• 전기학회논문지
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• 제60권11호
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• pp.2171-2175
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• 2011

The objective of this paper is to discuss technologies on assessing reliability of arc detectors by composing a system that generates and simulates occurrence of arc caused by loss of contact between pantographs and contact wires in a laboratory condition. In order to establish the arc simulator, a device that generates light having the bandwidth of arcs that occur between carbon-metal. The simulator was designed under conditions of EN 50317 and simulations were conducted using the developed device. According to the results, it was possible to conduct certification tests following regulations of international standards and the precision of the simulator was satisfactory. The proposed arc detector assessment system is expected to enhance precision of current collection quality performance assessment methods at high-speed lines and conventional lines while being referred as fundamental technologies for development of detectors suiting international conditions.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1995년도 하계학술대회 논문집 A
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• pp.455-459
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• 1995

Catenary/pantograph system consists of overhead lines which have non-uniform elasticity and pantographs which move at high speed and give force to the lines, therefore happen to be failed in contacts between both from time to time. In this study, as the first step to develop a dynamic simulation program, the general theory is discussed for catenary/pantograph system and appropriate modelling. And comparison is conducted with the references after making a program which referred to the contact force equation algorithm. On this algorithm, the unknown contact force is computed by the equations which was induced as combining catenary and pantograph motion equations expressed in finite difference form. Another simulation program based on the assumed contact forces algorithm was developed. In this algorithm, numerical integraion of both the overhead line and pantograph equations, which without combining, are effected for two assumed values of contact force. The correct contact force is then obtained from these two sets of results by linear interpolation to satisfy the contact condition. Through the comparative review on the outputs from this program, it is verified that this algorithm is reliable.

• Tribology and Lubricants
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• 제35권2호
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• pp.94-98
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• 2019

The riblet structure like shark skin has been widely studied owing to its drag reduction and anti-fouling properties. In this study we simulated the wettability of an oil droplet on a riblet surface. We developed a numerical analysis method using the Wenzel equation and Cassie-Baxter equation that can estimate the contact angle with a penetrated depth of the droplet on rough surfaces. Riblet surfaces with nine scales composed of five hemi-elliptical ribs are generated numerically. The variation of contact angles with fractional depth of penetration for the generated riblet surfaces with and without coatings is demonstrated in the condition of solid-air-oil and solid-water-oil interfaces. The contact angle for the uncoated surface decreases with increasing fractional depth of penetration more drastically than that for the coated surface. For the effect of surface roughness on the contact angle of the droplet, the oleophilic surface gives lower contact angle when the surface is rougher, whereas the oleoophobic surface gives higher contact angle with higher roughness To verify the analysis results, the wetting angle was measured in the solid-air-oil interface and solid-water-oil interface for the shark-skin template and shark-skin replica. The effects of teflon coating were also evaluated. It is shown that the simulation results cover the experimental ones.

• 한국안광학회지
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• 제16권2호
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• pp.135-145
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• 2011

목적: 본 연구는 소프트 콘택트렌즈의 보관 용기의 관리 실태를 조사하고 보관 용기의 균 오염도가 소프트 콘택트렌즈 착용 기간과 보관 용기에서의 렌즈 보관 기간에 따라 어떻게 달라지는지 알아보고자 수행되었다. 방법: 소프트 콘택트렌즈 보관 용기의 관리 실태는 총 63명을 대상으로 한 설문조사를 통하여 알아보았다. 소프트 콘택트렌즈를 착용 기간을 달리하여 각각 1일, 3일, 7일, 14일 동안 착용하게 하고 이들 렌즈를 보관 용기에서 1일, 3일, 7일간으로 각 착용군마다 보관 기간을 달리하여 보관하였다. 보관 용기의 균 오염도는 일반 세균, 그람음성균 및 진균 수를 측정하여 판단하였다. 결과: 장기간 소프트 콘택트렌즈를 보 관하였을 때 콘택트렌즈 보관 용기를 사용 후 솔로 문질러 닦아 헹구고 뒤집어 말린 후 재사용하는 사람은 14%에 불과하였다. 또한 다목적용액의 교체 없이 그대로 보관 용기에 장기간 담가 둔다고 한 사람이 54%에 달하였다. 1일 동안 착용한 소프트 콘택트렌즈를 다목적 용액으로 세척한 후 보관 용기에서 1일간 보관하였을 때에도 각각 정도의 차이는 있지만 일반 세균, 그람음성균 및 진균 모두 보관 용기에서 검출되었다. 소프트 콘택트렌즈의 보관 기간을 달리한 보관 용기 모두에서 일반 세균, 그람음성균 및 진균의 수가 증가하였으며 장기간 착용으로 인하여 소프트 콘택트렌즈의 오염도가 증가할수록 보관 용기의 균 오염도 역시 증가함을 확인하였다. 또한, 다목적 용액의 교체없이 보관 용기에서 보관하였을 경우에는 보관 기간이 길어질수록 보관 용기에서 검출되는 일반 세균, 그람음성균 및 진균의 수의 증가가 모두 통계적으로 유의하게 증가하였다. 결론: 본 연구를 통하여 소프트 콘택트렌즈 착용자들의 보관용기 관리가 미흡한 것으로 확인되었고 소프트 콘택트렌즈의 착용 기간과 보관 기간의 증가에 따라 보관 용기의 오염도 또한 높아짐을 알 수 있었으므로 이에 대한 주의 및 교육이 강조되어야 할 것으로 여겨진다.

