• Proceedings of the Korea Water Resources Association Conference
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• 2005.09b
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• pp.842-845
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• 2005

A method for the numerical simulation of two-dimensional free-surface flow resulting from the propagation of regular gravity waves over topography with arbitrary bottom shape is presented. The method is based on the numerical solution of the Euler equations subject to the fully nonlinear free-surface boundary conditions and the appropriate bottom, inflow and outflow conditions using a hybrid finite-differences and spectral-method scheme. The formulation includes a boundary-fitted transformation, and is suitable for extension to incorporate large-eddy simulation (LES) and large-wave simulation (LWS) terms for turbulence and breaking wave modeling, respectively. Results are presented for the simulation of the free-surface flow over two different bottom topographies, with constant slope values of 1:10 and 1:20, two different inflow wave lengths and two different inflow wave heights. An absorption outflow zone is utilized and the results indicate minimum wave reflection from the outflow boundary. Over the bottom slope, lengths of waves in the linear regime are modified according to linear theory dispersion, while wave heights remain more or less unchanged. For waves in the nonlinear regime, wave lengths are becoming shorter, while the free surface elevation deviates from its initial sinusoidal shape.

• Journal of the Society of Naval Architects of Korea
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• v.61 no.4
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• pp.236-246
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• 2024

The present study aims to identify the effects of the oblique inflow and vertical acceleration on a marine propeller's hydrodynamic force and moment. Computational Fluid Dynamics analysis is performed for a rotating propeller in open water conditions with heave motion after performing validation against experiment in straightforward conditions. The oblique inflow results in a linear increase of the off-axial component of the hydrodynamic force and moment rather than the axial one. Pitch and yaw moments due to the hull motion are dominated by the heave force and the moment arm of the propeller location. Additionally, the vertical acceleration leads to a linear augmentation of off-axial hydrodynamic force and moment, implying the added mass and moment of inertia. Notably, it is found that the off-axial hydrodynamic force and moment are dominated by the oblique inflow velocity rather than the acceleration.

• Journal of Korean Tunnelling and Underground Space Association
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• v.10 no.1
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• pp.49-57
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• 2008

One of the most important design concerns for undersea tunnels is to establish design water load and flow rate. These are greatly dependent on the hydraulic factors such as water head, cover depth, hydraulic boundary conditions. In this paper, the influence of the hydraulic design factors on the ground loading and the inflow rate was investigated using the coupled finite element method. A horse shoe-shaped tunnel constructed 30 m below sea bottom was adopted to evaluate the water head effect considering various water depth for varying hydraulic conditions and relative permeability between lining and ground. The effect of cover depth was analysed for varying cover depth with the water depth of 60 m. The results were considered in terms of pore water pressure, ground loading and flow rate. Ground loading increases with an increase in water head and cover depth without depending on hydraulic boundary conditions. This points out that in leaking tunnels an increase in water depth increases seepage force which consequently increases ground loading. Furthermore, it is identified that an increase in water head and cover depth increases the rate of inflow and a decrease in the permeability ratio reduces the rate of inflow considerably.

• 한국신재생에너지학회:학술대회논문집
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• 2007.11a
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• pp.387-390
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• 2007

Recently the diameter of the 5MW wind turbine reaches 126m, and the tower height is nearly the same with the wind turbine diameter. The blade will experience periodic inflow oscillation due to blade rotation inside the ground shear flow region, that is, the inflow velocity is maximum at uppermost position and minimum at lowermost position. In this study we compare the aerodynamic data between two inflow conditions, i.e, uniform flow and normal wind profile. From the computed results all of the relative errors for oscillating amplitudes increased due to the ground shear flow effect. Especially My at hub and $F_x$, $M_y$, $M_z$ at LSS increased enormously. It turns out that the aerodynamic analysis including the ground shear flow effect must be considered for fatigue load analysis.

