Showing papers on "Dynamic Vibration Absorber published in 2004"

Vibration Control to Avoid Stick-Slip Motion:

Abstract: Friction-induced self-sustained oscillations result in a very robust limit cycle that characterizes stick-slip motion. This type of motion should be avoided under any circumstances because it creates noise, wear, and damage. In this paper we show, by simple models, how stick-slip motion can be avoided. Effective methods are: (i) appropriate increase of internal damping that compensates the negative damping induced by a friction characteristic, which decreases with increasing sliding speed; (ii) external excitation that breaks up the limit cycle (however, this often leads to chaotic motion); (iii) passive vibration control by fluctuating normal forces. The last mentioned mechanism is new and will be investigated in detail. The stick-slip oscillator is extended by an additional degree of freedom, which couples the slipping motion to the normal force. The dynamic behavior of the system has been worked out by analytical investigations and numerical integration. Scanning a broad range of values, parameters of ...

Application of a dynamic vibration absorber to a piecewise linear beam system

Abstract: This paper deals with the application of a linear dynamic vibration absorber (DVA) to a piecewise linear beam system to suppress its first harmonic resonance. Both the undamped and the damped DVAs are considered. Results of experiments and simulations are presented and show good resemblance. It appears that the undamped DVA is able to suppress the harmonic resonance, while simultaneously many subharmonics appear. The damped DVA suppresses the first harmonic resonance as well as its super- and subharmonics.

Development of the Smart Spring for Active Vibration Control of Helicopter Blades

Abstract: Significant structural vibration is an undesirable characteristic in helicopter flight that leads to structural fatigue, poor ride quality for passengers and high acoustic signature for the vehicle...

Structural vibration control using an active resonator absorber: modeling and control implementation

Abstract: A new dynamic vibration absorber referred to as an active resonator absorber (ARA) is proposed; we explore its practical implementation using piezoelectric ceramic (PZT) inertial actuators. The ARA is a passive absorber with an additional dynamic feedback compensator within the PZT actuator. Without any controller, it becomes a passive vibration absorber due to internal damping and elasticity properties of the piezoelectric materials; hence, it is inherently fail-safe. For active operation, the compensator parameters are designed such that a resonance condition is intentionally created within the absorber subsection to mimic the vibratory energy from the system of concern to which it is attached. The resonance condition can be created through the appropriate design of the compensator and implemented through adjusting the external electrical voltage applied to the PZT actuator. Although PZT materials inherently possess nonlinear characteristics (e.g., hysteresis), an equivalent linearized model is developed for the actuator subsystem. An experimental set-up is then constructed to validate the proposed linearized model and estimate the actuator parameters using a nonlinear least squares algorithm. Because the parameters of the PZT actuators (i.e. stiffness, damping, and effective mass) are approximate, the compensator designs based on these parameters would result in partial vibration suppression when utilized in real applications. An auto-tuning method is used to effectively tune the compensator parameters to improve the vibration suppression quality. The effectiveness and stability of the proposed auto-tuning scheme when implemented on a single-degree-of-freedom primary system are demonstrated.

Tuned vibration absorber for suppression of rest tremor in Parkinson's disease.

Abstract: A simple approach for the suppression of the tremor associated with Parkinson's disease is presented. The proposed system is a tuned vibration absorber (TVA), which has been very effective in the suppression of vibrations in an experimental model of the human arm with two degrees of freedom. Theoretical and numerical methods were used to study the behaviour of the arm model and to develop an effective tremor reduction approach. Based on these studies, a vibration absorber was designed, tested numerically and fabricated for experimental testing. Expermental investigations indicated that optimum control performance was related to the position of the controller and the excitation frequency. With a distance of 160 mm from the end of forearm, the TVA was found to have the best performance, and, for different tremor frequencies, the vibration of the experimental model was reduced by more than 80%.

Snap-Through Truss as a Vibration Absorber

Abstract: In this paper we consider the possibility of elastic oscillation absorption using the snap-through truss. This truss was introduced by Mises in 1923. A single-degree-of-freedom linear oscillator is chosen as the most simple model of a continuous elastic system. The nonlinear absorber with three equilibrium positions (the snap-through truss) is attached to this oscillator. The dynamics of this system is studied by the nonlinear normal vibration mode approach. The construction and stability analysis of the localized and non-localized nonlinear normal modes are developed. If the localized mode is realized, the system energy is concentrated in the nonlinear absorber. This situation is the most appropriate to absorb vibrations.

