Dr Gyani Shankar Sharma

The overarching aim of my research is to develop noise prediction tools and mitigation strategies. My current research activities are summarised below:

• Acoustic characterisation of metamaterials: Acoustic metamaterials are composite media comprising resonant inclusions arranged periodically in a host material. An underwater application of acoustic metamaterials is an anechoic coating on marine vessels to reduce the transmission of onboard machinery noise in the ambient marine environment as well as to absorb external acoustic waves. I have developed significant analytical and numerical capabilities to predict the acoustic performance of soft media embedded with voided and/or hard inclusions. My analytical approach is based on homogenisation, which is a powerful method to model an inhomogeneous structure as a homogeneous medium with effective properties. The analytical models employ analogies between disciplines such as acoustics, fluid dynamics and electrostatics. I have expertise in multiphysics finite element analysis, which I use to validate the analytical models.
• Marine vessels covered with acoustic metamaterials: While acoustic metamaterials have been widely studied in the literature, previous work has mainly focussed on their acoustic characterisation using a planar array of inclusions in a host medium. The external hull of a marine vessel can be approximated as a cylindrical shell for its acoustic characteristics. This project integrated these two fields and developed a fully analytical framework of a cylindrical shell coated with an acoustic metamaterial. 
• Uncertainty quantification in acoustic metamaterials: Uncertainties are inevitable in design parameters of acoustic metamaterials arising from the manufacturing process and inhomogeneity of material properties. I have developed stochastic models based on nonintrusive polynomial chaos expansion theory and Monte Carlo simulations to investigate uncertainty in the material and geometric properties of metamaterials on its acoustic performance. 
• Sound radiation from a submerged hull near free sea surface: This project developed analytical and numerical tools to predict the sound radiation from a submarine hull submerged in water near the free sea surface. 
• Novel environmental noise control strategies: I demonstrated a novel concept of local noise control along specific receiver directions by controlling the directivity of the radiated or transmitted noise. This approach is particularly useful for practical low frequency noise where global noise control is difficult to attain. The directivity pattern of the radiated or transmitted noise was controlled by attaching a lumped mass to the structure. The mass location to minimize sound pressure in a target direction was obtained using an optimization technique.