A NEW SHIP RECOVERY CONCEPT AND DESIGN USING ADAPTIVELY CONTROLLED BUOYANCY SYSTEMS AKD Velayudhan 1 , N Srinil 1 , N Barltrop 1 ABSTRACT In this paper, attention is placed on the salvage of a sunken ship resting on the seafloor by introducing a new design concept based on the adaptively-controlled buoyancy (gas-inflating) systems. A mathematical model describing a ship rigid-body motion in a vertical diving plane accounting for the heave and pitch degrees of freedom will be presented and analyzed with respect to both hydrostatic and hydrodynamic loads. A new design approach is implemented by integrating a fuzzy logic algorithm with the sliding mode controller to bring together the advantages of both controllers. An adaptive fuzzy sliding-mode control strategy (Conventional or Two input fuzzy sliding mode controller and Single input fuzzy sliding mode controller) ensuring a safe and stable ascending ship dynamics will be presented along with the discussion of a practical aspect of automatic controller design regulating the gas inflating flow rate. Computational simulations with a series of parametric studies based on an experimental ship model will be carried out to show the effectiveness of the proposed adaptive fuzzy sliding mode controllers and its comparative performance with conventional sliding mode controller. It is found that both fuzzy sliding mode controllers show about 30 % of improvement in tracking performance over the conventional controller in which single input fuzzy sliding mode controller is the optimum choice due to less tuning effort and computational time. KEY WORDS Marine Salvage; Buoyancy Systems; Breakout Force; Two Input & Single Input Fuzzy Sliding Mode Controller. INTRODUCTION As far as marine salvage operation is concerned literature sources reporting systematic data and information useful for system modeling are relatively few. Studies regarding the dynamics of salvage operation are of course complicated by the fact that, in addition to the influence of complicated hydrodynamic forces and moments and breakout forces, the external disturbances and uncertainty are to be taken in to account. There are three methods commonly used in the marine salvage industry to extract the sunken objects from the sea bottom, i.e. by using the floating cranes, the Remotely Operated Vehicles (ROVs) and the buoyancy systems. Floating cranes can be used for water depths of 2000 m with a good controllability; however the weight of cables becomes more than that of the payload for deeper lifts and hence the process becomes awkward and costly. As the cranes are fitted onto a moving vessel, there will be the operational constraints due to the limiting sea state affected by weather conditions. Excessive cost of hiring and the limited availability of cranes are the major problems facing the salvage industry. ROVs, on the other hand, can be used in higher water depths and they are highly controllable. Nevertheless, they can be only used for lifting smaller objects as the lifting capacity is limited by the size and power of the thrusters used for the propulsion (Nicholls-Lee, et al 2009). As an advantage, buoyancy systems can be used for lifting any size of objects from any depths with comparatively less costs. The concept of using a buoyancy system (e.g. the gas inflated bags) for salvaging sunken vessels from the deep ocean has been around for centuries. This operation is based on the well-known ‘Archimedes’ principle for which the force on the object can be determined by subtracting the dry weight of the object from the weight of the fluid displaced by that object (Rawson & Tupper 2001). In general, the bottoms of inflatable bags (e.g. balloons) are attached to the payload to be lifted and inflated using pipes from the gas generating system. The main drawback of using the inflating bags for marine salvage operation is due to the difficulty in controlling the vertical speed as the ship ascends. A large buoyancy force may be initially 1 Department of Naval Architecture & Marine Engineering, University of Strathclyde, Glasgow UK