Modeling tracked vehicle dynamics using vibration modes.

Abstract

There is a need for low-order tracked vehicle models that capture the essential features of track vibration. Accurate estimates of track vibration levels are vital to understanding how new track designs can improve track durability, vehicle manuevering, and the noise and vibration environment inside the vehicle hull. Existing multi-body dynamic track models capture track vibration, however, they do so at the expense of model size; that is, the resulting models contain on the order of one to several hundred degrees-of-freedom. In contrast, track models focused on kinematics which assume the track to be a massless band (quasi-static) inherently cannot capture track vibration. The purpose of this study is to develop alternative track models, based on a continuum model for the track, which can be used to support rapid simulations of tracked vehicle dynamics at frequencies characteristic of track vibration. To this end, a hierarchy of models for an example military vehicle have been developed; each subsequent model describing track vibration to higher fidelity through use of increasingly complex continuum elements. These hybrid models contain both continuous and discrete elements and govern the coupled response of the track and the rotational response of the drive sprocket, road and idler wheels, and support rollers. Solution efficiency in each of the models derives from the use of modal coordinates, which allows track circuit response to be accurately calculated using a small number of degrees-of-freedom. Results of an experimental validation study confirm use of the continuum approximation in modeling dynamics of the pitched track over a specific frequency range. This conclusion is reached by evaluating the ability of the continuum theory to predict the frequency response of a representative (7-pitch) track span. The most complete continuous track model described in this study captures the coupled transverse/longitudinal vibration of a sagged, translating track element. Free and forced response analyses of a track circuit model based on this element are developed and simulations of track response to excitation sources such as front and rear roadwheel motion and polygonal action are presented. The presence of low frequency vibration modes (near 3 Hz) indicate the limitations of models employing a massless track representation for the example military vehicle considered. Results from a standard bump-course traversal reveal the importance of including track vibration modes in predicting measures of dynamic response, such as dynamic track tension and dynamic contact forces. From this study, it is concluded that continuous track elements can be successfully employed in developing low-order vehicle models capturing dominant low-frequency track vibration.