• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2000년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Fall 2000
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• pp.448-454
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• 2000

Piled multi-block system has been frequently adopted in the historic structures or monuments of cultural heritage. It is well known that such a structural system is very vulnerable to the earthquake shaking. If the structure is of slender type, then it may experience overturning at very low level intensity of ground shaking. One of the methods used to protect such structures from earthquake is seismic isolation system. But the behavior of multi-block systems mounted on the isolated basis is not well understood yet. In this paper we investigate the dynamic behavior of single slender rigid block mounted on the three different isolation systems, i.e., P-F system, FPS and LRB system. Sliding at the isolation interface of P-F system and FPS is formulated based on Coulomb friction. The mounted single block is assumed undergoing rocking or sticking only. Impacting of a single block is described using distinct element method (DEM). Free vibrations due to a prescribed initial conditions are studied. Responses to the harmonic excitation and earthquake motions are calculated

• 소성∙가공
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• 제4권2호
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• pp.131-140
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• 1995

In this paper damage propagation of a material during forming is investigated with the concept of continuum damage mechanics. An isotropic damage model based on the theory of materials of type N is adopted to describe the damage process of a ductile material with large elasto-viscoplastic deformation. The stiffness degradation of the loaded material is chosen as a damage measure. The highly nonlinear equilibrium equations are reduced to the incremental weak form and approximated by the total Lagrangian finite element method. To simulate contact condition, extended interior penalty method with modified coulomb friction law is adopted. The displacement control method along with the modified Riks' continuation technique is used to solve the incremental iterative equations. As numerical examples, upsetting problem and backward extrusion problem are simulated and the results of damage propagation and $J_2$ stress contours with and without friction are presented.

• 한국기계가공학회지
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• 제10권3호
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• pp.94-99
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• 2011

Micro-scale surface pattern has an benefit of tribological application under lubricated sliding contact. Therefore, a special pattern, that has to reduce the coulomb friction under contact, is considered to be necessary for improved efficiency of machines. The current study investigated the friction property of angle effect for micro-scale grooved crosshatch pattern on bearing steel surface using pin-on-disk type. The samples fabricated by photolithography process and then these are carry out the electrochemical etching process. We discuss the friction property due to the influence of hatched-angle on contact surface. We could be explained the lubrication mechanism for a Stribeck curve. It was found that the friction coefficient depend on an angle of the crosshatch on contact surface. It was thus verified that micro-scale crosshatch grooved pattern could affect the friction reduction.

• Structural Engineering and Mechanics
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• 제21권1호
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• pp.1-18
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• 2005

Foschi's connector model is used as a basic component in the development of nonlinear analysis programs for timber structures. This paper presents the extension of the model to include the effect of shaft frictional forces. The wood medium is modeled using the Foschi embedment model, while shaft friction is modeled using an elastic Coulomb-type friction model. The initial confining pressure for the case of driven fasteners is accounted for by a lateral shift of the load-embedment curve. The model is used to compute the cyclic response of both driven and inserted fasteners. The results obtained from the cases studied indicate that initial confining pressure and friction do not have a significant effect on the computed hysteretic response, however, they significantly affect the computed amount of fastener withdrawal. This model is particularly well-suited for modeling the hysteretic response of shear walls with moderate fastener withdrawal under lateral cyclic or earthquake loading.

• JSTS:Journal of Semiconductor Technology and Science
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• 제11권2호
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• pp.80-87
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• 2011

Low temperature hole transport characteristics of gate-all-around p-channel metal oxide semiconductor (PMOS) type silicon nanowire field-effect-transistors with the radius of 5 nm and lengths of 44-46 nm are presented. They show coexisting two single hole states randomly switching between each other. Analysis of Coulomb diamonds of these two switching states reveals a variety of electrostatic effects which is originated by the potential of a single hole captured in the trap near the nanowire.

• Journal of Power Electronics
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• 제10권2호
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• pp.181-186
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• 2010

This paper presents a new method for the estimation of State of Charge (SOC) for NiMH batteries. Among the conventional methods to estimate SOC, Coulomb Counting is widely used, but this method is not precise due to error integration. Another method that has been proposed to estimate SOC is by using a measurement of the Open Circuit Voltage (OCV). This method is found to be a precise one for SOC estimation. In NiMH batteries, the hysteresis characteristic of OCV is very strong compared to other type of batteries. Another characteristic of NiMH battery to be considered is that the OCV of a NiMH battery under discharging mode is lower than it is under charging mode. In this paper, the OCV is modeled by a simple method based on a hyperbolic function which well known as Takacs’s model. The OCV model is then used for SOC estimation. Although the model is simple, the error is within 10%.

