• Title/Summary/Keyword: Bottom Roughness

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Improvement of Tidal Circulation in a Closed Bay using Variation of Bottom Roughness (해저조도 변화를 이용한 폐쇄성 만의 해수순환 개선)

  • BOO SUNG YOUN
    • Journal of Ocean Engineering and Technology
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    • v.19 no.1 s.62
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    • pp.1-7
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    • 2005
  • Tidal circulation in a closed bay using a variation of bottom roughness was investigated through the numerical experiments based on a finite difference multi-level model. Various distributions of bottom roughness in the bay were implemented to determine their effects. It hadbeen determined that residual currents can be generated from the differences of the bottom roughness between streaming and reverse flow directions. The magnitude of residual currents and volume flow rate increase when the relative ratio of bottom roughness between streaming and reverse flow directions increase. Circulation in the closed bay is also improved by the employment of the change of bottom roughness.

A Study on the Most Suitable Shape of 3-Dimensional Bottom Roughness with Directional Resistance Properties (방향성 저항특성을 가진 3차원 저면조도의 최적형상에 관한 연구)

  • 국승기
    • Journal of Korean Port Research
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    • v.14 no.4
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    • pp.441-450
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    • 2000
  • In order to improve the water quality in semi-enclosed bays, Gug et al. (1997) have proposed a new method to activate the tidal exchange by creation and control of tidal residual current through the addition of artificial elements to creation and control of tidal residual current through the addition of artificial elements to create bottom roughness, so, ot is advisable to arrange as few of these as possible from a point of cost-benefit view. This paper attempts to develop the most suitable shape of artificial bottom roughness units with which to create and control an optimal tidal residual current. Several simple shapes were examined as fundamental cases. Subsequently 38 types of artificial bottom roughness units based on a few simple effective shapes, were examined experimentally. As a result of this research, two types to create artificial roughness.

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Frequency Dependence of High-Frequency Bottom Reflection Loss Model (주파수 종속성을 갖는 고주파 해저면 반사손실 모델)

  • 박순식;윤관섭;나정열;석동우;주진용;조진석
    • The Journal of the Acoustical Society of Korea
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    • v.23 no.5
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    • pp.362-369
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    • 2004
  • The High-frequency (30 ∼ 120 ㎑) bottom reflection loss at rough water-sediment interface is affected by the gram size distribution of the sediments. The roughness of the bottom surface is represented by "acoustical roughness. g/sub R/" The grain size of sandy sediments is g/sub R/∼O(1) and the dependence as a function of frequency. We suggest the modified bottom reflection loss model (HYBRL model , HanYang university Bottom Reflection Loss model) that include in the deviation of the reflection loss as a function of the grain size distribution and frequency dependence. And bottom reflection loss model of frequency dependence and deviation of bottom properties is verified by water tank and field experiments.

Characteristics of the Ekman Layer Flow over a Rough Bottom (거친 바닥 위의 에크만 경계층 내의 흐름의 특성)

  • Na, Jung-Yul;Kim, Tae-Yeon
    • The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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    • v.3 no.2
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    • pp.53-58
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    • 1998
  • Ekman layer equation with rough-bottom boundary condition has been solved to determine the effect of roughness on the magnitude of Ekman veering. The bottom boundary condition and the flow field were expanded in a power of roughness (h) which is always smaller than the Ekman layer thickness (${\delta}_E$). By changing the magnitude of roughness parameter (h/${\delta}_E$), the magnitude of the veering, which rotates counterclockwise from the interior geostrophic flow, has been computed. At a fixed depth within the Ekman layer, the magnitude of veering increases as the roughness parameter increases. However, the cross-isobar flux turns out to decrease with increasing roughness. To verify the analytic solution, laboratory experiments were carried out. Rough-bottom cylinderical container filled with homogeneous fluid was sit on a rotating table. The flow pattern during the period of steady spin-up shows that the degree of veering coincides well with the analytic results for various roughness parameters.

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Bottom Loss Variation of Low-Frequency Sound Wave in the Yellow Sea (황해에서 저주파 음파의 해저손실 변동)

  • Kim, Bong-Chae
    • Ocean and Polar Research
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    • v.29 no.2
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    • pp.113-121
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    • 2007
  • The sound wave in the sea propagates under the effect of water depth, sound speed structure, sea surface roughness, bottom roughness, and acoustic properties of bottom sediment. In shallow water, the bottom sediments are distributed very variously with place and the sound speed structure varying with time and space. In order to investigate the seasonal propagation characteristics of low-frequency sound wave in the Yellow Sea, propagation experiments were conducted along a track in the middle part of the Yellow Sea in spring, summer, and autumn. In this paper we consider seasonal variations of the sound speed profile and propagation loss based on the measurement results. Also we quantitatively investigate variation of bottom loss by dividing the propagation loss into three components: spreading loss, absorption loss, and bottom loss. As a result, the propagation losses measured in summer were larger than the losses in spring and autumn, and the propagation losses measured in autumn were smaller than the losses in spring. The spreading loss and the absorption loss did not show seasonal variations, but the bottom loss showed seasonal variations. So it was thought that the seasonal variation of the propagation loss was due to the seasonal change of the bottom loss and the seasonal variation of the bottom loss was due to the change of the sound speed profile by season.

