Grech La Rosa, Andrea; (2023) Reinventing the Bulbous Bow. Doctoral thesis (Ph.D), UCL (University College London).

Text AGLR_Thesis_Final.pdf - Accepted Version Access restricted to UCL open access staff until 1 February 2033. Download (54MB)

Abstract

The International Maritime Organisation has stipulated targets for the shipping industry to halve its total Green House Gas Emissions by 2050. This goal can only be met by revisiting the way ships are designed and implementing greener technologies to improve their performance. The bulbous bow is a staple in hull form design and is widely used in the industry. This rigid form bulging from the vessel's bow beneath the waterline aims to reduce the vessel's resistance by impacting the viscous and pressure flow components. However, as the ship changes its operational characteristics, such as speed or displacement, the bulbous bow does not adapt the flow it generates resulting in it operating outside its intended design condition. Despite their popular use, bulbous bow design remains a challenge. In this thesis, the design and characteristics of bulbous bows were investigated using data analysis and computational fluid dynamics. The project also proposed the concept of a configurable bow appendage where a conventional bulbous bow is replaced by a device capable of reproducing the flow generated by a bulbous bow and modifying it over an expanded range of operating conditions. A classification of bulbous bows was created from a sample of data to identify the appropriate ship and bulbous bow types that would benefit from an unconventional bulbous bow or bow appendage. This process also revisited the way in which bulbous bows are mathematically defined and characterised. A preliminary bulbous bow sizing tool that applies machine learning principles to the data sample of existing vessels was also created. Based on a set of inputs, the tool recommends whether a bulbous bow should be fitted and, if it should be, what its longitudinal profile should be. A case study consisting of four vessels was conducted to demonstrate this novel application of machine learning. This led to the creation of a validated virtual towing tank to conduct computational fluid dynamic (CFD) tests on a benchmark vessel known as the Kriso Container Ship (KCS). A new approach to assess the bulbous bow of the vessel by isolating it from the rest of the ship was introduced. This enabled the key flow features generated by the bulbous bow to be understood in greater detail and aided in isolating the desired features to include in the unconventional bulbous bow or bow appendage design. The overall objective of the project was to develop a concept for an unconventional bulbous bow or bow appendage that is able to modify its hydrodynamic flow and improve its performance over a wider range of operating conditions. The concept proposed was that of a configurable bow appendage which was found to successfully reduce the resistance of the equivalent hull form without a bulbous bow at different Froude numbers by altering its physical configuration.

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