• Smart Structures and Systems
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• v.14 no.3
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• pp.327-345
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• 2014

This paper presents a composite control strategy for the active suppression of vibration due to the unknown disturbances, such as external excitation, harmonic effects and control spillover, as well as high-frequency accelerometer measurement noise in the all-clamped stiffened plate. The proposed composite control action based on the modal approach, consists of two contributions including feedback part and feedforward part. The feedback part is the well-known PID controller, which is widely used to increase the structure damping and improve its dynamic performance close to the resonance frequencies. In order to get better performance for vibration suppression, the weight matrixes is optimized by chaos sequence. Then an improved disturbance observer (IDOB) as the feedforward compensation part is developed to enhance the vibration suppression performance of PID under various disturbances and uncertainties. The proposed IDOB can simultaneously estimate the various disturbances dynamically as well as measurement noise acting on the system and suppress them by feedforward compensation design. A rigorous analysis is also given to show why the IDOB can effectively suppress the unknown disturbances and measurement noise. In order to verify the proposed composite control algorithm (IDOB-PID), the dSPACE real-time simulation platform is used and an experimental platform for the all-clamped stiffened plate active vibration control system is set up. The experimental results demonstrate the effectiveness, practicality and strong anti-disturbances ability of the proposed control strategy.

• Structural Engineering and Mechanics
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• v.20 no.5
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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.

• Journal of Korean Association for Spatial Structures
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• v.11 no.2
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• pp.101-110
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• 2011

Many researchers have attempted to apply semi-active control systems in the civil engineering structures. Recently, magneto-rheological(MR) fluid dampers have been developed. This MR damper is one of semi-active dampers as a new class of smart dampers. This paper discusses the application of MR damper for seismic response control of adjacent buildings subjected to earthquake. Here, a controllable damping force of MR damper that is installed between adjacent buildings is applied to seismic response control. A hybrid model combines skyhook and groundhook control algorithm so that the benefits of each can be combined together. In this paper, hybrid control model are applied to the multi degree of freedom system representative of buildings in order to reduce seismic response of adjacent buildings. And the performance of hybrid control model is compared with that of others. It was demonstrated that hybrid control model or adjacent buildings with MR damper was effective for seismic response control of two adjacent buildings reciprocally.

• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.2 s.54
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• pp.47-56
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• 2007

In this study, tile performance of a passive tuned mass damper (TMD) and a semi-active tuned mass damper (STMD) was evaluated in terms of seismic response control of elastic and inelastic structures under seismic loads. First, elastic displacement spectra were obtained for the damped structures with a passive TMD, which was optimally designed using the frequency and damping ratio presented by previous study, and with a STMD proposed in this study. The displacement spectra confirm that STMD provides much better control performance than passive md with less stroke. Also, the robustness or the TMD was evaluated by off-tuning the frequency of the TMD to that of the structure. Finally, numerical analyses were conducted for an inelastic structure of which hysteresis was described by Bouc-Wen model and the results indicated that the performance of the passive TMD of which design parameters were optimized for a elastic structure considerably deteriorated when the hysteretic portion or the structural responses increased, while the STMD showed about 15-40% more response reduction than the TMD.

• Smart Structures and Systems
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• v.19 no.4
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• pp.341-350
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• 2017

Based on the super elastic properties of the shape memory alloy (SMA) and the inverse piezoelectric effect of piezoelectric (PZT) ceramics, a kind of hybrid semi-active control device was designed and made, its mechanical properties test was done under different frequency and different voltage. The local search ability of genetic algorithm is poor, which would fall into the defect of prematurity easily. A kind of adaptive immune memory cloning algorithm(AIMCA) was proposed based on the simulation of clone selection and immune memory process. It can adjust the mutation probability and clone scale adaptively through the way of introducing memory cell and antibody incentive degrees. And performance indicator based on the modal controllable degree was taken as antigen-antibody affinity function, the optimization analysis of damper layout in a space truss structure was done. The structural seismic response was analyzed by applying the neural network prediction model and T-S fuzzy logic. Results show that SMA and PZT friction composite damper has a good energy dissipation capacity and stable performance, the bigger voltage, the better energy dissipation ability. Compared with genetic algorithm, the adaptive immune memory clone algorithm overcomes the problem of prematurity effectively. Besides, it has stronger global searching ability, better population diversity and faster convergence speed, makes the damper has a better arrangement position in structural dampers optimization leading to the better damping effect.

• Smart Structures and Systems
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• v.18 no.1
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• pp.75-92
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• 2016

The design of a semi-active (SA) control system addressed to mitigate wind induced structural demand to high wind turbine towers is discussed herein. Actually, the remarkable growth in height of wind turbines in the last decades, for a higher production of electricity, makes this issue pressing than ever. The main objective is limiting bending moment demand by relaxing the base restraint, without increasing the top displacement, so reducing the incidence of harmful "p-delta" effects. A variable restraint at the base, able to modify in real time its mechanical properties according to the instantaneous response of the tower, is proposed. It is made of a smooth hinge with additional elastic stiffness and variable damping respectively given by springs and SA magnetorheological (MR) dampers installed in parallel. The idea has been physically realized at the Denmark Technical University where a 1/20 scale model of a real, one hundred meters tall wind turbine has been assumed as case study for shaking table tests. A special control algorithm has been purposely designed to drive MR dampers. Starting from the results of preliminary laboratory tests, a finite element model of such structure has been calibrated so as to develop several numerical simulations addressed to calibrate the controller, i.e., to achieve as much as possible different, even conflicting, structural goals. The results are definitely encouraging, since the best configuration of the controller leaded to about 80% of reduction of base stress, as well as to about 30% of reduction of top displacement in respect to the fixed base case.

