A series of studies compared the predictive performance of a physics-based trajectory modeler with t he conventional parametric prediction system currently employed in the operational Traffic Flow Management (TFM) decision support system. The results indicate that the physics-based system has increased performance over the parametric system for trajectories in which aircraft transition in altitude. These studies include a sample size covering thirtysix 24-hour periods in which traffic from 12 Continental US Air Route Traffic Control Centers were examined. Four TFM metrics were used in the studies: Meter Fix Arrival Time, Departure Center Exit Time, Sector Entry Time, and Sector Occupancy. The charts of the TFM metrics for a majority of the data samples share the same characteristics and strongly lead to a consistent interpretation of the results. These interpretations generalize across the metrics for total sample aggregate (all Centers, all dates).
Analyses of the effects of service conditions on the distribution of residual stresses in railroad commuter car wheels are presented. Novel software has been applied to estimate the effects of service conditions on the as-manufactured state of these wheels. Contact loads resulting from wheel and rail interaction and thermal loads from on-tread braking are considered. Results indicate that contact stresses acting alone result in increased net rim hoop compression. However, thermal stresses due to frictional heating reverse the as-manufactured residual compressive state. In particular, high-performance stop braking may result in large net hoop tension in the rim. When contact and thermal loads interact, the effects of braking dominate the process. The presence of tensile residual hoop stress at the wheel tread has been shown to favor the formation and growth of fatigue cracks, threatening the safety of train operations. The paper provides a description of the analytical methodology and results of its application to a representative class of commuter service. Comparisons of the predicted depth of rim stress reversal with the thermal cracking observed in the wheels of this fleet provides confidence in the ability of the technique to assess the likelihood of thermal crack development in other types of commuter operations and in railroad freight service.
The experience and findings of an exploratory effort to characterize the sound emitted by aircraft wake vortices near the ground are presented. A line array of four directional microphones was deployed and recorded the wakes of several commercial aircraft in the approach phase with particular attention being paid to the characterization of background noise. It is found that vortices near the ground emit broadband sound with frequency contents ranging from below 100 Hz to near 2000 Hz and possibly beyond. However, addressing the degree of consistency of the vortex sound would require deployment of a larger array. The mechanism of vortex sound generation and suggestions on future studies are discussed.
To mitigate safety hazards posed by near-ground vortex lateral transport, under instrument flight rules (IFR), parallel runway operations must adopt aircraft spacing standards that often reduce capacity. Once the phenomenon of lateral transport is understood, it is conceivable that, under IFR, new separation standards could restore some runway capacity. In this context, it is of interest to establish the probability that a wake vortex is still surviving in lateral transport t seconds after it began migrating. This paper applies survival data analysis methods to demonstrate how to generate predictions of survival probability that are specific to aircraft type. Modeling assumptions lead to a family of Weibull probability densities, a form that is useful for modeling wind phenomena.
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