Fourth Aircraft Interior Noise Workshop

The fourth in a series of NASA/SAE Interior Noise Workshops was held on May 19 and 20, 1992. The theme of the workshop was new technology and applications for aircraft noise with emphasis on source noise prediction; cabin noise prediction; cabin noise control, including active and passive methods; and cabin interior noise procedures. This report is a compilation of the presentations made at the meeting which addressed the above issues

3D-printing technology applied to the development of bio-inspired functional acoustic systems

Examples of bio-inspired technology can be found almost everywhere in society: robots with specific capabilities, materials with unique physical and chemical properties, aerodynamic systems, and architectonic structures are a few examples of taking profit of evolution-driven processes to solve common engineering problems. One field of research taking advantage of bio-inspiration is that of acoustical engineering, aiming to find solutions to problems arising from the miniaturisation of microphones and loudspeakers. Studying the auditory organs of insects to seek inspiration for new design structures is one of the best ways to solve such an important problem. Another discipline of science that has experienced a research boom is that of materials science, as development of new materials has attracted the attention of researchers. In addition, three-dimensional (3D) printers have contributed to further development in materials science making the production process more efficient. The aim of this research is to bring these fields of science together to develop novel bioinspired, polymer-based sensors presenting functional specific acoustic properties after 3D-printing. While the study of complex biological hearing systems provides inspiration to develop sensors featuring specific properties, the use of polymer-based materials allows the customization of the manufacturing process, as the produced parts adapt to the desired needs. In this thesis one such insect auditory system that has been thoroughly studied is that of the desert locust Schistocerca gregaria as it presents a simple structure that allows for acoustic frequency selectivity and displays nonlinear acoustic phenomena. Prior to the development of a bio-inspired system, a mathematical description of the mechanical response of such a structure is presented. Furthermore, the physical behaviours measured on the locust tympanal membrane have been studied using finite element analysis. The 3D-printed functional sensors have been used to determine the degree of accuracy between experimental and theoretical results.Examples of bio-inspired technology can be found almost everywhere in society: robots with specific capabilities, materials with unique physical and chemical properties, aerodynamic systems, and architectonic structures are a few examples of taking profit of evolution-driven processes to solve common engineering problems. One field of research taking advantage of bio-inspiration is that of acoustical engineering, aiming to find solutions to problems arising from the miniaturisation of microphones and loudspeakers. Studying the auditory organs of insects to seek inspiration for new design structures is one of the best ways to solve such an important problem. Another discipline of science that has experienced a research boom is that of materials science, as development of new materials has attracted the attention of researchers. In addition, three-dimensional (3D) printers have contributed to further development in materials science making the production process more efficient. The aim of this research is to bring these fields of science together to develop novel bioinspired, polymer-based sensors presenting functional specific acoustic properties after 3D-printing. While the study of complex biological hearing systems provides inspiration to develop sensors featuring specific properties, the use of polymer-based materials allows the customization of the manufacturing process, as the produced parts adapt to the desired needs. In this thesis one such insect auditory system that has been thoroughly studied is that of the desert locust Schistocerca gregaria as it presents a simple structure that allows for acoustic frequency selectivity and displays nonlinear acoustic phenomena. Prior to the development of a bio-inspired system, a mathematical description of the mechanical response of such a structure is presented. Furthermore, the physical behaviours measured on the locust tympanal membrane have been studied using finite element analysis. The 3D-printed functional sensors have been used to determine the degree of accuracy between experimental and theoretical results

A high-performance electromagnetic vibration energy harvester based on ring magnets with Halbach configuration: design, optimization, and applications

