곡선부에서 차륜 마모 저감을 위한 차륜답면 형상 설계

최하영(Ha-Young Choi),이동형(Dong-Hyong Lee),송창용(Chang-Yong Song),이종수(Jongsoo Lee) Korean Society for Precision Engineering 2012 한국정밀공학회지 Vol.29 No.6

The wear problem of wheel flange occurs at sharp curves of rail. This paper proposes a procedure for optimum design of a wheel profile wherein flange wear is reduced by improving an interaction between wheel and rail. Application of optimization method to design problem mainly depends on characteristics of design space. This paper compared local optimization method with global optimization according to sensitivity value of objective function for design variables to find out which optimization method is appropriable to minimize wear of wheel flange. Wheel profile is created by a piecewise cubic Hermite interpolating polynomial and dynamic performances are analyzed by a railway dynamic analysis program, VAMPIRE. From the optimization results, it is verified that the global optimization method such as genetic algorithm is more suitable to wheel profile optimization than the local optimization of SQP (Sequential Quadratic Programming) in case of considering the lack of empirical knowledge for initial design value.

유한요소해석을 이용한 해양 로딩암의 구조안전성 평가

송창용(Chang Yong Song),최하영(Ha Young Choi),심승환(Seung Hwan Shim) 한국해양공학회 2013 韓國海洋工學會誌 Vol.27 No.1

This paper present a structural design review of a marine loading arm used for the transfer of a liquid cargo from a ship or offshore plant. The marine loading arm is installed on a ship, offshore plant, or jetty in order to load or unload liquid cargo such as crude oil, liquefied natural gas(LNG), chemical products, etc. The structural design of this marine loading arm is obliged to comply with the design and construction specifications regulated by the oil companies and international marine forum (OCIMF). In this paper, the structural safety of the initial design for the marine loading arm is evaluated for the design load conditions required by various operational modes. The evaluated results based on a finite element analysis (FEA) are reviewed in relation to the OCIMF specifications.

차량 현가 부품의 근사 다목적 설계 최적화에 대한 메타모델 영향도

송창용(Chang Yong Song),최하영(Ha-Young Choi),변성광(Sung-Kwang Byon) 한국기계가공학회 2019 한국기계가공학회지 Vol.18 No.3

Herein, we performed a comparative study on approximate multi-objective design optimization, to realize a structural design to improve the weight and vibration performances of the knuckle—a car suspension component—considering various load conditions and vibration characteristics. In the approximate multi-objective optimization process, a regression meta-model was generated using the response surfaces method (RSM), while Kriging and back-propagation neural network (BPN) methods were applied for interpolation meta-modeling. The Pareto solutions, multi-objective optimal solutions, were derived using the non-dominated sorting genetic algorithm (NSGA-II). In terms of the knuckle design considered in this study, the characteristics and influence of the meta-model on multi-objective optimization were reviewed through a comparison of the approximate optimization results with the meta-models and the actual optimization.

보수적 근사모델을 적용한 신뢰성 기반 강건 최적설계 방법

심형민(Hyoung Min Sim),송창용(Chang Yong Song),이종수(Jongsoo Lee),최하영(Ha-Young Choi) 한국해양공학회 2012 韓國海洋工學會誌 Vol.26 No.6

The methods of robust design optimization(RDO) and reliability-based robust design optimization (RBRDO) were implemented in the present study. RBRDO is an integrated method that accounts for the design robustness of an objective function and for the reliability of constraints. The objective function in RBRDO is expressed in terms of the mean and standard deviation of an original objective function. Thus, a multi-objective formulation is employed. The regressive approximate models are generated via the moving least squares method(MLSM) and constraint-feasible moving least squares method (CF-MLSM), which make it possible to realize the feasibility regardless of the multimodality/nonlinearity of the constraint function during the approximate optimization processes. The regression model based RBRDO is newly devised and its numerical characteristics are explored using the design of an actively controlled ten bar truss structure.

