An Experimental Investigation on Reduction Effect of Damping Devices for the Recessing Type Moonpool with a Large Aspect Ratio

Abstract Compared with the square and circle moonpools, the rectangular moonpool with a large aspect ratio is more conducive to install the equipment. To reduce fluid motion in the rectangular moonpool with a large aspect ratio, a recess is installed in the moonpool. However, the fluid motion in a recessing type moonpool with a large aspect ratio has been rarely studied. In this study, a series of experiments are carried out to investigate on the hydrodynamic characteristics of fluid in the recessing type moonpool with a large aspect ratio. To facilitate the monitoring of the fluid motions, experiments are carried out in a transparent wave channel with the model made up of transparent acrylic. According to the experiment results, there are some complicated fluid motions in the moonpool. Under the resonance condition, the fluid moves violently in the moonpool. To reduce the fluid motion in the recessing type moonpool, three damping devices including the positive grid of flaps, the negative grid of flaps, and the grid of baffles are proposed. The reduction effect of the three damping devices is investigated experimentally. The damping devices have good reduction effects at most time. The smaller the incident wave period, the better is the reduction effect. Introduction The moonpools run vertically through the hull of ships or marine structures, providing a sheltered working environment under harsh ocean conditions. The fluid motion in the moonpool is similar to that in the slit between the ships or rectangular bodies (Faltinsen et al. 2007; Mavrakos & Chatjigeorgiou 2009; Ikeda et al. 2012; Chen et al. 2014; Heo et al. 2014; Zhang & Bandyk 2014; Faltinsen & Timokha 2015; Yu et al. 2017; Gao et al. 2019d). Two dominant types of fluid motions, the piston motion and the sloshing motion, are discussed (Fukuda 1977; Molin 2001; McIver 2005; Kristiansen & Faltinsen 2012; Zhou & Zhang 2013).