• 융합신호처리학회논문지
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• 제19권3호
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• pp.139-146
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• 2018

수중음향통신은 자원 및 지질탐사, 무인잠수정을 이용한 수중탐지 등 산업, 과학, 군사 분야에 다양하게 이용될 수 있으며 최근 들어 미국을 비롯한 선진국을 중심으로 활발하게 연구되고 있다. 그러나 수중음향통신은 지상에서의 무선통신과 달리, 느린 음파 전달속도로 인한 전송대역의 제한과 다중경로에 의한 심볼간 간섭과 이로 인한 심각한 신호왜곡 등의 치명적인 문제점을 갖는다. 본 논문에서는 이러한 문제점 중, 다중경로에 의한 심볼간 간섭을 제거하기 위한 방법으로 단일반송파 전송방식을 사용하는 주파수영역등화(FDE) 기법과 다중반송파 전송방식을 사용하는 직교주파수분할다중화 기법(OFDM)을 수중음향통신 채널에 적용하여 그 성능과 수중통신에서의 적용성 여부를 판단하였다. 이를 위해 모의된 수중채널을 바탕으로, SC-FDE와 OFDM 방식의 성능을 SER 관점에서 비교하였다. 수중채널은 벨홉모델을 이용하여 모의하였으며, 모의실험 결과, SC-FDE는 OFDM에 비해 $10^{-3}SER$ 기점을 기준으로 약 5dB 이상의 SNR 이득이 발생하였다. 모의실험 결과를 통해, SC-FDE가 수중 음향통신에 효율적으로 적용 가능한 시스템임을 보였다.

• Ocean and Polar Research
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• 제36권1호
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• pp.1-12
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• 2014

This study investigates spatial and temporal variations in the generation and propagation of internal tides around the Korea Strait using a three-dimensional high resolution model (Regional Ocean Modeling System; ROMS). The model results were verified through comparison with in-situ current measurements from an array of 12 acoustic Doppler current profilers (ADCPs) deployed in the Korea Strait. Fluxes and distributions of internal tidal energy were calculated using simulation results gathered in February and August. Our analyses reveal that energetic semidiurnal internal tides are generated in a region around the Korea Strait shelf break ($35.5^{\circ}N$, $130^{\circ}{\sim}130.5^{\circ}E$), where the strong cross-slope semidiurnal barotropic tidal currents interact with a sudden topographical change. The semidiurnal internal tidal energy generated in summer displays values about twice as large as values in winter. Propagation of semidiurnal internal tides also reveals seasonal variability. In February, most of the semidiurnal internal tides propagate only into the open basin of the East Sea due to weak stratification in the Korea Strait, which inhibits their southwestward propagation. In August, they propagate southwestward to $35.2^{\circ}N$ along the western channel of the Korea Strait because of strong stratification. In addition, semidiurnal internal tides generated in a region west of Tsushima Island are found to propagate to the coast of Busan. This can be explained by the intensified stratification due to the strong intrusion of bottom cold water in the western channel of the Korea Strait during summer.

• 한국음향학회지
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• 제41권6호
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• pp.601-609
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• 2022

2007년 8월 동해 연안에서 연안용승 현상이 발생 되었고, 이에 따른 수직적인 수온과 염분 자료가 실시간 해양관측부이를 통해 획득되었다. 시계열 관측자료를 기반으로 연안용승 발생 전·중·후의 수직적인 음속구조를 산출하였고, 연안용승의 수평적인 규모와 실제 해저지형 등을 고려한 음향모델링을 통해 연안용승이 수중의 음파 전달과 탐지환경에 어떠한 영향을 미치는지 분석하였다. 포물선 방정식 모델을 이용한 저주파(500 Hz) 음파 전달손실과 심도별 표적 탐지거리를 비교·분석한 결과, 동해 연안에서 용승이 발생하면 그렇지 않은 일반적인 음탐환경에 비해 최대 약 10 dB의 탐지이득을 기대할 수 있는 것으로 분석되었다. 또한, 이번 연구를 통해 용승 전·후 약 2 ~ 3일의 짧은 기간 내에서도 음파전달 특성이 크게 달라질 수 있음을 확인하였다.

