underbody-impact-data / metadata /TEMPORAL_SAMPLING.md
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Document simulation protocol and generation evidence for v1.1.0
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Temporal sampling and peak-event time

Raw solver output

Each LS-DYNA simulation terminates at 0.03 s. D3PLOT is requested at a nominal 0.0002-s interval. Actual floating-point state times can differ slightly from the nominal values and are therefore stored explicitly.

Compact 17-state sequence

Compact conversion uses stride 10 on both nodal displacement and shell stress, then appends the final available state when it is not already selected. Across all released cases, both time_indices and element_time_indices equal:

[0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 151].

The first 16 retained states therefore have a nominal spacing of 0.002 s. Index 151 is the appended terminal state and can be separated from index 150 by much less than 0.002 s. Consumers must use the stored time and element_time arrays rather than reconstructing timestamps from an assumed uniform interval.

Discrete peak-event definition

Let T17 be the 17 retained states, Vvalid the valid-node set, and u_i(t) the three-dimensional nodal displacement. The supplied peak-target builder uses

t* = argmax_(t in T17) max_(i in Vvalid) ||u_i(t)||_2.

The implementation flattens the node-by-retained-state magnitude array and uses the first maximum returned by torch.argmax. The displacement field and the shell von Mises effective-stress field at the same selected retained state form the paired peak-event target.

Accordingly, t* is quantized to the released 17-state grid. It is not an interpolated time and is not guaranteed to equal the continuous-time maximum over every raw solver state.