• Title/Summary/Keyword: velocity gradient

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A Simple Theoretical Model for the Upwind Flow in the Southern Yellow Sea (황해남부의 역풍류에 대한 단순 이론 모델)

  • 박용향
    • 한국해양학회지
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    • v.21 no.4
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    • pp.203-210
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    • 1986
  • A linear parallel transport model is formulated and applied to an idealized Yellow Sea, With this simple analytical model, the hither-to suspected upwind flow phenomena in the southern Yellow Sea can be reasonably explained. In deep waters where the local depth exceeds a critical depth (Hc=53m in the present model sea), pressure gradient force dominates over wind stress and contributes to an upwind flow. The estimated upwind flow velocity increases with wind speed and a maximum upwind flow occurs along the axis of the Yellow Sea embayment. For the typical south wind of 5-10 knots in summer, the upwind (southward) flow velocity along the axis of the Yellow Sea is estimated to be 1-5cm s$\^$-1/. While, for the typical north wind of 10-15 knots in winter, the upwind (northward) flow velocity is 5-12cm s$\^$-1/. These velocity ranges can be served as rough estimates for the intrusion velocity of the Yellow Sea Bottom Cold Water in summer and the Yellow Sea Warm Current in winter, respectively.

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Considerations of Permeability of Converter Slag for Recycling in vertical drainage method (연직배수공법에 있어서 제강슬래그의 재활용을 위한 투수성 연구)

  • 이광찬;정규향;김영남;이문수
    • Proceedings of the Korean Geotechical Society Conference
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    • 2000.02a
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    • pp.93-112
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    • 2000
  • The permeability of converter slag, replacing material of sand mat on improving soft clay foundation, was evaluated in the laboratory. The effects of grain size, flow water time and aging were investigated using sea and fresh water. Converter slag being submerged with fresh water, the coefficients of permeability in A and B samples less than 10mm grain sizes were measured as 6.52${\times}$10$\^$-2/cm/sec and 5.99${\times}$10$\^$-1/cm/sec, while changed as 1.88${\times}$10$\^$-2/cm/sec, 3.86${\times}$10$\^$-1/cm/sec under sea water condition. Also, the condition of turbulent flow may exit and was experimentally identified from the relationship between hydraulic gradient and seepage velocity. After 180 days on using sea water, the coefficients of permeability of sample A and B samples decreased ten times smaller than those initial values. And after that time continually decreased as for till 360 days. The reduction of permeability coefficient was considered to influence filled with voids in high-calcium quicklime(CaO). However, in-situ coefficient of permeability was practically satisfactory.

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Considerations of Permeability of Converter Slag for Recycling in vertical drainage method (연직배수공법에 있어서 제강슬래그의 재활용을 위한 투수성 연구)

  • 이광찬;정규향;김영남;이문수
    • Proceedings of the Korean Geotechical Society Conference
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    • 2000.02a
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    • pp.12-31
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    • 2000
  • The permeability of converter slag, replacing material of sand mat on improving soft clay foundation, was evaluated in the laboratory. The effects of grain size, flow water time and aging were investigated using sea and fresh water. Converter slag being submerged with fresh water, the coefficients of permeability in A and B samples less than 10mm grain sizes were measured as 6.52${\times}$10$\^$-2/cm/sec and 5,99${\times}$10$\^$-1/cm/sec, while changed as 1,88${\times}$10$\^$-2/cm/sec, 3.86${\times}$10$\^$-1/cm/sec under sea water condition. Also, the condition of turbulent flow may exit and was experimentally identified from the relationship between hydraulic gradient and seepage velocity. After 180 days on using sea water, the coefficients of permeability of sample A and B samples decreased ten times smaller than those initial values. And after that time continually decreased as for till 360 days. The reduction of permeability coefficient was considered to influence filled with voids in high-calcium quicklime(CaO). However, in-situ coefficient of permeability was practically satisfactory.

