Browse the threads and share your ideas with the COMSOL community. carefully of what it is that should be predicted and what physical phenomena that affect the results. A comparison of the resulting solidification front progression on the symmetry axis is proposed in Table 3. What I know is that this is the virtual memory number. In order to do so, the Newton-Raphson method isapplied, i.e. A general method can be to define maximum allowable stress or minimum factor of safety along with convergence criteria. Then COMSOL gave you a warning message that it could not converge lower than another larger number (.001 or similar if I recall). ... Convergence criteria of the nonlinear solver are met but not all linear solver conditions are fulfilled. This chapter on convergence will introduce our first analysis tool in numerical methods for th e solution of ODEs. For these parameters I expect the shedding time period to be around 6 seconds. Absolute solver convergence criteria, I have reduced as low as 0.01. An iterative solver with domain decomposition preconditioning should be considered as a memory-lean alternative to direct solvers. Else my impression is "just" that the steps must be small enough for the convergence criteria to control the algorithm that is why COMSOl often makes many, even hundred of intermediaqte time steps between each value it send "out" and stores as your demanded time value--Good luck Ivar as Josh described above, when your model has no unique solution. So, what I did is at 100 knots, I raised the convergence criteria to be slightly larger than the value from the warning message, and I get a much smoother, but less accurate surface. Convergence in FEA Mesh Convergence: h- and p-refinement in Finite Element Analysis. the convergence criteria in the shortest possible time to aid in the realization of the policy. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. For diagnostics the experimental setup provides measurements of the flow rate and surface height of … Only for one case, I cannot reach constant value of my intersted variables in some important regions within my domain or even at least having <1% differences. The convergence plot confirms that the initially sluggish convergence changes to a quick convergence in just a few iterations once the large residual has disappeared. Learn how to perform a mesh refinement study in COMSOL Multiphysics with these tips and tricks, including ideal mesh size and fineness. By default, the convergence criterion is 0.001. Convergence, Consistency, and Stability Definition A one-step finite difference scheme approximating a partial differential equation is a convergent scheme if for any solution to the partial differential equation, u(t,x), and solutions to the finite difference scheme, vn i, such that v0 i converges to u 0(x) as i∆x converges to x, then vn After each segregated step the results are passed back and forth untill all the systems are converged. This method is particularly useful for multiphysics systems where there are multiple dependent variables being solved for -- hence you see this method come up a lot in COMSOL. Nagi Elabbasi I would really tighten the convergence tolerances with both solvers to make sure that they reach the same solution. However, since we are limited by finite comp… Parcourez les fils de discussion et partagez vos idées avec la communauté COMSOL. Generally speaking, convergence is the achievement of a limiting behavior in the solution of the equations and is typically represented by the diminishing residuals of the numerical solution. The COMSOL discussion forum covers a wide variety of simulation topics. First, the capacitance due to the applied permittivity profile is computed then apparent permittivities (ε a mod) are obtained, for each capacitive array (LE1, ME1, SE2 and SE1). while I increase my mesh number, I reach my convergence criteria (1e-5 7 <0.01 for consevation target. Lines 14-16 report the solution time and memory requirements. Support. Iterative Solver Types. Introduction When I decided to learn the ConjugateGradient Method(henceforth, CG), I read four different descriptions, For a list of such trademark Choosing Relaxation Criteria. In our previous blog entry, we introduced the Fully Coupled and the Segregated algorithms used for solving steady-state multiphysics problems in COMSOL. I even attempted to get the initial conditions from the static by solving static at Re=100. ... or maybe just improve it? COMSOL was established in July, 1986 with a headquarters in Stockholm, Sweden. as Josh described above, when your model has no unique solution. ... Convergence criteria of the nonlinear solver are met but not all linear solver conditions are fulfilled. Whenever you use the finite element method, it is important to remember that the accuracy of your solution is linked to the mesh size. Application Notes. WELCOME TO THE COMSOL CONFERENCE 2017 Over the course of 3 days, expand your skills . • The direct solvers in COMSOL are: – MUMPS: fast, multi-core capable, cluster capable – PARDISO: fast, robust, multi-core capable (scales better than MUMPS on a single node with many cores) – SPOOLES: slow, uses the least memory, multi-core, cluster capable Their customer base at the time was around 3,200 at an average revenue of $65,000 per customer. 