Troubleshooting for 3D trusses, if anyone's out there. : r/COMSOL - reddit COMSOL Blog Series on COMSOL Multiphysics Solvers Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Required fields are marked *. The settings controlling the predictor type. 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. If you try to enter a variable that is undefined, the automatic syntax highlighting will identify this as you enter it, and it is best practice to resolve this immediately. Multiphysics problems are often nonlinear. For example, if there is a temperature-dependent material property such as: (COMSOL Multiphysics) : 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. P&S: COMSOL Design Tool for Photonic Devices. The issue here has do with the iterative algorithm used to solve nonlinear stationary models. Get notified about new Stationary Engineer jobs in Brea, California, United States. Not the answer you're looking for? Hi Jason, Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version The fully coupled and segregated approaches are discussed below. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. Once the error estimate is small enough, as determined by the convergence criterion (20-16) the software terminates the computations and returns a solution. 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. COMSOL does not assume any legal liability for the accuracy of the data disclosed. 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. This approach is known as a Continuation Method with a Constant predictor. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Your internet explorer is in compatibility mode and may not be displaying the website correctly. Segregated approach and Direct vs. 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. However, it is usually not possible to know this ahead of time. listed if standards is not an option). Connect and share knowledge within a single location that is structured and easy to search. Posted 26 set 2019, 17:57 CEST Mesh Version 5.3 0 Replies. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. Any trademarks referenced in this document are the property of their respective owners. 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. It may also reveal that the model itself is ill-posed in some way. Common Mistakes: Not assigning materials to all the domains. What version of COMSOL are you using? To start a new discussion with a link back to this one, click here. I am following the same model as Comsol provide us on the web. Computational Fluid Dynamics (CFD), API Not assigning proper boundary conditions: Especially if you have ports. One of the key concepts there was the idea of mesh convergence as you refine the mesh, the solution will become more accurate. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version 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. They are usually called comp1.u, comp1.v, and comp1.w though. Dun & Bradstreet gathers Office Supplies, Stationery, and Gift Retailers business information from trusted . The default Initial Values for the unknowns in most physics interfaces are zero. 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. Cooling and Solidification of Metal. Your internet explorer is in compatibility mode and may not be displaying the website correctly. Here, we begin an overview of the algorithms used for solving nonlinear static finite element problems. This involves a systematic reduction in the model complexity. 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. What are people saying about cards & stationery in Brea, CA? 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. 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. The memory requirements will always be lower than with the fully coupled approach, and the overall solution time can often be lower as well. This case is generally difficult, or impossible, to solve since this material property is non-smooth. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. Right-click on the Stationary Solver node and add either the Segregated or Fully Coupled feature. If both load ramping and nonlinearity ramping are still leading to slow convergence, refine the mesh. Can I tell police to wait and call a lawyer when served with a search warrant? Resources and documents are provided for your information only, and COMSOL makes no explicit or implied claims to their validity. The advantages of the continuation method are two-fold. The exceptions are the Heat Transfer interfaces, which have a default Initial Value of 293.15K, or 20C, for the temperature fields. That is, the material property changes instantaneously from 10W/m/K to 20W/m/K at 400K. Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. 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. It is thus always advised to start this procedure with a simplified 2D, or 2D-axisymmetric model. 0 Replies, Please login with a confirmed email address before reporting spam. Note: there is no way to couple this . If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. See also: Knowledge Base 1254: Controlling the Time Dependent solver timesteps. It may also reveal that the model itself is ill-posed in some way. If the model is nonlinear, see: Improving Convergence of Nonlinear Stationary Models. Despite this, the segregated approach can often converge very robustly, unless there are very strong couplings between the physics in the model. Top 10 Best Stationary Stores in Brea, CA - December 2022 - Yelp That is, start by first solving a model with a small, but non-zero, load. There are two approaches that can be used when iteratively solving the nonlinear system of equations: a Fully Coupled or a Segregated approach. It is sometimes necessary to manually scale the dependent variables. This algorithm was also useful for understanding what happens near a failure load. First, it is physically intuitive, often matching how one would perform an experiment. GCRO-DR is a method for Krylov subspace recycling. This involves a systematic reduction in the model complexity. Save my name, email, and website in this browser for the next time I comment. This parameter is used within the physics interfaces to multiply one, some, or all of the applied loads. See Knowledge Base 1240: Manually Setting the Scaling of Variables. 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. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. Most multiphysics problems are nonlinear. First, it is physically intuitive, often matching how one would perform an experiment. If these settings have been manually changed, you will see a small star symbol on the Solution feature, as shown in the screenshot below. 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. As P is ramped up, the continuation method uses the previous solutions to compute initial conditions for the more nonlinear cases. That is, when solving, the software starts with the user-specified initial values to evaluate all solution-dependent terms. 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. