• 한국소음진동공학회논문집
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• 제25권5호
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• pp.352-360
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• 2015

Squeal noise is a harsh, high-pitched sound that occurs when railways are running at sharp curve tracks. The cause of squeal noise is known to be the transient lateral traction force between wheel and rail. Field measurements are too difficult to control the parameters. Thus, the scaled test rig should have been made in order to investigate the generating mechanism of squeal noise. The unique feature of our test rig, HSTR(Hongik Squeal Testing Rig), is that DOFs of its wheelset are as close to as those of the real railway. The attack angle and running speed of the rail roller are controlled in real time for simulating a transient characteristic of driving curve. The environment conditions, such as given axle load, running speed, and wheel's yaw angle have been identified for generating squeal noise and the squeal noise itself has been measured. The relation between wheel creepage and creep force in lateral direction and the criteria for squeal noise have been investigated, which results has been verified by finite element method.

• 한국철도학회논문집
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• 제10권6호
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• pp.701-708
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• 2007

기존선 속도향상을 위해 개발된 틸팅열차는 기존열차에 비하여 승차감의 저하 없이 곡선부를 더욱 빠르게 주행할 수 있기 때문에 전체 운행시간을 단축시킬 수 있는 장점이 있다. 그러나 일반적으로 주행열차에 의해 궤도에 발생하는 힘은 주행속도의 함수로 표현되므로 주행속도가 증가하는 만큼 궤도가 부담해야할 힘의 크기도 증가하게 된다. 따라서 본 연구에서는 틸팅차량의 기존선 곡선부 주행 시 내 외측 레일의 탈선계수를 산정하여, 곡선반경 증속 여부, 선로개량 유 무에 따른 주행안정성을 평가하였으며, 기존에 운행중인 일반열차와 고속열차의 주행안정성을 비교, 분석하였다. 연구결과, 측정대상 구간에서 측정된 동적 윤중을 이용하여 산출한 동적 윤중 감소량은 차체진동을 고려한 차량 전복에 대한 동적윤중 감소한계치를 모두 만족하는 것으로 나타나 향후 틸팅차량 투입시 대상구간에서의 윤중 감소에 따른 열차탈선의 위험은 없을 것으로 판단된다.

• 반도체디스플레이기술학회지
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• 제6권4호
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• pp.11-15
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• 2007

As preparing electrode for the OLED with the sputtering process, in order to be lower damage of the bottom organic layer and increase the life-time of the OLED, we prepared Al electrode for that by using Facing Targets Sputtering (FTS) system. Al electrode directly deposited on the cell (LiF/EML/HTL/Bottom electrode). Deposition condition was the working gas (Ar, Kr and Ar+Kr) and working gas pressure (1 and 6 mTorr). The film thickness and I-V curve of Al/cell were evaluated by a $\acute{a}$-step profiler and a semiconductor parameter (HP4156A) measurement. The thin film surface image was observed by a Atomic Force Microscope (AFM). In result, in comparison with about 11 [V] of the turn-on voltage of Al/cell with using the pure Ar gas, when Al thin film was deposited using the Ar-Kr mixture gas, the surface morphology was improved in some region and the turn-on voltage of Al/cell could be decreased to about 7 [V].

• 한국구조물진단유지관리공학회 논문집
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• 제9권1호
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• pp.189-196
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• 2005

임펄스 비와 하중최대치의 비로 작성된 손상곡선을 이용하여 충격하중의 임펄스와 하중의 크기가 구조물의 거동에 미치는 영향을 분석하였다. 단기에 종료하는 충격하중의 경우 관성력의 영향으로 하중의 크기보다는 임펄스가 구조물 손상에 주요변수가 되며, 관성력을 극복할 충분한 시간을 갖는 장기하중이 작용하는 경우에는 임펄스보다는 하중의 크기가 구조물 손상에 주요변수가 된다. 지반충격에 의한 구조물의 손상은 단기인 경우에는 지반의 최대입자속도가 그러나 장기인 경우에는 최대입자가속도가 손상의 주요 변수가 된다.

• 천문학회보
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• 제44권1호
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• pp.48.2-48.2
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• 2019

Tidal disruption events (TDEs) provide evidence for quiescent supermassive black holes (SMBHs) in the centers of inactive galaxies. TDEs occur when a star on a parabolic orbit approaches close enough to a SMBH to be disrupted by the tidal force of the SMBH. The subsequent super-Eddington accretion of stellar debris falling back to the SMBH produces a characteristic flare lasting several months. It is theoretically expected that the bolometric light curve decays with time as proportional to $t^{-5/3}$. However, some of the observed X-ray light curves deviate from the $t^{-5/3}$ decay rate, while some of them are overall in good agreement with the $t^{-5/3}$ law. Therefore, it is required to construct the theoretical model for explaining these light curve variations consistently. In this paper, we revisit the mass fallback rates semi-analytically by taking account of the stellar internal structure, orbital eccentricity and penetration factor. We find that the mass fallback rate is shallower than the standard $t^{-5/3}$ decay rate independently of the polytropic index, and the orbital eccentricity only changes the magnitude of the mass fallback rate. Furthermore, the penetration factor significantly can modify the magnitude and variation of mass fallback rate. We confirm these results by performing the computational hydrodynamic simulations. We also discuss the relevance of our model by comparing these results with the observed light curves.

