• Title/Summary/Keyword: Equations

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A Three-Dimensional Galerkin-FEM Model with Density Variation (밀도 변화를 포함하는 3차원 연직함수 전개모형)

  • 이호진;정경태;소재귀;강관수;정종율
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.8 no.2
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    • pp.123-136
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    • 1996
  • A three-dimensional Galerkin-FEM model which can handle the temporal and spatial variation of density is presented. The hydrostatic approximation is used and density effects are included by means of conservation equation of heat and the equation of state. The finite difference grids are used in the horizontal plane and a set of linear-shape functions is used for the vertical expansion. The similarity transform is introduced to solve resultant matrix equations. The proposed model was first applied to the density-driven circulation in an idealized basin in the presence of the heat exchange between the air and the sea. The advection terms in the momentum equation were ignored, while the convection terms were retained in the heat equation. Coefficients of the vertical eddy viscosity and diffusivity were fixed to be constant. Calculation in a non-rotating idealized basin shows that the difference in heat capacity with depth gives rise to the horizontal gradient of temperature. Consequently, there is a steady new in the upper layer in the direction of increasing depth with compensatory counter flow .in the lower layer. With Coriolis force, geostrophic flow was predominant due to the balance between the pressure gradient and the Coriolis force. As a test in region of irregular topography, the model is applied to the Yellow Sea. Although the resultant flow was very complex, the character of the flow Showed to be geostrophic on the whole.

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Development of a Three-Dimensional, Semi-Implicit Hydrodynamic Model with Wetting-and-Drying Scheme (조간대 처리기법을 포함한 3차원 Semi-Implicit 수역학모델 개발)

  • Lee, Kyung-Sun;Park, Kyeong;Oh, Jeong-Hwan
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.12 no.2
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    • pp.70-80
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    • 2000
  • Princeton Ocean Model (POM) is modified to construct a three-dimensional, semi-implicit hydro¬dynamic model with a wetting-and-drying scheme. The model employs semi-implicit treatment of the barotropic pressure gradient terms and the vertical mixing terms in the momentum equations, and the velocity divergence term in the vertically-integrated continuity equation. Such treatment removes the external mode and thus the mode splitting scheme in POM, allowing the semi-implicit model to use a larger time step. Applied to hypothetical systems, both the semi-implicit model and POM give nearly the same results. The semi-implicit model, however, runs approximately 4.4 times faster than POM showing its improved computational efficiency. Applied to a hypothetical system with intertidal flats, POM employing the mode splitting scheme produces noises at the intertidal flats, that propagate into the main channel resulting in unstable current velocities. Despite its larger time step, the semi-implicit model gives stable current velocities both at the intertidal flats and main channel. The semi-implicit model when applied to Kyeonggi Bay gives a good reproduction of the observed tides and tidal currents throughout the modeling domain, demonstrating its prototype applicability.

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Numerical Analysis of Nonlinear Shoaling Characteristics over Surf Zone Using SPH and Lagrangian Dynamic Smagronsky Model (Lagrangian Dynamic Smagronsky 난류모형과 SPH를 이용한 쇄파역에서의 비선형 천수거동에 관한 연구)

  • Cho, Yong-Jun;Lee, Heon
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.19 no.1
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    • pp.81-96
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    • 2007
  • Nonlinear shoaling characteristics over surf zone are numerically investigated based on spatially averaged NavierStokes equation. We also test the validity of gradient model for turbulent stresses due to wave breaking using the data acquainted during SUPERTANK LABORATORY DATA COLLECTION PROJECT(Krauss et al., 1992). It turns out that the characteristics length scale of breaking induced current is not negligible, which firmly stands against ever popular gradient model, ${\kappa}-{\varepsilon}$ model, but favors Large Eddy Simulation with finer grid. Based on these observations, we model the residual stress of spatially averaged NavierStokes equation after Lagrangian Dynamic Smagorinsky(Meneveau et al., 1996). We numerically integrate newly proposed wave equations using SPH with Gaussian kernel function. Severely deformed water surface profile, free falling water particle, queuing splash after landing of water particle on the free surface and wave finger due to structured vortex on rear side of wave crest(Narayanaswamy and Dalrymple, 2002) are successfully duplicated in the numerical simulation of wave propagation over uniform slope beach, which so far have been regarded very difficult features to mimic in the computational fluid mechanics.

Two and Three Dimensional Analysis about the Reflection Coefficient by the Slit Caisson and Resulting Wave Pressure Acting on the Structure (슬리트케이슨제에 의한 반사율과 구조물에 작용하는 파압에 관한 2차원 및 3차원해석)

  • Lee, Kwang-Ho;Choi, Hyun-Seok;Baek, Dong-Jin;Kim, Do-Sam
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.22 no.6
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    • pp.374-386
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    • 2010
  • Recently, the theoretical and experimental research is being made actively in control character of waves of perforated-wall caisson breakwater like the slit caisson. This study showed that the character of reflection coefficient and the wave pressure acting on the front and inner of slit caisson were estimated in two and three dimensional numerical wave flume and compared each other. The numerical experiment was set and conducted by various cases as to a variety of wave steepness under 7 sec, 9 sec, 11sec and 13 sec period condition. In this study using a 2 and 3 dimensional numerical wave flume, it applied the Model for the immiscible two-phase flow based on the Naveir-Stokes Equations. This technique can easily reproduce a complicated physical phenomenon more than others and organize the program simply. According to the results of the experiment, the reflection coefficient was estimated high in short-period waves. However, 2-dimensional numerical experiment and 3-dimensional numerical experiment were the same in case of the long-period waves and high wave steepness. And to conclude in case of short-period waves the pressures were a relatively small difference between the two, but there was a big gap in longperiod waves and high wave steepness.

