Successful negotiation of water obstacles, effective crossing of canals and rivers, and capacity to perform limited amphibious maneuvers form an imperative prerequisite for amphibious armoured personnel carriers intended for battle in terrains whose characteristics are influenced by water obstacles. The location of CG in vehicle with front mounted power pack, integrated engine and transmission system, at an amphibious favourable position is a challenging task. The front mounted power pack, results in front heavy vehicle configuration and forward location of CG. Special design emphasis for creation of frontal shape that provides higher buoyancy and judicial location of systems and components within the functional constraints are required to create CB-ahead of-CG condition. Further, change of add-on armour from one threat level to other and change in level of the consumables present in the vehicle such as fuel, water and ammunition can alter the location of CG. Hence, a study on the effect of CG location on the stability of the vehicle in amphibian mode, especially at higher speeds, is of paramount importance in defining its amphibian capability in different variant configurations and at other operating conditions.
In the present work, it has been aimed to investigate the effect of forward shift in location of CG of vehicle on its stability and reduction in maximum achievable speed in amphibious mode. Experimental analysis using 1/5th scale model of vehicle and CFD analysis were carried out at different vehicle speeds. Details of flow pattern around the vehicle, reduction in max achievable speed at different CG locations, negative trim and flow of water over the hull at speeds higher than the stable speed have been adequately captured. Forward shifting of CG from original location has been found to result in decreased amphibious speed of vehicle. Good correlation has been found between the flow patterns and stability predictions obtained from towing tank tests and CFD simulations.
Keywords: Amphibious design, Model testing, Combat vehicle.