Aerospace Engineering Commons^™

Fitting B-Splines Curves To Coarse Data Cloud Using Modified Squared Distance Minimization Method, Vinay Vivek Mhala

Mechanical and Aerospace Engineering Theses - Archive

Additive manufacturing has made us realize that we can fabricate complex shapes that were difficult to manufacture with subtractive processes. Topology optimizations results have complex shapes and have rough surfaces which are difficult to manufacture even by additive manufacturing. To automate the process of converting rough surfaces into smooth surfaces for the benefit of manufacturability would be very desirable. Computing curve segments to approximate point cloud data that represents rough surfaces and then lofting it to have a smooth surface seems to be a promising methodology to achieve automation. We implement B-spline formulation along with Pottmann’s iterative method based on …

Study Of Crack Propagation Under Thermal Loading On A 3d Tsv Package, Subramanian R. Gowtham

Mechanical and Aerospace Engineering Theses - Archive

Today, there is a revolution in going for miniaturization in size of electronic packages. More thinner, lighter and complex packages are in use for almost every electronic device. This initiation was taken to the next level and gives us a whole new ideology called 3D packaging. Currently, 3D packaging is the on-going research in almost all the electronic packaging related industries. 3D package uses Through Silicon Via (TSV) technology that gained momentum in the development and helped packaging system for significant miniaturization and power reduction, which result in increased performance. However, the reliability assessment is needed to evaluate the critical …

Embedding Antenna Shear/Pressure Sensors In Prosthetic Liner Material, Shahanavaz Eilbeigi

Mechanical and Aerospace Engineering Theses - Archive

Published surveys indicated that 40-60% of prosthesis users experience discomfort and skin problems. These studies highlighted the needs for enhanced prosthetic performance and fit. It is extremely difficult to address these problems due to two reasons: first, ambulation create varying areas of shear and pressure on the residual limb, but it is not clear which shear/pressure combinations are acceptable and what is the safe stress level for users. In addition, the volume of the residual limb changes throughout the day and activity level. Therefore, there is a strong need to develop a light, thin, flexible, and wirelessly interrogated sensor for …

Risk-Based Approach To Assessment Of Advanced Technologies For Conceptual Design, Adipratnia Asmady

Master's Theses

The conceptual design phase of an aerospace system development program is typically characterized by short duration and relatively limited resources, yet design decisions are made that have critical implications on program risk. To address the more aggressive requirements, one of these decisions is the selection of advanced technologies. System developers need to assess advanced technologies early on, but are faced with uncertainties surrounding the potential net benefits. The concept introduced in this study is uncertainty characterization as a way to better understand the associated risk. A framework was developed to guide the interaction between the technology developer and the system …

Applications Of The Homotopy Analysis Method To Optimal Control Problems, Shubham Singh

Open Access Theses

Traditionally, trajectory optimization for aerospace applications has been performed using either direct or indirect methods. Indirect methods produce highly accurate solutions but suer from a small convergence region, requiring initial guesses close to the optimal solution. In past two decades, a new series of analytical approximation methods have been used for solving systems of dierential equations and boundary value problems.

The Homotopy Analysis Method (HAM) is one such method which has been used to solve typical boundary value problems in nance, science, and engineering. In this investigation, a methodology is created to solve indirect trajectory optimization problems using the Homotopy …

Numerical Methods For Low-Thrust Trajectory Optimization, Robert E. Pritchett

Open Access Theses

The spacecraft trajectory design process frequently includes the optimization of a quantity of importance such as propellant consumption or time of flight. A variety of methods for trajectory optimization are available, however the efficiency of an approach is dependent on the problem scenario it is applied to. Indirect and direct trajectory optimization methods are examined in this investigation with the goal of assessing the characteristics of each approach, and thereby determining the problem scenarios each is best suited for. Insight is gained from application of each optimization method to three sample problems; a circular-to-circular orbit transfer as well as two …

Fleet Level Environmental Evaluation Of Emission Taxing Scheme And Biofuel: A Combined Optimization And Multi-Actor Approach, Hsun Chao

Open Access Theses

The Fleet Level Environmental Evaluation Tool (FLEET) can assess environmental impacts of various levels of technology and environmental policies on fleet-level carbon emissions and airline operations. FLEET consists of different models to mimic airlines' behaviors and a resource allocation problem to simulate airlines' aircraft deployments on their networks. Additionally, the Multiactors Biofuel Model can conduct biofuel life-cycle assessments and evaluate biofuel developments and assess the effects of new technology on biofuel production costs and unit carbon emissions as well.