A Study on Performance Characteristics of Horizontal Axis Tidal Turbine Considering Nose Shape, Angle of Inflow and Tower Structure (수평축 조류발전 터빈의 노즈 형상 및 유입각도, 타워 구조물의 영향을 고려한 터빈 성능특성 분석)

  • Heo, Man-Woong;Kim, Dong-Hwan;Yi, Jin-Hak
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.32 no.1
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    • pp.17-25
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    • 2020
  • In this study, three-dimensional fluid flow analyses have been performed in order to investigate the performance characteristics of a horizontal axis tidal turbine (HATT) by solving three-dimensional Reynolds-averaged Navier-Stokes equations utilizing the shear-stress-transport turbulence model. The computational domain for the flow analysis has been composed of hexahedral grids, and the grid dependency test has been carried out so as to determine the optimum grid size. Performance characteristics of the HATT have been investigated in consideration of the effects of hub nose geometry, inflow angle, and the tower. It has been found that the power output can be enhanced along with an increase of the ratio of the length to the diameter of the turbine nose, and the power of HATT has been reduced by approximately 10% when the primary fluid flow had an inflow angle of 15°. The power output of downstream HATT is found to be lower than that of the upstream HATT by about 1%.

Correlation of Heavy Metal Concentrations between Total Digestion and Aqua Regia Digestion for Sediments from Yeongsan and Seomjin Watersheds (완전분해와 전분해 방법에 의한 영산강.섬진강수계 퇴적물의 중금속농도 상관관계)

  • Oh, Da-Yeon;Choi, Kyoung-Kyoon;Huh, In-Ae;Hwang, In-Seong;Kim, Young-Hoon;Hur, Jin;Shin, Hyun-Sang;Oh, Jeong-Eun;Shin, Won-Sik;Park, Jeong-Hun
    • Journal of Korean Society of Environmental Engineers
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    • v.33 no.1
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    • pp.32-38
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    • 2011
  • In this study, the correlations of concentrations in sediment heavy metals between two pretreatment methods, total digestion and aqua regia digestion, have been investigated. Total 43 samples had been collected from streams and lakes in Yeongsan and Seomjin watersheds. They were decomposed in two pretreatment methods and five metal components (Cd, Cr, Ni, Pb, Zn) were analyzed. Overall average concentrations of heavy metals were Zn>Cr>Pb>Ni>Cd in the order. The concentrations of aqua regia digestion were 35.0% (Cd), 53.8% (Cr), 66.2% (Ni), 64.4% (Pb) and 76.4% (Zn) of the concentrations of total digestion and heavy metal concentrations of total digestion were higher. Heavy metal concentrations in sediments from lakes were higher than those from streams. The correlation equations between the concentrations of total digestion and aqua regia digestion were obtained. The concentrations of Zn and Ni, which showed strong linear correlations, increased in aqua regia digestion as the concentration in total digestion increased. The linear correlation coefficients between two digestion methods for most analyzed metals were above the average correlation. However, these results can be applied with limitations due to heterogeneity of sediments.

Diversity and Biomass of Benthic Diatoms in Hampyeong Bay Tidal Flats (함평만 갯벌 저서규조류의 다양성과 생물량)

  • Lee, Hak Young
    • Korean Journal of Environmental Biology
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    • v.31 no.4
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    • pp.295-301
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    • 2013
  • The diversity and biomass distribution of benthic diatom flora at tidal flats of Hampyeong Bay were studied from 2006 to 2013 as a part of KLTER Program. A total of 83 species (77 strains in 2006, 65 strains in 2007, 41 strains in 2008, 45 strains in 2009, 54 strains in 2010, 55 strains in 2011, 56 strains in 2012 and 40 strains in 2012) were identified as benthic diatoms of Hampyeong Bay tidal flats. The most dominant species were Paralia sulcata and Cyclotella litoralis. Cyclotella sp., Diploneis sp., Entomoneis alata, Gyrosigma sp., Navicula abunda, Navicula gregaria, Navicula spp. and Nitzschia palea were the other common species which contributed to the high benthic diatom biomass in the Bay. The diversity of benthic diatoms varied according to the sample stations and seasons. The highest diversity was observed in August samples. The range of chlorophyll- a concentration in sediments of tidal flats for 8 years was 21~65 mg $m^{-2}$. The standing crops of benthic diatoms varied according to the studied stations and sampled seasons. The number of taxa and standing crops showed decreasing tendency year after year from all sampled stations. The distributions of standing crops and cell volumes of benthic diatoms showed similar pattern. The taxa and biomass of benthic diatoms showed low correlation coefficients with temperature variables expressed as the following equations $Y=-0.0208X^2+0.5264X+19.529(r^2=0.0269)$ and $Y=-0.9181X^2+27.011X+310.07(r^2=0.0797)$ respectively.

