• 한국지반공학회논문집
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• 제28권9호
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• pp.31-45
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• 2012

본 연구에서는 월파시 해안안벽에 작용하는 지진과 지진해일의 영향에 대하여 한계평형상태해석법을 적용하여 안정성을 검토하였다. 지진해일파력에 대하여 TWOPM-3D를 적용하였으며, 특히 안벽의 뒷채움재를 투과성재료로 가정하여 지진해일파가 월파 후에 안벽배후에 작용하는 파력을 산정하였다. 그리고, 수동상태와 주동상태 조건에서 해안안벽의 안정성에 영향을 주는 요인인 지진해일파고, 뒷채움재의 수위, 수평 수직지진가속도계수, 내부마찰각, 벽마찰각, 간극수압비 등을 변화하여 활동과 전도에 대한 안벽 안전율의 변화특성을 시간에 따라 검토하였다. 이로부터 지진과 지진해일파의 작용하에 지진해일파가 안벽을 월파하는 경우 수동상태에 대한 안전율은 결과적으로 안전율을 증가시키는 요인으로 작용하는 반면, 주동상태에 대하여 결과적으로 안전율을 감소시키는 요인으로 작용함을 확인할 수 있었다.

• Steel and Composite Structures
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• 제31권6호
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• pp.575-589
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• 2019

The main focus of this study is to numerically investigate the influence of strong earthquake and tsunami-induced wave impact on the response and behavior of a cable-stayed steel bridge with large caisson foundations, by assuming that the earthquake and the tsunami come from the same fault motion. For this purpose, a series of numerical simulations were carried out. First of all, the tsunami-induced flow speed, direction and tsunami height were determined by conducting a two-dimensional (2D) tsunami propagation analysis in a large area, and then these parameters obtained from tsunami propagation analysis were employed in a detailed three-dimensional (3D) fluid analysis to obtain tsunami-induced wave impact force. Furthermore, a fiber model, which is commonly used in the seismic analysis of steel bridge structures, was adopted considering material and geometric nonlinearity. The residual stresses induced by the earthquake were applied into the numerical model during the following finite element analysis as the initial stress state, in which the acquired tsunami forces were input to a whole bridge system. Based on the analytical results, it can be seen that the foundation sliding was not observed although the caisson foundation came floating slightly, and the damage arising during the earthquake did not expand when the tsunami-induced wave impact is applied to the steel bridge. It is concluded that the influence of tsunami-induced wave force is relatively small for such steel bridge with large caisson foundations. Besides, a numerical procedure is proposed for quantitatively estimating the accumulative damage induced by the earthquake and the tsunami in the whole bridge system with large caisson foundations.

• Structural Engineering and Mechanics
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• 제78권2호
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• pp.163-174
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• 2021

Track-bridge interaction has become an essential part in the design of bridges and rails in terms of modern railways. As a unique ballastless slab track, the longitudinal continuous slab track (LCST) or referred to as the China railway track system Type-II (CRTS II) slab track, demonstrates a complex force mechanism. Therefore, a comprehensive track-bridge interaction study between multi-span simply supported beam bridges and the LCST is presented in this work. In specific, we have developed an integrated finite element model to investigate the overall interaction effects of the LCST-bridge system subjected to the actions of temperature changes, traffic loads, and braking forces. In that place, the deformation patterns of the track and bridge, and the distributions of longitudinal forces and the interfacial shear stress are studied. Our results show that the additional rail stress has been reduced under various loads and the rail's deformation has become much smoother after the transition of the two continuous structural layers of the LCST. However, the influence of the temperature difference of bridges is significant and cannot be ignored as this action can bend the bridge like the traffic load. The uniform temperature change causes the tensile stress of the concrete track structure and further induce cracks in them. Additionally, the influences of the friction coefficient of the sliding layer and the interfacial bond characteristics on the LCST's performance are discussed. The systematic study presented in this work may have some potential impacts on the understanding of the overall mechanical behavior of the LCST-bridge system.

• 한국항공우주학회지
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• 제50권10호
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• pp.677-690
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• 2022

Actuator disk method 기반의 유동 해석자를 이용하여 수직 이착륙 복합형 비행체 중 하나인 이중 덕트 팬 항공기에 대한 공력해석을 수행하고 관련 지면 효과를 분석하였다. 회전 격자 기법을 이용한 해석결과와의 비교를 통해, 지면 효과 분석을 위한 해석자의 특성과 정확도를 함께 평가하였다. 지면과의 거리에 따른 공력 성능과 유동장 특성을 분석하였다. 지면과의 거리가 가까울수록 팬 추력은 증가하지만, 덕트, 동체, 날개의 수직력 감소로 인한 총 수직력 및 제자리 비행 효율의 저하를 확인하였다. 동체 하부의 유동장 분석으로부터 팬 후류와 지면 간의 상호작용에 의해 발생하는 지면 와류와 분수 유동을 확인하고, 이들이 비행체 공력 성능에 미치는 영향을 분석하였다. 속도 프로파일 비교/검토를 통해 비행체로부터의 거리와 방향에 따른 기체 주변 아웃워시의 강도와 특성을 분석하였다. 또한 콜렉티브 피치각에 따른 지면 효과의 영향을 확인하였다.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.89-90
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• 2002

Ball reducer (HERB Drive: High Efficient Wave Rolling Ball Drive) with waved grooves has many advantages over other types of reducers for high-reduction ratio, low noise and low energy loss, etc. The mechanism of force transmission is very similar to that of cam and follower in automobile valve train system especially in contact behaviors. In this study, we have investigated the traces of contact between ball and outer ring, and the dynamic contact behaviors of elastohydodynamic lubrication(EHL) with a certain reduction ratio. In order to verify the contact behaviors between ball and outer ring for the critical endurance lift, the contact velocity and load are computed for a cycle. During some intervals of a cycle, the contact velocity reverses its direction very suddenly. It is expected that changing the contact direction causes undesirable endurance performance because EHL film frequently col lapse at the moment of velocity reversal. From the computational investigation in this work, we hope to predict similar contact damages in other machinery due to this kind of contact behaviors, which is very typical in many contact phenomena.

