Roger Kinns

Fast Low-Storage Method for Evaluating Lighthill’s Volume Quadrupoles

An m-multipole particle-condensation method is proposed to spatially condense the volumetric quadrupole sources based on Lighthill’s acoustic analogy that are extracted from computational-fluid-dynamics data. The purpose of the method is to reduce both the amount of data that must be stored during the computational-fluid-dynamics analysis and the number of acoustic sources driving the subsequent acoustic-propagation analysis, while preserving the accuracy of the predicted sound pressure field. The method uses a particle approximation of the quadrupole source distribution and employs a Taylor series expansion of the harmonic Green’s function to spatially condense the underlying acoustic sources and preserve their multipole moments. Low-Mach-number flow around rigid-walled stationary bodies in a medium at rest at infinity is used to demonstrate the m-multipole particle-condensation method. The directivity of the sound pressure field due to the quadrupole sources is presented for the first four harmonics of ...

Effect of a serrated trailing edge on sound radiation from nearby quadrupoles

A periodic boundary element technique is implemented to study the noise reduction capability of a plate with a serrated trailing edge under quadrupole excitation. It is assumed for this purpose that the quadrupole source tensor is independent of the trailing edge configuration and that the effect of the trailing edge shape is to modify sound radiation from prescribed boundary layer sources. The flat plate is modelled as a continuous structure with a finite repetition of small spanwise segments. The matrix equation formulated by the periodic boundary element method for this 3D acoustic scattering problem is represented as a block Toeplitz matrix. The discrete Fourier transform is employed in an iterative algorithm to solve the block Toeplitz system. The noise reduction mechanism for a serrated trailing edge in the near field is investigated by comparing contour plots obtained from each component of the quadrupole for unserrated and serrated trailing edge plate models. The noise reduction due to the serrated trailing edge is also examined as a function of the source location.

Structural and acoustic responses of a fluid loaded shell due to propeller forces

The low frequency structural and acoustic responses of a fluid loaded shell to propeller induced fluid pressures are investigated. The propeller operates in the non-uniform wake field and produces fluctuating pressures on the blades of the propeller. This in turn generates acoustic waves and a near field that excites the surface of the shell. The resulting incident pressure is scattered and diffracted by the shell surface, and also excites structural vibration. A potential flow panel code is coupled with the Ffowcs-Williams and Hawkings acoustic analogy to predict the fluctuating propeller forces, blade pressures and the resulting incident field on the surface of the fluid loaded shell due to operation of the propeller in a non-uniform inflow. The propeller induced incident pressure field is then combined with a coupled three-dimensional finite element/boundary element model of the submerged shell to predict the vibro-acoustic and scattered field responses.

Influence of a resonance changer on the sound radiation of a submarine

In order to reduce the excitation of the submarine hull through the shaft, a vibration attenuation system, called a resonance changer, can be implemented in the propeller/propulsion system. The effectiveness of such a system in reducing the low frequency sound radiation characteristics of a submarine is investigated. Only sound radiation due to fluctuating propeller forces, which are generated by the operation of the propeller in a nonuniform wake, is considered. These fluctuating forces are transmitted to the submarine hull through the fluid, as well as through the propeller shaft. Both types of excitation cause hull vibration and sound radiation. The accordion modes of the pressure hull, are particularly efficient sound radiators. Parameters for the resonance changer system have been optimised previously by considering only excitation of the hull through the shaft. It is shown that the effectiveness of the resonance changer at different frequencies is modified significantly in a typical full‐scale imple...