invariant) models with nonlinearities may converge very slowly. This guide applies solely to nonlinear stationary models. That is, start by first solving a model with a small, but non-zero, load. Leverage your professional network, and get hired. Mesh The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. Again, introduce a Global Parameter that gets ramped from exactly zero to one. - Feature: Stationary Solver 1 (sol1/s1)Failed to find a solution. Stationary Engineer Jobs in Brea, California, United States, $87,400.00 See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. 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 Auxiliary Sweep can be used to implement ramping of any Global Parameter. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. 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. 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. Your internet explorer is in compatibility mode and may not be displaying the website correctly. The advantages of the continuation method are two-fold. Could you expand a little bit more why the coupling is impossible? Check the solver log to see if the continuation method is backtracking. It is sometimes necessary to manually scale the dependent variables. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. Hi Alexis, The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. Cecilia M. came from the backroom to help me and went out of her way to help me even though I had not called before going into the store. Again, introduce a Global Parameter that gets ramped from exactly zero to one. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) 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. If you have both as steps in the same study, then solve that study. Contact COMSOL at Bangalore on their telephone: +9180 25323003. Get email updates for new Stationary Engineer jobs in Brea, California, United States. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. This algorithm was also useful for understanding what happens near a failure load. Solve the stationary study then the time dependent study. The problem is that when I run my model this message appear: Undefined value found. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. Repeat this for every nonlinearity of the model. Note the star symbol on the Solution feature. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. 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. 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. 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