8 Conjugate Gradients 9 CG Convergence 11 Stop & Start 12 Preconditioning 14 Nonlinear CG This article is dedicated to every mathematician who uses figuresas abundantly as I have herein. the set of equations is locally linearized and solved. In both of these cases you can correct the problem by changing the contact definition or by increasing the maximum number of severe discontinuity iterations (see “Severe discontinuity iterations” in “Convergence criteria for nonlinear problems,” Section 7.2.3). Convergence Problems. It's probably me who cant find it in the documentation, some simple convergence criteria to change :/. ... Convergence criteria of the nonlinear solver are met but not all linear solver conditions are fulfilled. Similarly, a poorly chosen convergence criteria can lead to either poor results (when too loose) or … Posted 22-Mar-2013, 9:47 am GMT-7 Fluid, Interfacing, Computational Fluid Dynamics (CFD), Chemical Reaction Engineering, Geometry, Materials, Studies & Solvers Version 4.2a 0 Replies Convergence criteria of the nonlinear solver are met but not all linear solver conditions are fulfilled. b) Convergence criterion Similarly to the mesh convergence study, several convergence criteria are tested in order to select the most appropriate one. But, for results to be accurate, we must demonstrate that results converge to a solution and are independent of mesh size. To begin, let’s define a few key terms: Convergence: Mesh convergence determines how many elements are required in a model to ensure that the results of an analysis are not affected by changing the size of the mesh. After the analysis is finished, display the convergence information by clicking the Convergence Plot tab on the Output Bar. A general method can be to define maximum allowable stress or minimum factor of safety along with convergence criteria. Browse the threads and share your ideas with the COMSOL community. Posted 22-Mar-2013, 9:47 am GMT-7 Fluid, Interfacing, Computational Fluid Dynamics (CFD), Chemical Reaction Engineering, Geometry, Materials, Studies & Solvers Version 4.2a 0 Replies The convergence criterion is clearly explained in the COMSOL manual. User Guides. I'm doing a piezoelectric modeling, in my model I … Another option is to select convergence criteria, wherein the optimization process will complete if the change in weight between two sequential simulation iteration is less than convergence criteria. The default convergence criteria are sometimes too loose. The figure above shows a … You need some prior experience of your CFD code and your application to judge when a simulation is converged. Too much leads to numerical instabilities, while too little slows down convergence. Load Ramping and Nonlinearity Ramping Techniques My problem is that it does not seem that the eigenvalues are completely converging. The COMSOL discussion forum covers a wide variety of simulation topics. They should reach the same solution expect. Thus in COMSOL's aggregated error, in the case of equidistant mesh the elements belonging to the reaction zone are underweighted compared to the fixed(2) mesh. One of the most overlooked issues in computational mechanics that affects accuracy is mesh convergence. It’s important to keep in mind that a converged solution is not necessarily an accurate one. One of the most overlooked issues in computational mechanics that affects accuracy is mesh convergence. ... or maybe just improve it? solvers, time-step selection, parametric For example 145/172. It’s important to keep in mind that a converged solution is not necessarily an accurate one. Convergence criteria. Else my impression is "just" that the steps must be small enough for the convergence criteria to control the algorithm that is why COMSOl often makes many, even hundred of intermediaqte time steps between each value it send "out" and stores as your demanded time value--Good luck Ivar Hi again,, I'm trying to conduct mesh indepenace study for swirl flow induced by buoyancy. iii. For example, for a nonlinear time-dependent model, the menu that contains the nonlinear solver and Time-Dependent Solver (Generalized-alpha) as options. The default value is 0.01 in COMSOL. So I am ramping the load till 1 second. To control which solvers generate convergence plots, click the Convergence Plot Settings button on The Progress Window toolbar to select or clear the convergence plots for each solver. The primary criteria for determining convergence is that the change of each degree of freedom is minimized over a large range of iterations. Convergence criteria need to be established to judge whether the iterative quasi-Newton procedure converges within a preset tolerance or not. Linear in the COMSOL Multiphysics Programming Reference Manual. The selected in numerical simulation. Details about this approach can be found in any finite element textbook. To: ***@yahoogroups.com Date: Monday, October 27, 2008, 4:43 PM Hi all, I'm so stucked in this convergence problem and can't move further for 2 weeks..It's so frustrating. After the analysis is finished, display the convergence information by clicking the Convergence Plot tab on the Output Bar. While Loops and Converge Criteria for pseudo steady state