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This article presents a comparative analysis of the influence of different types of flows over fan noise propagation and scattering within the nacelle intake of aircraft turbofan engines. The methodology for the noise simulation is explained. First, the fan noise source is modeled using a boundary condition that represents all the uncorrelated cut-on modes in the interior of the nacelle duct. Then different types of flows and flight conditions are considered in order to determine the influence of the aerodynamic phenomenon in the noise emitted by the nacelle intake. The liner attenuation is also simulated by mean of Myers boundary condition. Finally the results for far field noise are validated against numerical data obtained from the literature for hard and lined wall conditions.

The Hybrid FE-SEA method is a recently developed numerical technique that deals with the so-called mid-frequency problem. Such problems involve the dynamic analysis of systems that include, at the same frequency range, components with high and low modal density. Systems with a reduced number of modes are usually modeled using deterministic methods, as the Finite Element (FE) Method, while modal dense systems need to be treated by means of statistical methods such as the Statistical Energy Analysis (SEA). Neither FE nor SEA can properly describe a system that displays the mid-frequency behavior due to a prohibitive computational cost (FE) or the lack of accuracy (SEA). The floor structure of an aircraft is a typical case of a mid frequency problem, where the floor beams are relatively rigid and have very few modes while the floor panels have a very high modal density.

Currently, the use of numerical and analytical tools during a vehicle development is extensive in the automotive industry. This assures that the required performance levels can be achieved from the early stages of development. However, there are some aspects of the vibro-acoustic performance of a vehicle that are rarely assessed through numerical or analytical analysis. An example is the modeling of sound transmission through vehicle sealing systems. In this case, most of the investigations have been done experimentally, and the analytical models available are not sufficiently accurate. In this paper, the modeling of the sound transmission through a vehicle door seal is presented. The study is an extension of a previous work in which the applicability of the Hybrid FE-SEA method was demonstrated for predicting the TL of sealing elements.

During the last decades, the application of noise control treatments in vehicles has targeted the main noise transmission paths to interior noise. These paths include vehicle body panels such as dash panel, doors and floor. Many improvements have been achieved on these areas, and, as a consequence, other transmission paths once thought as secondary became relevant. This is the case of the sound transmission through door seals and others sealing elements at mid and high frequencies. In this paper, the interest lies on the prediction of the transmission loss of door seals. A full nonlinear deformation/contact analysis is used to estimate the deformed geometry of a door seal in real conditions. The geometry is then used in a vibro-acoustic analysis to predict the in-situ transmission loss of the seal using a local Hybrid FE-SEA model. The channel between the door and the car structure where the seal is located is also included in the analysis.

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.

Noise transmission paths in an aircraft include, in many cases, both components with a few modes and others with a high modal density. The components with few modes display a long wavelength behavior and are usually modeled using the Finite Element Method (FEM). On the other hand, components with many modes show a short wavelength behavior and suit the application of the Statistical Energy Analysis (SEA). An example of this kind of transmission path is given by the vibration transmission from the fuselage to the floor panels through the floor beams. The fuselage and the floor panels possess a high modal density while the floor beams are considerably stiff and display a small number of modes. The prediction of the vibro-acoustic response of such systems is commonly called the “mid frequency problem” and, until recently, was difficult to be handled with traditional modeling approaches. A Hybrid method that rigorously couples SEA and FEM has been recently proposed.

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 is a problem that has been faced by several methods in the last decade. Among then, finite element analysis is proving to be a useful tool to predict the noise occurrence of a particular brake system during the design stage. The Finite Element Method (FEM) has been employed to detect unstable frequencies using a complex eigenvalue analysis. These unstable frequencies are related, in most cases, with high sound pressure levels generated during the brake system operation and its detection is an important step in order to produce quiet brake systems. Although the method is fast and provides guidance for solving engineering problems, it is very sensitive to input parameters like material properties and boundary conditions. For brake system modeling, the determination of the contact stiffness between rotor and pads is a crucial point, since one of the major contributing mechanisms to generate squealing frequencies is the modal coupling between these two components.

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.