stationary solver comsol

Again, introduce a Global Parameter that gets ramped from exactly zero to one. Hence Comsol solved for the stationary solution at different points of time. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. Posted 26 set 2019, 17:57 CEST Mesh Version 5.3 0 Replies. 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. By providing your email address, you consent to receive emails from COMSOL AB and its affiliates about the COMSOL Blog, and agree that COMSOL may process your information according to its Privacy Policy. First, it is physically intuitive, often matching how one would perform an experiment. Stationary Engineer Jobs in Brea, California, United States, $87,400.00 If the default iterative solver is not converging, try switching to a direct solver, as described here: Understanding the Fully Coupled vs. 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. Such problems must solved in the time domain. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. Mesh 3. Your internet explorer is in compatibility mode and may not be displaying the website correctly. 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. If you are unsure if your problem is linear and stationary, look at the Log. This guide applies solely to nonlinear stationary models. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. Some models are numerically ill-conditioned due to the setup. That is, they are tuned to achieve convergence in as many cases as possible. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. The other low-level default settings within the Stationary Solver are chosen for robustness. Under Initial values of variables solved for, the default value of the Settingslist is Physics controlled. Perhaps this approach could be adapted to represent your model. The difference between the phonemes /p/ and /b/ in Japanese. 140K views 8 years ago COMSOL Multiphysics Tutorial for Beginners Please note that an updated version of the content in this video can be found in the Modeling Workflow video in the COMSOL. . It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. Singular matrix., Make sure you defined your ports correctly:Boundary selectionType of port: e.g. 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. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. 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 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. so many cute little stationary items , hair". To switch between these solver types, go to the Stationary Solver node within the Study sequence. Save my name, email, and website in this browser for the next time I comment. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). - 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. Staging Ground Beta 1 Recap, and Reviewers needed for Beta 2, Simulation of effect of heated resistance on temperature distribution in laminar flow, COMSOL: Diffusion in Transport of Diluted Species Produces Unphysical Results. In this posting, we introduce the idea of ramping the nonlinearities in the problem to improve convergence. 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. Consult your product manuals for complete trademark details. replace it with the expression: She opened prepackaged 6-packs of Seegars to make ", All "stationary stores" results in Brea, CA, Search stationary stores in popular locations. How do/should administrators estimate the cost of producing an online introductory mathematics class? Repeat this for every nonlinearity of the model. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. Discussion Closed This discussion was created more than 6 months ago and has been closed. 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. P&S: COMSOL Design Tool for Photonic Devices. This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. 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. 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. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. Please dont hesitate to post comments below or send emails to us if you experience any other problems. COMSOL does not assume any legal liability for the accuracy of the data disclosed. If so, see: Knowledgebase 1030: Error: "Out of memory". Thanks for contributing an answer to Stack Overflow! If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. - An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. Common Mistakes: Not assigning materials to all the domains. - Variable: B1 - Defined as: 1/ ( ( (comp1.cH2 (unit_m_cf^3))/unit_mol_cf)^2.5) Failed to evaluate variable. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. 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. These can be used alone, or in combination with other interfaces. 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. 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 this was solved using the Solid Mechanics physics interface the thin walls of the container would need to be explicitly modeled, but the wall thickness is much smaller than the overall can dimensions. (Frequency Domain should be the last step) Once a simplified solvable version of the model has been found, gradually increase the model complexity again, re-introducing nonlinearities and multiphysics couplings. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. - This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. They are usually called comp1.u, comp1.v, and comp1.w though. 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. 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. 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. 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. There will always already be either a Segregated or Fully Coupled feature beneath this. Use this parameter to modify the nonlinearity expressions in the model. 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. 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. 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. Linear solvers. However, it is usually not possible to know this ahead of time. 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. Your internet explorer is in compatibility mode and may not be displaying the website correctly. COMSOL makes every reasonable effort to verify the information you view on this page. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. One of the key concepts there was the idea of mesh convergence as you refine the mesh, the solution will become more accurate. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. 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. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. With respect to any nonlinearities, replace them by a reasonable linearized term. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). 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. COMSOL makes every reasonable effort to verify the information you view on this page. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. That is, they are tuned to achieve convergence in as many cases as possible. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. This case is generally difficult, or impossible, to solve since this material property is non-smooth. (I am begginer in comsol) Thank you. The advantages of the continuation method are two-fold. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. Use either a very fine mesh throughout the simulation domain or use adaptive mesh refinement. Not meshing all the domains. 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. In such cases, see if one material (or the other) can be omitted from the analysis completely. The algorithm is, generally speaking, a Newton's method approach. I am following the same model as Comsol provide us on the web. The settings controlling the predictor type. Numerically ill-conditioned means that the system matrix is nearly singular and that it will be difficult to solve on a finite-precision computer. The fully coupled and segregated approaches are discussed below. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. 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. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. Cooling and Solidification of Metal. If these settings have been manually changed, you will see a small star symbol on the Solution feature, as shown in the screenshot below. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. This approach is known as a Continuation Method with a Constant predictor. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. 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. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. These are some cards & stationery with a large number of reviews in Brea, CA. 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. listed if standards is not an option). 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. 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. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. What are people saying about cards & stationery in Brea, CA? To switch between these solver types, go to the Stationary Solver node within the Study sequence. Does anyone know what should cause this problem? Therefore, an initial value of zero is almost always reasonable if a very small load is applied. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. - Feature: Stationary Solver 1 (sol1/s1)Failed to find a solution. This is relatively expensive to do, but will lead to the most robust convergence. Hi ! The conditions on the geometric aspect ratio are relatively more strict. Repeat this for every nonlinearity of the model. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. Not entering required material parameters. 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. Perhaps this approach could be adapted to represent your model. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. What version of COMSOL are you using? Tutti i diritti sono riservati. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version The issue here has do with the iterative algorithm used to solve nonlinear stationary models. The settings controlling the predictor type. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) To start a new discussion with a link back to this one, click here. Hi Jason, To subscribe to this RSS feed, copy and paste this URL into your RSS reader. See if these can be used instead of explicitly modeling parts with high-aspect ratio geometries.

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