• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.7
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• pp.497-504
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• 2020

A technique was developed for analysis on sonic boom created by supersonic flight and for prediction of its sound level and atmospheric propagation characteristics. It is of great importance to anticipate sound level of sonic boom because it causes environmental issue. For that purpose, the simplified sonic-boom prediction method was applied to calculate sound pressure according to physical properties and flight information of the object and distance to measurement site, in this study. Propagation characteristics of shock wave emanated from a flying object was analyzed by using line-of-sight vector and ray tracing method which dealt with refraction of wave due to atmospheric density distribution along altitude. Predicted results agreed well with measured data from real flight.

• Journal of IKEEE
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• v.23 no.4
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• pp.1360-1365
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• 2019

In this paper, we describe a sound source localization(SSL) system which can be applied to mobile robot and automatic control systems. Usually the SSL method finds the Interaural Time Difference, the Interaural Level Difference, and uses the geometrical principle of microphone array. But here we proposed another approach based on the deep neural network to obtain the horizontal directional angle(azimuth) of the sound source. We pick up the sound source signals from the two microphones attached symmetrically on both sides of the robot to imitate the human ears. Here, we use difference of spectral distributions of sounds obtained from two microphones to train the network. We train the network with the data obtained at the multiples of 10 degrees and test with several data obtained at the random degrees. The result shows quite promising validity of our approach.

• The Journal of the Acoustical Society of Korea
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• v.20 no.8
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• pp.31-37
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• 2001

Following the recent trends of reducing the size of multimedia devices, we tried for the development of a compact-sized speaker to produce low-frequency sounds efficiently. For this work, equivalent-circuit analysis was used to get fundamental resonant frequency and then the structure of speaker components has been changed appropriately. As a result, an 80mm small-sized speaker was developed. The performance test showed that the resonant frequency of our system is 79 Hz while that of numerical analysis was 81Hz. At a distance of 1m from our speaker, the frequency ranges 80 Hz to 15kHz and the average sound pressure was found to be 84±2 dB. The second (at 400 Hz) and the third (at 100 Hz) high-frequency distortions of our system were 0.5% and 1.8% respectively, which is to be compared with the distortions of 0.9% and 6% in conventional speakers.

• Journal of the Society of Naval Architects of Korea
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• v.50 no.3
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• pp.190-198
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• 2013

In order to predict acoustic pressure distributions by exterior incident wave at Cylindrical Hydrophone Array (CHA) sensor's positions, acoustic pressure analysis is performed by using beam tracing method. Beam tracing method is well-known of reliable pressure analysis methods at high-frequency range. When an acoustic noise source is located at the center of rectangular room, acoustic pressure analysis is performed by using both beam tracing method and Power Flow Boundary Element Method (PFBEM). By comparing with results of beam tracing method and those of PFBEM, the accuracy of beam tracing method is verified. We develop the CHA pressure analysis program by verified beam tracing method. The developed software is composed of model input, sensor array creator, analysis option, solver and post-processor. We can choose a model option of 2D or 3D. The sensor array generator is connected to a sonar which is composed of center position, bottom, top and angle between sensors. We also can choose an analysis option such as analysis frequency, beam number, reflect number, etc. The solver module calculates the ray paths, acoustic pressure and result of generating beams. We apply the program to 2D and 3D CHA models, and their results are reliable.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1995.10a
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• pp.39-43
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• 1995

대형 상용차용 내연기관에서 방출되는 소음의 음압 레벨은 경우에 따라 140dBA 이상으로 환경소음 배출규제에 부합되는 배출 소음을 위하여는 소음기의 적절한 설계가 필요하다 하겠다. 소음기는 방출 소음을 저감시키는 기본적인 작용 이외에 엔진의 효율을 저하시키는 배압(back-pressure) 상승의 효과를 동반할 뿐만 아니라 차체에의 장착을 위하여 크기와 무게의 제약을 받는다. 따라서 소음기는 설계자의 경험과 과거에 사용되어 온 소음기에 대한 이해, 소음기를 구성하는 단위 요소에 대한 음향학적 해석이론, 제작 과정에서의 경험과 튜닝 등에 바탕을 두고 설계되어져 왔다. 본 연구에서는 대형 상용차에 장착되는 기존 소음기 구성요소의 투과 손실(Transmission Loss: TL)을 전달 행렬법으로 해석하여 음향학적 특성을 규명하고 개별 소음기 요소에 대한 기존의 연구 결과를 바탕으로 공명기와 다공 요소를 이용하여 기존 소음기를 재설계함으로써 배출 소음의 저감을 이루어 나간 과정을 소개하고 이를 적용 사례를 중심으로 살펴보고 있다. 소음기의 설계를 위하여 고려할 수 있는 음향학적 요소는 그 기능과 형태면에서 다양하나 본 연구에서는 대형 상용차용 소음기에 주로 사용 가능한 공명기와 다공관을 주된 설계요소로 생각하였다. 공명기는 공명 주파수 대역의 소음을 저감하는 역할을 하므로 일정한 엔진 회전수 하에서 엔진의 방출 소음중 폭발 성분에 의한 소음을 줄이는데 효과적으로 사용될 수 있지만 가속 주행시에는 회전수(rpm)의 변화에 따라 폭발 주기가 변화하게 되므로 공명기의 설계에 주의를 기울여야 한다. 내연 기관용 소음기에 빈번하게 쓰이는 다공 요소의 해석 방법으로는 Sullivan[1], Kim and Yoon[2] 등의 분할 접근 방법(Segmentation approach)과 Jayaraman and Yam[3], Munjal[4], Peat[5] 등의 연성 제거 방법(Decoupling Approach)등이 제시되었고 평면파 영역에 한하여 해서되어져 왔다. 본 논문에서는 분할 접근 방법(Segmentation Approach)을 이용하여 다공 요소로 이루어진 소음기를 해석하는데 적용하였다.

