The aim of suspension systems in vehicles is to provide the best balance between ride and handling depending on the operating conditions of a vehicle. Active suspensions are far more effective over a variety of different road conditions compared to passive suspension systems. This is because of their ability to store and dissipate energy at different rates. Additionally, they can even provide energy of their own into the rest of the system. This makes active suspension systems an important topic of research in suspension systems. The biggest benefit of having an active suspension system is to be able to provide energy into the system that can minimize the response of the sprung mass. This is done using actuators. Actuator design in vehicle suspension system is an important research topic and a lot of work has been done in the field but little work has been done to estimate the peak control force and bandwidth required to minimize the response of the sprung mass. These two are very important requirements for actuator design in active suspensions. The aim of this study is estimate the peak control force and bandwidth to minimize the acceleration of the sprung mass of a vehicle while it is moving on a compliant surface. This makes the road surface a bi-lateral boundary and hence, the total system is a combination of the vehicle and the compliant road. Generalized vehicle and compliant road models are created so that parameters can be easily changed for different types of vehicles and different road conditions. The peak control force is estimated using adaptive filtering. A least mean squares (LMS) algorithm is used in the process. A case study with fixed parameters is used to show the results of the estimation process. The results show the effectiveness of an adaptive LMS algorithm for such an application. The peak control force and the bandwidth that are obtained from this process can then be used in actuator design. / Master of Science

In 2010, there were 6,714,288 total registered drivers in New Jersey. Approximately 4% (267,485) of these drivers had a suspended driver's license. The intent of suspending a driver's license is to keep hazardous drivers off of the roads, in hopes of having a safer driving environment for others on the road. Drivers in New Jersey can have their driver's license suspended for a number of reasons. These include dangerous driving behaviors such as reckless driving and driving under the influence of alcohol or drugs. However, there are also reasons for suspension that have little or nothing to do with driver behavior, such as failure to pay child support, failure to pay MVC insurance surcharge, or failure to appear in court. While these offenses are all due of consequence, they have little or nothing to do with driver behavior. This research program will conduct an analysis of the issues and implications of implementing a restricted-use license program for suspended New Jersey drivers, detailing key issues associated with restricted-use license programs. It was found that over two-thirds of suspended drivers in New Jersey receive driver's license suspensions for both driving and non-driving-related offenses, whereas only about four-percent of suspended drivers in New Jersey receive a driver's license suspension for driving-related reasons only. It was also found that drivers suspended for non-driving related reasons have different driver behavior than drivers suspended for driving related reasons. Surveying both New Jersey police chiefs, as well as U.S. state motor vehicle agencies, it was found that there is a generally positive perception of restricted driver's license programs. Overall, it is recommended that the New Jersey Motor Vehicle Commission implement a restricted driver's license program in New Jersey. / Master of Science

The advent of finite element methods has changed the tire industry's design process over the past three decades. Analyses, previously impractical using analytical methods and physically limited by experimental methods, can now be performed using computational methods. This decreases the cost and time associated with bringing a new design to the marketplace; however some physical testing is still required to validate the models. The design, fabrication, installation, and operation of a tire, suspension, and chassis test fixture (TiSCTeF) is detailed as part of this study. This fixture will support the validation of effective, parametric finite element models currently under development, as well as the design and testing of suspension and chassis components for the Virginia Tech Formula SAE team. The fixture is designed to use the Formula SAE race car as the test platform. Initially, the fixture is capable of performing static load-deflection and free-rolling tire tests. Provision has been made in the design for incremental upgrades to support cornering tests and additional instrumentation. An initial load-deflection test has proven that the fixture is capable of creating reproducible data sets. Specific recommendations are made concerning the improvement of data quality for future tests. This study also presents a process for analyzing existing tire cornering data and eliminating anomalies to improve the effectiveness of normalization techniques found in the literature. The process is shown to collapse tire cornering data, which is partially ill- conditioned, onto master curves that consistently display the effect of inclination angle and tire inflation pressure on tire response. / Master of Science

