Search Results

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.

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.

Vibration levels of structures can be significantly reduced by adding some damping materials to the vibrating surfaces. The viscoelastic behavior of these materials induces losses of kinetic energy when they undergo cyclic deformation. A good estimate of the damping loss factor is an important design parameter allowing the creation of efficient damping treatments. For Statistical Energy Analysis (SEA) purposes, the damping loss factor is usually estimated through the Power Injection Method (PIM). This paper presents the application of PIM to obtain the damping loss factor of a typical fuselage panel. In this case, the structure under study is a curved ribbed-stiffened panel. Tests are carried out for undamped and damped conditions. The added damping is provided by layers of viscoelastic material attached to the fuselage skin. The results show the applicability of the method for this kind of structure.

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.

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.

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.