• Title/Summary/Keyword: Wall reflection

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Estimation of Optimal Slit Length of Perforated Wall below Still Water Level: Single Chamber Condition (정수면 아래 최적 유공부 길이 산정 : 유공 1실 조건)

  • Kim, Young Taek;Lee, Jong In
    • Journal of Korea Water Resources Association
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    • v.46 no.4
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    • pp.327-334
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    • 2013
  • In this study, the optimal slit length of perforated wall with single chamber below the still water level (SWL) is studied through the two dimensional test. The relationship between the reflection coefficient and the shape of structures such as chamber width(B) and slit length(S) are investigated by applying the various wave conditions. The random waves were used for the test by using Bretschneider-Mitsuyasu frequency spectrum. Minimum reflection coefficient is obtained at $B/L_s{\approx}0.15$ condition, this result is different from the regular wave condition. Also the minimum reflection coefficients are measured at $S/H_s{\approx}2.5$. This means that the optimal slit length below the still water level is 2.5 times of the incident wave height.

Numerical Study on the Suppression of Shock Induced Separation on a Strongly Heated Wall (강하게 가열된 벽면 위에서 충격파에 의한 경계층 박리의 제거에 관한 수치 연구)

  • LEE Doug-Bong;SHIN Joon-Cheol
    • Journal of computational fluids engineering
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    • v.2 no.2
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    • pp.59-72
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    • 1997
  • A numerical model is constructed to simulate the interactions of oblique shock wave / turbulent boundary layer on a strongly heated wall. The heated wall temperature is two times higher than the adiabatic wall temperature and the shock wave is strong enough to induce boundary layer separation. The numerical diffusion in the finite volume method is reduced by the use of a higher order convection scheme(UMIST scheme) which is a TVD version of QUICK scheme. The turbulence model is Chen-Kim two time scale model. The comparison of the wall pressure distribution with the experimental data ensures the validity of this numerical model. The effect of strong wall heating enlarges the separation region upstream and downstream. In order to eliminate the separation, wall suction is applied at the shock foot position. The bleeding slot width is about same as the upstream boundary layer thickness and suction mass flow is 10% of the flow rate in the upstream boundary layer. The final configuration of the shock reflection pattern and the wall pressure distribution approach to the non-viscous value when wall suction is applied.

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A Low-Reynolds Number Second Moment Closure for Turbulent Heat Fluxes (저레이놀즈수 2차 모멘트 난류 열유속모형 개발에 관한 연구)

  • 신종근;최영돈;이건휘
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.12
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    • pp.3196-3207
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    • 1993
  • A second moment turbulent closure for the turbulent heat flux near a wall is developed by modification of model constants in pressure interaction term as the variables of the turbulent Reynolds number using the universal properties of turbulent heat flux near the wall. The present model shows that model constant for the wall reflection term in pressure interaction is most important in modelling of the near wall heat flux. Fully developed pipe flows with constant wall heat flux are tested to validate the proposed model. In most of calculation region, the predicted turbulent properties agree better with the experimetal data than the results from standard algebraic heat flux model which use the uniform model constants.

On the Hydraulic Characteristics of Efficient Long Wave Energy Absorber-Eco-breaker 2 (장파 제어체 Eco-breaker 2의 수리특성)

  • Cho, Yong Jun;Kim, Ho Min
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.28 no.5B
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    • pp.547-558
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    • 2008
  • With the advent of super cargo ship due to the explosive increase in the amount of cargo shipped via seas, some mega ports are under construction in South Korea, to accommodate the super cargo ship, and some of them already enter their final phase. To sustain the harbor tranquility, mega ports usually comprise huge vertical type breakwaters which are intrinsically vulnerable to the attack of long waves. In this rationale, we present the chamber type breakwater with a circular curtain wall - Eco-breaker 2, to alleviate the reflection of long waves and numerically investigate the hydraulic characteristics of Eco-breaker 2. As a wave driver, we use the Navier-Stokes eq., the most robust wave driver, using SPH (Smoothed Particle Hydrodynamics) and LES (Large Eddy Simulation). For the verification of numerical results, we also carried out hydraulic model test. It is shown that Eco-breaker 2 can effectively alleviate the reflection of long waves with its inherited large organized eddies encompassing the water chamber and some region off the curtain wall of varying size. It is also shown that the scope and strength of large organized eddies strongly depends on the incident wave period, and the reflection coefficient can be lowered to 0.18 by tuning the size of water chamber such that resident time at the chamber is just short of the half period of incident waves. Based on these results, we present the specification of Eco-breaker 2 to boost its use on the development of water environment friendly harbor worldwide.

Feasibility test on EDZ detection by using borehole radar survey

  • Cho, Seong-Jun;Kim, Jung-Ho;Son, Jeong-Sul;Kim, Chang-Ryol;Sugn, Nak-Hun
    • 한국지구물리탐사학회:학술대회논문집
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    • 2006.06a
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    • pp.239-244
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    • 2006
  • Borehole radar reflection surveys were carried out in the horizontal borehole to detect EDZ while constructing the tunnel for the research facility of the nuclear waste disposal in Korea. The horizontal borehole has been bored at a length of 35 m from shelter to be parallel with the tunnel which would be planed. While the tunnel has been constructing with the explosive excavation, the borehole radar reflection surveys carried out 5 times with the interval of 2 or 4 days for monitoring EDZ. The most typical change of the reflection event resulted from the face of the wall of tunnel which had been produced newly by the excavation of the tunnel daily, EDZ has been detected with constructing images of difference between two measurement stages, and also the change of EDZ through the time has been done, which is due to the generation of crack and weakening of the rock strength of the face of the tunnel's wall near previous portion of the face of a blind end of tunnel according to explosive excavation.

