Computational Simulations of Wide-Beam Air-Cavity Hull in Waves

Abstract

Abstract An effective method to reduce ship drag is to supply air under specially profiled bottom with the purpose to decrease the wetted surface area of the hull and thus its water resistance. Although such systems have been installed on some vessels, the broad implementation of this technique has not yet occurred. A major problem is how to sustain air lubrication in rough water. Modeling of air-ventilated flows is challenging, but modern computational fluid dynamics tools can provide valuable insight. In this study, a wide-beam, shallow-draft hull with a bottom air cavity is considered. This hull imitates a semiplaning boat that can be used for fast transportation of cargo from large marine vessels to shallow shores. To simulate fluid flow around this hull in calm water and head waves, as well as heave and pitch motions of the boat, CFD (computational fluid dynamics) software Star-CCMþ has been employed. It is found that the air cavity effectiveness decreases in waves; vertical accelerations exhibit high-frequency oscillations; and heave, pitch, and vertical accelerations increase, while time-averaged heave, pitch, and added drag show nonmonotonic behavior with increasing wave amplitude. The air-cavity hull also demonstrates substantially lower vertical accelerations in waves in comparison with a similar solid hull without bottom recess. Time histories of kinematic parameters and distributions of flow field variables presented in this article can be insightful for developers of air-cavity hulls. Introduction The development of systems that can lead to ship fuel savings, accompanied by the decrease in pollutant emissions, is a part of global sustainability efforts in the maritime engineering industry. Reducing the hydrodynamic drag of marine vessels can effectively address this goal. One of the methods that was proposed over a century ago but only recently started to appear on ships involves air injection under hull bottoms (Butuzov et al. 1981; Latorre 1997; Dern et al. 2015; Pavlov et al. 2020). Among several air-based methods, the formation of continuous air cavities attracted significant attention in the past and is addressed in this article. A concept of a hull with an air cavity formed inside a bottom recess is shown in Fig. 1.