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24.3.3 Solution Procedure

Before solving the coupled fluid flow and heat transfer problem, you may want to patch an initial temperature or solve the steady conduction problem as an initial condition. The coupled problem can then be solved as either steady or unsteady. Because of the nonlinear nature of these problems, however, in most cases an unsteady solution approach is preferred.

You can specify the under-relaxation factor applied to the liquid fraction equation in the Solution Controls panel.

Solve $\rightarrow$ Controls $\rightarrow$ Solution...

Specify the desired value in the Liquid Fraction Update field under Under-Relaxation Factors. This sets the value of $\alpha_\beta$ in the following equation for updating the liquid fraction from one iteration ( $n$) to the next ( $n+1$):

 \beta_{n+1} = \beta_n + \alpha_\beta \Delta \beta (24.3-1)

where $\Delta \beta$ is the predicted change in liquid fraction.

In many cases, there is no need to change the default value of $\alpha_\beta$. If, however, there are convergence difficulties, reducing the value may improve the solution convergence. Convergence difficulties can be expected in steady-state calculations, continuous casting simulations, simulations involving multicomponent solidification, and simulations where a large value of the mushy zone constant is used.

next up previous contents index Previous: 24.3.2 Procedures for Modeling
Up: 24.3 Using the Solidification/Melting
Next: 24.3.4 Postprocessing
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