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Daniel Guggenheim School of Aerospace Engineering

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https://hdl.handle.net/1853/70742

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College of Engineering

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Aerospace Design Group

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Aerospace Systems Design Laboratory (ASDL)

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Air Transportation Laboratory

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Cognitive Engineering Center

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Space Systems Design Laboratory (SSDL)

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https://finding-aids.library.gatech.edu/agents/corporate_entities/106

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Publication Search Results

Now showing 1 - 10 of 249

Evaluation of Deployable Aerosurface Systems for Mars Entry

(Georgia Institute of Technology, 2012-12-14) Cruz-Ayoroa, Juan G.

One of the challenges presented by the exploration of Mars is the entry, descent and landing (EDL) of payloads to the surface. Current robotic missions to Mars are reaching the limist of existing Viking heritage EDL technologies. A number of EDL technology improvements can be made to extend the capabilities beyond the current landed mass limits, including increasing the entry vehicle hypersonic drag and lift capability. Technologies being currently studied include inflatable aerodynamic decelerators, which are designed to increase vehicle drag. Many of these concepts center on axisymmetric designs, which provide high drag but relatively low lift and are most easily integrated to blunt entry vehicles. However, due to packaging density and launch vehicle fairing constraints, it is likely that future missions will require the use of slender bodies. This study investigates three deployable concepts designed to provide better integration into a slender vehicle while augmenting its performance by increasing its hypersonic drag. The deployable aerosurfaces are applied to a 5 meter diameter slender vehicle for a robotic mission at Mars with entry masses ranging from 10 to 60t. A multidisciplinary design optimization framework is used to estimate the landed mass capability of each system. Results show that the deployable concepts can significantly improve payload mass capability by reducing the terminal propulsion propellant required. Initial feasibility studies show that the concepts are hypersonically statically stable and comply with mechanical and thermal material capabilities
Implementation of a Mesomechanical Material Model for IAD Fabrics within LS-DYNA

(Georgia Institute of Technology, 2012-12-14) Hill, Jeremy

The implementation and evaluation of a high fidelity material model for dry fabrics is the main objective of this paper. Inflatable Aerodynamic Decelerators (IADs) and other air inflated structures quite often utilize woven fabrics due to their lightweight and high loading carrying capabilities. Design optimization of these inflated structures relies on a detailed understanding of the woven fabric mechanics. Woven fabrics are composite orthotropic materials that respond differently under load from traditional solid mechanics. While low fidelity fabric materials usually assume a continuous medium, a higher fidelity model needs to account for the reorientation of yarns and weave geometry. An existing mesomechanical material model within the LS-DYNAÒ commercial non-linear finite element software package is utilized. In this paper, experimental stress-strain data for Kevlar 129 samples are validated against numerical simulations of models with matching geometry and loading conditions.
Structural Design, Analysis, and Test of the Prox-1 Spacecraft

(Georgia Institute of Technology, 2012-12-01) Willingham, Allison L.

HE Prox-1 spacecraft is Georgia Institute of Technology’s entry into the 7th University Nanosatellite Program Competition, a two year cycle competition for the AFRL where university teams consisting of both graduate and undergraduate students design, build, and test a 50 kg nanosatellite for a team-specified mission. Judging is based on various presentations to the AFRL review teams, importance of the mission to AFRL objectives, and development of a sound nanosatellite system among other criteria [5]. Prox-1 is a nanosatellite which will demonstrate the use of low-thrust propulsion for automated safe trajectory control during proximity operations. Passive, image based observations will be used for the navigation and closed loop attitude control of Prox-1 relative to a deployed CubeSat. Prox-1’s objectives include: Rendezvous and proximity operations with a target CubeSat, automated relative navigation and trajectory control, closed-loop attitude control based upon automated image processing, and relative orbit determination using image-based angle and range estimates, validated by the Mission Operations System [4]. The student’s particular research involved design, build, and test of the structural components of the Prox-1 satellite. This paper will describe what design information was based on previous Prox-1 structure iterations, what design modifications were made to improve the structure’s capabilities and meet requirements, what analysis and testing was performed to validate those requirements, and what was needed to integrate with the subsystem components. When referring to different plate orientations in this document, the Prox-1 body coordinate frame is used. This is centered at the middle of the Lightband interface ring on the bottom plate, and in the same plane as the Launch Vehicle Interface. In the final structure configuration, the X-axis is pointing toward the Ppod deployment direction and cameras, the positive Y-axis is in the direction opposite of the thruster, and the Z-axis is pointing from the LVI plate toward the top plate [2]. All figures depicting the spacecraft will have this body coordinate frame pictured
SPORE Parachute Design and Selection

(Georgia Institute of Technology, 2012-12-01) Stout, Stephanie E.

