• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2003년도 봄 학술발표회 논문집
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• pp.313-320
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• 2003

The efficient and well organized database is essential for the management of information in every industrial field. In this study, a practical and effective database which can handle 3-D information of steel bridges is built on the basis of a STEP-based data model. The data model of steel bridge information is classified into geometric and non-geometric part and the design information is represented by linking geometric information and life cycle supported non-geometric information. Especially, the shape information is represented by boundary representation method, which is one of the representative methods of solid model information. In this study, ISO/STEP(STandard for the Exchange of product model data) AP203(configuration controlled design) EXPRESS schema is used to represent the shape information of steel bridge. The syntax of EXPRESS schema of developed data model is verified by NIST Expresso - is a tool for parsing and compiling EXPRESS schema. Also, this study verifies the conformance of the data model by applying to the real data of Hannam bridge. Therefore, the constructed database using STEP-based data model of steel bridges can be used effectively in the concurrent engineering point of view with transferring and sharing steel bridge information.

• Wind and Structures
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• 제18권1호
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• pp.1-20
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• 2014

Modern design of long suspension bridges must satisfy at the same time spanning very long distances and limiting their response against several external loads, even if of high intensity. Structural Control, with the solutions it provides, can offer a reliable contribution to limit internal forces and deformations in structural elements when extreme events occur. This positive aspect is very interesting when the dimensions of the structure are large. Herein, an updated numerical model of an existing suspension bridge is developed in a commercial finite element work frame, starting from original data. This model is used to reevaluate an optimization procedure for a passive control strategy, already proven effective with a simplified model of the buffeting wind forces. Such optimization procedure, previously implemented with a quasi-steady model of the buffeting excitation, is here reevaluated adopting a more refined version of the wind-structure interaction forces in which wind actions are applied on the towers and the cables considering drag forces only. For the deck a more refined formulation, based on the use of indicial functions, is adopted to reflect coupling with the bridge orientation and motion. It is shown that there is no variation of the previously identified optimal passive configuration.

• Journal of Power Electronics
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• 제14권3호
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• pp.507-518
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• 2014

This paper presents a new cascaded asymmetrical single phase multilevel converter with a lower number of power semiconductor switches and isolated DC sources. Therefore, the number of power electronic devices, converter losses, size, and cost are reduced. The proposed multilevel converter topology consists of two H-bridges connected in cascaded configuration. One H-bridge operates at a high frequency (high frequency inverter) and is capable of developing a two level output while the other H-bridge operates at the fundamental frequency (low frequency inverter) and is capable of developing a multilevel output. The addition of each power electronic switch to the low frequency inverter increases the number of levels by four. This paper also introduces a hybrid switching algorithm which uses very simple arithmetic and logical operations. The simplified hybrid switching algorithm is generalized for any number of levels. The proposed simplified switching algorithm is developed using a TMS320F2812 DSP board. The operation and performance of the proposed multilevel converter are verified by simulations using MATLAB/SIMULINK and experimental results.

• 전기전자학회논문지
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• 제23권2호
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• pp.636-641
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• 2019

저항형 센서 브리지들을 인터페이싱 하기 위한 간단한 저항 편차-시간 주기 변환기를 제안한다. 제안된 변환기는 두 개의 2세대 전류 컨베이어(current conveyor II: CCII)로 구성된다. 제안된 변환기는 연산 증폭기 또는 연산 트랜스컨덕턴스 증폭기(OTA)로 구성되는 기존의 변환기들보다 회로 구성이 간단하다는 장점을 가진다. 제안된 변환기를 AD844로 구현한 CCII를 이용하여 PSPICE 시뮬레이션을 진행하였다. 실험 결과는, 변환기가 $100{\sim}500{\Omega}$의 저항 편차 범위에 걸쳐서 $0.01934ms/{\Omega}$의 변환 감도를 가지며 선형 오차는 ${\pm}0.002%$ 이내라는 것을 보여준다.

• 전기전자학회논문지
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• 제23권4호
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• pp.1218-1223
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• 2019

HVDC 시스템에서 풀-브리지 서브 모듈 구조는 하프브리지 서브 모듈에 비해 부품 수가 증가하지만 100 % 여유율 확보가 가능하여 고장률을 크게 줄일 수 있다. 그러나 풀-브리지 서브 모듈은 여유율 보장과 암(arm) 단락 방지를 위한 데드 타임(dead-time)을 확보하기 위해 복잡한 제어 알고리즘이 필요하다. 이 문제를 해결하기 위해 풀-브리지 서브 모듈과 동일한 부품 수와 100 % 여유율을 갖는 병렬 하프브리지 구성의 고장률을 분석한다. 기존의 부품 고장 분석에 고장나무분석 방법을 적용하여 서브 모듈의 동작 위험을 반영함으로써 서브 모듈의 수명주기를 보다 정확하게 예측할 수 있다. 병렬 하프브리지 서브모듈의 타당성 검증을 위해 FTA 기반 분석 방법과 기존의 PCA 기반 방법으로 분석된 고장률을 비교한다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2006년도 정기 학술대회 논문집
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• pp.283-290
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• 2006

