• 소성∙가공
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• 제32권3호
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• pp.129-135
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• 2023

The use of engineering plastic products in internal combustion engine and electric cars to improve stiffness and reduce weight is increasing significantly. Among various lightweight materials, engineering plastics have significant advantages such as cost reduction, improved productivity, and weight reduction. In particular, engineering plastics containing glass fibers are used to enhance stiffness. However, the stiffness of glass fibers can increase or decrease depending on their orientation. Before developing plastic products, optimal designs are determined through injection molding and structural analysis to enhance product reliability. However, reliable analysis of products with variable stiffnesses caused by anisotropy cannot be achieved via the conventional isotropic structural analysis, which does not consider anisotropy. Therefore, based on the previously reported study "the Effect of Impacted Fracture in Glass Fiber Orientation with Injection Molding & Structural Coupled Analysis," this study aims to investigate the structural analysis and degradation mechanisms of various polymers. In particular, this study elucidates the actual mechanism of plastic fracture by analyzing various fracture conditions and their corresponding simulations. Furthermore, the objective of this study is to apply the injection molding and structural coupled analysis mechanism to develop engineering plastic products containing glass fibers. In addition, the study aims to apply and improve the plastic fracture mechanism in actual products by exploring anisotropy and stiffness reduction owing to the unfilled polymer weld line.

• Computers and Concrete
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• 제30권5호
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• pp.323-337
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• 2022

This paper proposes a numerical model to simulate the rotational behavior of steel fiber in fresh cement-based materials in the presence of a magnetic field. The results indicate that as the aspect ratio of fiber increases, the required minimum magnetic field intensity to make fiber rotate in viscous fluid increases. The optimal magnetic field intensity is 0.03 T for aligning steel fiber in fresh cement-based materials to ensure that the applying time of the magnetic field can be conducted concurrently with the vibrating process to increase the aligning efficiency. The orientation factor of steel fiber in cement mortar can exceed 0.85 after aligning by 0.03 T of the uniform magnetic field. When the initial angle of the fiber to the magnetic field direction is less than 10°, the magnetic field less than 0.03 T cannot make the fiber overcome the yield stress of fluid to rotate. The coarse aggregate in steel fiber-reinforced concrete is detrimental to the rotation and alignment of the steel fiber. But the orientation factor of ASFRC under the 0.03T of the magnetic field can also exceed 0.8, while the orientation factor of SFRC without magnetic field application is around 0.6.

• 대한화학회지
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• 제57권1호
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• pp.147-158
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• 2013

본 연구는 화학교육의 동기전략에 영향을 끼치는 학습관련 변인들의 인과관계에 대한 최적 모형을 찾고자 한다. 이를 위하여 광주광역시 소재 G와 I 고등학교에서 화학교육에 참여한 487명을 대상으로 하였다. 동기전략에 영향을 주는 학습관련 변인들의 경로모형을 탐색하기 위해, '자기효능감, 성취욕구, 지능신념'이 목표지향성을 매개로 하여 동기전략인 자기핸디캡경향과 학습전략으로 가는 모형을 Model I로 설정했다. 그리고 목표지향성을 근본 동기변인으로 하고 '자기효능감, 성취욕구, 지능신념'을 매개로 하여 '자기핸디캡경향과 학습전략'에 이르는 모형을 Model II로 설정했다. 이들 기본모형들을 기반으로 하여, 목표지향성(숙달목표, 수행접근목표 및 수행회피목표), 자기효능감, 성취욕구, 지능신념, 자기핸디캡경향 및 학습전략 간에 경로모형을 알기위해 통계분석을 통해 단계적으로 살펴보았다. 그 결과 Model I과 Model II 중에서 Model II가 선택되었고, 이 모형의 주요한 통계적 적합도 지수들을 확인하고 분석하면서 경로의 추가 및 삭제를 했고, 5차 수정한 결과, Model II-5의 경로모형이 본 연구의 최적 모형으로 채택되었다. 이 최적 모형을 분석한 결과, ${\chi}^2$의 p값도 0.267를 보임으로써 Model II-5가 측정자료와 아주 잘 일치한 모형임을 알 수 있었다. 본 연구에서는 15개의 경로들이 통계적으로 p <.05에서 유의미하게 학습전략에 영향을 주고 있음을 알 수 있다.

