Showing papers on "Dynamic Vibration Absorber published in 1985"

Dynamic absorber device for use with disk drives

Abstract: A dynamic absorber device for absorbing undesirable vibrations and resonances in dynamic machines, such as disk drives, is formed with a viscoelastic link element, an absorber base and an absorber mass. The link element is disposed between the absorber base and the absorber mass to absorb vibratory forces, and to minimize the effects of bending and deformation. The absorber device is assembled to disk drive components, such as the base casting or carriage, to effectively reduce vibrations, undesirable resonances and noise.

Helicopter air-spring vibration absorber

Abstract: A tunable vibration absorber in a helicopter rotor hub arrangement with a central mass suspended in a symmetrical outer casing over the rotor hub, including an air spring for variably stiffly supporting said central mass in three dimensions.

Inertial actuator design for maximum passive and active energy dissipation in flexible space structures

Abstract: The selection of the passive parameters for passive and active inertial vibration absorbers intended for use in large flexible space structures is investigated. Optimal passive vibration absorbers are designed for one and two WF structural representations using three parameter optimization techniques: minimum maximum steady-state response; pole placement; and quadratic cost minimization. The three techniques yield nearly identical results. Theoretically, a single mode damping ratio of 5% of critical damping can be achieved with a passive vibration absorber mas that is equal to 2% of the structural modal mass. Control actuators, which incorporate passive absorber components are also designed. Optimal gains for specific passive component values are determined using Linear Quadratic Regulator formulations. The optimal actuator is the one that's combined passive components and active gains minisizes the quadratic cost. The optimal actuator's passive design is near that of the optimal passive vibration absorber leading to a near optimal sequential design technique. Proof of concept laboratory tests were performed on a quasi free-free beaa. Electromagnetic, inertial-reaction devices usable in both active and passive configurations were implemented. Experimentally, a single mode damping of

Vibration isolator and shock absorber device

Abstract: A vibration isolator and shock absorber device is presented wherein elastomeric vibration isolation elements interact with reaction elements to form differential springs, i.e., springs in which the deflection and load characteristics change with load. In the present invention, the load characteristics change from shear at low loading to compression at high loading, with a smooth transition between shear and compression.

Experiences with vibration absorbers on footbridges

Abstract: Design calculations indicated that the stoke lane and frankwell footbridges might often vibrate uncomfortably in normal use. To avoid this possibility, vibration absorbers were fitted to both structures. The type of vibration absorber in question is a free standing device, about the size of a small beer barrel, consisting of a sprung mass and a viscous damper. When inserted into the footbridge near to the principal antinode it raises the apparent damping considerably. Bridge response under controlled loading by a pedestrian was reduced to about a quarter in both structures. The effectiveness of the absorbers was checked regularly over a three- year period. Little change occurred at the stoke lane site but at frankwell modifications had to be made to the absorber to ensure that it stayed in full working order. Subsequently its performance has proved satisfactory. The experiences have shown that the absorber is a practical device that can be constructed and installed without a great deal of specialist knowledge using fairly simple equipment (a).

Vibration absorber with hydraulic damping

Abstract: A vibration absorber comprises a hub, a fly-ring and an elastomer body connecting both parts to one another. Openings are formed between the hub and the fly-ring, i.e. through the elastomer body, and these openings serve to accommodate individual or multi-part damping elements interacting with the hub or the fly-ring.

Curved rail type vibration absorber

Abstract: PURPOSE:To make it possible to obtain a small size vibration absorber having it damping coefficient which is adjustable and a long oscillating period, by disposing dampers between a plurality of carrier vehicles oscillating on a plurality of curved rails whose relative positions are adjustable CONSTITUTION:Vehicles 4, 4' mounted thereon with weights are carried on and guided by curved rails 2, 2' which are secured on bases 1, 1' adjustably in their relative positions Further, dampers 6, 6' are disposed on shafts 5, 5' attached to stems 11, 11' provided to the carrier vehicles 4, 4', and therefore, couples between both vehicles 4, 4'

Vibration control of flexible beams using an active hinge

Abstract: The use of an active hinge to attenuate the transverse vibrations of a flexible beam is examined. A slender aluminum beam is suspended vertically, cantilevered at the top. An active hinge is placed at the node of the second vibration mode. The active hinge consists of a torque motor, strain gauge, and tachometer. A control law is implemented using both beam-bending strain and the relative angular velocity measured at this hinge, thereby configuring the hinge to act as an active damper. Results from implementing this control law show little improvement in the first mode damping ratio, 130 percent increase in the second mode damping ratio, and 180 percent increase in the third mode damping ratio. The merits of using a motor with a gearbox are discussed.

