• KIEAE Journal
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• v.12 no.3
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• pp.27-32
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• 2012

In recent years, the quality of the outdoor thermal environment has come to be regarded as important as that of the indoor thermal environment. Since the outdoor thermal environment is composed of many elements and is affected by many factors, it is not easy to evaluate the impact of each factor separately. Hence, a comprehensive assessment method is required. In order to evaluate the pedestrian level comfort of an outdoor climate, it is necessary to investigate not only wind velocity but also various physical elements, such as temperature, moisture, radiation, etc. Prediction of wind and thermal environment for a large scale buildings is one of the most important targets for research. Wind and thermal change in a city area is a very complicated phenomenon affected by many physical processes. The purpose of this study is to develop a design plan for wind environment at a large Buildings. In this study, we analyze outdoor wind environment and thermal environment on buildings using the CFD (Computational Fluid Dynamics) method. The arrangement of building models is an apartment in Jeonju. These prediction of wind and thermal environment for a large scale buildings is necessary in a plan before a building is built.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.33 no.4
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• pp.321-325
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• 2020

Atmospheric environmental problems have a major impact on human health and lifestyle. In humans, inhalation of nitrogen oxides causes respiratory diseases, such as bronchitis. In this paper, thermal analysis of a gas sensor was carried out to design and fabricate a wearable nylon-yarn gas sensor for the detection of NO_x gas. In the thermal analysis method, the thermal diffusion process was analyzed while operating the sensors at 40 and 60℃ to secure a temperature range that does not cause thermal runaway due to temperature in the operating environment. Thermal diffusion analysis was performed using the COMSOL software. The thermal analysis results could be useful for analyzing gas adsorption and desorption, as well as the design of gas sensors. The thermal energy diffusion rate increased slightly from 10.05 to 10.1 K/mm as the sensor temperature increased from 40 to 60℃. It was concluded that the sensor could be operated in this temperature range without thermal breakdown.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1627-1632
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• 2003

The effect of (1) phonon dispersion in thermal conductivity model and (2) the differentiation of group velocity and phase velocity for Ge is examined. The results show drastic change of thermal conductivity regardless of using same relaxation time model. Also the contribution of transverse acoustic (TA) phonon and longitudinal acoustic (LA) phonon is changed by considering more rigorous dispersion model. Holland model underestimates the scattering rate for high frequency TA, so misleading conclusion, i.e. TA is dominant heat transfer mode at high temperature. But the actual reduction of thermal conductivity is much larger than the estimation by Holland model and high frequency TA is no more dominant heat transfer mode. Another heat transfer mechanism may exist for high temperature. Two possible explanations are (1) high frequency LA by Umklapp scattering and (2) optical phonon.

• Structural Engineering and Mechanics
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• v.57 no.2
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• pp.369-387
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• 2016

In this work, random homogenization analysis for the effective thermal properties of a three-dimensional composite material with unidirectional fibers is presented by combining the equivalent inclusion method with Random Factor Method (RFM). The randomness of the micro-structural morphology and constituent material properties as well as the correlation among these random parameters are completely accounted for, and stochastic effective thermal properties as thermal expansion coefficients as well as their correlation are then sought. Results from the RFM and the Monte-Carlo Method (MCM) are compared. The impact of randomness and correlation of the micro-structural parameters on the random homogenized results is revealed by two methods simultaneously, and some important conclusions are obtained.

• Proceedings of the KIPE Conference
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• 2017.07a
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• pp.290-291
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• 2017

This study deals with an evaluation method for testing the robustness of the 4 kW commercial power electronic cooling system to the thermal environment. The power electronic cooling system consists of a cascaded push-pull DC / DC converter, a three-phase DC / AC inverter, and an electric compressor. The system manufactured by the thermal environment evaluation test (heat distribution test, thermal impact test, high temperature operation test, temperature cycle test, low temperature operation test) for the commercial electric power cooling system for commercial vehicle proves that it is robust against thermal environment.

