Composite materials have been increasingly used in marine structures due to their advantages in specific strength, fatigue performance, and anti-erosion. Designs of composite hydrofoils require different considerations compared to airfoils due to much higher fluid density and other unique physics, such as cavitation. Cavitation is one of the main limitations to hydrofoil performance when operating at high-speeds or near-free-surface conditions. The objective of this work is to design hydrofoils to delay cavitation inception, to increase efficiency, and to ensure structural safety by optimizing the shape and composite fiber orientation angle using a gradient-based optimization method with high-fidelity CFD and FEM models. Cavitation occurs when the local absolute pressure drops to or below the saturated vapor pressure, which can be avoided by imposing a stringent constraint on the cavitation-inceptive area on the hydrofoil surface during optimization. We performed single-point optimizations for both composite and metallic hydrofoils at two different conditions. We first showed the result for one optimized composite hydrofoil and the comparison with the baseline. We also compared the performance of optimized composite hydrofoils to optimized aluminum hydrofoils. All optimized hydrofoils showed significantly delayed cavitation inception and improved efficiency compared to the corresponding baseline hydrofoils. For single-point optimization, the optimized designs of the composite hydrofoil and the aluminum hydrofoils are shown to be very similar in terms of the final geometry, efficiency, and susceptibility to cavitation. The composite hydrofoils are much less susceptible to structural failure compared to metallic hydrofoils due to the intrinsic high strength, making composite structure advantageous over conventional metallic structure in structural safety and endurance.
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