Hu N, Utyuzhnikov S
Department of Fluids and Environment, University of Manchester, Manchester, M13 9PL, UK.
Heliyon. 2024 Sep 11;10(18):e37670. doi: 10.1016/j.heliyon.2024.e37670. eCollection 2024 Sep 30.
In the present paper, we consider active control of noise propagating from a long cylinder. For that purpose control sources are distributed on the external surface of the cylinder. They provide a secondary sound field which enables them to compensate for the noise field propagating outside. To implement active noise control, we apply an approach based on the Calderón potentials that have the projection property. Numerical simulations to attenuate broadband noise with different numbers of control sources per wavelength are carried out. The effect of the cylinder on the Green's function and consequent noise attenuation is studied. There are two key findings in this paper. First, the results demonstrate that the level of relative noise attenuation remarkably increases along with the growth of the distance. Second, it is shown that even less than two control sources per wavelength can provide essential noise cancelation. At first glance, this result contradicts the well-known Nyquist-Shannon sampling theorem. A theoretical explanation of this result is provided.
在本文中，我们考虑对从长圆柱体传播的噪声进行有源控制。为此，控制源分布在圆柱体的外表面。它们提供一个次级声场，使其能够补偿向外传播的噪声场。为了实现有源噪声控制，我们应用一种基于具有投影特性的卡尔德隆势的方法。进行了数值模拟，以衰减每波长具有不同数量控制源的宽带噪声。研究了圆柱体对格林函数以及随之而来的噪声衰减的影响。本文有两个关键发现。第一，结果表明相对噪声衰减水平随着距离的增加而显著提高。第二，结果表明每波长甚至少于两个控制源也能提供基本的噪声抵消。乍一看，这个结果与著名的奈奎斯特 - 香农采样定理相矛盾。本文提供了对此结果的理论解释。
