• Tribology and Lubricants
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• v.36 no.6
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• pp.378-384
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• 2020

The friction surfaces of mechanical parts are heat-treated or coated with hard materials to minimize wear. Increasing the hardness is a very useful way to reduce abrasive wear. The general Brinell hardness test, which is widely used for metallic materials, is not suitable because it hardly shows any change in hardness when coated with thin films. In this study, we propose a basis for the application of the new Brinell hardness test method to the coated friction surface. An indentation analysis of the rigid sphere and elastic-perfectly plastic materials is performed using a commercial finite element analysis software. The results indicate that their loadto-diameter ratio is the same; the Brinell hardness test method can be applied even when the indenter diameter is on the micrometer scale. In the case of hard coating, it is difficult to calculate Brinell hardness using the diameter of the indentation, but the study revealed, for the first time, that it can be calculated using the depth of the indentation regardless of coating. The change in hardness owing to thin film coating over a wide load range implies that the hardness evaluation method is appropriate. Additional studies on various properties related to the substrate and coating material are required to apply the proposed method.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.7
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• pp.48-57
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• 2021

The main research content of this paper is to evaluate the structural integrity and the cooling performance of 4250 kVA power transformer with ONAN(Oil Natural and Air Natural) mode. The dynamic analysis is used to verify the structural safety of the transformer by seismic loading. The transformer structure is simplified and NX software is used to build a three-dimensional model, and ANSYS commercial software is used to calculate the stress and deformation by applying corresponding load. The analysis result was evaluated whether it satisfies the design requirements according to the IEEE Std 693 standard. In terms of thermal analysis to evaluate the cooling performance, the thermal physical model is used to calculate the heat exchange between the radiator and the tank in the steady state, and the result is input into the Fluent software to calculate the internal temperature field of the transformer tank, which reduces the calculation cost of thermal fluid. Comparing the simulated hot spot temperature and top oil temperature of the transformer with the calculation results of the IEC60076 classic model, it is found that the error is only 1.9%.

• Structural Engineering and Mechanics
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• v.84 no.6
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• pp.823-829
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• 2022

This study considered the experimental parameters (Nano-graphene oxide reinforced polycarbonate, GFRP) under low-velocity impact load and vibration analysis. The effect of nano-graphene oxide (NGO) on a polycarbonate-based composite was studied. Two test procedures were adopted to obtain experimental results, vibration analysis. The mechanical tests were performed on damaged and non-damaged specimens to determine the damaging effect on the composite specimens. After the test was carried out, the effect of NGO was measured and damping factors were ascertained experimentally. 0. 2 wt% NGO was determined as the optimum amount that best affected the Vibration Analysis. The experiments revealed that the composite's damping properties were increased by adding the nanoparticles to 0.25 wt% and decreased slightly for the specimens with the highest nanoparticles content. Cyclic sinus loading was applied at a frequency of 3.5 Hz. This paper study the frequency effect of 3.5khz frequency damage on mechanical results. Found that high frequency will worthlessly affect the fatigue life in NGO/polycarbonate composite. In 3.5 Hz frequency, it was chosen to decrease the heat by frequency. Transmission electron microscopy (TEM) micrographs were used to investigate the distribution of NGO on the polycarbonate matrix and revealed a homogeneous mixture of nano-composites and strong bonding between NGO and the polycarbonate which increased the damping properties and decreased vibration. Finally, experimental modal analysis was conducted after the high-velocity impact damage process to investigate the defect on the NGO polycarbonate composites.

• International conference on construction engineering and project management
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• 2007.03a
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• pp.625-634
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• 2007

Energy-saving is one of important issues in multi-family housing projects in South Korea. According to the study by Yu et al. (2002), the balcony conversion causes energy loss approximately one and a half times. Therefore, it is important to select the economical glass type in the balcony window. In order to identify the most economical glass type of balcony conversion in multi-family housing projects, the most typical type of the multifamily housing projects in the metropolitan area was selected as a candidate project. The selected candidate project has been simulated using ENERGY-10 program to estimate the heat load by the different five types of glasses as well as their life cycle cost analysis (LCCA) using present worth method. Finally, sensitivity analysis has been conducted to determine the most economical glass types under a different discount rate (interest rate) and service life of building.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.19 no.2
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• pp.163-170
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• 2023

Since spent nuclear fuel assemblies (SFA) are transported to interim storage or final disposal facility after cooling the decay heat, finite element analysis (FEA) with simplification is widely used to show their integrity against cladding failure to cause dispersal of radioactive material. However, there is a lack of research addressing the comprehensive impact of shape and element simplification on analysis results. In this study, for the optimization of a typical pressurized water reactor SFA, different types of finite element models were generated by changing number of fuel rods, fuel rod element type and assembly length. A series of FEA in use of these different models were conducted under a shock load data obtained from surrogate fuel assembly transportation test. Effects of number of fuel rods, element type and length of assembly were also analyzed, which shows that the element type of fuel rod mainly affected on cladding strain. Finally, an optimal finite element model was determined for other practical application in the future.

