- Feature: Stationary Solver 1 (sol1/s1) 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. Why? It is also possible to manually refine the mesh. Segregated approach and Direct vs. Check the solver log to see if the continuation method is backtracking. listed if standards is not an option). This guide applies solely to nonlinear stationary models. Direct Iterative , Direct . 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. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. replace it with the expression: Not assigning proper boundary conditions: Especially if you have ports. Solve the stationary study then the time dependent study. (I am begginer in comsol) Thank you. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. I highly recommend this flower shop. It is also possible to manually refine the mesh. In this posting, we introduce the idea of ramping the nonlinearities in the problem to improve convergence. With respect to any nonlinearities, replace them by a reasonable linearized term. 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. It is sometimes necessary to manually scale the dependent variables. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. First, it is physically intuitive, often matching how one would perform an experiment. What is the purpose of this D-shaped ring at the base of the tongue on my hiking boots? That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. Most multiphysics problems are nonlinear. There will always already be either a Segregated or Fully Coupled feature beneath this. In such cases, see if one material (or the other) can be omitted from the analysis completely. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. P&S Comsol Team: Yannik Horst, Manuel Kohli, Xinzhi Zhang. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version I want to conduct a simulation to find a solution (u) and its first derivative (ux) using a 3D stationary model. Solver . ", "Absolutely the best place to shop for flowers and greenery, I spent an hour just looking around for fun prior to purchasing a bouquet, they have the best customer service people all over the place and it's a huge place", "Recently came in here to pick up 45 chocolate Seegars (cigars) for a dinner banquet in honor of my baby nephew. Examine the model and identify all terms that introduce nonlinearities, such as multiphysics couplings, nonlinear materials relationships, and nonlinear boundary conditions. Different physics have different default solvers. Check the solver log to see if the continuation method is backtracking. In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. This solver is automatically used when a Stationary or Frequency Domain study is added to the model. This is relatively expensive to do, but will lead to the most robust convergence. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. I personally liked emailing them the file, ", "This flower shop is the best! As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. 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. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. Feature: Stationary Solver 1 (sol1/s1) Attempt to evaluate nonintegral power of negative number. Save my name, email, and website in this browser for the next time I comment. Your Discussion has gone 30 days without a reply. See Knowledge Base 1240: Manually Setting the Scaling of Variables. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. 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. Your internet explorer is in compatibility mode and may not be displaying the website correctly. (Frequency Domain should be the last step). That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. The algorithm is, generally speaking, a Newton's method approach. The fully coupled and segregated approaches are discussed below. Nonlinearity ramping is an especially useful technique if any of the nonlinear terms in the model are very abrupt. Not assigning proper boundary conditions: Especially if you have ports. Click the link in the email we sent to to verify your email address and activate your job alert. Once the error estimate is small enough, as determined by the convergence criterion (20-16) the software terminates the computations and returns a solution. 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. Reviews on Stationary Stores in Brea, CA - Typo, Mievic, Posh Paper, Morning Glory, Select Graphics & Printing, Daiso Japan, Urban Outfitters, Office Depot, Barnes & Noble Such problems must solved in the time domain. Repeat this for every nonlinearity of the model. 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. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). Use this parameter to modify the nonlinearity expressions in the model. 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. COMSOL 22.9K subscribers Adding a study to your simulation is necessary in order to solve your problem. 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. Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. 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. Posted 26 set 2019, 17:57 CEST Mesh Version 5.3 0 Replies. 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 algorithm was also useful for understanding what happens near a failure load. Iterative , Direct . What did people search for similar to stationary stores in Brea, CA? Therefore, an initial value of zero is almost always reasonable if a very small load is applied. 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. Again, introduce a Global Parameter that gets ramped from exactly zero to one. A Global Parameter has to be introduced (in the above screenshot, P) and is ramped from a value nearly zero up to one. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. 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. This approach is known as a Continuation Method with a Constant predictor. Create the time-dependent step or study. The solver settings are stored at Study > Solver Configurations > Solution. Segregated approach and Direct vs. Iterative linear solvers, Time dependent function and stationary study, Combining Adaptive Mesh Refinement with Data Filtering, What to do when a linear stationary model is not solving, Galleria dei Modelli e delle App di Simulazione, 2023 da COMSOL. The Fully Coupled solution approach, with the Plot While Solving enabled. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. What is the purpose of non-series Shimano components? This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. The default Initial Values for the unknowns in most physics interfaces are zero. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. 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. Does ZnSO4 + H2 at high pressure reverses to Zn + H2SO4? Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. 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. 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. $130,000.00. replace it with the expression: Perhaps this approach could be adapted to represent your model. Stationary (time-invariant) models with nonlinearities may converge very slowly. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. The settings controlling the predictor type. Direct PARDISO Solver , PARDISO . (Frequency Domain should be the last step) k(T) = 10[W/m/K]*exp(-(T-293[K])/100[K]) Could you expand a little bit more why the coupling is impossible? 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. Use this parameter to modify the nonlinearity expressions in the model. The fully coupled and segregated approaches are discussed below. Stationary Solver Use the Stationary Solver () to find the solution to linear and nonlinear stationary problems (also called static or steady-state problems). That is, start by first solving a model with a small, but non-zero, load. Communication over the phone, in person, and through email was very easy. Connect and share knowledge within a single location that is structured and easy to search. This is a review for cards & stationery in Brea, CA: "Love this store!!! New Stationary Engineer jobs added daily. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. Hello, Stationary (time-invariant) models with nonlinearities may converge very slowly. Consult your product manuals for complete trademark details. 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. That is, start by first solving a model with a small, but non-zero, load. The settings controlling the predictor type. Under Initial values of variables solved for, the default value of the Settingslist is Physics controlled. 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. Is there a way to use the stationary solution obtained in Comsol 4.2 as the initial conditions in a time dependent model? 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. Trying to understand how to get this basic Fourier Series. 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. - 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 issue here has do with the iterative algorithm used to solve nonlinear stationary models. 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. Acidity of alcohols and basicity of amines. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. I am trying to solve the coupling between a waveguide and a microring resonator. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. Function: / Failed to evaluate expression. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. Your email address will not be published. There will always already be either a Segregated or Fully Coupled feature beneath this. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Wrong ordering of study steps. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. The technique of load ramping is not always reasonable for all problems. Does anyone know what should cause this problem? The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. 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. Here we introduce a more robust approach to solving nonlinear problems. Use a manually defined mesh to avoid elements with extreme aspect ratios and perform a mesh refinement study, as described here: Performing a Mesh Refinement Study, For problems that are ill-conditioned, using a direct solver is often called for. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: Multiphysics problems are often nonlinear. "I chose this print shop based off yelp reviews and was very happy with the outcome! Few days back i was also facing this problem in . This segregated approach is used by default for most 3D multiphysics models, and the software will automatically segregate the problem into appropriate groups. 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. 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. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. P&S: COMSOL Design Tool for Photonic Devices. The settings controlling the predictor type. 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. - the incident has nothing to do with me; can I use this this way? numeric (each ports needs their ownboundary mode analysis in the study if they are numerically defined)Wave excitation: on/off(input/output), - Feature: Stationary Solver 1 (sol1/s1) Division by zero. First, it is physically intuitive, often matching how one would perform an experiment. The default solver for most 3D models is an iterative solver, which is more sensitive to ill-conditioned problems.