Direct sound radiation from random structures

This dissertation reports a theoretical and numerical study on direct sound radiation from vibrating structures having uncertainties. The motivation for this research is the lack of existing statistical calculations for direct sound radiation. Statistical Energy Analysis is a method commonly used in analyzing complex dynamic systems in high frequency ranges. However, direct sound radiation from the system is not widely investigated yet. A plate and a sphere were selected as two basic vibrating structures, and the uncertainties are modelled using randomly positioned point masses on the structures. Previous researches on sound radiation and statistics related to this dissertation are first summarized. Then, deterministic analysis of radiation is studied for a plate and a closed spherical shell. The relation of modal coefficient of the vibration to modal radiation is considered in the radiation response. The critical frequency of the sphere is investigated, and its effect on radiation behaviour is discussed. Vibration and direct radiation from a random plate are numerically simulated and theoretically estimated. In the numerical simulation, ensemble statistics for vibration are found to depend on the parameters of the randomness, and characteristics of radiation dependent on the randomness are introduced. Theoretical estimates of the ensemble statistics of vibration are then derived, considering the effects of reflection at boundaries and wave attention due to random point masses. Radiation estimates are calculated using the Rayleigh integral, and their statistical behaviours are discussed. These estimates compare well with the numerical simulation.EThOS - Electronic Theses Online ServiceGBUnited Kingdo