Control System and Hydrodynamic Analysis for TUMS (Towed Unmanned Submersible) (1982)

Abstract This paper discusses the analytical model, hydrodynamic testing, and control system design for the TUMS contract to Sperry Systems Management (SSM) for the Royal Navy. The TUMS system employs a two body approach, depressor and tethered vehicle. The vehicle carries a variety of acoustic, optic, and magnetic sensors along with a hydraulic manipulator. The depressor encloses the vehicle during launch and recovery and decoup1es ship motions from the vehicle. Vehicle stability criteria requires precise heading and rate control consistent with long range acoustic devices while regulating altitude, pitch angle, and pitch rate in severe sea states. The analytical model was developed to predict the dynamic behavior of the two body system. The model includes depressor motion, dynamic tether behavior, and a six degree of freedom model of the vehicle dynamics. Using the model, control strategies were developed and tested to satisfy the design requirements of automatic heading control, automatic pitch control, and automatic altitude control. In order to refine the estimates of hydrodynamic coefficients scale models were fabricated and tested on a LAPMM (large amplitude planer motion mechanism) and in open water. The experimentally derived coefficients were compared to the predicted values and incorporated into the analytical model. During the analysis and design phase, it became evident that a thruster allocation scheme was required to balance desired thrust and available hydraulic power, using a optimization technique. To verify the control strategy, the vehicle's onboard microprocessors (two in tandem) were interfaced with Perry's HP-IOOO mini-computer for final control system testing. Following successful open water testing, new standards will be achieved for commercial submersible control. Introduction The TUMS system operates from the Royal Navy's HMS CHALLENGER, the vessel for new seabed operations.1 Operating depths enable missions beyond the capabilities of diving systems and ship mounted sensors for coverage of 90% of the ocean bottom. During launch and recovery the TUMS vehicle is latched inside the depressor's protective housing. At the mission depth the vehicle is released from the depressor at the end of a neutrally buoyant tether. The system has two modes of operation. The first is a search mode with the depressor and vehicle towed behind the surface ship, using a combination of sensors. During this mode the vehicle either passively follows the depressor or employs its thrusters to make excursions in altitude or side-to-side. The second mode is for suspended operations with the vehicle hovering independent of the depressor, performing work tasks with its manipulator. Both modes use a depressor to decouple surface-borne ship motions from the vehicle. The variety of tasks performed range from search, identification, classification, to recovery of objects from full ocean depths (Figure 1). The vehicle, shown in Figures 2 and 3, provides a stabilized platform for sensor and work suits. Complete vehicle fairings minimize hydrodynamic drag to maximize vehicle surge speed. The large rectangular tail ensures good passive stability while being towed by the depressor. Tow point selection is chosen to minimize tether induced yaw torques. Five high performance hydraulic thrusters give the vehicle the necessary maneuvering capabilities.