The purpose of the present study is to develop a three-dimensional efficient interactive model and a numerical procedure to simulate a tire on soft ground, which can be applied to multibody dynamics for off-road vehicles. For motion analysis of the tire on soft ground, it is necessary to describe the elastic deformable behavior of the tire and the behavior with large displacement and local disruption of soft ground. A three-dimensional analysis must be conducted in order to express the complex

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... ehavior of the tire on soft ground due to the deformation of the tire and the landform of soft ground, such as ground heaving in the vicinity of the tire side edge. As the tire model, we adopt a distributed lumped mass-spring model, in which a rigid wheel is connected to a number of tire-masses by Voigt elements. This tire model allows us to describe the local deformation of the tire and the distributed contact pressure between the tire and soft ground. In addition, as the soft ground model, we adopt a discrete element (DE) model, in which soft ground consists of a number of rigid soil particles. This ground model allows us to express the discrete behavior of soft ground. Furthermore, the contact between the tire and the soft ground is defined as the contact between the tire patches constructed of tire-masses and the soil particles of soft ground. Numerical simulations of the tire behavior on soft ground have been carried out under several conditions using the proposed model. The numerical results revealed that three-dimensional motion analysis of the tire behavior on soft ground is possible, and that the proposed model and the numerical procedure could be validated through comparison with previous experimental results on the tractive and cornering performance of the tire on soft ground.