• 한국자동차공학회논문집
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• 제22권4호
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• pp.131-137
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• 2014

The SUV has a risk of rollover because of the highness of center of mass. In this paper the roll-behavior of a SUV in turning motion is analyzed. Dynamic model of the vehicle on the slope is developed and simulation is carried out using the software ADAMS/Car. The results show that the relational expression between the ground force acting on the tire and the roll motion is well established. It is also identified that the driving state of the vehicle becomes unstable at the lower or upper position of the slope.

• 소성∙가공
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• 제13권2호
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• pp.154-159
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• 2004

Deformation surrounding the hole in the tube during the hydropiercing process has been investigated in this study. The tube is expanded and internally pressurized between upper and lower dies, and a piercing punch is driven forcefully through a cross passage in the die and through the wall of the tube. The pressurized fluid within the tube provides support to the wall of the tube during a piercing step to form a hole in the tube having less deformation surrounding the hole in the tube. The deformation area may be fully retracted to a substantially flat form or partially retracted to a countersunk form. In this study, a mathematical model that can predict deformation surrounding the hole has been proposed and experimentally verified by actual hydropiercing test.

• 한국정밀공학회지
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• 제21권4호
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• pp.132-139
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• 2004

The open section members have been used as the members of vehicle such as automotives, airplanes and trains. When vehicles are crashed, these members have absorption of the energy and it is necessary for retainment of the survival space, and as the result, the prediction for the displacement of members in this case of the crash of vehicles is very important. The displacements of members in this case of the crash of automotives show combined aspect of both axial collapse and bending collapse. In the rollover accident when bending collapse happen, the collapse of each members is progressed by the plastic hinge which made from bending moment, and therefore the research for the behavior of members under bending moment after collapse is necessary to determine the internal energy which the members can absorb and the deformed shapes of the members on the step of design. In this paper, the characteristics of bending collapse at the members of the open cross-section were studied with experiment and numerical analysis. We made a comparative studied of the result of the experiment, and changed the axis according to the parallel-axis theorem.

• 한국자동차공학회논문집
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• 제20권2호
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• pp.47-55
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• 2012

This work deals with dynamic analysis of a monorail system with magnetic caterpillar where magnets are embedded inside each articulated element of the caterpillar, augmenting traction force of main rubber wheels to climb up slope up to 15 degree grade. Considerations are first given to determine stiffness of the primary and secondary suspension springs in order for the natural frequencies of car body and bogie associated with vertical, pitch, roll and yaw motion to be within generally accepted range of 1-2 Hz. Equations for calculating magnetic force needed to climb up given slope are derived, and a magnetic caterpillar system for 1/6 scale monorail is designed based on the derivation. To assess the hill climbing ability and cornering stability, and make sure smooth operation of the side and vertical guiding wheels which is critical for safety, a multibody model that takes into account of every component level design characteristics of car, bogie, and caterpillar is set up. Through hill climbing simulation and comparison with measurement of the limit slope, the validity of the analysis and design of the magnetic caterpillar system are demonstrated. Also by studying the curving behavior, maximum curving speed without rollover, functioning of lateral motion constraint system, the effects of geometry of guiding rails are studied.

• 드라이브 ㆍ 컨트롤
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• 제16권2호
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• pp.8-14
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• 2019

A typical gantry crane is generally used to lift and transport objects in various workplaces. Most of the supporting structures in a gantry crane are fixed on the ground while the moving hoist is running overhead along the girder. There are some disadvantages to its long installation time and high installation cost. Therefore, a hydraulic based gantry crane was studied to solve the issues of typical gantry cranes. The supporting structure of the proposed gantry crane consisted of a hydraulic cylinder and telescopic boom. The dimension of the proposed gantry crane can be decreased due to its simplified structure. The analytical and theoretical methods were used to verify the structural stability of the proposed crane. The most severe load condition was considered for the analysis, and the stress and deflection of the structure are analyzed. The simulation results were as expected from the theoretical analysis. Finally, the structural and dynamic safety of the proposed hydraulic based gantry crane was validated. The obtained results can be used as guidelines in the design process of the hydraulic based gantry crane.

• Design & Manufacturing
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• 제16권3호
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• pp.28-33
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• 2022

The recent increasing application rate of advanced high-strength steel(AHSS) for automotive parts makes it difficult to ensure the durability of forming tools. Significant load and friction generated during the piercing process of AHSS increase the wear rate and the damage degree to dies. These harsh process conditions also yield product failures, such as dimensional inconsistency of pierced holes and insufficient quality of hole's sheared edge. This study analyzed the effect of punch wear on the sheared surface of pierced parts and the forming load during the piercing process. Wear-shaped punches showed approximately 20% higher piercing load than normal-shaped punches, and the rollover ratio of the sheared surface also increased. It is considered that the dull edge of wear-shaped punches does not penetrate directly into the material but shears after tensioning it in a piercing direction. In addition, wear-shaped punches experienced compressive load even after completing the piercing process during the down-stroke and tensile load during the up-stroke. This load variation is related to the smaller diameter piercing holes produced by wear-shaped punches compared to normal-shaped punches. Thus, we demonstrated the predictability of the wear level of dies through a comparative analysis of the piercing load pattern.

