• The Journal of the Acoustical Society of Korea
• /
• v.35 no.6
• /
• pp.436-444
• /
• 2016

Uniformity in transducer performance is a must-have to ensure the reliable acoustic performance of a tile projector, used for active echo reduction. However, practical limitations imposed by variations in material properties and fabrication errors lead to performance variations among unit transducers, which could degrade the radiation characteristics (transmitting voltage response and directivity) of the tile projector and ultimately the echo reduction performance. In this paper we present a method to minimize these adverse effects via an appropriate placement of unit transducers within the tile projector. To this end, we perform a series of coupled acoustic-piezoelectric simulations, assuming a group of 36 unit transducers having 6 dB variations in transmitting voltage response, to analyze and compare the radiation characteristics of tile projectors under different transducer placement schemes.

• The Journal of the Acoustical Society of Korea
• /
• v.42 no.3
• /
• pp.227-232
• /
• 2023

Underwater noise pollution has a significant impact on the marine environment. This study proposed a simple approach to estimate the acoustic radiation efficiency of structures with air bubble layers. The method considered the insertion loss caused by the air bubble layer through post-processing of numerical results, assuming that insertion loss is equivalent to attenuation as demonstrated by previous studies. The proposed approach was validated by comparing it with a fully coupled analysis for plate structure models. The commercial finite element program COMSOL Multiphysics was used for the acoustic-structure interaction analysis, and the acoustic characteristics of air bubble layer for the fully coupled analysis was simulated by on the Commander and Prosperetti theory. The trends indicated good agreement between the simple approach and the fully coupled analysis in terms of radiation efficiency. It is confirmed that the proposed method is providing insight into the principal mechanism of underwater noise reduction for the bubble layer on the wedge-shaped structure.

• The Journal of the Acoustical Society of Korea
• /
• v.19 no.5
• /
• pp.84-90
• /
• 2000

The bearing detection of radiated target noise is very important at underwater acoustic measurement and passive detection. It differs the arrival tines of received signal at each sensor. Therefore, the bearing can be obtained from the time delay. This paper proposes a new algorithm using the RLSL adaptive filter for TDE. The proposed method is particularly attractive when there is a limitation of priori information about the received signal spectra and when the delay is subject to variation. As the simulation results, it is shown that the proposed algorithm has better convergence characteristics and TDE speed, and so that the usefulness of proposed algorithm is confirmed.

• Journal of the korean Society of Automotive Engineers
• /
• v.8 no.4
• /
• pp.43-55
• /
• 1986

In the studies of noise reduction, it is important to know the generation mechanism of noise in order to identify the noise source. The relation between the structural vibration and the radiated sound is very complex and so this paper deals with a simplified radiation model that was originally developed as a verification tool for the acoustic intensity measurement procedure. As the first step for the identification of the noise source, this study deals with the noise evaluation by measuring sound pressure. On the next step, the acoustic radiational pattern is determined by the acoustic intensity method and this paper established that the acoustic intensity method is effective on the detection of noise. In the study, furthermore, the method could be used to predict the change in the sound radiational characteristics with the attachment of absorber and could be used in determining the attachment position.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.11 no.7
• /
• pp.2328-2333
• /
• 2010

A direct boundary element method(DBEM) is widely applied for various acoustic wave problems. But this method has numerically non-unique solutions around the eigenfrequencies of the interior Dirichlet problem for the region enveloped with the acoustic boundary. A CHIEF method had been generally adopted to resolve the non-uniqueness problem and a new technique called ICA-Ring method has been suggested recently. In this paper, the characteristics of two techniques for avoiding the non-uniqueness of DBEM are examined and numerical codes embodying both techniques are developed. Numerical calculations are also carried out for an uniformly pulsating sphere, of which the results are investigated by including the comparisons with theoretical solutions.

