1. Phononic Band Gaps: From Continuous Structures to Granular Systems

Gizem Acar, Ph.D – Postdoctoral Research Associate, Balakumar Balachandran, Ph.D.  – Professor, University of Maryland, College Park

2. Design and characterization of tabletop anechoic and sonication chambers

Olivia Ott, The Johns Hopkins University

3. Application of the CAF-Mapping Algorithm to Marine Bio-Acoustics

David Lechner, The Catholic University of America

4. Experimental design for the accurate measurement of ultra-low damping of simple structures. 

Hubert Seth Hall, James J. Dlubac, and Michael Kim (Naval Surface Warfare Center Carderock Division

5. Considerations of Damping in the Design of Arrays of Tuned Mass Dampers*

John Sterling, PhD Candidate, The Catholic University of America

Abstracts

1. Phononic Band Gaps: From Continuous Structures to Granular Systems

Gizem Acar, Ph.D – Postdoctoral Research Associate, University of Maryland, College Park

Balakumar Balachandran, Ph.D.  – Professor, University of Maryland, College Park

Phononic band gaps are the frequency ranges where elastic waves cannot propagate. They may exist in continuous systems, as well as discrete arrays. This talk focuses on two systems: a 2-D periodic structure with a band gap, and a 1-D granular array with a prohibited band. i) The 2-D structure is composed of beam-like unit links, where the first mode of the unit link is similar to an inertial amplification mechanism. The first modal frequency of the unit link is significantly lower compared to its second mode, due to its amplified effective inertia. A 2-D structure built from these unit links has a band gap between the first and the second modal frequencies of the unit link. ii) The 1-D granular system has a prohibited band due to its discrete nature. The array cannot transmit frequencies higher than its out of phase periodic orbit frequency. Since the system is nonlinear, the frequencies are amplitude dependent. We present the band zones at different energy levels. Furthermore, we investigate how a uniform pre-compression applied to the granular array changes the band limits of the system response.

2. Design and characterization of tabletop anechoic and sonication chambers

Olivia Ott, The Johns Hopkins University

Access to anechoic chambers for acoustic testing can be an expensive and limited resource for acousticians. The purpose of this work was to develop small scale, portable anechoic and sonication chambers that could be used for rapid and simultaneous testing. Using consumer off the shelf (COTS) products, a low cost anechoic and sonication chamber were designed and built. Upon completion the prototypes were characterized for their acoustic performance. Both the anechoic and sonication chambers were characterized by their ability reduce ambient noise. The characterization was completed by measuring transmission loss (TL) through the chamber walls. Secondly, the sonication chamber was tested for spatial sound pressure level (SPL) variation. The procedure for spatial testing inside the chamber included measuring SPL along a horizontal stage using mini microphones. The performance and characterization of these chambers will be presented and discussed.

3. Application of the CAF-Mapping Algorithm to Marine Bio-Acoustics

David Lechner, PhD Candidate, The Catholic University of America

This presentation will discuss the adaptation of the Cross Ambiguity Function Mapping (CAF Map) algorithm and adaptations developed to use it in acoustics.  The CAF Map algorithm provides a useful means of generating a geographic visualization of acoustic data when the acoustic sources are moving.  It can be used to develop tracks of acoustic energy without first detecting and classifying the signal or used as a temporal/spatial filter to detect specific types of target movement.  The algorithm is also able to provide discrimination between multiple signals when they are broadcasting in a partially synchronized manner.  This may make the algorithm useful to detect, visualize, and track multiple marine mammal sources and observe acoustic interactions.  Application to multiple sound sources will be presented, including possible blue whale (Balaenoptera musculus),  right whales (Eubalaena australis) data and simulated humpback whale (Megaptera novaeangliae) calls.

4.  Experimental design for the accurate measurement of ultra-low damping of simple structures.  Hubert Seth Hall, James J. Dlubac, and Michael Kim (Naval Surface Warfare Center Carderock Division, 9500 MacArthur Blvd., West Bethesda, MD 20817, hubert.hall@navy.mil, james.dlubac@navy.mil, michael.kim1@navy.mil)

As a means of validating numerical models, recent research has shown a need for methodology to measure the structural damping of very lightly damped structures (loss factor < 0.005) to a high level of accuracy.  Traditional experimental methods of measuring structural damping must be altered to accurately capture the lightly damped response.  Otherwise, inaccurate damping values will be calculated that are larger than those intrinsically found in the material/structure.  This presentation focuses on experimental technique modifications required for frequency domain methods of measurement of ultra-low damped structures.  First, the implications of less accurate capture of resonant peaks in frequency response functions will be explored.  Typical short frame, uniform frequency spacing can result in large measurement errors with lightly damped test articles.  Instead, long time histories, focused sine-based testing, zero-padding, and peak approximation methods should be utilized for improved accuracy.  Additionally, the effects of isolation-related boundary conditions and instrumentation mass to measurement accuracy are explored and quantified.

5. Considerations of Damping in the Design of Arrays of Tuned Mass Dampers*

John Sterling, PhD Candidate, The Catholic University of America

Abstract:  Multiple Tuned Mass Dampers (MTMDs) have been analyzed in the literature for some time.  The distribution of masses and stiffnesses of the attached oscillators can craft a flat frequency response over a desired band.  This response modification can be a significant improvement over classical dynamic vibration absorbers (DVA) that attenuate response at one target frequency while increasing the frequency response amplitude at nearby side frequencies. Performance of the SOA can be highly sensitive to the uncertainty or disorder in the mechanical properties of the system.  This presentation considers the effects of damping in the attachments to mitigate the sensitivity to this disorder