Showing papers on "Dynamic Vibration Absorber published in 2002"

Analytical Solutions to H∞ and H2 Optimization of Dynamic Vibration Absorbers Attached to Damped Linear Systems

Abstract: H∞ and H 2 optimization problems of the Voigt type dynamic vibration absorber (DVA) are classical optimization problems, which have been already solved for a special case when the primary system has no damping. However, for the general case including a damped primary system, no one has solved these problems by algebraic approaches. Only the numerical solutions have been proposed until now. This paper presents the analytical solutions for the H∞and H 2 optimization of the DVA attached to the damped primary systems. In the H∞ optimization the DVA is designed such that the maximum amplitude magnification factor of the primary system is minimized; whereas in the H 2 optimization the DVA is designed such that the squared area under the response curve of the primary system is minimized. We found a series solution for the H∞ optimization and a closed-form algebraic solution for the H 2 optimization. The series solution is then compared with the numerical solution in order to check the accuracy in connection with the truncation error of the series. The exact solution presented in this paper is too complicated to handle by a hand-held calculator, so we proposed an approximate solution for the practical object.

Closed-Form Solutions to the Exact Optimizations of Dynamic Vibration Absorbers (Minimizations of the Maximum Amplitude Magnification Factors)

Abstract: A typical design problem for which the fixed-points method was originally developed is that of minimizing the maximum amplitude magnification factor of a primary system by using a dynamic vibration absorber This is an example of usual cases for which their exact solutions are not obtained by the well-known heuristic approach. In this paper, more natural formulation of this problem is studied, and algebraic closed-form exact solutions to both the optimum tuning ratio and the optimum damping coefficient for this classic problem are derived under assumption of undamped primary system. It is also proven that the minimum amplitude magnification factor, resonance and anti-resonance frequencies are entirely algebraic.

Adaptive Control of Flexible Structures Using a Nonlinear Vibration Absorber

Abstract: A nonlinear adaptive vibration absorber to control the vibrations offlexible structures is investigated. The absorber is based on thesaturation phenomenon associated with dynamical systems possessingquadratic nonlinearities and a two-to-one internal resonance. Thetechnique is implemented by coupling a second-order controller with thestructure through a sensor and an actuator. Energy is exchanged betweenthe structure and the controller and, near resonance, the structure'sresponse saturates to a small value.

State-Switched Absorber for Vibration Control of Point-Excited Beams:

Abstract: A system that has the capability to make instantaneous changes in its mass, stiffness, or damping may be termed a state-switchable dynamical system. Such a system will display different dynamical responses dependent upon its current state. State-switchable stiffness may be practically obtained through the control of the termination impedance of piezoelectric stiffness elements. If such a switchable stiffness element is incorporated as part of the spring element of a vibration absorber, the change in stiffness causes a change in the resonance frequencies of the system, thereby instantaneously 'retuning' the state-switched absorber to a new frequency. In between state switches, the operation of such a device is passive, being fundamentally a passive vibration absorber. This concept has improved performance over classical passive vibration absorbers or dampers, particularly for disturbances with multiple spectral components. This paper considers the application of such a device for the purpose of vibration control on beams subjected to harmonic point-force excitation.

A single-step automatic tuning algorithm for the delayed resonator vibration absorber

Abstract: The delayed resonator (DR) is an active vibration control approach where a passive mass-spring-damper arrangement is converted into an undamped real-time tunable dynamic absorber using partial state feedback with time delay. In the presented work, robustness of the control strategy against fluctuations in the structural parameters of the controlled system is addressed. A single-step automatic tuning algorithm based on online parameter identification is developed as a means of increasing robustness against uncertainties and variations in the mechanical properties of the absorber arrangement. The tuning process is completed within the absorber section of the controlled system with no external information from the primary structure. Implementation of the algorithm is illustrated by a numerical example, and demonstrated experimentally on a clamped-clamped flexible beam.

H2 Optimization of the Three-Element Type Dynamic Vibration Absorbers

Abstract: The dynamic vibration absorber (DVA) is a passive vibration control device which is attached to a vibrating body (called a primary system) subjected to exciting force or motion. In this paper, we will discuss an optimization problem of the three-element type DVA on the basis of the H 2 optimization criterion. The objective of the H 2 optimization is to reduce the total vibration energy of the system for overall frequencies; the total area under the power spectrum response curve is minimized in this criterion. If the system is subjected to random excitation instead of sinusoidal excitation, then the H 2 optimization is probably more desirable than the popular H∞ optimization. In the past decade there has been increasing interest in the three-element type DVA. However, most previous studies on this type of DVA were based on the H∞ optimization design, and no one has been able to find the algebraic solution as of yet. We found a closed-form exact solution for a special case where the primary system has no damping. Furthermore, the general case solution including the damped primary system is presented in the form of a numerical solution. The optimum parameters obtained here are compared to those of the conventional Voigt type DVA. They are also compared to other optimum parameters based on the H∞ criterion.

