• 한국해양공학회지
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• 제19권5호
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• pp.78-82
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• 2005

The motion response results of a submerged submarine section in waves are presented. The numerical method is based on Cauchy's integral and 3 degrees-of-freedom motions of submarine sections are calculated in two dimensions, in regular waves. The fully nonlinear free surface and body boundary conditions are applied to the present problem, and the viscous effects on the submarine are modeled by Morison's formulas. The motions of submarine sections in beam sea are directly simulated and the effects of wave frequency, snorkel depth, and bridge are discussed.

• 한국안전학회지
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• 제25권1호
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• pp.65-71
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• 2010

In this study, a series of finite element analysis using LUSAS were performed in order to assess the quantitative effects of repair and retrofit of stringer in steel plate girder railway bridge with fatigue cracks. And cutoff types of end part of upper flange were considered as right-angled type and round-angled type. Also, as a method of repair and retrofit of fatigue cracks in stringer, perforation of stop-hole and installation of bracket were considered. From the analysis result, it was possible to assess the fatigue safety and fatigue life of stringer with fatigue cracks, and to estimate the stress intensity factor range in cut-off part of stringer using J-integral method. Also, according to the method of perforation of stop-hole and installation of bracket, it was possible to calculate the crack propagation life at the cut-off part of stringer.

• Interaction and multiscale mechanics
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• 제2권4호
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• pp.431-454
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• 2009

This paper presents a simple model for studying the dynamic response of multi-span bridges resting on piers with different heights and subjected to earthquake forces acting transversely to the bridge, but varying spatially along its length. The analysis is carried out using the modal superposition technique, while the solution of the resulting integral-differential equations is obtained via the Laplace transformation. It has been found that the piers' height and the quality of the foundation soil can affect significantly the dynamic behavior of such bridges. Typical examples showing the effectiveness of the method are presented with useful results listed.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제51권11호
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• pp.645-651
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• 2002

In this paper, a multilevel PWM inverter employing a cascaded transformer is presented to reduce the harmonics of output voltage and load currents. The proposed PWM inverter consists of two full-bridge modules and their corresponding transformers. The secondarics of each transformer are series-connected. So continuous output voltage levels can be synthesized from the suitable selection of the turns ratio of trasformer. And it appears an integral ratio to input DC source. Because of the cascaded connection of transformers, output filter inductor is not necessary. The operational principles and analysis are explained, and it is compared with a conventional isolated H-bridge PWM inverter. The validity of proposed multilevel inverter is verified through simulated and experimental waveform and their FFT results.

• 헤리티지:역사와 과학
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• 제33권
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• pp.308-336
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• 2000

Bridge - Treading was a flok festival that was held on the night of the 1st full moon of the lunar new years. Men and women, both young and old, took pan in it in the belief that crossing a bridge, or bridges, back and forth, the same number of times as the number of years they were old, on this night would prevent all types of leg and foot ailments from occurring throughout the coming year. The practice was carried on mainly around the Seoul central region of Korea. Though it has now largely disappeared, it has been reatores in the Yeoju area. According to the Korean almanac and other chronicles, it was once practiced throughout the land. It is in the preserved was brige-treading festival of yeoju, however, that both the original form, transmission, and function are clarified and brought to light. In this regard, when compares to similar festivals of other region such as Songpa and Kwacheon, it is found that of Yeojo has a special characteristic. Accompanied by folksongs, music, and dance, this was not a religions festival in the strict sense, but rather an annual custom filled with mirth and merriment that formed an integral part of Korean folk culture.

• Structural Engineering and Mechanics
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• 제82권6호
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• pp.725-734
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• 2022

This work presents a simple exponential shear deformation theory for the flexural and free vibration responses of thick bridge deck. Contrary to the existing higher order shear deformation theories (HSDT) and the first shear deformation theory (FSDT), the proposed model uses a new displacement field which incorporates undetermined integral terms and involves only two variables. Governing equations and boundary conditions of the theory are derived by the principle of virtual work. The simply supported thick isotropic square and rectangular plates are considered for the detailed numerical studies. Results of displacements, stresses and frequencies are compared with those of other refined theories and exact theory to show the efficiency of the proposed theory. Good agreement is achieved of the present results with those of higher order shear deformation theory (HSDT) and elasticity theory. Moreover, results demonstrate that the developed two variable refined plate theory is simple for solving the flexural and free vibration responses of thick bridge deck and can achieve the same accuracy of the existing HSDTs which have more number of variables.

