A Disturbance Cancellation Perspective on Vibration Control Using a Bistable Snap-Through Attachment

2014 ◽  
Vol 136 (3) ◽  
Author(s):  
David R. Johnson ◽  
R. L. Harne ◽  
K. W. Wang

One approach to vibration control is to apply a force to a primary structure that opposes the excitation, effectively canceling the external disturbance. A familiar passive example of this approach is the linear-tuned mass absorber. In this spirit, the utility of a bistable attachment for attenuating vibrations, especially in terms of the high-orbit, snap-through dynamic, is investigated using the harmonic balance method and experiments. Analyses demonstrate the fundamental harmonic snap-through dynamic, having commensurate frequency with the single-frequency harmonic excitation, may generate adverse constructive forces that substantially reinforce the applied excitation, primarily at lower frequencies. However, both analyses and experiments indicate that such high-orbit dynamics may be largely destabilized by increased bistable attachment damping. Destructive forces, which substantially oppose the excitation, are unique in that they lead to a form of vibration attenuation analogous to strictly adding damping to the host structure, leaving its spectral characteristics largely unaltered. The experiments verify the analytical findings and also uncover nonlinear dynamics not predicted by the analysis, which render similar attenuation effects.

Author(s):  
David R. Johnson ◽  
R. L. Harne ◽  
K. W. Wang

One approach to vibration control is to apply a force to a primary structure which opposes excitation, effectively canceling the external disturbance. A familiar passive example of this approach is the linear tuned mass absorber. In this spirit, the utility of a bistable attachment for attenuating vibrations, especially in terms of the high-orbit, snap through dynamic, is investigated using the harmonic balance method and experiments. Analyses demonstrate the fundamental harmonic snap through dynamic, having commensurate frequency with the single-frequency harmonic excitation, may yield displacements either substantially in-phase or out-of-phase with the primary structure. During in-phase snap through, forces are generated by the bistable oscillator which reinforce the applied loading, resulting in dramatic amplification of primary system response. During out-of-phase snap through, forces are generated which are only partially opposed to the input, leading to a measure of host structure attenuation. The experiments verify the analytical findings and also uncover nonlinear dynamics not predicted by the analysis that have slightly favorable vibration suppression performance when compared with the out-of-phase, fundamental harmonic snap through action.


Machines ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 67
Author(s):  
Laixi Zhang ◽  
Chenming Zhao ◽  
Feng Qian ◽  
Jaspreet Singh Dhupia ◽  
Mingliang Wu

Vibrations in the aircraft assembly building will affect the precision of the robotic drilling system. A variable stiffness and damping semiactive vibration control mechanism with quasi-zero stiffness characteristics is developed. The quasi-zero stiffness of the mechanism is realized by the parallel connection of four vertically arranged bearing springs and two symmetrical horizontally arranged negative stiffness elements. Firstly, the quasi-zero stiffness parameters of the mechanism at the static equilibrium position are obtained through analysis. Secondly, the harmonic balance method is used to deal with the differential equations of motion. The effects of every parameter on the displacement transmissibility are analyzed, and the variable parameter control strategies are proposed. Finally, the system responses of the passive and semiactive vibration isolation mechanisms to the segmental variable frequency excitations are compared through virtual prototype experiments. The results show that the frequency range of vibration isolation is widened, and the stability of the vibration control system is effectively improved without resonance through the semiactive vibration control method. It is of innovative significance for ambient vibration control in robotic drilling systems.


2020 ◽  
Vol 15 ◽  
pp. 155892502098356
Author(s):  
Fuxing Chen ◽  
Hong Hu

Knitted spacer fabrics can be an alternative material to typical rubber sponges and polyurethane foams for the protection of the human body from vibration exposure, such as automotive seat cushions and anti-vibration gloves. To provide a theoretical basis for the understanding of the nonlinear vibration behavior of the mass-spacer fabric system under harmonic excitation, experimental, analytical and numerical methods are used. Different from a linear mass-spring-damper vibration model, this study builds a phenomenological model with the asymmetric elastic force and the fractional derivative damping force to describe the periodic solution of the mass-spacer fabric system under harmonic excitation. Mathematical expression of the harmonic amplitude versus frequency response curve (FRC) is obtained using the harmonic balance method (HBM) to solve the equation of motion of the system. Parameter values in the model are estimated by performing curve fit between the modeled FRC and the experimental data of acceleration transmissibility. Theoretical analysis concerning the influence of varying excitation level on the FRCs is carried out, showing that nonlinear softening resonance turns into nonlinear hardening resonance with the increase of excitation level, due to the quadratic stiffness term and the cubic stiffness term in the model, respectively. The quadratic stiffness term also results in biased vibration response and causes an even order harmonic distortion. Besides, the increase of excitation level also results in elevated peak transmissibility at resonance.


