• 한국전산구조공학회논문집
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• 제22권5호
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• pp.403-410
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• 2009

본 연구에서는 실험결과를 바탕으로 액체형 기둥감쇠기의 감쇠계수와 제어력에 참여하는 유효질량을 시스템 식별기법을 이용하여 정량적으로 평가하였다. 먼저, 두가지 형태의 동조액체형 기둥감쇠기를 제작하여 진동대 실험을 실시하였다. 다음으로 수조내부 액체의 수위를 변화시켜 가면서 조화하중 가진실험에 의한 감쇠기의 동적특성을 실험적으로 구하였다. 마지막으로 수치해석 모델과 실험결과와의 오차를 최소화하는 것에 의해 수위변화에 따른 감쇠기의 감쇠비와 유효질량을 정량적으로 평가하였다. 시스템 식별결과로부터 감쇠비와 유효질량이 감쇠기의 수위가 증가함에 따라 감소하는 것으로 나타났다.

• Wind and Structures
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• 제22권1호
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• pp.107-131
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• 2016

The need for a more affordable, reliable, clean and secure energy has led to explorations in non-traditional sources, particularly renewable energies. Wind is one of the cleanest energy sources that plays a significant role in augmenting sustainability. Wind turbines, as energy convertors, are usually tall and slender structures, and depending on their location (inland or offshore), they can be subject to high wind and/or strong wave loadings. These loads can cause severe vibrations with detrimental effects on energy production, structural lifecycle and initial cost. A dissipativity analysis study was carried out to know whether wind turbine towers require damping enhancement or rigidity modifications for vibration suppression. The results suggest that wind turbines are lightly damped structures and damping enhancement is a potential solution for vibration lessening. Accordingly, the paper investigates different damping enhancement techniques for vibration mitigation. The efficacy of tuned mass damper (TMD), tuned liquid column damper (TLCD), tuned sloshing damper (TSD), and viscous damper (VD) to reduce vibrations is investigated. A comparison among these devices, in terms of robustness and effectiveness, is conducted. The VD can reduce both displacement and acceleration responses of the tower, better than other types of dampers, for the same control effort, followed by TMD, TSD, and finally TLCD. Nevertheless, the use of VDs raises concerns about where they should be located in the structure, and their application may require additional design considerations.

• Structural Engineering and Mechanics
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• 제6권1호
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• pp.77-93
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• 1998

Some design formulas and design procedures for single and multiple tuned liquid column dampers (TLCDs) are proposed in this study. Previous studies show that if the properties of the TLCD system are properly selected then the TLCD could be as effective as the traditional tuned mass dampers. In addition, the TLCD system offers advantages such as flexibility in terms of installation, little maintenance required, and potentials for multiple usage, etc., which are incomparable by other mechanical types of dampers. In this paper, a set of optimal properties such as length and head loss of a TLCD system are derived under the assumption that the building vibrates in a dominate mode and is subjected to Gaussian white noise excitation. A design procedure for a single TLCD system will be illustrated and discussed. Due to the nonlinearity in the damping term, the TLCD system is sensitive to the loading intensity. This loading sensitivity could limit the application range of the TLCD system. It will be shown in this paper that such a nonlinear effect can be reduced by using multiple TLCDs. As a demonstrative example, the control effects on a flexible building modeled as a single degree-of-freedom system subjected to white noise excitation will be analyzed and discussed using single or multiple TLCDs.

• 한국전산구조공학회논문집
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• 제25권4호
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• pp.323-330
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• 2012

본 연구진은 최근 U자 형태인 액체댐퍼의 수직관을 다수의 셀(사각 기둥)로 나누어 셀 상부를 개폐함에 따라 다양한 고유진동수를 쉽게 재현하는 새로운 멀티셀 액체댐퍼를 제시하였다. 이러한 댐퍼를 1층 건물 모형에 설치하여 진동대 실험을 수행하여 건물응답이 감소되는 것을 검증하였다. 64층의 풍응답인 가속도를 제어할 수 있도록 댐퍼를 설계하기 위하여 건물을 1자유도계로 축소하였다. 가속도 기반 상사비인 1/20를 적용하여 1층 건물 모형과 새로운 댐퍼를 제작하였다. 설계 진동수인 0.65Hz가 구현되도록 모형건물의 질량과 강성을 쉽게 조절할 수 있도록 탈부착식으로 제작하였다. 모형건물은 중량을 부담하는 질량부와 하부에 스프링과 LM guide가 설치된 구동부로 나누어서 제작되었다. 18개의 셀을 가지는 액체댐퍼를 제작하여 고유진동수 조절 범위가 0.65Hz~0.81Hz인 것을 파악하였다. 대형 진동대에 설치한 모형건물의 일방향 가진을 통하여 모형의 응답을 측정하고 모형상부에 멀티셀 액체댐퍼가 설치되었을 경우 모형의 응답을 측정하여 비교하였다. 진동대 가속도를 입력과 모형건물의 가속도를 출력으로 하는 전달함수를 통해 결과를 나타내었다. 예상한 바와 같이 멀티셀 액체댐퍼의 고유진동수를 건물의 진동수에 동조시켰을 경우 건물의 가속도 응답이 감소함을 알 수 있었다.