• The Journal of Asian Finance, Economics and Business
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• 제9권1호
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• pp.133-142
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• 2022

This study examines the relationship between debt maturity structure and bankruptcy risk. There are various studies of leverage's effect on bankruptcy risk. Debt maturity, however, has not received the attention it deserves, especially in emerging markets with a high degree of information asymmetry. Using Vietnamese listed company data and various estimations, we find that leverage is positively associated with the likelihood of default. Importantly, short-term leverage shows a significantly positive effect on bankruptcy risk, while long-term leverage does not show significant results. The findings highlight that rollover risk firms are exposed to when using short-term debt increases bankruptcy risk. Meanwhile, firms do not cope with this risk in case of long-term debt adoption. High information asymmetry in emerging markets may be the main reason for the difference. The result is robust for subsamples of firms in different financial conditions, in concentrated and competitive industries, as well as for manufacturing and non-manufacturing companies. We also find that firms in a better financial situation and concentrated industries experience a higher short-term leverage effect than their counterparts. We, however, do not find a significant difference in the impact between manufacturing and non-manufacturing companies. This paper is among the first to examine the relation between debt maturity and bankruptcy risk in Vietnam.

• 대한교통학회지
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• 제26권2호
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• pp.7-15
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• 2008

자동차 안전도평가제도는 제작사가 보다 안전한 자동차를 제작하도록 유도하기 위해 충돌시험 등을 통하여 자동차의 안전성을 평가하고, 그 결과를 소비자에게 공개하고 있다. 이것은 자동차 사고로 인한 사회적 손실을 감소시킬 수 있는 효과적인 자동차 안전정책 중의 하나로써, 우리나라는 1999년부터 건설교통부 주관으로 신차평가를 실시하고 있다. 현재 안전도평가 대상차종이 크게 증가하여 안전도평가 대상 차종의 확대가 필요한 시점임에도 불구하고, 현실은 그렇지 못한 실정인데, 그 이유로는 평가인력, 시설 및 비용 등 여러 가지가 있겠으나, 가장 근본적인 이유는 자동차 안전도평가제도의 효과를 정확하게 파악하지 못하기 때문인 것으로 판단된다. 이에 본 연구에서는 자동차 안전도평가제도를 통해 자동차제작사가 자동차의 안전도를 향상시킴으로써 교통사고 발생시 사고의 심각도를 얼마나 줄여줄 수 있는지를 정량적으로 분석함으로써 자동차 안전도평가제도의 효과를 측정해 보고자 하였다. 안전도평가 항목 중 이용가능한 자료가 있는 정면충돌만을 대상으로 정면충돌로인한 사상자 수를 추정하고 안전도가 향상된 차종의 판매대수를 이용하여 자동차 안전도평가제도의 효과를 측정할 수 있는 방법을 개발하였다. 2005년도 자료를 이용하여 정면충돌사고 시 사상자 감소분을 추정해 본 결과, 자동차 안전도평가제도를 시행함으로써 자동차 안전도가 향상되어 2005년 1년 동안 교통사고로 인한 사망자는 약 1.51명, 부상자는 약 446명 감소한 것으로 나타났다.

• 제어로봇시스템학회논문지
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• 제20권1호
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• pp.87-93
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• 2014

Conventional two-wheeled balancing robots are limited in terms of turning speed because they lack the lateral motion to compensate for the centrifugal force needed to stop rollover. In order to improve lateral stability, this paper suggests a two-wheeled balancing mobile platform equipped with a tilting mechanism to generate roll motions. In terms of static force analysis, it is shown that the two-body sliding type tilting method is more suitable for small-size mobile robots than the single-body type. For the mathematical modeling, the tilting-balancing platform is assumed as a 3D inverted pendulum and the four-degrees-of-freedom equation of motion is derived. In the velocity/posture control loop, the desired tilting angle is naturally determined according to the changes of forward velocity and steering yaw rate. The efficiency of the developed tilting type balancing mobile platform is validated through experimental results.

• 항공우주시스템공학회지
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• 제11권6호
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• pp.17-25
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• 2017

항공기가 지상에서 주행할 때 지면과 타이어 사이에 걸리는 수직하중 정보는 마찰력, 횡력 계산 시 사용되는 등 항공기 거동에 있어서 주요한 변수이다. 그러나 실제 항공기 주행 시 실시간으로 수직하중 정보를 얻기 힘들고, 실제 시험에서 발생 가능한 비정상적 활주 상황을 방지하기 위하여 사전 해석을 통해 타이어 수직하중 및 항공기 지상 거동 특성을 예측해 볼 필요가 있다. 본 논문에서는 VI-Aircraft S/W를 이용하여 착륙장치 및 Full-Aircraft 모델을 구성하였고 조향 해석 및 활주시험 상황 모사 해석을 통하여 항공기 지상 거동 특성에 대하여 분석하였다.