Effect of elastic boundary supports and stiffening treatments on vibroacoustic response of plate-like structures

xx, 135 leaves : ill. ; 30 cm.PolyU Library Call No.: [THS] LG51 .H577P BSE 2011 OuMost of the complicated structures or systems in buildings or engineering industries can be modeled as thin plates. A better understanding of the vibroacoustic behavior of thin plates can be useful for improving the sound insulation of a practical structure. In this thesis, the vibroacoustic responses of unstiffened and stiffened, thin plates with arbitrary elastic boundary supports (or called "elastic boundary conditions") were investigated. Both the steady-state and the transient vibroacoustic behaviors of the plate were studied. The aim of this thesis was to examine the effects of the elastic boundary supports and the stiffeners on the vibroacoustic performance of plate structures in order to provide guidance to the design and installation of plate-like structures for sound insulation. A method was first developed to determine the actual boundary condition of the plate system; this was based on a coupled finite element and boundary element method (FEM/BEM) in frequency domain. The fluid loading effect was taken into account by coupling the acoustic equation with the elastic equation. This model was then improved and applied to predict the steady-state vibration and sound radiation (SVSR) of a stiffened plate; this allowed for an efficient computation of a plate with arbitrary boundary conditions and with arbitrarily located stiffeners. The effects of the stiffeners on the sound transmission loss (STL) of a window were then studied in the parametric studies. Another method was proposed to predict the transient vibration and sound radiation (TVSR) of a plate with arbitrary elastic boundary supports, which was based on the time-domain finite element method (TDFEM) and time-domain boundary element method (TDBEM). This model was then improved and applied to predict the TVSR of a stiffened plate. In parametric studies, the maximum acceleration and maximum radiated sound pressure were calculated to examine the effects of the boundary supports and the stiffeners. Extensive experiments were carried out in two connected semi-anechoic chambers at The Hong Kong Polytechnic University; these included the STL measurements of unstiffened and stiffened plate structures and the transient sound radiation measurements of unstiffened and stiffened plate structures. The proposed boundary condition identification method was used to identify the actual boundary conditions of the plate structures used in the experiments. The measured results were used to validate the prediction methods. The predicted results agreed well with measured data. Both the results of the experiments and the parametric studies clearly demonstrated the significant effects of the elastic boundary supports and the stiffeners on the vibroacoustic responses of a practical plate structure. It is believed that the sound insulation (or vibration isolation) performance of a plate structure can be improved through an appropriate use of the elastic boundary supports or stiffeners or both. The proposed prediction models can therefore be effective design tools for this purpose.Department of Building Services EngineeringPh.D., Dept. of Building Services Engineering, The Hong Kong Polytechnic University, 201