• 한국국방경영분석학회지
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• 제3권1호
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• pp.83-96
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• 1977

The combustion chamber and nozzle of an end burning, small spherical rocket is designed. A spherical external shape has a number of advantages such as fixed center-of-gravity and minimum aerodynamic precession torques during flight and a better mass distribution for gyro-stabilization as contrasted to a conventional ogive rocket shape. It is shown that the cross-sectional variation of the end burning solid propellant with length is an exponential geometry to provide a constant thrust-weight ratio of the rocket device during the propellant burning period, and that the factors which affect the attainment of the constant relationship of thrust to weight in the design are the initial propellant area, initial weight of the rocket and propellant density. The measurement of the transient thrust in the ground static test using black powder propellant supports the predicted results. A wind tunnel having a $30{\times}30{\times}75cm$ test section and Mach number 0.11 is constructed, and a simple balance-type device is designed for the measurement of the drag of a spinning sphere. The experimental results indicate that the. spinning has no effect on the magnitude of the drag up to the Reynolds number $3{\times}10^5$. Numerical computation of the flight trajectories for various launching angles is presented, and the gyro-stabilization of spinning sphere is discussed.

• 소성∙가공
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• 제26권3호
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• pp.156-161
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• 2017

In this study, the reason of die fracture occurring in hot forging of an aluminum fixed scroll was studied, based on experiments and finite element predictions. The material is assumed to be rigid-viscoplastic, and the die is rigid for the finite element predictions. The stress in the tension at the wrap root is known to cause brittle fracture, and the increase in the tensile stress is owing to the unbalanced filling of material into the die cavities between both sides of the warp. Based on the empirical and numerical achievements, the effects of geometrical parameters of the material on the die fracture were examined to find practical measures for elongated die life. It has been shown from the parametric study that the material with the optimized trapezoidal cross-section, which can be easily made during cutting or the optimized cylindrical billet with its eccentric placement in the die cavity, can considerably reduce the magnitude of the tensile stress around the die corner fractured, indicating that economical manufacturing with reduced number of stages and elongated die life can be realized at once using the optimized practical initial material.

• Structural Engineering and Mechanics
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• 제84권4호
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• pp.547-560
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• 2022

By presetting various reinforcement diameters in topology optimization with the discrete model finite element analysis, an algorithm of bidirectional evolutionary structural optimization of multi-level reinforcement diameter is presented to obtain the optimal reinforcement topologies which describe the degree of stress of different parts. The results of a comparative study on different reinforcement feasible domain demonstrate that the more angle types of reinforcement are arranged in the initial domain, the higher utilization rate of reinforcement of the optimal topology becomes. According to the nonlinear finite element analysis of some deep beam examples, the ones designed with the optimization results have a certain advantage in ultimate bearing capacity, although their failure modes are greatly affected by the reinforcement feasible domain. Furthermore, the bearing capacity can be improved when constructional reinforcements are added in the subsequent design. However the adding would change the relative magnitude of the bearing capacity between the normal and inclined section, or the relative magnitude between the flexural and shear capacity within the inclined section, which affects the failure modes of components. Meanwhile, the adding would reduce the deformation capacity of the components as well. It is suggested that the inclined reinforcement and the constructional reinforcement should be added properly to ensure a desired ductile failure mode for components.

• Structural Engineering and Mechanics
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• 제47권4호
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• pp.575-598
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• 2013

