While the learned helplessness effect has been reliably found in dogs and other species (e.g., cats, mice, fish, and humans), it has been somewhat difficult to obtain in rats. In addition, it has been demonstrated that electroconvulsive shock (ECS) reverses learned helplessness in dogs, but ECS induced reversal has not been demonstrated in the rat. Thus, the purpose of this dissertation was twofold: (1) to determine if the learned helplessness effect could be reliably demonstrated in rats; and (2) if so, will a single ECS attenuate this phenomenon. If it could be shown that ECS attenuates helplessness, then two purposes would be served: (a) it would extend the generality of learned helplessness theory by indicating additional parallels between dog helplessness and rat helplessness; and (b) it would expand the parallels between learned helplessness and human depression, thereby increasing the validity of the learned helplessness model of depression. In Experiment 1, rats were randomly assigned to one of three groups: escape, yoked-inescapable, and no shock control. Each rat in the escape group received 80 trials of unsignaled escapable shock. The escape group rats were required to perform a progressive fixed-ratio bar press to escape shock. The yoked-inescapable group received exactly the same intensity, frequency, and duration of shock its escape partner received; but no response would escape shock. The no-shock control group received only pre-exposure to the training apparatus. The following day all rats were tested on a FR-2 shuttlebox escape/avoidance task. After test, half the rats in each group were given a single ECS and then were retested 24 hours later in the shuttlebox. The learned helplessness effect was clearly demonstrated during the test phase. In addition, a single ECS attenuated the learned helplessness effect in rats. In Experiment 2 rats were given training exactly as described in Experiment 1. Following training, one-third of the rats in the escape and yoked-inescapable groups were given a single ECS immediately, one-third were given a single ECS 23.5 hours later, and one-third received no treatment. In the no-shock control group one-third of the rats were given a single ECS 24 hours prior to test, one-third of the rats were given ECS 30 minutes prior to test, and one-third of the rats were not given ECS. Then, all rats were tested 24 hours following training. The test session was identical to the test session in Experiment 1. The learned helplessness effect was clearly demonstrated during test in the NO-ECS condition. In addition, it was demonstrated that ECS attenuates or reverses learned helplessness training when given immediately following training. Delayed ECS also reverses helplessness, but less dramatically than immediate ECS. In both experiments the criteria which characterize learned helplessness were matched: (1) Failure to initiate the escape response in the presence of shock; (2) failure to maintain escape behavior even after occasional escape response occur; and (3) that conditions 1 and 2 above are a result of inescapability and not a result of shock per se. In addition, since ECS attenuates helplessness, the generality of helplessness theory was extended to rats, and the validity of learned helplessness model of depression was strengthened. / Doctor of Philosophy

Catamarans provide vast deck space, high thrust efficiency, and excellent transverse stability, however, in rough conditions they can be susceptible to deck slamming from head seas or bow diving in following seas and a pitch-roll coupling effect that can lead to uncomfortable corkscrew motion under bow-quartering seas. A new class of catamaran called Wave-Adaptive Modular Vessels (WAM-V™) aims to help mitigate oceanic input from the cabin by allowing for the relative motion of components not common to classic catamaran design. This thesis presents a set of multi-body dynamics simulation models created for two active WAM-Vs™ along with analysis on their suspension characteristics. Both models provide conclusive and realistic results, with the final model being validated against on-water testing data from a 12-ft unmanned prototype WAM-V. The first of these simulations serves primarily as a tool to evaluate WAM-V™ response characteristics with respect to a variety of parametric variations. The modeling environment is highlighted along with details of the parametric simulation and how it was created. The results fall in line with our expectations and are presented along with analysis of the sensitivity of each parameter at three longitudinal locations. The final simulation attempts to model the response of a 12-ft unmanned surface vessel (USV) prototype of the WAM-V™ configuration. Testing data is collected, processed, and applied to the model for validation of its prediction accuracy. The results of the sea tests indicate that the simulation model performs well in predicting USV motions at sea. Future considerations for testing WAM-Vs™ can include changes in suspension and mass parameters as well as limiting particular degrees-of-freedom by making their joints rigid. / Master of Science

Toxic shock events can be detrimental to wastewater treatment systems and can result in long-term losses of system performance. If warned of an impending toxic shock, operators would have the opportunity to implement process controls that could help mitigate the effects of the shock event. The objective of this project was to evaluate the effectiveness of a developed corrective action strategy (involving aerobic endogenous respiration) on an enhanced biological phosphorus removal (EBPR) wastewater treatment plant (WWTP) shocked with chlorine. Three identical, laboratory-scale systems were designed to mimic one train of the Long Creek Water Resources Reclamation Facility (WRRF, Gastonia, NC). The basis of this study is a comparative performance analysis among the three trains; a negative control (unshocked and operated normally), a positive control (shocked with hypochlorite and operated normally), and the corrective action (shocked with hypochlorite and process controls implemented). Comparative performance analysis among the three trains was based on effluent quality, performance stability, and biomass kinetics as indicated by rates of respiration and phosphate release and uptake. The shock event and corrective action strategy both inhibited EBPR. After an initial perturbation, the positive control matched the performance of the negative control. The corrective action, however, exhibited significant instability in EBPR performance. Regardless of whether aerobic or anaerobic sludge storage conditions are selected, endogenous respiration will still result in system instability. It is recommended, therefore, that measures be taken to avoid imposing endogenous conditions on isolated sludge during a short-term toxic shock event. / Master of Science

