• Title/Summary/Keyword: regular wave

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Hydraulic Experiments for the Reflection Characteristics of Perforated Breakwaters (유공방파제의 반사특성에 관한 수리실험)

  • 박우선;전인식;이달수
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.5 no.3
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    • pp.198-203
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    • 1993
  • Hydraulic experiments were carried out to investigate the reflection characteristics of perforated breakwaters in regular wave conditions varying the width of wave chamber and the shape of perforated wall. It was found that the reflection coefficient of the perforated breakwater was very sensitive to the change of wave chamber width. giving its minimal value when the width of the wave chamber is approximately 0.2 times the wave length in the wave chamber. This phenomenon may be resulted from the wave resonance inside the wave chamber. The reflection coefficients slightly varied for all shapes of perforated wall. i.e., vortical slit, horizontal slit or circular hole. However, the reflection trend of the structure was not significantly affected by the shape of the perforated wall.

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Numerical Analysis of Shock-Wave Focusing from a Two-Dimensional Parabolic Reflector (2차원 포물형 반사경에 의한 충격파의 촛점형성에 대한 수치해석)

  • 최환석;백제현
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.3
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    • pp.612-623
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    • 1994
  • Shock-wave focusing from a two-dimensional parabolic reflector was simulated using an explicit finite volume upwind TVD scheme. Computations were performed for three different incident shock speeds of $M_s$ = 1.1, 1.2 and 1.3, corresponding to the relatively weak, intermediate, and strong shock waves, respectively. Numerical solutions nicely resolved all the waves evolving through the focusing process. As the incident shock strength increase, a transition was observed in the shock-fronts geometry that was caused by the change in the reflection type of converging shock fronts on the axis of symmetry, from regular-type to Mach-type reflection. The computed maximum on-axis pressure amplification and the trajectories of three-wave intersections showed good agreement with experimental results. The strong nonlinear effect near the focal region which determines the shock-fronts geometries at and behind the focus and at the same time confines the pressure amplification at the focus was clearly revealed from the present numerical simulation.

Coupled Vibration of Stiffened Plates due to Motion of Stiffeners (보강재의 운동으로 인한 보강판의 연성진동)

  • 이현엽
    • Journal of KSNVE
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    • v.7 no.1
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    • pp.153-159
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    • 1997
  • In a stiffened plate reinforced on one of its sides by beam type stiffeners, the asymmetry about the plate mid-plane induces coupling between flexural wave and longitudinal wave. In this research interactions between flexural and longitudinal wave motion are analyzed in a stiffened plate which is reinforced only in one direction. The plate is modelled as a beam to which offset spring-mounted masses are attached at regular intervals. Propagation constants of the coupled waves and corresponding characteristic waves are derived by using periodic structure theory, and a computer code is developed. Also, sample calculations are carried out and the results are discussed.

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Estimation of Wave Energy Extraction Efficiency for a Compact Array System of Small Buoys (밀집 배열 부이시스템의 파랑에너지 추출 효율 추정)

  • Choi, Yoon-Rak
    • Journal of Ocean Engineering and Technology
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    • v.25 no.1
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    • pp.8-13
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    • 2011
  • A compact array system of small buoys is used for wave energy extraction. To evaluate the performance of this system, hydrodynamic analysis is carried out in regular waves using the higher order boundary element method. The motion response of each buoy is calculated considering hydrodynamic interactions caused by other buoys. The effect of energy extraction device is modeled as a linear damping load. The efficiencies of energy conversion are compared using the various sizes and arrangements of the array system and the damping coefficients for energy extraction. The increase in size or the packing ratio of the system gives better efficiency. However, the wave condition and the cost for the system should be considered to optimize performance from the perspective of engineering and economics. The proposed nondimensionalized damping coefficient for energy extraction is 0.1~0.5.

A Study of Wave and Current Forces on Cylinders (실린더에 작용하는 파력 및 조류력에 관한 연구)

  • 박광동;조효제;구자삼
    • Journal of Ocean Engineering and Technology
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    • v.15 no.4
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    • pp.14-19
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    • 2001
  • In this paper, the wave and current forces acting on cylinders are investigated by theoretical and experimental methods. The models used are one-cylinder, four-cylinder and semi-submersible types. The theoretical investigations are carried out by the Morison equation and three dimensional source distribution method to calculate exciting forces in waves with and without currents. The experimental investigations are carried out in the wave tank which can generate currents in both directions. In these tests, the models have been exposed to the regular waves with and without currents. It is shown that the exciting forces acting on the one-cylinder or four-cylinders can be approximately estimated by the Morison equation and also by the diffraction theory. However, the Morison equation seems to be not appropriate to estimate the exciting forces on the present type of semi-submersible.

