• 융합신호처리학회논문지
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• 제10권2호
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• pp.127-131
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• 2009

디지털 도파관 모델은 파동 방정식의 일반해를 이용하여 진행파를 표현하고 이 진행파의 파동이동을 지연 라인으로 나타낸다. 일반적인 도파관 모델에서의 단일 지연은 샘플링 시간 간격을 의미하지만, 공간 기준 도파관 모델의 단일 지연은 샘플링된 공간의 거리를 의미한다. 이러한 차이점으로 인해 파동의 이동 거리를 직접적으로 조절할 수 있는 공간기준 도파관 모델이 비브라토 음과 같이 피치가 변하는 음을 합성할 수 있다고 알려져 있다. 본 논문에서는 지연라인의 길이의 비로서 피치가 변하는 음을 합성할 수 있는 시간 기준 디지털 도파관 모델을 제안하고 기존의 공간 기준 도파관 모델과의 성능을 비교하였다.

• Smart Structures and Systems
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• 제32권4호
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• pp.195-205
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• 2023

The contact acoustic emission (AE) monitoring system is time-consuming and costly for monitoring concrete structures in large scope, in addition, the great difference in acoustic impedance between air and concrete makes the detection process inconvenient. In this work, we broaden the conventional AE source localization method for concrete to the non-contact (air-coupled) micro-electromechanical system (MEMS) microphones array, which collects the energy-rich leaky Rayleigh waves, instead of the relatively weak P-wave. Finite element method was used for the numerical simulations, it is shown that the propagation velocity of leaky Rayleigh waves traveling along the air-concrete interface agrees with the corresponding theoretical properties of Lamb wave modes in an infinite concrete slab. This structures the basis for implementing a non-contact AE source location approach. Based on the experience gained from numerical studies, experimental studies on the proposed air-coupled AE source location in concrete slabs are carried out. Finally, it is shown that the locating map of AE source can be determined using the proposed system, and the accuracy is sufficient for most field monitoring applications on large plate-like concrete structures, such as tunnel lining and bridge deck.

• Smart Structures and Systems
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• 제15권6호
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• pp.1463-1479
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• 2015

Lamb waves have been a promising candidate for quantitative damage identification for various engineering structures, taking advantage of their superb capabilities of traveling for long distances with fast propagation and low attenuation. However, the application of Lamb waves in damage identification so far has been hampered by the fact that the characteristic signals associated with defects are generally weaker compared with those arising from boundary reflections, mode conversions and environmental noises, making it a tough task to achieve satisfactory damage identification from the time series. With awareness of this challenge, this paper proposes a time reversal-based technique to enhance the strength of damage-scattered signals, which has been previously applied to bulk wave-based damage detection successfully. The investigation includes (i) an analysis of Lamb wave propagation in a plate, generated by PZT patches mounted on the structure; (ii) an introduction of the time reversal theory dedicated for waveform reconstruction with a narrow-band input; (iii) a process of enhancing damage-scattered signals based on time reversal focalization; and (iv) the experimental investigation of the proposed approach to enhance the damage identification on a composite plate. The results have demonstrated that signals scattered by delamination in the composite plate can be enhanced remarkably with the assistance of the proposed process, benefiting from which the damage in the plate is identified with ease and high precision.

• 한국가시화정보학회지
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• 제15권1호
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• pp.47-52
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• 2017

In droplet-based microfluidic systems, in-droplet preconcentration of a sample is one of the important prerequisites for biochemical or medical analysis. There have been a few studies on preconcentration in a moving droplet, but they are limited to practical applications since 1) their method are time-consuming or 2) they require specific properties such as electric and magnetic properties. In this study, we demonstrated the position control of polystyrene particles of 5 and $10{\mu}m$ in diameter inside a moving water-in-oil droplet using traveling surface acoustic waves. Since the frequencies for effective control of each diameter were found, microparticles with no labels could be utilized. In addition, the proposed method enabled on-demand preconcentration inside a polydimethylsiloxane microchannel. In-droplet preconcentration of microparticles was realized by splitting a mother droplet with manipulated particles at a downstream bifurcation zone. Given these advantages, the proposed system is a promising acoustofluidic lab-on-a-chip platform for preconcentration inside a droplet.

• 대한원격탐사학회지
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• 제15권1호
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• pp.61-71
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• 1999

한국 남쪽 해역에서 획득한 SAR 영상들로부터 해양 표면에 나타난 물리 현상등이 관측되었다. 1994년 10월 11일 제주도 남서쪽 연안에서의 ERS-1 SAR 영상에서는 남쪽으로부터의 너울 형태의 파랑이 관측되었으며 변도 전달함수를 적용하여 영상으로부터 파랑 스펙트럼을 구하였다. 1996년 8월 15일 제주도 북쪽 연안의 RADARSAT SAR 영상에서 관측된 내부파는 여름철의 성층화된 해수에서 조류 전류시 조류가 해저 지형과의 상호 작용에 의하여 발생한 것으로 추측되며 솔리톤의 형태를 띠고 있다. 1997년 4월 3일 거제도 부근에서 발생한 유류오염 사고 3일 후에 획득한 RADARSAT SAR 영상에서는 사고 당시 유출된 기름들이 잘 나타났으나 복잡한 해안 지형과 생화학적 요인에 의한 다른 Slicks들도 함께 나타났다.