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. That is, within each outer Newton-type iteration, the segregated approach solves for each segregated group sequentially. These are some cards & stationery with a large number of reviews in Brea, CA. The segregated approach, on the other hand, solves sets of unknowns separately. listed if standards is not an option). Could you expand a little bit more why the coupling is impossible? By creating this job alert, you agree to the LinkedIn User Agreement and Privacy Policy. We are planning to continuously update this page throughout the semester and hopefully, this will become a reference during your projects as well. Use this parameter to modify the nonlinearity expressions in the model. Specify Material Properties in COMSOL Multiphysics (3/8) If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. [COMSOL_Users] output of stationary solver as input to time-dependent Have you taken a look at this blog post? An example model that combines the techniques of nonlinearity ramping and adaptive mesh refinement with multiple study steps is: Such problems must solved in the time domain. There will always already be either a Segregated or Fully Coupled feature beneath this. The idea behind the GCRO-DR method is to retain the subspace determined while solving previous systems and use it to reduce the cost of solving the next system. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. Common Study Step Settings - COMSOL Multiphysics 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. Each physics is thus solved as a standalone problem, using the solution from any previously computed steps as initial values and linearization points. What to do when a linear stationary model is not solving - COMSOL What is the purpose of non-series Shimano components? Save this information to a file. Office Supplies, Stationery, and Gift Retailers Companies in Brea Common Errors in Comsol - P&S: COMSOL Design Tool for Photonic Devices Starting from zero initial conditions, the nonlinear solver will most likely converge if a sufficiently small load is applied. How to Add a Study to Your Simulation in COMSOL Multiphysics 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. Also, keep in mind that a linear stationary model should solve regardless of how coarse the mesh is (albeit to a low accuracy) so you can always start with as coarse a mesh as possible, and refine the mesh (See also: Knowledgebase 1030: Performing a Mesh Refinement Study. The "Values for dependent values" in study step settings should be set to the default ("Physics-controlled" in 5.2). Understanding the Fully Coupled vs. 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. - With respect to any nonlinearities, replace them by a reasonable linearized term. Your internet explorer is in compatibility mode and may not be displaying the website correctly. 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. The stationary solver is used both for Stationary (time-invariant) and Frequency Domain (time-harmonic) study types. To switch between these solver types, go to the Stationary Solver node within the Study sequence. Feature: Stationary Solver 1 (sol1/s1) Adaptation gives the same mesh: adaptmesh1. 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. The following are possible reasons why a linear stationary model will fail to solve, along with resolutions: The combination of the constraints and boundary conditions must be sufficient to define a unique solution to the problem, in terms of the field variables being solved. This is for COMSOL 5.2, but should be similar for 4.2: Create the stationary study. This approach is used by default for most 1D, 2D, and 2D-axisymmetric models. The default Initial Values for the unknowns in most physics interfaces are zero. k(T,P) = 10[W/m/K]*((1-P)+P*exp(-(T-293[K])/100[K])) 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. This approach is known as a Continuation Method with a Constant predictor. Cooling and Solidification of Metal. Ideally, one would use small elements in regions where the solution varies quickly in space, and larger elements elsewhere. In the COMSOL Multiphysics software, this step of the modeling workflow is made. . This solver is automatically used when a Stationary or Frequency Domain study is added to the model. This guide applies solely to nonlinear stationary models. Discussion Closed This discussion was created more than 6 months ago and has been closed. This will use the initial conditions you specified in your physics setting (usually 0 is used in the physics settings). It is also possible to manually refine the mesh. Convergence can be poor when the initial values do not provide a good starting point for this iterative approach. Studysteps might be listed in wrong order: Not assigning materials to all the domains. Contact COMSOL at Bangalore on their telephone: +9180 25323003. Second, the continuation method will automatically take smaller load increments if a solution cannot be found. How can I use it? Improving Convergence of Nonlinear Stationary Models, Knowledgebase 1030: Error: "Out of memory", Knowledgebase 1030: Performing a Mesh Refinement Study, Understanding the Fully Coupled vs. Find centralized, trusted content and collaborate around the technologies you use most. The coupling terms between the different groups are thus neglected. if I want to do an adaptive mesh refinement, I get this error. Using a predictor of type Constant will take the solution from the iteration and use it as the initial value for the iteration. Changes to these low-level settings from the defaults will usually be quite model- and case-specific. If instead the model is linear, see: Knowledgebase 1260: What to do when a linear stationary model is not solving. 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. 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. This is useful since the software will then return an estimation of the maximum possible loadcase for which the solver can converge. The default solver for most 3D models is an iterative solver, which is more sensitive to ill-conditioned problems. Multiphysics problems are often nonlinear. $125,000.00, Project Engineer (In-person/Hybrid/Remote), $100,000.00 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. 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. 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. Direct Iterative , Direct . To subscribe to this RSS feed, copy and paste this URL into your RSS reader. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Posted Sep 9, 2020, 1:44 p.m. EDT 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. 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. 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. Please dont hesitate to post comments below or send emails to us if you experience any other problems. My comment is perhaps a bit nave but it seems to me that you could simply deactivate the \frac{\partial \cdot}{\partial t} term of the background field equation but keep its connexion to the solid to get what you want.
Speeding Ticket Cost Calculator Ohio, Amy Carlson Mother God Images, Articles S