• Journal of Korean Society of Transportation
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• v.14 no.4
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• pp.7-29
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• 1996

The optimal solution obtained by a linear programming model is to maximize the ramp inflow rate. It is argued in this paper that the maximization of inflow rate is different from the maximization of outflow rate under congested conditions. Therefore, this paper proposes a systematic searching procedure from a linear programing formulation to a integer programming : first obtain the optimal solution by a linear programming and then adding weight to linear programming then. solve the optimal solution again by integer programming i.e. The proposed method is an interactive approach. Measure of effectiveness by simulation models regards the real time data(O/D, queue, delay, etc), can be utilized in the proposed interactive process.

• Korean Journal of Ecology and Environment
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• v.35 no.4 s.100
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• pp.285-294
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• 2002

The purpose of this study was to evaluate the relationships between purification characteristics and hydraulic conditions, and to clarify the basic and essential factors required to be considered in the construction and management of artificial wetland system for the improvement of reservoir water quality. The artificial wetland system was composed of a pumping station and six sequential plants beds with five species of macrophytes: Oenanthe javanica, Acorus calamus, Zizania latifolia, Typha angustifolia, and Phragmites australis. The system was operated on free surface-flow system, and operation conditions were $3,444-4,156\; m^3/d$ of inflow rate, 0.5-2.0 hr of HRT, 0.1-0.2 m of water depth, 6.0-9.4 m/d of hydraulic loading, and relatively low nutrients concentration (0.224-2.462 mgN/L, 0.145-0.164 mgP/L) of inflow water. The mean purification efficiencies of TN ranged from 12.1% to 14.3% by showing the highest efficiency at the Phragmites australis bed, and these of TP were 6.3-9.5% by showing the similar ranges of efficiencies among all species. The mean purification efficiencies of SS and Chl-A ranged from 17.4% to 38.5% and from 12.0% to 20.2%, respectively, and the Oenanthe javanica bed showed the highest efficiency with higher concentration of influent than others. The mean purification amount per day of each pollutant were $9.8-4.1\;g{\cdot}m^{-2}{\cdot}d^{-1}$ in BOD, $1.299-2.343\;g{\cdot}m^{-2}{\cdot}d^{-1}$ in TN, $0.085-1.821\;g{\cdot}m^{-2}{\cdot}d^{-1}$ in TP, $17.9-111.6\;g{\cdot}m^{-2}{\cdot}d^{-1}$ in SS and $0.011-0.094\;g{\cdot}m^{-2}{\cdot}d^{-1}$ in Chl-a. The purification amount per day of TN revealed the hi링hest level at the Zizania latifolia bed, and TP showed at the Acrous calamus bed. SS and Chl-a, as particulate materials, revealed the highest purification amount per day at the Oenanthe javanica bed that was high on the whole parameters. It was estimated that the purification amount per day was increased with the high concentration of influent and shoot density of macrophytes, as was shown in the purification efficiency. Correlation coefficients between purification efficiencies and hydraulic conditions (HRT and inflow rate) were 0.016-0.731 of $R^2$ in terms of HRT, and 0.015-0.868 of $R^2$ daily inflow rate. Correlation coefficients of purification amounts per day with hydraulic conditions were 0.173-0.763 of Ra in terms of HRT, and 0.209-0.770 daily inflow rate. Among the correlation coefficients between purification efficiency and hydraulic condition, the percentages of over 0.5 range of $R^2$ were 20% in HRT and in daily inflow rate. However, the percentages of over 0.5 range of correlation coefficients ($R^2$) between purification amount per day and hydraulic conditions were 53% in HRT and 73% in daily inflow rate. The relationships between purificationamount per day and hydraulic condition were more significant than those of purifi-cation efficiency. In this study, high hydraulic conditions (HRT and inflow rate) are not likely to affect significantly the purification efficiency of nutrient. Therefore, the emphasis should be on the purification amounts per day with high hydraulicloadings (HRT and inflow rate) for the improvement of eutrophic reservoir withrelatively low nutrients concentration and large quantity to be treated.