• 한국안전학회지
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• 제17권3호
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• pp.7-12
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• 2002

The object of this paper is to investigate collapse characteristics of CF/Epoxy(Carbon Fiber/Epoxy resin) composite tubes on the change of interlaminar number and fiber orientation angle of outer and to evaluate reappearance of collapse characteristics on the change of tension strength of fibers under static and impact axial compression loads. When a CF/Epoxy composite tube is mushed, static/impact energy is consumed by friction between the loading plate and the splayed fiends of the tube, by fracture of the fibers, matrix and their interface. In general, CF/Epoxy tube with 6 interlaminar number(C-type) absorbed more energy than other tubes(A, B, D-types). The maximum collapse load seemed to increase as the interlaminar number of such tubes increases. The collapse mode depended upon orientation angle of outer of CF/Epoxy tubes and loading status(static/impact). Typical collapse modes of CF/Epoxy tubes are wedge collapse mode, splaying collapse mode and fragmentation collapse mode. The wedge collapse mode was shorn in case of CF/Epoxy tubes with 0$^{\circ}$ orientation angle of outer under static and impact loadings. The splaying collapse mode was shown in only case of CF/Epoxy tubes with 90$^{\circ}$ orientation angie or outer under static loadings, however in impact tests those were collapsed in fragmentation mode. So that CF/Epoxy tube with 6 interlaminar number and 90$^{\circ}$ outer orientation angle presented to the optimal collapse characteristics.

• 한국CDE학회논문집
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• 제2권3호
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• pp.195-210
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• 1997

In Rapid Prototyping process, the time required to build multiple prototype parts can be reduced by packing several parts optimally in a work volume. Interactive arrangement of the multiple parts is a tedious process and does not guarantee the optimal placement of all the parts. In this case, packing is a kind of 3-D nesting problem because parts are represented by STL files with 3-D information. 3-D nesting is well known to be a problem requiring an intense computation and an efficient algorithm to solve the problem is still under investigation. This paper proposes that packing 3-D parts can be simplified into a 2-D irregular polygon nesting problem by using the characteristic of rapid prototyping process that the process uses 2-dimensional slicing data of the parts and that slice of the STL parts are composed of polygons. Our algorithm uses no-fit-polygon (NFP) to place each slice without overlapping other slices in the same z-level. The allowable position of one part at a fixed orientation for given parts already packed can be determined by obtaining the union of all NFP's that are obtained from each slice of the part. Genetic algorithm is used to determine the order of parts to be placed and orientations of each part for the optimal packing. Optimal orientation of a part is determined while rotating it about the axis normal to the slice by finite angles and flipping upside down. This algorithm can be applied to any rapid prototyping process that does not need support structures.

• Clinical Endoscopy
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• 제56권2호
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• pp.229-238
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• 2023

Background/Aims: Shear wave elastography (SWE) is used for liver fibrosis staging based on stiffness measurements. It can be performed using endoscopic ultrasound (EUS) or a transabdominal approach. Transabdominal accuracy can be limited in patients with obesity because of the thick abdomen. Theoretically, EUS-SWE overcomes this limitation by internally assessing the liver. We aimed to define the optimal technique for EUS-SWE for future research and clinical use and compare its accuracy with that of transabdominal SWE. Methods: Benchtop study: A standardized phantom model was used. The compared variables included the region of interest (ROI) size, depth, and orientation and transducer pressure. Porcine study: Phantom models with varying stiffness values were surgically implanted between the hepatic lobes. Results: For EUS-SWE, a larger ROI size of 1.5 cm and a smaller ROI depth of 1 cm demonstrated a significantly higher accuracy. For transabdominal SWE, the ROI size was nonadjustable, and the optimal ROI depth ranged from 2 to 4 cm. The transducer pressure and ROI orientation did not significantly affect the accuracy. There were no significant differences in the accuracy between transabdominal SWE and EUS-SWE in the animal model. The variability among the operators was more pronounced for the higher stiffness values. Small lesion measurements were accurate only when the ROI was entirely situated within the lesion. Conclusions: We defined the optimal viewing windows for EUS-SWE and transabdominal SWE. The accuracy was comparable in the non-obese porcine model. EUS-SWE may have a higher utility for evaluating small lesions than transabdominal SWE.

