Date:10 Jun 2019 ( Monday)
Time:2:30 pm – 3:30 pm



ABSTRACT: In this talk, a quick review on the recent and current research works conducted within the Acoustics Lab in the Mechanical Eng. Dept. at KAIST will be delivered. Topics will be centered on the recent and present MS and PhD projects. It is noted that the past works are mostly related to the duct acoustics, vibro-acoustic source identification, modeling of sound propagation in gaseous and soild media, product sound quality, and design/development of quiet machines. In contrast, many recent works are concerned on the vibro-acoustic rendering, electro-acoustic sensors and actuators, and design and implementation of new vibro-acoustic elements and systems. As the major methodology, the vibro-acoustic inverse problem is employed very usefully for various tasks.


ABSTRACT: The hair dryer noise is dominated by the flow noise which is involved in various parts in the interior. In general, the flow speed and the amount of turbulence strength are the important points in the low-noise design, but the designer will meet a trade-off condition of the flow rate that is related to the drying speed. In this work, the state-of-the-art techniques for the quiet design strategies of major air-borne sources such as the fan, shroud, exhaust nozzle, and inlet grille are studied first and the characteristics of their major parameters are identified. Then, each noise source part is redesigned to produce the lowest noise, while obstructing the flow minimally. Instead of using a single fan, multiple smaller fans are employed to reduce the broadband noise. Two types of quarter-wavelength tubes are installed within the shroud to reduce the blade passing frequency (BPF) tones. Additionally, a fan with unevenly-spaced blades is tested to eliminate the BPF. The jet noise at the exhaust nozzle is reduced by using the dual-tube: slow flow speed in the outer tube reduces the shear. The inner tube end is shaped with lobes. Spiral grille pattern is used for the lowest inlet turbulence and noise. Sound reduction through the shell is calculated. The acoustical and aerodynamic performance of the final prototype, which is an assembly of all low-noise design parts, is evaluated. Compared with the 4 commercially competitive products in the market, the developed hair dryer reveals that the flow rate is higher by 20%, the overall sound level smaller by 6 dB, the loudness smaller by 30%, the sharpness by 15%, and the roughness by 9%. (with JH Lee).


J.-G. Ih has been a Professor at the Department of Mechanical Engineering of the Korea Advanced Institute of Science and Technology (KAIST) at Daejeon in Korea since 1990. He had been the Director of the Center for Noise and Vibration Control at KAIST. During 2012-2014, he served as the Chair of the School of Mechanical, Aerospace, and Systems Engineering. During 2014-2017, he had been the Dean of College of Engineering at KAIST.

He had served as the Secretary General of the Inter-Noise 2003 held at Korea. He is a founding member of the Acoustical Society of Korea (ASK) and the Korean Society for Noise and Vibration Engineering (KSNVE). Currently, he is the President Emeritus of the ASK, for which he served as the Vice President and President during 2006-2010. He was the Director of the International Institute of Acoustics and Vibration (IIAV), and the Board Member of the International Commission for Acoustics (ICA). He is currently the Vice President of the International Commission for Acoustics (ICA). He has been involved in the Scientific Committees of ICSV, ISNVH, NOVEM conferences and serves as a Theme Organizer of Inter-Noise conference. He is organizing the ICA2022 to be held at Gyeongju in Korea as the President.

He was invited as a speaker for the Plenary Speech at 6 major international conferences. He is an editor of Applied Acoustics journal and Chinese Journal of Acoustics. He is a co-author of a book titled “Acoustic Array Systems: Theory, Implementation, and Application,” published by John Wiley & Sons in 2013.