Experimental and numerical study on the adjustment of twin hydrofoils of a variable-structure SWATH

The form-changeable unmanned surface vehicles (USVs) have garnered considerable research interest due to their wide-ranging applicability and robust combat capabilities. This paper specifically addresses the longitudinal motion stability of a variable-structure Small Waterplane Area Twin-hull Ship (SWATH) equipped with twin hydrofoils, aiming to evaluate the impact of hydrofoils on sailing attitudes. Initially, model tests were systematically conducted under different form-states, both with and without hydrofoils, in calm water conditions. Subsequently, verification and validation of computational fluid dynamics (CFD) simulations were performed against the experimental results. Finally, strategies to mitigate bow-diving during high-speed tests were proposed based on the validated CFD simulations, focusing on adjusting hydrofoil attack angles. The test results indicate that with outwardly spreading struts, the bow tends to dip down more as speed increases. Model tests, combined with CFD simulations, serve as a reference for stable sailing at full speeds, presenting strategies for adjusting attack angles under varying form-states and speeds. Moreover, effective foil adjustment modes are identified to suppress bow-diving, considering thrust. Strategies for adjusting attack angles during the acceleration process are summarized, verifying the stability of the optimal 10° form-state at high speeds.