• Wind and Structures
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• 제18권3호
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• pp.235-252
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• 2014

An effective numerical technique to calculate the reactions of a multi-spanned transmission line conductor system, under arbitrary loads varying along the spans, is developed. Such variable loads are generated by High Intensity Wind (HIW) events in the form of tornadoes and downburst. First, a semi-closed form solution is derived to obtain the displacements and the reactions at the ends of each conductor span. The solution accounts for the nonlinearity of the system and the flexibility of the insulators. Second, a numerical scheme to solve the derived closed-form solution is proposed. Two conductor systems are analyzed under loads resulting from HIW events for validation of the proposed technique. Non-linear Finite Element Analyses (FEA) are also conducted for the same two systems. The responses resulting from the technique are shown to be in a very good agreement with those resulting from the FEA, which confirms the technique accuracy. Meanwhile, the semi-closed form technique shows superior efficiency in terms of the required computational time. The saving in computational time has a great advantage in predicting the response of the conductors under HIW events, since this requires a large number of analyses to cover different potential locations and sizes of those localized events.

• Smart Structures and Systems
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• 제18권4호
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• pp.683-705
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• 2016

A semi-active algorithm for edgewise vibration control of the spar-type floating offshore wind turbine (SFOWT) blades, nacelle and spar platform is developed in this paper. A tuned mass damper (TMD) is placed in each blade, in the nacelle and on the spar to control the vibrations for these components. A Short Time Fourier Transform algorithm is used for semi-active control of the TMDs. The mathematical formulation of the integrated SFOWT-TMDs system is derived by using Euler-Lagrangian equations. The theoretical model derived is a time-varying system considering the aerodynamic properties of the blade, variable mass and stiffness per unit length, gravity, the interactions among the blades, nacelle, spar, mooring system and the TMDs, the hydrodynamic effects, the restoring moment and the buoyancy force. The aerodynamic loads on the nacelle and the spar due to their coupling with the blades are also considered. The effectiveness of the semi-active TMDs is investigated in the numerical examples where the mooring cable tension, rotor speed and the blade stiffness are varying over time. Except for excessively large strokes of the nacelle TMD, the semi-active algorithm is considerably more effective than the passive one in all cases and its effectiveness is restricted by the low-frequency nature of the nacelle and the spar responses.

• Wind and Structures
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• 제11권3호
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• pp.179-192
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• 2008

In a wind tunnel experiment employing a reduced scale model, Reynolds number (Re) can hardly be respected. Its effects on the aerodynamics of closed-box bridge decks have been the subject of research in recent years. Stonecutters Bridge in Hong Kong is a cable-stayed bridge having an unprecedented central span of 1018m. The issue of Re sensitivity was raised early in the design phase of the deck of Stonecutters Bridge. The objective of this study is to summarise the results of various wind tunnel experiments in order to demonstrate the effect of Re on the steady state aerodynamic force coefficients. The results may provide an insight on the choice of scale for section model experiments in bridge design projects. Computational Fluid Dynamics (CFD) analysis of forces on bridge deck section was also carried out to see how CFD results are compared with experimental results.

• Structural Engineering and Mechanics
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• 제54권5호
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• pp.909-922
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• 2015

The dynamic response and the mooring line tension of a 1/75 scale model of spar-type platform for 2.5 MW floating offshore wind turbine subject to one-dimensional regular harmonic wave are investigated numerically and verified by experiment. The upper part of wind turbine which is composed of three rotor blades, hub and nacelle is modeled as a lumped mass the scale model and three mooring lines are pre-tensioned by means of linear springs. The coupled fluid-rigid body interaction is numerically simulated by a coupled FEM-cable dynamics code, while the experiment is performed in a wave tank with the specially-designed vision and data acquisition system. The time responses of surge, heave and pitch motions of the scale platform and the mooring line tensions are obtained numerically and the frequency domain-converted RAOs are compared with the experiment.

• Wind and Structures
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• 제32권1호
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• pp.71-80
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• 2021

In steel cable bridges, the use of magnetorheological (MR) dampers between butt cables is constantly increasing to dampen vibrations caused by rain and wind. The biggest problem in the actual applications of those devices is to launch a kind of appropriate algorithm that can effectively and efficiently suppress the perturbation of the tie through basic calculations and optimal solutions. This article discusses the optimal evolutionary design based on a linear and quadratic regulator (hereafter LQR) to lessen the perturbation of the bridges with cables. The control numerical algorithms are expected to effectively and efficiently decrease the possible risks of the structural response in amplification owing to the feedback force in the direction of the MR attenuator. In addition, these numerical algorithms approximate those optimal linear quadratic regulator control forces through the corresponding damping and stiffness, which significantly lessens the work of calculating the significant and optimal control forces. Therefore, it has been shown that it plays an important and significant role in the practical application design of semiactive MR control power systems. In the present proposed novel evolutionary parallel distributed compensator scheme, the vibrational control problem with a simulated demonstration is used to evaluate the numerical algorithmic performance and effectiveness. The results show that these semiactive MR control numerical algorithms which are present proposed in the present paper has better performance than the optimal and the passive control, which is almost reaching the levels of linear quadratic regulator controls with minimal feedback requirements.

