Vibroacoustics of plates excited by water drop impacts

Rainfall on windows and roofs of buildings, and the roofs and windscreens of cars can generate high levels of re-radiated sound that may adversely affect speech communication or other activities. This thesis concerns the prediction and experimental analysis of vibroacoustics of plates excited by water drop impacts. The impact force applied by single raindrops on both dry and wet surfaces is quantified experimentally. Single liquid water drops with 2 and 4.5 mm diameter were tested at a range of drop velocities when the plate is dry and with a shallow water layer. Force transducer measurements and wavelet deconvolution were used to measure the time-dependent force. When the response signal has a low SNR value (<10 dB), wavelet deconvolution becomes less robust and the sparse representation method was used to improve the accuracy and preserve the initial phase of the impact force. The validity of theoretical models for the impact force from a drop on a dry surface has been assessed through comparison with experimental data. The inability of these models to describe the time-dependent force provided the motivation to develop empirical formulae. Based on the experimental data, empirical formulae were developed for 2 and 4.5 mm drops falling at (a) different velocities up to and including terminal velocity onto a dry glass surface, (b) terminal velocity onto dry glass or glass with a shallow water layer up to 10 mm and (c) different velocities below terminal velocity onto dry glass or glass with a shallow water layer up to 10 mm. A correction to the empirical model for drop impacts at an oblique angle was accounted for by using the perpendicular velocity component, which was validated with experiments. Numerical models have been validated using Statistical Energy Analysis (SEA) and Finite Transfer Matrix Method (FTMM) with the empirical model to estimate the vibration and sound radiation from a single glass plate and a multilayer plate represented by a plate-foam-plate system. To improve computational efficiency, an order reduced integral with travelling wave method for finite plate size correction of FTMM method has been proposed. An experiment with artificial rainfall was used to assess the accuracy of the numerical models for terminal velocity and the lower velocity (3.65 m drop height). The empirical model was used to quantify the power input into a plate from natural rainfall using numerical experiments

John F. Kennedy Space Center's Technology Development and Application 2006-2007 Report

Topics covered include: Reversible Chemochromic Hydrogen Detectors; Determining Trajectory of Triboelectrically Charged Particles, Using Discrete Element Modeling; Using Indium Tin Oxide To Mitigate Dust on Viewing Ports; High-Performance Polyimide Powder Coatings; Controlled-Release Microcapsules for Smart Coatings for Corrosion Applications; Aerocoat 7 Replacement Coatings; Photocatalytic Coatings for Exploration and Spaceport Design; New Materials for the Repair of Polyimide Electrical Wire Insulation; Commodity-Free Calibration; Novel Ice Mitigation Methods; Crack Offset Measurement With the Projected Laser Target Device; New Materials for Structural Composites and Protective Coatings; Fire Chemistry Testing of Spray-On Foam Insulation (SOFI); Using Aerogel-Based Insulation Material To Prevent Foam Loss on the Liquid-Hydrogen Intertank; Particle Ejection and Levitation Technology (PELT); Electrostatic Characterization of Lunar Dust; Numerical Analysis of Rocket Exhaust Cratering; RESOLVE Projects: Lunar Water Resource Demonstration and Regolith Volatile Characterization; Tribocharging Lunar Soil for Electrostatic Beneficiation; Numerically Modeling the Erosion of Lunar Soil by Rocket Exhaust Plumes; Trajectory Model of Lunar Dust Particles; Using Lunar Module Shadows To Scale the Effects of Rocket Exhaust Plumes; Predicting the Acoustic Environment Induced by the Launch of the Ares I Vehicle; Measuring Ultrasonic Acoustic Velocity in a Thin Sheet of Graphite Epoxy Composite; Hail Size Distribution Mapping; Launch Pad 39 Hail Monitor Array System; Autonomous Flight Safety System - Phase III; The Photogrammetry Cube; Bird Vision System; Automating Range Surveillance Through Radio Interferometry and Field Strength Mapping Techniques; Next-Generation Telemetry Workstation; GPS Metric Tracking Unit; and Space-Based Range

Modelling, Simulation and Data Analysis in Acoustical Problems

Modelling and simulation in acoustics is currently gaining importance. In fact, with the development and improvement of innovative computational techniques and with the growing need for predictive models, an impressive boost has been observed in several research and application areas, such as noise control, indoor acoustics, and industrial applications. This led us to the proposal of a special issue about “Modelling, Simulation and Data Analysis in Acoustical Problems”, as we believe in the importance of these topics in modern acoustics’ studies. In total, 81 papers were submitted and 33 of them were published, with an acceptance rate of 37.5%. According to the number of papers submitted, it can be affirmed that this is a trending topic in the scientific and academic community and this special issue will try to provide a future reference for the research that will be developed in coming years

Predicting and auralizing acoustics in classrooms

Although classrooms have fairly simple geometries, this type of room is known to cause problems when trying to predict their acoustics using room acoustics computer modeling. Some typical features from a room acoustics point of view are: Parallel walls, low ceilings (the rooms are flat), uneven distribution of absorption, and most of the floor being covered with furniture which at long distances act as scattering elements, and at short distance provide strong specular components. The importance of diffraction and scattering is illustrated in numbers and by means of auralization, using ODEON 8 Beta

