Philip A. Feurtado

A normalized wave number variation parameter for acoustic black hole design

In recent years, the concept of the Acoustic Black Hole has been developed as an efficient passive, lightweight absorber of bending waves in plates and beams. Theory predicts greater absorption for a higher thickness taper power. However, a higher taper power also increases the violation of an underlying theory smoothness assumption. This paper explores the effects of high taper power on the reflection coefficient and spatial change in wave number and discusses the normalized wave number variation as a spatial design parameter for performance, assessment, and optimization.

Wavenumber transform analysis for acoustic black hole design

Acoustic black holes (ABHs) are effective, passive, lightweight vibration absorbers that have been developed and shown to effectively reduce the structural vibration and radiated sound of beam and plate structures. ABHs employ a local thickness change that reduces the speed of bending waves and increases the transverse vibration amplitude. The vibrational energy can then be effectively focused and dissipated by material losses or through conventional viscoelastic damping treatments. In this work, the measured vibratory response of embedded ABH plates was transformed into the wavenumber domain in order to investigate the use of wavenumber analysis for characterizing, designing, and optimizing practical ABH systems. The results showed that wavenumber transform analysis can be used to simultaneously visualize multiple aspects of ABH performance including changes in bending wave speed, transverse vibration amplitude, and energy dissipation. The analysis was also used to investigate the structural acoustic coupling of the ABH system and determine the radiation efficiency of the embedded ABH plates compared to a uniform plate. The results demonstrated that the ABH effect results in acoustic decoupling as well as vibration reduction. The wavenumber transform based methods and results will be useful for implementing ABHs into real world structures.

Investigation of boundary-taper reflection for acoustic black hole design

In recent years the concept of the acoustic black hole (ABH) has been developed as an efficient, passive, lightweight absorber of bending waves in beams and plates. ABHs are implemented into structures by introducing a smoothly decreasing local change in the thickness of a beam or plate according to a power law function. By having the beam or plate thickness decrease to zero the bending wave speed theoretically goes to zero and the waves never reflect back from the thin edge; thus they are “absorbed.” ABH theory does not account for impedance mismatches between a uniform beam, and impedance mismatches within the ABH taper, which can cause bending waves to reflect off of an ABH, hindering performance. In this study numerical models were used to investigate the reflection of bending waves from ABHs attached to uniform beams with and without anechoic terminations. It was shown that the reflection of bending waves trended similarly to the normalized wavenumber variation, a parameter that determines whether or not fundamental theoretical assumptions are valid. The results will be useful for the design, characterization and optimization of vibration attenuation performance of acoustic black holes.

Multi-objective optimization of acoustic black hole vibration absorbers

Structures with power law tapers exhibit the acoustic black hole (ABH) effect and can be used for vibration reduction. However, the design of ABHs for vibration reduction requires consideration of the underlying theory and its regions of validity. To address the competing nature of the best ABH design for vibration reduction and the underlying theoretical assumptions, a multi-objective approach is used to find the lowest frequency where both criteria are sufficiently met. The Pareto optimality curve is estimated for a range of ABH design parameters. The optimal set could then be used to implement an ABH vibration absorber.

Progressive phase trends in plates with embedded acoustic black holes

Acoustic black holes (ABHs) have been explored and demonstrated to be effective passive treatments for broadband noise and vibration control. Performance metrics for assessing damping concepts are often focused on maximizing structural damping loss factors. Optimally performing damping treatments can reduce the resonant response of a driven system well below the direct field response. This results in a finite structure whose vibration input-output response follows that of an infinite structure. The vibration mobility transfer functions between locations on a structure can be used to assess the structures vibration response phase, and compare its phase response characteristics to those of idealized systems. This work experimentally explores the phase accumulation in finite plates, with and without embedded grids of ABHs. The measured results are compared and contrasted with theoretical results for finite and infinite uniform plates. Accumulated phase characteristics, their spatial dependence and limits, are examined for the plates and compared to theoretical estimates. The phase accumulation results show that the embedded acoustic black hole treatments can significantly enhance the damping of the plates to the point that their phase accumulation follows that of an infinite plate.

