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Abstract
Traditional marine propellers that are manufactured using alloys have a fixed shape. These propellers are designed to achieve the highest propulsion efficiency at the cruise condition of the vessel. However, if the flow conditions change from the vessel’s cruise condition, the propulsion efficiency reduces significantly. The objective of this thesis is to develop flexible shape-adaptive (self-morphing) blades using high performance composite materials, with particular focus on Carbon Fibre Reinforced Polymer (CFRP). By careful tailoring of fibre angle of composite layers, composite laminates can be catered to optimally change its twist under various lateral loading conditions. This special characteristic is proposed to be used for optimal change of pitch of the propeller blade based on incoming flow conditions.
An in-house optimisation algorithm has been developed to search for the optimum fibre angle of each carbon fibre layer that can enable the required shape change. The optimisation algorithm uses the Genetic Algorithm (GA) coupled with the state-of-the-art Finite Element techniques such as Cell-Based Smoothed Finite Element Method (CS-FEM) and Iso-Geometric FEM. The CS-FEM uses a stable triangular element scheme, while the NURBS based iso-geometric FEM has the capability of representing the complex geometry without any mesh based approximations. The finite element techniques also take into account ply terminations of the blade and hygrothermal effects that may be present in the composite. An iterative procedure to search for the initial shape of the blades was also developed.
The developed techniques were used to optimise a hydrofoil using experimental data from cavitation tunnel tests of a non-optimised hydrofoil. The optimised hydrofoil was then manufactured and was subjected to rigorous structural testing in order to ensure the strength and safety of the hydrofoil and to validate the reliability of the manufacturing technique. Additionally, hydrodynamic tests were conducted at the cavitation tunnel facility to characterise the performance of the optimised hydrofoil and compare against previously tested identical non-optimised hydrofoils. The optimised hydrofoil indeed showed more favourable results in terms of lift to drag (L/D) ratio of the hydrofoil and hydrodynamic fluctuations and uncertainties due to turbulence. The cavitation tunnel results were then validated against Fluid-Structure Interaction (FSI) simulations and were found to be in good agreement with the predictions.