The study presents the results of an experimental program concerning the shear force transfer between reinforced concrete (RC) jackets and existing columns with damages. In order to investigate the effectiveness of the repair method applied and the contribution of each shear transfer mechanism of the interface. It includes 22 concrete columns (core) (of 24,37MPa concrete strength) with square section (150mm side, 500 mm height and scale 1:2). Ten columns had initial construction damages and twelve were subjected to initial axial load. Sixteen columns have full jacketing at all four faces with 80mm thickness (of 31,7MPa concrete strength) and contain longitudinal bars (of 500MPa nominal strength) and closed stirrups spaced at 25mm, 50mm or 100mm (of 220MPa nominal strength). Fourteen of them contain dowels at the interface between old and new concrete. All columns were subjected to repeated (pseudo-seismic) axial compression with increasing deformation cycles up to failure with or without jacketing. Two load patterns were selected to examine the difference of the behavior of columns. The effects of the initial damages, of the reinforcement of the interface (dowels) and of the confinement generated by the stirrups are investigated through axial- deformation (slip) diagrams and the energy absorbed diagrams. The results indicate that the initial damages affect the total behavior of the column and the capacity of the interface to shear mechanisms and to slip: a) the maximum bearing load of old column is decreased affecting at the same time the loading capacity of the jacketed element, b) suitable repair of initially damaged specimens increases the capacity of the jacketed column to transfer load through the interface.

• 한국건설관리학회논문집
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• 제19권3호
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• pp.70-78
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• 2018

기후변화에 대한 우려가 커지면서 건설산업에서도 환경부하를 줄이기 위해 지속적으로 노력하고 있으며, 환경부하를 산정하기 위한 효과적인 방법론으로써 LCA (life cycle assessment)가 제시되고 있다. 그러나, LCA는 환경부하량 산정을 위해 작업에 투입되는 자원량에 대한 정보가 필요하기 때문에 이러한 정보의 확보가 어려운 초기 설계단계의 환경적 검토에는 활용되지 못하고 있다. 이 연구에서는 도로의 배수시설물을 대상으로 표준단면에 기반한 작업물량산출체계를 개발하고 환경부하량을 산출할 수 있는 모델에 활용하였다. 이 모델은 초기 설계단계의 가용정보만으로 LCA에 필요한 자원량을 산정함으로써 환경부하량을 산출할 수 있다. 모델의 유효성을 검증하기 위해 5개의 검증사례를 적용하였으며 원단위추정모델 및 회귀모델과 비교하였다. 그 결과 평균 9.94%의 절대오차율평균을 나타내 다른 모델보다 상대적으로 정확하며 초기 설계단계에서 사용할 수 있는 유효한 모델이라는 점이 확인되었다.

• 대한교통학회지
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• 제20권4호
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• pp.151-162
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• 2002

경인고속도로가 개통된 1969년 이후로 우리나라 고속도로는 국토의 대동맥으로서 꾸준한 확장과 신설을 거듭해 왔으며, 조만간 고속도로 3.000km시대를 맞이하게 될 전망이다. 이에 고속도로는 건설과 확장 위주에서 효율적 운영이 중요성이 과거 그 어느 때보다도 강조되고 있다. 최근 고속도로망이 복잡해져감에 따라 교통정보의 가치가 점점 높아지고 있고, 더욱이 정보통신기술의 급격한 발달과 함께, 휴대폰, PDA, PNS 등의 보급이 증가함에 따라 교통정보의 수요가 급증하고 있다. 특히, 통행시간 정보의 경우, 혼잡이 있는 도로망에서 최적의 경로선택을 하고. 경로간에 적절한 교통량분산을 통해 자원의 효율적 배분을 달성하는데 있어 필수적인 정보로서 그 중요성을 더해 가고 있는 실정이다. 본 연구에서는 고속도로 통행료수납시스템(TCS)에서 수집되는 톨게이트간 통행시간 데이터를 기반으로 TCS 통행시간 데이터의 속성과 시계열적 패턴을 규명하고, 이를 바탕으로 모듈라 신경망모형(Modular Neural Network Model)을 이용한 통행시간 예측모형을 개발하였다. 우선, 단거리(서울->수원)와 장거리(서울->대전) 그리고 평일과 주말로 구분하여 TCS 데이터에 대한 시계열 패턴 분석을 한 결과, 단거리와 장거리 공히 충분한 범위의 예측가능한 시간적 범위를 가지고 있으며, 복잡한 정도는 장거리가 높은 것으로 나타났다. 다만. 단거리구간이 장거리 구간에 비해 초기조건에 대한 민감성이 큰 이유로 상대적으로 장기예측이 어려운 것으로 분석되었다. 한편, 모형 적용 현장의 요구기능을 분석하여 모듈라 신경망 구조를 가진 예측모형을 개발하였으며, 최소한 약 80분 이상의 장기예측이 요구되는 서울->대전구간에 적용한 결과, 대부분 10분 이내의 낮은 오차를 보였다. 본 연구에서 개발된 모형은 예측범위가 고정적인 대부분의 시계열모형과는 달리 최소의 입력(3개)을 가지면서 하나의 신경망으로 학습한 최대/최소의 예측시간 범위내에서 그 크기에 상관없이 거의 동일한 수준의 예측력을 보이는 장점을 가지고 있다.

