Theoretical Study On Structural Noise Of Box Beam

With the rapid development of urban rail transit, the problems of urban rail transit vibration and noise pollution have received more and more attention from the public. And the environment pollution of vibration and noise badly affects the living of inhabitants and the daily using of high-precision instruments in the high-tech production enterprises, hospitals, research institutions and so on along the railroad. How to effectively control the vibration and noise has become one of hot topics in the field of environmental protection. Urban elevated tracks mainly use concrete box beams which radiate the low-frequency noise. The characteristics of low-frequency noise are slow attenuation and strong penetrating power. And the studies show that low-frequency noise caused by the human body function damage, organic and mental damage. Therefore, reducing the low-frequency noise has practical significance.The problem of acoustic radiation of the vibrating box beam is essentially the one of fluid-structure vibroacoustic coupling, which is always a frontier in structural acoustics and noise control, and also a recognized intricate problem. The major researches are almost limited to underwater circular cylindrical shells. Little has been reported on the acoustic radiation from the box beam using analytical method or semi-analytical method, because of the complexity of the motion equations induced by the curvature varying in the circumferential direction. The contents are listed as follows:1. Discussing several solving analytical method of acoustic radiation from the box beam. Firstly, the article studies the infinite concrete cylindrical shell in air. And the influences of parameters such as size of the external excitation force, distance of observation point, radius of shell, material of shell, property of fluid, structural damping are also investigated. Then, based on the fluid-structure coupling theory about circular cylindrical shells, theoretical analysis on the structure noise of box beam is carried out respectively based on thin shell theory, thin plate theory and conformal mapping theory. Because of the curvature varying in the circumferential direction of the box beam, the acoustic radiation problem of box beam is very difficult to gain the analytical conclusion.2. Analyzing the semi-analytical method of acoustic radiation from the box beam. The article is based on the extended homogeneous capacity high precision integration method and the spectrum method of virtual boundary with a complex radius vector for 2-D Helmholtz exterior problems. A semi-analytical method, which has satisfactory computation effectiveness and precision, is presented for solving the acoustic radiation from an infinite concrete box beam in the air by means of the Fourier integral transformation and stationary phase method. And the paper gains a semi-analytical solution for acoustic radiation from the box beamThe key of solving the acoustic radiation from the box beam is solving the equation of fluid-structure coupling about the structural dynamic equation, the Helmholtz equation, the Sommerfield radiation condition and the coordination condition which is at the interface between air and box beam. Then, radiated sound pressure of the box beam can be solved. The paper is established in the theoretical study on structural noise of the box beam. In order to finding out interrelated effect factor about structural noise and adopting effective measures to radically reducing the noise. Theoretical study on acoustic radiation of the box beam is carrying out. It's very significant for further understanding the acoustic radiation characteristic of the urban elevated railroad box beam, controlling noise of the built railroad and prophase forecasting noise of the planning railroad, and doing the cross-section optimization design of the box beam.