• 대한수학회지
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• 제51권4호
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• pp.703-719
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• 2014

This paper is concerned with the traveling wave solutions of nonlocal dispersal models with nonlocal delays. The existence of traveling wave solutions is investigated by the upper and lower solutions, and the asymptotic behavior of traveling wave solutions is studied by the idea of contracting rectangles. To illustrate these results, a delayed competition model is considered by presenting the existence and nonexistence of traveling wave solutions, which completes and improves some known results. In particular, our conclusions can deal with the traveling wave solutions of evolutionary systems which admit large time delays reflecting intraspecific competition in population dynamics and leading to the failure of comparison principle in literature.

• Journal of Communications and Networks
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• 제16권5호
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• pp.534-547
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• 2014

Large-scale failures resulting from natural disasters or intentional attacks are now causing serious concerns for communication network infrastructure, as the impact of large-scale network connection disruptions may cause significant costs for service providers and subscribers. In this paper, we propose a new framework for the analysis and prevention of network service disruptions in large-scale failure scenarios. We build dynamic deterministic and probabilistic models to capture the impact of regional failures as they evolve with time. A probabilistic failure model is proposed based on wave energy behaviour. Then, we develop a novel approach for preventive protection of the network in such probabilistic large-scale failure scenarios. We show that our method significantly improves uninterrupted delivery of data in the network and reduces service disruption times in large-scale regional failure scenarios.

• 대한토목학회논문집
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• 제14권3호
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• pp.583-594
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• 1994

자연사면 붕괴의 주요인의 하나는 연약층에서의 간극수압 상승이다. 따라서 이 연약층내의 간극수압 계측이 중요하다. 본 연구는 피압지하수위, 풍화암반 파쇄대의 투수성 그리고 연약층의 풍화정도를 고려한 간극수압 계측의 실내모형 실험이다. 제3기층 붕괴형과 붕괴성 붕괴형의 모형으로 피압지하수 상태에서 filter의 투수성에 따른 연약층내에서의 간극공기압 및 간극수압의 반응을 측정하였다. 간극압의 반응양상에 있어서 제3기층 붕괴형은 시간 변화에 따라 반응양상이 계단형(step type)으로 나타났고 붕괴성 붕괴형은 파형(wave type)으로 나타났다. 간극수압 반응율은 제3기층 붕괴형이 붕괴성 붕괴형보다 크며, 연약층의 풍화도의 증가에 따라 간극수압 반응율은 감소하였다.

• 한국해안·해양공학회논문집
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• 제21권4호
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• pp.267-277
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• 2009

혼성제 케이슨의 활동파괴모드에 대한 목표파괴수준에 따른 저항 및 하중 그리고 신뢰함수의 부분안 전계수를 산정하였다. 이를 위해 파력의 편이를 고려한 혼성제 케이슨의 활동파괴모드에 대한 신뢰함수를 수립하 고, 관련 확률변수의 불확실성에 대해 분석하였다. Level II AFDA 해석법을 이용하여 여러 수심조건 및 단면조건 그리고 파랑조건에 대해 신뢰성 해석을 수행하였다. 특히 대산항, 동해항 그리고 포항항의 실제 혼성제 케이슨의 활동파괴에 대한 신뢰성 해석도 수행하였다. 마지막으로 목표수준에 따른 혼성제 케이슨의 최소 소요 폭을산정하는 방법으로 본 연구에서 산정된 부분안전계수에 대한 비교 평가를 실시하였다. 비교 결과, 목표수준 1%에서는 약간의 차이를 보이고 있으나 다른 모든 수준에서는 비교적 잘 일치하고 있다.

• Structural Engineering and Mechanics
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• 제50권3호
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• pp.287-304
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• 2014

A computer based iterative numerical procedure has been developed to analyse reinforced high strength concrete columns subjected to horizontal wave loads and eccentric vertical load by taking the material, geometrical and wave load non-linearity into account. The behaviour of the column has been assumed, to be represented by Moment-Thrust-Curvature relationship of the column cross-section. The formulated computer program predicts horizontal load versus deflection behaviour of a column up to failure. The developed numerical model has been applied to analyse several column specimens of various slenderness, structural properties and axial load ratios, tested by other researchers. The predicted values are having a better agreement with experimental results. A simplified user friendly hydrodynamic load model has been developed based on Morison equation supplemented with a wave slap term to predict the high frequency non-linear impulsive hydrodynamic loads arising from steep waves, known as ringing loads. A computer program has been formulated based on the model to obtain the wave loads and non-dimensional wave load coefficients for all discretised nodes, along the length of column from instantaneous free water surface to bottom of the column at mud level. The columns of same size and material properties but having different slenderness ratio are analysed by the developed numerical procedure for the simulated wave loads under various vertical thrust. This paper discusses the results obtained in detail and effect of slenderness in resisting wave loads under various vertical thrust.