Active suspension technologies are well known for improving ride comfort and handling of ground vehicles relative to passive suspensions. They are ideally suited for mitigating single-event road obstacles. The work presented in this thesis aims to develop a structured approach for finding the peak force and bandwidth requirements of actuators for active suspensions, to mitigate single-event road obstacles. The approach is kept general to allow for application to different vehicle models, ride conditions and performance objectives. The current state-of-art in active suspensions was first evaluated. Based on these findings, the objectives of the simulation models and approach was defined. A quarter-car model was developed in Matlab to simulate the behavior of active suspensions over unilateral boundary conditions due to different road obstacle profiles. The obstacle profiles were obtained from existing standards and literature and then processed to replicate the interaction of tires on road. A least-mean-squares (LMS) algorithm for adaptive filtering, with the help of look-ahead preview was used to determine the ideal control force profile to achieve the performance objective of the active suspension. A case study was conducted to determine the requirements of the actuator in terms of bandwidth and peak force for different single-event road obstacle profiles, vehicle speeds and look-ahead preview distances. The results of the study show that the vehicle velocity and type of road obstacle have a strong influence on the required peak force and bandwidth of the actuator, while look-ahead preview will be much more important for real time controller implementation. / Master of Science

This research provides a thorough flow characterization study to compare the functionality of two types of load-leveling valves that are commonly used for air suspension systems of commercial trucks. The first valve features a simple disk/slot design and is relatively compact for installation. The second type is larger and has a sophisticated, chambered design, which allows for considerably quicker fill and exhaust response times in the transient region. A new approach is introduced to estimate the transient mass flow rate of a load-leveling valve under different suspension pressures, without requiring a mass flow meter. An extensive series of dynamic tests are conducted to characterize and compare the two load-leveling valves. A generic heavy-truck pneumatic suspension, consisting of load-leveling valves, airspring, air tank, and air-hose fittings, is configured for testing. The test setup is used to evaluate the transient performance of each type of load-leveling valve in a typical truck suspension. The flow behavior of the system is validated by the force/pressure responses of the air spring due to various displacement excitations. The experimental results describe the detailed flow behavior of both valves. The flow characterization results can be incorporated as one of the most critical parameters for future model development of pneumatic systems. The tests indicate that the leveling valve with chambered design has a far faster transient flow response than the disk valve, although it is more complicated in its mechanical design and therefore costs more. To take advantage of the design simplicity of the disk valve, while also enabling it to have a faster transient response (compared with the chambered design), it is re-designed with larger flow openings and other elements to match the performance of the chambered valve for transient flow. A comparison of the experimental results and simulations validates that the re-designed rotary disk valve performs nearly the same as the chambered valve, but is simpler and costs less. The study's results are directly applicable to improving the transient dynamics of heavy truck air suspensions by providing a better understanding of how load-leveling valves can be used not only to provide ride-height control, but also to influence the roll and pitch dynamics of heavy trucks. / Master of Science

Most commercial vehicles currently on the market are still equipped with a passive suspension system, while some luxury brands may already use an adaptive suspension. Active suspension systems on the other hand are rarely found, however, they offer great opportunities to close the gap of the well-known trade-off between ride comfort and handling. Besides that, they can also be used to mitigate single event disturbances, an objective of the USA army as announced in a solicitation which initiated and motivated this research. In addition to that, several studies were found stating the impact and danger of potholes and their impact on the vehicle and passenger. Reviewing the literature, several control strategies for controlling active suspension systems were found. However, most of these approaches used feedback control and did not try to mitigate single event disturbances. Since literature also suggested making use of look ahead preview, research at the Performance Engineering Research Lab at Virginia Tech was started in 2015 combining look ahead preview and an adaptive system to generate optimal force profiles. This introductory research succeeded and proved the used approach to be very promising. However, the used adaptive system was not designed to operate in real-time and did not show any correlation between different road profiles. Therefore, the main objective of this research project is to evaluate and analyze each of the adaptive systems by searching for correlations in their solutions. The results then should be used in order to design a control law which emulates the adaptive system and can be used in a real-time environment. First, an overall research methodology was derived. According to this a software application was developed which extracts ideal force profiles from single event disturbance signals in order to mitigate their impact to the vehicle. The application uses a quarter car model with a partially loaded active suspension system, a set of predefined road profiles, a road profile preprocessor, and an adaptive algorithm. The preprocessing includes geometric filtering using a Tandem-Cam Model and the adaptive processor used an iterative version of the Filtered-X Last-Mean-Square algorithm. During evaluation and analysis of several generated data sets, high correlations in the generated and adjusted adaptive systems were discovered. From these an empirical and theoretical universal filter model was derived, which was then used to design an open-loop control law named Optimal Force Control. The original control law and an adjusted version designed for a real-time environment were tested for all predefined road profiles over all considered vehicle velocities and prove to perform much better than the offline solution using the adaptive system. In summary, a control law named Optimal Force Control was designed which can be used and implemented in a vehicle to extract an analytical and ideal force profile given a road profile input. Implementing an active suspension system with tracking controller, this approach can be used in order to mitigate single event disturbance signals by reducing the vertical vehicle acceleration. / Master of Science

