• International Journal of Naval Architecture and Ocean Engineering
• /
• 제13권1호
• /
• pp.163-177
• /
• 2021

Numerical simulations of the Vortex-Induced Vibration (VIV) about a large-scale flexible pipe subject to shear flow were carried out in this paper. Efficiency verification was performed firstly, validating that the proposed fluid-structure interaction solution strategy is competent in predicting the VIV response. Then, the VIV characteristics related to multi-mode and spanwise hybrid waveform about the flexible pipe attributed to shear flow were investigated. When inflow velocity rises, higher vibration modes are apt to be excited, and the spanwise waveform easily convertes from a standing-wave-dominated status to a hybrid standing-traveling wave status. The multi-mode or even multiple-dominant-mode is prone to occur, that is, the dominant mode is often followed by several apparent subordinate modes with considerable vibration energy. Hence, the shedding frequencies no longer obey Strouhal law, and vibration trajectories become intricate. According to the motion analysis concerning the coupled cross-flow and in-line vibrations, as well as the corresponding wake patterns, a tight coupling interaction exists between the structural deformation and the wake flow behind the flexible pipe. In addition, the evolution of the vortex tube along the pipe span and a strong 3D effect are observed due to the slenderness of the flexible pipe and the variability of the vortex shedding attributed to the shear flow.

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

• 한국전자파학회지:전자파기술
• /
• 제8권1호
• /
• pp.29-37
• /
• 1997

CW나 pluse의 형태로 RF를 발진하는 고출력 전자파 발진기는 레이더 체계의 기본요소이다. 레이더 체계의 성공적인 운행을 위한 요건 중에 적합한 전자파 발진기의 선택과 개발을 무시할 수 없다. 이차세계대전을 전후로 활발히 개발되었던 전자파 발진기들 중에는 널리 알려진 Magnetron과 klystron 이 있고 TWT(traveling wave tube)도 그 후 널리 사용되는 발진기이다. 지난 반세기를 지나오며 성능 및 신뢰도 등에서 괄목할만한 발전을 이루었으며 밀리미터파대역의 고출력 발진을 위해 gyrotron 등이 지난 30년간 개발되었다. 현재는 성능, 크기(무게) 및 가격의 문제뿐 아니라 고정밀 영상을 위한 고주파 발진기의 개발이 추진되고 있다. 여기서는 현재 레이더에 쓰이고 있는 magnetron, klystron, TWT 및 gyrotron에 대한 간략한 배경, 원리 및 특성 등을 비교 설명하였다.

• 대한전기학회논문지
• /
• 제40권1호
• /
• pp.18-23
• /
• 1991

Recently SLAMECKA suggested the mathematical dynamic arc model of the SF6 gas circuit breaker [1]. The author applied the above dynamic arc model to the E.H.V. transmission line and investigated the interrupting capability of the SF6 gas circuit breaker. In particular the Runge-Kutta-England numerical method suitable for the use in systems that involve nonlinear dynamic arc and traveling wave was used by converting the current source into the voltage source in the DOMMEL's method [2]. The successful computer resultls were obtained and it was found that the arc time constant and the second derivative of the arc conductance are closely related to the interrupting capability of the SF6 gas circuit breaker.

• 전력전자학회:학술대회논문집
• /
• 전력전자학회 2003년도 춘계전력전자학술대회 논문집(1)
• /
• pp.256-259
• /
• 2003

In this paper describes the development testing results of high density High Voltage Power Supply(HVPS) that employ microwave TWTs. The HVPS consist of number of modules connected in series. A new design that adapt resonant circuit and high density pulse transformer to the high voltage modules makes the HVPS much more reliable. Also High voltage Solid-State modulation using fast switching devices(FET's) and the test results of modulator modules development are represented.

• 한국전자파학회논문지
• /
• 제17권9호
• /
• pp.852-859
• /
• 2006

본 논문에서는 위성통신용 EHF(Extremely High Frequency) 대역 진행파관 증폭기(TWTA: Traveling Wave Tube Amplifier)의 개발 방안을 제안한다. RF(Radio Frequency) 특성 및 이득 향상을 위해 증폭기 설계 및 구현시 선형화기(linearizer)와 구동 증폭기(drive amplifier)를 활용하였다. 80 W급 EHF 대역 진행파관 증폭기의 구현 및 시험을 통하여 제안한 방안이 설계 규격을 만족시키는 결과를 얻었다. 따라서 본 논문에서 제안한 방안은 매우 유용하며, 차후 EHF 대역 유사 장비 개발시 적용 가능할 것으로 판단된다.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2009년도 제40회 하계학술대회
• /
• pp.30_31
• /
• 2009

송전선로에서 고장이 발생할 경우 가능한 빠르게 고장을 검출하고 고장점을 파악하여 수리하는 것은 전력 공급의 신뢰도 및 전력품질 향상에 매우 중요하다. 고장점 추정을 위한 방법은 크게 전압과 전류의 기본파를 이용한 임피던스 계산 방법과 과도신호에 기반한 진행파 해석 방법으로 분류할 수 있다. 과도신호에 기반한 진행파 해석 방법은 매우 빠른 응답을 갖는다는 장점을 갖고 있으나 진행파의 특징을 추출하여 고장거리를 계산하는데에는 어려움이 따른다. 따라서 본 논문에서는 송전선로에서 고장이 발생할 경우 나타나는 진행파의 특징을 분석하고 진행파로부터 고장점 정보를 추출하기 위한 방법을 제시하였다.

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

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2000년도 하계학술대회 논문집 A
• /
• pp.437-439
• /
• 2000

This paper describes a fault location technique using wavelets in underground transmission cable system Estimation of fault location is performed using data sampled at two ends of underground system. In the case of 50% fault of total underground transmission line, fault location is calculated using sampled single-end data in underground transmission line. Traveling wave is utilized in capturing the travel time of the transients along the monitored lines between the relay and the fault point. This travel time information is provided by the wavelet. Simulation was performed using EMTP. ATP Draw and MATLAB. The results of fault location shown in this paper will be evaluated as an effective suggestion for fault to location in real underground transmission line.

• 한국정보통신설비학회:학술대회논문집
• /
• 한국정보통신설비학회 2003년도 하계학술대회
• /
• pp.35-37
• /
• 2003

본 논문에서는 진행파형 전계 흡수 광 변조기를 3차원 FDTD를 이용하여 도파관의 폭과 진성영역의 두께 그리고 N-도핑층의 도핑수준을 변화시키면서 최적화된 구조를 설계하였다. 제작된 소자의 구조는 진성영역의 두께는 $0.9{\mu}m$, 도파관의 폭은 $6{\mu}m$이며 전체 소자의 길이는 $700{\mu}m$ 이다. 제작된 소자의 마이크로파 특성을 측정하였으며 마이크로파 특성과 광 특성을 사용하여 주파수 응답특성을 추정하였다. 소자의 길이가 $400{\mu}m$ 일 때 17.8 GHz의 주파수 응답특성을 얻었다.