• Structural Engineering and Mechanics
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• 제78권3호
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• pp.281-296
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• 2021

This article analyzed the modulus degradation of concrete subjected to multi-level compressive cyclic loading. The evolution of secant elastic modulus is investigated based on measurements from top loading platen and LVDT in the middle part of concrete. The difference value of the two secant elastic moduli is reduced when close to failure and could be used as a fatigue failure precursor. The fatigue hardening is observed for concrete during cyclic loading. When the maximum stress is smaller the fatigue hardening is more obvious. The slight increase of maximum stress will lead to the "periodic hardening". The tangent elastic modulus shows a specific "bowknot" shape during cyclic loading, which can characterize the hysteresis of stress-strain and is influenced by the cyclic loading stresses. The deterioration of secant elastic modulus acts a similar role with respect to the P-wave speed during cyclic loading, can both characterize the degradation of the concrete properties.

• 한국산업융합학회 논문집
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• 제23권5호
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• pp.835-842
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• 2020

This paper considers a method of reproducing abnormal and fault operation for smart monitoring of thrust bearing used in wave power generation system. In order to develop smart monitoring technology, abnormal and failure data of actual equipment are required. However, it is impossible to artificially break down the actual equipment in operation due to safety and cost. To tackle this problem, a test bed that can secure data through reproduction of a faulty operating environment should be developed. Therefore, in this study, test bed that can reproduce each situation was developed and the operation result was analysis after identifying the situation to be reproduced through the failure factor analysis of the thrust bearing.

• 한국방재학회 논문집
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• 제10권1호
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• pp.65-72
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• 2010

본 연구에서는 댐 붕괴로 인한 홍수파에 영향을 미치는 도시지역의 효과에 대해 두 가지 수리모형실험에 근거하여 수치적으로 분석되었으며, 계산된 지점별 수심은 측정결과와 비교적 잘 일치하였다. 첫 번째 수리모형실험에 대해 도시지역 전반부에서 상대적으로 높은 수심영역과 흐름의 지체현상이 발생하였으며, 홍수파의 원활한 전파에 큰 장애요소가 됨을 알 수 있었다. 두번째 수리모형실험에 대해서는 유입량의 증가에 따라 도시지역의 전반부에서 후반부로 전파될 때 수심은 급격히 감소하는 구간과 느리게 감소하는 구간으로 구별되며, 도시지역 전반부에 도달하는 홍수파의 최초시간은 유입량이 증가함에 따라 감소되는 경향을 나타내었다.

• Structural Engineering and Mechanics
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• 제64권4호
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• pp.427-436
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• 2017

Concrete technologists have used ultrasonic pulse velocity test for decades to evaluate the properties of concrete. However, the presented research work focuses on the use of ultrasonic pulse velocity test to study the degradation in steel-concrete bond subjected to increasing loading. A detailed experimental investigation was conducted by testing five identical beam specimens under increasing loading. The loading was increased from zero till failure in equal increments. From the experimentation, it was found that as the reinforced concrete beams were stressed from control unloaded condition till complete failure, the propagating ultrasonic wave velocity reduced. This reduction in wave velocity is attributed to the initiation, development, and propagation of internal cracking in the concrete surrounding the steel reinforcement. Using both direct and semidirect methods of testing, results of reduction in wave velocity with evidence of internal cracking at steel-concrete interface are presented. From the presented results and discussion, it can be concluded that the UPV test method can be successfully employed to identify zones of poor bonding along the length of reinforced concrete beam. The information gathered by such testing can be used by engineers for localizing repairs thereby leading to saving of time, labor and cost of repairs. Furthermore, the implementation strategy along with real-world challenges associated with the application of the proposed technique and area of future development have also been presented.

• 한국해안해양공학회지
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• 제19권4호
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• pp.336-344
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• 2007

항만 구조물의 피복재를 설계하는 경우 경험식의 불확실성에 따른 영향뿐만 아니라 사용년수에 따른 파고분포한수를 직접적으로 고려할 수 있는 부분안전계수 산정 모형이 개발되었다. 동일한 재현기간 그리고 사용년수에서 구조물의 파괴에 대한 목표수준이 증가함에 따라 저항력과 파고에 대한 부분안전계수가 커지는 등의 특성들을 잘 재현하고 있다. 따라서 본 연구에서 산정 된 각 경험식들의 저항력 그리고 파고에 대한 부분안전계수를 이용하면 현행의 결정론적 설계법과 동일한 형태의 설계식을 사용하면서도, 확률변수들의 불확실성, 사용년수 그리고 파괴에 대한 목표수준을 고려하여 설계하는 것이 가능하다