This study provides a comprehensive performance analysis of Wave-Adaptive Modular Vessels (WAM-V) using simulations and testing data. WAM-Vs are a new class of marine technology that build upon the advantages of lightweight, low-draft, catamaran construction. Independent suspensions above the hulls isolate the passengers and equipment from the harsh sea environment. Enhanced understanding of the relationship between suspension and vehicle performance is critical for future missions of interest to the U.S. Navy. Throughout this study, the dynamic properties of three different WAM-Vs were evaluated. A multi-body dynamics simulation was developed for the 100-ft WAM-V 'Proteus' based on an automotive 4-post shaker rig. The model was used to characterize the sensitivities of different suspension parameters and as a platform for future models. A 12-ft unmanned surface vessel (USV) was instrumented and sea trials were conducted in the San Francisco Bay. A dynamic 4-post simulation was created for the USV using displacement inputs calculated from acceleration data via a custom integration scheme. The data was used to validate the models by comparing the model outputs to sensor data from the USV. A vertical hydrodynamics testing rig was developed to investigate the interaction between the pontoons and the water surface to improve the understanding of how hydrodynamic forces affect suspension performance. A model was created to accurately simulate the hydrodynamic forces that result from vertical pontoon motion. The model was then scaled to fit a 33-ft WAM-V prototype. The 33-ft WAM-V was instrumented and sea trials were conducted in Norfolk, VA. The WAM-V's suspension was upgraded based on the testing results. A 2-post rig was also built for evaluating the 33-ft WAM-V's dynamics. Two dynamic models were made for the 33-ft WAM-V to evaluate different suspension designs. The results from this study have numerous impacts on the naval community and on the development of WAM-Vs. The methodology for testing and evaluation will allow for future WAM-V designs to be compared under controlled circumstances. The performance of WAM-Vs can then be compared against conventional platforms to determine their suitability for future missions. Simulation development will enable future WAM-Vs to be evaluated prior to undergoing sea trials. The hydrodynamic models become a powerful design tool that can be easily scaled and combined with the 4-post models. By providing the simulations and test data to future vessel designers, the designers will be able to intelligently evaluate numerous iterations early in the design phase, improving performance and safety. / Ph. D.

Currently, in the railroad industry, the lack of electrical sources in freight cars is a problem that has yet to find practical solutions. Although the locomotive generates electricity to power the traction motors and all the equipment required to operate the train, the electrical power cannot, in a practical manner, be carried out along the length of the train, leaving freight cars unpowered. While this has not been a major issue in the past, there is a strong interest in equipping modern cars with a myriad of devices intended to improve safety, operational efficiency, or health monitoring, using devices such as GPS, active RFID tags, and accelerometers. The implementation of such devices, however, is hindered by the unavailability of electricity. Although ideas such as Timken's generator roller bearing or solar panels exist, the railroads have been slow in adopting them for different reasons, including cost, difficulty of implementation, or limited capabilities. The focus of this research is on the development of vibration-based electromechanical energy harvesting systems that would provide electrical power in a freight car. With size and shape similar to conventional shock absorbers, these devices are designed to be placed in parallel with the suspension elements, possibly inside the coil spring, thereby maximizing unutilized space. When the train is in motion, the suspension will accommodate the imperfections of the track, and its relative velocity is used as the input for the harvester, which converts the mechanical energy to useful electrical energy. Beyond developing energy harvesters for freight railcar primary suspensions, this study explores track wayside and miniature systems that can be deployed for applications other than railcars. The trackside systems can be used in places where electrical energy is not readily available, but where, however, there is a need for it. The miniature systems are useful for applications such as bicycle energy. Beyond the design and development of the harvesters, an extensive amount of laboratory testing was conducted to evaluate both the amount of electrical power that can be obtained and the reliability of the components when subjected to repeated vibration cycles. Laboratory tests, totaling more than two million cycles, proved that all the components of the harvester can satisfactorily survive the conditions to which they are subjected in the field. The test results also indicate that the harvesters are capable of generating up to 50 Watts at 22 Vrms, using a 10-Ohm resistor with sine wave inputs, and over 30 Watts at peak with replicated suspension displacements, making them suitable to directly power onboard instruments or to trickle charge a battery. / Ph. D.