• Structural Engineering and Mechanics
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• 제63권6호
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• pp.809-824
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• 2017

The accurate evaluation of wind characteristics and wind-induced structural responses during a typhoon is of significant importance for bridge design and safety assessment. This paper presents an expectation maximization (EM) algorithm-based angular-linear approach for probabilistic modeling of field-measured wind characteristics. The proposed method has been applied to model the wind speed and direction data during typhoons recorded by the structural health monitoring (SHM) system instrumented on the arch Jiubao Bridge located in Hangzhou, China. In the summer of 2015, three typhoons, i.e., Typhoon Chan-hom, Typhoon Soudelor and Typhoon Goni, made landfall in the east of China and then struck the Jiubao Bridge. By analyzing the wind monitoring data such as the wind speed and direction measured by three anemometers during typhoons, the wind characteristics during typhoons are derived, including the average wind speed and direction, turbulence intensity, gust factor, turbulence integral scale, and power spectral density (PSD). An EM algorithm-based angular-linear modeling approach is proposed for modeling the joint distribution of the wind speed and direction. For the marginal distribution of the wind speed, the finite mixture of two-parameter Weibull distribution is employed, and the finite mixture of von Mises distribution is used to represent the wind direction. The parameters of each distribution model are estimated by use of the EM algorithm, and the optimal model is determined by the values of $R^2$ statistic and the Akaike's information criterion (AIC). The results indicate that the stochastic properties of the wind field around the bridge site during typhoons are effectively characterized by the proposed EM algorithm-based angular-linear modeling approach. The formulated joint distribution of the wind speed and direction can serve as a solid foundation for the purpose of accurately evaluating the typhoon-induced fatigue damage of long-span bridges.

• 한국건설관리학회:학술대회논문집
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• 한국건설관리학회 2006년도 정기학술발표대회 논문집
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• pp.680-685
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• 2006

교량시설물은 차량소통을 용이하게 하는 주요 사회간접자본 시설의 하나로 도로교통에서 매우 중요한 구조물로, 시공 이후 사용에 따른 열화부위 발생 시 그 교체가 어렵고 교통에 많은 영향을 미치기 때문에 유지관리를 위한 주기적인 점검 및 진단이 요구된다. 하지만 열악한 작업 환경과 점검작업을 통해 발생하는 데이트의 객관성 확보 및 체계적인 관리에 많은 제약이 따라 이를 해결하기 위한 방안으로 자동화 장비를 도입하는 것을 고려할 수 있다. 본 연구는 이를 위해 경제적 타당성 검토를 위한 모델을 제안하고 기존 작업과 자동화 도입에 따라 예상되는 요소들을 비교하여 교량시설물 점검작업을 자동화할 때 경제적으로 어떤 가치가 있는지 알아보고자 하였다. 자료의 제약으로 인해 현 단계에서 명확한 경제적 타당성을 검토하는데 제약이 있으나 향후 연구를 통해 교량시설물 점검작업의 자동화에 대한 구체적인 가치를 제시하고자 한다.

• Smart Structures and Systems
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• 제6권8호
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• pp.939-951
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• 2010

A low-cost wireless sensor network (WSN) solution with highly expandable super and simple nodes was developed. The super node was designed as a sensing unit as well as a receiving terminal with low energy consumption. The simple node was designed to serve as a cheaper alternative for large-scale deployment. A 12-bit ADC inputs and DAC outputs were reserved for sensor boards to ease the sensing integration. Vibration and thermal field tests of the Chi-Lu Bridge were conducted to evaluate the WSN's performance. Integral acceleration, temperature and tilt sensing modules were constructed to simplify the task of long-term environmental monitoring on this bridge, while a star topology was used to avoid collisions and reduce power consumption. We showed that, given sufficient power and additional power amplifier, the WSN can successfully be active for more than 7 days and satisfy the half bridge 120-meter transmission requirement. The time and frequency responses of cables shocked by external force and temperature variations around cables in one day were recorded and analyzed. Finally, guidelines on power characterization of the WSN platform and selection of acceleration sensors for structural health monitoring applications were given.

• 한국구조물진단유지관리공학회 논문집
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• 제18권6호
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• pp.60-71
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• 2014

대표적인 장대교량 형식인 사장교는 공용 중에 케이블 손상이 발생하는 경우 전체 구조계의 손상을 유발할 수 있으므로 신속한 유지관리가 필요하다. 손상발생 이후 대응시간을 가능한 단축하기 위해서 손상신호로부터 직접 이상거동을 판단할 수 있는 알고리즘에 대한 많은 연구가 진행되고 있다. 이상거동 감지 알고리즘의 정확도를 향상시키기 위해서는 구조물의 다양한 손상에 대한 충분한 양의 계측결과가 필요하다. 그러나 공용중인 교량에 손상을 주어 이상거동을 계측할 수 없으므로 수치적인 방법으로 이상거동을 모사하는 것이 효율적인 대안이 될 수 있다. 사장교 케이블의 손상을 모사하는 지금까지의 연구는 케이블의 강성변화를 단순한 장력변화로만 모사하여 해석하는 방법이 주를 이루었다. 이러한 해석방법은 설계목적의 정밀도는 확보할 수 있지만 케이블의 손상에 의한 구조물의 정확한 응답을 재현하지 못한다. 본 연구는 사장교의 손상을 모사하기 위해 강성 및 질량의 변화를 고려하는 직접적분법 Gradual Bilinear Method (GBM)을 제안하고 해석프로그램을 개발하였다. 개발된 해석방법을 단순모델을 이용하여 검증하고 실제 사장교모델을 이용하여 손상시각 및 손상지연시간에 따른 응답의 변화를 관찰하였다. 수행된 연구결과는 향후 건축/대형구조물의 안전관리를 위한 고정밀도 이상거동 감지알고리즘을 개발하고 검증하는데 활용될 수 있다.