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With the increase in aircraft transportation and, consequently, aircraft noise in the last decades, measurement of acoustic liner impedance under grazing flow has become a point of interest. Different indirect methodologies have been developed by independent research groups to solve this problem. The Mode-Matching technique and, more recently, the Two-Port method are examples of developed methodologies that use acoustic pressure measurements in a test rig where a liner sample is subject to grazing mean flow to educe its impedance. In this paper, both methods are explained, implemented and used to educe the acoustic impedance of different liner samples in a recently developed grazing flow impedance eduction test rig. Additionally, both methods are compared based on their computational cost and limitations.

Statistical Energy Analysis (SEA) is an effective tool for evaluating the acoustic performance of a vehicle structure and sound package. SEA is typically used to predict both interior noise levels and to set noise reduction targets for various components. A typical full vehicle SEA model includes acoustic loads from airborne sources such as engine, tire and exhaust noise [1]. Each source is typically spatially compact (for example, a tire contact patch) but the source radiates sound that then propagates across the entire exterior surface of the vehicle. In order to characterize a source it is therefore necessary to know both the sound pressure level in the vicinity of the source and also the way in which sound from the source diffracts around the vehicle. A companion paper has investigated the numerical prediction of the diffraction of acoustic sources around a vehicle using the Fast Multipole Boundary Element Method [2].

Seals and slits are often an important transmission path for vehicle interior noise at mid and high frequencies, and they are therefore often included in system level SEA models of interior noise. The transmission loss of seals and slits in such models is typically either measured experimentally or predicted using simple analytical models. The problem with the former is that it is expensive to investigate different design options using test; the problem with the latter is that simple analytical models often do not contain enough detail. The objective of this paper is therefore to investigate how much detail is needed in order to predict the transmission loss of typical slits and seals. Typical door seals are not directly exposed to exterior and interior sound fields, but instead are inserted in complicated “channel” sections formed by the door and pillar or rail structures. This study is therefore divided in two parts.

The Finite Element Method (FEM) and the Statistical Energy Analysis (SEA) are standard methods in the automotive industry for the prediction of vibrational and acoustical response of vehicles. However, both methods are not capable of handling the so called “mid frequency problem”, where both short and long wavelength components are present in the same system. A Hybrid method has been recently proposed that rigorously couples SEA and FEM. In this work, the Hybrid FE-SEA method is used to predict interior noise levels in a trimmed full vehicle due to broadband structure-borne excitation from 200Hz to 1000Hz. The process includes the partitioning of the full vehicle into stiff components described with FE and modally dense components described with SEA. It is also demonstrated how detailed local FE models can be used to improve SEA descriptions of car panels and couplings.