Making statements based on opinion; back them up with references or personal experience. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. Set initial conditions in the physics to the appropriate dependent model variable names rather than the default 0. Any trademarks referenced in this document are the property of their respective owners. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. This approach is known as a Continuation Method with a Constant predictor. 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. Your internet explorer is in compatibility mode and may not be displaying the website correctly. The Auxiliary Sweep can be used to implement ramping of any Global Parameter. Improving Convergence of Nonlinear Stationary Models - COMSOL The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. That is, they are tuned to achieve convergence in as many cases as possible. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. 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. Get email updates for new Stationary Engineer jobs in Brea, California, United States. Nonlinearities arise as a consequence of the governing equation, as a material nonlinear expression, or as a coupling term between physics. COMSOL makes every reasonable effort to verify the information you view on this page. An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: $130,000.00. For example, in Solid Mechanics, if the Poisson Ratio set to 0.5, then the model will not solve, as this value in incompatible with the theory of linear elasticity. 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. What version of COMSOL are you using? This guide applies solely to nonlinear stationary models. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. Reviews on Stationary in Brea, CA - Mievic, Typo, Tokyo Japanese Lifestyle, Fancy, Posh Paper, Morning Glory, Velvet Fox Designs, Barnes & Noble, Michaels, Select Graphics & Printing Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. Solving for laminar flow using Comsol - YouTube Comsol help video number 2: Solving a laminar flow problem in a slit. For example, if there is a temperature-dependent material property such as: listed if standards is not an option). $131,100.00, Simplified Vehicle Operations Project Engineer, $115,000.00 The advantages of the continuation method are two-fold. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. To start a new discussion with a link back to this one, click here. Is there a way to use the stationary solution obtained in Comsol 4.2 as the initial conditions in a time dependent model? The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. Mesh This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. This solver is automatically used when a Stationary or Frequency Domain study is added to the model. Today's top 351 Stationary Engineer jobs in Brea, California, United States. 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. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. Not meshing all the domains. Once the error estimate is small enough, as determined by the convergence criterion (20-16) the software terminates the computations and returns a solution. Could you expand a little bit more why the coupling is impossible? 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 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. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. [COMSOL_Users] output of stationary solver as input to time-dependent How do/should administrators estimate the cost of producing an online introductory mathematics class? Segregated approach and Direct vs. In the extreme case, suppose one wants to model an instantaneous change in properties, such as: Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. - Feature: Stationary Solver 1 (sol1/s1) Does ZnSO4 + H2 at high pressure reverses to Zn + H2SO4? 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. Cooling and Solidification of Metal. (I am begginer in comsol) Thank you. Save this information to a file. 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. How to solve "Feature: Stationary Solver 1 (sol1/s1) Attempt - COMSOL 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. Therefore, an initial value of zero is almost always reasonable if a very small load is applied. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. The Continuation method is enabled by default when using the Auxiliary sweep study extension, as shown below. Click the link in the email we sent to to verify your email address and activate your job alert. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. 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. Here we introduce the two classes of algorithms used to solve multiphysics finite element problems in COMSOL Multiphysics. Here, we begin an overview of the algorithms used for solving nonlinear static finite element problems. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. 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. 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. Minimising the environmental effects of my dyson brain. k(T) = 10[W/m/K]+10[W/m/K]*(T>400[K]) What are people saying about cards & stationery in Brea, CA? - Therefore, an initial value of zero is almost always reasonable if a very small load is applied. Singular matrix., Make sure you defined your ports correctly:Boundary selectionType of port: e.g. Create the time-dependent step or study. Solving for laminar flow using Comsol - YouTube Connect and share knowledge within a single location that is structured and easy to search. In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. If it does so, use a finer increment in that range. Studysteps might be listed in wrong order: Not assigning materials to all the domains. replace it with the expression: P&S: COMSOL Design Tool for Photonic Devices - ETH Z Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. November 11, 2013. The objective here is to simplify the model to a state where the model will solve, with linear approximations. 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. If a good estimate to the solution field is known, this can be entered as an an expression in the Initial Value field. This information is relevant both for understanding the inner workings of the solver and for understanding how memory requirements grow with problem size. An example would be a linear static structural model of an aluminum beverage can. Why doesn't iterative solver converge in COMSOL? - ResearchGate Again, introduce a Global Parameter that gets ramped from exactly zero to one. A classic example of this is fluid flow around a cylinder with high, but constant, flow rates. . With respect to any nonlinearities, replace them by a reasonable linearized term. It is also possible to manually refine the mesh. Dun & Bradstreet gathers Office Supplies, Stationery, and Gift Retailers business information from trusted . This is relatively expensive to do, but will lead to the most robust convergence. 