H. Kook

Modeling and Simulation of Road Noise by Using an Autoregressive Model

ABSTRACT A new method for the simulation of the vehicles interior road noise is proposed in the present study. The road noise model can synthesize road noise of a vehicle for varying driving speed within a range. In the proposed method, interior road noise is considered as a stochastic time-series, and is modeled by a nonstationary parametric model via two steps. First, each interior road noise signal, obtained from constant speed driving tests performed within a range of speed, is modeled as an au-toregressive model whose parameters are estimated by using a standard method. Finally, the parame-ters obtained for different driving speeds are interpolated based on the varying driving speed to yield a time-varying autoregressive model. To model a full band road noise, audible frequency range is divided into an octave band using a wavelet filter bank, and the road noise in each octave band is modeled. * 기 호 설 명 a k : k 번째 모수 e ( t ): 스토캐스틱 시계열 모형의 잔여 n a : 자기회귀 모형의 차수 u ( t ): 주행 속도

Development of an active deflector system for sunroof buffeting noise control

Sunroof buffeting noise is annoying to drivers and passengers. The conventional method for suppressing sunroof buffeting noise is to use passive deflectors. A recent trend has been large sunroof openings, such as panoramic sunroofs, in accordance with customer preferences for a feeling of openness. Since sunroof buffeting noise tends to become louder as the sunroof opening area becomes larger, a conventional passive deflector may not be a solution in this case, and a new effective method for reducing the sunroof buffeting noise is required. Previous work showed that a strong, self-sustained tonal noise, generated from a Helmholtz resonator exposed to a grazing flow, could be significantly reduced by closed-loop control of an active deflector installed near the upstream edge of the resonator opening. The active deflector system is a cascade of a microphone sensor mounted inside the cavity, controller, power amplifier, and deflector mechanism vibrated by a voice coil actuator. Since the acoustic pressure inside the cavity is influenced by the shear layer modified by the active deflector, the active deflector and acoustic response of the cavity form a closed-loop control system. The main objective of the present study is to implement this technology on a real vehicle and evaluate whether the technology can be utilized to suppress sunroof buffeting noise. A simple active deflector system was assembled and installed in a compact-sized hatchback car with a sunroof opening length of 460 mm. The active deflector system was tested both in a wind tunnel and on a proving ground. The test results showed that the active deflector reduced the sunroof buffeting noise by as much as 25 dB. The active deflector was shown to be stable and robust regardless of changes in the wind speed and wind yaw angle.