• Structural Engineering and Mechanics
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• 제46권2호
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• pp.153-177
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• 2013

Pendulums can be used as passive vibration control devices in several structures and machines. In the present work, the nonlinear behavior of a pendulum-tower system is studied. The tower is modeled as a bar with variable cross-section with concentrated masses. First, the vibration modes and frequencies of the tower are obtained analytically. The primary structure and absorber together constitute a coupled system which is discretized as a two degrees of freedom nonlinear system, using the normalized eigenfunctions and the Rayleigh-Ritz method. The analysis shows the influence of the geometric nonlinearity of the pendulum absorber on the response of the tower. A parametric analysis also shows that, with an appropriate choice of the absorber parameters, a pendulum can decrease the vibration amplitudes of the tower in the main resonance region. The results also show that the pendulum nonlinearity cannot be neglected in this type of problem, leading to multiplicity of solutions, dynamic jumps and instability. In order to improve the effectiveness of the control during the transient response, a hybrid control system is suggested. The added control force is implemented as a non-linear variable stiffness device based on position and velocity feedback. The obtained results show that this strategy of nonlinear control is attractive, has a good potential and can be used to minimize the response of slender structures under various types of excitation.

• Earthquakes and Structures
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• 제13권1호
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• pp.51-58
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• 2017

Passive dynamic vibration absorbers (DVAs) are often used to suppress the excessive vibration of a large structure due to their simple construction and low maintenance cost compared to other vibration control techniques. A new type of passive DVA consists of two pendulums connected with spring and dashpot element is investigated. This research evaluated the performance of the DVA in reducing the vibration response of a two degree of freedom shear structure. A model for the two DOF vibration system with the absorber is developed. The nominal absorber parameters are calculated using a Genetic Algorithm(GA) procedure. A parametric study is performed to evaluate the effect of each absorber parameter on performance. The simulation results show that the optimum condition for the absorber frequencies and damping ratios is mainly affected by pendulum length, mass, and the damping coefficient of the pendulum's hinge joint. An experimental model validates the theoretical results. The simulation and experimental results show that the proposed technique is able be used as an effective alternative solution for reducing the vibration response of a multi degree of freedom vibration system.

• Structural Engineering and Mechanics
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• 제66권2호
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• pp.161-172
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• 2018

The passive control of structures using a pendulum tuned mass damper has been extensively studied in the technical literature. As the frequency of the pendulum depends only on its length and the acceleration of gravity, to tune the frequency of the pendulum with that of the structure, the pendulum length is the only design variable. However, in many cases, the required length and the space necessary for its installation are not compatible with the design. In these cases, one can replace the classical pendulum by a virtual pendulum which consists of a mass moving over a curved surface, allowing thus for a greater flexibility in the absorber design, since the length of the pendulum becomes irrelevant and the shape of the curved surface can be optimized. A mathematical model for a building with a pendular tuned mass damper and a detailed parametric analysis is conducted to study the influence of this device on the nonlinear oscillations and stability of the main system under harmonic and seismic base excitation. In addition to the circular profiles, different curved surfaces with softening and hardening characteristics are analyzed. Also, the influence of impact on energy dissipation is considered. A detailed parametric analysis is presented showing that the proposed damper can not only reduce sharply the displacements, and consequently the internal forces in the main structure, but also the accelerations, increasing user comfort. A review of the relevant aspects is also presented.

• Structural Engineering and Mechanics
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• 제57권1호
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• pp.161-178
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• 2016

This research is aimed to design and analyze the performance of double dynamic vibration absorber (DVA) using a pendulum and a spring-mass type absorber for reducing vibration of two-DOF vibration system. The conventional fixed-points method and genetics algorithm (GA) optimization procedure are utilized in designing the optimal parameter of DVA. The frequency and damping ratio are optimized to determine the optimal absorber parameters. The simulation results show that GA optimization procedure is more effective in designing the double DVA in comparison to the fixed-points method. The experimental study is conducted to verify the numerical result.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1996년도 춘계학술대회논문집; 부산수산대학교, 10 May 1996
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• pp.177-183
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• 1996

By utilizing the concept of normal modes, nonlinear dynamics is studied on pendulum dynamic absorber. When the spring mode loses the stability in undamped free system, a dynamic two-well potential is formed in Poincare map. A procedure is formulated to compute the forced responses associated with bifurcating mode and predict double saddle-loop phenomenon. It is found that quasiperiodic motion and stable periodic motion coexist in some parameter ranges, and only periodic motions or rotation of pendulum with chaotic fluctuation are observed in other ranges.

