• Proceedings of the KWS Conference
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• 2010.05a
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• pp.97-97
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• 2010

최근 자동차에서 경량화의 방안으로써 높은 강성을 요구하는 고장력강 사용이 증대 되고 있다. 그러나 고장력강은 저항 점용접 시 일반 강에 비해 높은 전류를 요구하며 계면파단 및 expulsion 발생이 용이하기 때문에 가용 전류 구간이 좁은 특성을 가진다. 많은 연구자들이 hold time, tempering 등의 process를 이용하여 고장력강의 저항 점용접성을 개선하고자 하였으나 생산 공정라인에 적용하기는 어려운 실정이다. 본 연구에서는 용접 공정 변수의 변화에 따른 용접성과 전극 형상 변화을 통한 고장력강 점 용접성 향상에 대한 연구를 실시 하였다. 고장력강의 점 용접성 비교하기 위해 표준 전극(S1)과 인위적으로 가공한 전극(M1)을 사용하였으며, 실험에 사용된 판재는 두께 1.4mm의 DP590이며, 그 결과 표준전극(S1) 보다 가공 전극(M1)의 가용 전류 구간이 0.5kA 정도 넓은 것으로 확인 되었다. 두 전극을 사용한 점용접 시험편들의 인장전단강도를 비교 해보면 표준전극(S1)을 적용한 점용접 시 인장전단강도는 KS B 0850 기준에 만족하나 계면 파단이 발생 하였다. 가공 전극(M1)을 적용한 점용접 시 인장전단강도는 규격 기준에 만족하나 버튼 파단이 발생 하였다. 두 전극을 적용한 점용접부 형상 및 용접부 온도 분포에대해 저항점용접 시뮬레이션 프로그램(SORPAS)을 이용하여 실험 결과 값과 비교 분석하였고 파단모드의 변화에 대한 원인 분석을 도출 하였다.

• Journal of the Korean earth science society
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• v.30 no.3
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• pp.381-397
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• 2009

The Modem Geodesy monitors physical and geometrical shape and motion of the Earth and, more importantly, its temporal variations with unprecedented precision. It provides accurate and stable reference frames for Earth observations in the Space era. Furthermore, with an aid of interdisciplinary approaches, it also traces the causes of the variations in shape and motion of the Earth and eventually contributes to a better understanding of the Earth system. The International Association of Geodesy (IAG) has established the Global Geodetic Observing System (GGOS) to integrate the multitude of geodetic tools and tried to contribute to the management of global environmental changes as a partner of the Global Earth Observation System of Systems (GEOSS). Here we introduce the contribution of geodesy to the various fields of Earth Science by focusing on GGOS and encourage interdisciplinary researches.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.5
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• pp.849-863
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• 1992

A very simple and computationally efficient numerical method is developed for the free vibration of isotropic and orthotropic composite triangular plates. A set of two-dimensional simple series functions is used as an admissible displacement functions in the Rayleigh-Ritz method to obtain the natural frequencies, nodal patterns and mode shapes for the plates. From the prescribed starting function satisfying only the geometric boundary conditions, the higher terms in the series functions are constructed with adding order of polynominal. Natural frequencies, nodal patterns and mode shapes are obtained for right triangular plates with three different support conditions. The obtained numerical results are presented, and the isotropic and some orthotropic cases are verified with other numerical methods in the liternature.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.7
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• pp.669-674
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• 2013

A three-dimensional hydrogel scaffold has been proposed for the effective production of biomimetic intestinal villi to reduce ethical and cost problems caused by animal testing in pharmaceutical development. This study explores an experimental approach to develop a new technique based on laser machining and microdrilling processes to produce a plastic mold for the fabrication of a three-dimensional hydrogel scaffold. For process optimization, both the laser machining and the microdrilling experiments are conducted by varying the experimental conditions, and structural characterization of the mold and intestinal villi were performed using SEM (scanning electron microscope) and OM (optical microscope) images. Polycarbonate (PC) was used as a candidate material. The experimental results show that intestinal villi can be fabricated by both laser and microdrilling machining processes.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.9
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• pp.823-828
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• 2013

To reduce the cost per watt of photovoltaic power, it is important to reduce the cell thickness of crystalline silicon solar cells. As the thickness of the silicon layer is reduced, two distinctive thermal expansion rates between the silicon and the aluminum layer induce bowing in a solar cell. With a thinner silicon layer, the bowing distance grows exponentially. Excessive bowing could damage the silicon wafer. In this study, we tried to measure an irregularly curved silicon solar cell more accurately using a 3D image scanner. For the detailed analysis of the three-dimensional bowing shape, a least square fit was applied to the point data from the scanned image. It has been found that the bowing distance and shape distortion increase with a decrease in the thickness of the silicon layer. An Ag strip on top of the silicon layer can reduce the bowing distance.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.4
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• pp.237-243
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• 2016

It is necessary to investigate the input power as well as the mass transfer characteristics of the aeration process in order to improve the energy efficiency of an aerobic water treatment. The objective of this study is to experimentally investigate the effect of orifice nozzle design and input power on the flow and mass transfer characteristics of a vertical two-phase flow. The mass ratio, input power, volumetric mass transfer coefficient, and mass transfer efficiency were calculated using the measured data. It was found that as the input power increases the volumetric mass transfer coefficient increases, while the mass ratio and mass transfer efficiency decrease. The mass ratio, volumetric mass transfer coefficient, and mass transfer efficiency were higher for the orifice configuration with a smaller orifice nozzle area ratio. An empirical correlation was proposed to estimate the effect of mass ratio, input power, and Froude number on the volumetric mass transfer coefficient.

