• Journal of the Korean Society for Marine Environment & Energy
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• v.6 no.4
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• pp.45-51
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• 2003

The reflection and transmission of submerged breakwater with trapezoidal type are computed numerically using boundary element method. The analysis method is based on the wave pressure function with the contlnuit? in the analytical region including fluid and porous structures. Wane motion within the porous structures is simulated by introducing the linear dissipation coefficient and added mass coefficient. The results indicate that transmission and reflection coefficient are determined due to the change of slope of submerged breakwater with trapezoidal type.

• Journal of the Korean Solar Energy Society
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• v.30 no.3
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• pp.47-54
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• 2010

Recently the researchers has been interested in the development of the high performance windows such as solar control window using automatic shading devices, air-flow window, selective coating window. In order to assess the energy performance of total fenestration system, the net energy gains or losses through the glazings and windows should be evaluated. It depends on the thermal transmittance (U-value) and the total solar energy transmittance (SHGC, g-value). This study aims to measure the solar heat gain coefficient according to the NFRC 201 standard test method. In results, we could find the result of different SHGC of the glazing system with a different slat angles. The SHGC in case of $90^{\circ}$ of internal slat angle with regard to the window surface is about 0.56, that in case of $45^{\circ}$ is about 0.49 and that in case of $0^{\circ}$ is about 0.33. Significant dependence on the solar radiation intensity and incident angle was found in comparison of the measured and simulated SHGC.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.29 no.10
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• pp.515-529
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• 2017

EnergyPlus, which is widely used in various fields, provides Simple Window Model, a window model that can be used practically. However, the results of building load using the model are different from those of the standard model. The main cause of the deviation by Simple Window Model was analyzed to be due to the assumption that all windows were considered as single layer. The purpose of this study is to propose a window model that improves the cause of deviation by Simple Window Model and can be easily calculated from the algebraic relations. The proposed window model solved the heat balance equation algebraically by using seven window characteristic coefficients. The coefficient relationships consisted of the heat transmission coefficient and solar heat gain coefficient as input parameters make practical use and calculation possible. As a result of comparing the deviation between each window model by implementing the dynamic analysis method, the proposed window model showed that the deviation of the total heating/cooling energy consumption was reduced to 1/3 compared to Simple Window Model for one year. Although the maximum energy consumption did not show any significant improvement, the indoor temperature evaluation showed significantly reduced deviation.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.2
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• pp.170-177
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• 1998

The purpose of superconducting magnetic bearing flywheel energy storage system(SMB-FESS) is to store unused nighttime electricity as kinetic energy and convert it to electricity during daytime. The SMB-FESS is proposed as an efficient energy storage system because there is no mechanical problems, such as friction and wear The flywheel over SMB is rotated at a high speed, 50,000rpm. The major source of energy loss in the SMB-FESS is vibration of flywheel. Therefore, the vibration characteristics of SMB-FESS should be identified. In this study, the axial/radial stiffness and damping coefficient of SMB are measured by a vibration test. Natural frequencies and natural modes of flywheel and magnet are analyzed by a finite element method. The modal analysis of system is performed using the modal parameters of each component and the measured stiffness/damping coefficient. So, natural at frequencies and mode shapes of the joined system can be obtained. According to critical speed analysis, the system has two rigid conical modes in the low speed range. Nevertheless, the system has not been affected by the critical speed in the main operating range.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.3
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• pp.146-151
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• 2015

The heat transfer performance of heating medium oil fluidized bed heat exchanger was measured. The operation variables were air flow rate, air inlet temperature, moisture content, water flow rate and water inlet temperature. The outside heat transfer coefficient was determined from the heat exchanger experiment and its experimental correlation was determined as a function of air velocity and viscosity of heating medium oil. Effect of viscosity was well agreed with the previous studies. Errors of the correlation equation was less than about 10% for outside heat transfer coefficient developed in this study when compared with the measured value. Hot water with the temperature greater than $77^{\circ}C$ could be produced by using the heating medium oil fluidized bed heat exchanger.

