• Title/Summary/Keyword: vertical mixing

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Consolidation Characteristics at the Constant Rate of Strain(CRS) Test (일정변형률(CRS) 시험에서의 압밀특성)

  • Lee, Dal-Won;Kim, Si-Jung
    • Korean Journal of Agricultural Science
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    • v.37 no.3
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    • pp.491-499
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    • 2010
  • This study was carried out to investigate the consolidation characteristics of the remolded clay by the oedometer and the constant rate of strain(CRS) consolidation tests. As the rate of strain increases, the settlement rapidly decreased. As the ratio of the sand in the specimen increases, its effect on the rate of strain to the settlement was reduced. As the effective stress increased, the void ratio decreased, while the rate of strain increased, it did not show a clear variation. The reduction of the void ratio was shown to be less than the oedometer test. The coefficient of vertical consolidation with effective stress showed very large variation around preconsolidation stress, but the rate of strain did not provide significant effects. The rate of strain with effective stress gradually decreased at all tests and mixed ratio of sand. The rate of strain at the constant rate of strain tests showed smaller than in the oedometer test. The coefficient of consolidation at the constant rate of strain tests showed much more increase than in the oedometer test. The ratio of the vertical coefficient of consolidation by the odometer and the constant rate of strain tests showed a large difference according to various tests method and mixing ratio. Therefore, it is recommended that careful attention should be paid to designing the soft ground improvement.

Oceanographic indicators for the occurrence of anchovy eggs inferred from generalized additive models

  • Kim, Jin Yeong;Lee, Jae Bong;Suh, Young-Sang
    • Fisheries and Aquatic Sciences
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    • v.23 no.7
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    • pp.19.1-19.14
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    • 2020
  • Three generalized additive models were applied to the distribution of anchovy eggs and oceanographic factors to determine the occurrence of anchovy spawning grounds in Korean waters and to identify the indicators of their occurrence using survey data from the spring and summer of 1985, 1995, and 2002. Binomial and Gaussian types of generalized additive models (GAM) and quantile generalized additive models (QGAM) revealed that egg density was influenced mostly by ocean temperature and salinity in spring, and the vertical structure of temperature, salinity, dissolved oxygen, and zooplankton biomass during summer in the upper quantiles of egg density. The GAM and QGAM model deviance explained 18.5-63.2% of the egg distribution in summer in the East and West Sea. For the principle component analysis-based GAMs, the variance explained by the final regression model was 27.3-67.0%, higher than the regular models and QGAMs for egg density in the East and West Sea. By analyzing the distribution of anchovy eggs off the Korean coast, our results revealed the optimal temperature and salinity conditions, in addition to high production and high vertical mixing, as the key indicators of the major spawning grounds of anchovies.

Thorpe Scale Analysis using CTD Observations on the Continental Slope of the Southwestern East Sea (동해 남서부 해역의 대륙사면에서 Thorpe 규모(scale)를 이용한 연직 난류 확산계수 추정)

  • Seo, Seongbong;Park, Young-Gyu;Park, Jae-Hun;Jeong, Hee-Dong
    • Ocean and Polar Research
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    • v.37 no.2
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    • pp.107-117
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    • 2015
  • Thorpe scale analysis was performed using two sets of 25-hour-long hourly CTD data. Raw density profiles collected on the continental slope of the southwestern East Sea were post-processed to reduce instrument noises and measurement errors. Density inversions were detected by applying the overturn ratio test proposed by Gargett and Garner (2008). The value of $K_z$ below the main thermocline estimated with the Osborn parameterization was $5.3{\times}10^{-4}(1.1{\times}10^{-4})m^2s^{-1}$ and that with the Shih parameterization was $5.9{\times}10^{-5}(2.4{\times}10^{-5})m^2s^{-1}$during the spring (neap) tidal period. This result suggests that internal tides can enhance vertical mixing in the observation region.