In addition, the European Union (EU) initiated an Emission Trading Scheme (ETS) in the European Economic Area, while International Civil Aviation …

Ab Initio Based State Specific Modeling Of N2+O System, Han Luo

Open Access Theses

Nitrogen and atomic oxygen play an important role in high temperature gas systems. Their Zeldovich reaction product nitric oxide not only affects aerothermal loads and emissions of hypersonic vehicles, but also has the possibility to influence the efficiency of hypersonic propulsion. Atomic oxygen induced nitrogen dissociation is another reaction mechanism of the N2+O system. However, due to the difficulty of conducting ground tests, there are no experimental data for this reaction now. Thermo-chemical nonequilibrium could make the problem more difficult since experiments could only track macroscopic gas properties instead of internal energy distribution. On the other hand, current reaction and …

Supporting Space Systems Design Via Systems Dependency Analysis Methodology, Cesare Guariniello

Open Access Dissertations

The increasing size and complexity of space systems and space missions pose severe challenges to space systems engineers. When complex systems and Systems-of-Systems are involved, the behavior of the whole entity is not only due to that of the individual systems involved but also to the interactions and dependencies between the systems. Dependencies can be varied and complex, and designers usually do not perform analysis of the impact of dependencies at the level of complex systems, or this analysis involves excessive computational cost, or occurs at a later stage of the design process, after designers have already set detailed requirements, …

Information Inference For Cyber-Physical Systems With Application To Aviation Safety And Space Situational Awareness, Sangjin Lee

Open Access Dissertations

Due to the rapid advancement of technologies on sensors and processors, engineering systems have become more complex and highly automated to meet ever stringent performance and safety requirements. These systems are usually composed of physical plants (e.g., aircraft, spacecraft, ground vehicles, etc.) and cyber components (e.g., sensing, communication, and computing units), and thus called as Cyber-Physical Systems (CPSs). For safe, efficient, and sustainable operation of a CPS, the states and physical characteristics of the system need to be effectively estimated or inferred from sensing data by proper information inference algorithms. However, due to the complex nature of the interacting multiple-heterogeneous …

Physical Properties, Evaporation And Combustion Characteristics Of Nanofluid-Type Fuels, Saad Tanvir

Open Access Dissertations

Nanofluids are liquids with stable suspension of nanoparticles. Limited studies in the past have shown that both energetic and catalytic nanoparticles once mixed with traditional liquid fuels can be advantageous in combustion applications, e.g., increased energy density and shortened ignition delay. Contradictions in existing literature, scarcity of experimental data and lack of understanding on how the added nanoparticles affect the physical properties as well as combustion characteristics of the resulting fuel motivated us to launch a detailed experimental and theoretical investigation.

The surface tension of ethanol and n-decane based nanofluid fuels containing suspended nanoparticles were measured using the pendant drop …

Analytical Methods For Gravity-Assist Tour Design, Nathan J. Strange

Open Access Dissertations

This dissertation develops analytical methods for the design of gravity-assist space- craft trajectories. Such trajectories are commonly employed by planetary science missions to reach Mercury or the Outer Planets. They may also be used at the Outer Planets for the design of science tours with multiple flybys of those planets’ moons. Recent work has also shown applicability to new missions concepts such as NASA’s Asteroid Redirect Mission.

This work is based in the theory of patched conics. This document applies rigor to the concept of pumping (i.e. using gravity assists to change orbital energy) and cranking (i.e. using gravity assists …

Implementing And Testing A Panel-Based Method For Modeling Acoustic Scattering From Cfd Input, S. Hales Swift

Open Access Dissertations

Exposure of sailors to high levels of noise in the aircraft carrier deck environment is a problem that has serious human and economic consequences. A variety of approaches to quieting exhausting jets from high-performance aircraft are undergoing development. However, testing of noise abatement solutions at full-scale may be prohibitively costly when many possible nozzle treatments are under consideration. A relatively efficient and accurate means of predicting the noise levels resulting from engine-quieting technologies at personnel locations is needed. This is complicated by the need to model both the direct and the scattered sound field in order to determine the resultant …

Evaluation Of Various Turbulence Models For Shock-Wave Boundary Layer Interaction Flows, Francis K. Acquaye

McKelvey School of Engineering Graduate Student Theses & Dissertations

Despite the modeling capabilities of current computational fluid dynamics (CFD), there still exist problems and inconsistencies in simulating fluid flow in certain flow regimes. Most difficult are the high-speed transonic, supersonic and hypersonic wall-bounded turbulent flows with small or massive regions of separation. To address the problem of the lack of computational accuracy in turbulence modeling, NASA has established the Turbulence Modeling Resource (TMR) website and has issued the NASA 40% Challenge. The aim of this challenge is to identify and improve/develop turbulence and transition models as well as numerical techniques to achieve a 40% reduction in the predictive error …