Exploitation de la phase en imagerie acoustique audible et ultrasonore

L’imagerie à partir d’ondes acoustiques permet de répondre à plusieurs besoins. D’une part, les ondes ultrasonores sont utilisées pour effectuer des échographies dans le domaine médical, mais aussi pour inspecter et suivre la santé de structures. D’autre part, en utilisant les ondes sonores, il est possible de localiser, caractériser, et évaluer l’intensité de diverses sources de bruits. Étant alimentées par des applications et visées différentes, les techniques d’imagerie proposées et utilisées dans les dernières décennies pour ces deux domaines se distinguent. Étant donné les bases communes à l’imagerie sonore et ultrasonore, il serait pertinent de faire bénéficier chaque domaine des avancées en traitement de signal de l’autre domaine. Ce projet de thèse suggère donc une revue des techniques d’imagerie des deux domaines d’imagerie afin d’identifier les outils et techniques d’imagerie prometteuses à adapter et tester sur l’autre domaine d’imagerie. Afin de tester et valider différentes approches d’imagerie, deux types de sources étendues ont été considérées dans le domaine de l’audible. Numériquement, des pistons et plaques simplement supportées bafflées ont été considérés. Pour la validation expérimentale, les cartographies obtenues à l’aide de différents algorithmes ont été comparées avec une mesure de référence obtenue par déflectométrie optique. Dans le domaine ultrasonore, un appareil de calibration (phantom CIRS Model 040GSE) a permis de comparer les résolutions et contrastes obtenus à l’aide de différents algorithmes. Il est montré que l’utilisation de la cohérence de phase dans le domaine de l’audible aide à la reconstruction de sources étendues. En effet, les formulations proposées sont basées sur une réduction du domaine d’imagerie à partir de la cohérence de phase. Cette réduction aide au conditionnement du problème et se traduit par une solution moins sensible au bruit. Aussi, contrairement aux techniques de formation de voies dans le domaine temporel, les algorithmes proposés permettent de reconstruire l’amplitude du champ vibratoire transitoire (vitesse/accélération normale) de sources étendues cohérentes. De plus, les cartographies obtenues présentent moins d’artefacts d’imagerie que les techniques de référence. En imagerie médicale par ultrasons, les résultats montrent que lorsque couplé avec une nouvelle métrique de cohérence de phase, l’algorithme Excitelet développé dans le formalisme de la Generalized Cross Correlation (répandue en imagerie acoustique) résulte en de meilleures résolutions et contrastes que l’algorithme de référence. Par ailleurs, l’utilisation de la métrique de cohérence de phase et du filtre fréquentiel proposé résulte en une diminution des artefacts d’imagerie. Enfin, étant flexible et grandement parallélisable, le formalisme d’imagerie proposé s’avère utile pour le suivi d’outils médicaux en anesthésie régionale guidée par ultrasons.Abstract : Imaging using acoustical waves can meet several needs. On the one hand, ultrasonic waves are used to perform ultrasound scans in the medical field, but also to inspect and monitor the health of structures. On the other hand, by using sound waves, it is possible to locate, characterize, and evaluate the intensity of various noise sources. Being driven by different applications and aims, the imaging techniques proposed and used in the last decades for these two fields differ. Given the common bases of sound and ultrasound imaging, it would be relevantto make each field benefit from the signal processing advances of the other field. This thesis project therefore suggests to firstly review the imaging techniques of the two imaging domains in order to identify promising imaging tools and techniques, and secondly adapt and use those concepts for the other imaging field. In order to test and validate different imaging approaches, two types of extended sources were considered in the audible domain. Numerically, baffled simply supported plates and pistons were considered. Experimentally, the maps obtained using different algorithms were compared with reference measurements obtained by optical deflectometry. In the ultrasonic field, a phantom (CIRS Model 040GSE) was used to compare the resolutions and contrasts obtained using different algorithms. It is shown that the use of phase coherence in acoustic imaging helps for the reconstruction of extended sources. Indeed, the proposed formulations are based on a reduction of the imaging domain using phase coherence. This reduction improves the conditioning of the problem and results in a less sensitive to noise solution. Also, contrary to delay and sum techniques, the proposed algorithm allows the reconstruction of the amplitude of the transient vibration field (normal acceleration) of the structure under consideration. In addition, the resulting images present fewer artifacts than the reference techniques. In medical ultrasound imaging, the results show that when coupled with a new phase coherence metric, the Excitelet algorithm developed in the formalism of Generalized Cross Correlation (widely used in acoustic imaging) results in better resolutions and contrasts than the reference algorithm. In addition, the use of the proposed phase coherence metrics and frequency filter results in a reduction of imaging artifacts. Finally, being flexible and highly parallelizable, the proposed imaging formalism shows potential for the monitoring of medical tools in ultrasound-guided regional anesthesia

Research and Technology Objectives and Plans Summary (RTOPS)

This publication represents the NASA research and technology program for FY87. It is a compilation of the Summary portions of each of the RTOPs (Research and Technology Objectives and Plans) used for management review and control of research currently in progress throughout NASA. The RTOP Summary is designed to facilitate communication and coordination among concerned technical personnel in government, in industry, and in universities. The first section containing citations and abstracts of the RTOPs is followed by four indexes: Subject, Technical Monitor, Responsible NASA Organization, and RTOP Number