Vibration Absorbers: A Review of Applications in Interior Noise Control of Propeller Aircraft:

Abstract: Control of interior noise levels in aircraft has been a significant research area over the last two decades. Vibration absorbers have often been researched as more efficacious solutions to this pro...

Vibration absorber for reduction of the in-plane vibration in an optical disk drive

Abstract: A new type of vibration absorber is developed to reduce the in-plane vibration of the feeding deck system in an optical disk drive. In order to derive the equations of motion for the feeding deck system with the absorbers, a vibration model is established. After the frequency response function is obtained from the equations, the effects of absorber mass, stiffness and damping are analyzed. The material properties and shape of the vibration absorber are determined from the analysis results. For the purpose of verification, the performance of the absorber is investigated through experiments. The test results show that the proposed absorber is able to considerably reduce vibration in a wide range of spindle motor speeds.

Testing of tuned liquid damper with screens and development of equivalent TMD model

Abstract: The tuned liquid damper (TLD) is increasingly being used as an economical and effective vibration absorber. It consists of a water tank having the fundamental sloshing fluid frequency tuned to the natural frequency of the structure. In order to perform efficiently, the TLD must possess a certain amount of inherent damping. This can be achieved by placing screens inside the tank. The current study experimentally investigates the behaviour of a TLD equipped with damping screens. A series of shake table tests are conducted in order to assess the effect of the screens on the free surface motion, the base shear forces and the amount of energy dissipated. The variation of these parameters with the level of excitation is also studied. Finally, an amplitude dependent equivalent tuned mass damper (TMD), representing the TLD, is determined based on the experimental results. The dynamic characteristics of this equivalent TMD, in terms of mass, stiffness and damping parameters are determined by energy equivalence. The above parameters are expressed in terms of the base excitation amplitude. The parameters are compared to those obtained using linear small amplitude wave theory. The validity of this nonlinear model is examined in the companion paper.

Control laws for an active tunable vibration absorber designed for rotor blade damping augmentation

Abstract: Most Individual Blade Control (IBC) approaches have attempted to suppress the rotor vibration by actively altering the varying aerodynamic loads on the blade using techniques such as trailing-edge servo-flaps or imbedded piezoelectric fibres to twist the blade. Unfortunately, successful implementation of these approaches has been hindered by electromechanical limitations of piezoelectric actuators. The Smart Spring is an unique approach that is designed to suppress the rotor vibration by actively altering the structural stiffness of the blade out of phase with the time varying aerodynamic forces. The Smart Spring system is able to adaptively alter the stiffness properties of the blade while requiring only small deformations of the actuator, which overcomes the major problems inherent in the former approaches. The theoretical characterisation of the Smart Spring system as a class of active Tunable Vibration Absorbers (TVA) is presented in the paper. A real-time adaptive control system was developed for a Smart Spring to suppress vibration. Initial aerodynamic wind tunnel test results using the proof-of-concept model of the device in a fixed blade indicate that the Smart Spring can evolve into a powerful approach for IBC.

Dynamic vibration absorber and dynamic vibration absorbing device using the same

Abstract: A dynamic vibration absorber (1), comprising a weight (2), a frame body (3) surrounding the weight (2), a total of four sets of vertical U-shaped plate springs (4, 5, 6, 7), each set comprising two springs, installed between the frame body (3) and the weight (2) to hold the weight (2) against the frame body (3) movably in all directions in a horizontal plane and unmovably in a vertical direction (V), and a damping mechanism (8) damping the vibration of the weight (2) in a horizontal plane.

Dynamics of structures with wideband autoparametric vibration absorbers: theory

Abstract: This article analyses the dynamics of a resonantly excited single–degree–of–freedom linear system coupled to an array of nonlinear autoparametric vibration absorbers (pendulums). Each pendulum is also coupled to the neighbouring pendulums by linear elastic springs. The case of a 1:1:…:2 internal resonance between pendulums and the primary oscillator is studied for stationary (harmonic) and non–stationary (slow frequency sweep) excitations. The method of averaging is used to obtain amplitude equations that determine the first–order approximation to the nonlinear response of the system. The amplitude equations are analysed for their equilibrium as well as non–stationary solutions as a function of the parameters associated with the absorber pendulums. For stationary excitation, most steady–state solutions correspond to modes in which only one pendulum and the primary system execute coupled motions. Conditions for the existence of manifolds of equilibria are revealed when the averaged equations are expressed in modal coordinates. In the non–stationary case with linear frequency sweep through the primary resonance region, delays through pitchforks, smooth but rapid transitions through jumps, and transitions from one stable coupled–mode branch to another are studied using numerical simulations of the amplitude equations. The array of autoparametric pendulums is shown to effectively attenuate the large–amplitude resonant response of structures over a wide band of excitation frequencies.

