This study provides a comprehensive modeling evaluation of the dynamic stability of Long Combination Vehicles (LCVs) that are commonly operated on U.S. highways, using multibody dynamic simulations in MATLAB/Simulink®. The dynamic equations for a tractor with two trailers connected by an A-frame converter dolly (A-Dolly) are developed. The dynamic model is used for running MATLAB® simulations, with parameters that are obtained through measurements or obtained from other sources. The simulation results are verified using track test data to establish a baseline model. The baseline model is used for parametric studies to evaluate the effect of trailer cargo weight, center of gravity (CG) longitudinal location, and trailer wheelbase. The dynamic model is further used to analyze both single-trailer and double-trailer trucks through nondimensionalization. The nondimensionalization method has the added advantage of enabling studies that can more broadly apply to various truck configurations. The simulation results indicate that increasing the trailer wheelbase reduces rearward amplification due to the damping effect of the longer wheelbase. A larger momentum ratio due to increased trailer gross weight increases rearward amplification. The detailed models of pneumatic disc and drum brakes in LCVs, including the airflow delay and thermal characteristics, are also developed and are coupled with the articulated vehicle dynamic models. The disc and drum brake braking performance are evaluated and compared in straight-line braking and combined steering and braking at a 150-ft J-turn maneuver. In straight-line braking, the simulation results indicate that disc brakes provide significantly shorter braking distance than drum brakes at highway speeds on a dry road, mainly due to their larger braking torque. On a slippery road surface, however, the greater braking torque causes more frequent wheel lockup and ABS activation at higher speeds, and disc brakes do not provide a substantially shorter braking distance than drum brakes. The simulations also point out that the disc brakes' cooling capacity is higher than the drum brake, with the cooling efficiency heavily dependent on the airflow speed. At higher driving speeds, the airflow accelerates to a turbulent flow and increases the convection efficiency. For braking in-turn maneuvers, at higher entering speeds, disc brakes decelerate the vehicle slightly sooner and then scrub speed faster, resulting in better roll stability when compared with drum brakes. / Doctor of Philosophy / Long combination vehicles (LCVs) are the combination of a tractor and two or more trailers and have been widely used on U.S. highways for cargo transport. Although LCVs have a larger cargo volume and provide more modularity in transporting goods, at higher speeds, they can be more prone to rollovers and require longer stopping distances and space to maneuver from one lane of travel to another. This study investigates the dynamic stability of an LCV, A-double trailer that includes a tractor, two trailers, and a dolly through modeling and simulation. The dynamic equations of each vehicle unit are derived based on Newtonian Mechanics (i.e., F = ma). The dynamic models are tuned to match the track testing results for similar vehicles, performed by the Center for Vehicle Systems and Safety (CVeSS) at Virginia Tech in the past. A novel evaluation method that nondimensionalizes the equations is used to allow for ease of use for LCVs with different cargo weights, lengths, and other similar variations. The dimensionless parameters are the function of vehicle parameters and express the relationship among the magnitude of vehicle parameters. Using the nondimensionalized model, the study performs a frequency analysis of the effect of trailer cargo weight, CG longitudinal position, and trailer wheelbase on roll stability and rearward amplification. Rearward amplification is the ratio of peak lateral acceleration between the tractor and the rearmost trailer. Slow-sweeping sinusoidal steering from 0.01 Hz to 0.6 Hz is used for the simulation analysis. The simulation results show that by increasing the trailer wheelbase—the distance from the trailer kingpin to the axle—the vehicle is more laterally stable because the longer wheelbases make the trailer more resistive to spinning around. Additionally, the pneumatic disc and drum brake models and thermal models are developed and coupled with the vehicle dynamic model. The disc and drum brake braking performance are investigated during both straight-line braking and combined steering and braking in a curve. The disc brakes generate a greater brake torque compared with drum brakes, and as such can decelerate the vehicle more efficiently on dry road surfaces, particularly at higher speeds such as highway speeds. This improves avoidance during emergency stops and roll stability during traveling in a curve, such as at a highway exit. The disc brakes also have greater cooling capacity because they can transfer the generated heat to the air due to the greater airflow and turbulence caused naturally by their design. This greatly helps to keep the brakes cooler on the track and to improve their stopping efficiency.

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