Multidimensional Modeling Of Pyrolysis Gas Transport Inside Orthotropic Charring Ablators,
2014
University of Kentucky
Multidimensional Modeling Of Pyrolysis Gas Transport Inside Orthotropic Charring Ablators, Haoyue Weng
Theses and Dissertations--Mechanical and Aerospace Engineering
During hypersonic atmospheric entry, spacecraft are exposed to enormous aerodynamic heat. To prevent the payload from overheating, charring ablative materials are favored to be applied as the heat shield at the exposing surface of the vehicle. Accurate modeling not only prevents mission failures, but also helps reduce cost. Existing models were mostly limited to one-dimensional and discrepancies were shown against measured experiments and flight-data. To help improve the models and analyze the charring ablation problems, a multidimensional material response module is developed, based on a finite volume method framework. The developed computer program is verified through a series of test-cases, …
Load Transfer In An Isolated Particle Embedded Within An Epoxy Matrix,
2014
University of Central Florida
Load Transfer In An Isolated Particle Embedded Within An Epoxy Matrix, Erik Durnberg
Electronic Theses and Dissertations
Particulate composites are widely used in many aerospace applications such as protective coatings, adhesives, or structural members of a body and their mechanical properties and behavior have gained increasing significance. The addition of modifiers such as alumina generally leads to improved mechanical properties. This addition also enables the non-invasive study of the load transfer between the particle and the matrix. Understanding the load transfer between the particulate and the matrix material is the first step to understanding the behavior and mechanical properties of the composite as a whole. In this work, samples with an isolated alumina particle embedded in an …
Ignition Studies Of Diisopropyl Ketone, A Second-Generation Biofuel,
2014
University of Central Florida
Ignition Studies Of Diisopropyl Ketone, A Second-Generation Biofuel, Owen Pryor
HIM 1990-2015
This thesis focuses on ignition of diisopropyl ketone (DIPK), a new biofuel candidate that is produced by endophytic conversion. The ignition delay times behind reflected shockwaves were modeled in a high-pressure shock tube. The ignition delay times were compared to other biofuels and gasoline surrogates. Parametric studies of the ignition delay experiments were performed between 1-10 atm and 900 -1200K. An OH optical sensor was developed in conjunction for the ignition delay experiments. The OH optical sensor uses a microwave discharge lamp to generate light at 308 nm that will then be shined through the combustion reaction. Using Beer-Lambert law …
Nondestructive Analysis Of Advanced Aerospace Materials Via Spectroscopy And Synchrotron Radiation,
2014
University of Central Florida
Nondestructive Analysis Of Advanced Aerospace Materials Via Spectroscopy And Synchrotron Radiation, Albert Manero
Electronic Theses and Dissertations
Advanced aerospace materials require extensive testing and characterization to anticipate and ensure their integrity under hostile environments. Characterization methods utilizing synchrotron X-Ray diffraction and spectroscopy can decrease the time required to determine an emerging material's readiness for application through intrinsic information on the material response and failure mechanisms. In this study, thermal barrier coating samples applicable to turbine blades of jet engines were studied using Raman and Photoluminescence spectroscopy as well as Synchrotron X-ray diffraction while Kevlar based fiber composites applicable to ballistic resistant armor were studied using Raman spectroscopy to investigate the mechanical state and corresponding damage and failure …
Keeping The Skies Safe,
2014
Embry-Riddle Aeronautical University
Keeping The Skies Safe, Massood Towhidnejad, Andrew J. Kornecki
Department of Electrical Engineering and Computer Science - Daytona Beach
Professors Massood Towhidnejad and Andrew Kornecki shine a light on how their lab is helping government and the aviation industry to enhance the safety and security of software-intensive systems.