model. This is a great way of ensuring license optimisation for these expensive COMSOL licenses. convergence criteria were met. The amount of over or under-relaxation used can be critical. Convergence in FEA Mesh Convergence: h- and p-refinement in Finite Element Analysis. Hi, I am trying to set boundaries in heat transfer study. Browse the threads and share your ideas with the COMSOL community. The COMSOL Multiphysics module AC/DC Electrostatics is used to compute the apparent permittivities by solving Eq. Convergence: Mesh convergence determines how many elements are required in a model to ensure that the results of an analysis are not affected by changing the size of the mesh. COMSOL has historical success in modeling MHD flows with these tools, and similar problems have been solved against widely agreed upon results for validation (10). The study recommends that relatively exposing the large informal sector, ensuring political ramification, and encouraging savings is key to achieving the nominal convergence criteria. Browse the threads and share your ideas with the COMSOL community. virtual memory. This minicourse covers solver convergence termination criteria, scaling, iterative linear . Different approaches exist in COMSOL to tackle the convergence criteria. So, what I did is at 100 knots, I raised the convergence criteria to be slightly larger than the value from the warning message, and I get a much smoother, but less accurate surface. ME469B/3/GI 1 Simulation of Turbulent Flows • From the Navier-Stokes to the RANS equations • Turbulence modeling • k-ε model(s) • Near-wall turbulence modeling . Convergence, Consistency, and Stability Definition A one-step finite difference scheme approximating a partial differential equation is a convergent scheme if for any solution to the partial differential equation, u(t,x), and solutions to the finite difference scheme, vn i, such that v0 i converges to u 0(x) as i∆x converges to x, then vn In this study, the unbalanced force is the most straightforward criterion, but numerical difficulties may arise for stiff structures. Subject: [COMSOL_Users] Comsol convergence problem!!! This is related to how small the elements need to be to ensure that the results of the finite element analysis are not affected by changing the size of the mesh. iv. . The COMSOL discussion forum covers a wide variety of simulation topics. It is composed by two metal layers (top and bottom), a middle layer (dielectric) and 144 vias (metal + … Posted Apr 29, 2019, 1:44 PM PDT 0 Replies . read 0 Replies 1095 Views. Summary on Using the Domain Decomposition Solver in COMSOL Multiphysics® When simulating problems with large memory requirements in the COMSOL® software, we are limited by the available hardware resources. If our study involves solving multiple equations, the value given here will be taken as default for all the equations. It's probably me who cant find it in the documentation, some simple convergence criteria to change :/. The following information also applies to the Krylov Preconditioner attribute. It also discusses the Convergence Criteria for Iterative Solvers and Selecting a Preconditioner for an Iterative Linear System Solver. Im trying to solve the Schrodinger equation for some structure in comsol 3.5a with matlab. The errors are always like: Failed to find a solution for the initial parameter. The COMSOL discussion forum covers a wide variety of simulation topics. Browse the threads and share your ideas with the COMSOL community. To find the solution at the end of a given increment a set of nonlinearequations has to be solved. I'm doing a piezoelectric modeling, in my model I … Improving Convergence of Nonlinear Stationary ... - comsol.it read 0 Replies 1091 Views. • The direct solvers in COMSOL are: – MUMPS: fast, multi-core capable, cluster capable – PARDISO: fast, robust, multi-core capable (scales better than MUMPS on a single node with many cores) – SPOOLES: slow, uses the least memory, multi-core, cluster capable An iterative method for finding the minimum: The Conjugate Gradient (CG) method Le forum de discussion COMSOL couvre une grande variété de sujets de simulation. Then COMSOL gave you a warning message that it could not converge lower than another larger number (.001 or similar if I recall). check the doc on the solver. Subject: [COMSOL_Users] Comsol convergence problem!!! The solver crashes just before reaching 1 sec. Convergence of Numerical Methods In the last chapter we derived the forward Euler method from a Taylor series expansion of un+1 and we utilized the method on some simple example problems without any supporting analysis. At the time of its acquisition by Siemens AG in 2016, CD-Adapco’s annual revenue was around $200M and was growing at a CAGR of 12%. Figure 2 summarizes performance of the optimization algorithm in terms of convergence speed, i.e. However, my geometry has many entities. For normal pure aero simulations without resolved walls, i.e. The default convergence criteria are sometimes too loose. In this particular model, the default solver used was the segregated method. × Warning Your internet explorer is in compatibility mode and may not be displaying the website correctly. Convergence criteria . To know when a solution is converged is