Author(s):  
P Bonello ◽  
K H Groves

An adaptive tuned vibration absorber (ATVA) can retune itself in response to a time-varying excitation frequency, enabling effective vibration attenuation over a range of frequencies. For a wide tuning range the ATVA is best realized through the use of a beam-like structure whose mechanical properties can be adapted through servo-actuation. This is readily achieved either by repositioning the beam supports (‘moveable-supports ATVA’) or by repositioning attached masses (‘moveable-masses ATVA’), with the former design being more commonly used, despite its relative constructional complexity. No research to date has addressed the fact that the effective mass of such devices varies as they are retuned, thereby causing a variation in their attenuation capacity. This article derives both the tuned frequency and effective mass characteristics of such ATVAs through a unified non-dimensional modal-based analysis that enables the designer to quantify the expected performance for any given application. The analysis reveals that the moveable-masses concept offers significantly superior vibration attenuation. Motivated by this analysis, a novel ATVA with actuator-incorporated moveable masses is proposed, which has the additional advantage of constructional simplicity. Experimental results from a demonstrator correlate reasonably well with the theory, and vibration control tests with logic-based feedback control demonstrate the efficacy of the device.


1994 ◽  
Vol 84 (6) ◽  
pp. 1991-2007 ◽  
Author(s):  
Jeffrey M. Babcock ◽  
Barry A. Kirkendall ◽  
John A. Orcutt

Abstract Observations of ocean bottom low-frequency noise and surface environmental data over a period of 27 days in the northern Atlantic during the SAMSON and SWADE experiments reveal how closely related the noise is to meteorological conditions. Double-frequency microseisms produced by nonlinear interactions of storm-induced surface gravity waves are especially evident in the frequency band 0.16 to 0.3 Hz and show a high variability in both amplitude and peak frequencies. Bifurcated at times, the peak that characterizes the microseism band contains local and distant or “teleseismic” components, which are generated at different locations. Weather and storm fetch appear to be the major contributions to the size and shape of microseism spectra. Storm development on the sea surface is associated with progressively lower microseism frequencies along with a concurrent increase in amplitude. The single-frequency microseism peak is a continuous feature and is observed to portray the same time-dependent spectral characteristics as the portion of the double-frequency peak associated with distant storms. Coherence studies confirm that both peaks (single and teleseismic double) originate at a distant source. These peaks are generated at roughly the same location with some storm component over the coastline.


Author(s):  
Haiping Liu ◽  
Dongmei Zhu

The paper concerns the dynamic responses and vibration energy harvesting characteristics in an electromagnetic vibration energy harvester comprising three-parameter mechanical vibration subsystem. For completeness and comparison, a two-parameter vibration energy harvester is also presented. The analytical expressions of the amplitude-frequency and phase-frequency responses of the inertial mass and the current in the electrical circuit are respectively derived by applying dimensionless method to the studied two- and three-parameter dynamic systems. Considering the effects of different types of ambient excitation, a single-frequency harmonic load and a periodic load are introduced into the analytical expressions on the dynamic performance of the vibration energy harvester. First of all, the influences of the designing parameters from the mechanical vibration subsystem and the electrical circuit subsystem on the vibration energy harvester are investigated. For evaluating the effects due to introducing the three-parameter mechanical vibration component, comparisons are made between two- and three-parameter vibration energy harvesters to convert the ambient excitations into electrical energy. And then, the expressions of the dimensionless average power which delivered into an electrical load under a single-frequency harmonic excitation or a periodic excitation are derived. The calculating results show that the energy conversion efficiency is enhanced significantly by changing the mechanical damping efficiency and the stiffness ratio for the three-parameter mechanical component of the energy harvester. At the same time, the average power of the three-parameter vibration energy harvester, which delivered into the electrical load, is also improved. However, the influences of the electrical circuit component on the ambient energy harvesting can be omitted when keeping the designing parameters of the mechanical part constant.


Author(s):  
Xuchu Jiang ◽  
Feng Jiang ◽  
Biao Zhang

Operational modal analysis (OMA) is a procedure that allows the modal parameters of a structure to be extracted from the measured response to an unknown excitation generated during operation. Nonlinearity is inevitably and frequently encountered in OMA. The problem: The traditional OMA method based on linear modal theory cannot be applied to a nonlinear oscillation system. The solution: This paper aims to propose a nonlinear OMA method for nonlinear oscillation systems. The new OMA method is based on the following: (1) a self-excitation phenomenon is caused by nonlinear components; (2) the nonlinear normal modes (NNMs) of the system appear under a single-frequency harmonic excitation; and (3) using forced response data, the symbolic regression method (SR) can be used to automatically search for the NNMs of the system, whose modal parameters are implicit in the expression structure expressing each NNM. The simulation result of a three-degree-of-freedom (3-DOF) nonlinear system verifies the correctness of the proposed OMA method. Then, a disc-rod rotor model is considered, and the proposed OMA method’s capability is further evaluated.


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