차륜-레일 구름접촉 시 슬립율에 따른 접촉응력의 변화 해석

이동형(Dong-Hyong Lee),서정원(Jung-Won Seo),권석진(Seok-Jin Kwon),최하영(Ha-Yong Choi),김재철(Chul-Jae Kim) 한국철도학회 2011 한국철도학회 학술발표대회논문집 Vol.2011 No.10

Fatigue crack in most rails take place by rolling contact between wheel and rail in railway industry. Therefore it is critical to understand the rolling contact phenomena especially for the three-dimensional situation. In this paper the steady-state rolling contact problem of KTX wheel and rail (UIC60) has been studied with three-dimensional finite element analysis. The variation of contact pressure and contact stresses on rolling contact surface were obtained using the finite element method. The three-dimensional distribution of contact stresses on the contact surface are investigated. Results show that the distribution of shear stress and contact stress (von Mises) on the contact surface varies rapidly as a result of the variation of stick-slip region. The contact stress at the leading edge is greater than at the trailing edge because of stick and slip phenomena.

레일표면손상이 접촉피로수명에 미치는 영향

서정원(Jung-Won Seo),이동형(Dong-Hyong Lee),함영삼(Young-Sam Ham),권성태(Sung-Tae Kwon),권석진(Seok Jin Kwon),최하영(Ha-Yong Choi) Korean Society for Precision Engineering 2012 한국정밀공학회지 Vol.29 No.6

Rails are subjected to damage from rolling contact fatigue, which leads to defects such as cracks. Rolling contact fatigue damages on the surface of rail such as head check, squats are one of growing problems. Another form of rail surface damage, known as “Ballast imprint” has become apparent. This form of damage is associated with ballast particles becoming trapped between the wheel and the surface of rail. These defects are still one of the key reasons for rail maintenance and replacement. In this study, we have investigated whether the ballast imprint is an initiator of head check type cracks and effect of defect size using Finite element analysis. The FE analysis were used to investigate stresses and strains in subsurface of defects according to variation of defect size. Based on loading cycles obtained from FE analysis, fatigue analysis for each point was carried out.

장점강화활동이 지적장애 초등학생의 수업참여행동에 미치는 영향

김태용,최하영 이화여자대학교 특수교육연구소 2013 특수교육 Vol.12 No.1

본 연구는 장점강화활동이 주의집중 시간이 짧고, 수업 중에 과제수행 행동을 보이지 않는 지적장애 초등학생의 수업참여행동에 미치는 영향을 알아보았다. 대상자간 중다간헐기초선 설계를 이용한 본 연구에는 초등학교 특수학급에서 시간제 특수교육 서비스를 받고 있는 지적장애학생 3명이 참여하였다. 선호도 검사, 장점중심 사정도구, 다중지능 검사, 행동사정 질문을 통해 파악한 대상 학생들의 장점을 분석한 후 각 학생별로 장점강화활동을 계획․실행하였다. 장점강화활동은 20회기로 구성되었고, 중재 종료 6주 후에는 기초선과 동일한 조건 하에 유지를 측정하였다. 연구 결과, 장점강화활동은 연구대상학생들의 수업참여행동(과제수행행동, 주의집중행동, 자발적 행동)에 긍정적인 영향을 미쳤고, 중재 종료 후에도 기초선보다 높은 수준으로 중재 효과가 유지된 것으로 나타났다. Meaningful class participation of students with intellectual disabilities has been recognized as the most significant element among education settings. The purpose of this study is to inquire how the strength-oriented activities affect on the class participation behaviors of students with intellectual disability. Three students with intellectual disabilities in a special education classroom participated in this study. Multiple probe baseline design across participants was employed to investigate the effects of strength-oriented activities. The class participation behaviors of targeted student are inquired in a special education classroom during intervention and maintenance phases. 20 sessions of intervention in which lasted 20 minutes prior to observed session were carried on for each participant. The class participation behaviors in this study include three types of behaviors; task engagement, attention and spontaneous behavior. The results showed that strength-oriented activity increases the incidence of development student’s task engagement, attention and spontaneous behavior. In addition, the effects of increased task engagement, attention and spontaneous behavior were maintained after 6 weeks when the strength- oriented activity was terminated. Based on the results a couple of points were discussed.