stationary solver comsol

k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) 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 memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. - That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. 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. 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. 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. 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. 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. The Fully Coupled solution approach, with the Plot While Solving enabled. To learn more, see our tips on writing great answers. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. Stationary (time-invariant) models with nonlinearities may converge very slowly. It may also reveal that the model itself is ill-posed in some way. If you try to solve such a model, there will be an error at runtime that will provide information about the variable name and where it is being called. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. Contact COMSOL at Bangalore on their telephone: +9180 25323003. Segregated approach and Direct vs. Iterative linear solvers, About the time step setting of the solver, Introducing Goal Seeking into the Segregated Solver. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. 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. I am solving a linear stationary finite element model but the software is not solving. 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. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. By creating this job alert, you agree to the LinkedIn User Agreement and Privacy Policy. Again, introduce a Global Parameter that gets ramped from exactly zero to one. In such cases, see if one material (or the other) can be omitted from the analysis completely. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. The Fully Coupled solution approach, with the Plot While Solving enabled. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. Save my name, email, and website in this browser for the next time I comment. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. 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. 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. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. If these settings have been manually changed, you will see a small star symbol on the Solution feature, as shown in the screenshot below. What are some highly rated cards & stationery in Brea, CA? This involves a systematic reduction in the model complexity. This can arise as a consequence of extreme variations in the material properties, or high aspect ratio geometry. 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. Mesh Second, the continuation method will automatically take smaller load increments if a solution cannot be found. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. See Knowledge Base 1240: Manually Setting the Scaling of Variables. 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. Cooling and Solidification of Metal. Building on these topics, we will now address how to prepare your mesh for efficiently solving nonlinear finite element problems. 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. Does ZnSO4 + H2 at high pressure reverses to Zn + H2SO4? replace it with the expression: It may also reveal that the model itself is ill-posed in some way. 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. The advantages of the continuation method are two-fold. Not entering required material parameters. The algorithm is, generally speaking, a Newton's method approach. This involves a systematic reduction in the model complexity. If one particular material is missing one property, that material will also be highlighted with a red cross over that material icon in the Model Builder. Here, we will examine techniques for accelerating the convergence of these two methods. 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. 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. Direct PARDISO Solver , PARDISO . (Frequency Domain should be the last step) The problem is that when I run my model this message appear: Undefined value found. thanks for reply 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. In this page, we will be sharing some common errors that might occur in Comsol and their solutions. You can unsubscribe from these emails at any time. If it does so, use a finer increment in that range. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. The coupling terms between the different groups are thus neglected. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. 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. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. 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. 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. Wish you all the best. Then use this file to provide the initial conditions in time dependent model. What is the purpose of this D-shaped ring at the base of the tongue on my hiking boots? k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) For example, if there is a temperature-dependent material property such as: P&S Comsol Team: Yannik Horst, Manuel Kohli, Xinzhi Zhang. Not assigning proper boundary conditions: Especially if you have ports. Discussion Closed This discussion was created more than 6 months ago and has been closed. 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. I personally liked emailing them the file, ", "This flower shop is the best! I have searched all over comsol forum to fix this stationary solver configuration and still doesn't work because I don't know the logic behind the solver system. 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. Minimising the environmental effects of my dyson brain. 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. 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. Reply . The coupling terms between the different groups are thus neglected. 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. How can I check before my flight that the cloud separation requirements in VFR flight rules are met? Then I stored the resulting solution, and used it to to solve the stationary solver again by using the solver manager. Review the model setup to resolve these. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); This site uses Akismet to reduce spam. 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. 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.) k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) The settings controlling the predictor type. Can I tell police to wait and call a lawyer when served with a search warrant? This case is generally difficult, or impossible, to solve since this material property is non-smooth. One of the key concepts there was the idea of mesh convergence as you refine the mesh, the solution will become more accurate. The default Initial Values for the unknowns in most physics interfaces are zero. Feature: Stationary Solver 1 (sol1/s1)" . The settings controlling the predictor type. 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. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) P&S Comsol Team: Arif Gngr , Yannik Horst , Stefano Valente. Multiphysics problems are often nonlinear. replace it with the expression: The issue here has do with the iterative algorithm used to solve nonlinear stationary models. Again, introduce a Global Parameter that gets ramped from exactly zero to one. 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. The other low-level default settings within the Stationary Solver are chosen for robustness. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Segregated approach and Direct vs. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings.

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