• 한국소음진동공학회논문집
• /
• 제23권3호
• /
• pp.226-233
• /
• 2013

Individual differences in head-related transfer functions(HRTFs) were calculated using boundary element(BE) models for three Korean adults. The BE models for the individuals were developed from the computerized tomography(CT) images of the individuals. The BE models were composed of the head, pinna, and ear canal. The frequency-dependent impedance boundary conditions were imposed on the skin, hair, and tympanic membrane. The HRTFs calculated from the individual BE models showed large difference above 2 kHz in magnitude and in the locations of peaks and valleys of the frequency spectrums, which should be considered in virtual auditory sound field. The identified individual differences in the HRTFs demonstrate that the developed BE models can be utilized successfully in order to obtain the HRTFs information of individuals.

• 한국소음진동공학회논문집
• /
• 제18권11호
• /
• pp.1206-1212
• /
• 2008

This paper presents a the method for estimating the noise source contribution on the road noise of the vehicle in a multiple input system where the input sources may be coherent with each other. By coherence function method, it is found that the biggest part of the noise source in the road noise is generated by structural vibration on the mechanical-acoustic transfer functions of vehicles. This analysis is modeled as four input/single output system because the noise is generated with four wheels that mechanism of the road noise is very complicated. The coherence function method is proved to be useful tool for identifying of noise source. The overall levels of the interior noise be coherence function method are compared with those measured and calculated by the frequency response function approach using mechanical excitation test. The experimental results have shown a good agreement with the results calculated by the coherence function method when the input sources are coherent strongly each other. The estimation of the road noise indicates that significant coherent can be achieved in the vehicle interior noise.

• 한국추진공학회지
• /
• 제22권4호
• /
• pp.99-107
• /
• 2018

본 연구에서는 제트 유동 증가에 따라 스피커로 제트와 스월 유동에 각각 가진을 가하여 기체-기체 동축형 제트-스월 분사기의 분사기 전달함수(Injector Transfer Function, ITF)을 측정하였다. 공급시스템의 길이를 변화시켜 ITF를 측정한 결과 공급시스템의 공진주파수에서 피크가 발생하는 것을 확인할 수 있었다. 제트 유동에 가진을 줄 때, 제트 유동이 증가함에 따라 ITF의 크기는 감소하다가 다시 증가하는 것을 확인할 수 있었다. 즉, 두 유동의 속도차가 클수록 ITF의 크기가 증가하였다. 스월 가진 시 제트 유동이 증가함에 따라 ITF가 감소하는 것을 확인할 수 있었는데, 이는 후단에서 일정 유량 대비 가진 에너지가 감소하기 때문이다.

• 한국추진공학회지
• /
• 제22권3호
• /
• pp.72-80
• /
• 2018

연소불안정 현상은 연소기 내부에서 열발생 섭동과 음향 압력 섭동 사이의 피드백 관계로부터 도출된다. 특히 항공용 엔진에 대한 배출 가스 규제가 강화되면서, 환형 연소기에서의 연소불안정 연구에 대한 관심이 크게 증가하고 있다. 본 연구에서는 환형연소기에서 다양한 음향 모드를 계산할 수 있는 열음향 네트워크 모델을 개발 및 사용하였고, 이때 연소 모델은 화염전달함수를 적용하였다. 이와 같은 네트워크 모델을 사용하여 벤치마킹한 환형연소기의 실험데이터와 비교 분석하여 연소불안정 해석을 진행하였다.

• 한국음향학회지
• /
• 제34권2호
• /
• pp.108-116
• /
• 2015

수중 음향 벡터센서는 음압 뿐 아니라 음파의 진행 방향에 관한 정보를 측정할 수 있는 센서이다. 본 논문에서는 미세 외팔보를 이용한 수중 음향 벡터 센서를 구현하기 위해 음향학적 이론을 바탕으로 음향과 기계 구조물의 상호작용을 이론적으로 정립하고자 하였다. 감응 방식으로 압전 효과를 이용한 두 가지 유니모프(unimorph)형태의 모델을 제시하였으며, 제시된 모델에 대하여 압전 미세 외팔보의 거동을 집중 질량 모델을 통해 음파가 임의의 주파수와 각도를 가지고 미세 외팔보로 입사할 때 나오는 신호의 크기를 구할 수 있는 전달함수를 유도하였다. 또한 이를 바탕으로 매우 얇고 유연한 구조물로 미세 외팔보를 설계하면 매질의 입자 속도에 관한 정보를 직접적으로 측정 가능한 센서로 활용할 수 있다는 것을 확인하였다.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2008년도 추계학술대회B
• /
• pp.2524-2529
• /
• 2008

The thermal system like a combustion chamber is believed to experience a significant instability problem with vibration in case that the thermal energy or the acoustic energy are transformed into a different form through a relevant path. This study deals with a numerically- predicted, Thermoacoustic instability in a Rijke tube by using a non-linear model for a heat source. The heating part where the energy transformation occurs actively is modeled after simulating two-dimensional cylinder case with constant surface temperature, and a nonlinear model that accounts for the transfer function of magnitude- and phase-characteristics is properly implemented so as to be dependent on the pulsation strength in the tube. The heat source model is observed to result in equivalent Thermoacoustic instabilities in the Rijke tube except low flow-rate cases in which the natural convection is dominant.

