• Smart Structures and Systems
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• 제26권2호
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• pp.147-156
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• 2020

This numerical study demonstrates the porosity conditions and the intensity of the interactions with the aggressive agents. It is established that the density as well as the elastic modulus are correlated to ultrasonic velocity The following investigation assessed the effects of cement grade and porosity on tensile strength, flexural and compressive of Ultra High Performance Concrete (UHPC) as a numerical model in PLAXIS 2d Software. Initially, the existing strength-porosity equations were investigated. Furthermore, comparisons of the proposed equations with the existing models suggested the high accuracy of the proposed equations in predicting, cement grade concrete strength. The outcome obtained showed a ductile failure when un-corroded reinforced concrete demonstrates several bending-induced cracks transfer to the steel reinforcement. Moreover, the outcome also showed a brittle failure when wider but fewer transverse cracks occurred under bending loads. Sustained loading as well as initial pre-cracked condition during the corrosion development have shown to have significant impact on the corrosion behavior of concrete properties. Moreover, greater porosity was generally associated with lower compressive, flexural, and tensile strength. Higher cement grade, on the other hand, resulted in lower reduction in concrete strength. This finding highlighted the critical role of cement strength grade in determining the mechanical properties of concrete.

• 한국정밀공학회지
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• 제16권4호통권97호
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• pp.57-63
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• 1999

A thin metal plate such as detent spring has the shape deformation due to the phenomenon of spring back after press machining and heat treatment process. This requires the correction of spring shape and force in final inspection process. To do correction of the shape deformation the impact force is manually applied to the bended part of detent spring after measuring the shape deformation and spring force. To develop the automatic spring force correction system, applied force of occurring plastic deformation must be derived from the experimental method. But frequent change of spring shape and material makes it difficult to accomplish the experimental method to be applied. This paper describes the analytical method for detent spring force correction system is to be substituted for the experimental method. FEM(Finite Element Method) is used to find the boundary value between elastic and plastic deformation in the analytical method. To confirm the validity of the analytical method, the result of two methods is compared each other at various applied force conditions. It shows that the simulation result of the analytical method is consistent with the result of the experimental method within the error bound ${\pm}$5%. The result of this paper is useful for development of the automatic spring correction system and reduction of the complicated and tedious processes involved in experimental method.

• Earthquakes and Structures
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• 제19권4호
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• pp.273-286
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• 2020

The pile group foundation is widely used for gravity pier of high-speed railway bridges in China. If a moderate or strong earthquake occurs, the pile-surrounding soil will exhibit obvious nonlinearity and significant pile group effect. In this study, an improved pushover analysis model for the pile group foundation with consideration of pile group effect is presented and validated by the quasi-static test. The improved model uses simplified springs to simulate the soil lateral resistance, side friction and tip resistance. PM (axial load-bending moment) plastic hinge model is introduced to simulate the impact of the axial force changing of pile group on their elastic-plastic characteristics. The pile group effect is considered in stress-stain relations of the lateral soil resistance with a reduction factor. The influence factors on nonlinear characteristics and plastic hinge distribution of the pile group foundation are discussed, including the pier height, longitudinal reinforcement ratio and stirrup ratio of the pile, and soil mechanical parameters. Furthermore, the displacement ductility factor, resistance increase factor and yielding stiffness ratio are provided to evaluate the seismic performance of soil-pile system. A case study for the pile group foundation of a railway simply supported beam bridge with a 32 m-span is conducted by numerical analysis. It is shown that the ultimate lateral force of pile group is not determined by the yielding force of the single one in these piles. Therefore, the pile group effect is essential for the seismic performance evaluation of the railway bridge with pile group foundation.