Characterization of Pt Bottom Electrode Deposited on Sputtered-Ru/polysilicon by Metalorganic Chemical Vapor Deposition (유기금속 화학증착법에 의해 Sputtered-Ru/Polysilicon 위에 증착된 Pt 전극의 특성)

  • Choe, Eun-Seok;Yang, Jeong-Hwan;Yun, Sun-Gil
    • Korean Journal of Materials Research
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    • v.9 no.4
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    • pp.368-372
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    • 1999
  • The suggested electrode structure of MOCVD-Pt/sputtered-Ru/polysilicon has an excellent adhesion with increasing annealing temperatures and shows a stable electrode structure up to $600^{\circ}C$. However, the ruthenium used for barrier layer increased the roughness of platinum bottom electrodes because ruthenium diffused through the Pt bottom electrode and reacted with oxygen during the annealing above $700^{\circ}C$. The surface roughness increased the resistivity of Pt bottom electrodes. The resistivity of samples annealed at $600^{\circ}C$ was about $13\mu$Ω.cm. The electrode structure was possible to apply for ferroelectric thin film integration of semiconductor memory devices.

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Effect of surface roughness on laminar flow in a micro-channel by using lattice Boltzmann method (격자 볼츠만 방법을 이용한 미소채널 내에서의 층류 유동에 대한 표면 거칠기의 영향)

  • Shin, Myung-Seob;Yoon, Joon-Yong;Byun, Sung-Joon;Kim, Kak-Joong
    • 유체기계공업학회:학술대회논문집
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    • 2006.08a
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    • pp.179-183
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    • 2006
  • Surface roughness is present in most of the microfluidic devices due to the microfabrication techniques. This paper presents lattice Boltzmann method (LBM) results for laminar flow in a microchannel with surface roughness. The surface roughness is modeled by an array of rectangular modules placed on top and bottom side of a parallel-plate channel. In this study, LBGK D2Q9 code in lattice Boltzmann Method is used to simulate flow field for low Reynolds number in a micro-channel. The effects of relative surface roughness, roughness distribution, roughness size and the results are presented in the form of the product of friction factor and Reynolds number. Finally, a significant increase in Poiseuille number is detected as the surface roughness is considered, while the effect of roughness on the microflow field depends on the surface roughness.

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A Study on the Cutting Surfaces in CNC Plasma Cutting of high tensile steel plate (고장력 강판의 CNC Plasma 절단시 절단면에 관한 연구)

  • 김인철;김성일
    • Proceedings of the Korean Society of Machine Tool Engineers Conference
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    • 2003.04a
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    • pp.149-154
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    • 2003
  • The cutting tests of high tensile steel plate(AH36) were carried out using CNC plasma arc cutting machine. Both top and bottom width of kerf and the surface roughness(Ra, Rmax) of cut surface are measured under various cutting conditions such as cutting speed, steel plate thickness, etc. In the CNC plasma arc cutting, the surface roughness decreases as cutting speed increases. The hardness is high up to 4mm depth from the cutting surface. In the cutting speed 1300~2100mm/min, the ratio of proper kerf width(Wt/Wb) is around 2.6. Through the series the series of experiments, the satisfactory cutting conditions of high tensile steel plate were found.

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A Study on Underwater Camera Image Correction for Ship Bottom Inspection Using Underwater Drone (수중드론을 활용한 선박 선저검사용 수중 카메라 영상보정에 대한 연구)

  • Ha, Yeon-chul;Park, Junmo
    • Journal of the Institute of Convergence Signal Processing
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    • v.20 no.4
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    • pp.186-192
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    • 2019
  • In general, many marine organisms are attached to the bottom of a ship in operation or a ship in construction. Due to this phenomenon, the roughness of the ship surface increases, resulting in loss of ship speed, resulting in economic losses and environmental pollution. This study acquires / utilizes camera images attached to ship's bottom and underwater drones to check the condition of bottom. The acquired image will determine the roughness according to marine life by the administrator's visual confirmation. Therefore, by applying a filter algorithm to correct the image to the original image can help in the correct determination of whether or not attached to marine life. Various correction filters are required for the underwater image correction algorithm, and the lighting suitable for the dark underwater environment has a great influence on the judgment. The results of the research test according to the calibration algorithm and the roughness of each algorithm are considered to be applicable to many fields.

Frequency Dependence of High-frequency Bottom Reflection Loss Measurements (고주파 해저면 반사손실의 주파수 종속성 측정)

  • 박순식;윤관섭;최지웅;나정열
    • The Journal of the Acoustical Society of Korea
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    • v.22 no.8
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    • pp.652-659
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    • 2003
  • High-frequency(40∼120 kHz) reflection loss measurements on the water-sandy sediment with a flat interface were conducted in a water tank for various grazing angles. The water tank(5×5×5 m) was filled with a 0.5 m-thick-flat bottom of 0.5ø-mean-grain-size sand. Reflection losses, which were experimentally obtained as a function of grazing angle and frequency, were compared with the forward loss model, APL-UW model (Mourad & Jackson, 1989). For frequencies below 60 kHz, the observed losses well agree with the reflection loss model, however, in cases for frequencies above 70 kHz, the observed losses are greater by 2∼3 dB than the model results. The model calculation, which does not fully account for the vertical scale of roughness due to grain size, produce less bottom losses compared to the observations that correspond to large roughness based on the Rayleigh parameter in the wave scattering theory. In conclusion, for the same grain-size-sediment, as frequencies increase, the grainsize becomes the scale of roughness that could be very large for the frequencies above 70 kHz. Therefore, although the sea bottom was flat, we have to consider the frequency dependence of an effect of roughness within confidential interval of grain size distribution in reflection loss model.