题目：The Anti-event-horizon of A Sonic “Black Hole”
时间：2026年10月20日 10:00-11:00
地点：机械与动力工程学院 F310会议室
邀请人：蒋伟康 教授（振动、冲击、噪声研究所）
Biography
Professor Lixi Huang, the Executive Director of the HKU Research Institute for Civil Low-Altitude Aviation and the Deputy Head of the Department of Mechanical Engineering. His current focus of research is noise control for environmental and aeronautical applications. He serves as an associate editor for mainstream acoustics journals: JASA, JSV, and npj Acoustics. He is a fellow of the Acoustical Society of America and an advisor for the Global Power and Propulsion Society.
Abstract
Over the past two decades, acoustic retarding structures, analogised to sonic “black holes”(SBH), have garnered significant attention for their potential to achieve perfect sound absorption. Typical designs feature annular rings with progressively smaller radii designed to bring sound waves to rest at zero radius. Yet these structures still reflect significant sound, a flaw widely attributed to the engineering impossibility of achieving a true zero radius with infinite acoustic admittance. In this study, we re-examine the analytical solution for a typical SBH configuration and conclude that sound waves cannot be trapped by slowing down to zero phase speed. We attribute this impossibility instead to the breakdown of the approximate side-wall boundary condition used in the original theory. When an accurate boundary condition for the configuration is used, and yet the fluid viscosity is ignored, the phase speed is found to increase to infinity leading to incompressible-flow behaviour (an anti-event-horizon). This result contrasts with what the astronomical term of black-hole may reasonably imply. With such clarifications, our focus is shifted to the practical performance of such a retarding structure, renamed as "cylindrical waveguide with impedance gradient" (CWIG), for broadband sound absorption. For a pink incident noise, it is found that CWIG with a theoretical anechoic terminal performs similarly to a traditional acoustic wedge but CWIG with practically optimized gradual damping may provide an excellent performance comparable to the latest acoustic "metamaterials", or an array of Helmholtz resonators.
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ENGLISH
地址：上海市东川路800号上海交通大学闵行校区机械与动力工程学院
邮编：200240
Email：sjtume@sjtu.edu.cn