• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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• pp.759-765
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• 2000

A composite material consists of two or more different material layers. Copper clad aluminum composite materials are being used for economic and structural reasons. This study is concerned with experimental investigation in the direct extrusion of copper clad aluminum rods through conical dies. The suggestion are given for the proper extrudability of copper clad aluminum rods via hot direct extrusion. This paper presents the variation of flow state and hardness at a variable of extrusion ratio and semi-angle of die. By measuring after and before extrusion radius ratio of Cu sleeve and Al core, proportional flow state has been considered. And also by measuring hardness, through extrusion way, a variation of hardness has been considered.

• 한국안전학회지
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• 제21권1호
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• pp.114-119
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• 2006

In this study, laminated composite umbrella type roofs structures such as stadium, exhibition, auditorium and museum are analyzed. These structures have not been dealt with so far because of the difficulty in modeling. These have been analyzed mostly by a simplified method or a grid analysis in design. In this study, better results can be obtained by using shell element. The behavior of umbrella type shell roof under self weight is analyzed for various parameters such as the influence of diaphragm, diaphragm type, ${\gamma}-angle$ type, height/chord ratio of segment, slope of roofs, number of conical segment and subtended angle.

• 한국분말재료학회지
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• 제2권1호
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• pp.44-52
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• 1995

Effects of the extrusion temperature and die angle on the tensile properties of SiCIyAl composites in powder extrusion have been investigated. SiCP/Al composites were extruded at various extrusion temperatures (450, 500, $550^{\circ}C$) under the extrusion ratio of 25 : 1. The ram speed was maintained at 13 cm/min for all the extrusion conditions. The surface of the extruded rod appeared to be smooth without tearing at 450 and 50$0^{\circ}C$, whereas it was very rough due to tearing at $550^{\circ}C$. It was found that the tensile strength and elongation of the composites extruded at $500^{\circ}C$ are greater than those of composites extruded at $450^{\circ}C$ This is due to the easier plastic deformation of composite extruded at $500^{\circ}C$, compared with the composites extruded at $450^{\circ}C$. The effect of die angle was examined under 20=60, 120, $180^{\circ}$die angles at extrusion temperature of $500^{\circ}C$ under 25:1 extrusion ratio. The tensile strength of the composites extruded with 20=$60^{\circ}$approved to be higher than that of the composties extruded with 28 : 120 and $180^{\circ}$This is attributable to the higher extrusion pressure, which mixed composite powders could be densely consolidated at elevated temperatures, resulting from high friction force between billet and sliding surface of conical die.

• 한국의학물리학회지:의학물리
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• 제26권1호
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• pp.18-27
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• 2015

컴프턴 산란 현상을 이용하여 전자적 집속 방법으로 영상화하는 컴프턴카메라는 고민감도 및 고에너지 해상도의 장점을 이용하여 핵의학 응용분야에 대한 잠재력이 큰 영상 시스템이다. 본 논문에서는 컴프턴카메라를 이용한 다중 추적자 영상의 효용성 평가와 정확한 3차원 단면영상 촬영을 위한 Orlov 조건을 만족하는 회전하는 컴프턴카메라의 구조를 조사하였다. 140/511 keV의 방사선원의 소프트웨어 모형을 구성하고 이에 대한 몬테카를로 전산모사 시뮬레이션을 수행하여 리스트모드 배열된 부분집합 기댓값 최대화 방법으로 재구성된 다중 추적자 영상으로 컴프턴카메라의 효용성을 검증하였다. 산란부와 흡수부를 평행하게 위치시킨 고정된 컴프턴카메라와 촬영대상 주위 $360^{\circ}$를 회전하는 컴프턴카메라를 구성하여 검출된 투사선의 구좌표계 각도에 대한 히스토그램을 비교 평가하였다. 140/511 keV의 동시 계측된 몬테카를로 전산모사 데이터의 다중 추적자 영상이 2차원 및 3차원 재구성 시 잘 구분되는 것을 확인하였으며, 회전된 컴프턴카메라의 경우, 회전각도에 반비례하여 3차원 영상재구성에 필요한 유효 투사선이 증가하였다. 26분의 계산 시간 및 5백만개의 적절한 유효 투사선의 개수를 고려할 때 컴프턴카메라의 회전각은 $30^{\circ}$가 현실적으로 적절할 것이며 증가한 검출 시간은 다중 컴프턴카메라를 구성하여 해결할 수 있다. 본 논문에서 고찰한 고민감도 및 고에너지 해상도를 가진 컴프턴 카메라는 다중추적자 영상화를 위해 적합한 시스템이며 생화학 및 생리학적 상태 변화에 대한 임상 정보를 제공하며 각종 질병 진단 및 치료 방법 개발 등에 기여할 수 있는 잠재력이 있는 영상 시스템이다.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• 제34권4호
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• pp.445-449
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• 2008

Unerupted or erupted supernumerary tooth may cause crowding, diastema, cyst formation, resorption, and displacement or rotation of adjacent teeth. However, there are few studies about prognosis about the pathologic condition and expectation of spontaneous eruption. The object of this study is to evaluate factors predicting the spontaneous eruption of supernumerary tooth. 431 patients (346 males and 85 females, aged from 5 to 29 years) who visited our institution from 2002-2006 and were shown to have 471 mesiodentes was reviewed. Supernumerary teeth were classified inverted and not inverted state. In case of not inverted supernumerary tooth, eruption rate ac cording to length of supernumenary tooth, width of the tooth, angle between the tooth and incisor tooth, location (inside the incisor or not) and shape (conical or tubercle) were investigated. The regression model showed that length, width and angle were all important determinants of influencing the eruption of supernumerary tooth (p < 0.001, Pearson R: 0.619). There is no relation between shape and eruption of supernumerary tooth (p > 0.05). Location of mesiodens has an effect on eruption of supernumerary tooth (p < 0.01).

