<p> This study contributes to a better understanding of ignition by hot combustion gases which finds application in internal combustion chambers with pre-chamber ignition as well as in wave rotor engine applications. The experimental apparatus consists of two combustion chambers: a pre chamber that generates the transient hot jet of gas and a main chamber which contains the main fuel air blend under study. Variables considered are three fuel mixtures (Hydrogen, Methane, 50% Hydrogen-Methane), initial pressure in the pre-chamber ranging from 1 to 2 atm, equivalence ratio of the fuel air mixture in the main combustion chamber ranging from 0.4 to 1.5, and initial temperature of the main combustion chamber mixture ranging from 297 K to 500 K. Experimental data makes use of 4 pressure sensors with a recorded sampling rate up to 300 kHz, as well as high speed Schlieren imaging with a recorded frame rate up to 20,833 frame per seconds. Results shows an overall increase in ignition delay with increasing equivalence ratio. High temperature of the main chamber blend was found not to affect hot jet ignition delay considerably. Physical mixing effects, and density of the main chamber mixture have a greater effect on hot jet ignition delay</p><p>

<p> Material testing is a major concern in many manufacturing and aeronautical industries, where structures require periodic inspection using equipment and manpower. Environmental Noise (EN) is the major concern when localizing the damage in real time. Inspecting underlying components involves destructive approaches. These factors can be alleviated using Non Destructive Testing (NDT) and a cost effective embedded sensor system. </p><p> This project involves NDT implementation of Structural Health Monitoring (SHM) with filtering techniques in real time. A spectrogram and a scalogram are used to analyze lamb response from an embedded array of Piezo Transducers (PZT). This project gives insights on implementing a real time SHM system with a sensor placement strategy and addresses two main problems, namely filtering and damage localization. An Adaptive Correlated Noise Filter (ACNF) removes EN from the lamb response of a structure. A damage map is developed using Short Time Fourier Transform (STFT), and Continuous Wavelet Analysis (CWA). </p>

abstract: Communications between air traffic controllers and pilots are critical to national airspace traffic management. Measuring communications in real time made by pilots and air traffic controllers has the potential to predict human error. In this thesis a measure for Deviations from Closed Loop Communications is defined and tested to predict a human error event, Loss of Separation (LOS). Six retired air traffic controllers were recruited and tested in three conditions of varying workload in an Terminal Radar Approach Control Facility (TRACON) arrival radar simulation. Communication transcripts from simulated trials were transcribed and coding schemes for Closed Loop Communication Deviations (CLCD) were applied. Results of the study demonstrated a positive correlation between CLCD and LOS, indicating that CLCD could be a variable used to predict LOS. However, more research is required to determine if CLCD can be used to predict LOS independent of other predictor variables, and if CLCD can be used in a model that considers many different predictor variables to predict LOS. / Dissertation/Thesis / Masters Thesis Human Systems Engineering 2020

<div>Here, we explore methods of counter autonomy defense for aerial autonomous multi-agent systems. First, the case is made for vast capabilities made possible by these systems. Recognizing that widespread use is likely on the horizon, we assert that it will be necessary for system designers to give appropriate attention to the security and vulnerabilities of such systems. We propose a method of learning-based resilient control for the multi-agent formation tracking problem, which uses reinforcement learning and neural networks to attenuate adversarial inputs and ensure proper operation. We also devise a learning-based method of cyber-physical attack detection for UAVs, which requires no formal system dynamics model yet learns to recognize abnormal behavior. We also utilize similar techniques for time signal analysis to achieve epileptic seizure prediction. Finally, a blockchain-based method for network security in the presence of Byzantine agents is explored.</div>

By utilizing passive and active methods of flow control, the aerodynamic performance of external and internal components can be greatly improved. Recently however, the benefits of applying active flow control methods to turbomachinery components for improved fuel efficiency, reduced engine size, and greater operational envelope has sparked a renewed interest in some of these flow control techniques. The more attractive of these, is active control in the form of jets in cross flow. With their ability to be turned on and off, as well as their negligible effect on drag when not being actuated, they are well suited for applications such as compressor and turbine blades, engine inlet diffusers, internal engine passages, and general external aerodynamics. This study consists of two parts. The first is the application of active control on a low-pressure turbine (LPT) cascade to determine the effectiveness of microjet actuators on flow separation at relatively low speeds. The second study, motivated by the first, involves a parametric study on a more canonical model to examine the effects of various microjet parameters on the efficacy of separation control and to provide a better understanding of the relevant flow physics governing this control approach. With data obtained from velocity measurements across the wide parametric range, correlations for the growth of the counter-rotating vortex pairs generated by these actuators are deduced. From the information and models obtained throughout the study, basic suggestions for microjet actuator design are presented. / A Dissertation submitted to the Department Mechanical Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Fall Semester, 2014. / July 24, 2014. / Flow Control, Jets in Crossflow, Microjets, Separation Control, Turbomachinery, Vortex Generator Jets / Includes bibliographical references. / Farrukh S. Alvi, Professor Directing Dissertation; Jianping Zheng, University Representative; Kunihiko Taira, Committee Member; Rajan Kumar, Committee Member; Emmanuel Collins, Committee Member.