• 한국해양공학회지
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• 제23권1호
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• pp.96-103
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• 2009

In 2006, Jeju Island in South Korea experienced a crisis, no electricity for three hours anywhere in the entire island. This incident was caused by a domino effect that occurred after one of the submarine power cables connecting the island to Haenam, a coastal city on the mainland, was damaged by an external load, probably from a ship anchor or a steel pile being used in marine farming. This study presents a collision analysis of a new submarine power cable protector called arch type reinforced concrete. For the analysis, a dynamic finite element program, ANSYS AUTODYN, was used to examine the displacement and stress of the submarine power cable protector using different material models (RHT concrete model, Mohr.Coulomb concrete model). In addition, two reinforcing bar spacings, 75 mm and 150 mm, were considered. From the analyses, the effects of the parameters (concrete model and spacing) on the results (displacement and stress) were analyzed, and the relations between the damage and parameters were found.

• 전자공학회논문지T
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• 제36T권2호
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• pp.32-41
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• 1999

CD(Compact Disc) 호환성을 가지는 고밀도 재생전용 및 기록재생용 DVD(Digital Video Disc) 기기의 광학픽업 2중 엑츄에이터 구조를 콤팩트하게 할 수 있는 단일 엑츄에이터 설계법을 제시한다. 설계된 엑츄에이터는 가동부에 CD용 대물렌즈와 DVD용 대물렌즈를 함께 장착하고, 사용 디스크에 따라 가동부를 축주위로 회전시켜서 대물렌즈를 전환하는 축습동형 구조를 하고, 자기 스프링에 의하여 부동된다. 감쇠방식으로서는 가동부와 축사이의 쿨롱마찰을 이용하고, 가동부는 유한요소법(FEM)을 통해, 서보대역내에서 2차 진동모드가 발생하지 않도록 한다. 본 논문의 설계법을 검증하기 위하여 시제품을 제작하고, 동특성을 측정, 평가한다.

• Geomechanics and Engineering
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• 제25권2호
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• pp.99-109
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• 2021

Tunnel provide faster, safer and convenient way of transportation for different objects. The region where it is construction and surrounding medium has significant influence on the overall stability and performance of tunnel. The present simulation has been carried out in order to understand the behaviour of rock tunnel under static loading condition. The present numerical model has been validated with the laboratory scaled model and field data of underground tunnels. Both lined and unlined tunnels have been considered in this paper. Finite element technique has been considered for the simulation of static loading effect on tunnel through Abaqus/Standard. The Mohr-Coulomb material model has been considered to simulate elastoplastic nonlinear behaviour of different rock types, i.e., Basalt, Granite and Quartzite. The four different stages of rock weathering are classified as fresh, slightly, moderately, and highly weathered in case of each rock type. Moreover, extremely weathered stage has been considered in case of Quartzite rock. It has been concluded that weathering of rock and overburden depth has great influence on the tunnel stability. However, by considering a particular weathering stage of rock for each rock type shows varying patterns of deformations in tunnel.

• 콘크리트학회논문집
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• 제28권2호
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• pp.167-176
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• 2016

이 연구는 다양한 콘크리트에 대해 전단마찰 거동에 의해 지배되는 부재에서 전단전달 기구를 설명하고 합리적인 전단마찰내력을 평가하기 위한 모델을 제안하였다. 제안된 모델의 기본식은 횡보강근과 작용 축응력을 고려하여 소성론의 상계치 이론(Upper-bound theorem)에 기반하여 유도하였다. 콘크리트는 수정 Coulomb 파괴 기준에 의해 완전한 소성 강체로 고려하였다. 콘크리트 유효강도에서 콘크리트 종류와 최대 골재 크기에 따른 영향을 적용하기 위해 Yang et al.의 압축 응력-변형률 모델과 CEB-FIP의 인장 응력-변형률 모델을 적용하였다. 이 응력-변형률 모델들을 이용한 완전 소성모델로의 변환을 통하여 유효압축강도계수, 유효강도비 그리고 콘크리트 마찰각을 간단한 식으로 일반화 하였다. 제시된 전단마찰내력 모델은 기존 연구에서 제시된 모델과 함께 91개의 직접전단 실험결과와 비교하였다. 그 결과로 이 연구에서 제시된 모델은 콘크리트 종류, 횡보강근 양 그리고 작용 축응력을 고려하여 전단마찰내력을 평가할 수 있었으며, 예측값에 대한 실험값의 비의 평균과 표준편차가 각각 0.95, 0.15로서 기존 식들에 비해 더 정확한 결과를 얻을 수 있었다.