Rotor system vibration absorber

Abstract: A rotor system vibration absorber for use with a helicopter of other rotocraft is disclosed in which spring forces are provided by a plurality of elongated rods (73) arranged in a selected pattern. The rods are coupled at one end to a fixed base (79) that is coupled to a rotor hub (55), and at the other end to a tuning weight (81).

Vibration absorber for an archery bow

Abstract: An apparatus for use with an archery bow which comprises a resilient elastomeric member having at least one end, a coupler for coupling the one end of the resilient elastomeric member to an archery bow and a stabilizer weight provided in the resilient elastomeric member adjacent an opposite end from the one end. In other embodiments the apparatus has another end, a coupling provided in the another end, is barreled and has energy dispersion rings.

Design of an Adaptive Vibration Absorber to Reduce Electrical Transformer Structural Vibration

Abstract: This paper considers the design of a vibration absorber to reduce structural vibration at multiple frequencies, with an enlarged bandwidth control at these target frequencies. While the basic absorber is a passive device a control system has been added to facilitate tuning, effectively giving the combination of a passive and active device, which leads to far greater stability and robustness. Experimental results demonstrating the effectiveness of the absorber are also described.

Smart Suspension Systems for Bridge-Friendly Vehicles

Abstract: In this paper, the effects of using semi-active control strategy (such as MR dampers) in vehicle suspensions on the coupled vibrations of a vehicle traversing a bridge are examined in order to develop various designs of smart suspension systems for bridge-friendly vehicles. The bridge-vehicle coupled system is modeled as a simply supported beam traversed by a two-degree-of-freedom quarter-car model. The surface unevenness on the bridge deck is modeled as a deterministic profile of a sinusoidal wave. As the vehicle travels along the bridge, the system is excited as a result of the surface unevenness and this excitation is characterized by a frequency defined by the speed of travel and the wavelength of the profile. The dynamic interactions between the bridge and the vehicle due to surface deck irregularities are obtained by solving the coupled equations of motion. Numerical results of a passive control strategy show that, when the lower natural frequency of the vehicle matches with a natural frequency (usually the first frequency) of the bridge and the excitation frequency, the maximum response of the bridge is large while the response of the vehicle is relatively smaller, meaning that the bridge behaves like a vibration absorber. This is undesirable from a bridge design viewpoint. Comparative studies of passive and semi-active controls for the vehicle suspension are performed. It is demonstrated that skyhook control can significantly mitigate the response of the bridge, while ground-hook control reduces the tire force impacted onto the bridge.

Vibration and noise reduction of an optical disk drive by using a vibration absorber

Abstract: Vibration and noise reduction of an optical disk drive by using a vibration absorber is presented in this paper In optical disk drives such as CD-ROM or DVD drives, vibration may become one of serious problems to be resolved as the rotating speed and the storage capacity increase It is practically difficult to overcome the off-track and off-focusing errors by only the servo control without reducing vibration In particular, when an optical disk drive has a wavy spinning disk, it may suffer from severe vibration Based on the vibration signals measured by a laser vibrometer and an accelerometer, the resonance frequency of the disk drive is identified For reduction of the vibration around the resonance frequency, a vibration absorber is designed and it is equipped on the feeding deck of the drive The proposed vibration absorber consists of a steel plate ring and a rubber bobbin, which play roles of inertia mass and a spring, respectively During the design procedure of the absorber, a finite element model is used to determine the required fundamental natural frequency of the absorber The test results of vibration and noise after being equipped with the absorber show that vibration and noise of the optical disk drive are considerably reduced

Passive Damping Augmentation Using Macro-Fiber Composite Actuators

Abstract: This paper aims at presenting the structural vibration-suppression capability of the recently developed Macro-Fiber Composite (MFC) actuator as a passive piezoelectric absorber using an inductive resonant shunt circuit. The resistance and inductance of the series RL shunt circuit are designed by the analogy with the single-degree-of-freedom mechanical damped vibration absorber and by using the maximum power transfer theorem of the electric network. Experimental test of a simple cantilevered beam demonstrates that the MFC actuator has excellent capability of improving the dynamic response of the beam as a piezoelectric damping system. The damping enhancement performance of the MFC actuator is superior to that of the conventional monolithic PZT actuator.Copyright © 2002 by ASME

