(A) study on the acoustic characterization of porous woven hoses

Abstract

The reduction of intake noise is a very important factor in controlling the interior noise levels of cars, particularly at low and major engine operating speeds. Several of the resonators in an intake system can be replaced by one porous hose section, thus suppressing the intake resonances. Additional advantage of the porous woven hose is the flexibility, which enables ease in the system layout and vibration isolation. Due to this fact, the porous woven hose is now considered to be a very promising and efficient silencing component. It is noted that overall physical characteristics of the porous woven hose have been rated by a parameter, which is mainly affected by the length, radius, weaving quality, and coating conditions. This parameter is referred to as the ``porous frequency`` in Hz by the manufacturers, as well as NVH engineers in major automotive companies in the world. For predicting the silencing performance of an intake system with a porous woven hose, information on the acoustic wall impedance is essential. However, accurate measurement of the impedance of porous woven hoses is not easy because of its peculiar acoustical and structural characteristics: very high flow resistance, thickness variation due to small corrugations, curvature of the whole hose segment, local inhomogeneities in materials composition and weaving, and the cylindrical shape. It appears that there are not many previous works about porous woven hoses to mention and no research has been given for measurement of impedance of porous woven hose. In this thesis, the study has been directed toward developing the measurement techniques for the acoustic impedance of a porous woven hose, which can overcome the difficulties related to its peculiar physical characteristics. Firstly, the acoustic properties and physical nature of the porous woven hose have been studied. The physical characteristics of company-specified ``porous frequency`` was investigated and a proper interpretation of its p...