• 한국음향학회지
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• 제21권2호
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• pp.110-119
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• 2002

수중퇴적물의 투과음향특성을 실험실 조건에서 고찰하였다. 물로 포화된 입자지름 0.5 mm이하의 모래퇴적물을 (재질의 두께가 1 mm이고 부피가100mm×100m×42m인 아크릴상자 안에) 형성시켜 수중모래퇴적물 시료를 제작하였다. 수중 모래퇴적물 시료의 다공율을 조절할 수 있도록 퇴적물 내부에 내경 3 mm, 길이 42 mm인 원통형 관들을 이용하여 물로 채워진 관을 위치시켜서, 원통다공율이 각각 0 %, 5%, 11%, 18%, 26%인 다섯 개의 수중 모래퇴적물 시료를 만들었다. 수중 모래퇴적물 시료의 음향특성을 다공율과 0.3 MHz에서 4 MHz의 구간에서 주파수의 함수로 분석하였다. 수중 모래퇴적물 시료를 투과한 음향신호는 시료 전체로부터 나온 첫번째파 (first-kind wave)와 관을 통하여 나온 두번째파 (second-kind wave)를 구분하여 관측하였다. 중심주파수 1 MHz에서는 첫번째파가 지배적이었으나 중심주파수 2.25 MHz에서는 두번째파가 지배적이었다. 첫번째파의 경우, 다공율이 증가되면 음압투과계수는 작아지고 음속은 물의 음속에 가깝게 낮아지며, 주파수가 증가되면 투과계수는 점차 작아지나 음속의 변화는 없었다. 두번째파의 경우, 다공율이 커지면 투과계수가 커지고 음속은 변화가 없었으며, 주파수가 증가되어도 투과계수와 음속의 변화는 없었다.

• 한국해안·해양공학회논문집
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• 제27권5호
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• pp.345-352
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• 2015

본 연구에서는 직립식 구조물의 전달파고계수 산정을 위한 2차원 수리실험을 실시하였다. 불규칙파를 입사파로 적용하였으며 직립식 구조물에 대한 전달파고계수 산정식을 제안하고, Goda(1969) 등의 결과와 비교하였다. Goda(1969)의 결과는 입사파로 규칙파를 적용한 결과로서 불규칙파를 적용한 본 실험의 결과와 차이를 보였다. Goda의 결과가 본 연구에 비하여 크게 전달파고계수를 제시하는 것을 알 수 있었다. 또한 Goda는 직립벽에 대하여 평균, 상한 및 하한에 대한 계수값을 제시하였으나(d=h조건), 본 연구에서는 각각의 설계요소(구조물 폭, 수심, 파장 등)가 전달파고계수에 주는 영향을 계수를 통하여 정량적으로 제시하였다. 또한 여유고가 0인 조건에 대한 에너지보존 및 전달파고 특성을 제시하였다.

• 반도체디스플레이기술학회지
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• 제13권4호
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• pp.59-63
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• 2014

Previous studies have selected wireless power transmission system using 2.45 GHz of ISM band, but the researches for 5.8 GHz microwave wireless power transmission have been relatively rare. The 5.8 GHz has some advantages compared with 2.45 GHz. Those are smaller antenna and smaller integrated system for RFIC. In this paper, the 5.8 GHz wireless power transmission system was developed and transmission efficiency was measured according to the distance. A transmitter sent the amplified microwaves through an antenna amplified by a power amplifier of 1W for 5.8 GHz, and a receiver was converted to DC from RF through a RF-DC Converter. In the 1W 5.8GHz wireless power transmission system, the converted currents and voltages were measured to evaluate transmission efficiency at each distance where LED lights up to 1m. The RF-DC Converter is designed and fabricated by impedance matching using full-wave rectifier circuit. The transmission-efficiency of the system shows from 1.05% at 0cm to 0.095% at 100cm by distance.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 춘계학술대회 초록집
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• pp.167.2-167.2
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• 2011

Motions in nature, for example ocean wave, has been playing a significant role for generating electricity production in our modern life. This paper presents an innovative approach for electric power conversion of the vast ocean wave energy. Here, a floating-buoy wave energy converter (WEC) using hydrostatic transmission (HST), which is shortened as HSTWEC, is proposed and designed to enhance the wave energy harvesting task during all wave fluctuations. In this HSTWEC structure, the power take-off system (PTO) is a combination of the designed HST circuit and an electric generator to convert mechanical energy generated by ocean wave into electrical energy. Several design concepts of the HSTWEC have been considered in this study for an adequate investigation. Modeling and simulations using MATLAB/Simulink and AMESim are then carried out to evaluate these design concepts to find out the best solution. In addition, an adaptive controller is designed for improving the HSTWEC performance. The effectiveness of the proposed HSTWEC control system is finally proved by numerical simulations.