• 대한기계학회논문집A
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• 제30권7호
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• pp.833-840
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• 2006

The paper presents a numerical solution to the problem of a hot rigid indenter sliding over a thermoelastic Winkler foundation with a thermal contact resistance at constant speed. It is shown analytically that no steady-state solution can exist for sufficiently high temperature or sufficiently small normal load or speed, regardless of the thermal contact resistance. However the steady state solution may exist in the same situation if the thermal contact resistance is considered. This means that the effect of the large values of temperature difference and small value of force or velocity which occur at no steady state can be lessened due to the thermal contact resistance. When there is no steady state, the predicted transient behavior involves regions of transient stationary contact interspersed with regions of separation regardless of the thermal contact resistance. Initially, the system typically exhibits a small number of relatively large contact and separation regions, but after the initial transient, the trailing edge of the contact area is only established and the leading edge loses contact, reducing the total extent of contact considerably. As time progresses, larger and larger numbers of small contact areas are established, unlit eventually the accuracy of the algorithm is limited by the discretization used.

• 한국세라믹학회지
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• 제42권6호
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• pp.399-404
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• 2005

Anti-reflection film was coated by using spherical silica nano colloidal particles and fumed silica particles. Silica colloid sol was reserved between two inclined slide glasses by capillary force, and particles were stacked to form a film onto the substrate as the upper glass was sliding. The deposition processes were studied to enhance the wavelength dependency of the light transmittance and to control the effective refractive index of the film. Both of the spherical and fumed silica particles showed an enhancement of $4.0-4.4\%$ in light transmittance by one step coating. The dependence of the transmittance on wavelength was largely improved at the longer wavelength by partial coating of fumed particles on the film of spherical particles. The effective refractive index of the film was controlled by removing latex particles that were co-deposited with silica particles. Using this process the light reflectance from one side of the glass substrate could be reduced from $4.2\%$ to $0.6\%$ although zero reflectance was not achieved due to the agglomeration of the latex particles.

• 한국지반공학회지:지반
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• 제6권4호
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• pp.53-64
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• 1990

말뚝의 지지력을 예측키 위한 수많은 방안들이 제안되어 왔으나,말뚝 재하시험에 의하는 방법 외에는 신뢰도가 낮은 실정이다. 그럼에도 불구하고 말뚝 재하시험 수행에는 많은 비용과 시간이 소요되어 극히 제한된 경우에만 적용되고 있다. 본 연구에서는 새로운 말뚝재하시험, "간편한 말뚝 재하시험 (SPLT)방법"을 소개한다. SPLT에서는 분리할 수 있는 선단부와 축소된 선단부가 시험말 뚝에 설계되어, 주면마찰력이 말뚝 선단부의 침하를 야기시키는 반력으로 작용하게 된다. 이에 따라 하중재하장치 또는 하중의 제작,설치 및 제거 과정이 생략될 수 있다. 생략될 수 있다.

• Tribology and Lubricants
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• 제22권3호
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• pp.127-130
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• 2006

DLC (Diamond Like Carbon) films show very desirable surface interactions with high hardness, low friction coefficient, and good wear-resistance properties. The friction behavior of hydrogenated DLC film is dependent on tribological environment, especially surrounding temperature. In this work, the tribological behaviors of DLC (Diamond-like carbon) films, prepared by the radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) method, were studied in elevated temperatures. The ball-on-disk tests with DLC films on steel specimens were conducted at a sliding speed of 60 rpm, a load of 10N, and surrounding various temperatures of $25^{\circ}C,\;40^{\circ}C,\;55^{\circ}C\;and\;75^{\circ}C$. The results show considerable dependency of DLC tribological parameters on temperature. The friction coefficient decreased as the surrounding temperature increased. After tests the wear tracks of hydrogenated DLC film were analyzed by optical microscope, scanning electron spectroscopy (SEM) and Raman spectroscopy. The surface roughness and 3-D images of wear track were also obtained by an atomic force microscope (AFM).

• Tribology and Lubricants
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• 제13권1호
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• pp.62-69
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• 1997

Rapid increase of refrigeration and air-conditioning systems 9r & a systems) in modern industries brings attention to the urgency of research & development as a core technology in the area. And it is required to the compatibility problem of r & a systems to alternative refrigerant for the protection of environment. The, it is requested to study the lubrication characteristics of refrigerant compressor which is the core technology in the r & a systems. The study of lubrication characteristics in the critical sliding component is essential for the design of refrigerant compressor. Therefore, theoretical investigation of the lubrication characteristics of rotary compressor for r & a systems is studied. The newton-Raphson method is used for the EHL analysis between vane and rolling piston in the rotary compressor. The results show that the rotational speed of a shaft and the discharge pressure influence significantly the friction force between vane and rolling piston. This results give important basic data for the further lubrication analysis and design of a rotary compressor.