Optimal tank design and directional dynamic analysis of liquid cargo vehicles under steering and braking

The stability and dynamic response characteristics of partially-filled tank vehicles are adversely influenced by the movement of the liquid cargo within the tank. The directional dynamics and stability characteristics of partially-filled tank vehicles are analyzed and enhanced through formulation of an optimal tank configuration, and analytical models for analyses of vehicle responses to steady and transient steering maneuvers, and combined steering and braking inputs. A generic tank cross-section is initially proposed based upon an analysis of the currently used tank configurations. Three different constrained multi-variable optimization functions are formulated and solved to derive optimal tank cross-sections corresponding to various liquid fill conditions. The performance potentials of the optimal tank configurations are initially evaluated in terms of the load transfer properties and static rollover threshold acceleration limit of a partly-filled tractor-semitrailer tank vehicle through development and analyses of a static roll plane model. The influence of tank geometry on the directional response and dynamic roll stability characteristics is further investigated through development and analyses of a constant-speed three-dimensional model of the tank vehicle. The static and dynamic roll response characteristics of the vehicle equipped with two optimal tanks are compared with those of the vehicle with conventional tanks, under various directional maneuvers and liquid fill conditions, to demonstrate the superior potential performance of the optimal tank designs.; A three-dimensional quasi-static model of the partially-filled generic tank is further developed to study instantaneous liquid load shift in both the roll and pitch planes under simultaneous applications of lateral and longitudinal accelerations. The tank model is integrated into a comprehensive variable-speed three-dimensional model of an articulated vehicle combination to investigate the impact of cargo shift on the dynamic response of partially-filled tank vehicles under braking-in-a-turn maneuvers. The dynamic characteristics of tank vehicles are compared with those of the equivalent rigid cargo vehicles to demonstrate the destabilizing effects of the liquid load shift. The dynamic responses of tank vehicles are further investigated in view of variations in vehicle maneuvers, fill volume, road condition, and tank cross-section. From the study, it is concluded that liquid cargo movement within a tank tends to reduce roll stability limits and yaw stability limits of the vehicle, when operating on a dry road and a wet/slippery road, respectively. The performance limits can be considerably enhanced through the use of the proposed optimal designs.