Electromagnetic vibration energy harvesting is a relatively modern technology that has received relevant attention in the last decade from the research community and industry as a potential complement or alternative to the inconvenient employment of batteries for powering ultra-low-power devices, microelectromechanical systems, and wireless sensor networks. However, there are still many flaws in this technology that require to be addressed to develop truly practical, reliable, and cost-effective electromagnetic generators, without which industries can still not avoid relying primarily on batteries for powering wireless devices. This dissertation is mainly concerned with developing a high-power, compact, and yet simplified electromagnetic vibration energy harvester capable of reaching high power density levels without the necessity of a complex design, which is generally accompanied by an increment in fabrication costs. For this purpose, a ring-shaped magnet structure consisting of three ring magnets in a linear Halbach configuration is proposed in the present thesis. This particular structure is also compared, in terms of their output performance, with several ring magnet arrangements that include single magnets, double magnet arrays, and an alternative Halbach configuration to determine the actual benefits of the employed Halbach array within the proposed architecture. Also, the coil-magnet parameters of the selected transducer have been further optimized, mainly as a function of the inner radius, the height, and the wire diameter of the coil, to maximize its power generation. Besides, a harvester prototype based on the proposed configuration has been fabricated to validate the modeling strategy used and to certify the reliability of the proposed design regarding its power generation capabilities. The results of the power density normalized to the square of the excitation amplitude obtained for the optimized device and the fabricated prototype are found to be significantly higher than the ones associated with devices described in the literature for similar applications. Furthermore, the proposed electromagnetic generator has been tested and simulated in the framework of two industrial applications to determine its feasibility and output performance: a railway tunnel and a water distribution system. In both cases, the most relevant characteristics of the site under evaluation and the field test setup employed for data acquisition are thoroughly described. The field test measurements and overall results are presented and discussed together with the performance simulations obtained for various scenarios, including different significant natural frequencies of the harvester and several locations of particular interest. Results demonstrate that the applicability of the proposed electromagnetic harvester in the context of underground railway systems is feasible, even for non-usual locations subjected to low vibration amplitudes. Also, for the case of water distribution systems, in which the vibration levels are extremely low, the output performance results of the proposed generator are found promising.La recolección de energía de vibración mediante transductores electromagnéticos es una tecnología relativamente moderna que ha recibido especial atención en la última década por parte de la comunidad científica e industrial como una potencial alternativa al uso de baterías para alimentar dispositivos de ultra baja potencia, sistemas microelectromecánicos y redes de sensores inalámbricos. Sin embargo, existen aún muchas problemáticas en esta tecnología que requieren ser atendidas para poder desarrollar generadores electromagnéticos realmente prácticos, confiables y económicos, necesarios para proveer a la industria de una solución confiable que permita no depender primordialmente de las baterías para alimentar dispositivos inalámbricos. Esta tesis doctoral se enfoca fundamentalmente en el desarrollo de un recolector de energía de vibración mediante transducción electromagnética, de alta potencia, compacto y simplificado, capaz de alcanzar altos niveles de densidad de potencia generada sin la necesidad de un diseño complejo, el cual, generalmente, viene acompañado de un incremento de los costes de fabricación. Para este propósito, esta tesis propone una estructura magnética formada por tres imanes anulares en configuración Halbach lineal. Para determinar los beneficios reales de la configuración Halbach empleada dentro de la arquitectura propuesta, esta estructura en particular se compara, en términos de rendimiento de salida, con varias configuraciones de imanes anulares: un único imán, dos imanes y una configuración Halbach alternativa. Además, los parámetros del sistema bobina-imán del transductor seleccionado han sido optimizados, principalmente en función del radio interno, la altura y el diámetro del cable de la bobina, para maximizar su generación de potencia. Adicionalmente, se ha fabricado un prototipo de recolector de energía basado en la configuración propuesta para validar la estrategia de modelado utilizada y certificar la fiabilidad del diseño propuesto con respecto a su capacidad de generación de energía. Los resultados en términos de densidad de potencia normalizada por cuadrado de la amplitud de excitación, obtenidos para el dispositivo optimizado y el prototipo fabricado, son significativamente más altos que los asociados con dispositivos descritos en la literatura para aplicaciones similares. Finalmente, el generador electromagnético propuesto ha sido probado y simulado en el marco de dos aplicaciones industriales para determinar su aplicabilidad y eficiencia en situaciones reales. Concretamente, la aplicaciones escogidas han sido un túnel ferroviario y un sistema de distribución de agua. En ambos casos, las características más relevantes del emplazamiento de estudio y la configuración de los ensayos de campo desarrollados para la adquisición de datos son descritas minuciosamente. Las medidas de campo y los resultados generales se presentan y discuten junto con las simulaciones de rendimiento de salida obtenidas para distintos escenarios, incluyendo diferentes frecuencias naturales significativas del dispositivo y varias locaciones de particular interés. Los resultados demuestran que la aplicabilidad del recolector de energía de vibración mediante transducción elec-tromagnética propuesto en el contexto de los sistemas ferroviarios subterráneos es factible, incluso para lugares no habituales sujetos a bajas amplitudes de vibración. Para el caso de los sistemas de distribución de agua, aunque los niveles de vibración obtenidos experimetales son extremadamente bajos, los resultados de rendimiento de salida del generador propuesto son prometedores.Postprint (published version

Load Estimation, Structural Identification and Human Comfort Assessment of Flexible Structures

