• International Journal of Automotive Technology
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• 제5권3호
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• pp.173-180
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• 2004

An intensive study was conducted for the crash worthy structural design of the recently developed Korean High Speed Train (KHST). Two main design concepts were set up to protect both crews and passengers from serious injury in heavy collision accidents, and to reduce damage to the train itself in light collision accidents. A collision against a movable 15-ton rigid obstacle at 110 kph was selected from train accident investigations as the accident scenario for the heavy collisions. A train-to-train collision at the relative velocity of 16 kph was used for the light collision. The crashworthiness behaviors of KHST were numerically evaluated using FEM. Analysis results using 1-D collision dynamics model of the full rake consist and 3-D shell element model of the front end structure showed good crashworthy responses in a viewpoint of structural design. Occupant analyses and sled tests demonstrated that KHST performed well enough to protect occupants under the considered accident scenarios. Finally our numerical approaches were evaluated by a real scale collision test.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.199-204
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• 2001

Big accidents of flyings, vessel, subways, gas equipments, buildings and bridge happens frenquently. Therefore many people are suffering harm of property. The destruction cause of macaine components is almost accused by fatigue. This study is test for STS304 specimen using pure and cantilever bending state. Rounded specimen and notched specimen including fracture surface investigation was comparatively experimented, fatigue life according to degree of surface finishing was examined. Fatigue fracture probability of notched canilever specimens were predicted by P-S-N curve, median rank and Weibull distribution. And at the relation with the rotational speed and stress, the fatigue life of the test specimen was higher at high speed than low speed.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2003년도 춘계학술대회 논문집
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• pp.724-729
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• 2003

The prototype of Korean high speed train (KHST), composed of two power cars, two motorized cars and three trailer cars, has been designed, fabricated and tested by the domestic researchers. In this paper, the body vibration has been reviewed from the viewpoint of the vehicle's safety and the vibration limits for components and sub-assemblies mounted on the car-body using by the experimental method. The on-line test of KHST has been carried out up to 260 km/h in the KTX line and proved that KHST has no problems in the vehicle's safety and the vibration limits at this speed. And the characteristics of body vibrations has been predicted at 300 km/h and 350 km/h by fitting curve about the measured acceleration signals.

• 대한토목학회논문집
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• 제33권5호
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• pp.2049-2056
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• 2013

정보통신의 발달로 정보화시대가 도래하면서 속도에 대한 인간의 욕구가 증가하고 있는 가운데, 교통분야에서도 이동성을 증대시키기 위한 초고속도로 건설에 대한 설계가 제기되고 있다. 본 연구는 설계속도가 120km/h를 초과하는 초고속도로 건설시 운전자가 설계속도의 수준으로 주행할 수 있는가를 분석하기 위한 연구를 수행하였다. 본 연구를 수행하기 위해서 설계속도가 상이하여 도로의 선형과 규격이 향상되면 운전자가 불안을 느끼는 주행속도도 증가하는지를 알아보았다. 실험은 피실험자 30명을 모집하여 뇌파분석기를 장착시킨 후 설계속도가 상이한 도로를 실제로 주행하고, simulator를 통해 가상으로 주행하면서 불안감을 느낄 때 발생하는 ${\beta}$파의 파워를 비교하였다. 이를 위한 실험구간은 강변북로(90km/h), 자유로(100km/h), 중앙고속도로(110km/h), 서해안고속도로(120km/h)로 선정하였다. 강변북로와 자유로는 주행속도가 80km/h - 130km/h, 중앙고속도로는 100km/h - 150km/h, 서해안고속도로는 110km/h - 160km/h 일 때의 불안뇌파 파워를 비교하였고, 시뮬레이션 주행은 일괄적으로 110km/h - 180km/h로 주행할 때 발생하는 불안뇌파 파워를 비교 분석하였다. 또한 paired t-test 검정을 통하여 불안뇌파가 증가하는 시점 속도를 통계적으로 검증하였다. 그 결과 시뮬레이션 주행 시 불안뇌파 증가시점의 속도는 실제 도로를 주행할 때 불안뇌파 증가시점보다 약 30km/h높게 나타났으며, 설계속도가 90km/h인 도로와 100km/h도로는 같은 속도에서 불안뇌파가 증가하여 도로의 선형과 규격에 차이가 적은 것으로 나타났다. 하지만 설계속도가 110km/h도로와 120km/h인 도로에서는 불안감을 느끼는 주행속도가 모두 증가하여 운전자는 도로의 선형과 규격이 향상됨에 따라 더 높은 속도로 주행할 수 있는 것으로 나타났다.