• Ocean and Polar Research
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• 제30권4호
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• pp.453-466
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• 2008

In order to examine the generation mechanism of long ocean waves along the west coast of Korea and to understand the amplification process of the long ocean waves, sea level, atmospheric pressure and wind data observed every minute from 2007 March 29 to 2007 April 1 were analyzed and onedimensional numerical ocean model experiments were performed. An atmospheric pressure jump propagated southeastward from Backryungdo to Yeonggwang along the west coast of Korea with speed of $13{\sim}27\;m/s$ between 2007 March 30 23:00 and 2007 April 1 1:30. Average magnitude of pressure jump was 4.2 hPa. As a moving atmospheric jump propagated from north to south along the coast, long ocean waves were generated and the sea level abnormally rose or fell at Anheung, Kunsan, Wido and Yeonggwang. Average amplitude of sea level rise (or fall) was about 113.6 cm. In a one-dimensional numerical ocean model, nonlinear shallow water equations were numerically integrated and a moving atmospheric pressure jump with traveling speed of 24 m/s was used as an external force. While the atmospheric pressure jump travels over 60 m depth ocean, a long ocean wave is generated. Because the propagation speed of the atmospheric jump is almost equal to that of the long ocean wave, Proudman resonance occurs and the long ocean wave amplifies. As the atmospheric pressure jump moves into the coastal area shallower than 60 m, the speed of the long ocean wave decreases and Proudman resonance effect decreases. However, the amplitude of the long ocean wave increases and wave length becomes shorter because of shoaling effect. When the long ocean wave hits the land boundary, amplitude of the long ocean wave drastically amplifies due to reflection. Data analysis and numerical experiments suggest that the southeastward propagation of an atmospheric pressure jump over the shallow ocean, which is a necessary condition for Proudaman resonance, generated the long ocean waves along the west coast of Korea on 2007 March 31 and the ocean waves amplified due to shoaling effect in the coastal area and reflection at the shore.

• 한국통신학회논문지
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• 제6권1호
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• pp.51-57
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• 1981

半導'||'&'||'#20307;內에서 運動하는 carrier는 Piezo 壓電物質을 進行하는 彈性波에 利得이나 損失을 줄 수 있게 된다. 本 論文에서는 半導 film에서의 drifting carrier와 Piezo 壓電 基板上을 進行하는 Rayleigh Wave間의 相互作用의 表面彈性波 增幅을 論하였다. Piezo 壓電媒質에서 表面波 의 電磁的 境界條件이 表面波 速度에 미치는 影響에 대한 式을 求하였다. 增幅에 필요한 bunching 電子 電子 散에 의해 抑制되므로 높은 周波數에서 利得의 低下를 招來하나 적당한 壓電 物質일 경우 超高周波 領域에서도 상당한 增幅이 기대됨을 알 수 있다.

• 대한기계학회논문집B
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• 제27권8호
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• pp.1081-1088
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• 2003

Numerical investigation on the structures of various Taylor vortices induced in the flow between two concentric cylinders, with the inner one rotating and with a pressure-driven axial flow imposed, is carried out, and compared with the experiments of Wereley and Lueptow [Phys. fluid, 11(12), 1999] who studied the Taylor vortices using PIV in detail. Especially, the properties of helical vortices and random wavy vortices are discussed, and their three-dimensional structures are visualized using the numerical data. Our simulation also predicts that random wavy vortices have quasi-periodic movement which can be explained by traveling waves formed in the azimuthal direction. The numerical results are well consistent with the experimental findings of Wereley and Lueptow.

• Korea-Australia Rheology Journal
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• 제12권2호
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• pp.119-124
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• 2000

Employing the Phan-Thien tanner (PTT) fluids model, dynamic behavior of the non-isothermal melt spinning has been investigated. Subjects such as draw resonance instability, the effects of spinline cooling and of the fluid viscoelasticity on the spinning dynamics have been studied using the governing equations of the system. In particular, the draw resonance criterion based on the traveling times of various kinematic waves in the spinline has been confirmed, the reason why the spinline cooling is stabilizing is analyzed, and the effect of fluid viscoelasticity on the spinline stability is summarized. It is believed that the same method as in this study can be applied with equal ease to other extension deformation processes like film casting and film blowing.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2009년도 제40회 하계학술대회
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• pp.1275_1276
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• 2009

Micropump is very useful component in micro/nano fluidics and bioMEMS applications. Using the flexural vibration mode of PZT bar, a piezopump is successfully made. The PZT bar is polarized with thickness direction. The proposed structure for the piezo-pump consists of an input and an output port, piezoelectric ceramic actuator, actuator support, diaphragm. The traveling flexural wave along the bar is obtained by dividing two standing waves which are temporally and spatially phase shifted by 90 degrees from each other. Fluid is drawn into a forming chamber, eventually the forming chamber closes trapping the fluid therein.