The effects of modal coupling on the acoustic power radiated from line forced panels of unit width with s-s (simply supported-simply supported) and c-c (clamped-clamped) end conditions have been studied. The expressions for the power radiated by the total square terms and by the coupling terms in these two one-dimensional problems were derived using Heckl’s power integral. A qualitative and quantitative discussion regarding the properties of Pmn (the power radiation coefficient of the m- and nth modes) and Dmn (the wavenumber cross-spectrum of modal velocities) for the s-s panel are presented. Numerical calculations (for both s-s and c-c cases) were carried out to investigate the relative importance of the modal coupling in the acoustic radiation. The results show that if the panel is under resonant excitation or if the driving force is at high frequency, then the effects due to modal coupling are negligible. At low frequency, however, or if the panel is under off-resonant excitation, then the contributions due to the modal coupling may be important.

Past analyses at NC State have indicated a positive correlation between students who struggle in their first calculus class and those who ultimately leave engineering at NC. The present study was conducted to investigate the effects of early intervention for engineering students who have performed poorly on their first calculus examination. This paper presents the problem, the approach taken in this project, the resulting data, our lessons learned, and strategies being considered to scale-up the intervention in subsequent semesters to include all first-semester engineering students. Introduction: The goal of this study was to understand the effects of intervention on engineering students who struggle in their first calculus course. We were mindful in conducting the study that, as it relates to students, ...

An analytical model of a compliant elastic coating attached to a submerged thin plate has been developed. A plane acoustic wave, representing the signal, is incident from the water on to the elastic coating. The normal and tangential velocity components induced in the coating by the acoustic wave are calculated. The effects of incidence angle, frequency, location throughout the coating, and coating properties on the signal response velocity components are evaluated. Many details of the coating velocity components are explained based on simple uncoupled waveguide characteristics of the coating. In general, the normal velocity components are several tens of decibels higher in amplitude than the tangential velocity components. It was shown, however, that the tangential velocity component could be increased by an average amount of about 20 dB, without serious degradation of the normal component, by altering the coating properties. In particular, combinations of high longitudinal wave speed and low shear wave speed were found to be advantageous.

The effects of external hydrostatic pressure fields and fluid loading on the structural and acoustic response of a point-driven infinitely long circular cylindrical shell were examined over a range of frequencies. The external pressure field was modeled using static prestress terms in the shell equations of motion, and the structural response was characterized by the driving point admittance and the circumferential resonant frequencies. The acoustic response was quantified through calculation of the radiated sound power, both in an overall sense and on an individual modal basis. The analysis was performed for the in-air case as well as for the in-water case. The structural response was found to be strongly affected by fluid and pressure, resulting in significant resonant frequency shifts. However, the overall acoustic response was shown to be nearly independent of the external pressure field, both in air and in water. In addition, it was shown that relatively fewer modes contribute significantly to the sound radiation for the submerged shell as compared to the shell in air. In both cases, the sound generation was controlled by the low-order nonresonant modes.

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