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Meshless Discrete Velocity Boltzmann Model for Porous Media Flow
No full textThis dissertation explores the combination of two sophisticated techniques for addressing computational fluid dynamics: the discrete velocity Boltzmann equation (DVBE) and the localized collocation meshless model with upwinding (U-LCMM). The DVBE is a high-level model that describes the foundations of transport phenomena by addressing the microscale motions of particles themselves and the effect of their aggregate behaviors on continuum principles. This equation integrates multiple scales of phenomena; while it can be used for fluid flow at Navier-Stokes scales, it can also resolve fine features that can only be described at the molecular level. This type of model is necessary for a wide range of applications, e.g., rarefied gases, multiphase flows, and chemically reactive transport. Additionally, this equation has recently experienced a large increase in focus because it is a highly parallelizable transport equation. This characteristic avoids the iterative difficulties typically associated with the Navier-Stokes equations. Most of this focus has been on using a Lagrangian approach to the Boltzmann equation—the lattice Boltzmann method—which is primarily solved on a grid. The lattice Boltzmann method requires significant assumptions and restrictions that can impact the efficiency or accuracy of the approximation of the Boltzmann equation.
Consequently, the second technique, meshless modeling, offers a solution to these limitations and becomes prominent. Meshless modeling is a class of techniques that removes the requirements of mesh generation and mesh dependencies in domain discretization and geometric representation. The U-LCMM can be used at any scale, allowing for regional variations in point densities without any inherent dependencies on underlying assumptions about the domain. As a modeling method, it can be used on any partial differential equation, but on the Boltzmann equation, it becomes a powerful tool. Both the Boltzmann equation and the U-LCMM are highly effective at addressing multiscale features. Together, they create a technique that can resolve transport through the simplest of channels or the tortuosities of a packed bed.
The focus of this dissertation is the comprehensive description of the numerical theory and methods used to combine these tools to build a complex fluid flow solver. The dissertation begins with a review of each topic and the individual specifications unique to each. Here, the DVBE is described in detail, which converts the continuous phase space Boltzmann equation into a discrete system of equations that can be computationally modeled. While much research has been done on the Boltzmann equation on structured grids, significantly less attention has focused on treating unstructured grids or meshless techniques, leaving gaps to be addressed. The most difficult of these concerns relates to boundary treatment, addressing macroscale properties like velocity and pressure at the particle level. This work builds the framework of applying the U-LCMM to the DVBE, from geometric representation using point generation, to the application of the DVBE for fluid transport.
Next, this method demonstrates its rigor in two manuscripts. In the first manuscript, the stability of the solver in terms of the Boltzmann stability criterion is addressed, including its strengths and limitations. The solver\u27s abilities are then demonstrated through a series of abecedarian exercises, including the Taylor-Green vortex flow, lid-driven square cavity flow, and channel flow over a circular cylinder. These illustrate the solver\u27s ability to address multiple boundary types, including periodic, Dirichlet, and zero-gradient boundaries. In the second manuscript, the solver is applied to address porous media. The complex multiscale nature of porous media makes it a challenging topic for traditional CFD solvers, as geometric and transport complexities require greatly varying length scales — once more, precisely a challenge fit for both the Boltzmann equation and the meshless modeling. In this manuscript, the numerical model demonstrates its ability to use microscale transport to recover the Darcy equation, a macroscale equation to describe flow across porous media, and explores the distinctions in macroscopic behavior between ordered and disordered porous structures. Additionally, the order of convergence and the timing complexity of the numerical method are addressed. These studies conclude that applying U-LCMM to the DVBE shows great potential to address complex transport phenomena
Autonomous Landing of an Unmanned Aerial Vehicle on an Unmanned Surface Vessel using Model Predictive Control with an Adaptive-Covariance Extended Kalman Filter