Stadiums, pedestrian bridges, dance floors, and concert halls are distinct from other civil engineering structures due to several challenges in their design and dynamic behavior. These challenges originate from the flexible inherent nature of these structures coupled with human interactions in the form of loading. The investigations in past literature on this topic clearly state that the design of flexible structures can be improved with better load modeling strategies acquired with reliable load quantification, a deeper understanding of structural response, generation of simple and efficient human-structure interaction models and new measurement and assessment criteria for acceptable vibration levels. In contribution to these possible improvements, this dissertation taps into three specific areas: the load quantification of lively individuals or crowds, the structural identification under non-stationary and narrowband disturbances and the measurement of excessive vibration levels for human comfort. For load quantification, a computer vision based approach capable of tracking both individual and crowd motion is used. For structural identification, a noise-assisted Multivariate Empirical Mode Decomposition (MEMD) algorithm is incorporated into the operational modal analysis. The measurement of excessive vibration levels and the assessment of human comfort are accomplished through computer vision based human and object tracking, which provides a more convenient means for measurement and computation. All the proposed methods are tested in the laboratory environment utilizing a grandstand simulator and in the field on a pedestrian bridge and on a football stadium. Findings and interpretations from the experimental results are presented. The dissertation is concluded by highlighting the critical findings and the possible future work that may be conducted

2D and 3D visualization of acoustic waves by optical feedback interferometry

The visualization of physical phenomena is one of the challenges that researchers are trying to overcome by designing and implementing different sensors that provide information close to realitythrough changes in one of the parameters they measure. Historically, the visualization of variations in physical phenomena has allowed for a better understanding of the problem being studied and has changed our perception of the world and ourselves forever. Over the last 300 years, in particular, many methods have been developed to visualize sound through a visual representation. In the field of acoustics, scientists have attempted to develop a visual representation of sound waves using transducers detecting two fundamental components of sound: sound pressure and particle velocity. In other words, the measurement of kinetic energy and potential, whose quantities provide information on the physical phenomenon of acoustic propagation. In this summary, we briefly present the work of the thesis entitled "2D and 3D Visualizations of Acoustic Waves by Optical Feedback Interferometry" in which a new visualization tool for acoustic phenomena was developed. This system is based on an optical sensor said reinjection in a laser diode and allows to reconstruct in 2D and 3D the image of a propagating acoustic wave. The manuscript is divided into 3 chapters: • a first chapter presents the known methods for the visualization of the acoustic phenomena and presents the context of the research carried out, • a second chapter, allows to detail the principle of measurement and its application to the realization of a two-dimensional image of the acoustic wave • finally, in the last chapter, we demonstrate how a tomographic method can be used to create a three-dimensional image

Introduction to modern instrumentation: for hydraulics and environmental sciences

