Bending vibration of flexible structures can be suppressed passively using piezoelectric electromechanical transducers and optimally tuned LR circuits. Since these systems include both mechanical and electrical elements, the governing equations consist of electrically coupled equations of motion. This paper describes a new method for deriving the governing equations that describe a system's vibration suppression based on the equilibrium of force principle and using an equivalent mechanical model of a piezoelectric element. Both series and parallel LR circuits are considered in the modeling approach. The optimum values for a mechanical vibration absorber can be formulated by using the two fixed points method. However, exact optimal values for the resistances of the LR circuits have not been formulated in the research literature thus far, and approximate values have been used. Analytical formulations are derived in this paper, and optimum values of the LR circuits are presented, not only in displacement, but also in terms of velocity and acceleration. The effects of the stiffness of the adhesive bond between the host structure and piezoelectric element, the dielectric loss in a piezoelectric element, and the internal resistance of an inductor are considered in the theoretical analysis. The effectiveness of the described analytical method is validated through simulations and experiments.
A method for measuring the characteristic impedance and propagation constant of porous materials is described in this paper. Measurements were performed based on a surface impedance method that required a set of distinct acoustic impedances derived at the material surface. This requirement is satisfied by arbitrarily changing the air space depth behind the material, and then a new formulation is derived so that a recently developed method of determination, called the transfer function method, can be applied. An appropriate set of air space depths is also discussed. Glass wool and porous aluminum were used to assess the usefulness of the present method. The normal acoustic impedance and normal absorption coefficient of the test materials with arbitrary thicknesses or with an arbitrary air space depth behind them were calculated from the obtained characteristic impedance and propagation constant and were compared with the measured values that were obtained directly by using the transfer function method. The good agreement achieved suggests that the present method is reliable and effective enough to measure the characteristic impedance and propagation constant over a broadband frequency range.
Semi-active systems with variable stiffness and damping have demonstrated excellent performance. However, conventional devices for controlling variable stiffness are complicated and difficult to implement in most applications. To address this issue, a new configuration using two controllable dampers and two constant springs is proposed. This paper presents theoretical and experimental analyses of the proposed system. A Voigt element and a spring in series are used to control the system stiffness. The Voigt element is comprised of a controllable damper and a constant spring. The equivalent stiffness of the whole system is changed by controlling the damper in the Voigt element, and the second damper which is parallel with the other elements provides variable damping for the system. The proposed system is experimentally implemented using two magnetorheological fluid dampers for the controllable dampers. Eight different control schemes involving soft suspension, stiff suspensions with low and high damping, damping on-off (soft and stiff), stiffness on-off (low and high), and damping and stiffness on-off control are explored. The time and frequency responses of the system to sinusoidal, impulse and random excitations show that variable stiffness and damping control can be realized by the proposed system. The system with damping and stiffness on-off control provides excellent vibration isolation for a broad range of excitations.
A vibration isolation system with variable damping and stiffness control is practical and has good performances. However, conventional devices of variable stiffness are usually complicated. A magnetorheological (MR) fluid damper only needs a small electric current to provide the magnetic field. It is easy to achieve variable damping with an MR damper in vibration systems. In this paper, two MR fluid dampers in series were used to achieve the variable damping and stiffness for the system. The passive, variable damping, variable stiffness, and variable damping and stiffness systems were investigated in experiment and theoretical calculation. The time and frequency responses to sinusoidal, sweep and random inputs showed that the system with a variable damping and stiffness had better properties.
Most passive vibration isolation systems are composed of springs and dampers. Although it is possible to improve the isolation performance by active vibration control, the complexity, power requirements and cost of such a system have restricted its use. A vibration isolation system with variable damping is practical and has good performance in the high frequency region, but it was found not to improve the responses in the low frequency region. On the base of a damping on-off control method, a stiffness on-off control method and a combination of damping and stiffness on-off control method were proposed. Comparison of the responses among the proposed methods and the conventional methods showed that the damping and stiffness on-off control method had the best isolation properties in the whole frequency region. A new system with controllable dampers of two Voigt elements in series was used to achieve the proposed idea.
This paper deals with reducing floor impact vibration and sound by using a momentum exchange impact damper. The impact damper consists of a spring and a mass that is contact with the floor. When a falling object collides with the floor, the floor interacts with the damper mass, and the momentum of the falling object is transferred to the damper. In this works a computational model is formulated to simulate dynamic floor vibration induced by impact. The floor vibration is simulated for various sized damper masses. A proof-of-concept experimental apparatus was fabricated to represent a floor with an impact damper. This example system consists of an acrylic plate, a ball for falling object, and an impact damper. A comparison between simulated and experimental results were in good agreement in suggesting that the proposed impact damper is effective at reducing floor impact vibration and sound by 25% and 63%, respectively.
This paper proposes an active control type of momentum exchange impact damper (AMEID) and its application to reducing shock vibration of the floor. The floor is modeled as a one-degree-of-freedom system. The active component of AMEID is realized by using a linear motor. The controller design of AMEID is based on the LQR optimal control theory. The simulation results show that the performance of AMEID is not affected by the mass ratio. In addition, the performance of AMEID is compared with the conventional passive momentum exchange impact damper (PMEID), the active mass damper (AMD) and the conventional active control method in reducing the floor shock vibration. It is shown that the shock reduction performance obtained by AMEID is larger than that obtained by PMEID. The power consumption and the stroke of the actuator for AMEID are lower than those of AMD. Furthermore, the transmitted force obtained by AMEID is smaller than that of the conventional active control.
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