• Proceedings of the KSR Conference
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• 1998.05a
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• pp.556-563
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• 1998

Railway bridges have a significant effect on the stress and displacement of continuous welded rail(CWR). Longitudinal compression force at high temperature, combined breaking or acceleration forces can introduce track buckling. On the other hand, longitudinal tensile forces, associated with low temperatures, in combination with breaking forces may break rail. Therefore, it is very important to work out thorough counter measures for those problems, specially in high speed rail which high safety is required. The exact evaluation of longitudinal force of rail has the key to the solution. The main aim of the present paper is to examine whether the longitudinal force of CWR's on Kyung-Bu-HSR satisfy the criteria to be fulfilled in the design of railway bridge. The analyses are carried out by using "CWRAP" program which was developed by our research group. The ballast resistance and breaking force effects on the longitudinal force of CWR are investigated.

• Proceedings of the KIPE Conference
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• 2018.07a
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• pp.261-263
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• 2018

본 논문에서는 다수의 고주파 단상 변압기를 사용하여 다수의 독립된 직류 전압원을 만들 수 있는, 여러 다이오드 정류기와 연결된 풀 브릿지 DC-DC 컨버터에 대한 분석 및 제어 기법을 제안한다. 본 토폴로지의 경우 제어 대상인 2차단 직류단이 다수이지만 1차단 스위칭 회로가 하나의 풀 브릿지 회로이기 때문에 2차단 전압의 개별 제어를 위한 자유도가 부족하다. 이에 따라 다수 직류단 전압의 평균 값을 제어하는 방식이 사용된다. 이때, 각 직류단에 다른 용량의 부하가 연결되어 있는 상황에 대하여 상세한 분석이 필요하다. 본 논문에서는 제시된 토폴로지(Topology)를 하드 스위칭 기반의 DCM(Discontinuous Conduction Mode) 및 CCM(Continuous Conduction Mode) 동작의 경우에 대해 분석한다. 이를 바탕으로, 직류단 전압 제어를 위한 전향 보상 및 안티 와인드업을 포함하는 Integral and Proportional (IP) 제어기를 구성하고, 제어기 이득 및 전향 보상을 수식화 한다. 최종적으로 구해지는 제어기의 전달 함수를 통해, 제어기가 정확하게 설계되었는지 컴퓨터 시뮬레이션으로 검증한다.

• Proceedings of the KSR Conference
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• 2003.05a
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• pp.382-387
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• 2003

This research has investigated structural characteristics of curved two girder bridges proposed for AGT system and analyzed the results of the structural analysis of three different modelings for 3 span continuous bridge, each modeled in grillage modeling, simplified 3D modeling, and detailed 3D modeling respectively. The grillage modeling appeared to be somewhat underestimated in deflection and overestimated in rotation with respect to 3D modelings. Also, it is impossible to make a detailed examination of local buckling and details of cross beams, etc. The point that warping effect cannot be considered may cause the structural analysis unsafe, accordingly the structural analysis of curved two girder bridges should be done with 3D modelings.

• Proceedings of the KSR Conference
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• 2005.11a
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• pp.376-381
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• 2005

This paper presents the rail structure interaction analysis of the elevated viaducts which contains the curved alignments with smallest radius of 300 metre. The aim of this study is to check the compatibility between the track and the curved structure in order to verify the safety of the continuous welded rail track under service conditions. To perform the rail structure interaction analysis, nonlinear static rail structure interaction calculation is implemented. The bridge structures, the rails and the track behaviour are modelled according to the UIC774-3 and the Eurocode prEN1991-2 recommendations. Criteria in Eurocode prEN1991-2 are investigated to check the compatibility between the track and the structure for the rail structure interaction effects.

• Proceedings of the KSR Conference
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• 2006.11b
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• pp.460-469
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• 2006

It is widely known that the temperature variation introduces the axial force along a CWR(Continuous Welded Rail) in the railway bridges. Additional axial forces are generated due to many other reasons. These includes the interaction between the bridge girder and the CWR; acceleration or deceleration of the vehicles; support rotation (or deflection) of the girder. Among aforementioned reasons, this study investigates the influence of the support rotation on additional axial forces throughout the numerical study and the field test. Several strains gauges are installed along the CWR and the strains are measured under passing trains. It is expected that the elaborated estimation of the axial force on CWR will be beneficial for future railway maintenance.

• Proceedings of the KIEE Conference
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• 1996.11a
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• pp.363-366
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• 1996

A FB-ZVS(Full Bridge Zero Voltage Switching) PWM DC/DC converter for electric vehicles is simulated and implemented in this paper. The converter considered is a step-down DC/DC converter with the ratings of 312/13.5V and 1.35kW. The steady state operation of this converter is divided into six operating modes in case of continuous current mode and eight operating modes in case of discontinuous current mode. Digital simulations using PSpice are carried out to verify the steady-state analysis. A prototype converter was built in the laboratory. MOSFETs were used for swithching devices and fast recovery diodes to reduce the charge storage problem of a pn-junction.

• Proceedings of the KIPE Conference
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• 2012.07a
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• pp.47-48
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• 2012

In generally, grid connected single-phase flyback inverter is operated as boundary or discontinuous conduction mode. However, the flyback inverter can be operated in continuous conduction mode (CCM) due to its operating conditions in spite of it is designed to operate under boundary or discontinuous conduction mode. This situation causes unintended distortion to output current. In this paper, a current shaping method on unfolding bridge to reduce the output current distortion.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.6
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• pp.483-500
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• 2007

Emerging sensor-based structural health monitoring (SHM) technology can play an important role in inspecting and securing the safety of aging civil infrastructure, a worldwide problem. However, implementation of SHM in civil infrastructure faces a significant challenge due to the lack of suitable sensors and reliable methods for interpreting sensor data. This paper reviews recent efforts and advances made in addressing this challenge, with example sensor hardware and software developed in the author's research center. It is proposed to integrate real-time continuous monitoring using on structure sensors for global structural integrity evaluation with targeted NDE inspection for local damage assessment.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1999.10a
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• pp.236-243
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• 1999

A comparative study on aseismatic performances of various base isolation systems for the multi-span continuous bridge is carried out. Several leading base isolation systems the LRB system the RF system the R-FBI system and the EDF system are considered, The displacement of the deck the deformation of the upper ends of the piers the shear force and the bending moment of the lower ends of the piers are obtained by using the accelerograms of the N00W component of El Centro earthquake(1940) and the N90W component of Mexico City earthquake(1985) Nonlinear time-history analysis is carried out. comparisons of the results with the conventional bearing show that the base isolation systems are very effective in reducing the forces transmitted to the superstructures. Furthermore the results also show that the friction-type base isolation systems are less sensitive to unexpected variations in frequency content of the ground acceleration. The R-FBI system shows a good aseismatic performance comparing with other base isolation systems.

• Journal of Ocean Engineering and Technology
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• v.27 no.5
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• pp.36-42
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• 2013

We present the optimum design for the cross-sectional(sizing) and shape optimization of truss structures with natural frequency constraints. The optimum design method used in this paper employs continuous design variables and the Harmony Search Algorithm(HSA). HSA is a meta-heuristic search method for global optimization problems. In this paper, HSA uses the method of random number selection in an update process, along with penalty parameters, to construct the initial harmony memory in order to improve the fitness in the initial and update processes. In examples, 10-bar and 72-bar trusses are optimized for sizing, and 37-bar bridge type truss and 52-bar(like dome) for sizing and shape. Four typical truss optimization examples are employed to demonstrate the availability of HSA for finding the minimum weight optimum truss with multiple natural frequency constraints.