A study of hydrodynamic dampers to reduce ship vibration

Abstract: This paper presents conclusions from experimental and theoretical investigations of two types of dynamic dampers for reducing ship vibration: a U-type hydrodynamic vibration damper and a spring and hydrodynamic type.

Experience with vibration absorbers on footbridges. research report

Abstract: Design calculations indicated that the Stoke Lane and Frankwell footbridges might often vibrate uncomfortably in normal use. To avoid this possibility, vibration absorbers were fitted to both structures. The type of vibration absorber in question is a free standing device, about the size of a small beer barrel, consisting of a sprung mass and a viscous damper. When inserted into the footbridge near to the principal antinode it raises the apparent damping considerably. Bridge response under controlled loading by a pedestrian was reduced to about a quarter in both structures. The effectiveness of the absorbers was checked regularly over a three-year period. Little change occurred at the Stoke Lane site but at Frankwell modifications had to be made to the absorber to ensure that it stayed in full working order. Subsequently its performance has proved satisfactory. The experiences have shown that the absorber is a practical device that can be constructed and installed without a great deal of specialist knowledge using fairly simple equipment. (Author/TRRL)

Forced Vibrations of a Circular Plate with a Nonlinear Dynamic Vibration Absorber

Abstract: In this report, first, the forced vibrations of a circular plate with a nonlinear dynamic vibration absorber are investigated theoretically. The plate is simply supported at the outer edge subjected to a sinusoidal motion of constant amplitude. The restoring force of the nonlinear dynamic vibration absorber is represented by a hardening spring having both linear and cubic nonlinear bahavior. In the analysis, the one-third order subharmonic and the third order superharmonic vibrations as well as the fundamental one are assumed. Second, it is demonstrated that the optimal tuning and damping parameters for a nonlinear magnetic dynamic vibration absorber with a hardening spring can be easily found by using the simplex method.

Antiseismic vibration isolator

Abstract: PURPOSE:To make a vibration isolator lightweight and improve the workability such as the antiseismic effect, transportation, installation by reducing the quantity of concrete used or the like constituting the upper frame to the minimum required. CONSTITUTION:An antiseismic vibration isolator 1 is constituted with an upper frame 2, a lower frame 3, and a vibration absorber 4. The upper frame 2 is composed of a plastic mold body 5 and a filling material such as concrete filled to unite the mold body 5 and a structural steelwork 6 in one body after they are assembled. The plastic mold body 5 has fixing recesses 7 and inclined grooves 8 for drainage on its upper surface and has a recess 12 formed with peripheral walls 11 on its reverse surface. The structural steelwork 6 is fitted in this recess 12, spaces formed between this structural steelwork 6 and the peripheral wall 11 on the reverse surface of the mold body 5 are filled with a filling material, and the mold body 5 and the structural steelwork 6 are united in one body as the filling material is solidified.

Development of Finite Active Control Elements for Large Flexible Space Structures.