No full textThis thesis presents the development of vision-based estimation and model predictive control (MPC) strategies to enable an Unmanned Aerial Vehicle (UAV) to land autonomously on an Unmanned Surface Vessel (USV) subjected to wave-induced motion. An innovative Adaptive-Covariance Extended Kalman Filter (AEKF) implementation was developed for the estimation of the 6 degree-of-freedom USV states using GPS and vision-based measurements of AprilTag markers on the USV landing platform. The AEKF employs an uncontrolled 6 degree-of-freedom nonlinear model augmented with second-order harmonic wave-induced motion dynamics. The AEKF implements two correction techniques: an adaptive covariance adjustment and an artificial covariance inflation regulated by a Normalized Innovation Square (NIS) check. These corrections ensure the stability and adaptivity of the filter in the presence of multiple added wave-induced estimation states or in scenarios where the covariance matrices are unknown. The AEKF was implemented in combination with a scheduled MPC algorithm to generate the control actions required for the UAV to perform safe landing maneuvers. The scheduled MPC was designed and implemented in three distinct phases: Approach and Follow, Descent, and Landing. An MPC cost function was designed specifically for each flight phase, and in each case, the optimal control is computed to minimize the cost function subject to constraints and a linearized UAV dynamics model. The performance of the combined AEKF and MPC algorithm was evaluated via simulation studies of a UAV landing on an USV under smooth, slight, and moderate sea conditions. In the simulations, a linear model of the sea state was employed based on Airy Theory. As part of these studies, the AEKF parameters, as well as the MPC prediction and control horizons, were optimized for the different flight phases and sea states. The simulation results show that the AEKF provides accurate estimation of the wave-induced USV states, but that higher wave disturbances require a larger number of states in the wave dynamics model along with a lower NIS threshold to ensure efficient filter performance. The results also demonstrate that, once the prediction and control horizons have been properly selected, the MPC controller results in a high landing success rate. It was also found that phases that rely on estimates of the vertical position and velocity, such as Descent and Landing, require smaller prediction and control horizons. This is due to small disturbances on the vertical axis states, which reduce the accuracy of the AEKF estimates. Finally, the constrained states and controls used to maintain the linearization of the UAV during the MPC optimization limit the controller to be feasible only in scenarios with static or slow moving USVs
What is it like to be a Female Pilot in the United States Air Force: A Gender Diversity Study
No full textThis research investigates the gender-based disparities faced by female pilots in the United States Air Force (USAF), providing a comprehensive analysis of their experiences compared to their male counterparts. Utilizing a mixed-methods approach quantitative and qualitative data explored the perceptions of treatment in areas such as policies, bias, representation, mentorship, and career advancement. The research highlights the industry statistic of female pilots, who make up only 6% of the pilot community, and examines systemic challenges, including gender bias, work-life balance issues, and career progression barriers.
Through surveys and open-ended, the study revealed that female pilots often perceive greater obstacles related to gender-based stereotypes and informal biases, which impact recruitment, diversity, retention, and operational effectiveness. The findings underscore the complex dynamics of working in a predominantly male profession, where females face additional stressors, including harassment, balancing family life with military demands, and a lack of senior female role models.
The results provide actionable insights for addressing gender disparities in USAF aviation, offering recommendations for policy changes, mentorship programs, and recruitment initiatives aimed at improving the retention and treatment of female pilots. By fostering a more inclusive environment, the USAF can enhance both operational readiness and diversity within its pilot corps. This study also contributes to the broader literature on gender diversity in aviation, with implications for commercial and collegiate aviation sectors. Ultimately, it advocates for systemic reforms that ensure equitable opportunities for female pilots, supporting the USAF’s mission to create a more diverse and effective force
Dawn of Midnight
No full textDawn of Midnight follows Jax Tartarus, a versatile flight engineer, aboard one of his travels on the retired URIS Polaris class ship the Dawn of Midnight. He is accompanied on this mission with six of his closest crew mates. They are tasked with the security and transportation of a group of medical personnel from the core planet of the galaxy to one on the outer rim of their republic
Thomas J Parry - Headstone
No full textHeadstone of RAF cadet Thomas John Parry who was killed in a plane crash on January 14, 1944, while training to be a pilot at 5BFTS. He is buried in the Commonwealth War Graves Commission British Plot. at Oak Ridge Cemetery, Arcadiahttps://commons.erau.edu/bfts-parry-images/1002/thumbnail.jp
Michael K Hinds - CWGC Certificate
No full textCommonwealth War Graves Commission (CWGC) Certificate for RAF cadet Michael K Hinds who was killed in a plane crash on July 13, 1944,, while training to be a pilot at 5BFTS. He is buried in the CWGC British Plot. at Oak Ridge Cemetery, Arcadia