QC 20110617

The aim of this study is to develop a sound transmission model that can be used to predict the vibration and noise levels of a submerged vessel. The noise transmitted from the mechanical vibrations of the hull of a submarine and the turbulent boundary layer excitation on the submarine are investigated. A simplified physical model of the submarine hull including the effects of bulkheads, end enclosures, ring stiffeners and fluid loading due to the interaction of the surrounding medium is presented in the study. An energy approach, i.e., Statistical Energy Analysis (SEA) is used for the analysis because the characterization of the hull of the structure can be done by a very large number of modes over the frequency range of interest and the deterministic analysis methods such as finite element and boundary element methods are limited to low frequency problems. The application consists of the determination of SEA subsystems and the parameters and the utilization of power balance equations to estimate the energy ratio levels of each subsystem to the directly excited subsystem. Through the implementation of SEA method, the sound pressure levels of the hull of the structure are obtained. In terms of military purposes, the sound levels of the submarine compartments are vital in the aspects of the preserving of submarine stealth.

This research demonstrates the usage of numerical acoustics to model sound and vibrational energy propagation in HVAC ducts and plenums. Noise and vibration in HVAC systems propagates along three primary paths that can be classified as airborne direct, airborne indirect and structure-borne. The airborne direct path was simulated using acoustic FEM with special boundary conditions to handle the diffuse acoustic field loading and the baffled termination. The insertion loss for a number of different plenum geometries was compared to published measurement results. Results were in good agreement both below and above the cutoff frequency. Additionally, the airborne indirect path, often termed breakout noise by the HVAC community, was assessed using Statistical Energy Analysis (SEA). This path was examined experimentally by placing a loudspeaker inside the air handler and measuring the sound power transmitted through the walls. SEA results compared favorably with the measured results in one-third octave bands even at low frequencies. Finally, the structure-borne path was considered by exciting the walls of the aforementioned air handler using an electromagnetic shaker. The panel vibration and the sound power radiated from the panels were measured. Results were compared with the SEA with good agreement provided that SEA loss factors were determined experimentally.

No description available.

Noise emission is a major drawback of the positive displacement machine. The noise source can be divided into structure borne noise source (SBNS) and fluid borne noise source (FBNS). Passive techniques such as valve plate optimization have been used for noise reduction of axial piston machines. However, passive techniques are only effective for limited operating conditions or at least need compromises in design. In this paper, active vibration control of swash plate is investigated for vibration and noise reduction over a wide range of operating conditions as an additional method to passive noise reduction techniques. A 75cc pump has been modified for implementation of active vibration control using the swash plate. One tri-axial acceleration sensor and one angle sensor are installed on the swash plate and a high speed servovalve is used for the swash plate actuation. The multi-frequency two-weight least mean square (LMS) filter synthesizes the servovalve input signal to generate a destructive interference force which minimizes the swash plate vibration. An experimental test setup has been realized using Labview field-programmable gate array (FPGA) via cRIO. Simulation and experimental studies are conducted to investigate the possibility of active vibration control.

A vibration isolator is designed to reduce the vibration and structure borne noise transmitted from a vibratory source, such as machinery and equipment, to the supporting structure. The vibration and structure borne noise transmitted depends upon the dynamic properties of the foundation, the source mounting point and the vibration isolator. Therefore knowledge of the frequency dependent dynamic properties of vibration isolators is a necessary part of the acoustic prediction and control/reduction process. Vibration isolators may be characterised by measuring their four-pole parameters. A measurement procedure is proposed that employs the floating mass method, measures the direct forces and corrects for the errors introduced by the direct force measurement. Compared to the basic method, it extends the frequency limits of measurement in both directions. The development of a novel vibration isolator test facility that implements the proposed measurement procedure is described, and its satisfactory operation is experimentally demonstrated. The vibration isolator test facility is capable of characterizing vibration isolators commonly used in industrial and maritime applications, under service conditions. A method is proposed for measuring the four-pole parameters of a uni-directional asymmetrical vibration isolator under static load. The method is called the two masses method, and is suitable for determining the four???pole parameters of active vibration isolators with feedback control. The method is also applicable to uni-directional symmetrical and bi-directional symmetrical and bi-directional asymmetrical vibration isolators. It may be regarded as a universal method for characterising vibration isolators. Experimental data is presented and the method is validated. Modelling of vibration isolators is complicated by the highly non-linear nature of their rubber elements. The notion of an effective rubber cylinder is proposed to account for the barrelling of rubber elements under static load. Consequently, a general static compression model is proposed that applies to vibration isolators having unfilled and filled rubber elements of regular prismatic shapes. The model predicts the dependence of the four-pole parameters on the compression ratio of the rubber element. The predictions derived from the effective rubber cylinder and general static compression model agree excellently with experimental work of this study and other researchers.

