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A future limitation of autonomous ground vehicle technology is the inability of current algorithmic techniques to successfully predict the allowable dynamic operating ranges of unmanned ground vehicles. A further difficulty presented by real vehicles is that the payloads may and probably will change with unpredictably time as will the terrain on which it is expected to operate. To address this limitation, a methodology has been developed to generate real-time estimations of a vehicle's instantaneous Maneuvering Manifold. This approach uses force-moment method techniques to create an adaptive, parameterized vehicle model. A technique is developed for estimation of vehicle load state using internal sensors combined with low-magnitude maneuvers. An unscented Kalman filter based estimator is then used to estimate tire forces for use in determining the ground/tire coefficient of friction. Probabilistic techniques are then combined with a combined-slip pneumatic trail based estimator to estimate the coefficient of friction in real-time. This data is then combined to map out the instantaneous maneuvering manifold while applying techniques to account for dynamic rollover and stability limitations. The algorithms are implemented in MATLAB, simulated against TruckSim models, and results are shown to demonstrate the validity of the techniques. The developed methodology is shown to be a novel approach that is capable of addressing the problem of successfully estimating the available maneuvering manifold for autonomous ground vehicles. / Ph. D.

A mathematical approach to the concepts of copolymerization of microtubules in the presence of anti-mitotic drugs is presented in this work. A general feature of the mathematical equations is presented. The possibility of having analytical steady state solutions of dynamic equations is investigated. The structure of equations is narrowed down for the specific brand of anti-mitotic drug, colchicine. The behavior of total T-tubulin concentration in the steady state in a regeneration system is investigated and analyzed through the numerical calculations. / Ph. D.

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.

Many researchers have devoted their work to the development of modal analysis extraction techniques in order to obtain more reliable identification of the modal parameters. Also, as a consequence of all this work, there are some other works devoted to the evaluation and comparison of these methods in order to find which one is the most reliable method with respect to certain characteristics. In this thesis the Rational Fraction Polynomial (RFP) Method, the Prony or Complex Exponential Method (CEM), the Ibrahim Time Domain (ITD) Method, and Hilbert Envelope Method are used to evaluate how the accuracy of the damping ratio is affected with respect to various parameters and conditions. The investigation focuses in the estimation of damping ratio because among the modal parameters, it is the most difficult to model. Each method is evaluated individually in order to understand how the damping ratio estimation is affected with respect to each method when the characteristics of the FRF are changed. Also, they are compared to show that, in general, the Rational Fraction Polynomial Method is a more reliable method than the other methods. To investigate this, a simulated analytical data and an experimental data are processed to estimate the modal parameters, but focusing in the damping ratio. For the simulated analytical data the damping ratio's percent of error were calculated. The highest damping ratio's percent of error of the RFP was 0.0073501%. In the other hand, for the CEM, ITD, and Hilbert Envelope Method their highest damping ratio's percent of error were 83.02%, 99.82%, and 4.077%, respectively. / Master of Science

Attacks on the heap are an increasingly severe threat. State-of-the-art secure dynamic memory allocators can offer protection, however their memory consumption is high, making them suboptimal in many situations. We introduce sys, a secure allocator whose design is driven by memory efficiency. Among other features, sys uses an efficient fine-grain size classes indexing mechanism and implements a novel dynamic canary scheme. It offers a low memory overhead due its size classes optimized for canary usage, its on-demand metadata allocation, and the combination of randomized allocations and over-provisioning into a single memory efficient security feature. sys protects against widespread heap-related attacks such as overflows, over-reads, double/invalid free, and use-after-free. Evaluation over a wide range of applications shows that it offers a significant reduction in memory consumption compared to the state-of-the-art secure allocator (up to 2x in macro-benchmarks), while offering similar or better security guarantees and good performance. / Master of Science / Attacks targeting on the runtime memory (heap allocator) are severe threats to software safety. Statistical results shown that the numbers of heap-related attacks has doubled since 2016. A large number of research works are designed to solve the security problems by offering different techniques to prevent some specific attacks. Not only are they very secure but also fast. However, these secure heap allocators sacrifice the memory usage, all of them at least double the memory consumption. Our work is trying to design and implement a heap allocator, in which it can defend against different attacks, as well as fast and memory-efficient. We carefully re-design some security features in our heap allocator while keep memory-efficient in mind. In the end, we evaluated sys and found that it offers significant reduction on different benchmarks suites. Evaluation also showed that sys can detect a lot of vulnerabilities in the software, while offer the same good performance as the state-of-the-art heap allocator.