A New Approach to Identify Optimal Properties of Shunting Elements for Maximum Damping of Structural Vibration Using Piezoelectric Patches

Abstract: The use of shunted piezoelectric patches in reducing vibration and sound radiation of structures has several advantages over passive viscoelastic elements, e.g., lower weight with increased controllability. The performance of the piezoelectric patches depends on the shunting electronics that are designed to dissipate vibration energy through a resistive element. In past efforts most of the proposed tuning methods were based on modal properties of the structure. In these cases, the tuning applies only to one mode of interest and maximum tuning is limited to invariant points when based on den Hartog's invariant points concept. In this study, a design method based on the wave propagation approach is proposed. Optimal tuning is investigated depending on the dynamic and geometric properties that include effects from boundary conditions and position of the shunted piezoelectric patch relative to the structure. Active filters are proposed as shunting electronics to implement the tuning criteria. The developed tuning methods resulted in superior capabilities in minimizing structural vibration and noise radiation compared to other tuning methods. The tuned circuits are relatively insensitive to changes in modal properties and boundary conditions, and can applied to frequency ranges in which multiple modes have effects.

Active vibration absorber and method

Abstract: An active vibration absorber is provided for absorbing vibrations in a member (21). An inertial mass (22) is mounted on the member with a stiffness (24) between the member and the mass. A force actuator arrangement (23) applies a force between the inertial mass and the member. A damping arrangement provides for damping of a resonance of the active vibration absorber. A first sensor arrangement (29) provides at least one first signal indicative of at least one movement and/or stress related parameter for the member and a second sensor arrangement (25) provides for at least one second signal indicative of a reaction of the inertial mass. A control arrangement (30) is provided for controlling the force actuator arrangement using the at least one first signal and the at least one second signal.

Quarter-Cycle Switching Control for Switch-Shunted Dampers

Abstract: Significant interest has been generated by the possibilities of active vibration control through the implementation of state switching, with a specific implementation embodied through piezoceramic shunting. A state-switched absorber (SSA) is a vibration absorber that has the unique ability to change its resonant state amongst multiple distinct resonant states while in motion, thereby increasing the effective bandwidth over that of a single frequency device and thereby allowing control of multi-frequency, transient, and time-varying disturbances. In contrast, a switch-shunted damper (SSD) is a variant of an SSA that is used to increase the damping of the structure to which the damper is applied. Active vibration control applications discussed in the literature indicate the potential advantages of SSDs which employ piezoelectric ceramics as switchable springs with control algorithms that require switching states at points of non-zero strain. However, consideration of the constitutive equations for piezoelectric materials indicates a discontinuity in the electrical and mechanical conditions imposed by switching the stiffness at non-zero strains. A prototype SSD has been built and tested to experimentally investigate switching control logic and electrical and mechanical discontinuities at switching points; experimental measurements with this prototype SSD indicate that quarter-cycle switching algorithms which include switching states at a condition of maximum strain yield enhanced damping effectiveness but also leads to the generation of potentially undesirable mechanical transients.

The analysis of the orientation effect of non-linear flexible systems on performance of the pendulum absorber

Abstract: In practical applications, many vibration absorbers are used to absorb oscillation of a structure, one of which is pendulum-type vibration absorbers. They are widely used in engineering applications where oscillations of a structure are constrained within a prescribed envelope. In this study, the primary structure consists of a flexible beam which has a single degree of freedom, and is subjected to a vertical sinusoidal base excitation. Non-linearity in the primary structure is due to large deflections. The rotation point of the pendulum-type absorber is attached to the tip of the primary structure. The primary structure and absorber together constitute a couple systems with two degrees of freedom. The primary objective of this study is to determine the effectiveness of pendulum-type passive vibration absorber attached to a primary structure whose orientation varies. In this study, the orientation at which the absorber is effective is established, and the factors that affect performance of the absorber are determined. The results are in good agreement with the experimental ones given in the literature.