Asymmetric jets are becoming more prevalent and may offer significant advantages over traditional axisymmetric nozzles for propulsion as well as fluidic mixing applications. The purpose of this work is two fold: 1) to investigate the effect nozzle exit geometry has on jet development and far field radiated noise of M = 0:9 jets and 2) to study the effect various levels of screech tone self excitation has on jet evolution and the production of streamwise vorticity. Three converging nozzles of various exit geometry (rectangular, elliptic, and round) were utilized to perform the first study, while a supersonic rectangular nozzle was employed to complete the second. All asymmetric nozzles in this work had an aspect ratio of 4:1. To study the flow field features, two dimensional streamwise particle image velocimetry (PIV) as well as three component PIV at select cross planes was performed. Far field acoustic measurements were acquired for the converging nozzles to determine the differences exhibited in the radiated exhaust noise from the major and minor axes of the asymmetric jets compared to the round jet. In comparing the effect exit geometry has on the development of a M = 0:9 jet, it was determined that the shear layers in the major and minor axes developed at similar rates, however, the jet half width in the minor axis exhibited a larger growth rate than the major axis. It was also determined that neither of the asymmetric sonic jets exhibited the axis-switching phenomenon within the measurement domain. Significant streamwise vorticity is noted on the low speed side of the shear layer for the asymmetric jets in the corner regions and areas of small curvature. Moreover, this streamwise vorticity was observed to significantly effect the jet half width in the major axis of the elliptic jet. Acoustic results reveal that there is a strong dependence on frequency range concerning the amount of energy propagated to the far field for each different jet and axis. At low frequencies, the round jet is louder than both axes of the asymmetric jets at polar angles larger than 110°. As the investigated range of frequencies is increased, the primary direction of propagation of noise shifts towards sideline angles for all jets and axes. At the highest range of frequencies investigated, the minor axis of the asymmetric jets produced more noise compared to the equivalent round jet while considerably less noise is produced at polar angles of about 120° – 130° in the major axis direction. Overall sound pressure levels (OASPL) show that the OASPL from the rectangular jet in the plane containing the major axis is lower than the equivalent round jet for aft quadrant angles; the main contributor to the overall reduction is from the highest frequency components. In order to determine the impact screech tone amplitude has on jet development, flow field characteristics of a moderate aspect ratio supersonic rectangular jet were examined at two overexpanded, a perfectly expanded, and an underexpanded jet conditions. The underexpanded and one overexpanded operating condition were of maximum screech, while the second overexpanded condition was of minimum screech intensity. The results show that streamwise vortices present at the nozzle corners along with vortices excited by screech tones play a major role in the jet evolution. The location of streamwise vortex amplification in cases of screech is strongly tied to the downstream shock cell number and the traditional source of the screech tone. All cases except for the perfectly expanded operating condition exhibited axis switching at streamwise locations ranging from 11 to 16 nozzle heights, h, downstream of the exit. The overexpanded condition of maximum screech showed the most upstream switch over, while the underexpanded case showed the farthest downstream. Both of the maximum screeching cases developed into a diamond cross sectional profile far downstream of the exit, while the ideally expanded case maintained a rectangular shape. The overexpanded minimum screeching case eventually decayed into an oblong profile. / A Thesis submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Master of Science. / Spring Semester 2016. / March 30, 2016. / Asymmetric Jets, Jet Noise, Mixing Enhancement, Particle Image Velocimetry / Includes bibliographical references. / Rajan Kumar, Professor Directing Thesis; Farrukh Alvi, Committee Member; Shangchao Lin, Committee Member.

