Noise Considerations for Propulsion System Evaluation

Abstract

The laws and regulations regarding the radiated noise and the on-board noise of the ship are expected to be stricter in the future. There is a big concern in this field, especially for the underwater noise. The radiated noise from the ship is harming the life of the underwater mammals while the on-board noise is threatening the health of the on-board crew. One of the main contributors to the noise generated by a vessel is the propulsion system. It is true that the noise reduction can be achieved by doing the corrective action in the later design stage, such as installing mounting and noise absorption material. Nevertheless, the decision in early-design stage often gives the highest impact on the noise generated by the propulsion system where the level of uncertainty is high. This thesis has two main goals; to determine the design choices of propulsion systems which affect the noise excitation, and to develop an evaluation methodology to assess a certain power configuration from the perspective of generated noise.
First, the aspects of the propulsion system that affect its noise are determined. Those are transmission types, number of engines, number of shafts and number of compartments. The loading point is also included as one of the parameters. Although it is not a design choice, it has a significant role in the noise generated by the propulsion system. Second, the selection of the significant noise source in the propulsion system needs to be done. There is much equipment inside a propulsion plant, but not all of them give sufficient contribution to the overall noise level. Based on the literature review, the equipment that is considered as the main noise sources are the diesel engine, the diesel generator set, the reduction gear and the electric motor.
A noise model from SNAME is implemented in this project to predict the airborne and structure-borne noise source levels of the equipment and the transmission losses to the receiver location. An engine room-sizing model is developed in this project since the transmission loss is a function of the compartment dimensions. Furthermore, the room dimensions depend on the equipment dimensions. Therefore, it is necessary to develop a model to predict the size of the equipment too. Afterwards, the evaluation methodology is established to quantify the effect of a certain design choice towards the noise of a propulsion system.
The effects of varying ship requirements are also investigated to see the behaviour of the model with a different input. These requirements are the ship installed power, the ship propulsion power and the ship auxiliary power
This project provides a general guideline for the marine engineer to evaluate the propulsion system based on the noise considerations in the early design phase. The evaluation methodology proves to be applicable to a wide range of propulsion plant type. It is possible to extend the application of this method for a ship with prime mover other than the diesel engine and the electric motor.