Zhengping Feng

H/sub /spl infin// autopilot design for an autonomous underwater vehicle

This paper presents the H/sub /spl infin// autopilot design for Subzero II-an autonomous underwater vehicle. The autopilot comprises two sub-controllers: the longitudinal controller for the forward speed and depth, and the lateral controller for the heading angle. The design of sub-controllers is formulated as the problem of minimizing the mixed sensitivity function, and then solved by the LMI-based H/sub /spl infin// method. The behaviour of the autopilot is assessed by simulations with a full nonlinear model of the vehicle.

GA-based path planning for multiple AUVs

In this paper, the genetic algorithm (GA), which is a simulation of Darwinian evolution and an efficient way for large-scale optimization subject to non-linear constraints, is applied to find economical and safe routes for a swarm of AUVs to revisit an area with waypoints and obstacles which are known a priori. The algorithm can be divided into three phases: (1) waypoint assignment: allocating the waypoints to individual AUVs; (2) route optimization: minimizing the total journey of the vehicles and (3) route validation: checking whether there exist stationary and/or moving collisions. A case study for three AUVs to survey a given area is also presented to verify the algorithm.

Line of Sight Guidance with Intelligent Obstacle Avoidance for Autonomous Underwater Vehicles

Intelligent obstacle avoidance is combined with line of sight (LOS) guidance for autonomous underwater vehicles (AUVs) in this paper. Through incorporating expert knowledge and experience, a fuzzy logic planner is utilized to generate steering commands for an AUV to avoid obstacles lying between two adjacent waypoints along the prescribed track lines. Although the AUV will be able to avoid the obstacle through the fuzzy logic planner, undesirable energy consumption due to overshoot is possible during the change of trajectory. As a result, a genetic algorithm is employed as an adaptive method for tuning the membership functions of the fuzzy logic planner and the results obtained affirm the potential of the combined methodology

Subzero III - A Low Cost Underwater Flight Vehicle

Abstract Subzero III is a low cost underwater flight vehicle and evolves from Subzero II which is a test bed for control techniques of underwater vehicles. This paper presents the redevelopment and enhancement in vehicle electronics, mechanical redesign, and the software in the control computer on the shore.

A low-cost testbed of underwater mobile sensing network

Comprised by a swarm of acoustically linked and cooperative autonomous underwater vehicles (AUVs) with onboard sensors, an underwater mobile sensing network (UMSN) will be a complementary means to fixed observatory networks e.g. seafloor observatory networks and moored buoy arrays. It has obvious advantages over single large AUV in higher efficiency due to parallel observation, stronger robustness to vehicle failures and lower cost. Although an UMSN can be viewed as a counterpart of wireless mobile sensing networks for air and terrestrial applications, it is much more challenging due to poor performance of underwater acoustic communication, poor performance of underwater positioning and high degree of uncertainty in vehicle dynamics and underwater environment. In order to verify key technologies involved in an UMSN, e.g. cooperation of multi-AUV based on acoustic communication, a low cost testbed has been developed for experimental study. The design of both hardware and software is introduced in this paper. Also the results of functional test for verification of the effectiveness of the testbed are presented.

Development and Validation of a Dynamic Model of an AUV

Abstract This paper presents the development and validation of the dynamic model of Subzero II, a torpedo-shaped flight vehicle. The model is based on standard submarine motion equations. To reduce model uncertainty, added mass coefficients are calculated in terms of the vehicle geometry. Moreover the effect of the communication cable attached is also considered. A numerical scheme which deals with cables of variable lengths is proposed. The validation results show that the model is acceptable although further improvements to the model of the control surfaces are required.

Formation stabilization of underwater mobile sensing networks

Formation control is essential for an underwater mobile sensing network (UMSN), an ad hoc network which wirelessly connects underwater vehicles of sensing and/or observing types via acoustic communications, to fulfill mobile sensing tasks. The problem of formation stabilization for an UMSN with varying communication topology is studied in this paper. Sufficient condition of formation stability is proposed in terms of stability analysis of linear time varying system and spectrum analysis of graph Laplacian of communication topology. Moreover, a design procedure for synthesis of formation controller is given.

Composite control of a tethered underwater flight vehicle

Abstract For tethered underwater vehicles, the behaviour of the feedback autopilots which are developed for un-tethered vehicles are subject to the tether effects. Therefore it is desirable to apply a composite scheme for the control of tethered underwater vehicles: while the feedback controller deals with the vehicle dynamics, a feed-forward compensator cancels the tether effects. This paper presents such a study for the control of a tethered underwater flight vehicle. The LMI-based H∞ approach was applied to develop the reduced-order feedback autopilots for the un-tethered vehicle, and the tether (communication cable) effects were reduced by the feed-forward compensator. Nonlinear simulation results showed the effectiveness of the scheme.