• 한국전자통신학회논문지
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• 제12권3호
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• pp.493-498
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• 2017

최근 국내 외에서 버스운행의 효율화 및 D2D(: Door to Door)서비스, 대중교통의 자율주행을 위해 교통데이터를 분석하여 다양한 분석결과를 도출해내고 있다. 하지만 대중교통, 특히 버스 지연시간의 예측을 위해 다양한 연구가 수행되고 있으나 단순분석, 데이터 취득의 한계로 현재까지의 연구는 미흡한 상태이다. 본 연구에서는 버스의 운행정보를 기반으로 요일, 날씨, 시간대 등의 데이터를 추가적으로 수집 가공하여 지연시간 추정을 수행하였다. 본 논문에서 제안하는 방법은 향후 변수를 추가하여 정확도를 향상시킴으로써 자율주행 대중교통 및 대중교통 관제시스템에 활용이 가능하다.

• Earthquakes and Structures
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• 제12권3호
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• pp.359-374
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• 2017

The seismic events in Northern Italy, May 2012, have revealed the seismic vulnerability of typical Italian precast industrial buildings. The aim of this paper is to present a seismic fragility model for Italian RC precast buildings, to be used in earthquake loss estimation and seismic risk assessment by comparing two building typologies and three different codes: D.M. 3-03-1975, D.M. 16-01-1996 and current Italian building code that has been released in 2008. Based on geometric characteristics and design procedure applied, ten different building classes were identified. A Monte Carlo simulation was performed for each building class in order to generate the building stock used for the development of fragility curves trough analytical method. The probabilistic distributions of geometry were mainly obtained from data collected from 650 field surveys, while the material properties were deduced from the code in place at the time of construction or from expert opinion. The structures were modelled in 2D frameworks; since the past seismic events have identified the beam-column connection as the weakest element of precast buildings, two different modelling solutions were adopted to develop fragility curves: a simple model with post processing required to detect connection collapse and an innovative modelling solution able to reproduce the real behaviour of the connection during the analysis. Fragility curves were derived using both nonlinear static and dynamic analysis.

• Smart Structures and Systems
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• 제18권6호
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• pp.1145-1167
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• 2016

This study presents a new method to computes analytical fragility curves of a structure subject to tsunami waves. The method uses dynamic analysis at each stage of the computation. First, the smooth particle hydrodynamics (SPH) model simulates the propagation of the tsunami waves from shallow water to their impact on the target structure. The advantage of SPH over mesh based methods is its capability to model wave surface interaction when large deformations are involved, such as the impact of water on a structure. Although SPH is computationally more expensive than mesh based method, nowadays the advent of parallel computing on general purpose graphic processing unit overcome this limitation. Then, the impact force is applied to a finite element model of the structure and its dynamic non-linear response is computed. When a data-set of tsunami waves is used analytical fragility curves can be computed. This study proves it is possible to obtain the response of a structure to a tsunami wave using state of the art dynamic models in every stage of the computation at an affordable cost.

• 소성∙가공
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• 제26권2호
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• pp.87-94
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• 2017

Center pillar, which is installed in the center of flank of car body, supports roof and door and ensures the safety of driver by reducing the damage of car body caused by impact. Recently, high-strength steel is widely used to manufacture the center pillar due to high stiffness and fuel efficiency. In this study, material properties of the high-strength steel, whose tensile strength is more than 780MPa, were obtained to produce the center pillar. Stamping was performed by considering the design parameters (blank holder force, press stroke, blank size and pad pressure) used in the actual filed. The drawbeads were included in the stamping process to reduce the amounts of wrinkling and spring back. Using the commercial software, Autoform R5.2 and Minitab, effects of design parameters of the stamping process upon spring back were analyzed and applied to the design process. The restriking process meets the target of under 0.5mm in the amount of spring back.

• 소성∙가공
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• 제28권6호
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• pp.347-353
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• 2019

The porthole extrusion process is a classic metal forming process to produce complex cross-section shaped aluminum profile. It is very difficult to design porthole die and extrusion process because of the complex shape of extrusion die and internal metal flow. The main variables in this process are ram speed, initial billet and tool temperature, and die shape. In general, the metal flow of porthole extrusion process can be divided into two steps. During the first step, the billet is divided into several parts in the porthole die bridge. During the second step, the divided billets are welded in the welding chamber. In the welding chamber, the level of welding pressure is very important for the quality of the final product. The purpose of this study is to increase the welding pressure in the welding chamber by using a two stage welding chamber. The porthole extrusion die was designed by using the Taguchi method with orthogonal array. The effectiveness of the optimized porthole die was verified by using the finite element analysis.

