As Java increases in popularity and maturity, many people find it desirable to convert legacy C++ or C programs to Java. Our hypothesis is that a tool which performs rigorous analysis on a C++ program, providing detailed output on the changes necessary, will make conversion a much more efficient and reliable process. MoHCA-J&a is such a tool. It performs detailed analysis on a C++ abstract syntax tree; the parameters of the analysis can be specified and extended very quickly and easily using a rule-based language. We have found that MoHCA-Java is very useful for identifying and implementing source code changes, and that its extensibility is a very important factor, specially to adapt the tool to assist in the conversion of C++ code that makes extensive use of libraries to Java code that uses similar libraries.

Acoustic metamaterials have already been shown to be effective for vibration reduction and control. Local resonances in the metamaterial cause waves at frequencies within band gaps to become evanescent, thus preventing wave propagation through the material. Active and adaptable local resonances enables the band gaps to be shifted in frequency and increased in bandwidth. Since metamaterial local resonances are usually composite, methods to specify optimal component configurations are helpful for passive metamaterials and almost necessary for adaptable metamaterials, where the metamaterial must be reconfigured for optimal performance at various frequency ranges. To assess band gap locations and bandwidths for metamaterials, a wavenumber spectrum is commonly computed. Commonly, a parameter study of adaptable unit cell variables will be performed to assess optimal configurations of adaptable metamaterials. In this paper, the complex wavenumber is proposed as a direct optimization objective for reconfiguration of active adaptable acoustic metamaterials for maximum vibration suppression at a frequency range of choice. By directly maximizing the imaginary part of the wavenumber, associated with wave attenuation, the unit cell configuration maximum vibration suppression can be obtained for an operating frequency of choice. Additionally, since the optimization problem requires constraints for feasible solutions and the example active piezoelectric metamaterial system shown here is electrically unstable at some configurations, we also explore an experimental method for bounding the optimization problem. Numerical results of the optimization problem are presented.

Acoustic metamaterials are composite materials exhibiting effective properties and acoustic behavior not found in traditional materials. Primarily through periodic subwavelength resonant inclusions, acoustic metamaterials can enable steering, cloaking, lensing, and frequency band control of acoustic waves. However, a common drawback of acoustic metamaterials is that effectiveness is limited to narrow frequency bands. Thus, investigation of practical active and adaptable acoustic metamaterials is valuable in achieving wider operation frequency bands. Here, a metamaterial consisting of active tunable piezoelectric shunts is investigated numerically and experimentally from the unit cell level. A physical model of the unit cell is developed using the finite element method. From the finite element model, the wave finite element method is applied to compute the dispersion and forced response of the periodic structure. It is demonstrated that the shunts introduce an additional degree of freedom by which adaptable bending wave attenuation can be accomplished. Since the periodic shunts are only effective at certain frequency bands, a known optimization method is implemented to tune the shunts. Additionally, a new optimization scheme is compared to the existing scheme found in literature.

An electronic speckle pattern interferometer (ESPI) is an optical system used to investigate vibrating objects and can be a great educational tool for visualizing mode shapes. At the Pennsylvania State University, the Acoustical Society of America student chapter acquired funds to build an ESPI for classroom and outreach use. The design of the ESPI was based on previously published work using equipment purchased for less than $5000. To approach this project, students were split into two groups where one developed a MATLAB application to collect and process images while the other arranged the optical components of the ESPI. To test the system, interferometry was performed on a banjo head which matched mode shapes found using a scanning Laser Doppler Vibrometer (LDV). Future work includes adapting our ESPI system to obtain images in real-time, developing educational demos involving the ESPI, and further refining the MATLAB application. This presentation provides a model for a multi-disciplinary project that could be implemented at the undergraduate or graduate level.

Acoustic metamaterials are composite materials exhibiting effective properties and acoustic behavior not found in traditional materials. Through periodic subwavelength resonant inclusions, acoustic metamaterials enable steering, cloaking, lensing, and frequency band control of acoustic waves. A common drawback of acoustic metamaterials is that the properties are limited to narrow frequency bands. Investigation of practical active and adaptable acoustic metamaterials is valuable in achieving wider operation frequency bands. Numerical predictions of wave propagation behavior in acoustic metamaterials are commonly presented in the form of elastic band structure diagrams. In previous work, the complex wavenumber dispersion properties of the metamaterial medium were proposed as optimization objectives for obtaining optimal adaptable metamaterial unit cell configurations for vibration reduction. To verify numerical wavenumber predictions, the current work presents an experimental method to obtain the wavenumber dispersion. First, the metamaterial beam is excited with a broadband pulse. Time domain responses are recorded at many locations on the structure. The resulting time series data is processed with a two dimensional Fourier transform. The result is a wavenumber versus frequency plot. The procedure is useful for plate and beam type metamaterial structures wherein local resonances and active inclusions cause wave attenuation if the above experimental procedures can be feasibly carried out.