This work is concerned with determining empirical parameters in stress and fiber orientation models required to accurately simulate the fiber orientation in injection molded composites. An independent approach aims to obtain the material parameters using a sliding plate rheometer to measure the rheology of fiber suspensions at increased fiber lengths subjected to transient shear flow. Fiber orientation was measured in conjunction with shear stress to determine the relationship between stress and fiber orientation. Using a compression molding sample preparation procedure, the transient shear stress response was measured for glass and carbon fiber suspensions up to a number average fiber aspect ratio (length/diameter) of 100. Increases in concentration or fiber aspect ratio caused the magnitude of the stress response to increase by as much as an order of magnitude when compared to the suspending matrix. The degree of shear thinning at low shear rates also increased with increases in aspect ratio and concentration. The compression molding sample preparation procedure provided poor control of the initial fiber orientation which led to the investigation of samples subjected to flow reversal and samples generated through injection molding. The samples prepared through injection molding provided improved repeatability in the measured shear stress response and fiber orientation evolution during the startup of flow compared to compression molded samples and samples subjected to flow reversal. From repeatable stress and orientation evolution data, models for stress and fiber orientation were assessed independently. Current theories for stress were unable to reflect the overshoot in the measured stress response and could at best capture the steady state. The transient behavior of the fiber orientation models were found to be highly dependent on the initial fiber orientation. The repeatable orientation data obtained from the injection molding sample preparation procedure provided material parameters in the strain reduction factor and reduced strain closure models. The injection molded samples provided evolution data from different initial fiber orientations to provide further scrutiny or validation of the material parameters. Orientation model parameters that provided reasonable agreement to multiple sets of fiber evolution data in simple shear flow should allow for a better assessment of the orientation models in complex flow simulations. / Ph. D.

This thesis is on molecular dynamics studies of drying suspensions of bidisperse nanoparticle mixtures. I first use an explicit solvent model to investigate how the structure of the dry film depends on the evaporation rate of the solvent and the initial volume fractions of the nanoparticles. My simulation results show that the particle mixtures stratify according to their sizes when the suspensions are quickly dried, consistent with the prediction of recent theories. I further show that stratification can be controlled using thermophoresis induced by a thermal gradient imposed on the drying suspension. To model larger systems on longer time scales, I explore implicit solvent models of drying particle suspensions in which the solvent is treated as a uniform viscous background and the liquid-vapor interface is replaced by a potential barrier that confines all the solutes in the solution. Drying is then modeled as a process in which the location of the confining potential is moved. In order to clarify the physical foundation of this moving interface method, I analyze the meniscus on the outside of a circular cylinder and apply the results to understand the capillary force experienced by a spherical particle at a liquid-vapor interface. My analyses show that the capillary force is approximately linear with the displacement of the particle from its equilibrium location at the interface. An analytical expression is derived for the corresponding spring constant that depends on the surface tension and lateral span of the interface and the particle radius. I further show that with a careful mapping, both explicit and implicit solvent models yield similar stratification behavior for drying suspensions of bidisperse particles. Finally, I apply the moving interface method based on an implicit solvent to study the drying of various soft matter solutions, including a solution film of a mixture of polymers and nanoparticles, a suspension droplet of bidisperse nanoparticles, a solution droplet of a polymer blend, and a solution droplet of diblock copolymers. / PHD / Drying is a ubiquitous phenomenon. In this thesis, I use molecular dynamics methods to simulate the drying of a suspension of a bidisperse mixture of nanoparticles that have two different radii. First, I use a model in which the solvent is included explicitly as point particles and the nanoparticles are modeled as spheres with finite radii. Their trajectories are generated by numerically solving the Newtonian equations of motion for all the particles in the system. My simulations show that the bidisperse nanoparticle mixtures stratify according to their sizes after drying. For example, a “small-on-top” stratified film can be produced in which the smaller nanoparticles are distributed on top of the larger particles in the drying film. I further use a similar model to demonstrate that stratification can be controlled by imposing a thermal gradient on the drying suspension. I then map an explicit solvent system to an implicit one in which the solvent is treated as a uniform viscous background and only the nanoparticles are kept. The physical foundation of this mapping is clarified. I compare simulations using the explicit and implicit solvent models and show that similar stratification behavior emerge in both models. Therefore, the implicit solvent model can be applied to study much larger systems on longer time scales. Finally, I apply the implicit solvent model to study the drying of various soft matter solutions, including a solution film of a mixture of polymers and nanoparticles, a droplet of a bidisperse nanoparticle suspension, a solution droplet of a polymer blend, and a droplet of a diblock copolymer solution.