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Nowadays, acoustic comfort is an important consideration in the design and operation of airplanes. In this context, an alternative approach, Statistical Energy Analysis (SEA) allows the study of energy diffusion in vibro-acoustic systems in mid and high frequency regions. This present study aims to describe the vibro-acoustic characterization of a structure similar to an aircraft fuselage. Several SEA models were considered to compare the analytical formulations found in the literature with measurement data. Two classes of the panels were investigated: simple and ribbed-stiffened. In this regard, the revised model for computing the coupling loss factors was evaluated and the results gave a good agreement with measured data.

Airborne sound transmission through vehicle panels is the main contributor to interior noise in high frequencies. This transmission can be reduced by the application of sound insulation materials. An insulator typically used in the dash panel treatment comprises a porous material layer bonded to a limp dense material. This porous layer dissipates sound energy mainly by viscous effects and reduces sound transmission. An accurate prediction of the insulator performance depends on the porous material model adopted and input material properties. Some simplified models take into account only a single longitudinal wave propagating in the porous medium since it is represented by an equivalent fluid with effective properties. More complex models, based on Biot's theory, also consider waves whose properties are more connected to the porous material frame. In this paper one-wave, two-wave and three-wave models are presented.

This paper presents an objective evaluation using order analysis to quantify the noise levels generated by the pumps of the power steering system mounted on a test stand and operating under two pressure load conditions (5 and 50 bar) in the working range between 500 and 5.000 rpm. Also, under these conditions experimental tests are carried out to verify the influence of the output pulsating pressure of the pump on the noise and vibration measurements.

The noise emitted by the heating, ventilation and air conditioning system (HVAC) has a great influence on the car acoustical comfort and quality perception. To improve its sound quality, physical properties which determine the subjective perception have to be identified. The HVAC-noise of twelve cars in different arrangements of fan speed and direction of air flow was recorded for later objective and subjective analysis. All cars were of the same model, but with three different types of HVAC-systems, and had just been manufactured. Objective analysis with sound quality software and subjective evaluations was carried out. Using multiple linear regressions on the subjective data, relations between subjective results and psychoacoustic metrics were determined and models to predict subjective response to HVAC sounds are proposed. It is shown that the annoyance caused by the HVAC-noise can be satisfactorily described by Zwicker's stationary loudness model.

The structural vibration modal parameters have to be optimize for any noise and vibration reduction aim. This paper shows the use of acoustic intensity to make a 4-cylinder diesel engine block experimental modal analysis. The results obtained by the acoustic intensity for natural frequencies were compared to the classical experimental modal analysis.

This paper presents the results of a vibro-acustic investigation carried out in a vehicle gearbox. The investigation consisted of modal analysis, measurements of insert loss and acoustic efficiency of the housing. A high insert loss was measured showing that the air-borne noise contribution can be neglected. On the other hand, the acoustic efficiency values for the gearbox housign show that the vibration characteristics of the structure have an essential influence on the structure-borne noise and noise radiation from the gear housing.

A model for piston slap force level prediction is being developed. The development project is scheduled to be carried out in three distinct steps, which are discussed here. Step one and part of two have already shown important features of the role of the oil film on the impact behavior. The Reynolds theory has been applied and a preliminary prediction model proposed. The piston-cylinder, wall-engine block structure is treated as 7 degree freedom system.

For the automotive industry, the sound quality inside the vehicles is very important. This importance has increased significantly in the last years within the globally competitive automotive market. The interior vibroacoustic behavior depends on the dynamic characteristics of the car body. Several treatments are used to reduce the structural energy of the body panels. For instance, it may be applied passive damping technology, by use of viscoelastic materials, to control their noise and vibrations. This paper presents a comparison of the vibroacoustic characteristics of two firewall panels, made with normal and quiet steel. Experimental and numerical (FEM and BEM) techniques are used to get modal and acoustic data.

Statistical Energy Analysis (SEA) is the standard method used to access noise and vibration levels in aircrafts and it has been applied to a wide range of problems in the aerospace industry. Even though much research has been carried on in the subject, some questions still remain about the process of modeling aircraft structures and the necessary validation steps. In this work, the development of a SEA model of a fuselage section is discussed. Special attention is given to the structure-borne noise transmission between the fuselage and floor panels and different modeling approaches are investigated. Data obtained through experimental tests were then used to verify the modeling approaches. It is seen that overall SEA results display a good agreement with tests. In the case of the floor panel, model results are very sensitive to modeling approaches and given that the transmission path is correctly represented, the SEA results reasonably match the experimental data.

The general spiral equation is an excellent tool in array development. However, some modifications can improve the array response for a certain range of frequencies. This work describes a different approach to the spiral equation aiming the project of a high frequency array (20 k - 35 k Hz). By constraining some of the array and measurements parameters, a geometry is proposed intending to maximize the dynamic range response at a focal point. The steps of this approach are discussed showing the results of the simulations for different parameters of this equation. Some of these parameters were fixed and for some others a parameter sweep was performed. The final geometry is intended to work with ultrasound applications, such as measurements of scale models, and also with the acoustic frequency range.

