Study On The Vibroacoustic Coupling Characteristics Of A Rectangular Enclosure With Multiple Flexible Panels And Adhesive Bonding Boundary Constraints

Although with a relatively late start, China’s automotive industry has been undergoing a rapid development in the past decade. Since the past three years, China has been consistently ranked No.1 worldwide in terms of car manufacturing and sales. With ever-increasing volume of cars on the road, the NVH performance concerning the ride comfort and environmental noise prolusion has attracted more and more attention. From NVH perspectives, interactions of vehicle body panels and the enclosed air cavity can be excited by many sources. To investigate the vehicle vibration and noise performance, characteristics of acoustic-structural coupled system are usually the first step to start.This study discusses the acoustic-structural responses of a rectangular enclosure consisting of one or more flexible panels under various external excitation conditions. A finite element model is developed to simulate a rectangular enclosure with a single flexible panel, dual flexible panels on opposite sides or dual flexible panels on adjacent sides. The structural-acoustic coupled characteristics of the enclosure is investigated for cases of reverberation filed excitation (RFE) and concentrated force excitation (CFE). For the CFE case, four point forces with phase difference of 0°,45°,90° and 180° are considered. And the relationship between the sound level in enclosure and difference between two phase degrees in concentrated force excitations are analyzed.Next, the simply supported boundary conditions of flexible plates is extended to arbitrary boundary conditions to discuss the effect of different boundary conditions on the structural-acoustic characteristics of a rectangular enclosure. A connection layer (CL) structure is added into the finite element model of this coupling system, and the parameters of connection layer including young’s modulus, poisson’s ratio, damping coefficient, density, thickness and width are varied to simulate arbitrary boundary conditions. Sound pressure responses under different parameters (thus different boundary conditions) are investigated. The simulation results are verified qualitatively using the modal coupling theory.Finally, using the analytical results obtained from the finite model, the adhesive bonded boundary condition (treated as the arbitrary condition in the model) effect on the structural-acoustic characteristics of an actual vehicle structure is investigated. In detail, the effect of vibration fatigue on modal properties of single lap adhesive joints is investigated both experimentally and analytically. Combing this result and the results obtained from the structural-acoustic finite element model containing arbitrary boundary conditions, an optimization method is then developed with which the adhesive boundary parameters can be optimized to minimize the noise radiation level inside a vehicle, thus increasing its NVH performance.