• The Journal of the Acoustical Society of Korea
• /
• v.11 no.1E
• /
• pp.50-55
• /
• 1992

팬의 익면 통과 주파수 소음은 총괄 소음 스펙트럼중에서 가장 명백한 성분이다. 그 소리는 일 반적으로 가장 불쾌한 성분이므로 저감이 요구된다. 따라서 그 소음치를 저감시키기 위해서는 정확한 축류형 팬의 소음원과 소음 방사 특성 규명이 요구된다. 본 연구에서는 푹류형 팬의 소음원과 소음 방 사 특성을 정의하였다. 음압 및 음향인텐시티를 이용한 음원 해석에서, 광센서를 이용한 축류형 팬의 동 기화가 수행되었고, 팬 날개에서의정확한 소음원의 위치를 결정하기 위해 Recording time의 결정이 제 안되었다. 팬 회전시, 소음원의 위치는 각 날개의 후단과 그 다음 날개의 선단사이에 각각 존재한다. 지 향성을 통하여 축류형 팬의 소음 방사 형태를 결정하였고, 벡터 에너지 흐름도로 음의 흐름을 가시화하 였다. 팬 익면에서의 회전 진동특성을 스트레인 게이지에 의하여 규명하였고, 또한 구조진동음의 음으로 의 기여도를 측정하였다. 또한 압전필름에 의한 팬 익면에서의 정압측정 가능성이 제시되었다.

• The Journal of the Acoustical Society of Korea
• /
• v.23 no.4
• /
• pp.309-315
• /
• 2004

To estimate the rate of noise contribution caused in each part of a vehicle in the course of a pass-by noise test. researches precedent have been made to study characteristics of nearby radiation noise measured on both sides of cars in a stationary state. With different revolutions per minute of engine. 2.800rpm and 3.200rpm respectively, in the measurement area of pass-by noise, the experiments have been conducted 7.5 meters away from the central axis of the test vehicle to study direction radiation according to frequencies. The results can be applied to reduce vehicle noise.

• The Journal of the Acoustical Society of Korea
• /
• v.33 no.4
• /
• pp.238-247
• /
• 2014

In this paper, rail vibration and its sound radiation are investigated, then the rail noise measurement by using microphone array is explored theoretically. A concrete slab track for domestic high speed trains is modeled as a Timoshenko beam on elastic support, regarding the moving of the excitation force on the rail. From the radiation characteristics of rail noise generated by a line source, the effect of moving load on sound radiation is obtained. Also it is found that the beam angle of the microphone array is a prominent factor to measure the rail noise level reliably because the rail noise propagates as a plane wave. In this investigation, a proper beam angle for the rail noise measurement by microphone array is suggested.

• Journal of KSNVE
• /
• v.5 no.4
• /
• pp.440-452
• /
• 1995

이 글에서는 능동소음제어에 있어서, 음장 혹은 음원을 표현하는 물리량은 음향에너지, 파워, 인텐시티를 통하여 제어 가격함수로서의 각 의미를 살펴보았다. 졍리하면 이 세가지 물량들은 음향에너지의 균형이라는 물리적 변칙에 의해 서로 단단히 결속되어 있으며, 이들은 음장의 형태와 성격 그리고 파장과 주파수 등과 관련이 있으므로, 능동소음제어 입장에서 제어 목적에 맞게 적절히 사용할 필요가 있다고 볼 수 있다. 음향 에너지의 제어 개념 즉, 음향에너지를 가격함수로 하는 제어 방법은, 원하는 정숙공간(zone of quiet)을 제어할 때 그 적절성이 있음을 보았 으며, 음향 파워는 그 물리량 자체가 어떤 음원의 특성을 표현하고 있으므로 제어에 의하여 방사 효율을 감소(weak radiator)시키고자 할 때 가장 자연스러운 가격 함수 가 됨을 살펴보았다. 또한 음향 인텐시티라는 물리량은 음향 에너지의 전달 특성을 대표하는 특성임을 살펴보았고, 따라서 소음 전파의 감소(noise transmission reduction)를 위한 제어 가격 함수로의 당위성을 확인하였다. 이러한 모든 제어 방법 들이 사실은 가관측성 및 가제어성을 가져야 함은 주지의 사실이며, 음향 파워나 인텐시티를 가격 함수로 하는 제어 방법의 경우 실제적인 가관측성상의 문제점들로 인하여 그 현실성이 아직은 거리가 있다 하겠다.

• The Journal of the Acoustical Society of Korea
• /
• v.29 no.7
• /
• pp.431-438
• /
• 2010

The radiation pattern of conformal transducers installed on a curved surface is likely to be complicated depending on the array pattern on the curved surface. In this research, the acoustic sources constituting a conformal transducer are arrayed in equi-angle, equi-interval, and geodesic dome forms, and the radiation pattern function of each of the array geometries has been derived, and therewith the radiation pattern has been analyzed for each array geometry. Based on the analysis result, we have determined the equi-interval array geometry that provides the widest beam width with the lowest side lobe level among the three array geometries. Results of the present work are expected to be utilized to the design of conformal transducer structures.