A vibration isolator is designed to reduce the vibration and structure borne noise transmitted from a vibratory source, such as machinery and equipment, to the supporting structure. The vibration and structure borne noise transmitted depends upon the dynamic properties of the foundation, the source mounting point and the vibration isolator. Therefore knowledge of the frequency dependent dynamic properties of vibration isolators is a necessary part of the acoustic prediction and control/reduction process. Vibration isolators may be characterised by measuring their four-pole parameters. A measurement procedure is proposed that employs the floating mass method, measures the direct forces and corrects for the errors introduced by the direct force measurement. Compared to the basic method, it extends the frequency limits of measurement in both directions. The development of a novel vibration isolator test facility that implements the proposed measurement procedure is described, and its satisfactory operation is experimentally demonstrated. The vibration isolator test facility is capable of characterizing vibration isolators commonly used in industrial and maritime applications, under service conditions. A method is proposed for measuring the four-pole parameters of a uni-directional asymmetrical vibration isolator under static load. The method is called the two masses method, and is suitable for determining the four???pole parameters of active vibration isolators with feedback control. The method is also applicable to uni-directional symmetrical and bi-directional symmetrical and bi-directional asymmetrical vibration isolators. It may be regarded as a universal method for characterising vibration isolators. Experimental data is presented and the method is validated. Modelling of vibration isolators is complicated by the highly non-linear nature of their rubber elements. The notion of an effective rubber cylinder is proposed to account for the barrelling of rubber elements under static load. Consequently, a general static compression model is proposed that applies to vibration isolators having unfilled and filled rubber elements of regular prismatic shapes. The model predicts the dependence of the four-pole parameters on the compression ratio of the rubber element. The predictions derived from the effective rubber cylinder and general static compression model agree excellently with experimental work of this study and other researchers.

