Nondestructive testing (NDT) using ultrasound band 1-5 MHz, has been widely used for the early-stage detection of structural failure; however, it fails to detectf material degradation, fatigue, and microcracks. NDT with nonlinear ultrasound (NLU) can detect a microscopic discontinuity or imperfection that may be a source of the second harmonic in the reflected signal. In this research, we focus on creating a metamaterial band filter that filters out nonlinearities induced by the instrument itself. A 1D elastic superlattice (SL) acoustic filter is designed with a bandgap in its frequency spectrum that covers the frequency range of second harmonic. The SL is made of periodically alternating Cu and Sn-Pb solder layers. We conducted analytical and numerical calculations to obtain the appropriate thickness of each layer. The metamaterial in this study has the pass band for the fundamental frequency of 5 MHz and the first stop band centered near the frequency of 10 MHz; 5 MHz was chosen because the second harmonic at 10 MHz can detect 200μm micro-scale damage. Experiments with aluminum as the reference specimen and with SL filter were conducted. A function-generator generates 3 pulses sine signal, within the frequency range from 2.5 MHz to 20MHz. Spectral analysis of …

Sequential single-axis vibration testing strategies often produce over-testing when qualifying system hardware. Multi-axis excitation techniques can simulate realistic service environments, but the hardware and testing strategies needed to do so tend to be costly and complex. Test engineers instead must execute sequential tests on single-axis shaker tables to excite each degree of freedom, which the previous two decades of vibration testing literature have shown to cause extensive over-testing when considering cross-axis responses in assessing the severity of the applied test environments. Traditional assessments assume that the test article responds only in the axis of excitation, but often significant response occurs in the off-axes as well. This paper proposes a method to address the over-testing problem by approximating a simultaneous multi-axis test using readily-available, single-axis shaker tables. By optimizing the angle of excitation and the boundary condition through dynamic test fixture design, the test article can be tested using a Single-Input, Multiple-Output (SIMO) test in a way that approximates a Multiple-Input, Multiple-Output (MIMO) test. This paper shows the proposed method in simulation with a 2D finite element box assembly with removable component (BARC) model attached to springs with variable stiffness. The results include quantified test quality assessment metrics with comparison to …

In this research work, an innovative method for measurement of thermal conductivity of a small volume of liquids, microsphere, and the single cancer cell is demonstrated using a micro-pipette thermal sensor (MPTS). The method is based on laser point heating thermometry (LPHT) and transient heat transfer. When a single pulse of a laser beam heats the sensor tip which is in contact with the surrounding liquids or microsphere/cells, the temperature change in the sensor is reliant on the thermal properties of the surrounding sample. We developed a model for numerical analysis of the temperature change using the finite element method (FEM) in COMSOL. Then we used MATLAB to fit the simulation result with experiment data by multi-parameter fitting technique to determine the thermal conductivity. To verify the accuracy in the measurement of the thermal conductivity by the MPTS method, a 10µl sample of de-ionized (DI) water, 50%, and 70% propylene glycol solution were measured with deviation less than 2% from reported data. Also, to demonstrate that the method can be employed to measure microparticles and a single spherical cell, we measured the thermal conductivity of poly-ethylene microspheres with a deviation of less than 1% from published data. We estimated the …

While ozone design values have decreased since 2000, the values measured in Denton Airport South (DEN), an exurban region in the northwest tip of the Dallas-Fort Worth (DFW) metroplex, remains above those measured in Dallas Hinton (DAL) and Fort Worth Northwest (FWNW), two extremely urbanized regions; in addition, all three sites remained in nonattainment of National Ambient Air Quality Standards (NAAQS) ozone despite reductions in measured NOx and CO concentrations. The region's inability to achieve ozone attainment is tied to its concentration of total non-methane organic compounds (TNMOC). The mean concentration of TNMOC measured at DAL, FWNW, and DEN between 2000 and 2018 were 67.4 ± 1.51 ppb-C, 89.31 ± 2.12 ppb-C, and 220.69 ± 10.36 ppb-C, respectively. Despite being the least urbanized site of the three, the TNMOC concentration measured at DEN was over twice as large as those measured at the other two sites. A factor-based source apportionment analysis using positive matrix factorization technique showed that natural gas was a major contributing source factor to the measured TNMOC concentrations at all three sites and the dominant source factor at DEN. Natural gas accounted for 32%, 40%, and 69% of the measured TNMOC concentration at DAL, FWNW, and DEN, …

Waste-heat-to-power (WHP) recovers electrical power from exhaust heat emitted by industrial and commercial facilities. Waste heat is available in enormous quantities. The U.S. Department of Energy estimates 5-13 quadrillion BTUs/yr with a technical potential of 14.6 GW are available and could be utilized to generate power by converting the heat into electricity. The research proposed here will define a system that can economically recover energy from waste heat through a thermal regenerative electrochemical system. The primary motivation came from a patent and the research sponsored by the National Renewable Energy Laboratory (NREL). The proposed system improves on this patent in four major ways: by using air/oxygen, rather than hydrogen; by eliminating the cross diffusion of counter ions and using a dual membrane cell design; and by using high concentrations of electrolytes that have boiling points below water. Therefore, this system also works at difficult-to-recover low temperatures. Electrochemical power is estimated at 0.2W/cm2, and for a 4.2 M solution at 1 L/s, the power of a 100 kW system is 425 kW. Distillation energy costs are simulated and found to be 504 kJ/s for a 1 kg/s feed stream. The conversion efficiency is then calculated at 84%. The Carnot efficiency for …