• Structural Engineering and Mechanics
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• 제6권6호
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• pp.633-641
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• 1998

Finite element solutions are presented for the optimal design of symmetrically laminated rectangular plates with various types of internal line supports. These plates are subject to a combination of simply supported, clamped and free boundary conditions. The design objective is the maximisation of the biaxial buckling load. This is achieved by determining the fibre orientations optimally with the effects of bending-twisting coupling taken into account. The finite element method coupled with an optimisation routine is employed in analysing and optimising the laminated plate designs. The effect of internal line support type and boundary conditions on the optimal ply angles and the buckling load are numerically studied. The laminate behavior with respect to fibre orientation changes significantly in the presence of internal line supports as compared to that of a laminate where there is no internal supporting. This change in behavior has significant implications for design optimisation as the optimal values of design variables with or without internal supporting differ substantially.

• Smart Structures and Systems
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• 제15권5호
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• pp.1177-1202
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• 2015

The present paper is concerned with the optimal control and/or design of symmetric and antisymmetric composite laminate with two piezoelectric layers bonded to the opposite surfaces of the laminate, and placed symmetrically with respect to the middle plane. For the optimal control problem, Liapunov-Bellman theory is used to minimize the dynamic response of the laminate. The dynamic response of the laminate comprises a weight sum of the control objective (the total vibrational energy) and a penalty functional including the control force. Simultaneously with the active control, thicknesses and the orientation angles of layers are taken as design variables to achieve optimum design. The formulation is based on various plate theories for various boundary conditions. Explicit solutions for the control function and controlled deflections are obtained in forms of double series. Numerical results are given to demonstrate the effectiveness of the proposed control and design mechanism, and to investigate the effects of various laminate parameters on the control and design process.

• Journal of the Korean Data Analysis Society
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• 제20권6호
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• pp.3101-3116
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• 2018

본 연구에서는 기업 경쟁력의 제고를 통하여 최적화된 경영환경을 조성하고, 기업의 효율성을 높이는데 필요한 혁신 수단인 공급사슬관리를 위한 동적역량의 활용 방향성과 전략을 찾을 수 있는 방안들에 대해 알아보고자 한다. 시장과 기술은 전략적 방향과 문화로 기업이 보유한 정형화된 동적역량에 맞추고, 프로세스에는 공급사슬관리를 위한 동적역량과 관련된 기술을 반영하여 활용할 때에 보다 높은 기업성과를 창출할 수 있을 것이다. 본 연구에서는 시장지향성과 기술지향성이 기업성과에 미치는 영향과 동적역량이 기업성과에 어떠한 영향을 미치는지를 실증적으로 분석하는데 그 목적이 있다. 연구 결과는 시장지향성과 기술지향성은 동적역량에 긍정적 영향을 미치고, 동적역량은 기업성과에 긍정적 영향을 미치는 것으로 나타났다. 즉 동적역량은 시장지향성, 기술지향성과 기업성과 간의 관계를 매개하는 것으로 검증되었으며, 동적역량의 매개효과로 기업의 시장지향성과 기술지향성이 기업성과에 중요한 영향을 미치는 것으로 실증 분석되었다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1997년도 한국자동제어학술회의논문집; 한국전력공사 서울연수원; 17-18 Oct. 1997
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• pp.175-178
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• 1997

This study was carried out to obtain an analytical expression for the specifications of the Stewart Platform that minimize the maximum force acting on the hydraulic cylinder. The position and orientation of the platform were calculated by means of the inverse kinematic analysis. The maximum force to be exerted on a cylinder was calculated using the Newton's second law for the case when the platform is moved along a horizontal axis with 0.6 g, the maximum translational acceleration possible. This paper suggests a mathematical model to minimize the maximum actuating force using radius and angle ratios as design variables. Finally, a fuzzy set for the minimum actuating force is proposed for this dynamic optimal design problem.