Eleven parachute types are investigated to determine the best option for the SPORE 1U LEO and 2x2U LEO configurations. The 1U LEO configuration must meet a 5 meters per second impact velocity requirement, and the 2x2U LEO configuration must meet a 40g acceleration limit throughout its trajectory, constraining both the impact deceleration and the parachute opening deceleration due to inflation. The suggested parachute types for the 2x2U LEO configuration are the ringslot, disk-gap-band, extended skirt 14.3% full, and conical ribbon parachutes, due to their low opening forces. The parachute should be deployed at a Mach number less than 0.65 to minimize opening decelerations. However, these designed parachutes do not consistently meet the impact deceleration requirement in a Monte Carlo simulation and should be oversized to account for variability. This strategy is applied to the 1U LEO configuration and results in approximately 49% confidence of meeting the impact velocity requirement with doubling the parachute area. Only 63% confidence is achieved by tripling the parachute area, indicating significantly diminished returns with increasing area. These approximate confidence levels are present with all eleven parachute types.
A robust multi-objective statistical improvement approach to electric power portfolio selection

(Georgia Institute of Technology, 2012-11-13) Murphy, Jonathan Rodgers

Motivated by an electric power portfolio selection problem, a sampling method is developed for simulation-based robust design that builds on existing multi-objective statistical improvement methods. It uses a Bayesian surrogate model regressed on both design and noise variables, and makes use of methods for estimating epistemic model uncertainty in environmental uncertainty metrics. Regions of the design space are sequentially sampled in a manner that balances exploration of unknown designs and exploitation of designs thought to be Pareto optimal, while regions of the noise space are sampled to improve knowledge of the environmental uncertainty. A scalable test problem is used to compare the method with design of experiments (DoE) and crossed array methods, and the method is found to be more efficient for restrictive sample budgets. Experiments with the same test problem are used to study the sensitivity of the methods to numbers of design and noise variables. Lastly, the method is demonstrated on an electric power portfolio simulation code.
Optimal allocation of thermodynamic irreversibility for the integrated design of propulsion and thermal management systems

(Georgia Institute of Technology, 2012-11-13) Maser, Adam Charles

More electric aircraft systems, high power avionics, and a reduction in heat sink capacity have placed a larger emphasis on correctly satisfying aircraft thermal management requirements during conceptual design. Thermal management systems must be capable of dealing with these rising heat loads, while simultaneously meeting mission performance. Since all subsystem power and cooling requirements are ultimately traced back to the engine, the growing interactions between the propulsion and thermal management systems are becoming more significant. As a result, it is necessary to consider their integrated performance during the conceptual design of the aircraft gas turbine engine cycle to ensure that thermal requirements are met. This can be accomplished by using thermodynamic modeling and simulation to investigate the subsystem interactions while conducting the necessary design trades to establish the engine cycle. As the foundation for this research, a parsimonious, transparent thermodynamic model of propulsion and thermal management systems performance was created with a focus on capturing the physics that have the largest impact on propulsion design choices. A key aspect of this approach is the incorporation of physics-based formulations involving the concurrent usage of the first and second laws of thermodynamics to achieve a clearer view of the component-level losses. This is facilitated by the direct prediction of the exergy destruction distribution throughout the integrated system and the resulting quantification of available work losses over the time history of the mission. The characterization of the thermodynamic irreversibility distribution helps give the designer an absolute and consistent view of the tradeoffs associated with the design of the system. Consequently, this leads directly to the question of the optimal allocation of irreversibility across each of the components. An irreversibility allocation approach based on the economic concept of resource allocation is demonstrated for a canonical propulsion and thermal management systems architecture. By posing the problem in economic terms, exergy destruction is treated as a true common currency to barter for improved efficiency, cost, and performance. This then enables the propulsion systems designer to better fulfill system-level requirements and to create a system more robust to future requirements.
Premixed flame kinematics in a harmonically oscillating velocity field

(Georgia Institute of Technology, 2012-11-13) Shin, Dong-hyuk

Air pollution regulations have driven modern power generation systems to move from diffusion to premixed combustion. However, these premixed combustion systems are prone to combustion instability, causing high fluctuations in pressure and temperature. This results in shortening of component life, system failure, or even catastrophic disasters. A large number of studies have been performed to understand and quantify the onset of combustion instability and the limit cycle amplitude. However, much work remains due to the complexity of the process associated with flow dynamics and chemistry. This thesis focuses on identifying, quantifying and predicting mechanisms of flame response subject to disturbances. A promising tool for predicting combustion instability is a flame transfer function. The flame transfer function is obtained by integrating unsteady heat release over the combustor domain. Thus, the better understanding of spatio-temporal characteristics of flame is required to better predict the flame transfer function. The spatio-temporal flame response is analyzed by the flame kinematic equation, so called G-equation. The flame is assumed to be a thin interface separating products and reactant, and the interface is governed by the local flow and the flame propagation. Much of the efforts were done to the flame response subject to the harmonic velocity disturbance. A key assumption allowing for analytic solutions is that the velocity is prescribed. For the mathematical tools, small perturbation theory, Hopf-Lax formula and numerical simulation were used. Solutions indicated that the flame response can be divided into three regions, referred to here as the near-field, mid-field, and farfield. In each regime, analytical expressions were derived, and those results were compared with numerical and experimental data. In the near field, it was shown that the flame response grows linearly with the normal component of the velocity disturbance. In the mid field, the flame response shows peaks in gain, and the axial location of these peaks can be predicted by the interference pattern by two characteristic waves. Lastly, in the far field where the flame response decreases, three mechanisms are studied; they are kinematic restoration, flame stretch, and turbulent flow effects. For each mechanism, key parameters are identified and their relative significances are compared.
Viscous hypersonic flow physics predictions using unstructured Cartesian grid techniques