Cable-stayed bridge is a bridge that consists of one or more pylons, with cables supporting the deck. Cable-stayed bridges have come into wide use recently because of their economy, stability, and excellent appearance. It is possible to achieve a uniform moment distribution in the stiffening girders mainly by prestressing the cables, which leads to a more economical design in material and weight than other types of bridges. However, to achieve a more uniform moment distribution is vague objective, so it cannot be easily defined as the optimization problem. In other words, the minimization of cost or weight as the objective is not directly related to the optimization of cable prestressing. Therefore, it has been considered as one of the most important, difficult and also interesting topics among many researchers and bridge engineers to determine the optimal tensioning strategy how to apply prestressing forces of the cables of cable-stayed bridge. A number of approaches (Wang et al. 1993, $Negr\~{a}o\;and\;Sim\~{o}es$ 1997, Agrawal 1997, Janjic et al. 2003) to determine the optimal cable tensions have been proposed in the literature. Among these approaches the unit load method (Janjic et al. 2003) is considered in this paper because it can take into account the actual construction process while other approaches are based on the configuration of the final structure only. In this paper, '2-step approach' based on the unit load method is proposed to find the optimal tensioning strategy especially for the atypical asymmetric bridge under construction, which has continuous deck supported by one pylon and stay cables. Some numerical results will be given to show the validity of the new approach suggested in this paper.

• Structural Engineering and Mechanics
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• 제74권2호
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• pp.157-173
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• 2020

In the finite element modelling of long-span cable-stayed bridges, there are a lot of uncertainties brought about by the complex structural configuration, material behaviour, boundary conditions, structural connections, etc. In order to reduce the discrepancies between the theoretical finite element model and the actual static and dynamic behaviour, updating is indispensable after establishment of the finite element model to provide a reliable baseline version for further analysis. Traditional sensitivity-based updating methods cannot support updating based on static and dynamic measurement data at the same time. The finite element model is required in every optimization iteration which limits the efficiency greatly. A convenient but accurate Kriging surrogate model for updating of the finite element model of cable-stayed bridge is proposed. First, a simple cable-stayed bridge is used to verify the method and the updating results of Kriging model are compared with those using the response surface model. Results show that Kriging model has higher accuracy than the response surface model. Then the method is utilized to update the model of a long-span cable-stayed bridge in Hong Kong. The natural frequencies are extracted using various methods from the ambient data collected by the Wind and Structural Health Monitoring System installed on the bridge. The maximum deflection records at two specific locations in the load test form the updating objective function. Finally, the fatigue lives of the structure at two cross sections are calculated with the finite element models before and after updating considering the mean stress effect. Results are compared with those calculated from the strain gauge data for verification.

• Wind and Structures
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• 제10권5호
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• pp.463-479
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• 2007

A series of wind tunnel sectional model dynamic tests of a twin-deck bridge were conducted at the CLP Power Wind/Wave Tunnel Facility (WWTF) of The Hong Kong University of Science and Technology (HKUST) to investigate the effects of gap-width on the self-excited vibrations and the dynamic and aerodynamic characteristics of the bridge. Five 2.9 m long models with different gap-widths were fabricated and suspended in the wind tunnel to simulate a two-degrees-of-freedom (2DOF) bridge dynamic system, free to vibrate in both vertical and torsional directions. The mass, vertical frequency, and the torsional-to-vertical frequency ratio of the 2DOF systems were fixed to emphasize the effects of gap-width. A free-vibration test methodology was employed and the Eigensystem Realization Algorithm (ERA) was utilized to extract the eight flutter derivatives and the modal parameters from the coupled free-decay responses. The results of the zero gap-width configuration were in reasonable agreement with the theoretical values for an ideal thin flat plate in smooth flow and the published results of models with similar cross-sections, thus validating the experimental and analytical techniques utilized in this study. The methodology was further verified by the comparison between the measured and predicted free-decay responses. A comparison of results for different gap-widths revealed that variations of the gap-width mainly affect the torsional damping property, and that the configurations with greater gap-widths show a higher torsional damping ratio and hence stronger aerodynamic stability of the bridge.

• Journal of Power Electronics
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• 제3권4호
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• pp.224-229
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• 2003

The rapid expansion of small computers over the last 10-odd years has brought about great changes in the circumstances affecting UPSs. There are strong demands that UPSs become much smaller and lighter, and more economical, which has resulted in the wide application of the circuit topology without transformer. A disadvantage of such UPS topology is that the DC link voltage is very high, which invites decreased reliability and increased cost of battery bank. Some circuit configurations were proposed to eliminate this disadvantage, but they still had problems. In this paper, a novel circuit configuration which eliminates these problems is proposed and evaluated by the experimental results of prototype UPS.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 추계학술대회 논문집 전력기술부문
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• pp.31-35
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• 2004

This paper proposes a new configuration of 36-pulse voltage source converter which consists of two 6-pulse bridges and a pulse-interleaving auxiliary circuit. The system topology of proposed converter was derived to increase the pulse number of converter output voltage without increasing the number of 6-pulse bridges. The gate pulse generation was analyzed using the theoretical approach of multi-pulse switching converter. The operational feasibility of proposed system was verified by computer simulations with PSCAD/TMTDC software and experimental works with 3kVA hardware prototype. The proposed converter can be widely used for the uninterruptible power supply, the power quality compensator, and the distributed power generation, such as solar and fuel fell power system.