not always that easy. × Warning Your internet explorer is in compatibility mode and may not be displaying the website correctly. C. Solver and convergence criteria Selection of a solver in COMSOL Multiphysics strongly depends on degree of non-linearity. The progression is expressed relatively to the case 4 (reference case). The COMSOL discussion forum covers a wide variety of simulation topics. (Further details about COMSOL's convergence criteria can be found in the 3rd section of the Supplementary Information.) System response (stress, deformation) will converge to a repeatable solution with decreasing element size. property of their respective owners, and COMSOL AB and its subsidiaries and products are not affiliated with, endorsed by, sponsored by, or supported by those trademark owners. When COMSOL tries to solve a complex multi-physics problem, it can either solve it directly (all variables at a time, or try a segregated group approach (uses less ram but takes longer) by solving (in a loop) for some variables, then using the results to solve for the others. I would really tighten the convergence tolerances with both solvers to make sure that they reach the same solution. What is the problem you are facing here ? 145 is the current virtual memory usage, and 172 is the peak virtual memory usage. 1 - Relative Tolerance is the convergence criteria value in COMSOL. While Loops and Converge Criteria for pseudo steady state model. 1. Support Notes. Convergence by Numerical Experiments ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ = − +l x x AE c uex x 2 3 6 ( ) ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ = = − + 2 2 2 ( ) l x AE c dx du εex x Since it is now possible to measure the error, a simple numerical example will be considered to show the FEM‘s convergence. System response (stress, deformation) will converge to a repeatable solution with decreasing element size. Create a new study (say Study 2). Generally speaking, convergence is the achievement of a limiting behavior in the solution of the equations and is typically represented by the diminishing residuals of the numerical solution. If you would like a live view of which users are consuming which licenses, with a dashboard to analyse past usage, including those potentially hoarding/abusing licenses - contact me now for a demo or free trial of LAMUM ( www.teameda.com ) ... One of the tutorials we attempted to run failed to hit the convergence criteria in over 4 hours on 16 cores. × Warning Your internet explorer is in compatibility mode and may not be displaying the website correctly. 2 - First solve the initial problem with Study 1. Here, we will examine techniques for accelerating the convergence of these two methods. The third column shows that some damping was used for the first two steps, but steps 3-6 were undamped. Posted 12 févr. 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. It’s important to keep in mind that a converged solution is not necessarily an accurate one. Quite another thing is what we call “budgetary convergence,” which means your solution is converged when you can’t afford any more computer time. I’ve reached that level of convergence many times. The primary criteria for determining convergence is that the change of each degree of freedom is minimized over a large range of iterations. I am trying to simulate the contact between tire and soil in COMSOL, but I am getting too many problems of convergence. The second thing we noticed is that these residuals are tracked every “cycle” and not “iteration”. The situation is that I often run out of memory, which I think is this kind of memory i.e. CAD Tool Quick Start Guides. To: ***@yahoogroups.com Date: Monday, October 27, 2008, 4:43 PM Hi all, I'm so stucked in this convergence problem and can't move further for 2 weeks..It's so frustrating. Im trying to solve the Schrodinger equation for some structure in comsol 3.5a with matlab. read 0 Replies 1091 Views. My problem is that it does not seem that the eigenvalues are completely converging. Another option is to select convergence criteria, wherein the optimization process will complete if the change in weight between two sequential simulation iteration is less than convergence criteria. They should reach the same solution expect. As mesh size decreases towards zero (leading to a model of infinite size), you move toward the exact solution for the equations you are solving. Tutorials and Training Materials. This is related to how small the elements need to be to ensure that the results of the finite element analysis are not affected by changing the size of the mesh. number of generations to meet convergence criteria (Objective function change < 10 −6).As shown in Figure 2a (right y-axis), using random-point crossover CO 2 purity as high as 0.827 is achievable, which was the highest among the achieved solutions. Convergence: Mesh convergence determines how many elements are required in a model to ensure that the results of an analysis are not affected by changing the size of the mesh. In Comsol, at the bottom corner on the right, there's a memory indicator. COMSOL primarily uses the finite element method(FEM) to compute single- and multiphysics simulations.
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