Several methods have been developed to capture shock waves in turbo machinery flows, such as Moore's pressure correction procedure and Denton's time marching procedure. The time marching procedure is traditionally used for transonic flow calculations, whereas the pressure correction method is better suited for incompressible and subsonic flows. However, the focus of this research is on the Moore pressure correction flow code, the Moore Elliptical Flow Program (MEFP) , to calculate shock waves in transonic compressor fans. A new pressure interpolation method, the 2M formula, is developed to improve the shock capturing capabilities of the MEFP flow code. The 2M formula is a two Mach number dependent formula, with Mach numbers Mi and M i + 1. The previously used pressure interpolation method, the M&M formula, is a one Mach number dependent formula, using the maximum of Mi and Mi + 1 . In the development of the 2M formula, J.G. Moore's stability criterion is applied to the pressure correction equation such that the center point coefficient is greater than the sum of the other positive coefficients. / Master of Science

This thesis investigates the use of the numerical modeling tools LS-DYNA and USA in modeling general far-field underwater explosions (UNDEX) by modeling a three-dimensional box barge that is subjected to a far-field underwater explosion. Past UNDEX models using these tools have not been validated by experiment and most are limited to very specific problems because of the simplifying assumptions they make. USA is a boundary element code that requires only the structural model of the box barge. LS-DYNA is a dynamic finite element code and requires both the structural model and the surrounding fluid model, which is modeled with acoustic pressure elements. Analysis of the box barge problem results finds that the program USA is a valid tool for modeling the initial shock response of surface ships when cavitation effects are not considered. LS-DYNA models are found to be very dependent on the accuracy of the fluid mesh. The accuracy of the fluid mesh is determined by the ability of the mesh to adequately capture the peak pressure and discontinuity of the shock wave. The peak pressure captured by the model also determines the accuracy of the cavitation region captured in the fluid model. Assumptions made in the formulation of the fluid model causes potential inaccurate fluid-structure interaction and boundary condition problems cause further inaccuracies in the box barge model. These findings provide a base of knowledge for the current capabilities of UNDEX modeling in USA and LS-DYNA from which they can be improved in future work. / Master of Science

A high-speed rotary device was designed to generate shock waves in a transonic blowdown wind tunnel cascade. The rotary device (Rotating Bar Mechanism) will be used in research conducted at Virginia Tech to study the effects of unsteady aerodynamic flow and heat transfer (resulting from upstream shock wave / wake passing) on turbine blades. The rotating bar mechanism (RBM) consists of: a rotor with flexible cable “bars” attached to the rim of the disk, a disk housing, a bearing housing, a driving air turbine, and a turbine mounting housing. The RBM is mounted to the side of the wind tunnel so that only the bars enter and exit the tunnel test section through a small slot. As the bars translate through the test section, the bars create shocks / wakes similar to those shed from the trailing edges of nozzle guide vanes of a transonic turbine. Considerable design effort was required for the RBM due to its relatively high operating speed. As the result of a finite element stress analysis, a unique method of securing the disk to the shaft was developed. This unique method reduced the stress concentration factor at the disk hub from 2.9 to 1.7. In addition to the stress analysis, a rotordynamic study was also performed. The study revealed that the RBM could not be designed to operate below the first natural frequency. A critical speed of 14,000 RPM was predicted for the rotary device. This prediction was later verified by testing. An integral component of the overall design was the development of a computer code to predict the RBM’s speed under various loading conditions. The loading on the device is due primarily to the aerodynamic drag on the flexible cable bars. Since the mechanism was designed to facilitate bars of different diameters, the prediction code was an essential design tool. The speed prediction code was also verified by testing. The RBM was tested to wind tunnel operating speeds in a spin pit filled with argon to verify the mechanical design. Based on test performance, it was concluded that the RBM is suitable to generate shock waves in a transonic wind tunnel. / 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.

A finite difference method of investigating the shock layer in the vicinity of the stagnation point in a two-dimensional supersonic flow past a circular cylinder is analyzed. This method differs from existing methods which have been used in the past for solving this type of problem in that it uses the properties along the stagnation streamline as initial conditions. However, the method can still be classified as one of the direct type. A potential flow solution along the stagnation streamline is used to approximate the initial conditions. The results are compared with existing solutions and available experimental data. / Master of Science

