The validation and application of a rotor acoustic prediction computer program

An essential prerequisite to reducing the acoustic detectability of military rotorcraft is a better understanding of main rotor noise which is the major contributor to the overall noise. A simple, yet accurate, Rotor Acoustic Prediction Program (RAPP) was developed to advance the understanding of main rotor noise. This prediction program uses the Ffowcs Williams and Hawkings (FW-H) equation. The particular form of the FW-H equation used is well suited for the coupling of the measured blade surface pressure to the prediction of acoustic pressure. The FW-H equation is an inhomogeneous wave equation that is valid in all space and governs acoustic pressure generated by thin moving bodies. The nonhomogeneous terms describe mass displacement due to surface motion and forces due to local surface stresses, such as viscous stress and pressure distribution on the surface. This paper examines two of the four types of main rotor noise: BVI noise and low-frequency noise. Blade-vortex interaction noise occurs when a tip vortex, previously shed by a rotor blade, passes close enough to a rotor blade to cause large variations in the blade surface pressures. This event is most disturbing when it happens on the advancing side of the rotor disk. Low-frequency noise includes hover and low to moderate speed forward flight. For these flight conditions, the low frequency components of the acoustic signal dominate

Productivity in American Whaling: The New Bedford Fleet in the Nineteenth Century

From the end of the War of 1812 until the Civil War the New Bedford whaling fleet grew spectacularly; thereafter it declined, equally spectacularly. By the end of the century New Bedford's day was over. During the 88 years of this period, the technical configuration of the fleet, the hunting grounds visited, and the types of whales pursued all changed dramatically, and more than once. The literature on whaling suggests that the collapse of the industry was due, in part, to declining productivity, occasioned by the disappearance of the whales (because of over-hunting) and the deterioration of the quality of labor. The shifts in the composition of the fleet are viewed, chiefly, as the result of efforts by whalemen to overcome their problems. In this paper, productivity data (superlative indexes), by voyage, are employed in multiple regression analysis to trace the relationships between the changes in the composition of the fleet and productivity. The propositions that declining labor quality and whale stocks had important consequences for productivity are subjected to test, while the impacts of technical changes on productivity are measured.

An Examination of Student Perceptions of Career and Technical Education Teachers\u27 Interpersonal Behaviors and Their Impact on Student Achievement

The purpose of this quantitative study was to examine career and technical education (CTE) students’ perceptions of CTE teacher interpersonal behaviors and their impact on student achievement. This study is important because teacher-student relationships impact student achievement and CTE struggles with students earning concentrators and/ or completers. Wubbels et al.’s (1985) 48-item student questionnaire of teacher interaction was administered to CTE students enrolled in CTE courses. Descriptive statistics revealed students perceive their teachers as having more leadership, understanding, and helping/friendly behaviors and less uncertain, student responsibility/freedom, admonishing, dissatisfied, and strict behaviors. Due to the small sample size, the nonparametric Spearman’s rank correlations and Whitney-Mann U-test were not conducted to determine the relationship between students’ grades and their perceptions of teachers’ interpersonal behaviors in the classroom. The implications of these findings suggest additional research in CTE as it relates to CTE teachers’ teaching behaviors of females, African American males, and secondary biology and management teachers