Discussions on locomotion and excavation systems of 'SROSD II'

Different types of submersible dredgers are conceived, modeled and even some prototype and full-scale vehicles are built for prospective subsea excavation purposes by various researchers and commercial companies. Most common type of submersible dredgers is tracked vehicle. Walking submersible dredgers are also available which can be further subdivided into passive legged systems (locomotion performed by moving frames) and active legged systems (locomotion performed by individually controlled legs). An Archimedian screw system is also conceived for a subsea mining vehicle. Continuous ground contact is necessary for tracks and Archimedan screw types of locomotion systems. Legged locomotion also requires intermittent contact with the terrain. Generation of adequate friction for locomotion purposes in very soft cohesive sediments or submerged rocky terrain is often critical. In soft cohesive terrain, the vehicle can capsize due to insufficient bearing capacity. Additional ground contact forces are necessary to counteract the excavation and environmental forces. In low-friction and/ or low bearing capacity subsea terrains, achieving the force balance for the stability of the above mentioned submersible dredgers can thus be difficult. Also, the subsea terrain can be uneven with steep slopes and can be unchartered. Hence, a conceptual design of a submersible remotely-operated swimming dredger (SROSD II) is conceived. The SROSD II can swim with the aid of multiple control planes and thruster system in order to avoid difficult subsea terrains. For disjointed working areas, SROSD II can swim and thus can significantly reduce the non-working time. During excavation, SROSD II can anchor itself with the help of hydraulically actuated spuds. The anchored spuds and the thrusters can provide the necessary reaction forces to counteract the excavation and environmental forces. Unlike other submersible vehicles, the SROSD II is an almost neutrally buoyant system. In this paper the ge- eral arrangement of the SROSD II, the proposed locomotion and excavation systems are discussed. A simplified model for position keeping during excavation is also presented.