• Journal of Mechanical Science and Technology
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• 제20권12호
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• pp.2052-2060
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• 2006

The wear of engine valve and seat insert is one of the most important factors which affect engine performance. Because of higher demands on performance and the increasing use of alternative fuel, engine valve and seat insert are challenged with greater wear problems than in the past. In order to solve the above problems, a simulator was developed to be able to generate and control high temperatures and various speeds during motion. The wear simulator is considered to be a valid simulation of the engine valve and seat insert wear process with various speeds during engine activity. This work focuses on the different degrees of wear at three different singular test speeds (10 Hz, 25 Hz & multi-Hz). For this study, the temperature of the outer surface of the seat insert was controlled at 350$^{\circ}C$, and the test load was 1960 N. The test cycle number was $6.0{\times}10^6$. The mean ($\pm$standard error) wear depth of the valve at 10 Hz and 25 Hz was 45.1 ($\pm$3.7)$\mu$m and 81.7 ($\pm$2.5)$\mu$m, respectively. The mean wear depth of the seat insert at 10 Hz and 25 Hz was 52.7 ($\pm$3.9)$\mu$m and 91.2 ($\pm$2.7)$\mu$m, respectively. In the case of multi-Hz it was 70.7 ($\pm$2.4)$\mu$m and 77.4 ($\pm$3.8)$\mu$m, respectively. It was found that higher speed (25 Hz) cause a greater degree of wear than lower speed (10 Hz) under identical test condition (temperature, valve displacement, cycle number and test load). In the wear mechanisms of valves, adhesive wear, shear strain and abrasive wear could be observed. Also, in the wear mechanisms of seat inserts, adhesive wear, surface fatigue wear and abrasive wear could be observed.

• Tribology and Lubricants
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• 제38권2호
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• pp.33-40
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• 2022

In this study, we present rotor dynamic analysis and operation test of a turbo expander for a hydrogen liquefaction plant. The turbo expander consists of a turbine and compressor wheel connected to a shaft supported by two hydrostatic radial and thrust bearings. In rotor dynamic analysis, the shaft is modeled as a rigid body, and the equations of motion for the shaft are solved using the unsteady Reynolds equation. Additionally, the operating test of the turbo expander has been performed in the test rig. Pressurized helium is supplied to the bearings at 8.5 bar. Furthermore, we monitor the shaft vibration and flow rate of the helium supplied to the bearings. The rotor dynamic analysis result shows that there are two critical speeds related with the rigid body mode under 40,000 rpm. At the first critical speed of 36,000 rpm, the vibration at the compressor side is maximum, whereas that of the turbine is maximum at the second critical speed of 40,000 rpm. The predicted maximum shaft vibration is 3 ㎛, whereas sub-synchronous vibration is not presented. The operation test results show that there are two critical speeds under the rated speed, and the measured vibration value agrees well with predicted value. The measured flow rate of the helium supplied to the bearing is 2.0 g/s, which also agrees well with the predicted data.

