• Journal of Korea Water Resources Association
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• 제40권1호
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• pp.51-62
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• 2007

To estimate more accurately the outflow over a sharp crested side weir, it is necessary to analyze the flow characteristics over side weir and to estimate the discharge coefficient in the weir equation. The purpose of this study is to estimate the discharge coefficients of sharp crested rectangular and triangular side weirs by means of hydraulic model experiments with the variations of upstream Froude number in the main channel and length and apex angle. Experimental results show that the discharge coefficients depend on the shape and geometric conditions of side weir as well as the upstream Froude number in the main channel. Through the multiple regression analysis, formulas of discharge coefficient for rectangular and triangular types are proposed and its applicability is confirmed by comparing estimated and measured discharges over side weirs.

• Journal of Korean Society of Coastal and Ocean Engineers
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• 제31권2호
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• pp.41-49
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• 2019

We approximately obtain heights of cnoidal waves overtopping on a porous breakwater using both the one-layer Boussinesq equations (Vu et al., 2018) and the two-layer Boussinesq equations (Huynh et al., 2017). For cnoidal waves overtopping on a porous breakwater, we find through numerical experiments that the heights of cnoidal waves overtopping on a low-crested breakwater (obtained by the Navier-Stokes equations) are smaller than the heights of waves passing through a high-crested breakwater (obtained by the one-layer Boussinesq equations) and larger than the heights of waves passing through a submerged breakwater (obtained by the two-layer Boussinesq equations). As the cnoidal wave nonlinearity becomes smaller or the porous breakwater width becomes narrower, the heights of transmitting waves obtained by the one-layer and two-layer Boussinesq equations become closer to the height of overtopping waves obtained by the Navier-Stokes equations.

• International Journal of Naval Architecture and Ocean Engineering
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• 제8권1호
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• pp.38-52
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• 2016

This paper describes the nonlinear dynamic motion behavior of a ship equipped with a portable dynamic positioning (DP) control system, under external forces. The waves, current, wind, and drifting forces were considered in the calculations. A self-tuning controller based on a neuro-fuzzy algorithm was used to control the rotation speed of the outboard thrusters for the optimal adjustment of the ship position and heading and for path tracking. Time-domain simulations for ship motion with six degrees of freedom with the DP system were performed using the fourth-order RungeeKutta method. The results showed that the path and heading deviations were within acceptable ranges for the control method used. The portable DP system is a practical alternative for ships lacking professional DP facilities.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 한국해양공학회 2000년도 춘계학술대회 논문집
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• pp.63-68
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• 2000

A very large floating structure has rather small motion characteristics as to the whole body, while the motion at end part of such structure becomes largest due to the elastic motion of the structure. This paper presents on the theoretical result on the relative motion characteristics and green water phenomena of VLFS in waves This phenomena affect not only to strength of the structure but also the determination of depth of structure. To predict motion responses of structure in regular waves, the source-dipole distribution method and F.E.M is used By irregular wave results, the probability of occurrence of green water and response of the structure were calculated.

• JSTS:Journal of Semiconductor Technology and Science
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• 제8권1호
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• pp.32-39
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• 2008

Tunnel oxide of non-volatile memory (NVM) devices would be very difficult to downscale if ten-year data retention were still needed. This requirement limits further improvement of device performance in terms of programming speed and operating voltages. Consequently, for low-power applications with Fowler-Nordheim programming such as NAND, program and erase voltages are essentially sustained at unacceptably high levels. A promising solution for tunnel oxide scaling is tunnel barrier engineering (TBE), which uses multiple dielectric stacks to enhance field-sensitivity. This allows for shorter writing/erasing times and/or lower operating voltages than single $SiO_2$ tunnel oxide without altering the ten-year data retention constraint. In this paper, two approaches for tunnel barrier engineering are compared: the crested barrier and variable oxide thickness. Key results of TBE and its applications for NVM are also addressed.

