The Draper Laboratory Vorticity Control Unmanned Undersea Vehicle (VCUUV) is the first mission-scale, autonomous underwater vehicle that uses vorticity control propulsion and maneuvering. Built as a research platform with which to study the energetics and maneuvering performance of fish-swimming propulsion, the VCUUV is a self-contained free swimming research vehicle which follows the morphology and kinematics of a yellowfin tuna. The forward half of the vehicle is comprised of a rigid hull which houses batteries, electronics, ballast and hydraulic power unit. The aft section is a freely flooded articulated robot tail which is terminated with a lunate caudal fin. Utilizing experimentally optimized body and tail kinematics from the MIT RoboTuna, the VCUUV has demonstrated stable steady swimming speeds up to 1.2 m/sec and aggressive maneuvering trajectories with turning rates up to 75 degrees per second. This paper summarizes the vehicle maneuvering and stability performance observed in field trials and compares the results to predicted performance using theoretical and empirical techniques.

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Current measurements from moored buoy systems are contaminated by mooring motion. A few examples of moored buoy systems are studied to illustrate the use of computer simulations for computing errors introduced by surface waves in the current meters attached to near‐surface moorings. Results presented show that for all cases studied the standard deviations of true flow components (relative to the current meters) are greater than the standard deviations of wave orbital velocities, except near the surface. Also, in one case which is closest to a surface‐following mooring, the standard deviations of true flow components (relative to the current meters) increase, rather than decrease, with depth over the upper 40–45 m depth. Effect of mooring line characteristics, environment and vertical cosine response on the simulated current meter error is shown. In all cases, for current meters located near the ocean surface, the error is comparable to the surface wave induced Stokes drift. Significant errors (>1 cm s−1) were computed at depths greater (up to 2 and 3 times) than the depth where Stokes drift becomes negligible. Simulations also show a great deal of variation (several centimeters per second, the order of Stokes drift) in the error due to variations in mooring line characteristics and environments.

An underwater vehicle’s design and operation requires prediction of its performance at various velocities and angles-of-attack or of sideslip. Traditional models based upon headway motion at substantial speeds use coefficient-based equations of motion. Simulations based upon these coefficients are not valid for hover, low speeds, or high angles-of-attack or of sideslip. To remedy this severe limitation, nonlinear hydrodynamic models valid for all attitudes of underwater vehicles have been developed and are presented here. These models are derived from the physics of hydrodynamic phenomena. Forces and moments for the total vehicle are obtained by relying on body-buildup techniques. For the vehicle’s hull, the models are profile drag, lift, crossflow force, and added mass. For appendages such as fins, the models are lift and drag when unstalled, normal force when stalled, transition between unstalled and stalled conditions, and hull interference effects. Whenever the equations contain parametric coefficients such as added-mass, drag, and lift, values are specified for all angles-of-attack and sideslip with a minimal use of empirical look-up tables. These models represent the state-of-the-art in low speed hydrodynamics at all angles-of-attack. The hydrodynamic models presented here have been improved and validated by analysis and comparison with test data. Sub-scale versions of two different vehicles have been tested in tow-tanks at all angles-of-attack. The models have been implemented in a C language computer code which runs at high speed with no iteration required. This code is utilized regularly in faster-than-real-time vehicle performance simulations.

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