Recent advances in manufacturing and growing concerns on the sustainability of aviation environment have led to a remarkable interest in electrical unmanned aerial systems (UASs) in the past decade. Among various UAS types, the newly designed quadrotor biplane tailsitter class is capable of delivering a wide range of civilian and military tasks, relying on its Vertical Take-Off and Landing (VTOL) capability as well as great maneuverability. Nevertheless, as such UASs employ rotors to generate thrust, and wings to generate lift, and operate at less-understood low to mid-Reynolds flow regime, they experience complicated flight aerodynamics with a noise generation mechanism which is different from common aircrafts. The present work aims at addressing this knowledge gap by studying the aerodynamics and aeroacoustics of a UAS of this type designed by the Army Research Lab. High-fidelity computational fluid dynamics (CFD) simulations are carried out for a wide range of operating conditions to understand the physics involved in the UAS aerodynamics and characterize its performance. Relying on the CFD results, a physics-informed reduced order model (ROM) is developed based on machine learning algorithms, to predict the propellers effects on the wings and calculate the dominant loads. The results of this study indicate that the …

An enhanced thermal imaging concept made possible through the development of a gradient-indexed metamaterial infrared detector that offers broadband transmission and reflection in THz waves. This thesis proposes a proof of feasibility for a metamaterial infrared detector containing an anti-reflective coating with various geometrically varying periodic metasurfaces, a gradient-indexed dielectric multilayer for near-perfect longpass filtering, and a gradient index of refraction (GRIN) metalens for enhanced focal plane thermal imaging. 2D Rigorous Coupled-Wave Analysis (RCWA) is used for understanding the photonic gratings performance based on material selection and varying geometric structure. Finite Difference Time Domain (FDTD) is used to characterize performance for a diffractive metalens by optimizing the radius and arrangement of cylindrical nanorods to create a desired phase profile that can achieve a desired focal distance for projections on a detector for near- to far-infrared thermal imaging. Through combining a micromachined anti-reflective coating, a near-perfect longpass filter, and metamaterial GRIN metalens, infrared/THz focal plane thermal imaging can obtain faster photo-response and image quality at targeted wavelengths, which allows for scientific advancements in electro-optical devices for the Department of Defense, aerospace, and biochemical detection applications.

This thesis is focused on understanding the correct method to simulate atomistic models to calculate coefficient of diffusion of water through the membrane. It also aims to fix the method previously used in molecular modelling in which the simulation results did not match the experimental results. These membranes will be used in air dehumidification systems. The four types of membranes namely, polyurethane, polyurethane with silica nano particles, polyurethane with silica nano particles and amine surface modifier, and polyurethane with silica nano particles and aniline surface modifier. These membranes were also simulated to understand the effects of temperatures and pressure using molecular dynamics. The software packages used are MAPS 4.3, Avogadro, EMC, OVITO, and LAMMPS. MAPS, Avogadro and EMC were used to model the membrane at an atomistic level while LAMMPS is used to simulate the model generated. OVITO is used to analyze the simulation visually. The movement of water vapor molecules were tracked through the membrane in the simulation and diffusion coefficient was calculated using Mean square displacement equation. To create a realistic model, silica was dispersed in the Polyurethane matrix, simulated under standard atmospheric conditions. These results will help in further optimizing the membrane for air dehumidification. This will …

Although the capability of computational fluid dynamics (CFD) in modeling ship hydrodynamics is well explored in many studies, they still have two main limitations. First, those studies ignore the effect of non-uniform shear current which exists in realistic situation. Second, the focus of most studies was laid more on the seakeeping/maneuvering performance and less attention was paid to survivability of ships due to extreme ship response events in waves, which are considered rare events but influential. In this thesis, we explore the capability of CFD in those two areas. In the first part of the thesis, the hydrodynamic performance of KCS in the presence of a non-uniform shear current is investigated for the first time using high-fidelity CFD simulations. Various shear current conditions with different directions were considered and results were compared with the ones with no shear current. The second part of the thesis focuses on study of rare events of ship responses by development of extreme response conditioning techniques to design the wave trail. Two conditioned techniques based on Gaussian and non-Gaussian processes are considered.

In this thesis, friction stir channeling (FSC) and its process parameters influence on geometry, surface quality and productivity are explored. The probe of the friction stir processing (FSP) tool used to perform these tests was a modified submerged bobbin tool made of MP 159 Co-Ni alloy. The body was made from H13 tool steel. To find the optimal channel conditions for a targeted range of process parameters, multiple 6061 aluminum samples were prepared with a U shape guide to test the effects of different spindle speeds and feed rates. Using a gantry-type computer numerical control (CNC) friction stir welding (FSW) machine, the aluminum coupons were subjected to calibration experiments, force control tests, and an increased production rate to test these effects. It was found through experimentation that the programmed feed rates, spindle speeds and forces produced by the machine had an impact on the channel geometry. It was determined from the force-controlled setup that 8.46 mm/s at 750 RPM was the best combination of results for the four conditions tested on a CNC friction stir processing-machine. It was then tested at 10.58 mm/s at 800 RPM, which had comparable results with the best combination of input parameters from the force-controlled …