Total Temperature Measurement At Pulse Detonation Engine Exhaust, Ninad Ramesh Kawle

Mechanical and Aerospace Engineering Theses - Archive

Pulse detonation engines (PDEs) are being studied in recent years as a potential means of power production. In PDEs, a supersonically travelling detonation wave traverses through the detonation tube. Total temperature of the exhaust of the PDE is not a well-known parameter. The objective of the research was to calibrate and employ miniature type E thermocouples for exhaust temperature measurement of the PDE. The probe making process along with the calibration techniques for AWG 20, AWG 24 and AWG 50 thermocouples are discussed at length. The time constants for thermocouples were determined. Reactive mixture containing hydrogen and oxygen was used …

Method Of Characteristics Verification Of Inverse Frequency Model Of Turbulent Pipe Flow Transients, Mohammad Saifullah Mohammad Zafar Shaikh

Mechanical and Aerospace Engineering Theses - Archive

Pressure transients in pipes with turbulent flow have classically been simulated using numerical techniques such as the method of characteristics. An alternative method utilizing an inverse frequency algorithm has recently been introduced for smooth pipe and determined to be computationally fast compared to the method of characteristics and in some cases more accurate. In addition, comparisons with experimental water hammer data has verified that the inverse frequency method is accurate out to Reynolds numbers of 15,800. This thesis investigates a comparison or the inverse frequency and method of characteristics methods for Reynolds numbers out to 200,000 for smooth pipes.

A Novel Stress Analysis Method For Laminated Composite Stiffener With Asymmetric Z-Section Under Mechanical And Thermal Loading Conditions, Sidhant Singh

Mechanical and Aerospace Engineering Theses - Archive

Composites structures are being used as load carrying members in latest aircrafts and performance automobiles, the design validation for such structures can be a time consuming and expensive process, if done by testing. Validation of a structure by analysis saves time and money for a design process and validation by analysis can be done by comparing the analytical solution with the finite element analysis of the structure, which requires availability of analytical expressions for every cross-sectional arrangement of the structural members. This research focuses on stress analysis of laminated composite stiffener with asymmetric Z-sections, where closed form analytical expressions are …

Optimal Design Of A Thermoelectric Cooling/Heating System For Car Seat Climate Control (Cscc), Abdulmunaem H. Elarusi

Masters Theses

In this work, optimal design of a thermoelectric device itself (element length, cross section area and number of thermoelements) applied in a car seat climate control (CSCC) is studied analytically using our newly developed optimization method. This method, which is based on the thermoelectric ideal equations along with dimensional analysis allows us to simultaneously obtain the best combination of the thermoelectric parameters in order to improve the performance of the thermoelectric device regarding the cooling/heating power and the coefficient of performance (COP). First, this method was implemented to investigate the optimal design of a readily existing air-to-air thermoelectric system. Then, …

Active Fault Tolerant Control For Vertical Tail Damaged Aircraft With Dissimilar Redundant Actuation System, Wang Jun, Wang Shaoping, Wang Xingjian, Shi Cun, Mileta M. Tomovic

Engineering Technology Faculty Publications

This paper proposes an active fault-tolerant control strategy for an aircraft with dissimilar redundant actuation system (DRAS) that has suffered from vertical tail damage. A damage degree coefficient based on the effective vertical tail area is introduced to parameterize the damaged flight dynamic model. The nonlinear relationship between the damage degree coefficient and the corresponding stability derivatives is considered. Furthermore, the performance degradation of new input channel with electro-hydrostatic actuator (EHA) is also taken into account in the damaged flight dynamic model. Based on the accurate damaged flight dynamic model, a composite method of linear quadratic regulator (LQR) integrating model …

Enhanced Thermal Conductance Of Polymer Composites Through Embedding Aligned Carbon Nanofibers, David S. Wood, Dale K. Hensley, Nicholas A. Roberts

Mechanical and Aerospace Engineering Faculty Publications

The focus of this work is to find a more efficient method of enhancing the thermal conduc-tance of polymer thin films. This work compares polymer thin films embedded with randomly oriented carbon nanotubes to those with vertically aligned carbon nanofibers. Thin films embedded with carbon nanofibers demonstrated a similar thermal conductance between 40–60 µm and a higher thermal con-ductance between 25–40 µm than films embedded with carbon nanotubes with similar volume fractions even though carbon nanotubes have a higher thermal conductivity than carbon nanofibers.