(Georgia Institute of Technology, 2012-11-12) Sekhar, Susheel Kumar

Aerothermodynamics is an integral component in the design and implementation of hypersonic transport systems. Accurate estimates of the aerodynamic forces and heat transfer rates are critical in trajectory analysis and for payload weight considerations. The present work seeks to investigate the ability of an unstructured Cartesian grid framework in modeling hypersonic viscous flows. The effectiveness of modeling viscous phenomena in hypersonic flows using the immersed boundary ghost cell methodology of this solver is analyzed. The capacity of this framework to predict the surface physics in a hypersonic non-reacting environment is investigated. High velocity argon gas flows past a 2-D cylinder are simulated for a set of freestream conditions (Reynolds numbers), and impact of the grid cell sizes on the quality of the solution is evaluated. Additionally, the formulation is verified over a series of hypersonic Mach numbers for the flow past a hemisphere, and compared to experimental results and empirical estimates. Next, a test case that involves flow separation and the interaction between a hypersonic shock wave and a boundary layer, and a separation bubble is investigated using various adaptive mesh refinement strategies. The immersed boundary ghost cell approach is tested with two temperature clipping strategies, and their impact on the overall solution accuracy and smoothness of the surface property predictions are compared. Finally, species diffusion terms in the conservation equations, and collision cross-section based transport coefficients are installed, and hypersonic flows in thermochemical nonequilibrium environments are studied, and comparisons of the off-surface flow properties and the surface physics predictions are evaluated. First, a 2-D cylinder in a hypersonic reacting air flow is tested with an adiabatic wall boundary condition. Next, the same geometry is tested to evaluate the viscous chemistry prediction capability of the solver with an isothermal wall boundary condition, and to identify the strengths and weaknesses of the immersed boundary ghost cell methodology in computing convective heating rates in such an environment.
Development and Evaluation of an Automated Path Planning Aid

(Georgia Institute of Technology., 2012-11) Watts, Robert ; Christmann, Hans Claus ; Johnson, Eric N. ; Feigh, Karen M. ; Tsiotras, Panagiotis

Handling en route emergencies in modern transport aircraft through adequate teamwork between the pilot, the crew and the aircraft’s automation systems is an ongoing and active field of research. An automated path planning aid tool can assist pilots with the tasks of selecting a convenient landing site and developing a safe path to land at this site in the event of an onboard emergency. This paper highlights the pilot evaluation results of a human factors study as part of such a proposed automated planning aid. Focusing on the interactions between the pilot and the automated planning aid, the presented results suggest that a particular implementation of the pilot aid interface, which uses a simple dial to sort the most promising landing sites, was effective. This selectable sorting capability, motivated by the anticipated cognitive mode of the pilot crew, improved the quality of the selected site for the majority of the cases tested. Although the presented approach increased the average time required for the selection of an alternate landing site, it decreased the time to complete the task in the case of emergencies unfamiliar to the pilot crew.
Reliability, multi-state failures and survivability of spacecraft and space-based networks

(Georgia Institute of Technology, 2012-10-30) Castet, Jean-François

Spacecraft fulfill a myriad of critical functions on orbit, from defense and intelligence to science, navigation, and telecommunication. Spacecraft can also cost several hundred millions of dollars to design and launch, and given that physical access for maintenance remains difficult if not impossible to date, designing high reliability and survivability into these systems is an engineering and financial imperative. While reliability is recognized as an essential attribute for spacecraft, little analysis has been done pertaining to actual field reliability of spacecraft and their subsystems. This thesis consists of two parts. The first part fills the gap in the current understanding of spacecraft failure behavior on orbit through extensive statistical analysis and modeling of anomaly and failure data of Earth-orbiting spacecraft. The second part builds on these results to develop a novel theoretical basis (interdependent multi-layer network approach) and algorithmic tools for the analysis of survivability of spacecraft and space-based networks. Space-based networks (SBNs) allow the sharing of on-orbit resources, such as data storage, processing, and downlink. Results indicate and quantify the incremental survivability improvement of the SBN over the traditional monolith architecture. A trade-space analysis is then conducted using non-descriptive networkable subsystems/technologies to explore survivability characteristics of space-based networks and help guide design choices.