• Journal of the Korean association of regional geographers
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• v.6 no.3
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• pp.83-99
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• 2000

This paper purposes to provide a new perspective for better development of geography texts. For this purpose, we have applied spatial cognition development theory to children's drawings. We have suggested that children's spatial operation ability has three development stages according to their age: topological space, projective space, euclidean space. This study turns out that Piaget and Inhelder's spatial concept development theory is on the right track. However, we make clear that their division according to the age is not always accurate due to children's individual differences. These findings have educational implications as the following: First, it is dubious that most children can understand pictures, pictorial maps and illustrations in the third grader's textbook. Second, current textbooks require pictorial map understanding and drawing to third grade students and map drawing to fourth grade students. However, according to this study, the placement of these tasks are not fit for children's developmental stage because both tasks correspond to euclidean space operation. Therefore, we should remove them from the textbook for children at the age.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.7
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• pp.1-10
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• 2002

Multidisciplinary Design Optimization (MDO) is a new design approach, which aims to reduce the design cycle and the development cost, while improving the performance of the product. In order to develop a framework software where the multidisciplinary design is possible, several methods about the analysis codes integration, the analysis and optimization process management, and the software architecture, are proposed in this study. Centralized DataBase Management System (DBMS) is adopted. Both the Dynamic Link Library(DLL) and the File Interface are suggested and implemented as analysis codes integration methods. To efficiently manage the optimization process and the data flow, the Graphic Programming approach is introduced. The proposed integration methods are verified by two test case examples: Simple house design example and the aircraft wing design problem using three dimensional Panel Code.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.178-178
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• 2011

군사용 장비의 전원장치, 인공위성, 해양개발용 등의 특정분야에 한정되어 이루어지던 열전물질에 대한 연구가 최근에는 에너지원의 다양화와 에너지 절약에 대한 필요성이 크게 대두됨에 따라 산업 폐열과 각종 열기관의 폐열 및 해수 온도차나 태양열과 같은 자연에너지를 이용하는 열전발전에 대한 연구로 영역이 확장되어 꾸준히 이루어지고 있다. 다양한 열전 재료 중에서 BixTey 계, BixSey 계, SbxTey 계, 혹은 이들의 합금계가 많이 연구되고 있다. 이 중에서 BixTey 계의 박막 성장 방법으로는 sputtering deposition, electrodeposition, flash evaporation, molecular beam epitaxy, chemical vapor deposition (화학적기상증착) 등이 있다. 이러한 다양한 방법들 중에서 화학적기상증착법은 양질의 두꺼운 막을 성장시킬 수 있음과 동시에 산업적인 생산에 적용될 수 있기 때문에 열전박막 증착을 위한 중요한 수단이 될 수 있을 것으로 생각되고 있다. 하지만 적절한 전구체(precursor)의 부족, tellurium (Te)의 재증발과 같은 문제점 때문에 화학적기상증착법을 이용한 BixTey 계 박막에 대한 전반적인 연구가 부족한 실정이다. 본 연구에서는 다양한 기판, 예를 들면, 실리콘(Si), 실리콘 산화물(SiO2), 백금(Pt) 등, 에 화학적기상증착법을 이용하여 BixTey 계 박막을 성장시키고, 온도와 압력 등의 조건 변화에 따른 박막의 형상과조성, 구조적 특성에 관한 연구를 진행하였다. 특히, 성장 조건에 따른 박막의 형상 연구를 통하여 성장 기구에 관한 고찰을 진행할 수 있었다. 나아가 투과전자현미경 연구를 통하여 기판과 박막의 계면 특성과 개별 결정립이 가지는 미세구조적 특성에 관한 연구를 진행하였다.

• Elastomers and Composites
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• v.35 no.2
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• pp.138-148
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• 2000

In order to investigate the possibility of EPDM micro cellular pad (MCP) as an impact sound insulation product, we studied static/dynamic properties and vibration transfer characteristics of EPDM MCP depending on shape, thickness, degrees of foaming by using material test system (MTS) and lab scale mock-up test apparatus. Static/dynamic rigidity is increased when shape is simple. thickness and degrees of foaming low. We could see that dynamic stiffness is proportional to the transmissibility of EPDM MCP. When dynamic stiffness is increased, characteristic peak at transmissibility curve moves high frequency range or snows increase of maximum value of transmissibility. For lab scale mock-up test and finite element method, EPDM MCP shows low vibration velocity and superior mode shape to just concrete plus slab structure. We could confirm that possibility of EPDM MCP as a impact sound insulation product is high.