Structure-borne noise of marine diesel engines: transfer-path analysis of onboard transmission and underwater radiation

Fragasso, Jacopo (2023) Structure-borne noise of marine diesel engines: transfer-path analysis of onboard transmission and underwater radiation. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Onboard machinery generates structure-borne noise that propagates onboard and underwater. Structure-borne noise has a direct influence on the onboard noise comfort and the underwater noise footprint of the vessel. Vibrational transfer-path analysis (TPA) can be used to understand how noise is transmitted from onboard noise sources to the ship structures or radiated underwater. The focus of this research is on the noise radiated from resiliently-mounted marine diesel engines because of their dominant impact on the noise signature of the vessel. With TPA, the main components of the vibrational transfer path are analyzed separately and then combined together. Noise levels at the receiver can be reduced by identifying the critical points in the transfer path and improving their design. The characterization of the vibration isolator mounted under the diesel engine is performed with the use of numerical models built and validated with the aid of experimental tests and response surface methodology (RSM). Similarly, a finite-element model for the analysis of underwater sound radiation of vibrating structures is developed using sound and vibration measurements acquired with acoustic measurements in a water tank. This work presents an experimental procedure for the characterization of the vibration isolator at different static preloads. The dynamic response of a numerical simulation is fit to the experimental response using a hyperelastic material model and an implicit timeintegration scheme. Moreover, the coupled acoustic-structural analysis of the underwater radiation yields accurate results and provides a coefficient of sound radiation (σ). An analytical formulation of the transfer path is developed to combine the contributions of the components of the transfer path to estimate noise and vibration levels at the receiving point. This thesis highlights the importance of numerical models in the TPA of structure-borne noise and shows how dynamic simulations can help ship designers estimate the contribution of the components of the transfer path using standardized testing procedures and model-scale experiments.

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