• The Journal of Engineering Geology
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• v.11 no.1
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• pp.13-23
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• 2001

Rock slope near the road or railroad is affected by the outside temperature and iterative freezing-thawing process during winter and early spring. The purpose of this study is to analyze the stability of rock slope which is iniluenced by deterioration due to the freezing-thawing. Method of analysis is homogenization method which find the strength property of discontinuous rock mass and as a strength failure criterion, Drucker-Prager failure criterion is used, The deterioration property of real rock is obtained by a freezing-thawing labordtory test of tuff and this quantitative property is used as a basic data of stability analysis of rock mass. To evaluate the deterioration depth due to the freezing-thawing in the field rock slope, one dimensional heat conductivity equation is used and as a a result we can find the depth of which is affected by a temperature. After determined the freezing-thawing depth of model slope, the pattern of rock mass strength value of model rock slope which excess the limit of self-load is analyzed.

• Journal of the Semiconductor & Display Technology
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• v.21 no.4
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• pp.18-22
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• 2022

Photovoltaics (PV) power generation efficiency is affected by meteorological factors such as temperature and wind speed. In general, it is known that the power generation amount decreases because photovoltaics panel temperature rises and the power generation efficiency decreases in summer. Photovoltaics Thermal (PVT) power generation has the ad-vantage of being able to produce heat together with power, as well as preventing the reduction in power generation efficien-cy and output due to the temperature rise of the panel. In this study, the amount of heat collected by season and time was calculated for photovoltaics thermal modules using the International Weather for Energy Calculations (IWEC) data provided by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). Based on this, we propose a method of predicting the temperature of the photovoltaics panel using thermal analysis and then calculating the flow rate of coolant to improve power generation efficiency. As the results, the photovoltaics efficiencies versus time on January, April, July, and October in Jeju of the Republic of Korea were calculated to the range of 15.06% to 17.83%, and the maxi-mum cooling load and flow rate for the photovoltaics thermal module were calculated to 121.16 W and 45 cc/min, respec-tively. Though this study, it could be concluded that the photovoltaics thermal system can be composed of up to 53 modules with targeting the Jeju, since the maximum capacity of the coolant circulation pump of the photovoltaics thermal system applied in this study is 2,400 cc/min.

• Proceedings of the KIEE Conference
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• summer
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• pp.123-125
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• 2004

This paper describes an optimal configuration of Community Energy System (CES) for the multi-energy consumers and analyzes economical feasibility for such system. The most of previous feasibility studies for Co-Generation plants of CES in Korea have shown negative results due to the abnormally low price of power rate in Korea. However, in order to overcome this situation a new approach was examined in this Paper. The efforts of this approach the selection of the low price but reliable facility and maximizing the capacity factor of the facility. MGT was selected in view of low price and good reliability. In order to maximize the capacity factor the system capacity should be quite lower than the actual required Electrical and Heat load of the subject entity. In this report 100 kW Co-Generation facility was selected in view of conservative analysis. The results of the analysis showed that pay back period may vary from 4 to 5 yens according to the application of LNG rates whether it is to-generation rate or the normal business rate. With the analysis in this paper we confirmed that CES is feasible even in Korea if we do not insist to select the capacity of CES to cover all the energy required but select a smaller size of CES compared to the actual requirement, which can allow full load operation of the system continuously.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.11
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• pp.2297-2304
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• 2002

Two-dimensional and three-dimensional finite element methods have been used to analyze the deformation behavior of a shadow mask due to thermal and tension load. The shadow mask inside the Braun tube of a TV set has numerous slits through which the electron beams are guided to land on the designed phosphor of red, green or blue. Its thermal deformation therefore causes landing shift of the electron beam and results in decolorization of a screen. For the realistic finite element analysis, the effective thermal conductivity and the effective elastic modulus arc calculated, and then the shadow mask is modeled as shell without slits. Next a transient thermal analysis of the shadow mask is performed, wherein thermal radiation is a major heat transfer mechanism. Analysis of the resulting thermal deformation is followed, from which the landing shift of the electron beam is obtained. The present finite element scheme may be efficiently used to reduce thermal deformation of a shadow mask and in developing prototypes of a large screen flat TV.

• Journal of the Korean Society of Combustion
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• v.18 no.3
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• pp.44-53
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• 2013

In this study, the economic evaluation for imported coals was conducted for power plant based on thermo-dynamical performance analysis. The number of coal types considered was 1,755 imported by five power generation companies in Korea during the 2010-2012. The higher heating value (HHV) of the coals ranged 4,000-6,500 kcal/kg, mostly sub-bituminous. The 1D thermo-dynamical performance modeling was performed for a 500 MWe standard power plant using PROATES code. It was founded that the low rank coals had negative effects on the plant efficiency mainly due to the increased heat loss by moisture, hydrogen and flue gas. Based on the performance analysis, the economic performance of the coals was evaluated. The apparent price of low-rank coals tended to be significantly lower than design coal; for example, the unit price of coal with a HHV of 4,000 kcal/kg was 57% of the reference coal having 6,080 kcal/kg. Considering the negative effects leading to a decrease in the thermal performance, heating value compensation, and increased parasite load, the corrected unit cost for the coal with 4,000 kcal/kg was 90.7% of the reference coal. Overall, the cost saving by imported coals was not high as expected.