Abstract: : A quasi free-free beam, simulating a flexible space structure, was equipped with inertial proof-mass actuators and sensors capable, in principle, of functioning in the space environment. Then tuning rules were derived which determine the optimal actuator passive stiffness and damping which minimizes the control effort required while increasing the modal damping in the structure. Active control using two local and one component level processor was demonstrated next. Lastly, multi-input, single output collocated feedback tests were performed. Optimal passive vibration absorber designs were derived to provide maximum structural damping. Theoretically, addition of an absorber mass equaling 0.5% of structural mass can result in a single mode structural damping ratio of 5%. Analysis of multimode damping using a single absorber indicated that the absorber stiffness should be tuned to the lowest mode in order to maximize the achievable damping in all the modes. Passive actuator components and active feedback gains were derived simultaneously and sequentially yielding identical results whose passive components equal those of the passive vibration absorber. Passive absorber and active feedback damping tests were performed. A single mode damping ratio of 4.2% was achieved by adding 2.3% of structural mass: 77% of which corresponds to 'dead' absorber mass. Multi-input, single-output control provided damping ratios ranging from 2% to 3%. This functioning collocated control element, composed of actuators, sensors and local and component level processors, constitutes the first stage of research and experimentation into distributed, hierarchic active control of elastic structural behavior.

Effect of Coulomb Friction on a Dynamic Vibration Absorber System with Harmonic Base Excitation : 2nd Report, Coulomb Friction in the Main System

Abstract: This report presents the effect of Coulomb friction combined with viscous damping in the main system, to which a viscous-damped dynamic vibration absorber is attached. The main system is subjected to harmonic base excitation, and in the analysis, a similar process is used to that explained in the previous report. The conclusions are : -(1) The numerical results of the analytical solution coincide very well with those of digital simulation. (2) Coulomb friction coexisting with the viscous damping in the main system, with a dynamic vibration absorber tuned so as to suppress the resonant response of the system in considering only viscous damping, reduces the maximum amplitudes of the main mass. The features of two equi-height maximums in the resonance curve vanish. (3) Since conventional expressions for the optimum tuning of the absorber do not fit in this case, other new empirical formulae are recommended.

Dynamic vibration absorber

Abstract: PURPOSE:To enable to asorb vibration in low frequency region by a structure wherein a weight and an elastic vibration absorbing material are joined together and cuts or cutouts are provided on the vibration absorbing material in order to reduce the spring constant without increasing the thickness of the vibration absorbing material CONSTITUTION:A dynamic vibration absorber is composed by joining a foamed material 2 with a weight 1 and joins to a matter to be absorbed its vibration 5 When the matter to be absorbed its vibration 5 vibrates, resonance occurs between the weight 1 and the foamed material 2 so that the weight 1 vibrates dynamically at the frequency determined by the spring constant of the foamed material 2 and the weight of the weight 1, resulting in reducing the vibration of the matter to be absorbed its vibration 5 In addition, the spring constant of the foamed material 2 is made small by providing cuts 3 or cutouts 4 on the foamed material 2, resulting in lowering the resonant frequency between the weight 1 and the foamed material 2

A vibration absorber and damper

Abstract: A damper which is adapted to support a static load of a device, for example an engine or a machine element, subjected to vibrations and movements and for pereventing transmission of and damping these vibrations and move­ ments comprises damping means (6,8,10) consisting of elastomeric material and a device (12) separated from said damping means for supporting substantially the whole static load so that the static load does not exert any influence on the function of preventing transmission of vibrations and the damping function of the damping means consisting of elastomeric material.

Reduction of Wind-Induced Random Vibrations by Use of an Optimal Dynamic Absorber

Abstract: The efficiency and stability of a dynamic vibration absorber in reducing wind-induced random vibrations of a structure will be investigated. The mean of the peak values of a critical stress resultant (design force) will be minimized by attaching an optimally tuned and damped linear absorber to the structure. The primary structure is modelled as a lightly-damped one-degree-of-freedom linear system. The influence of the inherent damping (not very well known in practice) of the primary structure on the choice of optimal absorber parameters and on the final response is found to be small. Alternative objective functions are studied. In a typical example, an absorber mass equal to one percent of the vibrating mass of the primary structure is found to reduce the mean of the peak values of the stress resultant by one third.

Free Vibration, Resonance and Damping

Abstract: In this chapter we shall examine the dynamic behaviour of a one degree of freedom system, introducing the terms and techniques which will be used in the later chapters. The equations of motion for a number of systems are derived. Then the behaviour of an undamped and a damped system are considered. Free vibration, response to sinusoidal forcing and finally the transient behaviour in response to general forcing are calculated.