• Korean Journal of Materials Research
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• v.33 no.12
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• pp.503-510
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• 2023

This comprehensive study delves into the intricate process of exfoliating and functionalizing boron nitride nanosheets (BNNSs) extracted from hexagonal boron nitride (h-BN), and meticulously explores their potential application within epoxy composites. The extensive research methodology encompasses a sequence of treatments involving hydrothermal and sonication processes aimed at augmenting the dispersion of BNNSs in solvents. Leveraging advanced analytical techniques such as Raman spectroscopy, X-ray diffraction, and FTIR spectroscopy, the study rigorously analyzes a spectrum of changes in the BNNS's properties, including layer count variations, interlayer interactions, crystal structure modifications, and the introduction of functional groups. The research also rigorously evaluates the impact of integrating BNNSs, specifically glycidyl methacrylate (GMA)-functionalized BNNSs, on the thermal conductivity of epoxy composites. The conclusive findings exhibit notable enhancements in thermal properties, predominantly attributed to the enhanced dispersion of fillers and enhanced interactions within the epoxy matrix. This pioneering work illuminates the wide potential of functionalized BNNSs for significantly enhancing the thermal conductivity of epoxy composites, paving the way for advanced materials engineering and practical applications.

• Journal of the Korea institute for structural maintenance and inspection
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• v.5 no.1
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• pp.176-187
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• 2001

Most bridges have expansion joints to accommodate thermal expansion and contraction without inducing large forces in the bridges. To evaluate the effects of earthquake-induced at expansion joints of concrete bridges, the first part of this paper deals with a collinear impact between concrete segments, which have the same cross section but different lengths. Especially, impact force, momentum, strain energy and kinetic energy are formulated in mathematically. These results are then used in the second part of this paper to simulate a realistic yet simple analysis of seismic pounding in concrete bridges. Analysis of seismic pounding in idealized concrete bridges is carried out by using a simple lumped-mass model and rationally determined values of the coefficient of restitution and the duration of impact.

• Journal of Power System Engineering
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• v.9 no.4
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• pp.137-142
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• 2005

The effects of temperature and initial crack length on impact fracture behavior of side plate material of 35 ton class FRP ship, which are composed by glass fiber and unsaturated polyester resin, were investigated. Impact fracture toughness of GF/PE composites displayed maximum value when the temperature of specimen is room temperature and $50^{\circ}C$, and with decrease in temperature of specimen, impact fracture toughness decreased. Impact fracture energy of GF/EP composites decreased with increase in initial crack length of specimen, and this value decreased rapidly when the temperature of specimen is lowest, $-25^{\circ}C$,. It is believed that sensitivity of notch on impact fracture energy were increased with decrease in temperature of specimen. As the GF/EP composites exposed in low temperature, impact fracture toughness of composites decreased gradually owing to the decrease of interface bonding strength caused by difference of thermal expansion coefficient between the glass fiber/polyester resin. Further, decrease of interface bonding strength of composites with decrease in specimen temperature was ascertained by SEM photograph of impact fracture surface.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.05a
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• pp.31-35
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• 2006

Degradation characteristics of filament-winded composites due to accelerated environmental aging have been evaluated under high temperature, water immersion and thermal impact conditions. Two kinds of laminated composites coated by an urethane resin have been used: carbon-fiber reinforced epoxy(T700/Epon-826, CFRP) and glass-fiber reinforced phenolic (E-glass/phenolic, GFRP). For tensile strength of $0^{\circ}$ composites, CFRP did high reduction by 25% under the influence of high temperature and water while CFRP showed little degradation. However for water-immersed $90^{\circ}$ composites both CFRP and GFRP showed high reduction in tensile strength. Bending strength and modulus of $90^{\circ}$ composites were largely reduced in water-immersion as well as high temperature environment. Urethane coating on the composite surface improved the bending properties by 20%, however hardly showed such improvement for water-immersed $90^{\circ}$ composites.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.295-298
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• 1997

Recycl ing of PP/EPR based bumper coated with polyester urethane paint has been per formed by chemical decoating method. Electronic Speckle Pattern Interferometry (ESP11 has been applied to characterize the deformation of polyolef in based bumper. In additon, physical properties and processability of recycled materials have been investigated by dynamic mechanical thermal analysis, impact test and melt flower index measurement. The results show that the deformation ratio of recycled material is higher than that of virgin one. The morphological change of EPR, degree of distribution and dispersion during the recycling process seem to be the most important factor for the deformation and the mechanical properties of recycled materials. The experimental results obtained show that ESPI is very powerful technique to study the thermal mechanical property of polyolefin bumper system.