Bubble-driven Convective Flow in the Liquid with Temperature Gradient (온도구배가 있는 액체 내에서 기포가 유발하는 대류유동)

  • Bae, Dae-Seok;Kim, Jeong-Soo
    • Journal of the Korean Society of Propulsion Engineers
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    • v.15 no.4
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    • pp.65-72
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    • 2011
  • Numerical simulation has been performed to investigate the bubbly flow in the liquid with vertical temperature gradient. The objective of this study is to establish an accurate numerical prediction program of gas-liquid two-phase flows in a vertical temperature gradient condition, whose mathematical model is formulated by the Eulerian-Lagrangian model. The present numerical results reveal the temperature mixing mechanism and the fluid dynamical characteristics induced by the bubbly flow in the liquid with stratified temperature. The effects of bubble radius, void fraction, and gas flow rate on bubble-driven convective flow are considered, too.

Three-dimensional Numerical Modeling of Water Temperature and Internal Waves in a Large Stratified Lake (대형 성층 호수의 수온과 내부파의 3차원 수치 모델링)

  • Chung, Se-Woong;Schladow, S. Geoffrey
    • Journal of Korean Society on Water Environment
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    • v.31 no.4
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    • pp.367-376
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    • 2015
  • The momentum and kinetic turbulent energy carried by the wind to a stratified lake lead to basin-scale motions, which provide a major driving force for vertical and horizontal mixing. A three-dimensional (3D) hydrodynamic model was applied to Lake Tahoe, located between California and Nevada, USA, to simulate the dominant basin-scale internal waves in the deep lake. The results demonstrated that the model well represents the temporal and vertical variations of water temperature that allows the internal waves to be energized correctly at the basin scale. Both the model and thermistor chain (TC) data identified the presence of Kelvin modes and Poincare mode internal waves. The lake was weakly stratified during the study period, and produced large amplitude (up to 60 m) of internal oscillations after several wind events and partial upwelling near the southwestern lake. The partial upwelling and followed coastal jets could be an important feature of basin-scale internal waves because they can cause re-suspension and horizontal transport of fine particles from nearshore to offshore. The internal wave dynamics can be also associated with the distributions of water quality variables such as dissolved oxygen and nutrients in the lake. Thus, the basin-scale internal waves and horizontal circulation processes need to be accurately modeled for the correct simulation of the dissolved and particulate contaminants, and biogeochemical processes in the lake.

The Vertical Growth of CNTs by DC Bias-Assisted PECVD and Their Field Emission Properties. (플라즈마 화학 기상 증착법에서 DC bias가 인가된 탄소나노튜브의 수직성장과 전계방출 특성)

  • 정성회;김광식;장건익;류호진
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.15 no.4
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    • pp.367-372
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    • 2002
  • The vertically well-aligned carbon nanotubes(CNTs) were successfully grown on Ni coated silicon wafer substrate by DC bias-assisted PECVD(Plasma Enhanced Chemical Vapor Deposition). As a catalyst, Ni thin film of thickness ranging from 15~30nm was prepared by electron beam evaporator method. In order to find the optimum growth condition, the type of gas mixture such as $C_2H_2-NH_3$ was systematically investigated by adjusting the gas mixing ratio at $570^{\circ}C$ under 0.4Torr. The diameter of the grown CNTs was 40~200nm and the diameter of the CNTs increased with increasing the Ni particles size. TEM images clearly showed carbon nanotubes to be multiwalled. The measured turn-on field was $3.9V/\mu\textrm{m}$ and an emission current of $1.4{\times}10^4A/\textrm{cm}^2$ was $7V/\mu\textrm{m}$. The CNTs grown by bias-assisted PECVD was able to demonstrate high quality in terms of vertical alignment, crystallization of graphite and the processing technique at low temperature of $570^{\circ}C$ and this can be applied for the emitter tip of FEDs.

