• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.176.1-176.1
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• 2011

세계적으로 석유 기반 자원의 고갈에 따른 부족, 기후변화협약 및 환경규제 강화에 의해 세계적으로 바이오소재를 이용하고자 하는 연구와 더불어 유리강화복합재료의 대체물질로 적합한 천연섬유를 보강재로 사용하는 바이오복합재료의 연구 또한 활발하게 진행되고 있다. 최근 새로운 신재생에너지원으로 각광 받고 있는 바이오에너지 중 해조류는 가장 자연친화적이고 생산력이 뛰어난 바이오매스로 알려져 있다. 해조류는 바닷물 속에 녹아 있는 탄소를 흡수할 뿐만 아니라 광합성을 통해서도 탄소를 흡수하면서 성장하기 때문에 탄소흡수원의 역할을 하게 되며, 해조류 바이오에너지를 생산할 경우 화석연료를 대체하여 지구온난화의 주범인 온실가스를 감축하는 기능을 한다. 본 연구에서는 해조류를 이용한 바이오에너지 생산 공정에서 2차적으로 발생하는 부산물을 보강재로 사용한 바이오복합재료의 제조와 제조된 바이오복합재료의 열적 특성 및 동역학적 특성을 분석하였다. 해조류 부산물의 화학적 전처리에 따른 Thermogravimetric analysis(TGA) 분석 결과로 cellulose 함량이 가장 높고 불순물이 적은 황산 처리한 파래를 이용해 파래/Polypropylene(PP) 바이오복합재료를 다양한 보강비율 (20-50wt%)로 압축성형 하였다. 파래/PP 바이오복합재료의 저장탄성률은 파래 함량이 40wt%일 때 4.0 Gpa으로 최대값을 보였으며 이는 PP 매트릭스와 비교했을 때 약 8.1% 향상된 결과이다. 파래/PP 바이오보합재료의 열팽창 특성은 파래 함량이 증가함에 따라 열팽창계수가 낮아지는 경향으로 50wt%일 때 가장 낮은 값을 나타내었으며 이는 PP 매트릭스와 비교했을 때 약 56% 향상된 결과이다. 따라서 비생분해성 고분자에 새로운 신재생 바이오매스인 해조류를 보강재로 사용하여 열적 특성 및 동역학적 특성이 향상된 친환경적인 바이오복합재료의 제조 가능성을 확인하였다.

• Journal of the Korean Society for Railway
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• v.16 no.6
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• pp.454-459
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• 2013

Pressure waves are generated and propagate in a tunnel when train enters tunnel high speed. A compression wave due to the entry of train head propagates along the tunnel and is reflected at tunnel exit as an expansion wave. An expansion wave due to the entry of the train tail propagates along the tunnel and is reflected at tunnel exit as a compression wave. These pressure waves are repeatedly propagated and reflected at the tunnel entrance and exit. Severe pressure changes causes ear-discomfort for passengers in the cabin and micro pressure waves around the tunnel exit. It is necessary to analyze the transient pressure phenomena in tunnels qualitatively and quantitatively, because pressure change rate is considered as one of the major design parameters for optimal tunnel cross sectional area and repeated fatigue force on car body. In this study, we developed a characteristics method based on a fixed mesh system and boundary conditions for crossing trains and analyzed this system using an X-t diagram. The results of the simulation show that offsetting of pressure waves occurs for special entry conditions of a crossing train.

• Journal of the Korean Society for Railway
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• v.15 no.5
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• pp.436-441
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• 2012

Pressure waves are generated and propagate in tunnel when train enters a tunnel with high speed. Compression wave due to the entry of train head propagates along the tunnel and is reflected at tunnel exit as expansion wave. While expansion wave due to the entry of train tail propagates along the tunnel and is reflected at tunnel exit as compression wave. These pressure waves are repeatedly propagated and reflected at tunnel entrance and exit. Severe pressure change per second causes ear-discomfort for passengers in cabin and micro pressure wave around tunnel exit. It is necessary to analyze the transient pressure phenomena in tunnel qualitatively and quantitatively, because pressure change rate is considered as one of major design parameters for an optimal tunnel cross sectional area and the repeated fatigue force on car body. In this study, we developed the characteristics method analysis based on fixed mesh system and compared with the results of real train test. The results of simulation agreed with that of experiment.

• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.5
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• pp.54-61
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• 2014

In this study, a plume exhausted from rocket nozzle is investigated by using an unstructured 2-dimensional axisymmetirc DSMC code at various altitude. The small back-pressure to total-pressure ratio($P_b/P_o$) and large $P_b/P_o$ represent low and high altitude condition, respectively. At low altitude, the plume shows a typical complicated structure (e.g. Mach disk) of underexpanded jet while the high altitude plume experiences plain expansion. The various features of exhaust plume is discussed including density, translational/rotational temperature, Mach number and Knudsen number. The results shows that even at 20 km altitude where the freestream Knudsen number is small as $1.5{\times}10^{-5}$, the transitional and rarefied flow regimes can occur locally within the plume. It confirms the necessity of DSMC computation at low altitude.

• Composites Research
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• v.35 no.6
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• pp.365-370
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• 2022

According to the rapid growth of electric vehicle (EVs) and E-mobility market, Li-ion batteries are one of the most progressive technologies. The demand of LIBs with high energy capacity, rate performance and fast charging is continuously increasing, hence high-performance LIBs should be developed. Si is considered as the most promising anode material to improve energy density because of its high theoretical capacity. However, Si suffers large volume chances during the charging and discharge process, leading to the fast degradation of cycle performance. Therefore, polymeric binders play a key role in electrochemical performance of Si anode by efficiently enduring the Si expansion and maintaining the binding networks in electrode. In this review, we explain the role of polymeric binders in electrode and introduce the anode binders with enhanced mechanical and chemical properties which can improve electrochemical performances of Si-based anode.