• Smart Structures and Systems
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• 제13권6호
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• pp.1015-1039
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• 2014

The widening project on Freeway No.1 in Taiwan has a total length of roughly 14 kilometers, and includes three special bridges, namely a 216 m long-span bridge crossing the original freeway, an F-bent double decked bridge in a co-constructed section, and a steel and prestressed concrete composite bridge. This study employed in-situ monitoring in conjunction with numerical modeling to establish a real-time monitoring system for the three bridges. In order to determine the initial static and dynamic behavior of the real bridges, forced vibration experiments, in-situ static load experiments, and dynamic load experiments were first carried out on the newly-constructed bridges before they went into use. Structural models of the bridges were then established using the finite element method, and in-situ vehicle load weight, arrangement, and speed were taken into consideration when performing comparisons employing data obtained from experimental measurements. The results showed consistency between the analytical simulations and experimental data. After determining a bridge's initial state, the proposed in-situ monitoring system, which is employed in conjunction with the established finite element model, can be utilized to assess the safety of a bridge's members, providing useful reference information to bridge management agencies.

• 한국의학물리학회지:의학물리
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• 제33권4호
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• pp.164-171
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• 2022

The number of facilities using radiation generators increases and related regulations are strengthened, the establishment of a shielding management and evaluation technology has become important. The characteristics of the radiation generator used in previous report differ from those of currently available high-frequency radiation generators. This study aimed to manufacture lead, iron, and concrete shielding materials for the re-verification of half-value layers, tenth-value layers, and attenuation curve. For a comparison of attenuation ratio, iron, lead, and concrete shields were manufactured in this study. The initial dose was measured without shielding materials, and doses measured under different types and thicknesses of shielding material were compared with the initial dose to calculate the transmission rate on 50-300 kVp X-ray. All the three shielding materials showed a tendency to require greater shielding thickness for higher energy. The attenuation graph showed an exponential shape as the thickness decreased and a straight line as the thickness increased. The difference between the measurement results and the previous study, except in extrapolated parts, may be due to the differences in the radiation generation characteristics between the generators used in the two studies. The attenuated graph measured in this study better reflects the characteristics of current radiation generators, which would be more effective for shield designing.

• Nuclear Engineering and Technology
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• 제52권7호
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• pp.1347-1354
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• 2020

To improve the efficiency of MC criticality calculation, an acceleration method of fission source convergence which gives an improved initial fission source is proposed. In this method, the MC global homogenization is carried out to obtain the macroscopic cross section of each material mesh, and then the nonlinear iterative solution of the SP3 equations is used to determine the fission source distribution. The calculated fission source is very close to the real fission source, which describes its space and energy distribution. This method is an automatic computation process and is tested by the C5G7 benchmark, the results show that this acceleration method is helpful to reduce the inactive cycles and overall running time.

• Steel and Composite Structures
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• 제13권6호
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• pp.539-560
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• 2012

This study uses an explicit numerical algorithm to evaluate the ultimate load capacity analysis of a unit Strarch frame, accounting for the initial imperfection effects of the stress-erection process. Displacement-based filament beam element and an explicit dynamic relaxation method with kinetic damping are used to achieve the analysis. The section is composed of the finite number of filaments that can be conveniently modeled by various material models. Ramberg-Osgood and bilinear kinematic elastic plastic material models are formulated to analyze the nonlinear material behaviors of filaments. The numerical results obtained in the present study are compared with the results of experiment for stress-erection and buckling of unit Strarch frames.