• Proceedings of the Korea Water Resources Association Conference
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• 한국수자원학회 2011년도 학술발표회
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• pp.156-159
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• 2011

횡월류위어를 천변저류지 등의 유입부에 설치하기 위해서는 정확한 월류량을 산정하는 것이 선행되어야 한다. 본 연구에서는 실제 하천에 적용성이 높은 것으로 판단되는 사다리꼴 수로에서 수리실험을 실시하였고, 횡월류위어의 형상변화에 따른 흐름분석 및 유량계수산정을 위하여 직사각형, 1:1사다리꼴, 1:2사다리꼴 형상의 횡월류위어를 설치하여 수리실험을 하였으며, 상류 Froude수, 위어높이, 위어길이, 본류수로폭, 수로경사 등을 고려하였다. 분석결과 광정횡월류위어에서 /y, ��/$y_{u}$, $Fr_{u}$, L B의 순서로 중요도가 큰 것을 확인하였고, 다중회귀분석을 통해 유량계수식을 제시하였다. 또한 기존 연구자들의 실험자료와 본 실험의 연구자료를 비교하였으며, 측정된 월류량과 계산된 월류량을 비교하여 유량계수식의 적용성을 확인하였다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• 제5권2호
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• pp.76-83
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• 1993

In this study, an approximate method for calculating the directional spectrum of waves encountering a current in shallow water is developed. The wave trains in tile directional spectrum are assumed to be linear and Gaussian; development of the spectrum requires that the waves also be short crested. The Miche's breaking criterion is imposed to determine the upper limit of wave height and to establish an expression for the breaking wave elevation in terms of the ideal wave's elevation and the second time derivative of wave elevation. Two examples are given; one for a Wallops directional spectrum encountering a shear current and another with an upwelling current.

• Journal of the Korean Institute of Navigation
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• 제22권2호
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• pp.99-112
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• 1998

It is very important to investigate the hull response of a fishing vessel in waves to ensure the safe navigation and fishing operation in rough seas by preserving excellent seakeeping qualities. For this purpose, we measured pitching and rolling response of three fishing vessels in seas using real seas experimental measuring system and analyzed the data by statisticawl and spectral analyzing method. We compared the measured results with theoretical results to give the validity of measuring system and experimental results. From the result we know that a good agreement between the experimental and theoretical results are shown except following seas. But there are little difference between both results in the other deirection too, which are caused by the effects of short crested waves of real seas.

• Bulletin of the Society of Naval Architects of Korea
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• 제21권3호
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• pp.35-42
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• 1984

In this paper, the lateral motions of a ship in the time domain are treated by applying the Impulse Response Function Technique. The acceleration, and displacement of a ship in the time domain are needed for the purpose of such automatic controls as the fire control system and the auto-pilot of ocean-going vessels, etc. The response Amplitude Operators of a ship are calculated by the Strip Method of Salvesen-Tuck-Faltinsen, and the Pierson-Moskowitz Spectrum multiplied by spreading function is used to represent the short crested ocean waves. The ocean wave elevations in the time domain are simulated according to the Method of Borgman. Finally the rudder effect is considered by simply adding the force and moment due to the rudder to the wave exciting force. And the results of lateral motions with and without rudder are shown.

• Proceedings of the Korea Water Resources Association Conference
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• 한국수자원학회 2022년도 학술발표회
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• pp.248-248
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• 2022

Hwang(2015)은 불연속 지형을 지나는 천수 흐름의 수치 해석에서 불연속 전면에 의한 추력(thrust)에 주목하여 그 영향을 흐름률(flux) 계산에 반영하는 새로운 기법을 제시하였다. 이 기법 덕분에 수심 적분 모형으로도 계단이나 보와 같이 직립한 하천 구조물의 불연속면을 경사로 완화하지 않고 직접 모의할 수 있다. 직립 측면 위어 실험에 Hwang(2015)의 기법이 적용됨으로써 연직면을 경사면으로 완화하여야 하는 기존의 수심 적분 모형에 비해 계산 격자 개수가 53%로 줄었다(Hwang, 2019). Hwang(2019)은 기존 모형과 비교를 통해, 정확도를 어느 정도 유지하면서도, 소요된 계산 시간이 20%에 불과하다고 주장하였다. 여기에서는 보다 다양한 직립 광정 위어 실험에 적용하여 수심 적분 모형에 의한 월류량을 검토하고자 한다.