Kenneth A. Cunefare

Performance of MRE-based Vibration Absorbers

The purpose of this work is to use magnetorheological elastomers (MREs) as field-dependent springs within three vibration absorber configurations, and to determine their vibration absorption characteristics. Magnetorheological elastomers are fabricated from silicone gel and iron microparticles, and implemented as tunable springs in three vibration absorber configurations, which excited the MREs in shear, squeeze mode, and compression. Each vibration absorber configuration exploits different magneto-mechanical properties, achieving very different results. The MRE iron concentration is varied to find the largest natural frequency shift for the squeeze-mode absorber due to an applied magnetic field. Absorbers with MREs containing 35% iron by volume exhibits the largest natural frequency shift, 507%. MREs containing 35% iron are placed into shear and longitudinal mode vibration absorber devices, which exhibit 470% and 180% frequency increases, respectively.

Vibration and Wave Propagation Control of Plates with Periodic Arrays of Shunted Piezoelectric Patches

Periodic arrays of shunted, piezoelectric patches are employed to control waves propagating over the surface of plate structures, and corresponding vibrations. The shunted, piezoelectric patches act as sources of impedance mismatch, which gives rise to interference phenomena resulting from the interaction between incident, reflected and transmitted waves. Periodically distributed mismatch zones, i.e., the piezo patches, produce frequency dependent, wave-dynamic characteristics, which include the generation of band gaps, or stop bands in the frequency domain. The extent of induced band gaps depends on the mismatch in impedance generated by each patch. The total impedance mismatch, in turn, is determined by the added mass and stiffness of each patch as well as the shunting electrical impedance. Proper selection of the shunting electric-circuit thus provides control over the attenuation capabilities of the piezo-plate structure, as well as the ability to adapt to changing excitation conditions. Control of wave-propagation attenuation and vibration reduction for plates with periodic, shunted, piezoelectric patches is demonstrated numerically, employing finite-element models of the considered structures.

Fundamentals of Noise and Vibration

Preface. Acknowledgements. List of contributors. An introduction to acoustics. Fundamentals of vibration. Fundamentals of human response to sound. Fundamentals of human response to vibration. Fundamentals to noise and vibration control. Fundamentals of signal processing. Fundamentals of underwater acoustics. Fundamental principles of measurement and analysis techniques. Appendix: List of symbols. Index.

State-Switched Absorber for Semi-Active Structural Control:

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. For example, 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. This paper briefly develops the fundamental analysis tools for a Single-Degree-of-Freedom state-switchable device, and then considers the application of such a device for the purpose of vibration control in a 2-DOF system. Simulation results indicate that state-switched vibration absorbers may be advantageous over classical passive tuned vibration absorbers under certain conditions.

A boundary element method for acoustic radiation valid for all wavenumbers

A boundary element method for solving the exterior acoustic radiation problem that is valid for all wavenumbers has been developed. The new formulation derives from the earlier work of Burton and Miller [Proc. R. Soc. London Ser. A 323, 201–210 (1971)], which uses a linear combination of the Helmholtz integral equation and its gradient to overcome the uniqueness problem. A main feature of this formulation is the absence of integral singularities. By restricting the field points of the kernels of the integrals to interior regions well away from radiating boundaries, the usual complication of dealing with singular kernels is circumvented. The new formulation has been named CHI, for coupled Helmholtz integrals. A corresponding computer program, CHI 4.35, can be used to compute the surface acoustic pressure on an arbitrary body for a given specified surface normal velocity. Results generated with CHI 4.35 are presented for the spherical monopole and dipole, along with results for parametric studies on the acc...

The minimum multimodal radiation efficiency of baffled finite beams

A technique for deriving the optimal surface velocity distribution on the surface of a finite baffled beam has been developed. The optimal velocity distribution minimizes the radiation efficiency of the beam for a specified maximum permissible mode and frequency. A modal expansion of the surface velocity in terms of unknown modal amplitude coefficients, the Rayleigh integral, and a far‐field intensity integration are employed to obtain a quadratic expression for the radiation efficiency of the beam. Application of a suitable constraint to avoid trivial solutions leads to an eigenvalue problem identical in form to the Rayleigh quotient employed in dynamic mechanical systems. The eigenvector of modal amplitude coefficients corresponding to the lowest eigenvalue yields the minimum radiation efficiency, while the eigenvalue itself is the actual value of the minimum radiation efficiency. Near and below coincidence, the optimal eigenvector of modal amplitude coefficients yields a radiation efficiency significan...

ON THE EXTERIOR ACOUSTIC RADIATION MODES OF STRUCTURES

The use of a modal‐style approach for the analysis of the exterior radiation characteristics of structures has recently received increasing attention. This approach generally seeks to find a set of orthogonal functions, or acoustic modes, that diagonalizes a radiation operator. These acoustic modes are found through an eigenfunction or singular value decomposition of the radiation operator. The eigenvalue or singular value associated with a given acoustic mode is directly proportional to the radiation efficiency of that acoustic mode. The acoustic mode represents a particular velocity pattern on the surface of the radiator. As with the analogous problem of finding structural natural frequencies and mode shapes, the accuracy of the acoustic modal representation depends on the number of degrees of freedom in the radiation operator. The radiation efficiency of the most efficient acoustic mode has a finite upper bound, and converges fastest with increasing degrees of freedom. Each additional degree of freedom...

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

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.

The radiation modes of baffled finite plates

The modal‐style approach for representing the exterior radiation characteristics of structures generally seeks to find a set of orthogonal functions, or acoustic modes, that diagonalize a radiation operator in the exterior domain of the structure. The choice of basis functions for the modal representation is arbitrary, though use of the natural modes of structural vibration tends to provide some physical insight. The acoustic modes are found through an eigen analysis or singular value decomposition analysis of the radiation operator. The eigenvalue or singular value associated with a given mode is directly proportional to the radiation efficiency of that mode. The dependency of the radiation efficiencies and mode shapes on the number of degrees of freedom permitted in the derivation of the radiation operator is investigated for a baffled finite rectangular plate. The accuracy of the acoustic modal representation depends on the number of degrees of freedom permitted in the derivation of the radiation opera...

Energy harvesting from hydraulic pressure fluctuations

State-of-the-art hydraulic hose and piping systems employ integral sensor nodes for structural health monitoring to avoid catastrophic failures. Energy harvesting in hydraulic systems could enable self-powered wireless sensor nodes for applications such as energy-autonomous structural health monitoring and prognosis. Hydraulic systems inherently have a high energy intensity associated with the mean pressure and flow. Accompanying the mean pressure is the dynamic pressure ripple, which is caused by the action of pumps and actuators. Pressure ripple is a deterministic source with a periodic time-domain behavior conducive to energy harvesting. An energy harvester prototype was designed for generating low-power electricity from pressure ripples. The prototype employed an axially-poled off-the-shelf piezoelectric stack. A housing isolated the stack from the hydraulic fluid while maintaining a mechanical coupling allowing for dynamic-pressure-induced deflection of the stack. The prototype exhibited an off-resonance energy harvesting problem since the fundamental resonance of the piezoelectric stack was much higher than the frequency content of the pressure ripple. The prototype was designed to provide a suitable power output for powering sensors with a maximum output of 1.2 mW. This work also presents electromechanical model simulations and experimental characterization of the piezoelectric power output from the pressure ripple in terms of the force transmitted into the harvester. (Some figures may appear in colour only in the online journal)