1 

A depthdependent formula for shallow water propagation
In shallow water propagation, the sound field depends on the proximity of the receiver to the sea surface, the seabed, the source depth, and the complementary source depth. While normal mode theory can predict this depth dependence, it can be computationally intensive. In this work, an analytical solution is derived in terms of the Faddeeva function by converting a normal mode sum into an integral based on a hypothetical continuum of modes. For a Pekeris waveguide, this approach provides accurate depth dependent propagation results (especially for the surface decoupling) without requiring complex calculation methods for eigenvalues and corresponding eigenfunctions. © 2014 Acoustical Society of America.

[Abstract]

2 

3D reconstruction of subwavelength scatterers from the measurement of scattered fields in elastic waveguides
In nondestructive testing, being able to remotely locate and size defects with good accuracy is an important requirement in many industrial sectors, such as the petrochemical, nuclear, and aerospace industries. The potential of ultrasonic guided waves is well known for this type of problem, but interpreting the measured data and extracting useful information about the defects remains challenging. This paper introduces a Bayesian approach to measuring the geometry of a defect while providing at the same time an estimate of the uncertainty in the solution. To this end, a Markovchain Monte Carlo algorithm is used to fit simulated scattered fields to the measured ones. Simulations are made with efficient models where the geometries of the defects are provided as input parameters, so that statistical information on the defect properties such as depth, shape, and dimensions can be obtained. The method is first investigated on simulations to evaluate its sensitivity to noise and to the amount of measured data, and it is then demonstrated on experimental data. The defect geometries vary from simple elliptical flatbottomed holes to complex corrosion profiles.

[Abstract]

3 

Travelling standing waves: a feasibility study
Lately, there has been significant interest in the noninvasive manipulation of particles and liquids. The reported acoustic methods rely on either the acoustic radiation force or acoustic streaming. The latter can be used in developed flows to induce fluid velocities angled to the liquid flow direction. These methods often use standing wave fields induced locally through continuous compressional waves. This has a drawback for industrial applications, i.e. continuous flow reactors, the standing wave field is excited locally, whereas it should be excited along the entire pipe length. Solving this by using numerous actuators along the pipe length is impractical and cost prohibitive. In this work the feasibility is investigated of using guided waves to induce a standing wave field over a pipe's radius, but traveling along a pipe's length. Also, it is investigated whether this standing wave field significantly affects the flow velocity field and fluid mixing. The method relies on exciting Lamb waves in the wall of a liquid filled pipe, which partially refracted into the liquid. The frequency was chosen such that: 1) a radial resonance was excited in the liquid, and 2) the reflected waves in the liquid interfere constructively with the refracted wave energy. The experimental geometry consisted of a copper pipe with an attached transmitting piezo of such dimensions that L(0,1) waves were excited. A 2nd piezo was mounted to detect and optimize the guided wave intensity. The pressure in the liquid was measured using a hydrophone. The effect of the pressure waves on the mixing of salt injections was measured using conduction probes at the inlet and outlet of the pipe. The 7th and 8th order standing wave fields were measured in the liquid at 650 and 770 kHz with transmit efficiencies of 20 and 22 kPa/V, respectively. This demonstrates the feasibility of inducing radial standing wave fields traveling along a pipe. Also, the salt concentration curves were altered in shape and surface area, if the ultrasound was switched on. This suggests that the convective mixing was increased by the induced radial fluid velocity components.

[Abstract]