Control of sound transmission into payload fairings using distributed vibration absorbers and Helmholtz resonators

Abstract: A new passive treatment to reduce sound transmission into payload fairing at low frequency is investigated. This new solution is composed of optimally damped vibration absorbers (DVA) and optimally damped Helmholtz resonators (HR). A fully coupled structural-acoustic model of a composite cylinder excited by an external plane wave is developed as a first approximation of the system. A modal expansion method is used to describe the behavior of the cylindrical shell and the acoustic cavity; the noise reduction devices are modeled as surface impedances. All the elements are then fully coupled using an impedance matching method. This model is then refined using the digitized mode shapes and natural frequencies obtained from a fairing finite element model. For both models, the noise transmission mechanisms are highlighted and the noise reduction mechanisms are explained. Procedures to design the structural and acoustic absorbers based on single degree of freedom system are modified for the multi-mode framework. The optimization of the overall treatment parameters namely location, tuning frequency, and damping of each device is also investigated using genetic algorithm. Noise reduction of up to 9dB from 50Hz to 160Hz using 4% of the cylinder mass for the DVA and 5% of the cavity volume for the HR can be achieved. The robustness of the treatment performance to changes in the excitation, system and devices characteristics is also addressed.

Vibration absorber of closed compressor liquid storage tank

Abstract: A vibration damper for the liquid accumulating cylinder of sealed compressor features that a mass regulator is attached to the external surface of said liquid accumulating cylinder for regulating its mass to prevent its resonance at particular frequency, and another unit is provided for generated vibration heat to lower the vibration effect.

Image heating device

Abstract: An image heating device according to an embodiment of the present invention includes a heat generator that has an outer surface and that generates heat by induction heating and a heater positioned close to the outer surface of the heat generator, the heater being configured to heat the heat generator by induction heating. A positioner is located close to an end of the heater, the positioner being configured to position the heater with respect to the heat generator. A vibration absorber is attached to the positioner and is configured, in one embodiment, to viscoelasticly absorb vibration of the heater produced by a vibration caused by an electromagnetic repulsive force acting between the heat generator and the heater when the heater heats the heat generator by induction heating.

The efficiency and robustness of a uni-directional tuned liquid damper and modelling with an equivalent TMD

Abstract: The current study reports the results of an experimental program conducted on a structure fitted with a liquid damper (TLD) and subjected to harmonic excitation. Screens were placed inside the TLD to achieve the required inherent damping. In the first part of the study, reduced scale models of the building-TLD systems were tested under two levels of excitation. The efficiency of the damper was assessed by evaluating the effective damping provided to the structure and comparing it to the optimum effective damping value, provided by a linear tuned mass damper (TMD). An extensive parametric study was then conducted for one of the three models by varying both the excitation amplitude and the tuning ratio, defined as the ratio of the TLD sloshing frequency to the natural frequency of the structure. The effectiveness and robustness of a TLD with screens were assessed. Results indicate that the TLD can be tuned to achieve a robust performance and that its efficiency is not significantly affected by the level of excitation. Finally, the equivalent amplitude dependent TMD model, developed in the companion paper is validated using the system test results.

Optimization of a state-switched absorber applied to a continuous vibrating system

Abstract: A state-switched absorber (SSA) is a device that is capable of switching between discrete stiffnesses, thus it is able to instantaneously switch between resonance frequencies. The state-switched absorber is essentially a passive vibration absorber between switch events; however, at each switch event the SSA instantly 'retunes' its natural frequency and maintains that frequency until the next switch event. The SSA has shown improved performance over classical tuned vibration absorbers at reducing the vibration in a base system. This paper considers the optimization of the state-switched absorber applied to a continuous vibrating system. The objective function to be minimized in the state-switching system is the average kinetic energy of the base to which the absorber is attached. Due to the discrete nature of the switch events of the SSA, this objective function is discontinuous as a function of tuning parameters, such as frequency and attachment location. Because of the discontinuities in the objective function, classical gradient-based optimization techniques cannot be employed. To avoid the problem of discontinuities in the objective function, a heuristic approach will be utilized to optimize the state-switched absorber. The optimized performance of the state-switched absorber will be compared to that of an optimized classical tuned vibration absorber. For the entire range of forcing frequencies considered, an SSA has improved performance over a TVA.