H 2 optimization of three-element type dynamic vibration absorbers

Abstract: The dynamic vibration absorber (DVA) is a passive vibration control device which is attached to a vibrating body (called a primary system) subjected to exciting force or motion In this paper, we will discuss an optimization problem of the three- element-type DVA on the basis of the H2 optimization criterion The objective of the H2 optimization is to reduce the total vibration energy of the system for overall frequencies; the total area under the power spectrum response curve is minimized in this criterion If the system is subjected to random excitation instead of sinusoidal excitation, then the H2 optimization is probably more desirable than the popular H(infinity ) optimization In the past decade there has been increasing interest in the three-element type DVA However, most previous studies on this type of DVA were based on the H(infinity ) optimization design, and no one has been able to find the algebraic solution as of yet We found a closed-form exact solution for a special case where the primary system has no damping Furthermore, the general case solution including the damped primary system is presented in the form of a numerical solution The optimum parameters obtained here are compared to those of the conventional Voigt type DVA They are also compared to other optimum parameters based on the H(infinity ) criterion© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering Downloading of the abstract is permitted for personal use only

Virtual Vibration Absorbers with Inherent Damping

Abstract: A physically motivated control algorithm is proposed to suppress nondecaying harmonic disturbances in mechanical structures and rotary machinery. The control scheme mimics a passive vibration absorber constructed of a symmetric pair of virtual mass-spring subsystems interconnected by a dashpot, which provides inherent damping to the controlled plant. When implemented as a feedback algorithm, this virtual absorber does not require velocity measurement to stabilize the system, and multisets of absorbers can be combined in parallel to suppress mixed-frequency vibrations. This virtual passive control technique not only ensures stability independent of detailed system structure and parameters, but also facilitates the design of a high-performance controller: It is shown that redundant sets of virtual absorbers containing different damping ratios can significantly reduce settling time. This paper starts with a single-degree-of-freedom plant and then extends to more complicated systems including multiple-degrees-of-freedom structures and a couple of nonlinear systems.

Development of the passive-active vibration absorber using piezoelectric actuators

Abstract: This paper is concerned with the development of the passive-active vibration absorber using piezoelectric actuators. The active vibration absorber system consists of 2 pairs of PZT actuators bonded on aluminum plates making s- shaped device. Hence, the active system is directly connected to the passive system. The rubber attached to the end of the beam is connected to the upper base as a structural member. It allows bending thus maximizing the vertical movement generated by the piezoceramic actuators. This paper also presents the development and the verification of the control techniques for the passive-active vibration absorber. The vibration absorber can be utilized as a passive vibration absorber when the controller is off. It is shown that vibrations can be reduced by 20dB for the first mode, when the SISO PPF controller is operated. The advantage of PPF controller provides us the most effective way of increasing damping for the particular mode of interest. However, the natural mode should be computed in the process of design, to maximize the performance. In reality the target natural frequency is estimated by the frequency response of the vibration-absorbing device and is later applied to the PPF controller as a filter frequency. In this paper, the adaptive PPF controller is considered to cope with the structural change, so that it can modify the filler frequency based on the measurement. It is found that the adaptive PPF controller is effective for the active vibration absorber when the external disturbance is applied with various excitation frequencies. It can be concluded that the proposed passive-active vibration absorber is an effective way of reducing the vibration amplitude of the precise devices in the harsh environments thus enhancing the precision.

Three-Dimensional Vibration

Abstract: The purpose of this chapter is to explore the three-dimensional vibration of an offshore platform. First, the equations of motion of the three-dimensional model are derived for two cases: a rigid structure and an elastic structure. Second, the free responses of the rigid and the elastic models are compared. The free response obtained using the rigid model allows us to gain confidence in the formulation and the numerical results obtained using the elastic model. Finally, the forced responses due to deterministic loads are investigated. Two cases are studied in particular. The first case is when a harmonic (in time) load is applied in one direction, and the second case is when steady and harmonic loads are applied in mutually perpendicular directions. The second case can be thought of as the three-dimensional loading arising from a current that also induces vortex shedding. The responses due to these simple fluid force models will prepare us for the study of responses due to more complicated fluid loading models. This subject has also been treated by Han and Benaroya [26].

Design of a Single-Crystal Piezoceramic Vibration Absorber

Abstract: The development of a new class of devices for the suppression of structural vibration becomes possible by exploiting the unique properties of single-crystal piezoceramics. These vibration absorbers will be compact, robust, and demand minimal power for operation. They will be characterized by frequency agility, which means that the absorber tuning parameters can adapt rapidly to controller command and tuning can be accomplished over a wide frequency range. Identified applications include control of turbomachinery vibration, flexible space structures, jitter control in optical systems, and vibration isolation in machinery mounts. The current state-of-the-art adaptive vibration absorber tuning range is fundamentally limited by the electromechanical coupling of presently available polycrystalline piezoceramic materials. The narrow tuning range characteristic of current vibration absorbers severely limits the implementation of the solid-state absorber concept.This work presents efforts related to the design of...