• Wind and Structures
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• 제38권4호
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• pp.309-323
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• 2024

The gust factor and turbulence intensity are two crucial parameters that characterize the properties of turbulence. In tropical cyclones (TCs), these parameters exhibit significant variability, yet there is a lack of established formulas to account for their probabilistic characteristics with consideration of their inherent connection. On this condition, a probabilistic analysis of gust factors and turbulence intensities of TCs is conducted based on fourteen sets of wind data collected at the Sutong Cable-stayed Bridge site. Initially, the turbulence intensities and gust factors of recorded data are computed, followed by an analysis of their probability densities across different ranges categorized by mean wind speed. The Gaussian, lognormal, and generalized extreme value (GEV) distributions are employed to fit the measured probability densities, with subsequent evaluation of their effectiveness. The Gumbel distribution, which is a specific instance of the GEV distribution, has been identified as an optimal choice for probabilistic characterizations of turbulence intensity and gust factor in TCs. The corresponding empirical models are then established through curve fitting. By utilizing the Gumbel distribution as a template, the nexus between the probability density functions of turbulence intensity and gust factor is built, leading to the development of a generalized probabilistic model that statistically describe turbulence intensity and gust factor in TCs. Finally, these empirical models are validated using measured data and compared with suggestions recommended by specifications.

• 한국전산구조공학회논문집
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• 제32권5호
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• pp.313-322
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• 2019

교량에서의 화재는 최근까지도 빈번하게 발생되고 있으며, 특히 케이블교량에서 화재가 발생될 시 케이블에 높은 온도상승으로 인해 케이블에 손상 및 파단이 발생될 수 있다. 본 연구에서는 케이블교량에서 발생될 수 있는 화재 시나리오를 설정하였다. 또한 실물차량 화재실험 결과를 토대로 화재강도모델을 제안하여 대상교량 케이블의 열전달 해석을 수행하였다. 해석 결과 단면적이 작은 케이블에서 더 높은 온도상승이 발생되며, 유조차를 제외한 차종의 경우 내화 성능 기준을 초과하지 않는 결과를 나타내었다. 유조차 화재의 경우 갓길에서 발생될 때 최소 단면적 케이블에서 내화 성능 기준을 초과하는 결과를 보이며, 기준을 초과하는 케이블의 높이는 약 14m로 나타나 이에 따른 대책 및 내화 보강의 필요성을 확인하였다. 본 연구결과를 통해 케이블교량에서 화재가 발생될 때 케이블의 온도변화에 대한 간접적인 평가가 가능한 것을 확인하였으며, 향후 화재 발생 시 바람에 영향을 고려한 열전달 해석과 케이블의 온도상승 시 교량의 사용성에 대한 추가적인 연구가 필요할 것으로 판단된다.

• 전기학회논문지
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• 제62권10호
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• pp.1383-1389
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• 2013

There were telecommunication noise and malfunctions of the electronic devices occurred over a wide area due to the high harmonic voltage and/or current levels of the Back-to-back converter in the DFIG wind power system even though the magnitude of all harmonics is within the international standards. The triangular carrier signals of the PWM used in the power converter system is related to the telecommunication noise because they are in the range of audible frequencies and amplified by a variety of the standing waves that were excited by harmonic voltage sources in the weak grid system such as a long distance distribution transmission lines. This paper describes the characteristics of the harmonics in the wind turbine-generator, numerical analysis and simulation of the harmonics resonance phenomena in the distribution lines as well as measuring induced voltage of the telecommunication lines in parallel with power lines in order to verify the root cause of the telecommunication noise. These noise problems can occur in a wind turbine power system with a non-linear converter at any time, as well as photovoltaic power system. So, the preliminary review of suitable filter devices and switching frequencies of the PWM have to be required by considering the stability of the controller at the design stage but as part of the measures the effect of the telecommunication cable shields was analyzed by comparing the measured data between multi-conductor with/without shields so as to attenuate the sources of the harmonics voltage induced into the telecommunication lines and to apply the most cost-effective measures in the field.

• 대한기계학회논문집A
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• 제35권11호
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• pp.1407-1413
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• 2011

소형풍력발전시스템의 복합재 블레이드에 대한 실규모 구조시험 및 이를 모사한 구조해석을 통하여 설계 타당성을 검증하였다. 먼저 IEC 61400-2 에 규정된 설계 요구조건의 만족을 위하여 정격 풍속 및 IEC 61400-2 Case H 의 최악 조건에 대한 구조해석을 수행하고 이를 통하여 적층 순서 및 적층 두께를 결정하였다. 또한 이러한 구조해석의 타당성 검증을 위하여 IEC 61400-23 에 따라 구조해석과 동일한 하중조건에서의 실규모 구조시험을 실시하였다. 이러한 실규모 구조시험을 통한 구한 블레이드의 하중-변위 선도 및 표면의 변형률 특성을 이용하여 블레이드의 구조적 안전성을 평가하였다.

• 전기전자학회논문지
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• 제24권3호
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• pp.691-698
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• 2020

해상풍력 발전단지의 전력망 연계방식에 따라 설치비용이나 고장전류의 크기가 달라진다. 그렇기 때문에 단지의 용량과 위치 등을 고려한 효율적인 전력망 연계 방법이 필요하다. 특히 해상풍력 발전단지의 전력케이블은 대부분 비용 및 효율적인 부분을 고려하여 3-core를 사용한다. 케이블 단락 같은 고장이 발생하면 케이블 전체를 교체해야 하므로 수리비용 및 터빈 정지 기간을 고려하였을 때 비용적인 측면에서 상당한 손실이 발생할 수 있다. 따라서 본 논문에서는 제주해상에 설치될 100 MW 풍력단지에 방사형, 링형, 성형 방식을 도입하여 이에 따른 3상 단락고장을 PSCAD/EMTDC 프로그램을 활용하여 컴퓨터 해석을 수행하고, 그 결과를 분석하여 모델 단지에 알맞은 전력망 연계방식을 제안하고자 한다.