Mastering the Manu-how humans create large splashes.

Abstract

Manu jumping, a popular water diving style among M $\overline{\text{a}}$ ori people in New Zealand, focuses on creating large splashes. Divers perform aerial manoeuvres such as the 'utkatasana' pose, entering the water in a V-shape, and executing underwater manoeuvres to enhance the splash size. Our study explores the underlying fluid dynamics of Manu jumping and demonstrates how two key parameters, the V-angle and the timing of body opening, can enhance Worthington jet formation. To accurately replicate human Manu jumping, we studied water entry of both passive solid objects with varying V-angles and an active body opening robot (Manubot). The analysis revealed that a 45° V-angle enhances Worthington jet formation, consistent with human diving data. This angle balances a large cavity size and a deep pinch-off depth. The body opening within a timing window of ${\hat{t}}_r=1.1-1.5$ synchronizes the robot's potential energies to be timely transferred to the cavity formation, producing the strongest and most vertical, i.e. ideal, Worthington jets. Based on our experimental findings, we propose a range of parameters for generating the large Manu splashes. These insights offer engineering perspectives on how to modulate underwater cavity dynamics using both passive and active body formations.