Vibration control of milling machine by using auto-tuning magnetic damper and auto-tuning vibration absorber

Abstract: This paper presents a method of micro-vibration control of milling machine heads by use of a vibration absorber. The principle used in this paper is different from that of usual absorbers. An auto-tuning vibration absorber is presented in which the absorber creates anti-resonance state. When the anti-resonance is used, the damping has to be significantly small, so it is difficult to suppress higher modal vibrations. In order to suppress higher modes, an auto-tuning magnetic damper is used. It damps higher modal vibrations, but it also increases the principal vibration. Then a method of optimal auto-tuning control is presented in which both principal and higher modal vibrations are suppressed. Experimental tests are carried out for an actual milling machine, and cutting tests are also performed.

Adaptive-passive structural vibration attenuation using distributed absorbers:

Abstract: A distributed dynamic vibration absorber with adaptive capability is presented to improve vibration suppression characteristics of harmonically excited structures. A double-ended cantilever beam carrying intermediate lumped masses forms the absorber subsection. The adaptive capability is achieved through concurrent adjustment of the positions of the moving masses, along the beam, to comply with the desired optimal performance. The necessary and sufficient conditions for the existence of periodic oscillatory behaviour, along with some physical bounds placed on the absorber parameters, form a constrained optimization problem for the optimum tuning strategy. Through numerical simulations it is shown that adaptive tuning is achieved by the variation of tuning mass locations such that the first-mode natural frequency is modulated on-line. The optimally tuned absorber provides considerable vibration suppression improvement over the passive and detuned absorbers.

Active control of flexible structures using a fuzzy logic algorithm

Abstract: This study deals with the development and application of an active control law for the vibration suppression of beam-like flexible structures experiencing transient disturbances. Collocated pairs of sensors/actuators provide active control of the structure. A design methodology for the closed-loop control algorithm based on fuzzy logic is proposed. First, the behavior of the open-loop system is observed. Then, the number and locations of collocated actuator/sensor pairs are selected. The proposed control law, which is based on the principles of passivity, commands the actuator to emulate the behavior of a dynamic vibration absorber. The absorber is tuned to a targeted frequency, whereas the damping coefficient of the dashpot is varied in a closed loop using a fuzzy logic based algorithm. This approach not only ensures inherent stability associated with passive absorbers, but also circumvents the phenomenon of modal spillover. The developed controller is applied to the AFWAL/FIB 10 bar truss. Simulated results using MATLAB© show that the closed-loop system exhibits fairly quick settling times and desirable performance, as well as robustness characteristics. To demonstrate the robustness of the control system to changes in the temporal dynamics of the flexible structure, the transient response to a considerably perturbed plant is simulated. The modal frequencies of the 10 bar truss were raised as well as lowered substantially, thereby significantly perturbing the natural frequencies of vibration. For these cases, too, the developed control law provides adequate settling times and rates of vibrational energy dissipation.

Design and dynamic analysis of an adjustable inertia absorber for semiactive structural vibration attenuation

Abstract: A new class of adaptive tuned vibration absorber, a variable effective inertia absorber, is presented to impart optimum vibration absorption. The tuning scheme has two facets: spectral analysis of the excitation and a concurrent in situ tuning of the absorber. The spectral analysis reveals the frequency content of the excitation. The online tuning uses the frequency content of the excitation to reposition a moving mass and change the damping coefficient of a variable rate damper for optimal (broadband) or tonal vibration suppression. The nonlinear differential equations of motion are linearized and then utilized to develop the online tonal and the broadband tuning of the variable effective inertia absorber. A case study is presented to demonstrate the novelty of the concept. The results show that the retuned absorber delivers considerable vibration suppression improvement over the detuned one.

Adaptive Gun Barrel Vibration Absorber

Abstract: : Gun barrel vibrations lead to dispersion in the shot patterns. Thus, reducing these vibrations should lead to increased accuracy. Since the muzzle is the anti-node for all vibration modes and its vibrations have the greatest effect on shot dispersion, it is the obvious location to attempt to dampen the vibrations. A model of the gun barrel was created in MATLAB(registered) and verified by modal impact testing. Modal impact testing was done for the barrel alone and for three different muzzle brake vibration absorber configurations. Significant reductions in muzzle vibrations were achieved using the vibration absorber. Methods of making the vibration absorber adaptive and models of such a system are presented.