Modeling and optimization of acoustic black hole vibration absorbers

Recent studies have shown that the acoustic black hole (ABH) effect can be used to provide vibration absorption and improved structural-acoustic response. In this talk, several aspects of the design and implementation of ABH vibration absorbers will be discussed. First, to address the competing nature of the best ABH taper for vibration reduction and the underlying theoretical assumptions, a multi-objective approach is used to find the best ABH parameters where both criteria are sufficiently met. Next, the modeling challenges associated with one- and two-dimensional ABH design will be discussed and a mesh convergence study will be presented. Finally, the use of multiobjective optimization for ABH design will be discussed for aerospace and marine applications.Recent studies have shown that the acoustic black hole (ABH) effect can be used to provide vibration absorption and improved structural-acoustic response. In this talk, several aspects of the design and implementation of ABH vibration absorbers will be discussed. First, to address the competing nature of the best ABH taper for vibration reduction and the underlying theoretical assumptions, a multi-objective approach is used to find the best ABH parameters where both criteria are sufficiently met. Next, the modeling challenges associated with one- and two-dimensional ABH design will be discussed and a mesh convergence study will be presented. Finally, the use of multiobjective optimization for ABH design will be discussed for aerospace and marine applications.

Transmission loss of plates with embedded acoustic black holes

In recent years acoustic black holes (ABHs) have been developed and demonstrated as an effective method for developing lightweight, high loss structures for noise and vibration control. ABHs employ a local thickness change to tailor the speed and amplitude of flexural bending waves and create concentrated regions of high strain energy which can be effectively dissipated through conventional damping treatments. These regions act as energy sinks which allow for effective broadband vibration absorption with minimal use of applied damping material. This, combined with the reduced mass from the thickness tailoring, results in a treated structure with higher loss and less mass than the original. In this work, the transmission loss (TL) of plates with embedded ABHs was investigated using experimental and numerical methods in order to assess the usefulness of ABH systems for TL applications. The results demonstrated that damped ABH plates offer improved performance compared to a uniform plate despite having less mass. The result will be useful for applying ABHs and ABH systems to practical noise and vibration control problems.

Wavenumber domain analysis of plates with embedded acoustic black holes

Acoustic black holes (ABHs) have been developed and demonstrated as effective, passive, lightweight bending wave absorbers that reduce the structural vibration and radiated sound power of plates. By introducing a gradual change in the local plate thickness, the bending wave speed is reduced and the transverse vibration amplitude is increased. Energy can then be effectively dissipated through material losses or attached damping treatments. In this paper, wavenumber spectra were generated from the vibrational responses of a uniform plate, an undamped ABH plate, and a damped ABH plate. The results showed that wavenumber transform analysis is a useful method for investigating and characterizing ABH performance and behavior. The results also demonstrated that ABHs can distribute supersonic bending waves into subsonic wavenumbers. The results will be useful for the design, characterization, and optimization of ABH systems for real structures

Experimental Analysis of Vibration and Radiated Sound Power Reduction Using an Array of Acoustic Black Holes

The Acoustic Black Hole (ABH) has been developed in recent years as an effective, passive, and lightweight method for attenuating bending wave vibrations in beams and plates. The acoustic black hole effect utilizes a local change in the plate or beam thickness to reduce the bending wave speed and increase the transverse vibration amplitude. Attaching a viscoelastic damping layer to the ABH results in effective energy dissipation and vibration reduction. Surface averaged mobility and radiated sound power measurements were performed on an aluminum plate containing an array of 20 two-dimensional ABHs with damping layers and compared to a similar uniform plate. Detailed laser vibrometer scans of an ABH cell were also performed to analyze the vibratory characteristics of the individual ABHs and compared with mode shapes calculated using Finite Elements. The diameter of the damping layer was reduced in successive steps to experimentally demonstrate the effect of damping layer distribution on the ABH performance. The experimental analysis demonstrated the importance of low order ABH modes in reducing the vibration and radiated sound power of plates with embedded ABHs. The results will be useful for designing the low frequency performance of future ABH systems and describing ABH performance in terms of design parameters.Copyright