• 한국정밀공학회지
• /
• 제25권12호
• /
• pp.107-116
• /
• 2008

The excitation force of a powertrain is one of major sources for the interior noise of a vehicle. This paper presents a novel approach to predict the interior noise caused by the vibration of the power rain by using the hybrid TPA (transfer path analysis) method. Although the traditional transfer path analysis (TPA) is useful for the identification of powertrain noise sources, it is difficult to modify the structure of a powertrain by using the experimental method for the reduction of vibration and noise. In order to solve this problem, the vibration of the power rain in a vehicle is numerically analyzed by using the finite element method (FEM). The vibration of the other parts in a vehicle is investigated by using the experimental method based on vibrato-acoustic transfer function (VATF) analysis. These two methods are combined for the prediction of interior noise caused by a power rain. Throughout this research, two papers are presented. This paper presents a simulation of the excitation force of the power rain exciting the vehicle body based on numerical simulation. The other paper presents a prediction of interior noise based on the hybrid TPA, which uses the VATF of the car body and the excitation force predicted in this paper.

• 대한공업교육학회지
• /
• 제33권2호
• /
• pp.273-286
• /
• 2008

수중에서 UUV(Unmanned Underwater Vehicle)에 장착되는 수중 음향 센서 배열은 UUV의 측면이나 전면에 부착하여 외부 신호를 탐지하게 된다. 이러한 센서 배열은 UUV의 특성상 곡면배열(Conformal array) 형태이며 유체 유기 소음의 영향을 받는다. 따라서 본 논문에서는 탄성층에 삽입된 하이드로폰이 외부 유입 소음의 영향을 받는 정도를 해석하였다. 유입 소음은 난류 경계층에서 발생하는 Corcos 모델을 이용하였고 주파수 밀도 함수를 이용하여 수치해석 하였다. x-방향의 파수인 kx에 다른 전달함수의 특성은 탄성층의 두께가 커질수록 전달함수의 적분값은 적어지므로 소음의 영향은 줄어드는 것으로 나타났다. 또한 탄성층 및 고정판의 탄성계수, 밀도 등의 변화가 전달함수 값의 변화를 일으키는지를 조사하였다. 향후 이러한 연구는 UUV에 장착되는 곡면 배열 센서의 설계에 활용할 수 있을 것으로 판단된다.

• 한국소음진동공학회논문집
• /
• 제23권4호
• /
• pp.315-323
• /
• 2013

Tire noise is divided into a road noise(structure-borne noise) and a pattern noise(air-borne noise). Whilst the road noise is caused by the structural vibration of the components on the transfer path from tire to car body, the pattern noise is generated by the air-pumping between tire and road. In this paper, a practical method to estimate the pattern noise inside a passenger car is proposed. The method is developed based on the sound intensity and airborne source quantification. Sound intensity is used for identifying the noise sources of tire. Airborne source quantification is used for estimating the sound pressure level generated by each noise source of a tire. In order to apply the airborne source quantification to the estimation of the sound pressure, the volume velocity of each source should be obtained. It is obtained by using metrics inverse method. The proposed method is successfully applied to the evaluation of the interior noises generated by four types of tires with different pattern each other.

• International Journal of Aeronautical and Space Sciences
• /
• 제18권4호
• /
• pp.797-806
• /
• 2017

In this study, the reflection coefficient (RC) and the flame transfer function (FTF) were measured by applying acoustic excitation to a duct-type model combustor and were used to predict the frequency of the combustion instability (CI). The RC is a value that varies with the excitation frequency and the geometry of the combustor as well as other factors. Therefore, in this study, an experimentally measured RC was used to improve the accuracy of prediction in the cases of 25% and 75% hydrogen in a mixture of hydrogen and methane as a fuel. When the measured RCs were used, an unstable condition was correctly predicted, which had not been predicted when the RCs had been assumed to be a certain value. The reason why the CI occurred at a specific frequency was also examined by comparing the peak of the FTF with the resonance frequency, which was calculated using Helmholtz's resonator analysis and a resonance frequency equation. As the CI occurred owing to the interaction between the perturbation in the rate of heat release and that in the pressure, the CI was frequent when the peak of the FTF was close to the resonance frequency such that constructive interference could occur.