Recent advances in nonlinear passive vibration isolators

https://hal.archives-ouvertes.fr/hal-01357931/document

Nonlinear normal modes, Part I: A useful framework for the structural dynamicist

Conventional passive periodic structures exhibit unique dynamic characteristics that make them act as mechanical filters for wave propagation. As a result, waves can propagate along the periodic structures only within specific frequency bands called the Pass Bands and wave propagation is completely blocked within other frequency bands called the Stop Bands. In this paper, the emphasis is placed on providing the passive structures with active control capabilities in order to tune the spectral width and location of the pass and stop bands in response to the structural vibration. Apart from their unique filtering characteristics, the ability of periodic structures to transmit waves, from one location to another, within the pass bands can be greatly reduced when the ideal periodicity is disrupted resulting in the well-known phenomenon of Localization. In the case of passive structures, the aperiodicity (or the disorder) can result from unintentional material, geometric and manufacturing variability. However, in the case of active periodic structures the aperiodicity is intentionally introduced by proper tuning of the controllers of the individual substructure or cell. The theory governing the operation of this class of Active Periodic structures is introduced and numerical examples are presented to illustrate their tunable filtering and localization characteristics. The examples considered include periodic/aperiodic spring-mass systems controlled by piezoelectric actuators. The presented results emphasize the unique potential of the active periodic structures in controlling the wave propagation both in the spectral and spatial domains in an attempt to stop/confine the propagation of undesirable disturbances.

Active Control of Periodic Structures

The purpose of this study is the theoretical and experimental investigation of targeted energy transfers from a two-degree-of-freedom primary structure to a nonlinear energy sink (NES). It is demonstrated that an NES can resonate with and extract energy from both modes of the primary structure. By facilitating these energy transfers, notably through excitation of appropriate periodic and quasi-periodic orbits, one can promote dissipation of a major portion of externally induced energy in the nonlinear attachment.

/pdf/theoretical-and-experimental-study-of-multimodal-targeted-dkpw8p45lw.pdf

Theoretical and experimental study of multimodal targeted energy transfer in a system of coupled oscillators

Nonlinear normal modes for vibratory systems under harmonic excitation

: Current space-based imaging platforms are significantly constrained in both size and weight by the launch vehicle. Increased payload size and weight results in increased cost and a decrease in launch responsiveness. The USAF Scientific Advisory Board (SAB) identified "Large lightweight structures for optics and antennas" as a revolutionary primary technology to be developed for the Air Force of the 21st Century. A membrane primary mirror in a space-based imaging system has the ability to overcome current payload constraints and meet evolutionary needs of the future. The challenge of membrane optics in space is the process of implementing adaptive optics technology to the membrane surface that will provide at least rough order of magnitude imaging, where small aberrations can be removed downstream in the system. The objective of this research was to develop a system to categorize surface properties of optical quality membrane material with the ability to interpret membrane mirror deformation. Coincident with this objective was the design and construction of membrane mirrors and associated test tooling, the design and application of in-plane zonal control for membrane mirrors, and mirror deformation analysis. The system provides wavefront analysis with both optical interferometry and Shack-Hartmann wavefront sensing, with good correlation, which compares favorably to Zygo interferometer data. Results from membrane static testing will be presented.

/pdf/optical-metrology-of-adaptive-membrane-mirrors-4wy2okyaks.pdf

Optical Metrology of Adaptive Membrane Mirrors

Precision inflatable space structures promise revolutionary change in spacecraft design over the next decade. Given the variety of previous applications and the potential of future concepts, development of advanced design tools is underway. Validation of these models requires experimental analysis of both ground and orbiting test articles. The present study examined the suitability of piezoelectric polymer materials (namely PVDF) to excite an inflated structure for modal testing. Experiments were undertaken using both a conventional electrodynamic shaker and a small sheet of PVDF bonded to an inflated torus. In addition, a linear finite element model of an inflated torus is compared to the experimental results. The results demonstrate the potential for PVDF to excite inflatable ground test articles.

Piezoelectric excitation of inflatable space structures for modal testing

Linear vibration absorbers are a valuable tool used to suppress vibrations due to harmonic excitation in structural systems While limited evaluation of the performance of nonlinear vibration absorbers for nonlinear structures exists in the literature for single mode structures, none exists for multi-mode structures Consequently, nonlinear multiple-degrees-of-freedom structures are evaluated The theory of nonlinear normal modes is extended to include consideration of modal damping, excitation and small linear coupling, allowing estimation of vibration absorber performance The dynamics of the N + 1-degrees-of-freedom system are shown to reduce to those of a two-degrees-of-freedom system on a four-dimensional nonlinear modal manifold, thereby simplifying the analysis Quantitative agreement is shown to require a higher-order model which is recommended for future investigation

Performance of Nonlinear Vibration Absorbers for Multi-Degrees-of-Freedom Systems Using Nonlinear Normal Modes

Adaptive structures technology for membrane optical surfaces

A novel approach for reducing mode localization of bladed-disk assemblies in turbomachinery is presented .A virtual shroud is created with piezoelectric coupling to reduce the sensitivity of the compressor disks to model localization. Both direct and resonant shunts are evaluated using a simple lumped-mass model. Resonant shunts are shown to be effective in reducing localization of certain structural modes.

Gregory S. Agnes

Papers

Optical Metrology of Adaptive Membrane Mirrors

Piezoelectric excitation of inflatable space structures for modal testing

Performance of Nonlinear Vibration Absorbers for Multi-Degrees-of-Freedom Systems Using Nonlinear Normal Modes

Adaptive structures technology for membrane optical surfaces

Piezoelectric coupling of bladed-disk assemblies