• Wind and Structures
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• 제20권5호
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• pp.643-660
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• 2015

The wind tunnel test of large-scale sectional model and computational fluid dynamics (CFD) are employed for the purpose of studying the aerodynamic appendices and mechanism on suppression for the vortex-induced vibration (VIV). This paper takes the HongKong-Zhuhai-Macao Bridge as an example to conduct the wind tunnel test of large-scale sectional model. The results of wind tunnel test show that it is the crash barrier that induces the vertical VIV. CFD numerical simulation results show that the distance between the curb and crash barrier is not long enough to accelerate the flow velocity between them, resulting in an approximate stagnation region forming behind those two, where the continuous vortex-shedding occurs, giving rise to the vertical VIV in the end. According to the above, 3 types of wind fairing (trapezoidal, airfoil and smaller airfoil) are proposed to accelerate the flow velocity between the crash barrier and curb in order to avoid the continuous vortex-shedding. Both of the CFD numerical simulation and the velocity field measurement show that the flow velocity of all the measuring points in case of the section with airfoil wind fairing, can be increased greatly compared to the results of original section, and the energy is reduced considerably at the natural frequency, indicating that the wind fairing do accelerate the flow velocity behind the crash barrier. Wind tunnel tests in case of the sections with three different countermeasures mentioned above are conducted and the results compared with the original section show that all the three different countermeasures can be used to control VIV to varying degrees.

• Wind and Structures
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• 제14권6호
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• pp.517-536
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• 2011

The assessment of wind-induced motion plays an important role in the development and design of the majority of today's structures that push the limits of engineering knowledge. A vital part of the design is the prediction of wind-induced tall building motion and the assessment of its effects on occupant comfort. Little of the research that has led to the development of the various international standards for occupant comfort criteria have considered the effects of the low-frequency motion on task performance and interference with building occupants' daily activities. It has only recently become more widely recognized that it is no longer reasonable to assume that the level of motion that a tall building undergoes in a windstorm will fall below an occupants' level of perception and little is known about how this motion perception could also impact on task performance. Experimental research was conducted to evaluate the performance of individuals engaged in a manual tracking task while subjected to low level vibration in the frequency range of 0.125 Hz-0.50 Hz. The investigations were carried out under narrow-band random vibration with accelerations ranging from 2 milli-g to 30 milli-g (where 1 milli-g = 0.0098 $m/s^2$) and included a control condition. The frequencies and accelerations simulated are representative of the level of motion expected to occur in a tall building (heights in the range of 100 m -350 m) once every few months to once every few years. Performance of the test subjects with and without vibration was determined for 15 separate test conditions and evaluated in terms of time taken to complete a task and accuracy per trial. Overall, the performance under the vibration conditions did not vary significantly from that of the control condition, nor was there a statistically significant degradation or improvement trend in performance ability as a function of increasing frequency or acceleration.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2008년도 정기 학술대회
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• pp.178-183
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• 2008

A robot crane truck is being developed by the Bridge Inspection Robot Development Interface(BRIDI) for an automated and/or teleoperated bridge inspection. At the end of the telescoping boom allows the operator to scan the bridge structure under the deck trough the camera. Boom vibration induced by wind and deck movement can cause serious problems in this scanning system. This paper presents a control system to mitigate such vibration of the robot boom In the proposed control system an actuator is installed at the end of the working boom. This control system is studied using a mathematical model analysis with LQ control algorithm and a scaled model test in the laboratory. The study indicates that the proposed system is efficient for the vibration control of the robot booms, thereby demonstrating its immediate applicability in the field.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.71-76
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• 2008

This paper is concerned with the active vibration control of elevator by means of the active roller guide. To this end, a dynamic model for the horizontal vibration of the elevator consisting of a supporting frame, cage and active roller guides was derived using the energy method. Free vibration analysis was then carried out based on the equations of motion. Active vibration controller was designed based on the equations of motion using the LQR theory and applied to the numerical model. Rail irregularity and wind pressure variation were considered as external disturbance in the numerical simulations. The numerical results show that the active vibration control of elevator is possible.

• 한국공간구조학회논문집
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• 제8권4호
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• pp.91-100
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• 2008

본 연구에서는 sky-bridge로 연결된 고층건물의 진동제어성능을 검토하여 보았다. Sky-bridge를 이용한 진동제어의 원리는 서로 다른 동적특성을 가진 구조물이 sky-bridge를 통하여 제어력을 발휘함으로써 전체 시스템의 응답을 줄이는 것이다. 본 연구에서는 실제 건설 중인 sky-bridge로 연결된 고층건물(49층 및 42층)을 대상으로 구조물의 변위, 가속도 및 베어링반력, sky-bridge의 응력 등을 해석적인 방법으로 검토하였다. 이를 위하여 역사지진, 인공지진 및 풍동실험을 통해서 얻은 풍하중 시간이력을 사용하였다. 해석결과 sky-bridge를 사용하여 고층건물의 풍응답 및 지진응답을 효과적으로 줄일 수 있는 것을 확인하였다.

