Static hydroelastic study of composite T-foils with beam and lifting line models

Abstract

Well-designed hydrofoils improve ship resistance and seakeeping by lifting the hull above the water. With greater speeds come greater loads, and the two-way interaction of structural deflections of lifting surfaces on the hydrodynamics must be considered. Tailored structural anisotropy can improve hydrodynamic and structural efficiency of lifting surfaces compared to rigid counterparts by exploiting the layup of composite materials. Structural efficiency here means reduced risk of structural failure for a given amount of material, and hydrodynamic efficiency means lower drag. A T-foil is a prototypical multi-component appendage, consisting of the foil wing and the strut, which we investigate in this work. We use simple composite beam and lifting line theory to explore the static fluid-structure interaction of a composite T-foil for a variety of fiber angles (θf = 0˝ , ˘15˝ ). We apply a simple approximation on lift coefficient at infinite Froude number (F n) to model the free-surface effects, which is valid at high depth-based Froude numbers (F nh ą
10a h/c) when CL is independent of F nh and the inertial effects dominate. Results for the moth rudder T-foil geometry studied here indicate that aligning composite fibers towards the leading edge results in a more hydrostructurally efficient foil and that free-surface effects are minor because of the large submergence for this flow condition.