Thermomechanical Properties And Stress Analysis Of 3-D Textile Composites By Asymptotic Expansion Homogenization Method,
2014
Missouri University of Science and Technlogy
Thermomechanical Properties And Stress Analysis Of 3-D Textile Composites By Asymptotic Expansion Homogenization Method, Muhammad Ridlo Erdata Nasution, Naoyuki Watanabe, Atsushi Kondo, Arief Yudhanto
Mechanical and Aerospace Engineering Faculty Research & Creative Works
This paper formulates asymptotic expansion homogenization method for the analysis of 3-D composites whereby thermomechanical effects are considered. The equivalent thermomechanical properties, viz. elastic constants and coefficient of thermal expansion, of 3-D orthogonal interlock composites are obtained based on a unit-cell derived from the optical microscopy observation. The Young's modulus and Poisson's ratio obtained from the analysis are compared with those obtained by experiments. The results show a good agreement especially for the Young's modulus. Localization analysis based on the present formulation is also presented to assess the stresses within the constituents of 3-D composites (fiber tows and resin region) …
Daily Area Of Snow Melt Onset On Arctic Sea Ice From Passive
Microwave Satellite Observations 1979–2012,
2014
University of Nebraska - Lincoln
Daily Area Of Snow Melt Onset On Arctic Sea Ice From Passive Microwave Satellite Observations 1979–2012, Angela C. Bliss, Mark R. Anderson
Department of Earth and Atmospheric Sciences: Faculty Publications
Variability in snow melt onset (MO) on Arctic sea ice since 1979 is examined by determining the area of sea ice experiencing the onset of melting during the melt season on a daily basis. The daily MO area of the snow and ice surface is determined from passive microwave satellite-derived MO dates for the Arctic Ocean and sub-regions. Annual accumulations of MO area are determined by summing the time series of daily MO area through the melt season. Daily areas and annual accumulations of MO area highlight inter-annual and regional variability in the timing of MO area, which is sensitive …
Nonlinear Development And Secondary Instability Of Traveling Crossflow Vortices,
2014
Missouri University of Science and Technology
Nonlinear Development And Secondary Instability Of Traveling Crossflow Vortices, Fei Li, Meelan M. Choudhari, Lian Duan, Chau-Lyan Chang
Mechanical and Aerospace Engineering Faculty Research & Creative Works
Building upon the prior research targeting the laminar breakdown mechanisms associated with stationary crossflow instability over a swept-wing configuration, this paper investigates the secondary instability of traveling crossflow modes as an alternate scenario for transition. For the parameter range investigated herein, this alternate scenario is shown to be viable unless the initial amplitudes of the traveling crossflow instability are lower than those of the stationary modes by considerably more than one order of magnitude. The linear growth predictions based on the secondary instability theory are found to agree well with both parabolized stability equations and direct numerical simulation, and the …
Crystallization In Nano-Confinement Seeded By A Nanocrystal -- A Molecular Dynamics Study,
2014
Missouri University of Science and Technology
Crystallization In Nano-Confinement Seeded By A Nanocrystal -- A Molecular Dynamics Study, Heng Pan, Costas Grigoropoulos
Mechanical and Aerospace Engineering Faculty Research & Creative Works
Seeded crystallization and solidification in nanoscale confinement volumes have become an important and complex topic. Due to the complexity and limitations in observing nanoscale crystallization, computer simulation can provide valuable details for supporting and interpreting experimental observations. In this article, seeded crystallization from nano-confined liquid, as represented by the crystallization of a suspended gold nano-droplet seeded by a pre-existing gold nanocrystal seed, was investigated using molecular dynamics simulations in canonical (NVT) ensemble. We found that the crystallization temperature depends on nano-confinement volume, crystal orientation, and seed size as explained by classical two-sphere model and Gibbs-Thomson effect.