• 한국지구과학회지
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• 제32권6호
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• pp.640-653
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• 2011

이 연구에서는 기존의 탄성파 모델링 알고리즘에 지진 송신원을 적용하고, 음향-탄성파 결합 매질을 구현하여 남극대륙 주변과 같은 극지해역에서 발생할 수 있는 지진파의 거동을 모사한다. 기존의 변위근사 유한차분법과 달리 속도-응력 식으로 구성되는 엇격자 유한차분법의 경우 다양한 송신원을 구현하는데 적합하므로 변위-속도-응력 식에 기초하여 개발된 3차원 엇격자 유한차분법 알고리즘과 이중 우력(Double Couple Forces)을 이용하여 구현한 지진 송신원을 접목시켜 지진파의 거동을 모사한다. 좌수향 주향이동단층, 정단층, 역단층 형태의 지진 송신원에 대해서 개발된 알고리즘을 검증한 결과 이론적으로 예측되는 P파의 초동을 정확히 모사할 수 있었고, 섭입대 모델에 대한 수치모형실험 결과 섭입대에서 역단층에 의해 발생된 후 대륙지각, 해양지각 및 해양에서 전파되는 지진파의 거동양상이 정확하게 모사되는 것을 확인할 수 있었다.

• 한국지구과학회지
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• 제28권3호
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• pp.367-373
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• 2007

지음향 모델링은 해저지층을 통한 음파 전달과정을 모형하기 위해 발달해 왔다. 이러한 작업은 음파 전달을 제어하는 지층의 지음향 특성값을 측정 추론 예측한 값을 필요로 한다. 동해안 옥계와 북평지역 연안에서, 해저지층은 제4기층과 함께 제3기 퇴적층, 음향학적 기반암 등으로 구성된다. 옥계 연안지역 해저지층의 기반암은 주로 고생대 평안층군의 암석으로 해석되며, 이 암석의 평균 P파와 S파 속도값은 각각 4276 m/s와 2400 m/s이다. 북평 연안지역 해저지층의 기반암은 주로 고생대 초기 조선누층군의 석회암으로 해석되며, 이 암석의 평균 P파와 S파 속도값은 각각 5542 m/s와 2742 m/s이다.

• 마이크로전자및패키징학회지
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• 제12권3호
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• pp.267-274
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• 2005

This paper presents the fabrication of surface acoustic wave (SAW)-based pressure sensor for long-term stable mechanical compression force measurement. SAW pressure sensor has many attractive features for practical pressure measurement: no battery requirement, wireless pressure detection especially at hazardous environments, and easy other functionality integrations such as temperature, humidity, and RFID. A $41^{\circ}$ YX $LiNbO_3$ piezoelectric substrate was used because of its high SAW propagation velocity and large values of electromechanical coupling factors $K^2$. A silicon substrate with $\~200{\mu}m$ deep cavity was bonded to the diaphragm with epoxy, in which gold was covered all over the inner cavity in order to confine electromagnetic energy inside the sensor, and provide good isolation of the device from its environment. The reflection coefficient $S_{11}$ was measured using network analyzer. High S/N ratio, sharp reflected peaks, and clear separation between the peaks were observed. As a mechanical compression force was applied to the diaphragm from top with extremely sharp object, the diaphragm was bended, resulting in the phase shifts of the reflected peaks. The phase shifts were modulated depending on the amount of applied mechanical compression force. The measured $S_{11}$ results showed a good agreement with simulated results obtained from equivalent admittance circuit modeling.

• Structural Engineering and Mechanics
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• 제42권6호
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• pp.831-847
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• 2012

Impact from water-borne debris during tsunami and flood events pose a potential threat to structures. Debris impact forces specified by current codes and standards are based on rigid body dynamics, leading to forces that are dependent on total debris mass. However, shipping containers and other debris are unlikely to be rigid compared to the walls, columns and other structures that they impact. The application of a simple one-dimensional model to obtain impact force magnitude and duration, based on acoustic wave propagation in a flexible projectile, is explored. The focus herein is on in-air impact. Based on small-scale experiments, the applicability of the model to predict actual impact forces is investigated. The tests show that the force and duration are reasonably well represented by the simple model, but they also show how actual impact differs from the ideal model. A more detailed three-dimensional finite element model is also developed to understand more clearly the physical phenomena involved in the experimental tests. The tests and the FE results reveal important characteristics of actual impact, knowledge of which can be used to guide larger scale experiments and detailed modeling. The one-dimensional model is extended to consider water-driven debris as well. When fluid is used to propel the 1-D model, an estimate of the 'added mass' effect is possible. In this extended model the debris impact force depends on the wave propagation in the two media, and the conditions under which the fluid increases the impact force are discussed.