• 소성∙가공
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• 제28권6호
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• pp.321-327
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• 2019

In this study, a hot and cold forging process was investigated to produce a complex-shaped hub of dual clutch transmission with low material loss and high productivity. The process was designed by the commercial finite element (FE) analysis program, DEFORM-2D (hot forging) and 3D (cold forging). And, the material flow and ductile fracture characteristics were studied to check the surface crack initiation of the specimen. The simulation results indicated that the proposed process could manufacture the complex-shaped hub with no surface crack and high-efficiency compared to the conventional machining process. For verification the numerical results, the hub of the SCM440 was fabricated by the proposed process and the mechanical properties and microstructure evolution were studied. It was demonstrated that the suggested hot and cold forging process might be useful in producing the key components of the automobile industry as a high-efficiency and environmentally friendly process.

• 소성∙가공
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• 제7권3호
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• pp.233-245
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• 1998

A new approach has been proposed for the incremental analysis of the nonsteady state large deformation of planar anisotropic elastic-plastic sheet forming. A mathematical brief review of a constitutive law for the incremental deformation theory has been presented from flow theory using the minimum plastic work path for elastic-plastic material. Since the material embedded coordinate system(Lagrangian quantity) is used in the proposed theory the stress integration procedure is completely objective. A new return mapping algorithm has been also developed from the general midpoint rule so as to achieve numerically large strain increment by successive control of yield function residuals. Some numerical tests for the return mapping algorithm were performed using Barlat's six component anisotropic stress potential. Performance of the proposed algorithm was shown to be good and stable for a large strain increment, For planar anisotropic sheet forming updating algorithm of planar anisotropic axes has been newly proposed. In order to show the effectiveness and validity of the present formulation earing simulation for a cylindrical cup drawing and front fender stamping analysis are performed. From the results it has been shown that the present formulation can provide a good basis for analysis for analysis of elastic-plastic sheet metal forming processes.

• 소성∙가공
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• 제7권3호
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• pp.260-273
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• 1998

A new blank design method is proposed to predict the optimum initial blank shape in the sheet metal forming process. The rollback method for blank shape design takes the difference between final deformed shaped and target contour shape into account. Based on the method a computer program composed of blank design module FE-analysis program and mesh generation module is developed. The rollback method is applied to square cup drawing process with the flange of unifiorm size around its periphery to confirm its validity. The optimum initial blank shape is obtained from an arbitrary square blank after three modification. Good agreements are recognized between the numerical results and the published results for initial blank shape and thickness strain distribution. The optimum blank shape for two parts of automobile sub-frame is designed, The thickness distribution and the level of punch load is improved. Also the method is applied to design the weld line in the tailor-welded blank. It is concluded that the rollback method is an effective and convenient method for an optimum blank shape design.

• 소성∙가공
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• 제4권1호
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• pp.28-38
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• 1995

An integrated process planning system can determine desirable operation sequences even if they have little experience in the design of multistage cold forging process. This system is composed of seven major modules such as input module, pre-design module, formability check module, forming sequence design module, forming analysis module, FEM verification module, and output module which are used independently or in all. The forming sequence for the part can be determined by means of primitive geometries such as cylinder, cone, convex, and concave. By utilizing this geometrical characteristics(diameter, height, and radius), the part geometry is expressed by a list of the primitive geometries. Accordingly, the forming sequence design is formulated as the search problem which starts with a billet geometry and finishes with a given product one. Using the developed system, the sequence drawing with all dimensions, which includes the dimensional tolerances and the proper sequence of operations for parts, is generated under the environment of AutoCAD. Several forming sequences generated by the planning system can be checked by the forming analysis module. The acceptable forming sequences can be verified further, using FE simulation.

• 소성∙가공
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• 제19권1호
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• pp.25-31
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• 2010

To achieve desired microstructure and mechanical property of a manufacturing product, heat treatment process is applied as a secondary process after forging. Especially, quenching process is used for improving strength, hardness, and wear resistance since phase transformation occurs owing to rapid heat transfer from the surface of the specimen. In the present paper, a study on surface temperature measurement for water quenching of eutectoid steel was investigated. In order to determine the temperature history in experiments, three different measuring schemes were used by varying installation techniques of K-type thermocouples. Depending on the measured temperature distribution at the surface of the specimen, convective heat transfer coefficients were numerically determined as a function of temperature by the inverse finite element analysis considering the latent heat generation due to phase transformation. Based on the inversely determined convective heat transfer coefficient, temperature, phase, and hardness distributions in the specimen after water quenching were numerically predicted. By comparing the experimental and computational hardness distribution at three different locations in the specimen, the best temperature measuring scheme was determined. This work clearly demonstrates the effect of temperature measurement on the final mechanical property in terms of hardness distribution.