• 한국구조물진단유지관리공학회 논문집
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• 제22권1호
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• pp.23-31
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• 2018

최근 사용 중인 중앙분리대의 성능 등급을 뛰어넘는 사고가 발생하고 있다. 그러므로 피해를 줄이기 위해 중앙분리대의 성능 등급을 현재의 SB5-B등급보다 상향된 기준에 맞춰 개선하는 것이 필요하다. 이에 본 연구에서는 중앙분리대 충돌시험결과를 활용하여 적절한 모델을 개발 및 검증하고 강도성능이 향상된 콘크리트 중앙분리대 개발을 목표로 하였다. 중앙분리대 성능은 SB6등급으로 목표성능등급을 설정하였고, 중앙분리대의 강도성능 개선 요소로 강성보강과 연성보강의 두 가지 형태를 고려하였다. 강성보강으로는 와이어 메쉬 직경 증가, 중앙분리대 상단 부위 철판보강을 고려하였고, 연성보강을 위해서는 중앙분리대 하단에 고무패드를 설치하여 성능향상을 컴퓨터 시뮬레이션을 통해서 확인하였다. 시뮬레이션 결과, 와이어 메쉬 직경이 증가할 수록 중앙분리대의 부피 손실은 감소하였으며, 고무패드 사용시 트럭의 충격에너지를 중앙분리대의 변형에너지로 전환하여 충격흡수에 효과적인 것으로 나타났다.

• 대한조선학회논문집
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• 제50권1호
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• pp.33-40
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• 2013

Since most of yacht sails are made of thin fabric, they form cambered sail shape that can efficiently generate lift power by aerodynamic interaction and by external force delivered from supporting structures such as mast and boom. When the incident flow and external force alter in terms of volume or condition, the shape of sail also change. This deformation in shape has impact on the peripheral flow and aerodynamic interaction of the sail, and thus it is related to the deformation of the sail in shape again. Therefore, the precise optimization of aerodynamic performance of sail requires fluid-structure interaction (FSI) analysis. In this study, the simplified sail without camber was under experiment for one-way FSI that uses the result of flow analysis to the structural analysis as load condition in an attempt to fluid-structure interaction phenomenon. To confirm the validity of the analytical methods and the reliability of numerical computation, the difference in deformation by the number of finite element was compared. This study reproduced the boundary conditions that sail could have by rigs such as mast and boom and looked into the deformation of sail. Sail has non-linear deformation such as wrinkles because it is made of a thin fabric material. Thus non-linear structural analysis was conducted and the results were compared with those of analysis on elastic material.

• International Journal of Internet, Broadcasting and Communication
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• 제7권1호
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• pp.75-92
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• 2015

This paper presents the application of the bond valence method to estimate the valence charge distribution in several perovskite systems: $La_{{\tilde{1}}x}Pb_xMnO_3$ (x=0.1-0.5), $La_{0.6}Sr_{0.{\tilde{4}}x}Ti_xMnO_3$ (x=0.0-0.25) and $La_{{\tilde{1}}x}Sr_xCoO_3$ (x=0.1-0.5); the reviewing of their crystal structures is also incorporated. The results showed the failure of the elastic bonding mechanism in all studied systems and revealed the general deficit of the valence charge in their unit cells. This valence deficit was not associated with the structural defects and was not equally localized in all coordination spheres. As the content of substitution increased, the charge deficit declined systematically from balanced level, signifying the transfer of valence charge from the ${\tilde{B}}O_6$ to ${\tilde{A}}O_{12}$ spheres. This transfer depended on the valence deviation of spheres and the average reached near 2 electron per unit cell. The possible impact of the limitted accuracy of the available structural data on the bond valence results has also been considered.

• 한국해안해양공학회지
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• 제8권1호
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• pp.81-86
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• 1996