• Advances in aircraft and spacecraft science
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• 제6권3호
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• pp.225-238
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• 2019

A spike attached to a blunt nosed body significantly alters its flow field and influences the aerodynamic coefficients at hypersonic speed. The basic body is an axisymmetric, with a hemisphere nose followed by a cylindrical portion. Five different types of spikes, namely, conical aerospike, hemisphere aerospike, flat-face aerospike, hemisphere aerodisk and flat-face aerodisk are attached to the basic body in order to assess the aerodynamic characteristic. The spiked blunt body without the aerospike or aerodisk has been set to be a basic model. The coefficients of drag, lift and pitching moment were measured with and without blunt spike body for the length-to-diameter ratio (L/D) of 0.5, 1.0, 1.5 and 2.0, at Mach 6 and angle of attack up to 8 degrees using a strain gauge balance. The measured forces and moment data are employed to determine the relative performance of the aerodynamic with respect to the basic model. A maximum of 77 percent drag reduction was achieved with hemisphere aerospike of L/D = 2.0. The comparison of aerodynamic coefficients between the basic model and the spiked blunt body reveals that the aerodynamic drag and pitching moment coefficients decrease with increasing the L/D ratio and angle of attack but the lift coefficient has increasing characteristics.

• Journal of the Optical Society of Korea
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• 제19권4호
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• pp.327-333
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• 2015

This paper reports the fabrication of various micro-lensed single-mode optical fibers through the use of an enhanced peak power $CO_2$ laser beam. The end faces of the optical fibers are exposed to the $CO_2$ laser beam to form convex, concave, and conical shape optical fiber tips. Peak power of the $CO_2$ laser beam was varied from 0.8 W to 1.5 W depending on the shape of the optical fiber tip. We also discover the dependence of the angle of the optical fiber tip on the rotation angle and the number of $CO_2$ laser irradiations. The angle shows an increasing trend with both these parameters. We achieve a wide range of lenticular fibers with end face angle varying from $4.47^{\circ}$ to $8.13^{\circ}$. Furthermore, we investigate the emission pattern of light from the developed micro-lensed fibers. The proposed $CO_2$ laser based optical fiber reshaping technique shows great consistency, and thus is suitable for commercial applications.

• 한국추진공학회지
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• 제22권2호
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• pp.115-124
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• 2018

본 연구에서는 초고속 비행체 고공환경 모사실험 설비에 대한 설계와 상온실험을 진행하였다. 시험 모델의 폐색율, 각도, 길이에 따른 변수실험을 진행하고, 변수에 따른 벽면압력변화를 확인하였다. 폐색율은 40%의 영역에서도 운용이 가능하며, 각도는 45도 이하의 크기에서 모델을 선정해야함을 확인하였다. 길이의 변수는 폐색율과 각도의 변수에 비하여 영향이 크지 않은 것을 확인하였다. 이를 통해서 초고속 비행체 시험설비에서 원뿔형 모델의 설계 변수에 따른 성능 데이터베이스를 확보하였다.

• 한국추진공학회지
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• 제3권1호
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• pp.1-8
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• 1999

풍전압력비와 2차 제트 분사구 위치에 따른 2차분사 추력방향 제어(SITVC: secondary injection thrust vector control) 성능특성 변화를 수치해석하였다. 2차 제트 분사에 의해 간섭된 수축-팽창노즐 내부의 초음속유동장을 대상으로 3차원 비정상 오일러 방정식을 내재적으로 근사인자분해된 Beam과 Warming의 방법을 사용하여 차분하였으며, 2차 분사 제트에 의한 추력비 비추력비 및 전향각에 대한 성능변화를 고찰하였다. 연구결과 측추력과 비추력비는 2차 분사 질량유량에 비래하여 증가하는 반면, 비추력 성능은 감소되어 2차 분사 질량유량이 적을 수록 추력 성능손실이 적어지는 것으로 나타났다. 또한 동일한 전압력비에 대하여 2차 제트 분사위치가 노즐의 하류에 위치할수록 고속기 주유동과의 간섭에 의한 강한 충격파로 인하여 측추력과 측비추력의 증가와 함께 추력방향 제어성능이 향상됨을 알 수 있었다.

• Steel and Composite Structures
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• 제26권6호
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• pp.771-791
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• 2018

This paper deals with the low velocity impact response and dynamic stresses of composite sandwich truncated conical shells (STCS) with compressible or incompressible core. Impacts are assumed to occur normally over the top face-sheet and the interaction between the impactor and the structure is simulated using a new equivalent three-degree-of-freedom (TDOF) spring-mass-damper (SMD) model. The displacement fields of core and face sheets are considered by higher order and first order shear deformation theory (FSDT), respectively. Considering continuity boundary conditions between the layers, the motion equations are derived based on Hamilton's principal incorporating the curvature, in-plane stress of the core and the structural damping effects based on Kelvin-Voigt model. In order to obtain the contact force, the displacement histories and the dynamic stresses, the differential quadrature method (DQM) is used. The effects of different parameters such as number of the layers of the face sheets, boundary conditions, semi vertex angle of the cone, impact velocity of impactor, trapezoidal shape and in-plane stresses of the core are examined on the low velocity impact response of STCS. Comparison of the present results with those reported by other researchers, confirms the accuracy of the present method. Numerical results show that increasing the impact velocity of the impactor yields to increases in the maximum contact force and deflection, while the contact duration is decreased. In addition, the normal stresses induced in top layer are higher than bottom layer since the top layer is subjected to impact load. Furthermore, with considering structural damping, the contact force and dynamic deflection decrees.