Gravity initialization

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Computational efficiency through an increased time step size

Gravity initialization using an explicit solver can be computationally demanding, especially if the ratio between the highest and the lowest eigenfrequency is large. The number of time steps required to reach equilibrium is more or less proportional to this ratio.

In order to circumvent (or at least reduce) the effect of high eigenfrequencis, a new command *FREQUENCY_CUTOFF has been implemented in IMPETUS Solver. This command allows the user to define a preferred time step size $\Delta t_{target}$. IMPETUS Solver will automatically identfy and suppress frequencies that, under normal circumstances, require a time step smaller than $\Delta t_{target}$.


The animation below shows the gravity initialization of a HIII Dummy on a simple foam seat. The time step size in *FREQUENCY_CUTOFF is set to $\Delta t_{target} = 4\mu s$. Physical time to reach equilibrium is about $0.17s$. This means roughly $40,000$ time steps and a wall clock time of about $2h$. This is less than $10 \%$ of the computational effort required if not using this command.

Further reading

A description of the command can be found on our manual page: *FREQUENCY_CUTOFF

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