Estudo sobre o descasamento de frequência em sistemas de controle ativo de ruído para ruídos de banda estreita

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia ElétricaEsta dissertação discute um problema inerente aos sistemas de controle ativo de ruído (active noise control - ANC) de topologia feedforward que visam atenuar exclusivamente ruídos acústicos de banda estreita (ruídos tonais). Nesse tipo de sistema, sensores de referência não acústicos (tacômetros, sensores ópticos, dentre outros) são utilizados para medir a frequência fundamental do ruído primário. Tal medida é utilizada para sintetizar sinais de referência senoidais que são processados por controladores adaptativos, os quais são responsáveis pela geração de um sinal de antirruído. Esse sinal, através de um transdutor, é inserido no domínio acústico visando se obter o cancelamento do ruído primário. Para essa classe de sistema de ANC é observada uma forte degradação de desempenho quando os sinais de referência são gerados com frequências distintas daquelas que compõem o ruído primário. Tal problema, comumente denominado descasamento de frequência, é o objeto principal dos estudos deste trabalho de pesquisa. Nesse contexto, os principais sistemas de ANC robustos ao problema de descasamento de frequência, encontrados na literatura, são estudados, culminando na proposta de um novo sistema com baixa sensibilidade a tal descasamento. Resultados de simulação atestam que o sistema proposto apresenta muito bom desempenho, especialmente quando o ruído a ser cancelado é não estacionário e o seu componente fundamental é o de maior potência.This dissertation presents an inherent problem of narrowband feedforward active noise control (ANC) systems. In this class of systems, nonacoustic reference sensors (tachometers, optic sensors, among others) are used to measure the fundamental frequency of the primary noise. The obtained measurement is used to synthesize sinusoidal reference signals that are processed by adaptive controllers, which are responsible for generating the antinoise signal. The antinoise is inserted into the acoustic environment by using a transducer, aiming to cancel the primary noise. In this class of ANC systems, a strong performance degradation is observed when the reference signals are synthesized with different frequencies of those that compose the primary noise. This problem, usually called frequency mismatch, is the main topic of study in this research work. In this context, the main ANC systems robust to frequency mismatch from the literature are dicussed as well as a new system exhibiting low sensibility to the frequency mismatch is proposed. Simulation results attest very good performance of the proposed system, particularly in scenarios in which the primary noise is nonstationary and its fundamental component has larger power

Active Control of Pressure Pulsation in a Switched Inertance Hydraulic System

The nature of digital hydraulic systems may cause pressure pulsation problems. For example, switched inertance hydraulic systems (SIHS), which are applied to adjust or control flow and pressure by a means that does not rely on dissipation of power, have noise problems due to the pulsed nature of the flow. An effective method to reduce the pulsation is important to improve system performance and increase efficiency. Although passive systems to reduce the noise have been shown to be effective in many situations, their attenuation frequency range is limited and they may be bulky. Furthermore, attenuation devices based on expansion chambers, accumulators or hoses are likely to be unsuitable for SIHS as they add compliance to the system and would impair the dynamic response. This thesis is concerned with issues relating to the development of an active noise canceller for attenuating the pressure pulsation which is caused primarily by pulsed flow from high-speed valves in SIHS. Active control methods are widely and successfully applied in the area of structureborne noise (SBN) and air-borne noise (ABN) cancellation. The idea is using the intentional superposition of waves to create a destructive interference pattern such that a reduction of the unwanted noise occurs. However, applications for fluid-borne noise (FBN) attenuation based on the ‘Active noise control (ANC) principle’ are rare due to the restriction of the hardware and experimental apparatus in previous researches. In this thesis, an adaptive controller has been developed for active control of pressure pulsation in hydraulic system. The principle of the adaptive LMS filter and details of the controller design are described and the implementation was carried out through simulation. The designed controller was applied on a vibration test rig initially prior to the hydraulic testing in order to investigate its advantages and limitations in practice. Extensive testing on a switched inertance hydraulic rig proved that the controller, which used a piezoelectric valve with fast response and good bandwidth, is effective and that it has several advantages over previous methods, being effective for low frequency cancellation, with a quick response, and is robust and versatile. A novel method for the accurate measurement of unsteady flowrate in a pipe was proposed. This was applied and validated on a pipe, and was shown to give good results. This method solves the difficulty for measuring the unsteady flowrate currently by using easy-measured signals, such as pressures. It can be used widely for predicting the unsteady flowrate along the pipe.EThOS - Electronic Theses Online ServiceGBUnited Kingdo