stationary solver comsol

In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. Iterative , Direct . COMSOL does not assume any legal liability for the accuracy of the data disclosed. 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. 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. This guide applies solely to nonlinear stationary models. Understanding the Fully Coupled vs. k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) The issue here has do with the iterative algorithm used to solve nonlinear stationary models. The problem is that when I run my model this message appear: Undefined value found. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. This approach is known as a Continuation Method with a Constant predictor. 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 use comsol multiphysics 5.2a and . 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 technique of load ramping is not always reasonable for all problems. 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. It may also reveal that the model itself is ill-posed in some way. listed if standards is not an option). Note: there is no way to couple this field with the time dependent nature of this physics. 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. Not meshing all the domains. Such a large difference in the materials properties can be challenging. In our previous blog entry, we introduced the Fully Coupled and the Segregated algorithms used for solving steady-state multiphysics problems in COMSOL. Then I stored the resulting solution, and used it to to solve the stationary solver again by using the solver manager. They deal with COMSOL package and train users. November 11, 2013. Version 5.3 By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Feature: Stationary Solver 1 (sol1/s1) Attempt to evaluate nonintegral power of negative number. (Frequency Domain should be the last step) Stationary Solver Iterative Direct . 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. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. Why doesn't iterative solver converge in COMSOL? - ResearchGate Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. - Variable: B1 - Defined as: 1/ ( ( (comp1.cH2 (unit_m_cf^3))/unit_mol_cf)^2.5) Failed to evaluate variable. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. there is no defined multiphysics for it as I know, I have a standing accoustic wave and a flow in the background but I don't see their connection. 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. The settings controlling the predictor type. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. 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 unknowns are segregated into groups, usually according the physics that they represent, and these groups are solved one after another. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. See Knowledge Base 1240: Manually Setting the Scaling of Variables. Asking for help, clarification, or responding to other answers. With respect to any nonlinearities, replace them by a reasonable linearized term. 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. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. GCRO-DR is a method for Krylov subspace recycling. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. 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. 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. Contact COMSOL at Bangalore on their telephone: +9180 25323003. Any trademarks referenced in this document are the property of their respective owners. The algorithm is, generally speaking, a Newton's method approach. 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. Common Mistakes: Not assigning materials to all the domains. In particular, choosing an improper initial condition or setting up a problem without a solution will simply cause the nonlinear solver to continue iterating without converging. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. This case is generally difficult, or impossible, to solve since this material property is non-smooth. The technique of load ramping is not always reasonable for all problems. 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. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. Common Errors in Comsol - P&S: COMSOL Design Tool for Photonic Devices 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. 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. Any trademarks referenced in this document are the property of their respective owners. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. Get notified about new Stationary Engineer jobs in Brea, California, United States. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. Why? The other low-level default settings within the Stationary Solver are chosen for robustness. Acidity of alcohols and basicity of amines. Stationary (time-invariant) models with nonlinearities may converge very slowly. (Frequency Domain should be the last step). Sign in to create your job alert for Stationary Engineer jobs in Brea, California, United States. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. there is no defined multiphysics for it as I know, I have a standing accoustic wave and a flow in the background but I don't see their connection. If the model is very large, and if you do not have very much memory in your computer, you may get an error message regarding memory. . Here we introduce a more robust approach to solving nonlinear problems. P&S Comsol Team: Arif Gngr , Yannik Horst , Stefano Valente. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: Specify Material Properties in COMSOL Multiphysics (3/8) Stationary Solver Use the Stationary Solver () to find the solution to linear and nonlinear stationary problems (also called static or steady-state problems). This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. P&S: COMSOL Design Tool for Photonic Devices. The fully coupled and segregated approaches are discussed below. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. They are usually called comp1.u, comp1.v, and comp1.w though. Dr.S.Ravindran Cite 1 Recommendation Popular answers (1). Check the solver log to see if the continuation method is backtracking. 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. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. How to Add a Study to Your Simulation in COMSOL Multiphysics I highly recommend this flower shop. Mesh [COMSOL_Users] output of stationary solver as input to time-dependent - Feature: Stationary Solver 1 (sol1/s1)Failed to find a solution. solving stationary solver after each time step - COMSOL Multiphysics Again, introduce a Global Parameter that gets ramped from exactly zero to one. Once the error estimate is small enough, as determined by the convergence criterion (20-16) the software terminates the computations and returns a solution. 3 Replies, Please login with a confirmed email address before reporting spam. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. Why is there a voltage on my HDMI and coaxial cables? The other low-level default settings within the Stationary Solver are chosen for robustness. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. Repeat this for every nonlinearity of the model. 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. 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. Understanding the Fully Coupled vs. Hi Alexis, In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version How to solve "Feature: Stationary Solver 1 (sol1/s1) Attempt - COMSOL This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. Such problems must solved in the time domain. Not entering required material parameters. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. If you have both as steps in the same study, then solve that study. 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. 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. Wish you all the best. 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. Use this parameter to modify the nonlinearity expressions in the model. 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. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. Note the star symbol on the Solution feature. This consent may be withdrawn. 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. replace it with the expression: This algorithm was also useful for understanding what happens near a failure load. This involves a systematic reduction in the model complexity. Using the first order optimality. 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. The fully coupled and segregated approaches are discussed below. 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. Required fields are marked *. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. 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. 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. To start a new discussion with a link back to this one, click here. Direct PARDISO Solver , PARDISO . 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. 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. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. Hi Jason, Have you taken a look at this blog post? If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. Find centralized, trusted content and collaborate around the technologies you use most. In many physics areas there exist alternative physics formulations specifically meant for solving cases where the geometry has an extreme aspect ratio. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. - Feature: Stationary Solver 1 (sol1/s1) From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. Your internet explorer is in compatibility mode and may not be displaying the website correctly. The default Initial Values for the unknowns in most physics interfaces are zero. View the Settings window for the Materials branch to get a list of all domains with undefined materials and add a material to those domains. 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. listed if standards is not an option). That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. The coupling terms between the different groups are thus neglected. The objective here is to simplify the model to a state where the model will solve, with linear approximations. What is the purpose of non-series Shimano components? The Auxiliary Sweep can be used to implement ramping of any Global Parameter. (Frequency Domain should be the last step) Does anyone know what should cause this problem? Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. Multiphysics problems are often nonlinear. Why do many companies reject expired SSL certificates as bugs in bug bounties? Reviews on Stationary Stores in Brea, CA - Typo, Mievic, Posh Paper, Morning Glory, Select Graphics & Printing, Daiso Japan, Urban Outfitters, Office Depot, Barnes & Noble Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. First, it is physically intuitive, often matching how one would perform an experiment. It can be useful while solving sequences of linear systems arising from, for example, nonlinear problems.

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stationary solver comsol

stationary solver comsol