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This paper presents an elasticity theory solution for computation of acoustic radiation by a point- or line-excited fluid-loaded laminated plate, which may consist of a stack of an arbitrary number of different isotropic material layers. A one-side water-loaded three-layer sandwich plate, which consists of a hard rubber core sandwiched between two steel plates of equal thickness, was used as an example of the laminated plates. The approximated equivalent sandwich plate solutions were compared with the elasticity theory solutions. These results show that the approximated solutions are, as expected, valid only at frequencies much lower than the coincidence frequency. The numerical result also shows that, even at about one-tenth of the coincidence frequency, the approximated solutions suffer substantial error. The differences between the dry-side- and the wet-side-excited radiated fields of a single-layer uniform plate and a sandwich plate were investigated and compared, and found to be significantly different at frequencies above the coincidence frequency. [S0739-3717(00)01803-1]

This paper examines the wavevector-frequency spectrum of the turbulent boundary layer wall pressure in the incompressive, inviscid domain in the intermediate and high frequencies range, i.e, wS'/l]^ > > 0.5. It is shown that the wavevectorfrequency spectrum can be normalized by a factor so that it becomes simply a function of nondimensional Strouhal wavenumber U c k,/ij) and U c k 3 /w, where U c is the convective flow velocity, and ki and k 3 are the wavenumbers in the plane of the wall along the streamwise and the crossflow directions, respectively. The normalization factor is the point pressure frequency spectrum times (U c /w) 2 . It follows that the normalized wavevector-frequency spectrum can be scaled with respect to the Strouhal wavenumbers U c k]/w and U c k 3 /o>. The rationale of using a linear regression model for estimating the normalized wavevector-frequency spectrum with a set of measured response data from a wavevector filter is presented. The contention is that the actual spectrum can be obtained by the multiplication of a trial spectrum with a correction spectrum. The correction spectrum is approximated by a polynomial in U c k,/w with a set of coefficients to be determined. The multiple linear regression model relates the response of a measuring system to these coefficients which are determined by least square minimization of a set of measured response data. The advantages of the regression approach are that it relaxes the requirements of the wavevector filter's ability to discriminate against the spectral elements outside the wavenumber bandwidth of the filter, and this approach is capable of better estimating the entire wavevector spectrum as compared to the existing methods which are limited to measurements of the low-wavenumber spectra. Some preliminary numerical results are presented.

Some drums have, typically, a hollow trunk (or a barrel) with a circular membrane at each of the two ends. In this type of drum structure, the two membranes interact with each other through the air between them inside the body. Even if the two membranes have an identical fundamental resonance frequency, the interaction results in two resonance frequencies. At the lower resonance, the two membranes vibrate in phase. Since the membranes must move the internal air, the frequency at the lower resonance is lower than that of the original resonance (without air loading). At the higher resonance, they vibrate out-of-phase, causing compression or expansion of the internal air simultaneously. The frequency at this resonance is higher than that of the original resonance since, in this case, the air works as a spring. In this paper, resonance frequencies and mode shapes of the coupled membranes are investigated using an analytical model. The membranes are assumed to be ideal (i.e., no bending stiffness) and the body is assumed to be ideally rigid. Since it is a common practice that the two membranes are slightly (intentionally) miss-tuned, the main interest of this paper is to simulate the effect of this miss-tuning on the resulting resonance frequencies and mode shapes. Numerical results for the case of a 48 cm diameter and 50 cm length Japanese drum are presented.

This paper presents an exploratory study of using external fluid loading on a vibrating tube for measuring the suspended sediment concentration (SSC) in bodies of water such as rivers and reservoirs. This new measuring concept provides an opportunity for an automated on-site monitoring of the conditions in a body of water by taking the fluid sample instantaneously in the area surrounding the vibrating tube. The physical properties of the fluid sample are those of the fluid that naturally flows around the tube, and are more representative of those of the water with SSC to be measured. The theoretical analysis presented in this paper shows that the resonance frequencies of an immersed vibrating tube change significantly with mass density variations that normally occur in bodies of water with suspended sediment. These changes are sensitive enough to have a possible 1% resolution of the measured fluid density. The signal processing issues are discussed, and a schematic of a conceptual measuring setup is proposed. Based on the theoretical analyses and other measurement issues presented in the paper, using the loading by external fluid on a vibrating tube is feasible for measuring the SSC in water bodies.