Active Acoustic Structure Configured To Optimize The Design

Sound radiation from a vibrating structure is an important problem encountered in numerous engineering applications. Generally, there are two main control strategies which are active structural acoustic control and active noise control. However, these two strategies have a common disadvantage, i.e., the performances of the control systems are heavily dependent on characteristics of the primary sources and acoustic environment. In order to avoid such problems, the concept of constructing an active acoustic structure has been proposed. As a basic theoretic research of the active acoustical structure, this thesis focuses on the following three aspects.Firstly, active control of low frequency sound radiation using planar secondary source is theoretically investigated. The sound power of the primary and secondary panels is calculated, and then a series of formulas are derived to obtain the optimum reduction in sound power based on the minimization of the total radiated sound power. According to the theoretic results, secondary panel arrangements for active acoustic structure are theoretically investigated and the quantitative control rules of how to choose and place the planar secondary sources are proposed from computer simulations.Secondly, error sensing strategies for active acoustic structure based on nearfield pressures are examined. Three kinds of cost functions using nearfield pressures are given. Owing to the engineering applications, the cost function using squared discrete pressures on the measuring plane is chosen to be used. According to theoretic analysis and computer simulations, the optimum arrangements for error sensors in active acoustic structure are obtained.Finally, the feasibility of sound power measurement based on nearfield pressures is examined based on experimental results. Then the optimum arrangements for error sensors in active acoustic structure are proved through the active noise control experiments.