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Title: Vibroacoustics of plates excited by water drop impacts
Author: Yu, Y.
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2019
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Rainfall on windows and roofs of buildings, and the roofs and windscreens of cars can generate high levels of re-radiated sound that may adversely affect speech communication or other activities. This thesis concerns the prediction and experimental analysis of vibroacoustics of plates excited by water drop impacts. The impact force applied by single raindrops on both dry and wet surfaces is quantified experimentally. Single liquid water drops with 2 and 4.5 mm diameter were tested at a range of drop velocities when the plate is dry and with a shallow water layer. Force transducer measurements and wavelet deconvolution were used to measure the time-dependent force. When the response signal has a low SNR value (< 10 dB), wavelet deconvolution becomes less robust and the sparse representation method was used to improve the accuracy and preserve the initial phase of the impact force. The validity of theoretical models for the impact force from a drop on a dry surface has been assessed through comparison with experimental data. The inability of these models to describe the time-dependent force provided the motivation to develop empirical formulae. Based on the experimental data, empirical formulae were developed for 2 and 4.5 mm drops falling at (a) different velocities up to and including terminal velocity onto a dry glass surface, (b) terminal velocity onto dry glass or glass with a shallow water layer up to 10 mm and (c) different velocities below terminal velocity onto dry glass or glass with a shallow water layer up to 10 mm. A correction to the empirical model for drop impacts at an oblique angle was accounted for by using the perpendicular velocity component, which was validated with experiments. Numerical models have been validated using Statistical Energy Analysis (SEA) and Finite Transfer Matrix Method (FTMM) with the empirical model to estimate the vibration and sound radiation from a single glass plate and a multilayer plate represented by a plate-foam-plate system. To improve computational efficiency, an order reduced integral with travelling wave method for finite plate size correction of FTMM method has been proposed. An experiment with artificial rainfall was used to assess the accuracy of the numerical models for terminal velocity and the lower velocity (3.65 m drop height). The empirical model was used to quantify the power input into a plate from natural rainfall using numerical experiments.
Supervisor: Hopkins, Carl Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral