This thesis is focused on quantifying the dynamic performance of lightweight metal sandwich systems under confined explosions, where this effort represents the first of a multi-phase comprehensive research program that is focused on developing blast damage mitigation techniques in submerged structures. A confined explosion occurrence inside such facilities may lead to paralyzing all operations depending on the functions of the affected sections. Subsequently, using sacrificial cladding placed as a physical barrier over critical components that might be vulnerable to a potential explosion is considered to be an effective blast damage mitigation technique. Furthermore, sandwich panels can be an ideal system to be used as sacrificial cladding, as it can be manufactured to possess high stiffness-to-weight ratio and superior energy absorption capabilities. Consequently, an experimental program was performed to investigate the performance of lightweight cold-formed steel sandwich panels under both quasi-static loads and confined explosions, where a total of fifty-seven sandwich panels were tested, considering various core configurations, different core sheet thickness, and different blast load intensity levels. The American ASCE/SEI 59-11 and The Canadian CSA/ S850-12 blast design standards predict the dynamic response of a structure component based on the static resistance function by applying dynamic increase factors. Subsequently, the static resistance functions for the proposed panel configurations were investigated experimentally and compared with the introduced analytical model, in order to quantify accurately the inelastic panel response. The quasi-static test program was performed in two stages, where the first included eighteen single layer core sandwich panels, which represented longitudinal and transverse corrugated core configurations. The results of the first stage configurations demonstrated an efficient strength and stiffness, but showed a lack in energy absorption capabilities and ductility capacity. Therefore, in the second stage, different core configurations were developed, including twenty-one panels representing Bi-directional and X-core double layered core configurations and its counterpart Uni-directional single layer core configuration. The results of the second stage demonstrated an enhancement in the ductility and energy absorption capabilities compared to the configurations tested in the first stage. The residual deformations and failure modes demonstrated were assessed and discussed in details, where web crippling, local buckling and global buckling induced by shear or flexurewere determined. In general the static resistance functions for each tested panel were used to quantify the panels’ yield loads, ultimate capacities, and corresponding displacement levels. Moreover, the influences of both the core configuration and the core sheet thickness on the panels’ stiffness, ductility levels and energy absorption were quantified. Based on the conclusions of the static testing and considering the ductility, capability of energy absorption, and the behavior beyond the elastic zone, two different core configurations were chosen to be tested under confined explosions. Eighteen panels were tested in a cylindrical shape blast chamber representing a typical submerged structure under different scaled distances ranged from 2.82 to 1.09 m/kg1/3, in order to demonstrate different damage state levels in accordance with the blast design standards (ASCE/SEI 59-11, CSA/ S850-12). In the blast testing results, the incident and reflected pressure time histories of the blast wave were measured, while the modified Friedlander equation was used to fit the first positive phase of the reflected pressure histories. In addition, the displacement response histories of the back face of the tested panels were recorded. The measured values of peak incident pressure, peak reflected pressure, incident impulse and the reflected impulse were compared to the predicted values using ConWep (Hyde 1990) considering the spherical explosion, and have shown a good agreement. Furthermore, the failure modes and the post blast damage were determined and compared to the static observations. In order to complement the experimental program, a nonlinear inelastic single degree of freedom model was developed in order to predict the dynamic response of the sandwich panels. The model used the recorded blast load and the static resistance while applying the dynamic increase factors recommended by the standards (ASCE/SEI 59-11, CSA/ S850-12). The model results were in a good agreement with the experimental data. Furthermore, the different ductility and support rotation values obtained experimentally and predicted analytically were related to the different damage levels specified by blast standards. Finally, the influence of sandwich panel core configuration on the dynamic blast response of the tested sandwich panels was discussed. / Thesis / Doctor of Philosophy (PhD)

No description available.

