Note: there is no way to couple this . . If your matrix is singular than no solver in the world can solve Ax=B. Any trademarks referenced in this document are the property of their respective owners. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. 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. Today's top 351 Stationary Engineer jobs in Brea, California, United States. 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. Segregated approach and Direct vs. For example, if there is a temperature-dependent material property such as: In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. The advantages of the continuation method are two-fold. Comsol help video number 2: Solving a laminar flow problem in a slit.. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. Stationary Engineer Jobs in Brea, California, United States, $87,400.00 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. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). Multiscale Modeling in High-Frequency Electromagnetics. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) There will always already be either a Segregated or Fully Coupled feature beneath this. 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. This case is generally difficult, or impossible, to solve since this material property is non-smooth. Have you taken a look at this [blog post](https://www.comsol.com/blogs/modeling-fluid-structure-interaction-in-multibody-mechanisms/)? With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. However, it is usually not possible to know this ahead of time. 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. so many cute little stationary items , hair". Discussion Closed This discussion was created more than 6 months ago and has been closed. Screenshot showing a Solver Configuration that has been altered. $140,000.00, $120,000.00 -Detail: NaN or Inf found when solving linear system using SOR. COMSOL makes every reasonable effort to verify the information you view on this page. To learn more, see our tips on writing great answers. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. Perhaps this approach could be adapted to represent your model. Such problems must solved in the time domain. 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. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Not meshing all the domains. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. Feature: Stationary Solver 1 (sol1/s1) Attempt to evaluate nonintegral power of negative number. If you are unsure if your problem is linear and stationary, look at the Log. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: 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. Posted Sep 9, 2020, 1:44 p.m. EDT Not entering required material parameters. Hi Alexis, . Hi ! 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. If the default iterative solver is not converging, try switching to a direct solver, as described here: Understanding the Fully Coupled vs. The default solver for most 3D models is an iterative solver, which is more sensitive to ill-conditioned problems. Thanks for contributing an answer to Stack Overflow! The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. The algorithm is, generally speaking, a Newton's method approach. Solver . Acidity of alcohols and basicity of amines. Consult your product manuals for complete trademark details. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. 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. 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. How can I check before my flight that the cloud separation requirements in VFR flight rules are met? They worked with me. Your internet explorer is in compatibility mode and may not be displaying the website correctly. The objective here is to simplify the model to a state where the model will solve, with linear approximations. Any trademarks referenced in this document are the property of their respective owners. Set "Values for dependent variables" in study step settings to User ControlledSolutionYour Stationary Study. Not assigning proper boundary conditions: Especially if you have ports. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. 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. Set initial conditions in the physics to the appropriate dependent model variable names rather than the default 0. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. The fully coupled and segregated approaches are discussed below. How do/should administrators estimate the cost of producing an online introductory mathematics class? Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. comp1.u2, comp1.v2, and comp1.w2 are usually variables associated with the x,y, and z component of deformation in COMSOL. With sufficient simplification, a model can be reduced to a linear problem, and if this simplified model does not converge, see: What to do when a linear stationary model is not solving. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. With sufficient simplification, a model can be reduced to a linear problem, and if this simplified model does not converge, see: What to do when a linear stationary model is not solving. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. 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. See if these can be used instead of explicitly modeling parts with high-aspect ratio geometries. listed if standards is not an option). 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. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) 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. SGP handled 7 different prints for me at once and they all came out perfectly, in a timely manner. Asking for help, clarification, or responding to other answers. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. Singular matrix., Make sure you defined your ports correctly:Boundary selectionType of port: e.g. What is \newluafunction? Why? 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. 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. Posted 26 set 2019, 11:57 GMT-4 The coupling terms between the different groups are thus neglected. Consult your product manuals for complete trademark details. 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. Hello, Check the solver log to see if the continuation method is backtracking. This can arise as a consequence of extreme variations in the material properties, or high aspect ratio geometry. It is sometimes necessary to manually scale the dependent variables. replace it with the expression: 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. For the Nozomi from Shinagawa to Osaka, say on a Saturday afternoon, would tickets/seats typically be available - or would you need to book? 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 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. 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, Galleria dei Modelli e delle App di Simulazione, 2023 da COMSOL. 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'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. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. 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. This approach is known as a Continuation Method with a Constant predictor. Unknown function or operator. Direct PARDISO Solver , PARDISO . This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. 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. 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. 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. Does ZnSO4 + H2 at high pressure reverses to Zn + H2SO4? Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. Contact COMSOL at Bangalore on their telephone: +9180 25323003. 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. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Therefore, an initial value of zero is almost always reasonable if a very small load is applied.
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