Wind-generated waves are often treated as stochastic processes. There is particular interest in their spectral density functions, which expressed some parametric form. Such functions used inputs when modelling structural response or other engineering concerns. Therefore, accurate and precise recovery of the parameters such a form, from observed wave records, important. Current techniques known ...

An analytic model is developed for the time-dependent ultrasound field reflected off a randomly rough vibrating surface for a continuously scanning ultrasound vibrometer system in bistatic configuration. Kirchhoff's approximation to Green's theorem is applied to model the three-dimensional scattering interaction of the ultrasound wave field with the vibrating rough surface. The model incorporat...

National Bureau of Standards Gaithersburg, MD 20899 Studies of transient wave propagation in plates were carried out to establish a basis for the impact-echo technique as a nondestructive test for flaw detection in concrete. The surface displacements caused by stress waves generated by point impact on a plate were calculated using both the Green's function solution and the finite element method...

Abstract Magnetic resonance elastography (MRE) is a technique to identify the viscoelastic moduli of biological tissues by solving the inverse problem from the displacement field of viscoelastic wave propagation in a tissue measured by MRI. Because finite element analysis (FEA) of MRE evaluates not only the viscoelastic model for a tissue but also the efficiency of the inversion algorithm, we d...

Noninvasive quantitation of the mechanical properties of tissue could improve early detection of pathology. Previously a method for detecting displacement from propagating shear waves using a phase-contrast MRI technique was developed. In this work it is demonstrated how a collection of data representing the full vector displacement field could be used to potentially estimate the full complex s...

A variable sensitivity displacement interferometer ~VSDI! used to monitor both normal and in-plane particle displacements in stress wave propagation experiments is introduced. The general system consists of two interferometers working in tandem. Normally reflected light is interfered with each of two symmetrically diffracted light beams generated by the specimen rear surface. In cases where the...

This paper is concerned with the inverse diffraction problem for an unbounded obstacle which is a ground plane with some local disturbance. The data is collected in the near-field regime with a distance above the surface displacement that is smaller than the wavelength. In this regime, the evanescent modes carried by the scattered wave are significant, which makes it different from the far-fiel...

We report the measurement and simulation of the transverse displacement spectrum of a multi-element nanomechanical oscillator at previously inaccessible frequencies of up to 3 GHz. The detected displacement signal is enhanced in the high-frequency range by the presence of high-order resonance modes generated by coherent motion of individual elements. The spectrum reveals a rich structure with g...