stationary solver comsol

Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. In this page, we will be sharing some common errors that might occur in Comsol and their solutions. They deal with COMSOL package and train users. With respect to any nonlinearities, replace them by a reasonable linearized term. Posted 26 set 2019, 17:57 CEST Mesh Version 5.3 0 Replies. 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. 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. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. Mesh Stationary (time-invariant) models with nonlinearities may converge very slowly. COMSOL makes every reasonable effort to verify the information you view on this page. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. Use this parameter to modify the nonlinearity expressions in the model. - Feature: Stationary Solver 1 (sol1/s1) As a rough rule of thumb, once the aspect ratio between the largest characteristic dimension to the smallest approaches 100:1, you might start to run into issues and should look to alternative ways of posing the problem, especially in a 3D model. What sort of strategies would a medieval military use against a fantasy giant? I personally liked emailing them the file, ", "This flower shop is the best! Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. Do you also know how to solve this problem: using stationary solution as the initial conditions in time dependent model, How Intuit democratizes AI development across teams through reusability. For example, if there is a temperature-dependent material property such as: Can I tell police to wait and call a lawyer when served with a search warrant? Find centralized, trusted content and collaborate around the technologies you use most. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: Cooling and Solidification of Metal. This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. Using this technique systematically, along with the techniques described previously, will usually identify the nonlinearities in the model that are leading to issues. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. If you see this, right-click on the Solution feature and select Reset Solver to Default. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. Learn how your comment data is processed. To switch between these solver types, go to the Stationary Solver node within the Study sequence. 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. Multiscale Modeling in High-Frequency Electromagnetics. comp1.u2, comp1.v2, and comp1.w2 are usually variables associated with the x,y, and z component of deformation in COMSOL. The objective here is to simplify the model to a state where the model will solve, with linear approximations. 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. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. The technique of load ramping is not always reasonable for all problems. Improving Convergence of Nonlinear Stationary Models, Knowledgebase 1030: Error: "Out of memory", Knowledgebase 1030: Performing a Mesh Refinement Study, Understanding the Fully Coupled vs. The algorithm is, generally speaking, a Newton's method approach. (Frequency Domain should be the last step) Once the error estimate is small enough, as determined by the convergence criterion (20-16) the software terminates the computations and returns a solution. 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. so many cute little stationary items , hair". k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. For more details, see: Performing a Mesh Refinement Study, Mesh refinement may often need to be combined with load or nonlinearity ramping and may require a set of studies, first starting with a relatively coarse mesh for nonlinearity ramping, refining the mesh, and the ramping further on the refined mesh. Tutti i diritti sono riservati. Posted Sep 9, 2020, 1:44 p.m. EDT First, it is physically intuitive, often matching how one would perform an experiment. 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 two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. Again, introduce a Global Parameter that gets ramped from exactly zero to one. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. 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 segregated approach, on the other hand, solves sets of unknowns separately. If the model is nonlinear, see: Improving Convergence of Nonlinear Stationary Models. What is the purpose of non-series Shimano components? k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) Please dont hesitate to post comments below or send emails to us if you experience any other problems. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. First, it is physically intuitive, often matching how one would perform an experiment. 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. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. The other low-level default settings within the Stationary Solver are chosen for robustness. 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. This involves a systematic reduction in the model complexity. - To learn more, see our tips on writing great answers. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. That is, they are tuned to achieve convergence in as many cases as possible. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. Does anyone know what should cause this problem? I use comsol multiphysics 5.2a and . Changes to these low-level settings from the defaults will usually be quite model- and case-specific. 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! 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. Posted 26 set 2019, 11:57 GMT-4 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. 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. Check the solver log to see if the continuation method is backtracking. 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. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. COMSOL makes every reasonable effort to verify the information you view on this page. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. Here we introduce a more robust approach to solving nonlinear problems. The unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. 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.) Consult your product manuals for complete trademark details. Your internet explorer is in compatibility mode and may not be displaying the website correctly. 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. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Hi Alexis, 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. Computational Fluid Dynamics (CFD), API Repeat this for every nonlinearity of the model. Why do many companies reject expired SSL certificates as bugs in bug bounties? P&S Comsol Team: Yannik Horst, Manuel Kohli, Xinzhi Zhang. 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. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: Stationary Engineer Jobs in Brea, California, United States, $87,400.00 The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. 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. Stationary in the COMSOL Multiphysics Programming Reference Manual Damped Newton Methods The nonlinear solver uses an affine invariant form of the damped Newton method as described in Ref. Could you expand a little bit more why the coupling is impossible? $131,100.00, Simplified Vehicle Operations Project Engineer, $115,000.00 The other low-level default settings within the Stationary Solver are chosen for robustness. For example, if ramping P over values of: 0.2,0.4,0.6,0.8,1.0 the nonlinear solver may fail to converge for a value of 0.8. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Your internet explorer is in compatibility mode and may not be displaying the website correctly. The algorithm is, generally speaking, a Newton's method approach. It may also reveal that the model itself is ill-posed in some way. Asking for help, clarification, or responding to other answers. Hello guys. Perhaps this approach could be adapted to represent your model. Stationary Solver Use the Stationary Solver () to find the solution to linear and nonlinear stationary problems (also called static or steady-state problems).

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