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Scouring Characteristics at the Toe of the Rubble Mound Breakwater (사석방파제 toe부에서의 세굴특성에 관한 연구)

  • 윤한삼;남인식;류청로
    • Journal of Ocean Engineering and Technology
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    • v.16 no.4
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    • pp.7-12
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    • 2002
  • This study is aimed to find the scouring mechanism at the toe of rubble mound structures. To investigate the characteristics of scouring in front of the structure, experiments were performed with regular waves in a 2-D flume. The results of this study are as follows. 1) It can be said the characteristics of incident wave causes rolling and sliding of armour block. The difference of wave pressure on the slope, internal flow as well as settlement of armour block due to the weight cause scouring. 2) It is observed that scouring depth at the toe increased when wave height or period increased. The location of ultimate scouring and deposition depth moved seaward when wave period increased. 3) The failure of rubble mound structure was caused by waves or scouring. Failure by erosion increased with high waves and long waves. 4) Using surf-similarity parameter including characteristics of incident waves and structure, scouring and deposition pattern were found and their limit was formulated.

Development of Millimeter wave Radar System for an Automobile (차량용 밀리파 레이더 시스템의 개발)

  • 박홍민;이규한;최진우;신천우
    • Proceedings of the IEEK Conference
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    • 2001.06e
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    • pp.25-28
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    • 2001
  • This paper introduce a millimeter-wave radar system. As Fig 1 shows, This system consists of millimeter-wave radar front-end and digital signal processing parts through receive waves regarding up-coming obstacles. The system works as follow process; (1) Generate regular tripodal waves using the FMCW pulse generator (2) Transmit/Receive waves regarding up-coming obstacles (3) Analog filtering (4) FIFO memory interface (5) FFT(Fast Fourier Transform) (6) Calculation of distance / speed between cars (7) Object display and calibration. We have progress to solve the problem like as increase of traffic accidents causing damage and injuries due to the increased number of motor vehicles and long distance driving, and Need for a device to help drivers who are in trouble due to bad weather conditions. We are expect to Take the lead as a core technology in the ITS industry and to develop circuit and signal processing technologies related to millimeter-wave bandwidth.

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Virtual Reality Technology for Multipurpose Numerical Simulation in Marine Environmental Engineering (해양환경공학의 다목적 수치시뮬레이션을 위한 Virtual Reality 기술)

  • Park, Jong-Chul
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • 2002.10a
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    • pp.174-180
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    • 2002
  • A virtual reality technology for multipurpose numerical simulation is developed to reproduce and investigate a variety of ocean environmental problems in a 3D-Numerical Wave Tank. The governing equations for solving incompressible fluid motion are Navier-Stokes equation and continuity equation, and the Marker-Density function technique is adopted to implement the fully-nonlinear free-surface kinematic condition. The marine environmental situations, i.e. waves, currents, wind, etc., are reproduced by use of multi-segmented wavemaker on the basis of the so-called "snake-principle". In this paper, some numerical reproduction techniques for regular and irregular waves, multi-directional waves, Bull's-eye wave, wave-current, and solitary wave are presented, and a model test in motion with large amplitude of roll angle is conducted in the developed 3D-NWT, using a overlaid grid system.

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The Effect of Wave Control in the Harbor by the Fixed Floating Structure (고정 부유 구조물에 의한 항만정온도의 제어효과)

  • Kim H.P.;Lee J.W.
    • Journal of Korean Port Research
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    • v.7 no.1
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    • pp.79-88
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    • 1993
  • This study deals with the case of a fixed floating structure(FFS) at the mouth of a rectangular harbor under the action of waves represented by the linear wave theory. Modified forms of the mild-slope equation is applied to the propagation of regular wave over constant water depth. The model is extended to include bottom friction and boundary absorption. A hybrid element approximation is used for calculation of linear wave oscillation in and near coastal harbor. Modification of the model was necessary for the FFS. For the conditions tested, the results of laboratory experiments by Ippen and Goda(1963), and Lee (1969) are compared with the calculated one from this model. The cases of flat cylinderical structures, both fixed and floating, were taken to be in an intermediate water depth.

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Experimental study on multi-level overtopping wave energy convertor under regular wave conditions

  • Liu, Zhen;Han, Zhi;Shi, Hongda;Yang, Wanchang
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.10 no.5
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    • pp.651-659
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    • 2018
  • A multi-level overtopping wave energy converter was designed according to the large tidal range and small wave heights in China. It consists of two reservoirs with sloping walls at different levels. The reservoirs share a common outflow duct and a low-head axial turbine. The experimental study was carried out in a laboratory wave-flume to investigate the overtopping performance of the device. The depth-gauges were used to measure the variation of the water level in the reservoirs. The data was processed to derive the time-averaged overtopping discharges. It was found that the lower reservoir can store wave waters at the low water level and break the waves which try to climb up to the upper reservoir. The upper sloping angle and the opening width of the lower reservoir both have significant effects on the overtopping discharges, which can provide more information to the design and optimization of this type of device.