• International Journal of Computer Science & Network Security
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• v.21 no.1
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• pp.6-11
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• 2021

Routing protocols play a pivotal role in the energy management and lifespan of any Wireless Sensor Network. Lower network lifetime has been one of the biggest concerns in LEACH protocol due to dead nodes. The LEACH protocol suffers from uneven energy distribution problem due to random selection of a cluster head. The cluster head has much greater responsibility compared to other non- cluster head nodes and consumes greater energy for its roles. This results in early dead nodes due to energy lost for the role of cluster- head. This study proposes an approach to balance the energy consumption of the LEACH protocol by using a semi-deterministic opportunity coefficient to select the cluster head. This is calculated in each node with the battery energy level and node ID. Ultimately, based on the opportunity cost, cluster head will be selected and broadcasted for which other nodes with higher opportunity cost will agree. It minimizes the chances of nodes with lower battery level being elected as cluster head. Our simulation experiments demonstrate that cluster heads chosen using our proposed algorithm perform better than those using the legacy LEACH protocol.

• Journal of the Korean Society of Radiology
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• v.9 no.6
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• pp.375-379
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• 2015

The purpose of this study is to determine the effective energy of a polyenegetic X-ray beam. The half value layer(HVL) of aluminum for 80 kVp X-ray beam was measured by using optically stimulated luminescent nanoDot dosimeters(OSLnDs). The linear attenuation coefficient(${\mu}$) was calculated using the measured HVL. And the mass attenuation coefficient(${\mu}/{\rho}$) was obtained by dividing the linear attenuation coefficient by the density(${\rho}$) of aluminum. The effective energy($E_{eff}$) of the obtained mass attenuation coefficient was determined using data of the X-ray mass attenuation coefficients for photon energies of aluminum given by National Institute of Standards and Technology(NIST). As a result, the HVL value is 2.262 mmAl. The ${\mu}$ value is $3.06cm^{-1}$. The ${\mu}/{\rho}$ value is $1.114cm^2/g$. And the $E_{eff}$ value was determined at 29.79 keV.

• Journal of applied mathematics & informatics
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• v.19 no.1_2
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• pp.385-395
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• 2005

A finite element scheme is considered for the viscous Cahn-Hilliard equation with the nonconstant gradient energy coefficient. The scheme inherits energy decay property and mass conservation as for the classical solution. We obtain the corresponding error estimate using the extended Lax-Richtmyer equivalence theorem.

• Journal of the Korean Dietetic Association
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• v.12 no.1
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• pp.44-54
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• 2006

The study was conducted to assess the energy expenditure of 102 elementary school children. Body weight and height were measured and one-day activity diaries were collected by interviewing with children. The children spent about 9 hours 14 minutes sleeping ; 3 hours 40 minutes resting. They spent 86.4% of 24 hours (one day) in 'very light activities' and 13.3% in 'light activities'. Activity coefficient (1.41$\pm$0.11) of boys was significantly higher than that of girls(1.35$\pm$0.07). Activity coefficient (1.41$\pm$0.11) of 4th grade elementary school children was higher than those of 2nd and 6th grade school children(p<0.05). Resting energy expenditure estimated by Harris-Benedict formula, formula based on body surface area and DRI formula for Koreans were 1240.9$\pm$147.4kcal/day, 1386.5$\pm$206.9kcal/day and 1284.5$\pm$199.8 kcal/day. And daily energy expenditure by using Harris-Benedict formula, body surface area formula and DRI formula were 1708.4$\pm$258.8kcal, 1909.8$\pm$341.8kcal and 1771.1$\pm$341.9kcal/day. These results suggested that nutrition and exercise program to increase the energy expenditures of primary school children should be developed.

• Journal of Energy Engineering
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• v.24 no.1
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• pp.42-50
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• 2015

To evaluate the heat removal capability of a condenser tube in the PCCS of an advanced nuclear power plant, a steam condensation experiment in the presence of noncondensable gas on a vertical tube is performed. The average heat transfer coefficient is measured on a vertical tube of 40 mm in O.D. and 1.0 m in length. The experiments covers the pressures of 2-4 bar, and the mass fraction of air ranges from 0.1 up to 0.7. From the experimental results, the effects of the total pressure and the concentration of air on the condensation heat transfer coefficient are investigated. The measured data are compared with the predictions by Uchida's and Tagami's correlations, and it is revealed that these models underestimate the condensation heat transfer coefficient of the steam-air mixture.