This article describes an objective methodology for measuring the noise attenuation of earmuff hearing protectors using as a reference the method known as microphone-in-real-ear (MIRE). The methodology implements the Insertion Loss (IL) paradigm, in which IL is measured using miniature microphones, specially designed to comply with ANSI and ISO standards for the MIRE technique. The results for a commercial hearing protector are compared with the subjective method known as real-ear-attenuation-at-threshold (REAT). Correction factors are included in the methodology to account for external effects such as physiological noise and bone conduction. The objective method predicted well the real protection of the earmuff and the proposed methodology showed lower standard deviation values than the REAT method.

During the last years, the automotive industry dedicated great efforts to understand and solve the noise problem from disc brake systems. There are several types of brake noise problems, each one related with a frequency range of occurrence. In most cases, the customer perceives the noise as a vehicle problem and demand having it fix by their dealer. As a consequence, disc brake noise is one of the major contributors to the automotive manufactures warranty costs, leading the automotive industry to look for ways to control it. A large class of disc brake noise problems is associated with the resonant behavior of an operating brake system. However, the detection of these brake system modes during the operating condition can be very expensive, demanding the use of inertial dynamometers and laser vibrometer measurements.

The acoustic development of vehicles is a very important step during its design to ensure its success in a competitive marketplace. In recent years, the advances on the noise and vibration control engineering in vehicles provided the production of quite and comfortable cars. The main noise and vibration sources in vehicles, i.e., engine, gearbox and exhaust systems, had its noise levels considered reduced, and, as a consequence, other noise sources became more easily observed. The noise generated by pumps of power steering systems is an example of this kind of problem. For the majority of automotive applications are used vane pumps. These pumps generate noise due the vane passing frequency. Basically, the hydraulic pump noise can be classified as Moan or Whine, regarding the operating condition. This work presents a methodology to approach the noise and vibration problem from hydraulic pumps of power steering systems.

The coincident of the excitation frequency, generated by the vehicle noise and vibration sources, with the acoustic resonance frequencies of the internal vehicle cavity, gives a full excitation of the acoustic modes and consequently a high noise pressure levels. The objective of this paper is to present experimental results and a numerical model by the finite element method for the determination of the resonance frequencies and acoustic modes of irregular shape of the vehicle cavity.

In recent years, SEA has been recognized as an important tool to model the vibro-acoustic behavior of vehicles in mid and high frequencies. Through SEA it is possible to develop vehicle models early in the design stage, reducing the risk of future noise problems and allowing the optimization of noise control treatments. Moreover, at the final design stages, a SEA model can be use to evaluate changes at the project, reducing costs with experiments. In a SEA model, the structure under study is divided in subsystems. The capacity of each subsystem of storekeeping, dissipating and transmitting energy is described by three parameters: modal density, loss factor and coupling loss factor. The noise and vibration sources are include in the model as power inputs to subsystem and, based on an equilibrium power balance, it is possible to calculate the energy of each subsystem.

Brake squeal noise has been under investigation by the automotive manufacturers for decades due to consistent customer complaints and high warranty costs. In most cases, the customer perceives the noise as a vehicle problem and demand having it fix by their dealer. J. D. Power surveys consistently show brake noise as one of the most critical vehicle quality measurements. Furthermore, the development of methods to predict the noise occurrence during the design of a brake system has been the target of many researchers in the last years. The complex eigenvalue analysis has been widely used to detect unstable frequencies in brake systems models. The method is fast and useful to provide design guidance, since operating parameters and control methods can be evaluated by a simulation procedure. This paper summarizes the application of the complex eigenvalue analysis in a finite element model of a commercial brake system.

The Statistical Energy Analysis – SEA is one of the main methods used to study the vibro-acoustic behavior of systems in the aeronautic, automotive and naval industries. The principal advantages of this method are the possibility of analysis in the mid and high frequencies range, the reduced computational costs when compared with other methods (like Finite Element Method or Boundary Element Method) and ease modeling of different sources of noise and vibration. As a statistical method, SEA provides results associated with average values in time, space and in an ensemble of similar structures. In aerospace applications, where the noise and vibration sources are usually random, SEA is particularly indicated. SEA also allows the straightforward modeling of the noise control treatments used in commercial aircraft and the further optimization of these treatments, reducing weight and costs. In this work, the steps followed at the development of an EMBRAER aircraft SEA model are presented.

In this study an objective metric is presented to evaluate the hiss noise of hydraulice power steering. The correlation between subjective tests and psychoacoustics metrics is investigated. The objective metric is obtained using multilinear regression where the psychoacoustics metric and the results of the subjective tests are the dependent and independent variables of the linear regression, respectively.

The application of sound quality tools in the design process of electro-hydraulic power steering (EHPS) is investigated in this paper. The EHPS acoustics performance is investigated by studying the correlation between objective measurements and subjective evaluation of the noise from the EHPS.

The use of a microphone array for acoustic measurements in wind tunnels is known to degrade the sound pressure levels and dynamic range of the acoustic image, due to the decorrelation between each pair of microphones, after the acoustic wave has crossed the turbulent boundary layer of the wind tunnel. Based on a large number of studies in the areas of radiophysics, underwater acoustics and atmospheric science, this paper describes research on a physical model of wave propagation in a turbulent medium and its stochastic solution, obtaining as a solution the statistical momentum of the wave signal after it has propagated through the turbulent medium. The parabolic equation for acoustic wave propagation is considered and the Markov approximation is assumed for the stochastic solution of the wave. The signal coherence between each pair of microphones is the amount considered responsible for the decorrelation of the signals.