INVESTIGATIONS INTO MECHANISMS UNDERLYING EXTREME WAVE FORMATIONS AND COMPUTATIONALLY INTENSIVE SIMULATIONS

Various mechanisms have been proposed to explain extreme waves or rogue waves in an oceanic environment including directional focusing, dispersive focusing, wave-current interaction, and nonlinear modulational instability. The Benjamin-Feir instability (nonlinear modulational instability), however, is considered to be one of the primary mechanisms for rogue-wave occurrence. The nonlinear Schrodinger equation is a well-established approximate model based on the same assumptions as required for the derivation of the Benjamin-Feir theory. Solutions of the nonlinear Schrodinger equation, including new rogue-wave type solutions are presented in the author's dissertation work. The solutions are obtained by using a predictive eigenvalue map based predictor-corrector procedure developed by the author. Features of the predictive map are explored and the influences of certain parameter variations are investigated. The solutions are rescaled to match the length scales of waves generated in a wave tank. Based on the information provided by the map and the details of physical scaling, a framework is developed that can serve as a basis for experimental investigations into a variety of extreme waves as well localizations in wave fields. To derive further fundamental insights into the complexity of extreme wave conditions, Smoothed Particle Hydrodynamics (SPH) simulations are carried out on an advanced Graphic Processing Unit (GPU) based parallel computational platform. Free surface gravity wave simulations have successfully characterized water-wave dispersion in the SPH model while demonstrating extreme energy focusing and wave growth in both linear and nonlinear regimes. A virtual wave tank is simulated wherein wave motions can be excited from either side. Focusing of several wave trains and isolated waves has been simulated. With properly chosen parameters, dispersion effects are observed causing a chirped wave train to focus and exhibit growth. By using the insights derived from the study of the nonlinear Schrodinger equation, modulational instability or self-focusing has been induced in a numerical wave tank and studied through several numerical simulations. Due to the inherent dissipative nature of SPH models, simulating persistent progressive waves can be problematic. This issue has been addressed and an observation-based solution has been provided. The efficacy of SPH in modeling wave focusing can be critical to further our understanding and predicting extreme wave phenomena through simulations. A deeper understanding of the mechanisms underlying extreme energy localization phenomena can help facilitate energy harnessing and serve as a basis to predict and mitigate the impact of energy focusing.

Investigation of Blast Wave Propagation: Correlating External Pressures to Brain Injury Predictors

Blast-induced Traumatic Brain Injury (bTBI) is the signature injury of the Iraq and Afghanistan wars; however, current understanding of bTBI is insufficient. In this study, novel analysis methods were developed to investigate correlations between external pressures and brain injury predictors. Experiments and simulations were performed to analyze placement of helmet-mounted pressure sensors. A 2D Finite Element model of a helmeted head cross-section was loaded with a blast wave. Pressure time-histories for nodes on the inner and outer surfaces of the helmet were cross-correlated to those inside the brain. Parallel physical experiments were carried out with a helmeted headform, pressure sensors, and pressure chamber. These analysis methods can potentially lead to better helmet designs and earlier detection and treatment of bTBI.

The Effect of Supportive Social Interaction Priming on Children's Prosocial Comforing Responses to Distressed Others

The ability to sensitively care for others’ wellbeing develops early in ontogeny and is an important developmental milestone for healthy social, emotional, and moral development. One facet of care for others, prosocial comforting, has been linked with important social outcomes such as peer acceptance and friendship quality, underscoring the importance of determining factors involved in the ability to comfort. Although social support has been linked with a number of important social outcomes, no study has directly examined whether felt social support can foster children’s positive behavior toward others. The purpose of the current investigation was to use an experimental priming paradigm to demonstrate that felt social support a) enhances children’s ability to respond prosocially to the distress of others and b) decreases children’s expressions of personal distress when faced with the distress of another person. Participants were 94 4-year-old children (M = 53.56 months, SD = 3.38 months; 52 girls). Children were randomly assigned to either view pictures of mothers and children in close, personal interactions (supportive social interaction condition), happy women and children in separate pictures, presented side-by-side (happy control condition), or pictures of colorful overlapping shapes (neutral control condition). Each set of 20 pictures was presented in the context of a categorization computer game that participants played 4 times throughout the course of the study. Immediately following the first three computer games, children were given the opportunity to comfort someone who was distressed; twice it was the adult experimenter working with the child, and once it was an unseen infant crying over a monitor that participants had been trained to use. Comforting behaviors and distress/arousal were coded in 10-second time segments and yielded a global comforting score and a distress proportion score for each task. Results indicated that priming condition had no effect on either prosocial comforting behavior or expressions of personal distress. I discuss these null findings in light of the available literatures on priming mental representations in children and on prosocial comforting, and suggest some future directions for continued investigation in both fields.