• Structural Engineering and Mechanics
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• 제51권5호
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• pp.743-754
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• 2014

Investigations of regular and chaotic vibrations of the autoparametric pendulum absorber suspended on a nonlinear coil spring and a magnetorheological damper are presented in the paper. Application of a semi-active damper allows controlling the dangerous motion without stooping of system and additionally gives new possibilities for designers. The investigations are curried out close to the main parametric resonance. Obtained numerical and experimental results show that the semi-active suspension may reduce dangerous motion and it also allows to maintain the pendulum at a given attractor or to jump to another one. Moreover, the results show that, for some parameters, MR damping may transit to chaotic motions.

• Structural Engineering and Mechanics
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• 제89권6호
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• pp.549-556
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• 2024

A serial pendulum dynamic vibration absorber (DVA) was designed to suppress the vibration of two degrees of freedom (Two-DOF) structure model. The optimal DVA parameters are selected using a genetic algorithm (GA) by minimizing the fitness function formulated from the system's frequency response function (FRF). Two fitness function criteria, using one and two target frequency ranges, were utilized to calculate the optimal DVA parameters. The optimized serial pendulum DVA parameters were used to reduce structural vibration under free and forced excitation conditions. The simulation study found that the serial pendulum DVA can effectively reduce the vibration response for a small excitation amplitude. However, the DVA performance decreases for a large excitation amplitude due to the nonlinearity of pendulum motion, and the percentage of vibration response attenuation is smaller than that obtained using a small excitation amplitude.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2010년도 추계학술대회 논문집
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• pp.83-88
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• 2010

• 대한조선학회논문집
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• 제32권3호
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• pp.1-18
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• 1995

중력진자식과 원심진자식의 두가지 형의 소형동흡진기를 이용한 구조물 진동의 제어시스템을 개발하였다. 개발된 본 시스템은 step 및 servo motor, 소형흡진기, metor drive unit와 제어장치로 구성되어 있으며, 구조물의 진동을 수진기로 감지하고, 이 신호를 받아 소형흡진기의 기능을 최적 제어하여 구조물의 진동을 제어한다. 제어시스템의 제어성능 검증시험을 위해 상자형 강판구조물($L{\times}W{\times}H{\times}T=800mm{\times}700mm{\times}1500mm{\times}7mm$) 중량 180kg를 제작하여 시험을 수행하였으며, 실험결과 중력진자식 흡진기는 95%의 흡진성능을, 원심진자식 흡진기는 88%의 흡진성능을 가지게 됨이 확인되었다.

• Structural Engineering and Mechanics
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• 제32권4호
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• pp.517-529
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• 2009

A passive vibration mitigation architecture is proposed to damp transverse vibrations of guyed masts. The scheme is based on a number of pendula attached to the mast and tuned to the vibration modes to be controlled. This scheme differs from the well-known autoparametric pendulum absorber system. The equations of motion of the guyed mast with an arbitrary number of pendula are obtained. The leading bending behaviour of a typical truss mast is described by an equivalent beam model whereas the guys are conveniently modeled as equivalent transverse springs whose stiffness comprises the elastic and geometric stiffness. By assuming a mast with an inertially and elastically isotropic cross-section, a planar model of the guyed mast is investigated. The linearization of the equations of motion of the mast subject to a harmonic distributed force leads to the transfer functions of the structure without the dampers and with the dampers. The transfer functions allow to investigate the mitigation effects of the pendula. By employing one pendulum only, tuned to the frequency of the lowest mode, the effectiveness of the passive vibration potential in reducing the motion and acceleration of the top section of the mast is demonstrated.