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A Study of Flow Pattern around the Two-Dimensional Dual Subsea Pipeline on Sea Bottom (해저면에 설치된 2차원 복합해저관로 주위의 유동특성에 관한 실험적 연구)

  • 나인삼;조철희;정우철;김두홍
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • 2001.10a
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    • pp.122-127
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    • 2001
  • As pipelines are often used to transport gas, oil, water and oil products, there are more than one pipeline installed in the offshore field. The size and space of pipelines are various depending on the design specifications. The pipelines are to be designed and installed to secure the stability to external loads during the installation and operation period. The flow patterns are very complex around the pipelines being dependent on incoming flow velocity, pipelines size and space. To investigate the flow patterns, number of experiment are conducted with visualization equipment in a circulating water channel. The flow motion and trajectory were recorded from the laser reflected particles by camera. From the experiment the flow patterns around spaced pipelines were obtained. Also pressure gradient was measured by mano-meter to estimate the hydrodynamic forces on the behind pipeline. The results show that the various sizes and spaces can be affected in the estimation of external load. The complex flow patterns and pressure gradients can be effectively used in the understanding of flow motion and pressure gradient.

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ATTITUDE CONTROL OF SMALL SCIENTIFIC SATELLITE USING GEOMAGNETISM (지구자기장을 이용한 소형과학위성의 자세조정)

  • 배성구;석재호;최규홍
    • Journal of Astronomy and Space Sciences
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    • v.8 no.1
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    • pp.85-98
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    • 1991
  • Geomagnetism was used to control the attitude of the small scientific satellite at low altitude in sun-synchronous orbit. First, we analyzed the telemetry data. The rotation state of the satellite, can be known from the magnitude and variations of the magnetic field which is measured from the 3 axis magnetometer. In axisymmetric case, it is possible to control the attitude of the satellite by changing the rotation velocity of each 3 axis. The algorithm and the program were developed to calculate the supply time of the current operating the magnetorquer. This attitude control can be applied when the satellite is in tumbling motion and after passive control is attained by the Gravity gradient boom.

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A Study on the Characteristics of Cylinder Wake Placed in Thermally Stratified Flow(II)(Par II. Turbulent Characteristics of Stratified Wake) (열성층유동장에 놓인 원주후류의 특성에 대한 연구(2)(Part 2. 성층후류의 난류유동특성))

  • 김경천;정양범;강동구
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.5
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    • pp.1322-1329
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    • 1994
  • The effect of thermal stratification on the stratified flow past a circular cylinder was examined in a wind tunnel. Turbulent intensities, the rms values of temperature and turbulent convective heat flux as well as the velocity and temperature profiles in the cylinder wake with a strong thermal gradient of $200^{\circ}C/m$ were measured by using a hot-wire and cold-wire combination probe. It is found that the temperature field affects as an active contaminant, so that the vertical growth of vortical structure is suppressed and the strouhal number decreases with increasing the extent of stratification. And also, the wake structure can not sustain their symmetricity about the wake centerline and vertical turbulent motion dissipates faster than that of the neutral case when such a strong thermal gradient is superimposed. It is evident that the turbulent mixing in the upper half section is stronger than that of the lower of the wake in a stably stratified flow because the turbulent intensities and convective heat flux in the upper half section are larger than those of the lower half of the wake.

Modeling and assessment of VWNN for signal processing of structural systems

  • Lin, Jeng-Wen;Wu, Tzung-Han
    • Structural Engineering and Mechanics
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    • v.45 no.1
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    • pp.53-67
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    • 2013
  • This study aimed to develop a model to accurately predict the acceleration of structural systems during an earthquake. The acceleration and applied force of a structure were measured at current time step and the velocity and displacement were estimated through linear integration. These data were used as input to predict the structural acceleration at next time step. The computation tool used was the Volterra/Wiener neural network (VWNN) which contained the mathematical model to predict the acceleration. For alleviating problems of relatively large-dimensional and nonlinear systems, the VWNN model was utilized as the signal processing tool, including the Taylor series components in the input nodes of the neural network. The number of the intermediate layer nodes in the neural network model, containing the training and simulation stage, was evaluated and optimized. Discussions on the influences of the gradient descent with adaptive learning rate algorithm and the Levenberg-Marquardt algorithm, both for determining the network weights, on prediction errors were provided. During the simulation stage, different earthquake excitations were tested with the optimized settings acquired from the training stage to find out which of the algorithms would result in the smallest error, to determine a proper simulation model.