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. She opened prepackaged 6-packs of Seegars to make ", All "stationary stores" results in Brea, CA, Search stationary stores in popular locations. 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. 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. From there, if an additional small load increment is applied, the previously computed solution is a reasonable initial condition. Why do many companies reject expired SSL certificates as bugs in bug bounties? The segregated approach, on the other hand, solves sets of unknowns separately. Screenshot showing a Solver Configuration that has been altered. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. What is the purpose of this D-shaped ring at the base of the tongue on my hiking boots? Note: there is no way to couple this field with the time dependent nature of this physics. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. 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. Does anyone know how to solve error in stationary solver in COMSOL That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. thanks for reply They are usually called comp1.u, comp1.v, and comp1.w though. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. solving stationary solver after each time step - COMSOL Multiphysics Why? 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. 351 Stationary Engineer jobs in Brea, California, United States (15 new) Not assigning proper boundary conditions: Especially if you have ports. If the material properties entered are incorrect for the governing equation, the model will generate an error at runtime, usually a Singular Matrix error. 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. 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. It can be useful while solving sequences of linear systems arising from, for example, nonlinear problems. As part of our solver blog series we have discussed solving nonlinear static finite element problems, load ramping for improving convergence of nonlinear problems, and nonlinearity ramping for improving convergence of nonlinear problems. 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. The default Initial Values for the unknowns in most physics interfaces are zero. P&S Comsol Team: Manuel Kohli, Raphael Schwanninger, Feature: Stationary Solver 1 (sol1/s1) To switch between these solver types, go to the Stationary Solver node within the Study sequence. 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. Solve the stationary study then the time dependent study. Stationary (time-invariant) models with nonlinearities may converge very slowly. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. However, it is usually not possible to know this ahead of time. Not assigning proper boundary conditions: Especially if you have ports. Repeat this for every nonlinearity of the model. Does anyone know what should cause this problem? If you have both as steps in the same study, then solve that study. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. 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. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. This is a review for cards & stationery in Brea, CA: "Love this store!!! Instead, use a nonlinear material property expression that ramps from a very smooth function to a very nearly discontinuous one. Such a case would be better to address instead with the Shell physics interface, which is specially formulated for handling thin-walled structural parts. 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. $125,000.00, Project Engineer (In-person/Hybrid/Remote), $100,000.00 Stationary Solver Iterative Direct . Common Study Step Settings - COMSOL Multiphysics 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. For example, if there is a temperature-dependent material property such as: In such cases it will be particularly helpful to ramp the load gradually in time, from consistent initial values. (Frequency Domain should be the last step). Ramping the nonlinearities over time is not as strongly motivated, but step changes in nonlinearities should be smoothed out throughout the simulation. The other low-level default settings within the Stationary Solver are chosen for robustness. Can someone help me fix the COMSOL error below? | ResearchGate COMSOL 22.9K subscribers Adding a study to your simulation is necessary in order to solve your problem. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. The finite element mesh must be fine enough to resolve the spatial variations in the solution fields. 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. With the exception of some thermal problems however, it is often difficult to estimate the solution, so alternative approaches are needed. If it does so, use a finer increment in that range. 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. 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. 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. Could you expand a little bit more why the coupling is impossible? Hi Jason, When you use an iterative solver, COMSOL Multiphysics estimates the error of the solution while solving. listed if standards is not an option). In such cases, use the same continuation method, but instead ramp the nonlinearities in the model. Unknown function or operator. COMSOL does not assume any legal liability for the accuracy of the data disclosed. 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. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. 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. Such problems must solved in the time domain. The former approach solves for all unknowns in the problem at once, and considers all coupling terms between all unknowns within a single iteration. - Function: ^ Failed to evaluate variable. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). Under Initial values of variables solved for, the default value of the Settingslist is Physics controlled. 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, 2023 by COMSOL. With respect to any nonlinearities, replace them by a reasonable linearized term. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. 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.
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