Actively Controlled Hood for Machinery Noise

该项目致力于机械噪声的主动控制。在大多数情况下，通过隔音罩的被动控制来降低噪音。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供暖、通风和空调系统。在被动控制中，引擎盖的设计是通过在空气腔中提供声学阻尼和在围墙中提供结构阻尼来衰减室内声场。使用这些技术实现的性能受到体积、重量和成本的限制。另一方面，主动控制方法适用于时滞、稳定性和带宽问题非常重要的闭环系统反馈控制器的设计。这个项目的方法是设计一种尽可能接近刚性膜的封闭结构。这种结构的响应以超音速结构振型为主。通过使外壳表面的法向响应最小化来消除外部噪声。该方法将进行测试，并与现有的主动控制策略进行比较。这种方法的预期优势包括减少观察围墙响应所需的表面传感器数量，以及确保抑制较短波长干扰激励的空间滤波。

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.