• 한국음향학회:학술대회논문집
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• 한국음향학회 1998년도 학술발표대회 논문집 제5권
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• pp.18-24
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• 1998

최근의 연구를 통해 해양의 내부파가 음파전달에 영향을 주어 비정상적인 손실을 일으키는 것을 밝혀졌다. 한국 동해세서도 강한 수온약층을 중심으로 내부파가 존재할 것으로 여겨져 왔으며, 이를 규명하고자 '98년 6월 각종 장비를 동원한 해양 관측을 동해항 근해에서 실시하였다. 또한 내부파에 의한 음파의 전파 특성을 추정학자 음원과 수신기를 고정한 상태에서 음향 실험을 실시하였다. 실험 결과 전형적인 내부파는 주기가 약 5-12분이고 최대 진폭은 15m 정도임이 밝혀졌다. 특히 10여개의 내부파 묶음이 약 36cm/sec 의 속도로 이동하고 있음도 확인하였다. 15개의 음향센서로 이뤄진 수직선배열 수신기와 음원을 이용한 음향 실험결과 역시 4-12분 주기에서 부분적으로 스펙트럼이 높게 나타났으며, 특히 주파수 1kHz 인 경우에는 4, 6분 주기에서 15개의 센서에 대해 일관되게 높은 스펙트럼 준위가 나타났다. 내부파에 의한 이러한 음파의 특성은 음파의 모든간 결함으로 나타나는 일종의 간섭 현상으로 설명될 수 있다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.336-340
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• 2017

초음속 유동이 덕트와 같은 내부를 지날 때 의사충격파라는 유동 구조가 생성된다. 의사충격파는 충격파-경계층 상호작용의 결과이며 이를 정확히 모사하기 위해서는 충격파 구조 뿐만 아니라 경계층 거동 역시 정확히 예측해야 한다. 따라서 본 연구에서는 유동의 정확한 입구조건을 알아내고 이를 이용하여 사각 덕트 내부에서 발생하는 의사충격파를 2차원 전산유동해석으로 해석한다.

• 한국통신학회논문지
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• 제34권11A호
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• pp.904-908
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• 2009

The PZT(lead, zirconium, titanium) based ceramics which, are reported to be ferroelectric materials have their important applications in the areas of surface acoustic waves (SAW), filters, infrared detectors, actuators, ferroelectric random acess memory, speakers, electronic switches etc. Moreover, these PZT materials possess the large electromechanical coupling factor, large spontaneous polarization, low dielectric loss and low internal stress etc. Hence, keeping in view the unique properties of PZT piezoelectric ceramics we also tried to synthesize indigenously the small sized PZT ceramic powder in the laboratory by using the modified sol-gel approach. In this paper, Propyl alcohol based sol-gel method was used for preparation of PZT piezoelectric ceramic. The powder obtained by this sol-gel process was calcined and sintering to reach a pyrochlore-free crystal phase. The characterization of synthesized material was carried out by the XRD analysis and the surface morphology was determined by high resolution scanning electron microscopy.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2002년도 추계학술대회 논문집
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• pp.240-244
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• 2002

Mathematical and numerical modelling is proposed to evaluate the horizontal behavior of a wave-driven upwelling device and then, the horizontal behavior and the structural ability are inspected for the regular and irregular waves in East sea. Analysis results indicate that the buoy moves with the water particle and the pipe behaves cantilever beam. Also, it is found that the strength of pipe is sufficient to resist the internal moment

• 대한전기학회논문지
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• 제40권12호
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• pp.1203-1210
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• 1991

This paper proposes a new distance relaying method based on fault initiated travelling waves for transmission line protection. The characteristics of this method are ultra high speed and excellent sensitivity. Travelling wave technique which is one of the distance relaying methods uses the discrete cross correlation function for discrimination between internal and external fault is remarkably reduced in case of a close up fault and an inception angle near or equal to zero fault. To cope with this problem, a new fast algorithm which uses backward wave summation method with fixed window is presented. The proposed method has been tested by numerical simulations using the EMTP.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.103-106
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• 2005

This paper reviews the dynamic load phenomenon referred to as 'silo quaking', caused shock vibration and loud noise, during gravity discharge in coal silos. Quaking in tall silo is examined using experimental data obtained from a Coal Power Plant and several experimental and numerical investigations available in the published literature. In the experiment, the acceleration was measured at various height on the silo column and floor and by doing so, not only could the variation of the amplitude of the quaking be observed, but also the propagation of waves could clearly be seen. Through an overview of recent research on this subject, it is shown that the current silo quaking is produced by slip-stick friction between the internal wall of silo and the granular material, i.e. coal.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 1995년도 제5회 학술강연회논문집
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• pp.69-83
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• 1995