• 대한토목학회논문집
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• 제30권1A호
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• pp.27-33
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• 2010

본 연구에서는 소형 풍력발전기를 교량에 설치하여 전력생산과 아울러 내풍안정성을 개선할 수 있는 방안을 연구하였다. 이를 위하여 기존 공기역학적 진동억제 대책과 유사하게 교량에 풍력발전기를 설치하기 위한 방법과 풍력에너지 추정 방법을 제시하였다. 풍동실험 결과를 보면, 페어링처럼 소형 풍력발전기를 설치하면 와류진동을 거의 억제할 수 있는 것으로 나타났고, 이때 교축방향 최적 이격 거리는 터빈 직경의 3-4.5배인 것으로 나타났다. 그리고 풍력발전기를 설치하면 항력계수는 낮아지고 양력계수의 기울기도 음에서 양의 값으로 바뀌어 전반적인 내풍안정성이 향상되는 것으로 나타났다. 한편 풍하측의 풍력발전기는 평균풍속이 낮아 발전을 못하지만, 풍상측의 풍력발전기는 상당량의 전기에너지를 생산하는 것으로 나타났다.

• 한국전산구조공학회논문집
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• 제20권5호
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• pp.557-563
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• 2007

사장교 케이블은 구조적으로 휨강성과 감쇠력이 작아 풍우에 의해 쉽게 유해진동이 발생한다. 이러한 풍우진동을 저감시키기 위한 효과적인 방법으로 부가댐퍼를 장착하여 케이블의 감쇠력을 증가시키는 제어시스템이 널리 사용되어왔다. 그러나 댐퍼를 케이블의 정착부 부근에 설치할 수밖에 없는 구조적 한계로 인하여 충분한 감쇠력을 발휘하기 어렵다. 그러므로 본 논문은 수동제어시스템 보다 효과적으로 풍하중에 의한 케이블 진동을 제어하기 위한 능동제어시스템을 제안하였다. 제안된 능동제어시스템은 케이블의 정착단에 베어링 장치를 장착하여 케이블 단부에서 횡방향 변위가 가능하도록 모델링 하였으며, 앵커리지 내부에 장착된 능동댐퍼를 이용하여 적절한 제어력을 제공하도록 하였다. 능동제어를 위하여 최적제어 이론을 이용 LQG 조정기를 설계하였으며, 수치해석은 실제 교량인 서해대교의 최장 케이블을 대상으로 하여 기존의 댐퍼 시스템과 수동, 능동 댐퍼 부착에 따른 케이블의 진동제어성능을 비교 및 분석하였다. 연구결과 제안된 능동제어시스템은 효과적으로 사장교 케이블의 진동을 저감시킬 수 있는 시스템임을 입증하였으며, 기존의 부가댐퍼 시스템 보다 효과적으로 진동을 저감시킬 수 있을 것으로 사료된다.

• Smart Structures and Systems
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• 제22권6호
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• pp.727-741
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• 2018

To mitigate vibrations, tuned mass dampers(TMD) are widely used for long span bridges or high-rise buildings. Due to some durability concerns, such as fluid degradation, oil leakage, etc., the alternative solutions, such as the non-contacted eddy current damping (ECD), are proposed for mechanical devices in small scales. In the present study, a new eddy current damping TMD (ECD-TMD) is proposed and developed for large scale civil infrastructure applications. Starting from parametric study on finite element analysis of the ECD-TMD, the new design is enhanced via using the permanent magnets to eliminate the power need and a combination of a copper plate and a steel plate to improve the energy dissipation efficiency. Additional special design includes installation of two permanent magnets at the same side above the copper plate to easily adjust the gap as well as the damping. In a case study, the proposed ECD-TMD is demonstrated in the application of a steel arch bridge to mitigate the wind-induced vibrations of the flexible hangers. After a brief introduction of the configuration and the installation process for the damper, the mitigation effects are measured for the ambient vibration and forced vibration scenarios. The results show that the damping ratios increase to 3% for the weak axis after the installation of the ECD-TMDs and the maximum vibration amplitudes can be reduced by 60%.

• KIEE International Transactions on Power Engineering
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• 제3A권2호
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• pp.109-114
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• 2003

This paper presents observations made on four-bundled conductor transmission lines concerning the behavior of conductors under the effect of natural winds. To know the wind-induced vibration status and how to control it, wind-induced vibrations have been recorded and analyzed from the real transmission lines. From the field observation and analysis results, subspan oscillation was found to be the main type of vibration. In addition, the data also revealed some common characteristics of the observation sites with high maintenance rates. The results will be used in controlling the subspan oscillations and protecting the conductors.

• 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.