• Ocean and Polar Research
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• 제43권4호
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• pp.205-217
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• 2021

A shallow channel between Jeju and Udo Islands, which is located in the northeastern Jeju Island, is influenced by storm- or typhoon-induced currents and surface waves as well as strong tidal currents. This study examines the typhoon-induced current and wave patterns in the channel, using Acoustic Doppler Current Meter (ADCP) measurements and an ocean-wave coupled modeling experiment. Three typhoons were chosen - Chaba (2016), Soulik (2018), and Lingling (2019) - to investigate the responses of currents and waves in their pathways. During the pre-typhoon periods, dominant northward flow and wave propagation were observed in the channel due to the southeasterly winds before the three typhoons. After the passage of Chaba, which passed over the eastern side of Jeju Island, the northward flow and wave propagation were totally reversed to the opposite direction, which was attributed to the strong northerly winds on the left side of the typhoon. In contrast, in the cases of Soulik and Lingling, which passed over the western side of Jeju Island, strong southerly winds on the right side of the typhoons continuously intensified the northward current and wave propagation in the channel. The model-simulated current and wave fields reasonably coincided with observational data, showing southward/northward flow and wave propagation in response to the right/left side of the typhoon pathways. Typhoon-induced downwind flows, and surface waves could enhance up to 2m/s and 3m due to the strong winds that lasted for more than 12 hours. This suggests that the flow and wave patterns in the Udo channel are highly sensitive to the pathway of typhoons and accompanying winds; thus, this may be a crucial factor with regard to the movement of seabed sediments and subsequent coastal erosion.

• 한국음향학회지
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• 제33권4호
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• pp.232-237
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• 2014

함정의 수동소나는 여러 개의 지향성과 무지향성 센서로 구성되어 있다. 함정 소나에 수신되는 음향 신호를 모의할 때, 일반적으로 임의의 소음원으로부터 소나에 장착된 모든 센서간의 음파 전달 모델링이 필요하다. 그러나 모든 센서에 대한 통합적인 계산은 시간이 많이 소모되며 소나 시뮬레이터의 성능을 저하시킨다. 본 연구에서는 음선 정보가 알려진 기준 센서가 존재한다고 할 때 그에 인접한 센서 위치에서의 소나 신호를 추정하는 근사적인 방법을 제안한다. 이 방법은 음선의 도달 시간에 대한 테일러 급수를 이용하여 개발되었으며 소나 개구면에 대한 Fraunhofer와 Fresnel 근사와 유사하다. 제안된 기법을 검증하기 위해 수동 소나에 대해 여러 수치실험이 수행되었다. 2차 항까지 테일러 근사를 적용한 근사법이 보다 우수한 결과를 보였다. 추가적으로 각각의 근사 해에 대한 오차 한계가 제시되었다.

• International journal of advanced smart convergence
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• 제10권4호
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• pp.241-255
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• 2021

The human auricle is the first part to receive sound from the outside. In this part, the frequency range of human recognizable form is divided and organized. In this study, we propose modeling by applying a single sound source to the surface of the human auricle. This means that when the sound pressure of a low frequency (low frequency) sound enters the pinna, the impedance felt at the tip of a part of the non-linear surface of the pinna is mainly due to the tensile force at the end of the part of the non-linear surface of the pinna. By expressing the situation of moving at a very small speed, the characteristic impedance of the pinna was confirmed to be negative infinity, and it was also confirmed that the speed at the tip of a part of the non-linear surface of the pinna was 0 in the anti-resonance state. It was found that the wave propagation phenomenon that determines the characteristics of the filter is determined by how large the wavelength, kL, is compared to the length of the tip of a part of the non-straight surface of the pinna. Humans first receive sounds from outside through their ears. The auricle is non-linear and has a curved shape, and it is known that it analyzes frequencies while receiving external sounds. The human ear has an audible frequency range of 20Hz - 20,000Hz. Through the study, we applied the characteristics of the notch filter to hypothesize that the human audible frequency range is separated from the auricle, and applied filter theory to analyze it, and as a result, meaningful results were obtained. The curved part and the inner part of the auricle function as a trumpet, collecting sounds, and at the same time amplifying the weak sound of a specific band. The point was found and the shape of the envelope detected in the auricle was found. Selectivity for selecting sounds coming from the outside is the formula of the pinna that implements the function of Q. The function of distinguishing human-recognizable sound from the pinna from low to high through frequency analysis is performed in the pinna, and the 2-3kHz area, where human hearing threshold is the most sensitive, is also the acoustic impedance of the most recessed area of the pinna. It can be seen that starting from.