A study of brass instrument acoustics using an artificial lip reed mechanism, laser Doppler anemometry and other techniques

The self-sustained oscillation of a brass wind musical instrument involves a complex aerodynamic coupling between a multimode mechanical vibratory system (the lips of the player) and a multimode acoustical vibratory system (the air column of the instrument). In this thesis the behaviour of the coupled system near the threshold of oscillation is investigated using a simplified model in which a single mechanical lip mode is coupled to a single mode of the acoustical resonator by air flow through the lips. The theoretical threshold behaviour is compared with the measured threshold behaviour of a trombone sounded by an artificial lip reed mechanism. Comparability between theory and experiment is ensured by using model parameter values derived from mechanical response measurements on the artificial lips and input impedance measurements on the trombone.The mechanical response measurements can be used to classify mechanical modes of the artificial lips unambiguously as either "inward striking" or "outward striking". Each of the embouchures considered is found to have at least one mechanical mode of each category. The experimentally observed threshold frequencies of the coupled system suggest a behaviour which passes smoothly from "inward striking" to "outward striking" character as the trombone slide is extended or the embouchure parameters changed. It seems unlikely that this type of behaviour can be explained using a lip model with only a single degree of freedom.After a discussion of the theory of laser Doppler anemome!ry (LDA), the technique is applied to the problem of measuring the instantaneous acoustic particle velocity within a standing wave pipe driven by a loudspeaker. The resulting Doppler signals display quasi-periodic amplitude modulation with a fundamental frequency equal to the frequency of the acoustic field. The phenomenon of amplitude modulation is investigated in some detail.Two different methods of analysing Doppler signals are compared: the digit~l Hilbert transform and the Disa analogue frequency tracker; the analogue tracker is found to offer the greater signal-to-noise ratio and dynamic range. Experiments are carried out to establish how phase errors introduced by the analogue tracker can be minimised:,Velocity measurements extracted from Doppler signals using the analogue tracker are compared with the velocity deduced by applying basic theory to probe microphone pressure measurements. It is found that the acoustic particle velocity amplitude can be measured accurately over the entire frequency range considered, and the phase of the acoustic particle velocity also agrees well with theory, but not at low frequencies. LDA is successfully applied to the measurement of multi-harmonic sound fields. The technique of ensemble averaging velocity signals is shown to be particularly useful.LDA is used to measure the velocity in the backbore of a specially designed transparent mouthpiece, driven by the artificial lip reed. Although significant levels of turbulence are encountered, it is shown that acoustic components can still be clearly distinguished in frequency domain representations of the measured velocity. However LDA measurements in the mouthpiece are restricted to conditions where the acoustic particle velocity amplitude and the turbulent intensity are sufficiently low to ensure that the bandwidth of the Doppler signal is less than the bandwidth of the apparatus used to capture or process the Doppler signal.LDA measurements in brass instrument mouthpieces should provide a better understanding of the air flow into the mouthpiece and may lead to an improved model for self-sustained oscillation of the coupled system which more accurately describes the air flow

Measurements, Models, Systems and Design

531 s.

Applied Measurement Systems

Measurement is a multidisciplinary experimental science. Measurement systems synergistically blend science, engineering and statistical methods to provide fundamental data for research, design and development, control of processes and operations, and facilitate safe and economic performance of systems. In recent years, measuring techniques have expanded rapidly and gained maturity, through extensive research activities and hardware advancements. With individual chapters authored by eminent professionals in their respective topics, Applied Measurement Systems attempts to provide a comprehensive presentation and in-depth guidance on some of the key applied and advanced topics in measurements for scientists, engineers and educators

Precision Pointing Control System (PPCS) system design and analysis

The precision pointing control system (PPCS) is an integrated system for precision attitude determination and orientation of gimbaled experiment platforms. The PPCS concept configures the system to perform orientation of up to six independent gimbaled experiment platforms to design goal accuracy of 0.001 degrees, and to operate in conjunction with a three-axis stabilized earth-oriented spacecraft in orbits ranging from low altitude (200-2500 n.m., sun synchronous) to 24 hour geosynchronous, with a design goal life of 3 to 5 years. The system comprises two complementary functions: (1) attitude determination where the attitude of a defined set of body-fixed reference axes is determined relative to a known set of reference axes fixed in inertial space; and (2) pointing control where gimbal orientation is controlled, open-loop (without use of payload error/feedback) with respect to a defined set of body-fixed reference axes to produce pointing to a desired target

Current source inverters for PM machine control

Brushless permanent magnet (PM) drive systems offer a high efficiency over a wide power/torque-speed operating envelope, however, there are a number of problems that may limit, or complicate, their operation particularly in automotive and aerospace vehicular applications, i.e. the loss of control of the power silicon gate drive circuitry during fluxweakening operation, control of high-speed low-inductance machines and the presence of large electrolytic capacitors on the inverter DC link. Current Source Inverters (CSIs) could potentially address some or all of the above issues. However, they have found little application to date due to the wide use of the Voltage Source Inverter (VSI) circuit topology.This thesis investigates feasibility of utilising Current Source Inverters (CSIs) to control permanent magnet synchronous machines in automotive and aerospace actuation systems. CSIs, switching at the fundamental frequency, were used in some of the first semiconductor based, electronic variable speed drive systems that utilised the simple, low maintenance AC induction motor. However, the rapid progress of semiconductors and discovery of Pulse Width Modulation (PWM) techniques soon resulted in the Voltage Source Inverter (VSI) replacing the CSI in all but the highest power applications. Modern power electronics and (micro-processor based) control systems mean that the advantages of VSI systems may no longer be significant and combined with the unique environmental conditions that automotive and aerospace applications present, could allow the CSI to offer advantages over VSIs in these applications.The thesis presents the switching and control logic for CSIs and mapping to the more conventional VSI logic. Analysis is made of the various loss mechanisms in VSI and CSI power circuitary. Simulation models of the VSI and CSI structures are presented and representative drive systems designed, built and tested to validate the model developed. Comparisons are made of the two inverter topologies based on power conversions and loss audits of the test validation hardware.EThOS - Electronic Theses Online ServiceThe University of Manchester Alumni FundGBUnited Kingdo

Основи схемотехніки електронних систем

Basics of circuitry are stated, principles of operation are considered, it is given calculations of analog, digital and pulse devices of electronic systems, based on semiconductor devices, integrated operational amplifiers and integrated logic circuits of TTL, MOS, CMOS types, construction principles of systems of control by electronics devices based on microprocessors and microcontrollers. For students of institutions of higher education. It can be useful for specialists on electronic engineering, specializing in the area of development, fabrication and maintenance of electronic systems and devices

NASA Tech Briefs, June 2001

Topics covered include: Sensors; Electronic Components and Systems; Software Engineering; Materials; Manufacturing/Fabrication; physical Sciences; Information Sciences

Modelling and Control of Switched Reluctance Machines

Today, switched reluctance machines (SRMs) play an increasingly important role in various sectors due to advantages such as robustness, simplicity of construction, low cost, insensitivity to high temperatures, and high fault tolerance. They are frequently used in fields such as aeronautics, electric and hybrid vehicles, and wind power generation. This book is a comprehensive resource on the design, modeling, and control of SRMs with methods that demonstrate their good performance as motors and generators