Autonomous underwater gliders

Abstract

This chapter discusses the characteristics, design considerations, and performance of autonomous underwater (UW) gliders. These buoyancypropelled, winged vehicles can be categorized as: (1) profiling gliders that traverse in bobbing trajectories to collect vertical profiles of ocean properties and (2) cross-country gliders designed for pointto- point horizontal transport efficiency. Horizontal transport efficiency is quantified by net transport economy and specific energy consumption. The latter metric for a glider is equal to its inverse lift-to-drag ratio (also called finesse) and is equivalent to the glide slope in steady-state, nonturning glides. Increases in efficiency can be obtained by: 1. Increasing the loaded mass (with larger buoyancy engines) and increasing the overall size of the glider, which increases the glider’s speed and maintain sufficiently high Reynold’s numbers to avoid the drag crisis. 2. Reducing the ratio of the total vehicle wetted area to wing area, via use of flying wing or blended wing body shapes, and 3. Increasing the wing aspect ratio, within structural strength and stiffness limitations. Gliders have an intrinsic advantage in transport efficiency over conventional prop-driven autonomous underwater vehicles (AUVs) due to the simpler vortex dynamics of a wing versus a propeller. As a result, gliders can fly cooperatively with other winged vehicles or employ multielement wings to further improve transport efficiency. Although a glider must change depth to move forward, these depth changes not only allow the collection of vertical profiles of ocean properties, but also enable the extraction of energy from the ocean’s vertical temperature gradients (thermal glider).