A great number of experimental data indicating shock-induced separation(SIS) in internal or external supersonic flows were reviewed to make clear the mechanism of SIS and to present the criterion of turbulent boundary layer separation. The interesting conclusions were obtained for the considerably wide range of flow geometries that the incipient separation is almost independent of the flow geometries, and that it is relatively unaffected by changes in gas specific heat, and boundary layer Reynolds number, Furthermore, the pressure rise necessary to separate boundary layer in external flows was found to be applicable to SIS in overexpanded propulsion nozzles. This is due to the fact that the SIS phenomenon caused by the interaction between shock waves and turbulent boundary layers is processed through a supersonic deceleration. This is, the SIS in almost all of interacting flow fields is governed by the concept of free interaction, and criterion of SIS is only a Function of upstream Mach number.

• International Journal of Naval Architecture and Ocean Engineering
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• 제13권1호
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• pp.178-186
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• 2021

The wave power extraction by multiple Wave Energy Converters (WECs) deployed in a Y-shaped Water Channel Resonator (WCR) has been investigated. A WCR consists of a long water channel, and a V-shaped wave guider installed at the entrance of a water channel. If the period of the incident waves coincides with the natural periods of the fluid in a WCR, resonance occurs, as a result, the internal fluid in a WCR is greatly amplified. To estimate the wave power by multiple WECs placed at the antinodal points in a WCR, the heave motion response, time-averaged power, and capture width ratio were calculated for several design parameters. Also, the systematic model tests were conducted in a 2D wave tank. The numerical results are in good agreement with the experimental data. It was verified that a WCR helps the WECs to produce electricity more effectively by amplifying the wave energy in a WCR.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2021년도 가을 학술논문 발표대회
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• pp.146-147
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• 2021

In this study, the deterioration of concrete subjected to high temperature was evaluated using harmonics. When concrete is exposed to high temperatures, its mechanical properties deteriorate. In order to evaluate this deterioration, a method of analyzing the waveform of elastic waves was applied. As the heating temperature increased, the fundamental wave of the 50 kHz elastic wave passing through the concrete decreased. In addition, harmonics were generated at each temperature, and the higher the heating temperature, the greater the ratio of harmonics. The higher the compressive strength, the greater the amplitude of the fundamental wave, and this phenomenon is thought to be due to the internal structure of concrete.

• 대한한방내과학회지
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• 제27권1호
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• pp.276-287
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• 2006

Background & Objective : The herbal medicine Sojukgunbihwan granule has been used for the treatment of functional dyspepsia, generally categorized as a gastric dysmotility disease. However, its mechanisms are not yet well known. Therefore, the effects of Sojukgunbihwan granules on gastric motility in rats was investigated. Methods : The myoelectrical activity of the gastric smooth muscle was recorded by a bipolar electrode placed at the gastric antrum of rats. The contractile waves were measured for 30 minutes before and after intragastric administration of each solution(normal saline, Pyungwisan 40mg/kg, Sojukgunbihwan granules 60mg/kg) and expressed as the motility index. Gastric emptying was measured by the number of glass beads expelled from the stomach(containing one hundred 1mm glass beads) within an hour after glass beads and test drugs(normal saline, Pyungwisan 40mg/kg, Pyungwisan 120mg/kg, Sojukgunbihwan granules 60mg/kg, Sojukgunbihwan granules 180mg/kg) were administered. In another series of experiments to evaluate the mechanisms of Sojukgunbihwan granules under delayed conditions, the rats were treated with atropine sulfate(1 mg/kg, s.c.), cisplatin(10mg/kg, i.p.), and NAME($N^G$-nitro-L-arginine methyl ester, 75mg/kg, s.c.) respectively. Results : Intragastric administration of Sojukgunbihwan granules increased the myoelectrical activity significantly, gastric motility index rose 25%, and gastric emptying of glass beads was significantly enhanced over a period of 60minutes. Under the delayed gastric emptying induced by atropine sulfate, cisplatin, and NAME, Sojukgunbihwan granules aggravated gastric emptying in the atropine sulfate($5.71{\pm}3.45\;vs\;3.71{\pm}4.42$) and cisplatin($13.86{\pm}3.53\;vs\;5.14{\pm}5.05$, p<0.01) treated groups, but enhanced gastric emptying in the NAME treated group($5.00{\pm}3.21\;vs\;11.71{\pm}5.65$, p<0.05). Conclusions : Results suggest that Sojukgunbihwan granules stimulate gastric motility through cholinergic and 5-hydroxytryptamine 3 receptors. Results are indicative of Sojukgunbihwan as an especially effective remedy in dysmotility-like functional dyspepsia with impaired reservoir functions such as gastric adaptive relaxation.