This thesis describes a procedure to measure the transient effects in a fuel cell air delivery system. These methods were applied to model the 20 kW automotive fuel cell system that was used in Animul H2, a fuel cell-battery hybrid sedan developed by a group of engineering students at Virginia Tech. The air delivery system included the air compressor, the drive motor for the compressor, the motor controller, and any plumbing between the fuel cell inlet and the compressor outlet. The procedure was to collect data from a series of tests of the air delivery system with no load (zero outlet pressure) and at several loads. The air compressor speed, outlet pressure, and motor controller current were measured in response to a variety of speed requests. This data was fit to transfer functions relating the compressor speed, outlet pressure, or motor controller current to the speed request. The fits were found using a least squares optimization technique. After the experimental model was developed, it was augmented with an analytical model of the rest of the fuel cell system. The mass flow of the air was determined from the air compressor speed and outlet pressure with the compressor map. The fuel cell current was found by assuming a constant stoichiometric ratio. The power out of the fuel cell was calculated from the fuel cell current and the pressure with the polarization curve. The model of the fuel cell system was implemented in Matlab/Simulink. Several open and closed loop simulations were run to test the functionality of the fuel cell system model. The gross and net powers of the fuel cell system were found as a function of the compressor operating speed. The time it took for the system to come up to power as a function of idle speed was also found. A PID controller was implemented to allow the system to track a reference power request. The key contributions of this work were to develop a method to test the air delivery system to determine the dynamics of the system, to develop a model based on these tests and some analytical knowledge of fuel cells, and to use the model to simulate the operation and control of a fuel cell system. / Master of Science

In recent years, with the rapid development of electric and electronic technology, the All-Electric Aircraft (AEA) concept has attracted more and more attention, which only utilizes the electric power instead of conventional hydraulic and pneumatic power to supply all the airframe systems. To meet the power requirements under various flight stages and operating conditions, the AEA approach has resulted in the current aircraft electrical power generation capacity up to 1.6 MW. To satisfy the power quality and stability requirements, the advanced power electronic interfaces and more efficient power distribution systems must be investigated. Moreover, with the purpose of taking the full advantages of available electrical power, novel dynamic power distribution management research and design for an AEA must be carried out. The main objective of this thesis is to investigate and develop a methodology of more efficient power distribution management with the purpose of minimizing the rated power generating capacity and the mass of the electrical power system (EPS) including the power generation system and the power distribution system in an AEA. It is important to analyse and compare the subsistent electrical power distribution management approaches in current aircraft. Therefore the electrical power systems of A320 and B777, especially the power management system, will be discussed in this thesis. Most importantly the baseline aircraft, the Flying Crane is the outcome of the group design project. The whole project began in March 2008, and ended in September 2010, including three stages: conceptual design, preliminary design and detailed design. The dynamic power distribution management research is based on the power distribution system of the Flying Crane. The main task of the investigation is to analyse and manage the power usage among and inside typical airframe systems by using dynamic power distribution management method. The characteristics and operation process of these systems will be investigated in detail and thoroughly. By using the method of dynamic power distribution management, all the electrical consumers and sub-systems powered by electricity are managed effectively. The performance of an aircraft can be improved by reducing the peak load requirement on board. Furthermore, the electrical system architecture, distributed power distribution system and the dynamic power distribution management system for AEA are presented. Finally, the mass of the whole electrical power system is estimated and analysed carefully.

Machine emulation allows for the simulation of a real or virtual machine, the source machine, on various host computers. A machine emulator interprets programs that are compiled for the emulated machine, but normally at a much reduced speed. Therefore, in order to increase the executions peed of such interpreted programs, a machine emulator may apply different dynamic optimization techniques. In our research we focus on emulators for real machines, i.e. existing computer architectures, and in particular on dynamic binary translation as the optimization technique. With dynamic binary translation, the machine instructions of the interpreted source program are translated in to machine instructions for the host machine during the interpretation of the program. Both, the machine emulator and its dynamic binary translator a resource and host machine specific, respectively, and are therefore traditionally hand-written. In this thesis we introduce the Walkabout/Yirr-Ma framework. Walkabout, initially developed by Sun Micro systems, allows among other things for the generation of instrumented machine emulators from a certain type of machine specification files. We extended Walkabout with our generic dynamic optimization framework ‘Yirr-Ma’ which defines an interface for the implementation of various dynamic optimizers: by instrumenting a Walkabout emulator’s instruction interpretation functions, Yirr-Ma observes and intercepts the interpretation of a source machine program, and applies dynamic optimizations to selected traces of interpreted instructions on demand. One instance of Yirr-Ma’s interface for dynamic optimizers implements our specification-driven dynamic binary translator, the major contribution of this thesis. At first we establish two things: a formal framework that describes the process of machine emulation by abstracting from real machines, and different classes of applicable dynamic optimizations. We define dynamic optimizations by a set of functions over the abstracted machine, and dynamic binary translation as one particular optimization function. Using this formalism, we then derive the upper bound for quality of dynamically translated machine instructions. Yirr-Ma’s dynamic binary translator implements the optimization functions of our formal framework by modules which are either generated from, or parameterized by, machine specification files. They thus allow for the adaptation of the dynamic binary translator to different source and host machines without hand-writing machine dependent code.

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