Wind power generation device

Abstract: PROBLEM TO BE SOLVED: To provide a wind power generation device capable of effectively suppressing imbalance vibration or vibration caused by torque fluctuation generated in a drag-type or lift-type vertical shaft wind power generation device equipped with a plurality of windmill blades and comprising a simple vibration control structure manufactured at low cost. SOLUTION: The wind power generation device 1 includes a vertical shaft windmill 2 equipped with a plurality of blades 2a and generating torque by wind acting on the blades 2a, a pole 8 supporting the windmill 2 from a lower end side, and a dynamic vibration absorber 7 mounted to an upper end of the pole 8 or an upper part of the pole 8. The dynamic vibration absorber 7 is composed of a cylindrical weight 7a and a rubber isolator 7b mounted to the weight. COPYRIGHT: (C)2009,JPO&INPIT

Adaptable vibration absorber employing a magnetorheological elastomer with variable gap length and methods and systems therefor

Abstract: The inventions include an adaptive vibration absorber (AVA) and variation thereof including variations in methods and systems of usage. An exemplary AVA may operate adaptively over an appropriate relatively wide bandwidth or frequency range in vibration absorption without adding energy to the system and the problems associated with such energy addition. Further, the exemplary AVA may be of low cost as well sa lightweight and compact.

Dynamic vibration absorber

Abstract: PROBLEM TO BE SOLVED: To provide a dynamic vibration absorber having stable vibration damping effects at all times without being influenced by parameter fluctuations of a vibration damping object or the dynamic vibration absorber itself. SOLUTION: The dynamic vibration absorber 1 comprises a plurality of spring members 6a, 6b extending from a common supporting member 2, weights 7 mounted at the ends of the spring members 6a, 6b, respectively, and rockingly supported in a cantilevered fashion, and a damping member 12 for damping the rocking of the weights 7. COPYRIGHT: (C)2004,JPO&NCIPI

Tuned vibration absorber

Abstract: A tuned vibration absorber is disclosed that includes a base, a spring mounted to the base, and a mass mounted to the spring. The absorber is particularly, advantageous when mounted to a specific vehicle component via a mounting bolt that is already employed to mount that particular component. For example, a tuned vibration absorber may be mounted to a cam cover bolt on a cam cover in order to absorb undesirable vibrations at a particular frequency.

Method for producing an element for elastic coupling of a component to another component involves provision of this element with stiffening, fixing, positioning, force diversion, stop and sealing means

Abstract: The method for producing an element for elastic coupling of a component to another component serving as a vibration absorber involves provision of this element with stiffening, fixing, positioning, force diversion, stop and sealing means. Independent claims are also included for: (A) a resultant coupling element; (B) an arrangement of two components elastically coupled to one another for purposes of vibration absorption.

Design and testing of a compact layered isolator for high- frequency helicopter gearbox isolation

Abstract: Meshing gear pairs in rotorcraft transmissions are a significant source of vibration and cabin noise. This tonal, high-frequency gearbox noise (500 Hz – 2000 Hz) is primarily transmitted to the fuselage through rigid connections, which do not appreciably attenuate vibratory energy. Because periodically-layered elastomer and metal isolators exhibit transmissibility “stop bands,” or frequency ranges in which there is very low transmissibility, they may provide an elegant passive vibration control solution. Analytical investigations suggest that the addition of fluidic, inertial amplifiers between layers is particularly effective in significantly lowering the beginning stop band frequencies without adding excessive mass. Also, the tuned fluid masses together with the stiffness of the elastomer layers cause internal, tuned vibration absorber effects. A preliminary, multi-layered fluidic isolator was fabricated and tested to experimentally validate the utility of fluidic elements as highfrequency inertial amplifiers. This initial specimen, however, is relatively heavy and generally unfeasible for incorporation into gearbox suspensions. Two configurations of a new, lightweight, compact specimen were therefore designed subject to estimated gearbox isolation design constraints. Experimental and analytical transmissibilities of both the preliminary and compact specimens are compared. The compact specimen was capable of reducing transmitted vibrations by factor of 100 within the stop band. Also, the effect of precompression on elastomer stiffness properties was experimentally investigated and axial quasi-static stiffness tests were conducted to compare analytical stiffness predictions to experimental results.