• Journal of Environmental Science International
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• v.28 no.11
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• pp.1005-1017
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• 2019

Environmental factors and changes in phytoplankton community structure before (August 5, 2017), during (August 18 and 25) and after (August 30 and September 15) freshwater input were analyzed to investigate the effects of freshwater input from Ganwol and Bunam lakes located in the upper part of Cheonsu Bay. Due to the large amount of freshwater input in the Cheonsu Bay, the surface salinity of the bay decreased by more than 8 psu, and the thermocline existing in the bay during August weakened. In addition, hypoxic phenomena occurred temporarily in the bay as the low oxygen water mass from the freshwater lakes flowed into the bay, and chemical oxygen demand, nutrients, and N/P increased with freshwater inflow. The density of phytoplankton during the freshwater inflow increased owing to their input from the freshwater lakes. Diatom species (Eucampia zodiacus) dominated the phytoplankton community in the bay before freshwater input; nanoflagellates, chlorophyta, cyanobacteria, and diatoms (Pseudonitzschia delicatissima, Chateocceros spp.) entered during freshwater input; and after freshwater inflow ended, diatoms (Chateocceros spp.) again became predominant indicating a return to previous conditions. The amount of phytoplankton standing crops increased sharply due to the inflow of freshwater species into the bay on the second day of discharge compared to before freshwater input; pre-discharge conditions were restored at most stations except at some sites close to the Bunam Lake three days after discharge. Therefore, the large amount of freshwater flowing into the bay affects not only the geochemical circulation in the bay but also the phytoplankton community structure. In particular, the high concentration of nutrients in the freshwater lake affect the marine ecosystem of the bay during August.

• Journal of Korean Society on Water Environment
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• v.22 no.1
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• pp.91-96
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• 2006

Many small scale Sewage Treatment Plants (STPs) are currently being constructed at many rural areas. The STPs in rural area suffer from low concentration and large inflow quantity fluctuation during wet weather mainly due to illicit combined sewer system. Sequencing Batch Reactor (SBR) is a process effectively coping with these obstacles. The main objective of this study was to evaluate SBR with high hydraulic loading and low inflow concentration. The operating conditions tested were: organic loading rate = $0.17-0.42KgBOD/m^3/d$, hydraulic loadings = $12.1-61.5m^3/m^2/d$, average MLSS concentration = 2500 mg/L, F/M ratio = 0.026-0.17 KgBOD/Kg MLSS, HRT = 9-12 hr HRT, and SRT = 5.6-33.6 days. Organic loading rate on SBR did not impact significantly on BOD and SS removal efficiencies. To increase treatment efficiencies, low hydraulic loading rate with low concentration was required. The results suggested that low influent concentration with high inflow rates during wet weather requires extended time for settling.

• 한국연소학회:학술대회논문집
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• 2006.10a
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• pp.209-219
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• 2006

The supersonic combustion experiments are carried out using T3 free-piston shock tunnel. Different shock tube fill pressures have various inflow conditions. $15^{\circ}$ inclined hydrogen fuel injection is located before the cavity. Oblique shock is generated at the trailing edge of the cavity and reflects off the top and bottom wall. For non-reacting flow, static pressures in low equivalence ratio are similar to those in no fuel injection. As equivalence ratio is increased, static pressures are increased in the duct. In the similar equivalence ratio, static pressures are increased when total enthalpy is decreased. For reacting flow, the flame is occurred near the cavity. The combustion is weak locally in the middle of the duct. The up and down pressure distribution in the duct means that the supersonic combustion is generated.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.6
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• pp.1590-1597
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• 1994

The aerodynamic analysis of a $6{\times}6$ counter-rotating propfan around a missile-like-body has been completed analytically using a frequency domain panel method. The present method requires Fourier transformation of flow field around the propfan in computing the velocities normal to the propfan lifting surfaces. The aerodynamic performance curve is determined by angle of attack and nonuniform inflow conditions. The inflow conditions result from the variations of missile flight speed, angle of attack, propfan location relative to control surfaces and control surface deflection angle. The two cases of propfan location relative to control surface, front and behind, are analyzed and the aerodynamic results are presented.