Spacecraft and satellites in orbit are under an increasing threat of impact from orbital debris and naturally occurring meteoroids. While objects larger than 10 cm are routinely tracked and avoided, collisions inevitably occur with smaller objects at relative velocities exceeding 10 km/s. Such hypervelocity impacts (HVI) create immense shock pressures and can melt or vaporize aerospace materials, even inducing brief plasmas at higher speeds. Sacrificial shields have been developed to protect critical components from damage under these conditions, but the response of many materials in such an extreme event is still poorly understood. This work presents the summary of computational analysis methods to quantify the relevant physical mechanisms at play in a hypervelocity impact. Strain rate-dependent behavior was investigated using several models, and fluid material descriptions were used to draw parallels under high shear rate loading. The production and expansion of impact plasmas were modeled and compared to experimental evidence. Additionally, a parametric study was performed on a multitude of possible material candidates for sacrificial shield design, and new shielding configurations were proposed. A comparison of material models indicated that the Johnson-Cook and Steinberg-Cochran-Guinan-Lund metallic formulations yielded the most consistent results with the lowest deviation from experimental measures in the strain rate regime of interest. Both meshless Lagrangian and quasi-Eulerian meshed schemes approximated the qualitative and quantitative characteristics of HVI debris clouds with average measurable errors under 5%. While the meshless methods showed better resolution of interfaces and small details, the meshed methods were shown to converge faster under several metrics with fewer regions of spurious instability. Additionally, a new technique was introduced using hypothetical viscous fluids to approximate debris cloud behavior, which showed good correlation to experimental results when such models were constructed using the shear rates seen in hypervelocity impacts. Formulations using non-Newtonian fluids showed additional capability in approximating solid behavior, both quantitatively and qualitatively. Such fluid models are significant, in that they reproduced the qualitative and quantitative characteristics of evolving debris clouds with better fidelity than purely hydrodynamic models using inviscid fluids. This indicates that while inertial effects can dominate overdriven shock phenomena, neglecting shear forces invariably introduces errors; such forces can instead be simplistically approximated via viscous models. The viscous approximation also allowed for a successful scaling analysis using dimensionless Pi terms, which was unfeasible using solid constitutive relations. Attempts to model plasma dynamics saw success in the simulation of a laser ablation-driven flyer plate by using a hot gas with solid initial conditions; similar strategies were used to analyze plasma production in hypervelocity impacts with reasonable correlation to experimental measurements. Lastly, the analysis of bumper material candidates showed that metals with a low density such as beryllium and magnesium yield a higher specific energy and momentum reduction of incident projectiles with lower weight requirements than a similarly constructed bumper using aluminum. Investigations of bumpers using a combination of materials and variations in microstructure showed promise in increasing weight-normalized efficacy. Through these computational models, the parameters which influence damage and debris in hypervelocity impacts are more critically understood. / PHD

The study of shock-waves in supersonic plasma jets is essential to understanding the complex dynamics involved in many physical systems. Specifically, ion-species separation caused by a shock wave propagating through a plasma is an important but not yet well understood phenomenon. In inertial confinement fusion implosions, a shock wave precedes the rapid compression of a fuel pellet to ignition conditions that theory and computational studies suggest may be separating the fuel and reducing the neutron yield. In astrophysics, the shock wave produced when a supernovae explodes has been shown to have an effect on nucleosynthesis as a result of shock heating. In both these cases the time and length scales make them difficult to study experimentally, but experiments on more reasonable scales can shed light on these phenomena. This body of work provides the basis for doing just that. The work begins by describing the development of a small, linear, plasma-armature railgun designed to accelerate plasma jets in vacuum to high-Mach-number. This is followed by discussion of an experimental campaign to establish a plasma parameter space for the jets, in order to predict how effectively the accelerator can be used to study centimeter-scale shock structures in jet collisions. The final section presents an experimental campaign in which jet collisions are induced, and the resultant structures that appear during the collision are diagnosed to assess how conducive the experiment is to the future study of shock-wave induced species separation in laboratory plasmas. This work is a foundation for future experimental studies of ion-separation mechanisms in a multi-ion-species plasma. This research was supported in part by the National Science Foundation under grant number PHY-1903442. / Doctor of Philosophy / Plasma, the so-called fourth state of matter, is an ionized gas that often behaves like a fluid but can also become magnetized and carry an electric current. This combination leads to a lot of interesting yet often un-intuitive physics, the study of which is very important for understanding a wide array of topics. One subset of this field is the study of shock-wave induced species separation. Just like the shock-wave a jet aircraft produces when it moves through the air at a speed greater than the speed of sound, a plasma shock is characterized by a large change in parameters like density, temperature, and pressure across a very small region. A shock-wave propagating through a plasma can cause different ion species present to separate out, a phenomenon that is driven by the gradients that are present across a shock front. Understanding how these mechanisms work is important to a number of applications, including fusion energy research and astrophysical events. The first section of this work discusses the design and development of a plasma-armature railgun, a device that can produce and accelerate jets of plasma to high-Mach-number within a vacuum chamber. The next and most substantive section of the work presents results from experimental campaigns to characterize the accelerated plasma jets and then to induce plasma-jet collisions with the hope of producing shock-waves that exist on time and spatial scales that can be readily measured in a laboratory setting. This work is a foundation for future experimental attempts to measure separation induced by a shock-wave in order to better understand these complex phenomena.