• Journal of the Korean Society for Library and Information Science
• /
• v.50 no.3
• /
• pp.429-453
• /
• 2016

This study analyzes circulation patterns of books with checkout transaction count by 11 subject areas, 5 positions, and 5 divisions with a Use Factor developed by Bonn in an Academic Library. 20% of the loan books occupies more than half of circulation and these are regarded as core collection. It proposes a 'Loan books 20/50 rule' that 20% core collection accounts for 50% of its circulation. It analyzes the proportion of core collection from the aspect of each subject area with a use factor, monthly change trend and loan period. It also defines 'book usage' considering checkout frequency of each title and loan period. Circulation patterns of core collection are compared and analyzed in terms of both checkout frequency and book usage. Core collection occupies about more than half of both total checkout transactions and total book usages and they all show a Power Law distribution.

• Journal of Ocean Engineering and Technology
• /
• v.23 no.1
• /
• pp.109-113
• /
• 2009

Several tidal current power plants are being planned and constructed in Korea utilizing the strong tidal currents along the west and south coasts. A tidal current reaches 9.7 m on the west coast; there are few potential regions for tidal current power generation. The construction of a dam to store water can prevent the circulation of water, causing a great environmental impact on the coast and estuary. The tidal barrage could produce a large amount of power, but it should be carefully considered. The purpose of developing renewable energies is to minimize the environmental impact and to maximize the utilization of clean energy. To produce a great quantity of power, tidal current farms require the placement of numerous units in the ocean. The power generation is very dependent on the size of the rotor and the incoming flow velocity. Also, the interactions between devices contribute greatly to the production of power. The efficiency of a power farm is estimated to determine the production rate. This paper introduces 3 D interaction problems between rotating rotors, considering the axial, transverse, and diagonal distances between horizontal axis tidal current devices.

• International Journal of Fluid Machinery and Systems
• /
• v.9 no.4
• /
• pp.325-331
• /
• 2016

A bathtub vortex above the outlet of a rotating barrel is simulated. By analyzing the Ekman layer theory, it can be found that the main flow circulation is inversely proportional to the thickness of Ekman layer. The thicker the Ekman boundary layer, the weaker the rotational strength and the shorter of the length of gas core is. According to this law, models of barriers with rods of different heights are established. The reduction of air-core length in this air entrainment vortex and weakening the strength of rotation field were achieved.

• Journal of Biomedical Engineering Research
• /
• v.40 no.6
• /
• pp.235-241
• /
• 2019

The purpose of this study was to investigate the effect of the body temperature peripheral circulation with vibration shoes in healthy 10 adults. The magnetic vibration device with non-electric power was mounted in the midsole of the vibration shoes. The experiment was divided into two groups: vibration shoes and no vibration shoes. Subjects were randomly selected and measured body surface temperature by digital infrared thermal imaging (DITI) and non-invasive capillaries change by nailfold microscope (NFM). After walking in a treadmill for 15 minutes at 4.0 km/h speed wearing normal shoes or vibration shoes, DITI and NFM were measured. The walking with vibration shoes showed the body surface temperature shift from the proximal to the distal. In addition, the diameter of the nailfold capillary in the vibration shoes group was thicker and clearer due to the increased blood flow than that of the no vibration shoes group. The vibration shoes are easy to apply to anyone who can walk because it can give vibration stimulation by walking without additional time, cost, and effort in daily life. Further studies are needed to explain the physiological effects of vibration frequency and intensity on the long-term perspective of target subjects resulting from vascular dysfunction.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.26 no.12
• /
• pp.2615-2623
• /
• 2002

In this paper, a systematic design approach for a three shaft hydromechanical transmission(HMT) system is proposed by considering the power characteristics and speed ratio range. Using network analysis, possible configurations of the 3 shaft HMT are analyzed and it is found that the influence of HSU stroke on the power distribution of the HMT can be investigated by the network analysis. In addition, design methods are presented from the viewpoint of (1) power distribution and (2) speed ratio range. From the power distribution and the speed ratio range, a HMT configuration can be constructed, which minimizes the power circulation and provides the desired speed ranges. Based on the 3 shaft HMT analyses and the proposed design approach, a 3 shaft HMT is designed which provides 4 speeds in forward and 1 speed in reverse while keeping the power circulation less than 150% of the input power. It is expected that the design method suggested in this study can be used in a systematic design of the 3 shaft HMT.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2023.05a
• /
• pp.125-125
• /
• 2023