Thermomechanical Modeling Of Cone Sample Of Zrb2-Sic Ceramic Under Arc-Jet Conditions,
2014
Missouri University of Science and Technology
Thermomechanical Modeling Of Cone Sample Of Zrb2-Sic Ceramic Under Arc-Jet Conditions, Lokeswarappa R. Dharani, Jun Wei
Mechanical and Aerospace Engineering Faculty Research & Creative Works
The effects of oxidation on mechanical behavior of a cone sample of ZrB2-SiC ceramic under arc-jet test conditions is studied by a finite element (FE) model. First a steady-state heat transfer FE method was employed to conduct the thermal analysis and obtain the temperature distribution in the inner body of the cone. Then, resulting temperature distribution is applied to the thermomechanical finite element analysis to calculate the thermal stress distribution in the cone body. Due to the mismatch of material properties between the bulk ZrB2-SiC and its new products after oxidation, the outer oxide layers constrain the thermal deformation of …
Assessment Of Multi-Mode Spacecraft Micropropulsion Systems,
2014
Missouri University of Science and Technology
Assessment Of Multi-Mode Spacecraft Micropropulsion Systems, Steven P. Berg, Joshua L. Rovey
Mechanical and Aerospace Engineering Faculty Research & Creative Works
Multi-mode spacecraft micro propulsion systems which include a high-thrust chemical mode and high-specific impulse electric mode are assessed with specific reference to cube sat-sized satellite applications. Both cold gas Freon-14 propellant and ionic liquid chemical monopropellant modes were investigated alongside pulsed plasma, electrospray, and helicon electric thruster modes. Systems involving chemical monopropellants have the highest payload mass fractions for a reference mission of a 500 m/s delta-V and 6U sized cube sat for electric propulsion usage below 55% of total delta-V. For higher electric propulsion usage, cold gas thrusters delivered a higher payload mass fraction due to lower system inert …
Optimal Switching Of Nonlinear Systems With Free Mode Sequence,
2014
Missouri University of Science and Technology
Optimal Switching Of Nonlinear Systems With Free Mode Sequence, Ali Heydari, S. N. Balakrishnan
Mechanical and Aerospace Engineering Faculty Research & Creative Works
Approximate dynamic programming is utilized in this study to develop solutions for optimal switching problems. The order of the active subsystems and the number of switches are free, and an online solution is developed that produces optimal performance. Motivated by the development in the adaptive critic's literature, the proposed method uses a critic and as many actors as the number of subsystems in order to conduct optimal scheduling in real-time based on the instantaneous states of the system. It is observed that once the neural networks are trained offline based on the proposed algorithm, they provide solutions for a range …
Adaptive Architectures For Distributed Control Of Modular Systems,
2014
Missouri University of Science and Technology
Adaptive Architectures For Distributed Control Of Modular Systems, Tansel Yucelen, Jeff S. Shamma
Mechanical and Aerospace Engineering Faculty Research & Creative Works
We consider the distributed control of large-scale modular systems, i.e., systems consist of physically interconnected (and possibly heterogeneous) submodules that use local information to achieve a given set of global objectives. A graph-theoretic approach is used to model the unknown physical interactions between submodules and utilize an adaptive control algorithm to learn and cancel the effect of such interactions as well as the submodule-level modeling uncertainties asymptotically by allowing submodules to locally communicate with each other through the graph. The key feature of our framework is to bound the mismatch error between the actual and desired closed-loop modular system performance …
Proper Orthogonal Decomposition Technique For Sub-Optimal Control Of Flexible Aircraft Wings Using Discrete Actuators,
2014
Missouri University of Science and Technology
Proper Orthogonal Decomposition Technique For Sub-Optimal Control Of Flexible Aircraft Wings Using Discrete Actuators, M. Kumar, S. N. Balakrishnan
Mechanical and Aerospace Engineering Faculty Research & Creative Works
Distributed parameter systems are, generally, described by a set of partial differential equations. Control design of these systems is a very complex task as compared to that of the lumped parameter systems that are defined by a set of ordinary differential equations. In this paper, we present a stabilizing state-feedback control design approach for a class of second order system, where the system can be controlled by discrete actuators in the spatial domain. The control methodology is developed by combining the technique of 'Proper Orthogonal Decomposition' and Approximate Dynamic Programming. The Proper Orthogonal Decomposition technique is utilized to obtain a …
Decentralized Adaptive Control Of Uncertain Systems With Gain Scheduled Reference Models,
2014
Missouri University of Science and Technology
Decentralized Adaptive Control Of Uncertain Systems With Gain Scheduled Reference Models, Mehrdad Pakmehr, Tansel Yucelen
Mechanical and Aerospace Engineering Faculty Research & Creative Works
