• 소성∙가공
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• 제4권4호
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• pp.390-397
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• 1995

A simple kinematically admissible velocity field is proposed to determine the final-stage extrusion load and the average extruded length in the square-die forward extrusion of non-axisymmetric bars from circular billets. The proposed velocity field is applied to the square-die extrusion of trochoidal gear-shaped bars and rectangular-shaped bars. The profile function of a rectangle is approximated by using a Fourier series. Experiments have been carried out with hard solder billets at room temperature. The theoretical predictions of the extrusion load are in good agreements with the experimental results and there is generally reasonable agreements in average extruded length between theory and experiment.

• 한국정밀공학회지
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• 제20권12호
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• pp.89-95
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• 2003

A PID controller integrated with a velocity feedback is designed for fluid power elevator model system in this study. In this case, for outside disturbance load a hydraulic cylinder and a pressure control valve are used. In this method overshoot is reduced and settling time becomes also shorter than the values achieved from the PID controller system only In conclusion a PID controller integrated with a velocity feedback is considered a suitable control method for fluid power elevator system.

• 한국정밀공학회지
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• 제17권11호
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• pp.158-164
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• 2000

In this study a computer program is developed for analyzing the elasto-plastic dynamic behaviors of the plate subjected to line-loading by a low-velocity impactor. The equilibrium equation associated with the Hertzian contact law is formulated to evaluate the transient dynamic behaviour of the impacted plate. Compared with an elastic analysis, the effects of material plasticity are presented. Consequently, in the case of elasto-plastic analysys, impulse decreases, displacements increase and contact time duration is longer than the elastic case for same finite element model. And the time variation of the impacting load is not significant due to the plasticity except at the beginning of impact duration, and the induced stresses of the plate are more realistic.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 1999년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Fall
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• pp.91-98
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• 1999

In this study a modified ground strain model is developed for an equivalent earthquake load and is applied to the seismic analysis of buried pipelines, The ground strain can be obtained using the ratio of a maximum ground velocity to a wave propagation velocity. To reflect soil conditions and seismic characteristics the wave propagation velocity is evaluated by a proposed dispersion curve based on wave energy distribution. In order to verify the procedures the observed earthquake data and the results of this study are compared. For the application of an equivalent earthquake load to the seismic analysis the buried pipelines are modeled using the beam theory. the results of the analyses are compared with those of a dynamic analysis code and those obtained from the response displacement method. Finally various parametric studies considering different soil conditions and seismic loads are examined.

• 대한토목학회논문집
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• 제4권4호
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• pp.13-23
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• 1984

본(本) 연구(硏究)의 목적(目的)은 조류(潮流)에 의한 부유사(浮遊砂)의 확산(擴散)현상에 대하여 2차원 비정상확산(非定常擴散)방정식을 유한차분법(有限差分法)을 이용하여 부유사의 농도분포(分布)를 계산할 수 있는 수치모형(數値模型)을 개발하는데 있다. 바닥으로부터 부상량(浮上量)의 계산은 개수로에서 얻어진 공식(公式) 이용하였으며, 확산계수는 Coleman의 경험공식(公式)을 사용하였다. 특히, 침강속도 감쇠효과와 연직유속이 고려되었다. 여러 가지 경우의 계산예(計算例) 통하여, 유속조차, 연직유속, 침강속도의 감쇠효과 같은 각(各) 변수(變數)들이 부유사의 농도분에 미치는 영향이 검토 되었다.

• 한국기계가공학회지
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• 제12권6호
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• pp.69-76
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• 2013

This paper presents the development of the FCF method for the manufacturing of final products using numbers related to the minimum amount of work. The utilized product is a drum clutch, which is part of the transmission of an automobile. A double acting press is secured first and a prediction of the forming load on the practical material is made through an experiment with a plasticine model. Also, a finite element simulation using product shape and properties is performed, as well as a press experiment. A double acting press is manufactured that is suitable for a double acting experiment with a conventional hydraulic press(200 tons). A peripheral device for the press is additionally designed for experimental purposes. And, the press has as its essential points the drive speed, stroke control, etc., all of which influence the forming and is modified. Especially, a laser system is used for velocity measurement of two punches. The forming load of a practical material is predicted in order to derive a forming load formula for cold conditions on the basis of approximate similarity theory. Finite element analysis of the relative velocity ratio(RVR), etc., for most suitable flow defect(unfilling, etc.) prevention is achieved as well. The results are verified through a press experiment.