Influence of the Vertical Flame holder on Heat Transfer Characteristics of Ramjet Combustor (세로축 화염안정기 형상이 램제트 연소실에서의 열전달 특성에 미치는 영향)

  • Yang, Kang-Mo;Lee, Keon-Woo;Song, Ji-Woon;Cho, Hyung-Hee;Hwang, Ki-Young
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2008.11a
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    • pp.305-309
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    • 2008
  • This experimental study has been conducted to investigate the installation of the vertical flame holder shape in ramjet combustor, which affects on the film cooling effectiveness. All slot position, the film cooling effectiveness decreases because of the shear layer and high turbulence intensity between separated flows and coolant flows. When the flame holder is installed, film cooling effectiveness decreases abruptly on the beginning of the slot exit region due to the mixing effect. As the blowing rate increases, the film cooling effectiveness is increased for all cases due to the augmented momentum of injected coolant from the slot.

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A Numerical Model Study of the Coastal Ocean Flow Due to the Turbulence Parameterization (亂流의 媒介變數化에 따른 沿岸流의 수치모델)

  • YOU, KWANG WOO
    • 한국해양학회지
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    • v.29 no.1
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    • pp.50-63
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    • 1994
  • A three-dimensional time-dependent coastal ocean model experiment of two different turbulence parameterizations is conducted. One of the turbulence parameterization is the constant eddy-mixing formulation, C1, and the other a stratification dependent eddy-mixing formulation, C2. The flow in C2 in strongly baroclinic, and limits vertical mixing of fresh and saline waters. The outflow discharged from an estuary is highly inertial and form a strong front of plume in C2 than that in C1. Because of the stronger outflow in C2, supercritical flow state, for which the near surface outflow velocity exceeds the baroclinic phase speed, can exist off the mouth of the estuary. The adjustment process of flow in the less saline waters are quite different for C1 and C2, which is dictated by the strongly baroclinic nature of the flow in C2.

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Development of Depth-averaged Mixing Length Turbulence Model and Assessment of Eddy Viscosity (수심평균 혼합거리 난류 모형의 개발 및 와점성계수의 평가)

  • Choi, Seung-Yong;Han, Kun-Yeun;Hwang, Jae-Hong
    • Journal of Wetlands Research
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    • v.13 no.3
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    • pp.395-409
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    • 2011
  • The objective of this study is to develop an accurate and robust two-dimensional finite element method for turbulence simulation in open channels. The model is based on Streamline Upwind/Petrov-Galerkin finite element method and Boussinesq's eddy viscosity theory. The method developed in the study is depth-averaged mixing length model which assumes anisotropic and local equilibrium state of turbulence. The model calibration and validation were performed by comparing with analytical solutions and observed data. Several numerical simulations were carried out, which examined the performance of the turbulence model for the purpose of sensitivity analysis. The uniform channels that appear horizontal flow and vertical flow were carried out. The model was also applied to the Han river was in for the applicability test. The results were compared with the observed data. The suggested model displayed reasonable flow distribution compare to the observed data in natural river flow. As a result of this study, the two-dimensional finite element model provides a reliable results for flow distribution based on the turbulence simulation in open channels.

Numerical Experiment for the formation of the Yellow Sea cold Water mass (황해저층냉수의 형성에 관한 수치실험)

  • AN, HUI SOO;LEE, HYUN CHUL
    • 한국해양학회지
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    • v.28 no.2
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    • pp.101-106
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    • 1993
  • A simple three-dimensional cubic model is applied to the formation of the Yellow Sea Cold Water Mass in Summer. We studied how the tidal mixing and the Kuroshio Water Mass affect the formation of the Yellow Sea cold Water. The tidal mixing effect is parameterized into the vertical diffusion coefficient because of the technical difficulties in the numerical model In this study, the thermal front along the coast could be formed only by the tidal mixing effect. However, the southern front of the Yellow Sea Cold Water Mass has to consider the warm Kuroshio water. the resultant shows the opposite temperature distribution in upper layer and lower layer. the center of the model is warmer in the upper layer and colder in the lower layer than the coast. The resultant circulation pattern is also reverse, clockwise circulation in the upper layer and counter-clockwise circulation in the lower layer.

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