Estuarine dams are dams constructed in estuaries for reasons such as securing freshwater resources, controlling water levels, and hydroelectric power generation. These estuarine dams alter the flow of freshwater to the coastal ocean and the tidal properties of the estuaries which has implications for the estuaries' circulation and sediment transport. A previous study has analyzed the effect of estuarine dams on 1D (along-channel) circulation and sediment transport. However, the effect of estuarine dams on the transverse variability of along-channel and across-channel circulation and sediment transport has not been studied and is not known. In this study, a coupled hydrodynamic-sediment dynamic numerical model (COAWST) was used to analyze the transverse variability of along-channel and across-channel flow and sediment transport in estuaries with estuarine dams. The estuarine dam was found to change the 3D structure of circulation and sediment transport, and the result was found to depend on the estuarine type (i.e., strongly stratified (SS) or well-mixed (WM) estuary). The SS estuary had inflow in the channel and outflow over the shoals, consistent with estuarine circulation. Longer discharge interval reduced the estuarine circulation. The WM estuary had inflow over the shoals and outflow in the channel, consistent with tide-induced circulation. As the estuarine dam was located nearer to the estuary mouth, the tide-induced circulation was reduced and replaced with estuarine circulation. The lateral circualtion was the greatest in the tide-dominated estuaries. It was reduced and changed direction due to differential advection change as the dam was located nearer the mouth. Overall, the WM estuary transverse flow structure changed the most. Lateral sediment flux was important in all estuaries, particularly for transporting sediments to the tidal flats.

• Transactions of the Korean hydrogen and new energy society
• /
• v.29 no.4
• /
• pp.393-400
• /
• 2018

To confirm the operating range of two oxygen carriers for chemical looping combustion system, the effects of operating variables on solid circulation rate were measured and discussed using a two-interconnected circulating fluidized bed system at ambient temperature and pressure. Moreover, suitable operating ranges to avoid choking of the fast fluidized bed (air reactor) were confirmed for two oxygen carriers. A continuous long-term operation of steady-state solid circulation more than 24 hours was also demonstrated within the operating windows. Finally we could confirm that those two oxygen carriers are suitable for chemical looping combustion system with high solid circulation rate and smooth solid circulation.

• Nuclear Engineering and Technology
• /
• v.54 no.1
• /
• pp.72-83
• /
• 2022

This paper presents a numerical investigation of two-phase natural circulation flows established when external reactor vessel cooling is applied to a severe accident of the APR1400 reactor for the in-vessel retention of the core melt. The coolability limit due to external reactor vessel cooling is associated with the natural circulation flow rate around the lower head of the reactor vessel. For an elaborate prediction of the natural circulation flow rate using a thermal-hydraulic system code, MARS-KS1.5, a three-dimensional computational fluid dynamics (CFD) simulation is conducted to estimate the flow rate and pressure distribution of a liquid-state coolant at the brink of significant void generation. The CFD calculation results are used to determine the loss coefficient at major flow junctions, where substantial pressure losses are expected, in the nodalization scheme of the MARS-KS code such that the single-phase flow rate is the same as that predicted via CFD simulations. Subsequently, the MARS-KS analysis is performed for the two-phase natural circulation regime, and the transient behavior of the main thermal-hydraulic variables is investigated.

• Journal of the Korean Solar Energy Society
• /
• v.29 no.6
• /
• pp.88-93
• /
• 2009

This study was conducted to improve the power of PV module using a surface cooling system One of the unique characteristics of PV module is power drop as a module surface temperature increases due to the characteristics of crystalline silicon used in a solar cell. To overcome the output power reduction by temperature effect, module surface cooling using water circulation was performed. By cooling effect, module surface temperature drops maximally $20.3^{\circ}C$ predicting more than 10% power enhancement. Maximum deviation of voltage and current between a control and cooled module differed by 5.1 V and O.9A respectively. The maximum power enhancement by cooling system was 12.4% compared with a control module. In addition, cooling system can wash the module surface by water circulation so that extra power up of PV module can be achieved by removing particles on the surface which interfere solar radiation on the cells. Cooling system, besides, can reduce the maintenance cost and prevent accidents as a safety precaution while cleaning works. This system can be applied to the existing photovoltaic power generation facilities without any difficulties as well.

• 한국태양에너지학회:학술대회논문집
• /
• 2009.11a
• /
• pp.309-313
• /
• 2009

This study was conducted to improve the power of PV module using a surface cooling system. One of the unique characteristics of PV module is power drop as a module surface temperature increases due to the characteristics of crystalline silicon used in a solar cell. To overcome the output power reduction by temperature effect, module surface cooling using water circulation was performed. By cooling effect, module surface temperature drops maximally $20.3^{\circ}C$ predicting more than 10% power enhancement. Maximum deviation of voltage and current between a control and cooled module differed by 5.1V and 0.9A respectively. The maximum power enhancement by cooling system was 12.4% compared with a control module. In addition, cooling system can wash the module surface by water circulation so that extra power up of PV module can be achieved by removing particles on the surface which interfere solar radiation on the cells. Cooling system, besides, can reduce the maintenance cost and prevent accidents as a safety precaution while cleaning works. This system can be applied to the existing photovoltaic power generation facilities without any difficulties as well.