Kinetic Behavior of Immobilized Tyrosinase on Carbon in a Simulated Packed-Bed Reactor (충전층에서 탄소에 고정시킨 Tyrosinase의 반응속도에 관한 연구)

  • Shin, Sun Kyoung;Kim, Kyeo-Keun
    • Analytical Science and Technology
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    • v.10 no.1
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    • pp.66-74
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    • 1997
  • Influence of the axial dispersion on immobilized enzyme catalytic bed was investigated in order to examine the kinetic behavior of the biocatalysis. The enzyme employed in this study was the tyrosinase(EC 1.14.18.1) immobilized on carbon support : this system requires two substrates of phenol and oxygen. This enzyme has potential application for phenol degradation in waste water. A simulated reactor was a packed-bed reactor of 2.54cm in diameter and 10cm long, loaded with the immobilized carbon particle with an average diameter of $550{\mu}m$. A phenol feed in the strength of 55.5mM(5220ppm) was used to observe the behavior of the immobilized enzyme column at three different dissolved oxygen levels of 0.08445mM(2.7ppm), 0.1689mM(5.4ppm) and 0.3378mM(9.5ppm) with the flow rates in the range of 60(1mL/s) to 180mL/min(3mL/s). Examination of the Biot number and Damkolher numbers of the immobilized system enables us to eliminate the contribution of external mass transfer to set of differential equations derived from the dispersion model. Solution of the equation was finally obtained numerically with the application of the Danckwert boundary conditions and the assumed zero-and first order rates on the non-linear two substrate enzyme kinetics. Higher conversion of phenol was observed at the low flow rates and at the higher oxygen concentration. Comparison of axial dispersion and plug flow model showed that no detectable difference was observed in the column outlet conversion between the axial and the plug flow models which was in complete agreement with the previous studies.

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The Earth-Moon Transfer Trajectory Design and Analysis using Intermediate Loop Orbits (중개궤도를 이용한 지구-달 천이궤적의 설계 및 분석)

  • Song, Young-Joo;Woo, Jin;Park, Sang-Young;Choi, Kyu-Hong;Sim, Eun-Sup
    • Journal of Astronomy and Space Sciences
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    • v.26 no.2
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    • pp.171-186
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    • 2009
  • Various Earth-Moon transfer trajectories are designed and analyzed to prepare the future Korea's Lunar missions. Minimum fuel trajectory solutions are obtained for the departure year of 2017, 2020, 2022, and every required mission phases are analyzed from Earth departure to the final lunar mission orbit. N-body equations of motion are formulated which include the gravitational effect of the Sun, Earth and Moon. In addition, accelerations due to geopotential harmonics, Lunar J2 and solar radiation pressures are considered. Impulsive high thrust is assumed as the main thrusting method of spacecraft with launcher capability of KSLV-2 which is planned to be developed. For the method of injecting a spacecraft into a trans Lunar trajectory, both direct shooting from circular parking orbit and shooting from the multiple elliptical intermediate orbits are adapted, and their design results are compared and analyzed. In addition, spacecraft's visibility from Deajeon ground station are constrained to see how they affect the magnitude of TLI(Trans Lunar Injection) maneuver. The results presented in this paper includes launch opportunities, required optimal maneuver characteristics for each mission phase as well as the trajectory characteristics and numerous related parameters. It is confirmed that the final mass of Korean lunar explorer strongly depends onto the initial parking orbit's altitude and launcher's capability, rather than mission start time.

Effects of Water Activity on the Non-Enzymatic Browning Reaction of Dry Milk (수분활성도(水分活性度)가 분유(粉乳)의 비효소적(非酵素的) 갈변(褐變)에 미치는 영향(影響))

  • Chang, Kyu-Seob;Chang, Yeong-Il;Chun, Ki-Chul;Lee, Seong-Gu
    • Applied Biological Chemistry
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    • v.28 no.4
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    • pp.261-270
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    • 1985
  • This study was carried out he effects of water activity on the nonenzymatic browning reactions of dry milk powders. Samples (Dry Whole Milk DWM, Nonfat Dry Milk NFDM) stored at $55^{\circ}C$ were analyzed for $O_2,\;CO_2$ and $H_2O$ by Gas chromatographic method. The brown color which developed from the Maillard reaction was also measured by a reflective spectrophotometer. And linear regression equations and the correlation coeffcients were determined for $O_2,\;CO_2$ and brown color vs. storage, and the results are as follows. The amount of brown and off-flavor development increase as the water activities increase about 0.44 Aw during storage. Both DWM and NFDM milk products show a plateau in water absorption between the 0.33 and 0.44 water activities. DWM produced more browning than NFDM which may be partially due to the carbonyl amine reaction. The $CaCl_2$ solution may exude a water activity lower than 0.44 and varies greatly with temperatures. Oxygen is depleted as brown color development.

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