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On an Analysis of Reflection and Transmission Coefficients by a Vertical Slit Plate (직립 슬릿판에 의한 반사율과 투과율 해석)

  • 조일형;김남형
    • Journal of Ocean Engineering and Technology
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    • v.16 no.3
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    • pp.1-7
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    • 2002
  • In this paper, a numerical model to analyze the performance of a vertical slit-type wave absorber is developed under the assumption of inviscid water waves. The formulation combines the linear potential theory with a semi-empirical description of the eddy-shedding at a slit-type wave absorber. We investigated the reflection coefficients over a wide frequency range for a vertical slit-type wave absorber both with and without a solid rear wall. Model test was conducted at KRISO' s two dimensional wave tank to validate the theoretical results. It is found that the agreement between theoretical results and experimental data is surprisingly good. We found that the wave absorbing system using a vertical slit plate has sufficient potentials for breakwaters for ocean development.

Environmental Perception Considering Beam Opening Angle and Specular Reflection of Ultrasonic Sensors (초음파센서의 지향성 및 경면반사현상을 고려한 환경인식)

  • Ha, Yun-Su;Kim, Duck-Gon
    • Journal of Advanced Marine Engineering and Technology
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    • v.30 no.8
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    • pp.919-926
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    • 2006
  • To move in unknown or uncertain environment, a mobile robot must collect informations from various sensors and use it to construct a representation of the external world. Ultrasonic sensor can provide range data for this purpose in a simple cost-effective way. However conventional ultrasonic sensor system for a mobile robot are not sufficient for environment recognition because of their large beam opening angle, specular reflection. This paper describe on environmental perception algorithm which can solve these problems in case using ultrasonic sensor. The algorithm consist of two parts. One is to solve beam opening angle problem by fusion from multiple ultrasonic sensors. The other is to cope with specular reflection problem in wall line extract, which is based on Hough Transform. Experiments to verify the validity of the proposed algorithm are carried out, and the results are provided at last part in this paper.

An Experimental Study on Wave Absorber Performance of Combined Punching Plate in a Two-Dimensional Mini Wave Tank

  • Jung, Hyen-Cheol;Koo, Weoncheol
    • Journal of Ocean Engineering and Technology
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    • v.35 no.2
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    • pp.113-120
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    • 2021
  • In order to perform a precise wave tank experiment, it is necessary to maintain the incident wave generated by the wavemaker in a steady state and to effectively remove the reflected waves. In this paper, a combined sloping-wall-type punching plate wave absorber was proposed to attenuate reflected waves effectively in a two-dimensional mini wave tank. Using the four-point reflection separation method, the reflected waves were measured to determine the reflection coefficients. Experiments were conducted under various punching plate porosities, sloping plate angles, and incident wave conditions to evaluate the performance of the combined punching plate wave absorber. The most effective wave absorbing performance was achieved when the porosity was 10% and the inclination angle of the punching plate was 18.6° under the present condition. It was also found that the installation of the sloping plate could improve the wave attenuation performance by generating the shoaling effect of the incident wave.

Comparison of Simulated PEC Probe Performance for Detecting Wall Thickness Reduction

  • Shin, Young-Kil;Choi, Dong-Myung;Jung, Hee-Sung
    • Journal of the Korean Society for Nondestructive Testing
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    • v.29 no.6
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    • pp.563-569
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    • 2009
  • In this paper, four different types of pulsed eddy current(PEC) probe are designed and their performance of detecting wall thickness reduction is compared. By using the backward difference method in time and the finite element method in space, PEC signals from various thickness and materials are numerically calculated and three features of the signal are selected. Since PEC signals and features are obtained by various types and sizes of probe, the comparison is made through the normalized features which reflect the sensitivity of the feature to thickness reduction. The normalized features indicate that the shielded reflection probe provides the best sensitivity to wall thickness reduction for all three signal features. Results show that the best sensitivity to thickness reduction can be achieved by the peak value, but also suggest that the time to peak can be a good candidate because of its linear relationship with the thickness variation.

The Study of Supersonic Flow with Condensation Along a Wavy Wall in a Channel (波形壁 流路내에서 凝縮이 수반되는 超音速유동에 대한 硏究)

  • 권순범;김병지;김흥균
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.2
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    • pp.424-431
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    • 1994
  • The characteristics of supersonic flow with condensation along a wavy wall of a small Smplitude in a channel is investigated experimentally and numerically. In the present study for the case of supersonic moist air flow, the dependency of location of reflection of oblique shock wave generated by the wavy wall, and the distributions of flow properties in the flow field, on the stagnation relative humidity and temperature is clarified by the plots of streamline, iso-Mach number and iso-flow properties of numerical result and the schlieren photographs of experiment. And. experimental and numerical results are in good agreement.