• Structural Engineering and Mechanics
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• 제77권3호
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• pp.369-381
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• 2021

The seismic responses of elevated tanks considering liquid-structure interaction are presented under horizontal earthquake. The scaled model tank is fabricated to study the dynamic responses of anchored tank and newly designed uplift tank with replaced dampers. The natural frequencies for structural mode are obtained by modal analysis. The dynamic responses of tanks are completed by finite element method, which are compared with the results from experiment. The displacement parallel and perpendicular to the excitation direction are both gained as well as structural acceleration. The strain of tank walls and the axial strain of columns are also obtained afterwards. The seismic responses of liquid storage tank can be calculated by the finite element model effectively and the results match well with the one measured by experiment. The aim is to provide a new type of tank system with vertical constraint relaxed which leads to lower stress level. With the liquid volume increasing, the structural fundamental frequency has a great reduction and the one of uplift tank are even smaller. Compared with anchored tank, the displacement of uplift tank is magnified, the strain for tank walls and columns parallel to excitation direction reduces obviously, while the one perpendicular to earthquake direction increases a lot, but the values are still small. The stress level of new tank seems to be more even due to uplift effect. The new type of tank can realize recoverable function by replacing dampers after earthquake.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문집
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• pp.399-403
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• 2002

Squeeze film dampers (SFDs) are designed and analyzed for radial superconducting bearings. The designed SFDs are mounted on the superconductors submerged in liquid nitrogen such that the dampers should supply additional damping to the relatively underdamped superconducting bearing support . Basic theory of SFD assembled with superconductors is introduced. Rotordynamic simulations are provided to support the feasibility of the superconducting bearings mounted on SFDs for a horizontal flywheel energy storage system.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문초록집
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• pp.343.2-343
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• 2002

Squeeze film dampers(SFDs) are designed and analyzed for radial superconducting bearings. The designed SFDs are mounted on the superconductors submerged in liquid nitrogen such that the dampers should supply additional damping to the relatively underdamped superconducting bearing support. Basic theory of SFD with superconducting bearing are introduced. Rotordynamic simulations are provided to support the feasibility of the superconducting magnetic bearings mounted on SFDs for a horizontal flywheel energy storage system.

• Smart Structures and Systems
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• 제11권5호
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• pp.435-451
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• 2013

High-rise buildings are a common feature of urban cities around the world. These flexible structures frequently exhibit large vibration due to strong winds and earthquakes. Structural control has been employed as an effective means to mitigate excessive responses; however, structural control mechanisms that can be used in tall buildings are limited primarily to mass and liquid dampers. An attractive alternative can be found in outrigger damping systems, where the bending deformation of the building is transformed into shear deformation across dampers placed between the outrigger and the perimeter columns. The outrigger system provides additional damping that can reduce structural responses, such as the floor displacements and accelerations. This paper investigates the potential of using smart dampers, specifically magnetorheological (MR) fluid dampers, in the outrigger system. First, a high-rise building is modeled to portray the St. Francis Shangri-La Place in Philippines. The optimal performance of the outrigger damping system for mitigation of seismic responses in terms of damper size and location also is subsequently evaluated. The efficacy of the semi-active damped outrigger system is finally verified through numerical simulation.

• Structural Engineering and Mechanics
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• 제20권5호
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• pp.543-558
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• 2005

The natural frequencies of a long span bridge vary during its construction and it is thus difficult to apply traditional tuned liquid column dampers (TLCD) with a fixed configuration to reduce bridge vibration. The restriction of TLCD imposed by frequency tuning requirement also make it difficult to be applied to structure with either very low or high natural frequency. A semi-active tuned liquid column damper (SATLCD), whose natural frequency can be altered by active control of liquid column pressure, is studied in this paper. The principle of SATLCD with adaptive tuning capacity is first introduced. The analytical models are then developed for lateral vibration of a structure with SATLCD and torsional vibration of a structure with SATLCD, respectively, under either harmonic or white noise excitation. The non-linear damping property of SATLCD is linearized by an equivalent linearization technique. Extensive parametric studies are finally carried out in the frequency domain to find the beneficial parameters by which the maximum vibration reduction can be achieved. The key parameters investigated include the distance from the centre line of SATLCD to the rotational axis of a structure, the ratio of horizontal length to the total length of liquid column, head loss coefficient, and frequency offset ratio. The investigations demonstrate that SATLCD can provide a greater flexibility for its application in practice and achieve a high degree of vibration reduction. The sensitivity of SATLCD to the frequency offset between the damper and structure can be improved by adapting its frequency precisely to the measured structural frequency.

• Structural Engineering and Mechanics
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• 제83권5호
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• pp.655-669
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• 2022

Passive vibration control devices like tuned liquid column dampers (TLCD) not only significantly reduce buildings' vibrations but also can serve as a water storage facility. The recently introduced modified form of TLCD known as tuned liquid column ball damper (TLCBD) suppressed external vibration efficiently compared to traditional TLCD. For excellent performance, the mass ratio of TLCBD should be in the range of 5% to 7%, which does not include the mass of the ball. This additional mass of the ball increases the overall structure mass. Therefore, in this paper, an effort is made to reduce the mass of TLCBD. For this purpose, a new modified version of TLCBD known as tuned liquid column hollow ball damper (TLCHBD) is proposed. The existing mathematical modeling of TLCBD is used for this new damper by updating the numerical values of the mass and mass moment of the ball. Analytically the optimal design parameters are obtained. Numerically the TLCHBD is investigated with a single degree of freedom structure under harmonic and seismic loadings. It is found that TLCHBD performance is similar to TLCBD in both loadings' cases. To validate the numerical results, an experimental study is conducted. The mass of the ball of TLCHBD is reduced by 50% compared to the ball of TLCBD. Both the arrangements are studied with a multi-degree of freedom structure under harmonic and seismic loadings using a shake table. The results of the experimental study confirm the numerical findings. It is found that the performance behavior of both the dampers is almost similar under harmonic and seismic loadings. In short, the TLCHBD is lighter in weight than TLCBD but has a similar vibration suppression ability.