• Journal of Power System Engineering
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• v.3 no.3
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• pp.60-69
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• 1999

The noise and vibration sources of rotary compressor for room air-conditioner are pressure pulsation of compression process, cavity resonance of inner space, structural radiation noise of shell and impact noise of discharge valve. Among them, pressure pulsation is very important noise and vibration source. Because it transferred various kinds of noise and vibration like as mentioned above. In this reason, muffler and resonator are used in order to absorb and remove these noises. But an analytical prediction using acoustic analysis does not coincident with the experimental result. The difference between analysis and actual state is due to the assumption of analysis. This paper covered with new concept of muffler design based on the turbulence kinetic energy of flow by using CFD. From this analysis, it is possible to decide the best position of discharge port of muffler. Therefore $2{\sim}3dB$ noise reduction effect is acquired in rotary compressor of 5000 BTU grade. Also new approach of resonator design is suggested. From this study, the characteristics of resonator and surge hole (a kind of resonator without pipe length) are identified. The former is useful for pure tone noise (narrow frequency band), and the latter is effective for broad frequency band. This paper shows that it is very available to use 3 dimensional analysis of resonator in order to predict more exact tuning frequency. The result is proved by a lot of experiments. From combination of fluid analysis and acoustic analysis, up stream position is effective location of resonator concerning turbulence motion of fluid.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2004.04a
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• pp.55-60
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• 2004

The paper describes measurement techniques for an acoustic transfer characteristic of ship's bridge stimulated by a whistle sound. The response sounds, according to the opening-shutting conditions of bridge doors for T／S ‘SAENURI’, are measured by B＆K 2260D equipment, and then extracted the frequency responses by B＆K 7830 software. To evaluate the measured transfer characteristic, the 128th order FIR (Finite Impulse Response) filters, containing the frequency characteristic, are constructed based on the frequency sampling-based design method. Using evaluation indexes with six scales, psychological assessments by five subjects are carried out with test sounds which are convolved source sound and FIR filters. As results of tests, the test sounds gives A／sub s／=3.3∼4.7 which means the psychological sense of 'it is almost similar sound as original ones in a real world', and thus it is cleary seen tint the proposed method can be suit for the measurement of an acoustic transfer characteristic of ship's bridg.

• Journal of Dental Rehabilitation and Applied Science
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• v.34 no.1
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• pp.56-62
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• 2018

When it comes to treat patient with loss of vestibule, conventional denture impression have limitation which can cause problems of excessive border extension. Suction denture with closed mouth technique which was introduced to solve this problem, forms negative pressure being sealed denture flanges by mobile mucosa when the patient swallows and chews. Also, it can decrease patient's visiting time by taking impression and gothic arch tracing at once. In this case, considering patient's chief complain which is a loose fit of present lower denture, suction dentures with closed mouth technique was planned.

• The Journal of the Acoustical Society of Korea
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• v.20 no.1
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• pp.68-76
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• 2001

Sonar is the system that detects objects and finds their location in water by using the echo ranging technique. In order to have excellent performance in variable environment, acoustic characteristics of this system must be analyzed accurately. In this paper, based on the finite element analysis, modeling and analysis of acoustic characteristics of underwater acoustic sensors are preformed. Couplings between piezoelectric and elastic materials, and fluid and structure systems associated with the modeling of piezoelectric underwater acoustic sensors are formulated. In the finite element modeling of unbounded acoustic fluid, IWEE (Infinite Eave Envelop Element) is adopted to take into account the infinite domain. When an incidence wave excites the surface of Tonpilz underwater acoustic sensor, the scattered wave on the sensor is founded by satisfying the radiation condition at the artificial boundary approximately. Based on this scattering analysis, the electrical response of the underwater acoustic sensor under incidence, so called RVS (Receiving Voltage Signal) is founded accurately. This will devote to design Sonar systems accurately.

• Journal of the Korean Society of Marine Environment & Safety
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• v.12 no.3 s.26
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• pp.193-199
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• 2006

The noise levels on board ship recognized at Europe in the early 1970s and the noise regulations on the ship began to put in a statutory form. After that, in 1982 'International Code on Noise Levels on Board Ships' adopted by IMO and it became a standards to the newly built ship and it remains up to recently. Especially, the ship engine room, which have huge main engine and various kinds of subsidiary machines, is under an extremely loud condition and so the worker who works in it is easy to lose his hearing. Recently, each nation regulates the allowable noise exposure time by law to protect the industrial employee from the occupational hardness of hearing. In our country, the allowable noise exposure time is regulated by the labor. standard law but the international provisions regulated by IMO have been applied in case of the ship engine room. In this paper, the cabin's noise levels of cargo-passenger ships plies south-west coast line were investigated.