• Korean Journal of Optics and Photonics
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• v.32 no.6
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• pp.266-275
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• 2021

In this paper, a method for evaluating optical-system performance and an athermal structure through thermal analysis of the Korsch telescope was studied. In the case of an optical system having a complex asymmetrical structure, there is a limit to implementing the satellite structure by applying the coefficient of thermal expansion (CTE) in the optical-design software, so it is difficult to evaluate the performance of the optical system against temperature changes. To solve this problem, using mechanical design software all length changes were implemented in all structures that affect the optical system according to temperature, and the value of the change in distance between optical components due to temperature change was organized. Also, the values of changes in shape and thickness of the optical components against temperature changes are organized in the optical-design software. All changes derived from both software packages were applied in the optical software to evaluate the performance of the optical system. As a result, it was found that the MTF for a spatial resolution of 71.4 cycles/mm was maintained at more than 25% in the range from 9 ℃ to 33 ℃. In addition, the performance of the optical system applying the improved structure was evaluated, by finding the structure that had the most influence on the optical system's performance change, and deriving an athermal structure to reduce the effect. As a result, it was found that the MTF for a resolution of 71.4 cycles/mm was maintained at over 67% in the range from 9 ℃ to 33 ℃.

• Journal of the Microelectronics and Packaging Society
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• v.17 no.4
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• pp.49-60
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• 2010

Semiconductor packages are increasingly moving toward miniaturization, lighter and high performance. Futhermore, packages become thinner. Thin packages will generate serious reliability problems such as warpage, crack and other failures. Reliability problems are mainly caused by the CTE mismatch of various package materials. Therefore, proper selection of the package materials and geometrical optimization is very important for controlling the warpage and the stress of the package. In this study, we investigated the characteristics of the warpage and the stress of several packages currently used in mobile devices such as CABGA, fcSCP, SCSP, and MCP. Warpage and stress distribution are analyzed by the finite element simulation. Key material properties which affect the warpage of package are investigated such as the elastic moduli, CTEs of EMC molding and the substrate. Geometrical effects are also investigated including the thickness or size of EMC molding, silicon die and substrate. The simulation results indicate that the most influential factors on warpage are EMC molding thickness, CTE of EMC, elastic modulus of the substrate. Simulation results show that warpage is the largest for SCSP. In order to reduce the warpage, DOE optimization is performed, and the optimization results show that warpage of SCSP becomes $10{\mu}m$.

• Journal of the Korean Electrochemical Society
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• v.18 no.2
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• pp.68-74
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• 2015

To compare the microstructure and electrochemical properties between two binary alloys (Cr-Si, Ni-Si), two composition of binary alloys with the same capacity were selected using phase-diagram and prepared by matrix-stabilization method to suppress the volume expansion of Si by inactive-matrix. Master alloys were made by Arc-melting followed by fine structured ribbon sample preparation by Rapid Solidification Process (RSP, Melt-spinning method) under the same conditions. Also powder samples were produced by wet grinding for X-Ray Diffraction (XRD) and electrochemical measurements. As predicted from the phase diagram, only active-Si and inactive-matrix ($CrSi_2$, $NiSi_2$) were detected. The results of Scanning Electron Microscope (SEM) and Transmission Electron Microscopy - Energy Dispersive X-ray Spectroscopy (TEM-EDS) show that Cr-Si alloy has finer microstructure than Ni-Si alloy, which was also predictable through phase diagram. The electrochemical properties related to microstructure were evaluated by coin type full- and half-cells. Separately, self-designed test-cells were used to measure the volume expansion of Si during reaction. Volume expansion of Cr-Si alloy electrode with finer microstructure was suppressed significantly and improved in cycle capability, in comparison Ni-Si alloy with coarse microstructure. From these, we could infer the correlation of microstructure, volume expansion and electrochemical degradation and these properties might be predicted by phase diagram.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.6
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• pp.3442-3447
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• 2014

A simple method to evaluate the hygroscopic characteristics of polymer of microelectronic plastic package is suggested. To evaluate the characteristics, specimens were prepared, and the internally absorbed moisture masses were measured as a function of the absorbing time and calculated numerically. The hygroscopic pressure ratio was calculated by heat transfer analysis supported by commercial FEM code because the hygroscopic diffusion equation has the same form as the heat transfer equation. The moisture masses were then summed by the self developed code. The nonconductive polymers had quite different characteristics for the different lots, even though they were the same products. The absorbed moisture mass variations were calculated for several different characteristics, and the optimal curve of the mass variation close to experimental data was selected, whose solubility and diffusivity were affected by the hygroscopic characteristics of the material. The method can be useful in the industrial fields to quickly characterize the polymer material of the semiconductor package because the fast correspondence is normally required in industry. The weight changes in the aluminum-nonconductive-polymer joint due to moisture absorption were measured. The deformed system was also measured using the Moire Interferometry system and compared with the results of finite element analysis.

• Journal of Energy Engineering
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• v.23 no.3
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• pp.116-124
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• 2014

In the plants operated under high temperature condition, piping system load analysis is often performed to prevent accidents caused by thermal deformation and also to locate inspection prioritity points of the piping system. In this study, piping system stress analysis was performed for a pipe system between the reactors in a process plant. The piping system includes typically installed hangers and expansion joints. In order to evaluate the effects of structural components such as hangers and expansion joints, the case for the expansion joint or the hanger under abnormal operation is considered. By comparison anlaysis results of piping system during normal operation and abnormal operation, the role of each pipe components are studied.