해저 파이프라인은 해저 석유 및 천연가스 생산의 전반에 걸쳐 중요한 역할을 하나, 열악한 해양환경하에 있어 여러 가지 외부 요인에 의해 손상될 가능성이 높으며 그로 인한 피해는 막대하다. 본 논문에서는 해저 파이프라인의 안정성을 위협하는 주된 요인 중의 하나인 동적 자유경간을 해석하였으며, 해저 파이프라인 설계에 있어서 중요한 자유경간의 허용길이를 산출하였다. 자유경간의 허용길이는 와동방출의 진동수와 자유경간의 고유진동수와의 상관관계를 이용하여 산출하였고 경계조건에 따른 허용길이의 변화를 규명하였다. 자유경간 양단의 해저지반은 탄성기초로 간주하였으며, 이를 선형 및 회선 스프링으로 치환하여 경계조건을 일반화하였다. 본 연구를 통하여 여러 가시 지반조건에 대한 동석 자유경간의 정확한 허용길이를 간단하게 얻을 수 있는 무차원화 된 곡선을 구하였으며, 그 결과를 우리나라 동남해역 천연가스전에 설치예정인 해저 파이프라인에 적용하였다.

• 항공우주시스템공학회지
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• 제13권5호
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• pp.94-101
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• 2019

복합재료 반사판 안테나의 전개 특성을 해석 모델을 통하여 살펴보고 실험을 통하여 검증하고자 한다. 두 개의 회전 자유도를 가지며 스프링의 탄성 에너지에 의해 작동되는, 전개 메커니즘을 기반으로 반사판 안테나의 동역학적 해석 모델을 수립하였다. 유연 다물체 동역학 해석 프로그램인 ADAMS를 이용하여 패널의 전개 속도, 구조 변형 그리고 충격력을 분석하였다. 중력보상 장치를 이용하여 탄소섬유 강화 플라스틱(CFRP)으로 제작된 안테나 패널의 전개거동 특성을 실험적으로 검증/분석하였다. 안테나 패널이 전개되는 동안 발생하는 충격 응답 및 진동 문제를 확인하고, 댐퍼를 이용하여 안정적으로 전개가 됨을 확인하였다.

• Tribology and Lubricants
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• 제35권3호
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• pp.158-168
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• 2019

This paper presents the investigation of two types of rotordynamic modeling issues for 2.2 kW-class, rated speed of 1,800 rpm, squirrel-cage type induction motors. These issues include the lamination structure of rotor cores, and the radial clearance of ball bearings that support the shaft of the motor. Firstly, we focus on identifying the effects of rotor core lamination on the rotordynamic analysis via a 2D prediction model. The influence of lamination is considered as the change in the elastic modulus of the rotor core, which is determined by a modification factor ranging from 0 to 1.0. The analysis results show that the unbalanced response of the rotor-bearing system significantly varies depending on the value of the modification factor. Through modal testing of the system, the modification factor of 0.079 is proven to be appropriate to consider the effects of lamination. Next, we investigate the influence of ball bearing clearance on the rotordynamic analysis by establishing a bearing analysis model based on Hertz's contact theory. The analysis results indicate that negative clearance greatly changes the bearing static behavior. Rotordynamic analysis using predicted bearing stiffness with various clearances from -0.005 mm to 0.010 mm reveals that variations in clearance result in a slight difference in the displacement of the system up to 18.18. Thus, considering lamination in rotordynamic analysis is necessary as it can cause serious analysis errors in unbalanced response. However, considering the effect of the bearing clearance is optional because of its relatively weak impact.

• Advances in nano research
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• 제7권3호
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• pp.191-208
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• 2019

In the present work the dynamic analysis of the functionally graded rectangular nanoplates is studied. The theory of nonlocal elasticity based on the quasi 3D high shear deformation theory (quasi 3D HSDT) has been employed to determine the natural frequencies of the nanosize FG plate. In HSDT a cubic function is employed in terms of thickness coordinate to introduce the influence of transverse shear deformation and stretching thickness. The theory of nonlocal elasticity is utilized to examine the impact of the small scale on the natural frequency of the FG rectangular nanoplate. The equations of motion are deduced by implementing Hamilton's principle. To demonstrate the accuracy of the proposed method, the calculated results in specific cases are compared and examined with available results in the literature and a good agreement is observed. Finally, the influence of the various parameters such as the nonlocal coefficient, the material indexes, the aspect ratio, and the thickness to length ratio on the dynamic properties of the FG nanoplates is illustrated and discussed in detail.