A spectral analysis of the tones of five flutes constructed of different materials

The purpose of this investigation was to systematically analyze the tonal spectra of five modern Boehm-system flutes constructed of different materials, i.e., white gold, 14 karat gold, palladium, and sterling silver (2), and produced with the same specifications by a single manufacturer. The questions of concern in the study involved the influence of wall material, intensity level, frequency level, and the performer on the harmonic structure of tones produced on each flute used in the investigation. Two professional flutists played a sustained tone using no vibrato on three frequencies representing three registers of the flute range, i.e., 392 Hz, 784 Hz, and 1568 Hz. Each frequency investigated was played on each flute at two intensity levels corresponding to the forte and piano dynamic levels. Three trials were conducted for each frequency at a single intensity by each performer

Mechanical systems readiness assessment and performance monitoring study

The problem of mechanical devices which lack the real-time readiness assessment and performance monitoring capability required for future space missions is studied. The results of a test program to establish the feasibility of implementing structure borne acoustics, a nondestructive test technique, are described. The program included the monitoring of operational acoustic signatures of five separate mechanical components, each possessing distinct sound characteristics. Acoustic signatures were established for normal operation of each component. Critical failure modes were then inserted into the test components, and faulted acoustic signatures obtained. Predominant features of the sound signature were related back to operational events occurring within the components both for normal and failure mode operations. All of these steps can be automated. The structure borne acoustics technique lends itself to reducing checkout time, simplifying maintenance procedures, and reducing manual involvement in the checkout, operation, maintenance, and fault diagnosis of mechanical systems

Performance of direct power controlled grid-connected voltage source converters

PhD ThesisIn this thesis the performance of direct power controlled grid-connected voltage source converters (VSCs) is investigated. Of particular interest is the stability of the controller with the third-order LCL filter employed as the grid filter, effect of grid impedance variations and grid voltage distortion, and current limitation during voltage dips. The control scheme implemented is virtual-flux direct power control with space vector modulation (VF-DPC-SVM). By mathematical modelling and stability analysis, it is found that the closed-loop power control system is stable for all values of proportional gain when the current sensors are on the inverter side of the LCL filter. The inverter current together with the estimated grid virtual-flux is used to estimate the active power and the reactive power. The difference between the estimated reactive power and the reactive power on the grid side is compensated for, using a new reactive power error compensation scheme based on the estimated capacitor current. The control system is found to be robust to changes in grid inductance, and remains stable for a range of grid inductance values, and controller proportional gain. It is demonstrated in simulation and experimentally that the total harmonic distortion (THD) of the current injected by the VSC is less than the limit of 5 %, set by standards, for all different values of grid inductance and proportional gain. This is true even in the presence of significant grid voltage distortion. To control the VSC during voltage dips without damaging the semiconductor devices, a new current limiting algorithm is proposed and implemented. The positive-sequence component of the virtual-flux is used for synchronization and power estimation to achieve balanced, undistorted currents during unsymmetrical voltage dips. Experimental results show that the current achieved during unsymmetrical voltage dips is balanced and has a THD of less than 3 %.Commonwealth Scholarship and Fellowship Plan, Copperbelt Universit

Engineering Data Compendium. Human Perception and Performance, Volume 1

The concept underlying the Engineering Data Compendium was the product an R and D program (Integrated Perceptual Information for Designers project) aimed at facilitating the application of basic research findings in human performance to the design of military crew systems. The principal objective was to develop a workable strategy for: (1) identifying and distilling information of potential value to system design from existing research literature, and (2) presenting this technical information in a way that would aid its accessibility, interpretability, and applicability by system designers. The present four volumes of the Engineering Data Compendium represent the first implementation of this strategy. This is Volume 1, which contains sections on Visual Acquisition of Information, Auditory Acquisition of Information, and Acquisition of Information by Other Senses