• Structural Engineering and Mechanics
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• v.29 no.5
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• pp.505-530
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• 2008

This paper proposes the application of active multiple tuned mass dampers (AMTMD) for translational and torsional response control of a simplified two-degree-of-freedom (2DOF) structure, able to represent the dynamic characteristics of general asymmetric structures, under the ground acceleration. This 2DOF structure is a generalized 2DOF system of an asymmetric structure with predominant translational and torsional responses under earthquake excitations using the mode reduced-order method. Depending on the ratio of the torsional to the translational eigenfrequency, i.e. the torsional to translational frequency ratio (TTFR), of asymmetric structures, the following three cases can be distinguished: (1) torsionally flexible structures (TTFR < 1.0), (2) torsionally intermediate stiff structures (TTFR = 1.0), and (3) torsionally stiff structures (TTFR > 1.0). The even distribution of the AMTMD within the whole width and half width of the asymmetric structure, thus leading to three cases of installing the AMTMD (referred to as the AMTMD of case 1, AMTMD of case 2, AMTMD of case 3, respectively), is taken into account. In the present study, the criterion for searching the optimum parameters of the AMTMD is defined as the minimization of the minimum values of the maximum translational and torsional displacement dynamic magnification factors (DMF) of an asymmetric structure with the AMTMD. The criterion used for assessing the effectiveness of the AMTMD is selected as the ratio of the minimization of the minimum values of the maximum translational and torsional displacement DMF of the asymmetric structure with the AMTMD to the maximum translational and torsional displacement DMF of the asymmetric structure without the AMTMD. By resorting to these two criteria, a careful examination of the effects of the normalized eccentricity ratio (NER) on the effectiveness and robustness of the AMTMD are carried out in the mitigation of both the translational and torsional responses of the asymmetric structure. Likewise, the effectiveness of a single ATMD with the optimum positions is presented and compared with that of the AMTMD.

• Earthquakes and Structures
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• v.12 no.4
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• pp.425-436
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• 2017

Vibration control using a tuned mass damper (TMD) is an effective technique that has been verified using analytical methods and experiments. It has been applied in mechanical, automotive, and structural applications. However, the damping of a TMD cannot be adjusted in real time. An excessive mass damper stroke may be introduced when the mass damper is subjected to a seismic excitation whose frequency content is within its operation range. The semi-active tuned mass damper (SATMD) has been proposed to solve this problem. The parameters of an SATMD can be adjusted in real time based on the measured structural responses and an appropriate control law. In this study, a stiffness-controllable TMD, called a leverage-type stiffness-controllable mass damper (LSCMD), is proposed and fabricated to verify its feasibility. The LSCMD contains a simple leverage mechanism and its stiffness can be altered by adjusting the pivot position. To determine the pivot position of the LSCMD in real time, a discrete-time direct output-feedback active control law that considers delay time is implemented. Moreover, an identification test for the transfer function of the pivot driving and control systems is proposed. The identification results demonstrate the target displacement can be achieved by the pivot displacement in 0-2 Hz range and the control delay time is about 0.1 s. A shaking-table test has been conducted to verify the theory and feasibility of the LSCMD. The comparisons of experimental and theoretical results of the LSCMD system show good consistency. It is shown that dynamic behavior of the LSCMD can be simulated correctly by the theoretical model and that the stiffness can be properly adjusted by the pivot position. Comparisons of experimental results of the LSCMD and passive TMD show the LSCMD with less demand on the mass damper stroke than that for the passive TMD.

• Smart Structures and Systems
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• v.13 no.2
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• pp.281-303
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• 2014

In order to suppress the wind-induced vibrations of the Canton Tower, a pair of active mass driver (AMD) systems has been installed on the top of the main structure. The structural principal directions in which the bending modes of the structure are uncoupled are proposed and verified based on the orthogonal projection approach. For the vibration control design in the principal X direction, the simplified model of the structure is developed based on the finite element model and modified according to the field measurements under wind excitations. The AMD system driven by permanent magnet synchronous linear motors are adopted. The dynamical models of the AMD subsystems are determined according to the open-loop test results by using nonlinear least square fitting method. The continuous variable gain feedback (VGF) control strategy is adopted to make the AMD system adaptive to the variation in the intensity of wind excitations. Finally, the field tests of free vibration control are carried out. The field test results of AMD control show that the damping ratio of the first vibration mode increases up to 11 times of the original value without control.

• Structural Engineering and Mechanics
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• v.14 no.5
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• pp.521-542
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• 2002

Application of piezoceramic materials in actuation and sensing of vibration is of current interest. Potential and more popular applications of piezoceramics are probably in the field of active vibration control. However, the objective of this work is to investigate the effect of shunted piezoceramics as passive vibration control devices when bonded to a host structure. Resistive shunting of a piezoceramic bonded to a cantilevered duralumin beam has been investigated. The piezoceramic is connected in parallel to an electrical network comprising of resistors and inductors. The piezoceramic is a capacitor that stores and discharges electrical energy that is transformed from the mechanical motion of the structure to which it is bonded. A resistor across the piezoceramic would be termed as a resistively shunted piezoceramic. Similarly, an inductor across the piezoceramic is termed as a resonantly shunted piezoceramic. In this study, the effect of resistive shunting on the nature of damping enhancement to the host structure has been investigated. Analytical studies are presented along with experimental results.