• Journal of Advanced Marine Engineering and Technology
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• 제24권1호
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• pp.67-74
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• 2000

Recently, PTFE-polymide composites are being used self-lubricating parts for industrial field. Thus, this study is mainly concerned with friction and wear properties for the piston ring of non-lubricating air compressor which made of PTFE-polymide composites. The friction and wear test was carried out for the different composition ratio under the atomsphere room temperature and constant load of 7.69N and their friction and wear properties were compared with each other at various sliding speed. notable results are summarized as follows. PTFE 100% showed that friction coefficient was almost same values at 0.94 and 1.88m/s but the value was decreased at 2.83m/s because the friction temperature is higher than low speed. PTFE 80%-PI 20% showed the lowest mean friction coefficient at 2.83m/s. PTFE 20-PI 80% showed the highest friction coefficient at 0.94m/s and the value was decreased at high speed but the value is higher than other materials except PTFE 100 %. PI 100% showed the highest friction coefficient at 0.94 and 1.88m/s becuase adhesive wear mainly occurred that speed. PTFE 100% showed highest specific wear rate on the whole. Specific wear rate of PTFE 80%-PI 20% was almost the same value with PTFE 20%-PI80%. PI 100%showed the lowest value at high sliding speed because the friction surface was thicken and carbonated by high friction temperature.

• 설비공학논문집
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• 제15권1호
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• pp.25-31
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• 2003

This paper addresses an oil supply enhancement device to resolve a shortage of oil supply or no oil supply at all encountered at low speed operation for a variable speed reciprocating compressor used for household refrigerators. The oil supply enhancement device comprises a moving cylinder attached to the lower end of crankshaft and two of fluid diodes, each one at the inlet and outlet of the cylinder. Up-and-down movement of the cylinder against the lower end of the crankshaft together with the functioning of the two fluid diodes produces net oil flow from oil reservoir to inside the crankshaft. The experiment on the test bench has shown that enough oil supply into the oil feeding hole cu be made by using this device even at low speed range. Some analytical study has also been carried out to under-stand its oil supply mechanism.

• Tribology and Lubricants
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• 제9권1호
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• pp.62-69
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• 1993

Friction and wear behavior of a carbon/carbon composite material for aircraft brake material was experimentally investigated. Friction and wear test setup was designed and built for the experiment. Friction and wear tests were conducted under various sliding conditions. Friction coefficients were measured and processed by a data acquisition system and amount of wear measured by a balance. Stainless steel disk was used as the counterface material. Temperature was also measured by inserting thermocouple 2.5 mm beneath the sliding surface of the carbon/carbon composite specimen. Wear surfaces were observed by SEM, and analyzed by EDAX. The experimental results showed that sliding speed and normal force did not have significant effects on friction coefficient and wear factor of the composite. Temperature increase just below the surface was not large enough to cause any thermal degradation or oxidation which occurred at higher temperature when tested by TGA. Wear film was generated both on the specimen and on the counterface at relatively low sliding speed but cracks, grooves, and wear debris were observed at high sliding speed. Friction coefficient remained almost constant when the sliding speed or normal load was varied. It is believed that the adhesive and abrasive components contributed mainly to the friction coefficient. Wear behavior at low sliding speed was governed by wear film formation and adhesive wear mechanism. At high speed, fiber orientation, ploughing by counterface asperities, and fiber breakage dominated wear of the carbon/carbon composite.

• Tribology and Lubricants
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• 제18권6호
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• pp.377-383
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• 2002

The tribological role of mass transfer layer was studied with silver coatings under various ranges of load and sliding speed. Silver coating was performed with a functionally gradient coating method. Tests were per-formed in dry sliding conditions, using a ball-on-disk contact configuration, at the load of 0.0196-17.64 N and the sliding speed of 20-1,000 mm/s in ambient air. Optical microscope and EPMA analyses showed that contact surfaces were covered with the mass transfer layers of agglomerated wear particles depending upon the contact conditions, and they greatly influenced the tribological characteristics of the surfaces. However, the formation of mass transfer layer was suppressed as the sliding speed increased, and above a critical sliding speed, no mass transfer layer was able to form. For building up a general framework of triboiogical behavior of the coated silver films, all test data were summarized on a map whose axes are contact pressure and sliding speed.