• Korean Journal of Ecology and Environment
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• 제45권2호
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• pp.200-209
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• 2012

The current of the water body is very important information for the water quality management on reservoirs. It is applied to hydraulics and water quality model for simulation. In this regard, the current characteristic of water body is the basic information that can be used to predict various conditions. However, it is very slow flowing and is affected by the reservoir operations and external factors. As such, an accurate measurement of the current is a difficult problem. In order to measure the water current, we constructed a drifter. According to the result of flow survey at Yongdam reservoir, 5m and 10 m depth layer flow was investigated from the upstream to the downstream, during a flood period. Maximum flow rate of 5 m depth is 13.8 cm $sec^{-1}$ and 10 m depth shows 4 cm $sec^{-1}$, respectively. But 2m depth shows a backward flow and maximum flow rate is 4 cm $sec^{-1}$. Density currents flow plays the role of back flow in reservoirs. Flow velocity in the reservoir was measured in the range of 1~2 cm $sec^{-1}$, at normal flow season, and the flow direction were different for each survey. This phenomenon occurs because the reservoir volume is very large, compared to the inflow and outflow volume.

• Journal of Ocean Engineering and Technology
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• 제11권4호
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• pp.141-151
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• 1997

This paper deals with a numerical study of flow-guider applied to controlling current in a bay. Two dimensional numerical model for tidal currents based on the depth averaged equation is developed and standard k-.epsilon. model is adopted to determine the turbulence diffusion. Equations are described in a generalized coordinate system to be implemented by non-staggered grid system and discretized by using finite volume method. Unsteady flow is simulated by fully implicit scheme. Hybrid scheme and central differencing are used to compute the convective terms and source terms, respectively. The tidal current in a rectangular bay is simulated and it gives satisfactory results. The realistic and distinct models of a large structure placed in bay are also exemplified with or without flow-guiders. The simulation results show that the flow-guider gives the residual tidal current in the bay by the different flux with respect to the direction of tidal current.

• The Journal of Korean Physical Therapy
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• 제11권2호
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• pp.37-42
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• 1999

The purpose of this study was to determine whether percutaneous interferential current stimulation on thoracic sympathetic ganglia with amplitude modulated frequency (AMF) $90\~100$ bps and subthreshold of muscle contraction for 10 minutes on peripheral blood flow velocity in healthy subjects. Thirty-seven healthy volunteers were assigned randomly into an experimental group (n=25) and a control group (n=12). the experimental group received interferential current stimulation with subthreshold of the muscle contraction of current at AMF $90\~100$ bps on $1st\~5th$ thoracic sympathetic ganglial region for 10 minutes. The control group received same handling and electode placement, but no current was applied. Using a Doppler blood flow meter, the radial arterial blood flow velocities and the pulse raters were determined for two-way analysis of variance for repeated measures on time and group. There were no significant difference between the two groups with respect to the changes in arterial blood flow velocity and pulse rate over the four measurement times. Interferential current stimulation did not change in mean blood flow velocity and pulse rate. We conclude that interferential current stimulation on the thoracic sympathetic ganglia, as used in this study, did not dilate peripheral artery. This results suggests that interferential current stimulation dose not alter the activtiy of sympathetic nerve.

• Journal of Ocean Engineering and Technology
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• 제35권6호
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• pp.446-456
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• 2021

To build an environment facility of a large-scale ocean basin, various detailed reviews are required, but it is difficult to find data that introduces the related research or construction processes on the environment facility. The current generator facility for offshore structure safety evaluation tests should be implemented by rotating the water of the basin. However, when the water in the large basin rotates, relatively large flow irregularities may occur and the uniformity may not be adequate. In this paper, design and review were conducted to satisfy the performance goals of the DOEB through computational numerical analysis on the shape of the waterway and the flow straightening devices to form the current in the large tank. Based on this, the head loss, which decreases the flow rate when the large tank water rotates through the water channel, was estimated and used as the pump capacity (impeller) design data. The impeller of the DOEB current generator was designed through computational numerical analysis (CFD) based on the lift surface theory from the axial-type impeller shape for satisfying the head loss of the waterway and maximum current velocity. In order to confirm the performance of the designed impeller system, the flow rate and flow velocity performance were checked through factory test operation. And, after installing DOEB, the current flow rate and velocity performance were reviewed compare with the original design target values. Finally, by measuring the current velocity of the test area in DOEB formed through the current generator, the spatial current distribution characteristics in the test area were analyzed. Through the analysis of the current distribution characteristics of the DOEB test area, it was confirmed that the realization of the maximum current velocity and the average flow velocity distribution, the main performance goals in the waterway design process, were satisfied.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• 제58권2호
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• pp.159-174
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• 2022

Flow prediction was carried out through observational survey and three dimensional multi-layered numerical diagnostic model experiment to clarify the time and spatial structure of tidal current and residual flow dominant in the sea exchange and material circulation of the waters around Geumo Islands in the southern waters of Korea. The horizontal variation of tidal current is so large that it causes asymmetric tidal mixing due to horizontal eddies and the topographical effect creating convergence and dispersion of flow direction and velocity. Due to strong tidal currents flowing northwest-southeast, counterclockwise and clockwise eddies are formed on the left and right sides of the south of Sori Island. These topographical eddies are created by horizontal turbulence and bottom friction causing nonlinear effects. Baroclinic density flows are less than 5 cm/s at coastal area in summer and the entire sea area in winter. The wind driven currents assuming summer and winter seasonal winds are also less than 5 cm/s and the current flow rate is high in winter. Density current in summer and wind driven current in winter have a relatively greater effect on the net residual flows (tidal residual current + density current + density driven current) around Geumo Islands Sea area.