• 한국안광학회지
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• 제13권1호
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• pp.5-13
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• 2008

목적: 각막 부착 콘택트렌즈에는 어떠한 힘이 작용하며 또한 이 힘에 따른 렌즈의 운동을 알아보고자 본 해설을 작성하였다. 방법: 렌즈 아래 눈물층에는 모세관작용에 따른 힘이 발생하고 렌즈 회전에 따른 눈물층 간격변화에 기인하는 복원력이 발생한다. 눈깜빡임에 따라 콘택트렌즈는 눈꺼풀-렌즈 사이 마찰력과 눈꺼풀의 가속도에 의한 힘, 눈물층의 복원력 및 점성저항력에 의해 운동(움직임)이 결정된다. 눈깜빡임 도중/후 매순간 렌즈의 위치를 예측할 수 있는 미분방정식과 그 수치계산 프로그램 모델을 수립하였다. 이 컴퓨터 모델을 사용하여 눈깜빡임 주기, 렌즈의 BC, 눈꺼풀 압력 변화에 따른 매 순간 렌즈 위치를 예측할 수 있었다. 결과: 눈깜빡임 주기가 길수록, 눈꺼풀 압력이 클수록 눈꺼풀에 의한 마찰력 영향이 커져 렌즈 움직임이 커지며 BC가 증가할수록 눈물층 간격이 증가하여 점성저항력이 감소하며 따라서 렌즈 움직임이 커지는 것을 알 수 있었다. 눈깜빡임 후 렌즈는 눈물층 간격 변화에 따른 복원력과 눈물층의 점성저항력에 의해 진폭이 감소하는 진동을 하면서 평형위치로 복귀하게 된다. 이 경우 BC가 증가할수록 저항력이 감소하여 평형 위치로의 접근이 빨라진다. 결론: 콘택트렌즈의 움직임은 렌즈-각막 사이 눈물층의 물성 및 형상과 아울러 눈깜빡임에 의해 지배된다.

• 한국지반공학회논문집
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• 제23권4호
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• pp.79-90
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• 2007

모래지반에 대하여 계측기를 부착한 강널말뚝을 진동항타하고 항타과정을 통해서 계측된 자료를 분석하여 진동항타시 강널말뚝의 진동항타거동을 살펴보았다. 특히, 강널말뚝에 대한 진동항타시 말뚝에 작용하는 응력, 이론적인 항타력과 실제 말뚝에 전달되는 힘의 차이를 반영하는 효율계수, 강널말뚝의 강체거동 여부, 지반의 동적 저항특성, 강널말뚝의 관입특성 등을 분석하였다. 강널말뚝의 진동관입시 말뚝은 거의 강체로 거동하였으며 말뚝머리부에 작용하는 응력의 최대값은 재료의 인장강도보다 상당히 작았다. 진동관입중 실제 말뚝머리부에 전달되는 최대하중은 이론식에 의해 계산된 값의 72% 정도였다. 가속도-시간이력곡선으로부터 4개의 관입깊이에 대해 유도된 변위-시간이력곡선에서의 변위진폭값은 진동기 공운전시의 진폭값의 약 16$\sim$75% 정도인 것으로 나타났다.

• 한국강구조학회 논문집
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• 제8권3호통권28호
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• pp.139-150
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• 1996

H/T(High Tension) bolt is generally being used in joining the members of steel structure. It has some difficulties in management such as an adequate fastening force and a selection of proper instrument for fastening. T/S(Torque Shear Type High Tension) bolt which is more convenient and easier than H/T bolt in quality control has recently been developed. T/S bolts are produced and widely used these days in domestic, but those have not a detail regulation for their on. Those are only being used according to the specification for the H/T bolts. In this study, we tried to confirm the soundness of T/S bolts by the fatigue test of the modified specimens. First, we measured the reduction rate of the initial axial force with time at bolts. Second, we investigated the slip forces of bolts when the test specimen is loaded in tension. Third, we implemented the fatigue tests. During the test, we measured the variation of the axial forces of bolts under the cyclic loading. Finally, we compared and analyzed the fatigue behavior of H/T and T/S bolt, by S-N curve diagrams that are obtained in this study.

• International Journal of Safety
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• 제10권2호
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• pp.21-26
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• 2011

In 2001, an independent official board was constituted in Japan to investigate aircraft and railway accidents. In the past 10 years, many accidents and serious incidents have been investigated and these official reports were published by the board, on which the author had sat for 9 years as boarding member. In the interim, there were several train disasters which mocked our trust in railways and also many apparent trivial incidents. In recent years, serious incidents, which a door of running rail cars opens suddenly with some trouble, happen 2 or 3 times in a year. For the past 10 years, such incidents have happened 14 times and 13 cases of them were closed by the board mentioned above. In these 13 cases, no one fell off the rail car, so that the death toll was none luckily. In this paper, these 13 serious incidents are picked up among all the reports published by the board and outlined using some tables. Especially, fall accidents of passengers are discussed mainly from the view point of impact force and duration time. Then, the equation of HIC (Head Injury Criteria) and the risk curves in terms of the HIC are dealt with properly.

• 한국기계가공학회지
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• 제18권2호
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• pp.65-72
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• 2019

In long freight trains, there is a brake time delay in neighboring freight cars, which causes damage and fractures in the couplers, especially at their knuckle. A problem in the couplers of the cars can cause derailment and damages of human life and property. In this study, maximum forces on the couplers are studied when a long freight car brakes with the brake delay time and coupler gap. We make a dynamic model of 50 freight cars and couplers, applying contact between the couplers and a characteristic curve to express the force and displacement of the buffers using SIMPACK, which is a multi-body dynamics program. We use EN 14531-2, which is a standard of freight car brakes, to verify the dynamic model. Then, we compare the analyzed impact force with the coupler knuckle standard after applying the two carriages of a locomotive in the model based on the dispersed double head control system. The result shows that all coupler gap conditions satisfy the infinite lifetime of the material when the brake delay time is 0.1 second.