Orientador: Jose Roberto de França Arruda / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-06T11:13:15Z (GMT). No. of bitstreams: 1 Padilha_PauloEduardoFranca_M.pdf: 721382 bytes, checksum: 8fae387ba335cdb5b3e7b462935121c1 (MD5) Previous issue date: 2006 / Resumo: Neste trabalho é feita uma comparação de técnicas analíticas e experimentais de Análise de Caminhos de Transferência Vibroacústicos. A Análise de Caminhos de Transferência, ou TPA como é conhecida pela abreviatura em inglês, é uma ferramenta para se avaliar a contribuição de diferentes caminhos de propagação de energia vibroacústica entre uma fonte e um receptor ligados entre si por várias conexões. Uma aplicação típica de TPA é quantificar e determinar a importância relativa desses caminhos numa dada banda de freqüência, verificando-se a contribuição mais significativa para o receptor. Nessa análise, basicamente duas quantidades devem ser obtidas: as forças operacionais em cada caminho de transferência e a Função de Resposta em Freqüência desses caminhos. Essas funções podem ser obtidas tanto experimentalmente quanto analiticamente, considerando-se ou não a impedância mecânica da fonte vibroacústica. As forças operacionais podem ser diretamente obtidas de medições, usando um transdutor de forças, ou indiretamente estimadas a partir de medições auxiliares. Neste trabalho são apresentados dois métodos de obtenção indireta das forças operacionais ¿ o Método da Rigidez Complexa e o Método da Inversão de Matrizes ¿ associados com as duas possíveis configurações para determinação das Funções de Resposta em Freqüência ¿ incluindo e excluindo a impedância da fonte. Essas técnicas são aplicadas a dois modelos: um analítico e um experimental. avaliadas com esse modelo analítico, comentando-se suas vantagens e desvantagens. São avaliados ainda os efeitos do acoplamento entre fonte e receptor e entre os caminhos de transferência. Os experimentos foram realizados numa estrutura concebida como um modelo simplificado de um automóvel. As forças foram obtidas através dessas duas técnicas indiretas e comparadas com as medidas com transdutores de força. Como no modelo analítico, as forças e FRF foram estimadas na presença e na ausência da fonte, e a contribuição de cada caminho calculada através dessas técnicas e configurações. A resposta do receptor, calculada como uma combinação dos diferentes caminhos de transferência, foi comparada à medida nas condições operacionais, de modo a se verificar a exatidão de cada método utilizado. As vantagens e limitações desses métodos e configurações experimentais são então comentadas para uso em aplicações práticas / Abstract: In the present work, analytical and experimental techniques of Vibro-Acoustic Transfer Path Analysis are compared and discussed. Transfer Path Analysis (TPA) is a tool to evaluate the contribution of different vibro-acoustic energy propagation paths between a source and a receiver linked to each other by a number of connections. TPA is typically used to quantify and rank the relative importance of these paths in a given frequency band, determining the most significant one to the receiver. When applying TPA two basic quantities have to be determined: the operational forces at each transfer path and the Frequency Response Functions of these paths. These functions can be obtained either experimentally or analytically, considering or not the mechanical impedance of the source. Operational forces can be directly measured by force transducers or indirectly estimated from auxiliary response measurements. Two methods to obtain the operational forces indirectly ¿ the Complex Stiffness Method and the Matrix Inversion Method ¿ associated with two possible configurations to determine the Frequency Response Functions ¿ including and excluding the source impedance ¿ are presented and discussed in this work. These estimation techniques are applied to two models: an analytical and an experimental model. Analytically, these techniques are applied to a lumped parameter model. The advantages and drawbacks of them are commented and the effect of coupling between source and receiver and among transfer paths is analyzed with this theoretical approach. The experiments are done in a test structure conceived as a simplified model of an automotive vehicle. The forces are obtained via these two techniques and compared to those measured by force transducers. Like in the analytical model, forces and Frequency Response Functions are estimated in the presence and in the absence of the source, and the contribution of each path is calculated based on the combinations of these different estimation methods and setups. The contributions of the different paths at the receiver location are calculated using each estimation method and are compared to those obtained in the operational condition in order to verify the accuracy of these methods. The advantages and limitations of the methods and test setups are then discussed for use in practical applications / Mestrado / Mecanica Computacional / Mestre em Engenharia Mecânica

