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Reliability design of preventive maintenance scheduling for cumulative fatigue damage
백석흠,조석수,김현수,주원식 대한기계학회 2009 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.23 No.5
As the cumulative running times of a locomotive truck increases, degradation such as fatigue, wear, and deterioration occur. Particularly the container train and uncovered freight train, their maintenance cost during their lifetime is three times more than the manufacturing cost. Generally, for the freight train, corrective maintenance to repair a bad part after a breakdown is not adapted; however, preventive maintenance that fixes a bad part before a breakdown is. Therefore, it is important and necessary to establish a system of optimal preventive maintenance and exact maintenance period. This study attempts to propose a preventive maintenance procedure that predicts a repair period using reliability function and instantaneous failure rate based on fatigue test and load history data. Additionally, this method is applied to the end beam of an uncovered freight train, which is the brake part, and its usefulness is examined and analyzed.
Optimization of process parameters for recycling of mill scale using Taguchi experimenal design
백석흠,홍순혁,조석수,장득열,주원식 대한기계학회 2010 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.24 No.10
The present work submits an investigation about the optimum process parameters and quality improvement of mill scale recycling. With increasing concerns on environmental issues, the recycling of materials of all types has become an important issue. In this paper, an optimization method is developed to improve quality in mill scale recycling. The optimum configuration of process parameters to achieve high metallization efficiency was determined by experiments. The Taguchi method, the signal-to-noise (S/N) ratio, the analysis of variance (ANOVA) and rsponse surface optimization are employed to find the main effects and to determine their optimum process parameters. The significant process parameters were identified and their effects on mill scale recycling were studied. Finally, a confirmation experiment with the optimal levels of the process parameters was carried out to demonstrate the effectiveness of the Taguchi method.
Thermal design criteria for long-term durability of ceramic catalyst substrates
백석흠,조석수 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.10
The automotive industry has traditionally used ceramic honeycomb substrates as catalyst carriers. The long-term durability of a passenger car’s converter is assessed by examining the thermal stresses resulting from the temperature variations experienced under various driving conditions. These thermal stresses constitute the majority of the total stress that the ceramic catalyst substrate experiences while in service. The radial and axial temperature distributions were measured, and the thermal stress was calculated by using the thermal expansion coefficient according to the measured temperature. The threshold stress was determined from the fatigue constant, the required lifetime and the duration of the short term strength tests. The radial temperature variation was higher than the axial temperature variation,and the axial stress was higher than the radial stress because the thermal stress is dependent on the elastic modulus. The radial and axial stresses exist below the threshold thermal stress over the entire engine speed range.
통계학적 방법을 이용한 다목적 최적화에 관한 SQP의 적용
백석흠(Seok Heum Baek),이동우(Dong Woo Lee),이경영(Kyoung Young Lee),조석수(Seok Swoo Cho),주원식(Won Sik Joo) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.5
A recent research and development has the requirement for the optimization to shorten design time of modified or new product model and to obtain more precise engineering solution. General optimization problem must consider many conflicted objective functions simultaneously. Multi-objective optimization treats the multiple objective functions and constraints with design change. But. real engineering problem doesn't describe accurate constraint and objective function owing to the limit of representation. Therefore this study applies variance analysis on the basis of structure analysis and DOE to the vertical roller mill for portland cement and proposed statistical design model to evaluate the effect of structural modification with design change by performing practical multi-objective optimization considering mass stress and deflection.
메타모델 기반 다단계 해석을 이용한 순차적 최적설계 알고리듬
백석흠(Seok-Heum Baek),김강민(Kang-Min Kim),조석수(Seok-Swoo Cho),장득열(Deuk-Yul Jang),주원식(Won-Sik Joo) 대한기계학회 2009 大韓機械學會論文集A Vol.33 No.9
An efficient sequential optimization approach for metamodel was presented by Choi et al.(13) This paper describes a new approach of the multilevel optimization method studied in Refs. [2] and [20,21]. The basic idea is concerned with multilevel iterative methods which combine a descent scheme with a hierarchy of auxiliary problems in lower dimensional subspaces. After fitting a metamodel based on an initial space filling design, this model is sequentially refined by the expected improvement criterion. The advantages of the method are that it does not require optimum sensitivities, nonlinear equality constraints are not needed, and the method is relatively easy to understand and use. As a check on effectiveness, the proposed method is applied to an engineering example.