Acoustic Optimization Design Researchon Rail Transit Box Beam Structure Basedon Response Surface Method

In recent years, environmental vibration and noise problem become increasingly prominent with the fast development of urban rail transit. The noise of rail transit box beam vibration is mainly of low frequency. It is hard to decay in communication process. Besides, it immediately arouses quantities of complaints from residents because of high position of elevated line sound source, massive coverage of noise influence, strong penetrating power of low-frequency noise and great damage to human health. Therefore, it is practically significant to do research on noise control of low-frequency box beam structure.This thesis combines finite element method and boundary element method to establish finite-boundary coupled acoustic calculation model of rail transit box beam. Based on the understanding of influential law of box beam structure parameters on noise radiation with the numerical simulation technology, it establishes acoustic optimization design model of rail transit box beam structure by employing response surface method. The thesis aims at new approaches to reducing noise of low-frequency box beam structure from the perspective of structural acoustic optimization design. It mainly covers the following aspects:(1) It first establishes vehicle-track coupling system model based on UM software to solve rail forces on the condition of rail irregularity; then it analogically loads vertical forces of the rail onto orbit-bridge dynamic model to realize the coupling of sub-systems of the whole structure.(2) Treating vertical forces of the rail on the condition of rail irregularity as system vibration input, it establishes the finite model of box beam three-dimensional entity, to gain vibration response from bridge structure under train loading. It employs vibration velocity of nodes on model surface of every frequency point of box beam finite model as the boundary condition to be input into box beam acoustic boundary element model, with the aim of figuring out acoustic radiation characteristics.(3) It adopts box beam finite-boundary calculation model to analyze and calculate vibration and noise radiation characteristics of rail transit box beam structure. It analyzes the acceleration spectrum of output points of every vibration response of cross section, and figures out linear sound pressure level and two-dimensional acoustic field distribution of every sound point of cross section. Besides, it studies influence on noise radiation from parameters(beam height, board width, board thickness, dip angle of web and chamber structure) of box beam structure.(4) Based on the analysis of vibration and noise radiation characteristics of rail transit box beam structure, it makes some proper improvement on forms of box beam structure(like web perforation, web under-rail allocation, cross rib increasing of web, and transverse diaphragm flange setting), explores whether these improvement methods can reduce vibration and noise, and analyzes and evaluates its effects.(5) It brings the response surface method in acoustic optimization design of rail transit box beam structure, replaces complex structural acoustic numerical simulation model with considerable degrees of freedom with box beam acoustic response surface model, combines experiment design, response surface method and optimization calculation to establish the acoustic optimization model of rail transit box beam structure on the basis of response surface method, and studies issues of structural acoustic optimization of rail transit box beam under train loading. With 32-centimeter double simply supported box beam being research object, it employs optimization calculation to optimize box beam structure parameters based on the establishment of response surface of objective functions and constraint functions, and conducts error analysis of optimization results.