Keeping users’ and organizations’ data secure is a challenging task. The situation is made more complicated due to the ever-increasing complex dependencies among IT systems. In this scenario, current approaches for risk assessment and mitigation rely on industry best practices based on qualitative assessments that do not provide any measure of their effectiveness. In this Thesis, we argue that the rich availability of data about IT infrastructures and adversaries must be employed to quantitatively measure the risk and the effectiveness of security mitigation strategies. Our goal is to show that quantitative measures of effectiveness and cost using security data are not only possible but also beneficial for both individual users and organizations to identify the most appropriate security plan. To this aim, we employed a heterogeneous set of security data spanning from blacklist feeds and software vulnerability repositories to web third-party dynamics, criminal forums, and threat intelligence reports. We use this data to model attackers and security mitigation strategies and evaluate their effectiveness in mitigating attacks. We start with an evaluation of filter lists of privacy extensions to protect individuals’ privacy when browsing the Web. We then consider the security of billions of users accessing the Top 5K Alexa domains and evaluated the effectiveness and cost of security mitigations at different levels of the Internet infrastructure. We then evaluate the accuracy of SOC analysts in investigating alerts related to cyber attacks targeting a network. Finally, we develop methodologies for the analysis of the effectiveness of ML models to detect criminal discussions in forums and software updates to protect against targeted attacks performed by nation-state groups.

Shrinking and swelling in Yazoo Clay is a cause of concern for construction projects in Mississippi. This thesis investigated the effects of adding lime and Douglas Fir biochar on the shrinking and swelling capabilities of Yazoo Clay. Samples of Yazoo Clay were mixed with the additives in defined ratios and subjected to the free swell test and the COLE(rod) test. Biochar addition reduced the COLE(rod) of the samples a large amount, while increasing the swelling potential of the clay samples. The addition of lime slightly reduced both the shrinking and swelling potentials of the samples. The mineralogical variability of Yazoo Clay vertically and horizontally could limit the applicability of these results across the formation and is important to be considered before further application. While constrained to one location, this study showed the influence of biochar and lime on the shrinking and swelling capabilities of Yazoo Clay.

Detonation is the supersonic mode of combustion that occurs in munitions (military explosives and high explosives). These munitions result in blast waves that are hazardous to human life and structures. As a result, there is a high desire to mitigate these blast waves. One such method is to surround the explosive with mitigants (liquid, granular, and cellular porous material). For the safe storing and use of munitions, it is crucial to study the explosive dispersal of mitigant, the ensuing blast wave attenuation, and specifically, the mechanisms underlying this interaction. Current research involving mitigant blast wave attenuation is conducted in many configurations. The study aims to evaluate one configuration, shock tubes with particle suspension. Blast waves are simulated in the form of detonations initiated by DDT (deflagration-to-detonation) with mitigants in the form of dispersed particles. These dispersed particles included aluminum oxide, Al2O3, and aluminum, Al. The flame-flow interactions are experimentally studied using Particle Image Velocimetry (PIV) and pressure transducers. The effect of particle suspension on blast waves is revealed, portraying a decrease in mitigation performance.

Inception of the Clean Water Act in 1972 resulted in regulation of activities in wetlands through Section 404. Regulatory agencies like the Mississippi Department of Marine Resources (MDMR) have tried to find methods to rapidly evaluate wetlands. This study compares three rapid evaluation methods, Hydrogeomorphic Approach (HGM), Wetlands Rapid Assessment Procedure (WRAP), and Wetland Evaluation System (WES), based on their scoring of a group of reference and mitigation wetland sites. Repeatability was studied by scoring a group of sites twice. The non-parametric Spearman?s correlation was used to compare the three methods. In this study, HGM was most repeatable followed by WES and WRAP. Comparisons of overall scores using the Spearman correlation found the strongest correlation between HGM and WES, although all pairings were significantly correlated (p< 0.05). This study determined HGM was the optimum method for the MDMR because due to repeatability and producing results similar to the other two methods.

No description available.

No description available.

No description available.

No description available.