Preface Natural hazards and anthropic activities threaten the quality of the environment surrounding the human being, risking life and health. Among the different actions that must be taken to control the quality of the environment, the gathering of field data is a basic one. In order to obtain the needed data for environmental research, a great variety of new instruments based on electronics is used by professionals and researchers. Sometimes, the potentials and limitations of this new instrumentation remain somewhat unknown to the possible users. In order to better utilize modern instruments it is very important to understand how they work, avoiding misinterpretation of results. All instrument operators must gain proper insight into the working principles of their tools, because this internal view permits them to judge whether the instrument is appropriately selected and adequately functioning. Frequently, manufacturers have a tendency to show the great performances of their products without advising their customers that some characteristics are mutually exclusive. Car manufacturers usually show the maximum velocity that a model can reach and also the minimum fuel consumption. It is obvious for the buyer that both performances are mutually exclusive, but it is not so clear for buyers of measuring instruments. This book attempts to make clear some performances that are not easy to understand to those uninitiated in the utilization of electronic instruments. Technological changes that have occurred in the last few decades are not yet reflected in academic literature and courses; this material is the result of a course prepared with the purpose of reducing this shortage. The content of this book is intended for students of hydrology, hydraulics, oceanography, meteorology and environmental sciences. Most of the new instruments presented in the book are based on electronics, special physics principles and signal processing; therefore, basic concepts on these subjects are introduced in the first chapters (Chapters 1 to 3) with the hope that they serve as a complete, yet easy-to-digest beginning. Because of this review of concepts it is not necessary that the reader have previous information on electronics, electricity or particular physical principles to understand the topics developed later. Those readers with a solid understanding of these subjects could skip these chapters; however they are included because some students could find them as a useful synthesis. Chapter 4 is completely dedicated to the description of transducers and sensors frequently used in environmental sciences. It is described how electrical devices are modified by external parameters in order to become sensors. Also an introduction to oscillators is presented because they are used in most instruments. In the next chapters all the information presented here is recurrently referred to as needed to explain operating principles of instruments. Unauthenticated Download Date | 10/12/14 9:29 PM VIII Preface Chapters 1 to 4 are bitter pills that could discourage readers interested in the description of specific instruments. Perhaps, those readers trying this book from the beginning could abandon it before arriving at the most interesting chapters. Therefore, they could read directly Chapters 5 to 11, going back as they feel that they need the knowledge of the previous chapters. We intended to make clear all the references to the previous subjects needed to understand each one of the issues developed in the later chapters. Chapter 5 contributes to the understanding of modern instrumentation to measure flow in industrial and field conditions. Traditional mechanical meters are avoided to focus the attention on electronic ones, such as vortex, electromagnetic, acoustic, thermal, and Coriolis flowmeters. Special attention is dedicated to acoustic Doppler current profilers and acoustic Doppler velocimeters. Chapter 6 deals with two great subjects; the first is devoted to instruments for measuring dynamic and quasi static levels in liquids, mainly water. Methods to measure waves at sea and in the laboratory are explained, as well as instruments to measure slow changes such as tides or piezometric heads for hydrologic applications. The second subject includes groundwater measurement methods with emphasis on very low velocity flowmeters which measure velocity from inside a single borehole. Most of them are relatively new methods and some are based on operating principles described in the previous chapter. Seepage meters used to measure submarine groundwater discharge are also presented. Chapter 7 presents methods and instruments for measuring rain, wind and solar radiation. Even though the attention is centered on new methods, some traditional methods are described not only because they are still in use, and it is not yet clear if the new technologies will definitely replace them, but also because describing them permits their limitations and drawbacks to be better understood. Methods to measure solar radiation are described from radiation detectors to complete instruments for total radiation and radiation spectrum measurements. Chapter 8 is a long chapter where we have tried to include most remote measuring systems useful for environmental studies. It begins with a technique called DTS (Distributed Temperature Sensing) that has the particularity of being remote, but where the electromagnetic wave propagates inside a fibre optic. The chapter follows with atmosphere wind profilers using acoustic and electromagnetic waves. Radio acoustic sounding systems used to get atmospheric temperature profiles are explained in detail as well as weather radar. Methods for ocean surface currents monitoring are also introduced. The chapter ends with ground penetrating radars. Chapter 9 is an introduction to digital transmission and storage of information. This subject has been reduced to applications where information collected by field instruments has to be conveyed to a central station where it is processed and stored. Some insight into networks of instruments is developed; we think this information will help readers to select which method to use to transport information from field to office, by means of such diverse communication media as fibre optic, digital telephony, Unauthenticated Download Date | 10/12/14 9:29 PM Preface IX GSM (Global System for Mobile communications), satellite communications and private radio frequency links. Chapter 10 is devoted to satellite-based remote sensing. Introductory concepts such as image resolution and instrument?s scanning geometry are developed before describing how passive instruments estimate some meteorological parameters. Active instruments are presented in general, but the on-board data processing is emphasized due to its importance in the quality of the measurements. Hence, concepts like Synthetic Aperture Radar (SAR) and Chirp Radar are developed in detail. Scatterometers, altimeters and Lidar are described as applications of the on-board instruments to environmental sciences. Chapter 11 attempts to transfer some experiences in field measuring to the readers. A pair of case studies is included to encourage students to perform tests on the instruments before using them. In this chapter we try to condense our ideas, most of them already expressed throughout the book, about the attitude a researcher should have with modern instruments before and after a measuring field work. As can be inferred from the foregoing description the book aims to provide students with the necessary tools to adequately select and use instruments for environmental monitoring. Several examples are introduced to advise future professionals and researchers on how to measure properly, so as to make sure that the data recorded by the instruments actually represents the parameters they intend to know. With this purpose, instruments are explained in detail so that their measuring limitations are recognized. Within the entire work it is underlined how spatial and temporal scales, inherent to the instruments, condition the collection of data. Informal language and qualitative explanations are used, but enough mathematical fundamentals are given to allow the reader to reach a good quantitative knowledge. It is clear from the title of the book that it is a basic tool to introduce students to modern instrumentation; it is not intended for formed researchers with specific interests. However, general ideas on some measuring methods and on data acquisition concepts could be useful to them before buying an instrument or selecting a measuring method. Those readers interested in applying some particular method or instrument described in this book should consider these explanations just as an introduction to the subject; they will need to dig deeper in the specific bibliography before putting hands on.Fil: Guaraglia, Dardo Oscar. Universidad Nacional de la Plata. Facultad de Ingeniería. Departamento de Hidraulica. Area Hidraulica Basica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Pousa, Jorge Lorenzo. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Laboratorio de Oceanografía Costera y Estuarios; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentin

Acoustic Waves

The concept of acoustic wave is a pervasive one, which emerges in any type of medium, from solids to plasmas, at length and time scales ranging from sub-micrometric layers in microdevices to seismic waves in the Sun's interior. This book presents several aspects of the active research ongoing in this field. Theoretical efforts are leading to a deeper understanding of phenomena, also in complicated environments like the solar surface boundary. Acoustic waves are a flexible probe to investigate the properties of very different systems, from thin inorganic layers to ripening cheese to biological systems. Acoustic waves are also a tool to manipulate matter, from the delicate evaporation of biomolecules to be analysed, to the phase transitions induced by intense shock waves. And a whole class of widespread microdevices, including filters and sensors, is based on the behaviour of acoustic waves propagating in thin layers. The search for better performances is driving to new materials for these devices, and to more refined tools for their analysis