Optimizing steady and dynamic hydroelastic performance of composite foils with low-order models

Abstract

Predicting and controlling the steady and dynamic hydroelastic performance is a crucial challenge in marine composite lifting surface design. Excessive flow-induced vibrations and accelerated fatigue can be severe issues if not considered in the initial design. Most design optimizations only consider steady performance and neglect critical dynamic aspects of the marine environment, such as lower resonance frequencies and different band gaps between modal frequencies in water compared to in air. This work uses lower-order models to capture the steady and dynamic fluid–structure interaction behavior and optimize the design of composite hydrofoils. We formulate new objectives and constraints that consider the natural frequencies, damping, and frequency response spectra in addition to steady hydroelasticity to achieve the design intent. The optimization method is heuristic, which is appropriate for this level of model fidelity where holistic parameter trends are more of interest. Results for a 1/3 length-scale hydrofoil model showed a significant improvement in the optimized performance over the baseline. By tailoring geometric and material variables of the composite hydrofoil, we produced an optimal design. This design meets the steady design condition requirements and avoids excessive vibrations and dynamic load amplifications due to lock-in, resonance, flutter, and modal coalescence.