Control theoretic concepts for decentralized adaptive control of uncertain systems with gain scheduled reference model is developed. For each subsystem a single Lyapunov matrix is computed, using convex optimization tools, for multiple linearization near equilibrium and non-equilibrium points of the nonlinear closed loop gain scheduled reference subsystem. This approach guarantees stability of the closed loop gain scheduled reference model. Then, decentralized adaptive state feedback control architecture is developed and its stability is proved. Specifically, the resulting closed-loop system is shown to have bounded solutions with bounded tracking error for all the subsystems. Simulation results for two different models of a …
Reference Control Architecture In The Presence Of Measurement Noise And Actuator Dynamics,
2014
Missouri University of Science and Technology
Reference Control Architecture In The Presence Of Measurement Noise And Actuator Dynamics, Gerardo De La Torre, Tansel Yucelen, Eric Johnson
Mechanical and Aerospace Engineering Faculty Research & Creative Works
In this paper the command governor-based model reference control architecture is developed and analyzed for uncertain dynamical systems in the presence measurement noise and actuator dynamics. Specifically, the command governor is a dynamical system that adjusts the trajectory of a given command in order to enable an uncertain system to be able to follow an ideal reference system capturing a desired closed-loop dynamical system behavior both in transient-time and steady-state. In this paper, we present modifications to the original command governor approach in order to increase its robustness properties against measurement noise and actuator dynamics. In particular, the modified architecture …
Control-Oriented Modeling Of Laser Metal Deposition As A Repetitive Process,
2014
Missouri University of Science and Technology
Control-Oriented Modeling Of Laser Metal Deposition As A Repetitive Process, Patrick M. Sammons, Douglas A. Bristow, Robert G. Landers
Mechanical and Aerospace Engineering Faculty Research & Creative Works
Laser Metal Deposition (LMD) is an additive manufacturing process whose dynamics are driven by complex heat transfer and fluid flow phenomena. The LMD process, along with every additive manufacturing process, is fundamentally a two-dimensional process possessing both temporal (or spatial) domain dynamics and propagation of information from layer to layer. However, modeling the two-dimensionality of the process for use in control has received little attention. Here, a model aimed at capturing the important nonlinear two-dimensional physical processes of the melt pool shape, while maintaining simplicity, is presented. The model is expressed in a form that lends itself to the design …
Control-Oriented Modeling For Open-Cathode Fuel Cell Systems,
2014
Missouri University of Science and Technology
Control-Oriented Modeling For Open-Cathode Fuel Cell Systems, Joseph Ishaku, Nima Lotfi, Hesam Zomorodi, Robert G. Landers
Mechanical and Aerospace Engineering Faculty Research & Creative Works
Due to numerous advantages of Polymer Electrolyte Fuel Cells (PEMFCs), they are becoming the mainstream fuel cell of choice for different applications. Open-cathode PEMFCs, in particular, are gaining increased popularity in low to medium power applications due to their simple structure and low parasitic losses. However, in order to achieve safe operation, increased durability and optimal performance, advanced control algorithms, which typically require control-oriented models, need to be implemented on open-cathode fuel cell systems. The open-cathode fuel cell system includes the fuel cell stack and all of the auxiliary components that are vital for its operation. In this paper, control-oriented …
Extremum-Seeking For Nonlinear Discrete-Time Systems With Application To Hcci Engines,
2014
Missouri University of Science and Technology
Extremum-Seeking For Nonlinear Discrete-Time Systems With Application To Hcci Engines, H. Zargarzadeh, S. Jagannathan, J. A. Drallmeier
Electrical and Computer Engineering Faculty Research & Creative Works
For many control applications, identifying an optimal operating point by maximizing/minimizing a performance function is important. This paper applies the extremum-seeking method to nonaffine, nonlinear discrete-time systems stabilized by an optimal adaptive controller. First, a novel averaging method is used for the nonlinear discrete-time systems to show that their output unique extrema are stable equilibrium points. Then, a singular perturbation method in discrete time is employed to show that the overall closed loop system will dynamically converge to the extremum. The applicability of this scheme is numerically verified on a Homogeneous Charge Compression Ignition (HCCI) model validated experimentally and expressed …
Robust And Adaptive Nonlinear Control Of Limit Cycle Oscillations In Uavs Using Synthetic Jet Actuators,
2014
Embry-Riddle Aeronautical University
Robust And Adaptive Nonlinear Control Of Limit Cycle Oscillations In Uavs Using Synthetic Jet Actuators, Natalie Ramos Pedroza
Doctoral Dissertations and Master's Theses
Limit cycle oscillations (LCO), also known as utter, cause significant challenges in fight control of unmanned aerial vehicles (UAVs), and could potentially lead to structural damage and catastrophic failures. LCO can be described as vibrational motions in the pitching and plunging displacements of an aircraft wing. Even in low Reynolds number (low-Re) fight regimes, LCO can exceed the limiting boundary for safe UAV fight. Further, as practical considerations motivate the design of smaller, lighter weight UAVs, there is a growing need for UAV systems that do not require heavy mechanical actuators (e.g., ailerons). To address this, the use of synthetic …
