Submersible walking dredger/miner

The use of surface floating dredgers in deep inland reservoirs and continental shelves, either for dredging or mining purposes, is restricted by several operational limitations. Use of smaller surface floating dredgers in deep inland reservoirs is constrained by the ladder (a long truss like structure 'arm' that supports the excavation tool) length. Bigger dredgers have operational restrictions and mobilization problems. In shelf areas, the dredging operation is less precise due to currents, winds and waves. The floating pipelines, floats and winch wires are obstacles to navigational paths for other surface vessels. High investment costs are involved in the construction of bigger high capacity dredgers. It is difficult to modify such systems once they are constructed. The limitation of the existing technology served as the main motivation to design an active legged submersible dredger / miner, which is described in this thesis. The designed vehicle is named the 'Golden Tortoise' because it simulates the belly crawling motion of a tortoise or turtle. A full scale prototype vehicle was manufactured by Excavation & Equipment Manufacturing (P) Ltd., (EEM (P) Ltd.) India. The prototype vehicle is suitable for operation in deep inland reservoirs up to a depth of 50 m and is designed to excavate sand, silt or clay mixtures in various proportions. -- Parametric performance models were developed to evaluate the locomotion, excavation and transportation processes of the designed vehicle. Periodic gait plans were developed for straight line and curvilinear locomotion on natural terrain. Experimental validation of the theoretical gait plans was performed, which showed that the average slip was about 20% at the foot/soil interface in medium to relatively fine sands. Parametric models were developed for the evaluation of the locomotion cycle time of the designed vehicle. The locomotion cycle time was also measured from the gait plan tests and was found to be an average of 30 seconds. The static load incident at each foot as a function of the vehicle weight and the leg joint parameters was predicted by developing a two-dimensional model based on simple beam theory. Prototype tests were performed to measure the static load incident at each foot as a function of the leg swing angle. The maximum static load measured due to weight of the vehicle was approximately 13 kN. The subsequent soil settlement and failure were estimated based on the theories of elasticity and plastic equilibrium as well as the shallow foundation theories. The dynamic load as a function of the leg actuating hydraulic cylinders was also considered for predicting the soil response. Comparisons between the different performance parameters of tracked vehicles and the designed legged vehicle were made. The shear stress-shear displacement relationship for different types of terrain was considered to predict the traction available for each foot during locomotion under different slip conditions. It was observed that the foot with grousers (lugs or teeth underneath the foot) provided more tractive effort compared to a tracked vehicle of similar dimensions and weight in cohesive soils. -- Parametric performance models for the designed excavation system were developed based on the theories of earth moving machinery and their dynamics. The performance of the designed excavation system was evaluated based on the excavation production, spillage generated and the excavation power required under varying operational and soil conditions. -- Parametric models were developed for evaluation of the designed pump-pipeline system by integrating the two-phase flow theories developed by various previous researchers. The models predict the total head loss in the pipeline system and hence the required pump power and also the limiting settling velocity condition and thereby the chances of pipeline blockage. In the present design this means that the suitable pipeline diameter is between 0.15 to 0.3 m to achieve a production of 61 m³/hr with a maximum volumetric concentration of 18 %. The mean mixture velocity in the pipeline should vary between 2 to 5 m/sec to achieve the desired production and avoid pipeline blockage. A conceptual model was developed showing the complex interrelationships existing between the dredging and locomotion processes. -- The results from this thesis can now be used to design the requisite controllers for the automatic operation of the 'Golden Tortoise'