Review the model setup to resolve these. See Knowledge Base 1240: Manually Setting the Scaling of Variables. $140,000.00, $120,000.00 Could you expand a little bit more why the coupling is impossible? Why do many companies reject expired SSL certificates as bugs in bug bounties? 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. Hi Jason, From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. listed if standards is not an option). Posted Sep 9, 2020, 1:44 p.m. EDT Your internet explorer is in compatibility mode and may not be displaying the website correctly. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. However, if a lower-level change has been manually made to the solver settings, the software will not automatically use the correct default solver. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. P&S Comsol Team: Arif Gngr , Yannik Horst , Stefano Valente. 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. 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. Have you taken a look at this blog post? L'objectif de notre prsent travail se repose sur l'tude par simulation numrique du comportement de bton au jeune ge sous des conditions svres de temprature pendant les premires 24h aprs. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. Such a large difference in the materials properties can be challenging. What sort of strategies would a medieval military use against a fantasy giant? 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. The coupling terms between the different groups are thus neglected. 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. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. if I want to do an adaptive mesh refinement, I get this error. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. Leverage your professional network, and get hired. Check the solver log to see if the continuation method is backtracking. One of the key concepts there was the idea of mesh convergence as you refine the mesh, the solution will become more accurate. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. 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. COMSOL makes every reasonable effort to verify the information you view on this page. Feature: Stationary Solver 1 (sol1/s1)" . Cooling and Solidification of Metal. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. 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. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. The settings controlling the predictor type. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. 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. 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. Your internet explorer is in compatibility mode and may not be displaying the website correctly. The fully coupled and segregated approaches are discussed below. Any trademarks referenced in this document are the property of their respective owners. listed if standards is not an option). Consult your product manuals for complete trademark details. The solver settings are stored at Study > Solver Configurations > Solution. 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. 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. P&S Comsol Team: Manuel Kohli, Raphael Schwanninger, Feature: Stationary Solver 1 (sol1/s1) This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. (Frequency Domain should be the last step). If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. What version of COMSOL are you using? This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. 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. 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 does not assume any legal liability for the accuracy of the data disclosed. This solver is automatically used when a Stationary or Frequency Domain study is added to the model. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. This consent may be withdrawn. Singular matrix., Make sure you defined your ports correctly:Boundary selectionType of port: e.g. P&S Comsol Team: Yannik Horst, Manuel Kohli, Xinzhi Zhang. We are planning to continuously update this page throughout the semester and hopefully, this will become a reference during your projects as well. Discussion Closed This discussion was created more than 6 months ago and has been closed. It may also reveal that the model itself is ill-posed in some way. The advantages of the continuation method are two-fold. 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. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. 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. 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. However, it is usually not possible to know this ahead of time. SGP handled 7 different prints for me at once and they all came out perfectly, in a timely manner. Contact COMSOL at Bangalore on their telephone: +9180 25323003. Common Mistakes: Not assigning materials to all the domains. rev2023.3.3.43278. Then I stored the resulting solution, and used it to to solve the stationary solver again by using the solver manager. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. Communication over the phone, in person, and through email was very easy. The Fully Coupled solution approach, with the Plot While Solving enabled. How do/should administrators estimate the cost of producing an online introductory mathematics class? 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. - Function: ^ Failed to evaluate variable. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. To switch between these solver types, go to the Stationary Solver node within the Study sequence. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. Why? Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. 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. Full text of the 'Sri Mahalakshmi Dhyanam & Stotram'. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. The other low-level default settings within the Stationary Solver are chosen for robustness. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. Not the answer you're looking for? The algorithm is, generally speaking, a Newton's method approach. The objective here is to simplify the model to a state where the model will solve, with linear approximations. 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. Does ZnSO4 + H2 at high pressure reverses to Zn + H2SO4? Near the top of the Stationary Solver log, the software will report if a linear or nonlinear solver is being used. For example, if there is a temperature-dependent material property such as: By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. $130,000.00. 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. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. 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. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. 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. With respect to multiphysics couplings, rather than solving the problem using a fully coupled approach (the default) solve the problem sequentially, with one physics being solved after another. 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 such cases, use the same continuation method, but instead ramp the nonlinearities in the model. 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. - As we saw previously in the blog entry on Solving Nonlinear Static Finite Element Problems, not all nonlinear problems will be solvable via the damped Newton-Raphson method. We use COMSOL Multiphysics for solving distributed optimal control of un-steady Burgers equation without constraints and with pointwise control constraints. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. thanks for reply