Actively Controlled Hood for Machinery Noise

本项目涉及机械噪声的主动控制。在大多数情况下，被动控制，通过吸声罩，是用来减少噪音。一些应用包括工业环境中的制造机器，以及办公室或住宅空间的加热，通风和空调系统。在被动控制中，引擎盖被设计为通过在空气腔中提供声学阻尼和在外壳壁上提供结构阻尼来衰减内部声场。使用这些技术获得的性能受到体积、重量和成本的限制。另一方面，主动控制方法适用于闭环反馈控制器的设计，其中时间延迟，稳定性和带宽问题很重要。这个项目的方法是设计一个尽可能接近硬膜的外壳结构。这种结构的响应以超声速结构模态为主。通过最小化沿外壳表面的法向响应来消除外部噪声。该方法将与现有的主动控制策略进行测试和比较。这种方法的预期优点包括减少观察外壳壁响应所需的表面传感器的数量，以及空间滤波，以确保拒绝短波长的扰动的激发。

This project addresses the active control of noise for machinery. In most cases, passive control, by means of acoustical hoods, is used to reduce noise. Some applications include manufacturing machines in industrial environments, and heating, ventilating and air conditioning systems in office or residential spaces. In passive control, the hood is designed to attenuate the interior sound field by providing for acoustical damping in the air cavity and for structural damping in the enclosure walls. The performance achieved using these techniques is limited by constraints of volume, weight, and cost. On the other hand, the active control approach applies to the design of a closed loop feedback controller where issues of time delays, stability, and bandwidth are important. This project's approach is to design an enclosure structure that is as close to a stiff membrane as possible. Such a structure's response is dominated by supersonic structural modes. Cancellation of exterior noise is obtained by minimizing the normal response along the enclosure surface. This approach will be tested and compared with existing active control strategies. This approach's expected advantages include reduction of the number of surface sensors required to observe the response of the enclosure walls, and spatial filtering which insures rejection of excitation by shorter wavelength disturbances.