With advancements in technology, electric vehicles are dominating the world making Internal Combustion engines less relevant, and hence vehicles are becoming quieter than ever before. But noise levels remain a significant concern for both passengers and automotive manufacturers. The vehicle's interior noise can affect the overall driving experience and even the safety of the driver and the passengers. The two main sources of vehicle interior noise are attributed to air-borne noises and structure-borne noises. A modern automobile is a complicated vibration system with several excitation sources like the engine, transmission system, tire/road interface excitation, and wind noise. With electric vehicles on the rise, the engine and transmission noise is practically eliminated, and effective preventive measures and control systems are already in place to reduce the aerodynamic-based noise, vibrations, and harshness (NVH) in modern automobiles making the structure-borne noise the most crucial of the noise sources. Tire/road interaction noise being the most dominant among the structure-borne noise is the main concern of the vehicle interior noise. The two main sources of vehicle interior noise induced by the tire pavement interaction noise are structure-borne noise induced by the low-frequency excitation and air-borne noises produced by the mid and high-frequency excitation. The present study tested an all-season tire over varying operational conditions such as different speeds, normal loads, and inflation pressures on an asphalt surface. Two tri-axial accelerometers attached 1800 apart from each other on the inner liner of the tire of a Volkswagen Jetta were used to measure the circumferential, lateral, and radial acceleration data. An Inertial Measurement Unit (IMU) and velocity box (VBOX) were instrumented in the vehicle to measure the acceleration at the center of gravity (COG) position of the vehicle and the longitudinal velocity of the vehicle respectively. The vehicle was also equipped with a modified hybrid of Close Proximity Testing (CPX) and On-Board Sound Intensity (OBSI) sound measurement systems which were designed and manufactured in-house to measure the tire/road interaction noise at the leading and trailing edges of the tire/road contact patch. Another microphone was instrumented inside the passenger compartment of the vehicle at the passenger's seat right ear position over the tire mounted with the sound measurement system to measure the vehicle interior noise as interpreted by the passengers in the vehicle. Two data acquisition systems coupled with a real-time Simulink model were used to collect all the measured data, one for the noise signals and the other for velocity and acceleration signals. The focus of the current study is to review different generation and amplification mechanisms of the structure-induced tire/road interaction noise and find the relevant dominant frequency ranges of the vehicle interior noise induced by the structure-borne noises using already established physics-based models and correlation techniques. It also aims to find correlations between tire acceleration, vehicle interior noise, and tire pavement interaction noise and their effect on different operational conditions like load, inflation pressure, and velocity. All the signals are studied in the time, frequency, and spectral domain and insights have been drawn on different tire/road noise generation and amplification mechanisms. / Master of Science / Structure-induced vehicle interior noise is one of the main concerns surrounding the automotive NVH industry and tire/road interaction noise being the most dominant source among the structure-borne noises affecting the vehicle interior noise is a major problem to the tire and automotive manufacturers nowadays. It leads to discomfort for the driver and the passengers in the vehicle and can cause fatigue, which in turn can directly affect the vehicle's safety. Several attempts have been made to reduce vehicle interior noise using statistical, physics-based, and hybrid models, but the research is still nowhere near completion. The current study aims to identify the frequency ranges affecting the structure-borne noise-induced vehicle interior noise and uses data-driven approaches in estimating the vehicle interior noise using only the acceleration of the tire. A test setup was designed and developed in-house where a tri-axial accelerometer embedded inside the inner liner of the tire measures the X, Y, and Z acceleration signals. Several microphones are instrumented at the tire/road contact surface and inside the passenger cabin to measure the tire/road interaction noise and the vehicle interior noise. The longitudinal velocity of the vehicle and the accelerations at the center of gravity of the vehicle have also been measured. Multiple data-driven models have been developed to directly predict the vehicle interior noise and tire/road interaction noise using the accelerometer data. This research is directly helpful for the automotive and tire industries by giving them insights on designing and developing quieter tires by using data-driven approaches and further using these with active control systems can mask the vehicle interior noise to acceptable levels in real-time.

Noise emission is a major drawback of the positive displacement machine. The noise source can be divided into structure borne noise source (SBNS) and fluid borne noise source (FBNS). Passive techniques such as valve plate optimization have been used for noise reduction of axial piston machines. However, passive techniques are only effective for limited operating conditions or at least need compromises in design. In this paper, active vibration control of swash plate is investigated for vibration and noise reduction over a wide range of operating conditions as an additional method to passive noise reduction techniques. A 75cc pump has been modified for implementation of active vibration control using the swash plate. One tri-axial acceleration sensor and one angle sensor are installed on the swash plate and a high speed servovalve is used for the swash plate actuation. The multi-frequency two-weight least mean square (LMS) filter synthesizes the servovalve input signal to generate a destructive interference force which minimizes the swash plate vibration. An experimental test setup has been realized using Labview field-programmable gate array (FPGA) via cRIO. Simulation and experimental studies are conducted to investigate the possibility of active vibration control.