• Transactions of the Korean hydrogen and new energy society
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• 제26권4호
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• pp.324-330
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• 2015

The electrolyte flow rates of vanadium redox flow battery play very important role in terms of ion transfer to electrolyte, kinetics and pump efficiency in system. In this paper a vanadium redox flow battery single cell was tested to suggest the optimization criteria of electrolyte flow rates on the efficiencies. The compared electrolyte circulation flow rates in this experimental work were 15, 30 and 45 mL/min. The charge/discharge characteristics of the flow rate of 30 mL/min was the best out of all flow rates in terms of charging and discharging time. The current efficiencies, voltage efficiencies and energy efficiencies at the flow rate of 30 mL/min were the best. The IR losses obtained at thd current density of $40mA/cm^2$, at the flow rates of 15, 30 and 45 mL/min were 0.085 V, 0.042 V and 0.115 V, respectively. The charge efficiencies at the current density of $40mA/cm^2$ were 96.42%, 96.45% and 96.29% for the electrolyte flow rates of 15, 30 and 45 mL/min, respectively. The voltge efficiencies at the current density of $40mA/cm^2$ were 77.34%, 80.62% and 76.10% for the electrolyte flow rates of 15, 30 and 45 mL/min, respectively. Finally, the energy efficiencies at the current density of $40mA/cm^2$ were 74.57%, 77.76% and 73.27% for the electrolyte flow rates of 15, 30 and 45 mL/min, respectively. The optimum flow rates of electrolytes were 20 mL/min in most of operating variables of vanadium redox flow battery.

• Journal of Power Electronics
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• 제16권5호
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• pp.1743-1751
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• 2016

The increasing demand for high voltage DC grids resulting from the continuous installation of offshore wind farms in the North Sea has led to the concept of multi-terminal direct current (MTDC) grids, which face some challenges. Power (current) flow control is a challenge that must be addressed to realize a reliable operation of MTDC grids. This paper presents a reduced switch count topology of a current flow controller (CFC) for power flow and current limiting applications in MTDC grids. A simple control system based on hysteresis band current control is proposed for the CFC. The theory of operation and control of the CFC are demonstrated. The key features of the proposed controller, including cable current balancing, cable current limiting, and current nulling, are illustrated. An MTDC grid is simulated using MATLAB/SIMULINK software to evaluate the steady state and dynamic performance of the proposed CFC topology. Furthermore, a low power prototype is built for a CFC to experimentally validate its performance using rapid control prototyping. Simulation and experimental studies indicate the fast dynamic response and precise results of the proposed topology. Furthermore, the proposed controller offers a real solution for power flow challenges in MTDC grids.

• Journal of Wetlands Research
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• 제12권1호
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• pp.95-103
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• 2010

Discharge data examine the process of hydrologic cycle and used significantly in water resource planning and irrigation and flood control planning. However, it needs lots of time and money to get the discharge data. So discharge rating curve is usually used in converting discharge data. Therefore reliability of discharge rating curve absolutely depends on quality of discharge data. Many engineers who study hydrologic engineering make high quality discharge data to develop reliable discharge rating curve. And they carry out research on standard and method of discharge measurement, and equipment improvement. Now various flow meters are utilized to make discharge data in Korea. However, accuracy of equipment and experimental research data from measurement are not enough. In this paper, constant discharge flowed through standard concrete channel, and the velocity is measured using various flow meters. Also Discharge is calculated by measured data to compare and analyze. The equipment for the experiment is Price AA(USGS Type AA Current meter), flow meter, ADC, C2 small current meter, flow tracker, Electromagnetic current meter. The discharge got form various flow meters which are widely used for discharge measurement. The various depths of water were examined and compared such as 0.30 m, 0.35 m, 0.40 m, 0.45 m, 0.50 m, 0.55 m. The experiment progresses a round-measurement on 6-case. Wading measurement(one point method : the 60 % height in surface of the water) was applied to improve creditability and accuracy among measurement methods. USGS Type AA current Meter, Flow Meter, ADC, C2 Small Current meter got the certificate of quality guaranteed. So the results of experiment were used to compare discharge. The Results showed the difference based on USGS Type AA current Meter at average discharge and velocity. Electromagnetic current meter made differences over $\pm$ 10 % and Flow Meter made differences under $\pm$ 10 %. Also ADC, Flow Meter, C2 Small Current meter made differences under $\pm$ 5 %.

• Journal of Korean Society of Coastal and Ocean Engineers
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• 제12권3호
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• pp.130-138
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• 2000

The friction factor equation of open channel flow is developed by using Prandtl's mixing length theory and considering the flow characteristics of smooth or rough turbulent flow. BYO model considers vertical velocity profile for the (:omputation of bottom friction of surface waves and current flow. The model computes the mean bottom friction of combined wave-current flow by the vectorial summation of wave velocity and current velocity at Bijker point. The near bottom flow is discriminated by three flow regimes; smooth, transitional and rough turbulent flow. The model, BYO, has been further refined considering the combination of smooth turbulent flow and rough turbulent flow.

• Journal of Ocean Engineering and Technology
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• 제15권1호
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• pp.45-51
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• 2001

In order to clarify the seasonal variation of the residual current and the material transportation process in Hiroshima Bay, JAPAN, the real-time simulation of residual current and particle tracking by using the Euler-Lagrange model were carried out. The calculated tidal current, water temperature, and salinity showed good agreement with the observed ones. The residual currents showed a southward flow pattern at the upper layer, and a northward flow pattern at the lower layer. The flow structure of the residual current in Hiroshima Bay is an estuarine circulation affected by density flow and wind driven current. The residual current plays an important role of material transportation in the bay.