• 한국해안·해양공학회논문집
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• 제21권2호
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• pp.127-135
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• 2009

Reid and Kajiura(1957)은 해저면에 무한한 깊이의 투수층이 존재할 경우에의 파의 감쇠율을 유도하였다. 본 연구에서는 유한한 깊이의 투수층이 존재할 경우에의 파의 감쇠율을 선형파이론을 이용하여 유도하였다. 그리고 이를 확장하여 해저면에 재질이 다른 2 층 또는 3 층의 투수층이 존재할 경우에 파의 감쇠율을 제시하였다. 다음으로 이를 완경사 방정식에 적용하여, 해저면에 투수층이 존재할 경우에의 파의 투과율을 계산하였으며, 1층 투수층이 존재할 경우의 수치계산결과를 Flaten and Rygg(1991)의 적분식 방법과 비교하여 검증하였다.

• 산업기술연구
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• 제25권B호
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• pp.115-120
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• 2005

Impact seismic wave method is a method for non-destructive testing of concrete structure using of stress wave which is propagate and reflected from internal flaws within concrete structure and external surface. In this study, we performed frequency domain method using impact seismic wave test for safety diagnosis of civil engineering structure. And reflection method which is used for one-dimensional target such as tunnel lining and transmission method are compared with each other.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2001년도 춘계학술대회 논문집
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• pp.744-747
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• 2001

This paper shows shear wave behavior of CFRP composite laminates as a polar grid form to evaluate vibration pattern of ultrasonic transducers, which gives measured modelling fundamental contents of nondestructive evaluation. Polarized direction can be obtained by using a c-scanner and sensitivity of transducers is founded when using through-transmission method of two transducers. And modelling of vector decomposition is presented based on ply-to-ply method to apply practicable nondestructive evaluation of CFRP laminate lay up. This modelling decomposes the transmission of linearly polarized wave into orthogonal components through each ply of a laminate. It is found that a high provable shows between the model and experimental developed in characterizing layup of CFRP composite laminates.

• 한국해양공학회지
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• 제24권3호
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• pp.11-20
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• 2010

The purpose of this study is the investigation of the wave interaction with the rectangular floating breakwater. The flow profile obtained by PIV technique is represented to understand the vortical flow due to the wave interaction with a rectangular floating breakwater in the roll motion and the fixed condition. Also, the transmission coefficients are compared in both conditions over the extensive wave periods, which represent the performance of breakwater to attenuate the incoming waves. These results would be applied to design the floating breakwater having the mooring system to improve its performance for a certain wave period.

• 한국항만학회지
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• 제8권1호
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• pp.31-40
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• 1994

Experimental study is carried out to verify the advantages of an air chamber structure in controlling the wave transformation and its dynamic responses. The open, cross and vertical mooring systems are employed in experiments to investigate the variations of wave transmission ratio, natural period of the structures and tensile force acting on the mooring line according to the change of the initial air depth inside the air chamber structure. Experimental results show that the air chamber floating structure expresses the smaller wave transmission ratio and tensile force acting on the mooring line than general one without air chamber, expecially in the long period region of incident wave. Therefore, it is concluded that the air chamber structure suggested in this study can play good roles as a wave controlling castal structure, and a substitute structure of a general floating structure.

• 한국소음진동공학회논문집
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• 제23권6호
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• pp.574-580
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• 2013

At high frequencies, the statistical approach such as statistical energy analysis(SEA) and energy flow analysis(EFA) has been applied for estimation of vibroacoustic responses of various built-up structures. The energy coupling relationship between finite coupled structures is required to estimate vibrational energetics of built-up structures. Mindlin plate theory includes the rotatory inertia and shear deformation effects which are dominant as frequency increases. In this paper, the wave transmission analysis is successfully performed for EFA of co-planar coupled Mindlin plates.