• Journal of Mechanical Science and Technology
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• 제16권12호
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• pp.1687-1692
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• 2002

The problem analyzed here is a sheet metal forming process which requires a drawbead. The drawbead provides the sheet metal enough tension to be deformed plastically along the punch face and consequently, ensures a proper shape of final products by fixing the sheet to the die. Therefore, the optimum design of drawbead is indispensable in obtaining the desired formability. A static-explicit finite element analysis is carried out to provide a perspective tool for designing the drawbead. The finite element formulation is constructed from static equilibrium equation and takes into account the boundary condition that involves a proper contact condition. The deformation behavior of sheet material is formulated by the elastic-plastic constitutive equation. The finite element formulation has been solved based on an existing method that is called the static-explicit method. The main features of the static-explicit method are first that there is no convergence problem. Second, the problem of contact and friction is easily solved by application of very small time interval. During the analysis of drawbead processes, the strain distribution and the drawing force on drawbead can be analyzed. And the effects of bead shape and number of beads on sheet forming processes were investigated. The results of the static explicit analysis of drawbead processes show no convergence problem and comparatively accurate results even though severe high geometric and contact-friction nonlinearity. Moreover, the computational results of a static-explicit finite element analysis can supply very valuable information for designing the drawbead process in which the defects of final sheet product can be removed.

• 한국기계가공학회지
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• 제10권3호
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• pp.39-46
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• 2011

The automotive air conditioning hose is used for connecting the components of air conditioner in a vehicle. The hose is usually manufactured by the swaging process to connect the rubber hose with the metal fitting at the end of the hose. In case that the clamping force is small, the refrigerant gas in the hose can leak locally under the severe operating circumstances. The practical test of clamping force is performed by means of the measurement of separation force. In this study, the swaging process of a hose is simulated with the finite element method, to investigate the effect of friction coefficient on the clamping force. The contact condition is used in consideration of real manufacturing process, and the material properties for the Mooney-Rivlin model is obtained by the experimental results. The result interpretations are focused on the contact forces, which is displayed graphically with respect to friction coefficient, on the surfaces between the hose and the metal fittings.

• 제어로봇시스템학회논문지
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• 제14권11호
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• pp.1146-1154
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• 2008

This paper presents a method for the acceleration analysis of multi-legged walking robots in consideration of the frictional ground contact. This method is based on both unified dynamic equation for finding the acceleration of a robot's body and constraint equation for satisfying no-slip condition. After the dynamic equation representing relationship between actuator torques and body acceleration, is derived from the force and acceleration relationship between foot and body's gravity center, the constraint equation is formulated to reconfigure the maximum torque boundaries satisfying no-slip condition from given original actuator torque boundaries. From application of the reconfigured torques to the dynamic equation, interested acceleration boundaries are obtained. The approach based on above two equations, is adapted to the changes of degree-of-freedoms of legs as well as friction of ground. And the method provides the maximum translational and rotational acceleration boundaries of body's center that are achievable in every direction without occurring slipping at the contact points or saturating all actuators. Given the torque limits in infinite normsense, the resultant accelerations are derived as a polytope. From the proposed method, we obtained achievable acceleration boundaries of 4-legged and 6-legged walking robot system successfully.

• 제어로봇시스템학회논문지
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• 제15권1호
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• pp.99-104
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• 2009

This article describes the analysis of stable grasping for multi-fingered robot. An analysis method of stable grasping, which is based on the three-dimensional acceleration convex polytope, is proposed. This method is derived from combining dynamic equations governing object motion and robot motion, force relationship and acceleration relationship between robot fingers and object's gravity center through contact condition, and constraint equations for satisfying no-slip conditions at every contact points. After mapping no-slip condition to torque space, we derived intersected region of given torque bounds and the mapped region in torque space so that the intersected region in torque space guarantees no excessive torque as well as no-slip at the contact points. The intersected region in torque space is mapped to an acceleration convex polytope corresponding to the maximum acceleration boundaries which can be exerted by the robot fingers under the given individual bounds of each joints torque and without causing slip at the contacts. As will be shown through the analysis and examples, the stable grasping depends on the joint driving torque limits, the posture and the mass of robot fingers, the configuration and the mass of an object, the grasp position, the friction coefficients between the object surface and finger end-effectors.

• 전기학회논문지
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• 제66권4호
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• pp.727-732
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• 2017

This paper describes the dynamic characteristics depending on installation condition between a pantograph and an OCL (Overhead Contact Line) on a new high speed line in Korea. The current collection performance between the pantograph and the OCL was tested during train operation from Suseo to Jije stations. The current collection performance is evaluated based on the duration of an arc by using an arcing measurement system. The system consists of an optical sensor for measuring the duration of an arc and a camera for monitoring current collection performance. An arcing duration is defined as a percentage of arcing in international standards. This test aims to analyze the locations of repetitive arcing depending on installation conditions of OCLs on a new high speed line in order to use the result as reference data for correct construction and maintenance.

• 한국자동차공학회논문집
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• 제22권3호
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• pp.97-104
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• 2014

Automobile trunk latches enable trunks to be opened and closed by a latch mechanism, which can be selectively positioned between a locked condition and an open condition. To maintain structural and electronic performance of the trunk latch, the latch needs to endure impact load that occurs in its open and close motion, and a dynamic mechanism needs to be electronically controled by a contact switch connected with a small DC motor. A base plate, which is the most important component relating to the structural safety, commonly uses a high stiffness material SAPH440-P with high manufacturing cost. In this paper, through structural analysis and optimization, production cost is significantly reduced by replacing SAPH440-P used in some region of the base plate with engineering plastic PBT GF 20%. The optimized contact switch reduces difference between distributed pressures of its two legs, which leads to improve the electronic performance of the trunk latch.