A simplified 3D dynamic model of tracked vehicle crawling on cohesive soft soil is investigated. The vehicle is assumed as rigid body with 6-dof. Cohesive soft soil is modeled through relations: pressure to sinkage, shear displacement to shear stress, and shear to dynamic sinkage. Equations of motion of vehicle are derived with respect to the body-fixed coordinates. In order to investigate 3D transient dynamics of tracked vehicle, Newmark's method is employed by means of incremental-iterative algorithm. 3D dynamic simulations are conducted for a tracked vehicle model and steering performance is investigated.
Tracked vehicles find their marine applications, for instances, to underwater trenches, cable or/and pipe burying systems, dredges and support of researches, and military purposes (e.g. Ivanov and Karev 1990). Herrmann (1978) proposed a lightweight tracked vehicle together with Archimedean screw for a deep ocean running gear module. Muro (1983, 1988) studied on the trafficability of tracked vehicle on very soft bottom. Hong and Choi (2001) experimentally investigated grouser shape effects on trafficability of extremely soft seabed. In order to investigate the performance of tracked vehicles, a number of studies have been carried out since Bekker's pioneering study (1956). For soft ground, the interactions between track, road wheels and soil become so complex that the basic theory on pressure-sinkage and sheartraction force is restricted in its application. Wong et al. (1984) developed an analytical method for predicting the normal pressure distribution under a moving tracked vehicle, taking into account the response of the terrain to repetitive shear loading. Kitano and Kuma (1977) developed an analytical method for investigation of the steerability of tracked vehicles in time domain. They used the ground pressures at the road wheels to calculate the traction force of tracks in form of Coulomb friction, and assumed the motion of vehicle is planar.
