Accurate and efficient contact models for wheel–rail interaction are essential for the study of the dynamic behaviour of a railway vehicle. Assessment of the contact forces and moments, as well as contact geometry provide a fundamental foundation for such tasks as design of braking and traction control systems, prediction of wheel and rail wear, and evaluation of ride safety and comfort. This paper discusses the evolution and the current state of the theories for solving the wheel–rail contact problem for rolling stock. The well-known theories for modelling both normal contact (Hertzian and non-Hertzian) and tangential contact (Kalker's linear theory, FASTSIM, CONTACT, Polach's theory, etc.) are reviewed. The paper discusses the simplifying assumptions for developing these models and compares their functionality. The experimental studies for evaluation of contact models are also reviewed. This paper concludes with discussing open areas in contact mechanics that require further research for developing better models to represent the wheel–rail interaction.

The performance of three semiactive control policies, including the well-known skyhook control and two others that are referred to as “groundhook” and “hybrid” control, are studied experimentally. The experiments use a single suspension apparatus that is commonly referred to as “quarter-car” rig, and a magnetorheological damper that is built and tuned for the purpose of this study. Upon describing the mathematics of the three semiactive control policies and the construction of the quarter-car rig, the results of a series of experiments with each control policy are presented. The transmissibility plots of the test results confirm the features of each control policy, as discussed in the past analytical studies. The results indicate that skyhook control can significantly reduce the transmissibility of the sprung mass, as compared with passive dampers. Similarly, groundhook control substantially reduces the unsprung mass transmissibility. For vehicle applications, reducing the sprung mass transmissibility often results in improving the ride comfort, and reducing the unsprung mass transmissibility provides less wheel hop, therefore resulting in better road holding ability and improved vehicle stability. The test results for hybrid control, which is intended to provide a combined effect of skyhook and groundhook, indicate that it holds the promise of achieving a semiactive control policy that can be slowly adapted to the driving condition and vehicle dynamics for better vehicle stability and ride comfort.

The application of magneto rheological dampers for controlling recoil dynamics is examined, using a recoil demonstrator that includes a single‐shot 50 caliber BMG rifle action and a MR damper. The demonstrator is selected such that it can adequately represent the velocities that commonly occur in weapons with a recoil system, and can be used for collecting data for analyzing the effects of MR dampers on recoil dynamics. The MR damper is designed so that it can work effectively at the large velocities commonly occurring in gun recoil, and also be easily adjusted to reasonably optimize the damper performance for the recoil demonstrator. The test results show that it is indeed possible to design and use MR dampers for recoil applications, which subject the damper to relative velocities far larger than the applications that such dampers have commonly been used for (i.e., vehicle applications). Further, the results indicate that the recoil force increases and the recoil stroke decreases nonlinearly with an increase in the damping force. Also of significance is the fact that the adjustability of MR dampers can be used in a closed‐loop system such that the large recoil forces that commonly occur upon firing the gun are avoided and, simultaneously, the recoil stroke is reduced. This study points to the need for several areas of research including establishing the performance capabilities for MR dampers for gun recoil applications in an exact manner, and the potential use of such dampers for a fire out of battery recoil system.

Various control policies, such as skyhook and groundhook control, have often been considered for semi‐active vehicle suspensions. Past studies have shown the performance limitations of these policies, as well as others that have been considered for vehicle applications. This study will provide a look into an alternative control technique called "hybrid control", which attempts to merge the performance benefits of skyhook and groundhook control. The results of this study are based on an experimental evaluation of hybrid control using a quarter‐car rig and a magneto‐rheological damper. The control policy is employed and evaluated under a steady‐state or pure tone input, and a transient or step input. Peak‐to‐peak displacement and peak‐to‐peak acceleration are used to evaluate performance. The results indicate that hybrid control can offer benefits to both the sprung mass and the unsprung mass. The steady‐state results reveal that hybrid control can be used to reduce the peak‐to‐ peak displacements and accelerations of both bodies. The transient evaluation shows that hybrid control can be effective at reducing the peak‐to‐peak displacement of the sprung mass.

A novel active vibration control technique based on positive position feedback method is developed. This method, which is a modified version of positive position feedback, employs a first-order compensator that provides damping control and a second-order compensator for vibration suppression. In contrast, conventional positive position feedback uses a single second-order compensator. The technique is useful for strain-based sensors and can be applied to piezoelectrically controlled systems. After introducing the concept of modified positive position feedback, this paper investigates the stability of the new method for locating gain limits. Stability conditions are global and independent of the dynamical characteristics of the open-loop system. Using root locus plots, proper compensator frequency is identified and damping of the closed-loop system is studied. The performance of the modified positive position feedback for both steady-state and transient dynamic control is studied. The experimental and numerical results show that the proposed method is significantly more effective in controlling steady-state response and slightly advantageous for transient dynamics control, as compared with conventional positive position feedback.

A comprehensive review of technologies and approaches for active safety systems designed to reduce ground vehicle crashes, as well as the associated severity of injuries and fatalities, is provided. Active safety systems are commonly referred to as systems that can forewarn a driver of a potential safety hazard, or automatically intervene to reduce the likelihood of an accident without requiring driver intervention. The data from naturalistic drivers has shown that such systems are instrumental in improving vehicle safety in various conditions, particularly at higher speeds and under adverse road conditions. The increased integration of sensors, electronics, and real-time processing capabilities has served as one of the critical enabling elements in the widespread integration of active safety systems in modern vehicles. The emphasis is placed on control approaches for active safety systems and their progression over the years from antilock brakes to more advanced technologies that have nearly enabled semiautonomous driving. A review of key active safety control approaches for antilock braking, yaw stability, traction control, roll stability, and various collision avoidance systems is provided.