Fluent convergence criteria
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If more than 1000 iterations are performed i. For more simulation tips read: Mike Kuron, M. If the fluid is incompressible then its density should remain constant and, according to Eq. If you're doing a linear analysis, then you should consider looking at von Mises or Principals depends on the type of analysis. Note also that the frequency of the data storage will diminish towards the start of the solution as the number of solved iterations increases.

Include it only if you have time. We recommend that you solve transiently and review the convergence behaviour. Note that this definition of residual is also used by Fluent Inc. Checking boundary types: Checking face pairs. In those cases, it can be helpful to compare the total deformation and stress plots for the unconverged solution, along with those plots for the last converged solution, with the 1. You can indicate whether or not you want to monitor residuals for each variable by enabling or disabling the relevant check box in the Monitor list of the. Therefore, every cell in your model will have its own residual value for each of the equations being solved.

Let us say your ultimate is 100ksi, then model will have max stress of 100ksi. Do I need to perform time independence study to reach better convergence and after that start mesh independence study? This is complicated, however, by the fact that fluid flows tend to be oscillatory or even unstable. Using this information we made two changes to the model. I could not get any document on this. You can also specify the normalization factor the denominator in Equation or explicitly. It is always good practice to review whether the results achieved are physical after each simulation, regardless of whether the simulation was steady, or unsteady. This begs the question: How do I know when my solution has converged? Storing Residual History Points Residual histories for each variable are automatically saved in the data file, regardless of whether they are being monitored.

If a mesh independance analysis has been done with a steady-state flow, I wonder is the mesh independance study does still make sense when switching to a transient simulation for the same geometry. Do you think the total physical time will affect the results? If you are performing a large number of iterations, you will lose a great deal of residual history information at the beginning of the calculation. You can retrieve the current solution from this data file at any time. The drag coefficient will be compared to empirical equations obtained from the literature. Enter 5 for Turbulent Intensity. We average drag and lift over many iterations after the residuals reach the plateau, as much as 15 or 20 thousand.

Speed and simplicity Thoughtful changes permeate every screen, every step, making simulation a joy. Since the axis is scaled by the minimum and maximum values of all points in the plot, you can zoom in on the end of the residual history by setting Iterations to Plot to a value smaller than the number of iterations performed. Double-precision residuals can drop up to twelve orders of magnitude. As the calculation progresses, the residuals will be plotted in the graphics window Figure. The best method to implement a mesh independence check is to gradually refine and coarsen the mesh in the important regions; and then compare the final results and plot their difference. You can check the residence time either by having a look at the time on the streamlines or by dividing your volume by the volumetric flow rate. For example, the scaling of the continuity equation is based on the value of the continuity residual in the first five iterations.

Is there any recommendation according to the problem considered? Users can pick from several themes or chose the new, Japanese language localization. Their final suggestion for the mesh is to align it with the flow to enhance convergence. Examined the quality of the mesh. The traditional knobs to turn are to increase the number of substeps, decrease contact stiffness if contact is involved, perhaps add more points to the plasticity curve, etc. The measure of incompressibility is the divergence of the velocity, Ã‘ Â·U, which is equal to the time rate-of-change of fluid volume per unit volume. If the flow features in your initial steady state results are representative of the likely transient flow features, then you can confidently assume that your mesh fidelity is appropriate.

The goal of the iteration is to reduce the magnitude of the velocity divergence below some absolute numerical value, e, called the convergence criteria. In particular, view the boundary layer near the end of the plate. Run Calculation Check Case i. Depends on the nature of the problem, convergence criteria can be considered for force or displacement in structural analysis. See Section for information about judging convergence based on the different types of residual reports. Basic functional familiarity with computers. Second, we reduced the contact stiffness by changing Normal Stiffness from Program Controlled factor of 1.

When you use one of the density-based solver, the residual values for all solution variables are available in the Residuals. Volkswagen Motorsport engineers conducted complete virtual drive tests of the entire race and optimized the battery cooling system with minimal weight and aerodynamic drag loss. Since the axis is scaled by the minimum and maximum values of all points in the plot, you can zoom in on the end of the residual history by setting Iterations to a value smaller than the number of iterations performed. It is important to remember that your solution is the numerical solution to the problem that you posed by defining your mesh and boundary conditions. These values have been taken from the inflow boundary condition. Grid independence has been checked.

Select length in the Quantities list. Hi, Please let me know if somebody has info for the below In one of my problem I had nlgeom,contacts and nonlinear mps. Note that entering a value for Iterations to Plot does not necessarily mean solved iterations but rather stored or sampled data points. In general, it is difficult to judge convergence by examining the residuals defined by Equation since no scaling is employed. Checking number of cells per face. The Velocity Magnitude should still be 2. In this case, a high-quality triangular grid will produce a negligible difference in results with a quadrilateral grid, and the preparation time will be significantly reduced.

I have a question concerning mesh independence studies: As far as I know, a properly done mesh independence study requires a uniform and consistent refinement of the whole mesh i. The graphical display window will show the velocity vectors. The residuals for each iteration are printed out as well as plotted in the graphics window as they are calculated. However, for cases that have processes with widely different timescales, it is possible to have large imbalances even when the residuals are small. It is sometimes useful to determine how much a residual has decreased during calculations as an additional measure of convergence. I know that I have to check the influence of the time step when performing my new simulations but if the independance is reached for a steady flow, is it for a transient one? Note that unnormalized, unscaled residuals are stored in the data file regardless of whether the reported residuals are normalized or scaled.