Near-Wall Modelling of Turbulent Heat Fluxes by Elliptic Equation (타원방정식에 의한 벽면 부근의 난류열유속 모형화)

  • Shin, Jong-Keun;An, Jeong-Soo;Choi, Young-Don
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.28 no.5
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    • pp.526-534
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    • 2004
  • A new second-moment closure model for turbulent heat fluxes is proposed on the basis of the elliptic equation. The new model satisfies the near-wall balance between viscous diffusion, viscous dissipation and temperature-pressure gradient correlation, and also has the characteristics of approaching its respective conventional high Reynolds number model far away from the wall. The predictions of turbulent heat transfer in a channel flow have been carried out with constant wall heat flux and constant wall temperature difference boundary conditions respectively. The velocity field variables are supplied from the DNS data and the differential equations only fur the mean temperature and the scalar flux are solved by the present calculations. The present model is tested by direct comparisons with the DNS to validate the performance of the model predictions. The prediction results show that the behavior of the turbulent heat fluxes in the whole region is well captured by the present model.

Double-Diffusive Convection Due to Heating from Below in a Rotating Cylindrical Cavity (회전하는 원통형밀폐용기내의 아랫면가열에 의한 이중확산대류에 관한 실험적 연구)

  • 강신형;이태홍;이진호
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.7
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    • pp.1731-1740
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    • 1995
  • Experimental investigations have been made to study the double-diffusive nature of convection of an initially stratified salt-water solution due to heating from below in a rotating cylindrical cavity. The objective is to examine the flow phenomena and the heat transfer characteristics according to the changes in temperature gradient, concentration gradient and rotating velocity of cavity. Thermal and solutal boundary conditions at side wall are adiabatic and impermeable, respectively. The top and bottom plate are maintained each at constant temperature and concentration. The cavity is put into a state of solid body rotation. Like the stationary case, the types of initially-formed flow pattern are classified into three regimes depending on the effective Rayleigh number and Taylor number; stagnant flow regime, single mixed-layer flow regime and successively formed multi-mixed layer flow regime. At the same effective Rayleigh number, the number of initially-formed mixed layer and its growth rate decrease as the effect of rotation increases. The temperature and concentration profiles are both uniform in each layer due to convective mixing in the layered-flow regime, but look both liner in stagnant flow regime and single mixed-layer flow regime. At the interface between adjacent layers, the temperature changes smoothly but the concentration changes rapidly.

Numerical Analysis of the Two-Dimensional Pollutant Dispersion Over Hilly Terrain (산지 내 오염물질 확산의 2차원 수치해석)

  • 김현구;이정묵
    • Journal of Korean Society for Atmospheric Environment
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    • v.13 no.5
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    • pp.383-396
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    • 1997
  • Numerical prediction of the pollutant dispersion over a two-dimensional hilly terrain is presented. The dispersion model used in the present work is based on the gradient diffusion theory and the finite-volume method on a non-orthogonal boundary-fitted grid system. The numerical model is validated by comparing the results with the available experimental data for the flat-floor dispersion within a turbulent boundary-layer. The numerical error analysis is performed based on the guideline of Kasibhatla et al.(1988) for the elevated-source dispersion in the flat-floor boundary layer having a power-law velocity and linear eddy-diffusivity profile. The influences of the two-dimensional hilly terrain on the dispersion from a continuously released source are numerically investigated by changing the emission locations and heights. It is found that the distributions of ground-level concentration are strongly influenced by the source location and the emission height. Hence, the terrain amplification factor is greatly enhanced when the pollutant source is located within a flow separation region. Dispersion from a source of short duration is also simulated and the duration time of the pollutant is compared at several downstream locations on a hilly terrain. The results of the numerical prediction are applied to the evaluation of environmental impacts due to the automobile exhausts at the seashore highway with a parallel mountain range.

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