• Advances in nano research
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• 제13권4호
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• pp.369-378
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• 2022

Dynamic study of concrete plates under impact load is presented in this article. The main objective of this work is presenting a mathematical model for the concrete plates under the impact load. The concrete plate is reinforced by carbon nanoparticles which the effective material proprieties are obtained by mixture's rule. Impacts are assumed to occur normally over the top layer of the plate and the interaction between the impactor and the structure is simulated using a new equivalent three-degree-of-freedom (TDOF) spring-mass-damper (SMD) model. The structure is assumed viscoelastic based on Kelvin-Voigt model. Based on the classical plate theory (CPT), energy method and Hamilton's principle, the motion equations are derived. Applying DQM, the dynamic deflection and contact force of the structure are calculated numerically so that the effects of mass, velocity and height of the impactor, volume percent of nanoparticles, structural damping and geometrical parameters of structure are shown on the dynamic deflection and contact force. Results show that considering structural damping leads to lower dynamic deflection and contact force. In addition, increasing the volume percent of nanoparticles yields to decreases in the deflection.

• 한국자동차공학회논문집
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• 제19권6호
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• pp.68-75
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• 2011

A vehicle fuel economy is very important issue in view of fuel cost and environmental regulation. It has been improved according to the performance improvement of the vehicle engine, power train and many components. It was evaluated at given mode (LA-4, FTP-75, etc) on an engine dynamometer or computer simulation program. In this paper, the fuel economy improvement cruise control algorithms as controling a vehicle velocity by road load calculated and predicted in a real expressway with gradient was studied. Firstly, the altitude and distance data which was measured with GPS sensor was already installed in the ECU of a vehicle. Then the vehicle equipped with GPS receiver is driven the same expressway. The ECU calculates the gradient angle and the in-/decreasing velocity using the gradient angle by comparing the current received distance and altitude data from GPS with the saved data ahead of the vehicle. Therefore the ECU can calculate and predict the vehicle velocity considering tolerance velocity of next position with running. Then the ECU controls the vehicle velocity to meet this predicted velocity in all section. Three cruise control algorithms with the different velocity profiles for the improvement of fuel economy are proposed and compared with the computer simulation results that the vehicle runs on Youngdong expressway. The proposed CVELCONT2 and CVELCONT3 algorithms were improved 3.7% and 4.8% of fuel economy compared with CONSTVEL which is steady cruising algorithm. These two algorithms are recommended as the Eco-cruise drive methodologies in this paper.

• 한국방재안전학회논문집
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• 제10권1호
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• pp.75-84
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• 2017

내풍설계에서 기본풍속의 경우 우리나라는 10분 평균풍속을 이용하고 있지만, 기후변화와 태풍의 직간접 영향 및 강도증가로 인한 순간최대풍속이 구조물에 미치는 영향이 더 크다는 사실이 알려지고 있고, 일부 다른 나라에서는 이러한 순간풍속의 효과를 고려 3초의 평균풍속을 이용하고 있다. 본 논문에서는 1973-2016연까지의 일순간최대풍속의 확률과정, 통계적 성질, 난류의 특성 등을 평가하기 위하여 대표지점(17개 지점)을 선정했다. 선정된 각 지점에 대한 일순간최대풍속자료는 기상청으로부터 획득했다. 획득된 순간풍속의 해석결과 다음과 같은 결론을 얻었다. 1. 제주 서귀포 여수 부산에서의 8 7 9월에 0.2~0.35%로 나타났고, 서울 대관령은 3 4 5월에 0.25%로 나타났다. 2. 확률과정의 왜도평가에서 해안지역보다는 내륙지역에서의 더 큰 비정규성을 나타냈다. 3. 인접지역의 상관계수 평가에서 서울 인천(0.8), 대전 청주(0.75), 제주 서귀포(0.72) 순으로 나타났으며, 대관령 강릉은(-0.07), 전주 군산(0.0)은 인접지역의 영향이 거의 없는 것으로 나타났다.

• 대한토목학회논문집
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• 제2권3호
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• pp.15-22
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• 1982

이 연구(硏究)는 이동하중(移動荷重)과 축하중(軸荷重)이 작용(作用)하는 무한(無限)보에 휨모멘트를 해석(解析)하고 공진선도(共振線圖)를 나타낸다. 하중(荷重)과 함께 이동(移動)하는 좌표계(座標系)에서 정상해(定常解)를 구하였다. 지지(支持)된 기초(基礎)는 감쇠(減衰)를 포함하였고 축하중(軸荷重)과 감쇠(減衰)와 이동하중속도(移動荷重速度)가 보의 응답(應答)에 미치는 영향(影響)을 연구(硏究)하였다. 비감표(非減表)와 임계감표(臨界減表)의 경우에 대하여도 연구(硏究)하였다. 몇몇의 이동하중속도변수(移動荷重速度變數), 축하중변수(軸荷重變數), 감표변수(減表變數)에 따른 보의 휨모멘트 윤곽(輪廓)이 도표(圖表)로 나타내졌다.