Engineering Commons^™

Non-Linear Shunting Of Piezo-Actuators For Vibration Suppression, Anisetti Anusha

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Vibrations at a resonant frequency lead to catastrophic failure or at the very least, shorten the life span of the structure due to fatigue. These problems force engineers to implement damping techniques. Smart materials have been used over two decades to reduced vibration amplitudes. Recently, there has been much research and development on smart materials and structures.

This work introduces an innovative approach for vibration suppression using passively shunted piezolectric materials. Initially linear circuit elements such as resistors, capacitors, and inductances, or building a non-linear circuit with different impedance designs were used. Instead of such elements, a switched electromechanical shunt …

The Effect Of Dissolved Air On The Cooling Performance Of A Partially-Confined Fc-72 Spray, Rebekah Lee Puterbaugh

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The objective of this thesis is to investigate the heat transfer performance of a partially-confined FC-72 spray with varying dissolved air concentrations. An experimental test rig consisting of a spray chamber coupled to a fluid delivery loop system was used to obtain temperature, pressure, and critical heat flux (CHF) data. A downward facing nozzle within the spray chamber allowed the FC-72 fluid to be sprayed onto an upward facing, thick-film, resistor heater. The heater was mounted onto a glass post, with a sump system to allow removal of excess fluid. Type-E thermocouples were imbedded in the post to obtain temperature …

Design And Analysis Of A Mach 3 Dual Mode Scramjet Combustor, Christopher Ryan Corbin

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Low speed operation of a dual mode scramjet engine is important to the development of a two stage to orbit reusable launch vehicle. This study investigates the Mach 3 operation of a dual mode scramjet engine. SRGULL, a one-dimensional cycle code for scramjet engines, and VULCAN, a computational fluid dynamics code capable of solving reacting flows, are used in this study. Staged injection is investigated to allow more heat release at a low flight Mach number condition so that more thrust can be achieved and inlet unstart is avoided. The nominal case has one injector located 1.067 meters downstream of …

Risk Based Analysis And Design Af Stiffened Plates, Heather B. Dwire

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The traditional Risk Based Design (RBD) process involves designing a structure based on risk estimates obtained during several iterations of an optimization routine. This approach is computationally expensive for large-scale aircraft structural systems. The main objective of this research is to establish a RBD algorithm and produce RBD plots for stiffened plates. Basic steps to check functionality will be done by first analyzing a flat plate for which closed formed equations are available and then moving to more complex geometries like stiffened plates.

Therefore, the concept of RBD plots that can be used for both structural sizing and risk assessment …

Effect Of A Graded Layer On The Plastic Dissipation During Mixed-Mode Fatigue Crack Growth On Plastically Mismatched Interfaces, Craig M. Baudendistel

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Recent work has proposed a dissipated energy theory of fatigue crack growth in layered materials under mixed-mode loading. An inherent assumption of this prior work is that a perfect crack exists along the interface joining the top and bottom layers. The current work extends the approach of previous studies to incorporate a grading of plastic properties between the two layers through parametric finite element modeling with ABAQUS. An elastic-plastic 2D model using 8-node biquadratic elements was used to map the plastic dissipation of a two layer specimen with a grading of plastic properties parallel to the crack face. This property …

Global Optimization Of An Aircraft Thermal Management System Through Use Of A Genetic Algorithm, Christopher T. Allen

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Optimization algorithms utilize known information about the system to identify solutions that are more efficient and meet the requirements of the user. The algorithms require an objective function, or formula (linear or nonlinear) that models what the user is looking to optimize, in order to begin the search for a more feasible solution. Because optimization problems can involve either linearor non-linear functions, various algorithms have been created that can locate optimum solutions faster depending on the type of objective function being optimized.

This research focuses on optimizing an aircrafts thermal management system by using one such algorithm. This was performed …

The Influence Of Thickness On The Complex Modulus Of Air Plasma Sprayed Ceramic Blend Coatings, Jason Edgar Hansel

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Previous research suggests that damping of metallic beams that have a hard ceramic coating applied on them is proportional to the coating thickness. This indicates that the damping is a volume dependent material property. Since thickness variations are likely in an actual application, it is essential to understand the role that coating thickness plays in damping effectiveness. For this research, a series of tests were conducted using substrate beams of 90 mil Ti-6Al-4V, coated with 3 mils of an air plasma sprayed NiCrAlY bond coat followed by a Titania-Alumina ceramic blend coating applied via air plasma spray in one of …

The Effect Of Variable Gravity On The Cooling Performance Of A 16-Nozzle Spray Array, Levi J. Elston

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The objective of this thesis was to investigate the cooling performance of a 16-nozzle spray array, using FC-72 as the working fluid, in variable gravity conditions with additional emphasis on fluid management and flow stability. A flight test experiment was modified to accommodate a 16-nozzle spray array, which was then tested in the parabolic flight trajectory environment of NASA's C-9 reduced gravity aircraft. The 16-nozzle array was designed to cool a 25.4 x 25.4 [mm] area on a thick film resistive heater used to simulate electronic components. Data was taken and reduced as a result of flight tests conducted over …

Computational And Experimental Investigations Into Aerospace Plasmas, William Thomas Bennett

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Investigations into two different fields of plasma research are presented here. These include the study of ion engine performance and the use of plasma discharges for flow control. In the area of ion engine performance, optimizing electron confinement is the primary goal of this work. The work of prior researchers was expanded through the study of the cathode emission location and the energy of the primary electrons. Cathode position was shown to have minimal effect on confinement length. For electron energy values greater than 20eV the effect on confinement length was also found to be very small. The strength of …