In response to the increasing demand for jet noise studies performed at realistic conditions, the Florida Center For Advanced Aero-Propulsion at Florida State University has recently brought online an upgraded Anechoic High-Temperature Jet Facility. The function of this facility is to accurately simulate and characterize the aeroacoustic properties of exhaust from jet engines at realistic temperatures and flow speeds. This new addition is a blow-down facility supplied by a 3500 kPa, 114 cubic meter compressed dry air system and a sudden-expansion ethylene burner that is capable of producing ideally expanded jets up to Mach 2.6 and stagnation temperatures up to 1500 K. The jet exhausts into a fully anechoic chamber which is equipped to acquire acoustic and flow measurements including the temperature and pressure of the jet. The facility is capable of operating under free jet as well as in various impinging jet configurations pertinent to sea- and land-based aircraft, such as the F-35B. Compared to the original facility, the updated rig is capable of longer run times at higher temperatures. In this paper we demonstrate the facility's experimental capabilities and document jet aeroacoustic characteristics at various flow and temperature conditions. The anechoic chamber was characterized using ISO (3745:2003) guidelines and the lower cutoff frequency of the chamber was determined to be 315 Hz. Aeroacoustic properties of jets operating at subsonic conditions and supersonic Mach numbers ranging from 1.2 to 2.1 at temperatures of ~300 K to ~1300 K are documented. Where available, very good agreement was found when the present results were compared with data in the jet noise literature. / A Thesis submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Master of Science. / Fall Semester 2016. / November 11, 2016. / Acoustics, aerospace, Engineering, Facility Validation, FCAAP, Supersonic / Includes bibliographical references. / Farrukh Alvi, Professor Directing Thesis; Rajan Kumar, Committee Member; Emmanuel Collins, Committee Member.

No description available.

Vibration causes problems in many kinds of machinery including fighter aircraft. It can, for example, cause structural fatigue, malfunction in equipment and injuries to humans. The sources of vibration are engines, flow disturbance and separation of external loads, to mention some. To isolate sensitive equipment from the source of vibration it is common to use vibration isolators made of rubber. This master’s thesis is performed at Saab Aeronautics in Linköping at the Department of Environmental Engineering &amp; Thermal Analysis. The subject of the master’s thesis is to develop a methodology for the analysis of vibration isolating systems in aircraft. The work is performed by finite element analysis and laboratory tests using a shaker table. In the finite element analysis, part of the study, a method to condensate the structure to decrease the number of degrees of freedom is studied and used. Nonlinearities are investigated but only linear characteristics are implemented into the f inite element model. Rubber as a material has several non-linear characteristics that depend on the amplitude and frequency of the vibration. For example, the stiffness and damping are amplitude dependent. From laboratory results from tests on a shaker table, the stiffness and damping of the vibration isolators are extracted. To do this, the frequency transfer function is used by identifying eigenmodes and the eigenfrequency to calculate the stiffness and extract the damping by studying the shape of the peak. A finite element model with a condensed structure is used to find the eigenmodes and the eigenfrequencies. By exciting the finite element model the frequency response is also calculated. The tested vibration isolator shows large non-linearity for the stiffness and damping when varying the amplitude of a sinusoidal vibration. Using a condensed structure in finite element is a powerful tool to reduce computational time. If the solution of a simulation or calculation has to be very accurate or if the amplitudes of the vibration vary a lot, the non-linearities must be implemented into the simulation or calculation and accounted for.

This work aims to identify the key flow parameters that influence flame acceleration in a semi-confined square channel. A transverse fluidic jet was used as an active flow blockage mechanism and to introduce turbulence into the propagating flame. Three experimental parameters were used to examine the relative influence of (1) mixture reactivity defined here as system equivalence ratio (SER), (2) jet mixture composition (JMC), and the momentum ratio (MR) on the acceleration of laminar premixed methane flame. High-speed PIV and schlieren photography were utilized to characterize the instantaneous flow-field conditions throughout the flame-jet interaction. Using these diagnostic techniques, flame front positions and local velocity vector fields have been spatially and temporally resolved. Changes in flame properties including flame structure, velocity, and vorticity were tracked as a function of time. Stoichiometric equivalence ratios were more effective in the production of vorticity and the promotion of flame acceleration. The stoichiometric condition accelerated the flame to the highest final flame velocity of the three parameters examined. Different compositions of the jet mixture demonstrated that the flame acceleration is primarily affected by the jet turbulence and not on the reactivity of the jet compositions. Out of the three parameters examined, the momentum ratio parameter had the least amount of influence on the flow field and flame acceleration. The increase of 33 % in the momentum ratio had negligible effect in the final flame front velocity and implies that the jet turbulence is the main driving mechanism for flame acceleration.