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Turbine Cooling System with Energy Separation
No full textA method and system for cooling an engine and/or vehicle using energy separation is disclosed herein. An energy separation device is operable for separating a compressed gaseous coolant stream into a first relatively cooler coolant flow stream and a second relatively hotter coolant flow stream. The relative cooler coolant flow stream is directed to a first region requiring increased cooling and the relative hotter coolant flow stream is directed to a second region requiring lower cooling than the first region in the engine or vehicle
Magnetic Sensor Compensation Utilizing Factor Graph Estimation
Get PDFRecently, there has been significant interest in the ability to navigate without GPS using the magnetic anomaly field of the Earth (magnav). One of the key technical bottlenecks to achieving magnav is obtaining an accurate magnetic sensor calibration, taking into account own-ship and sensor effects. The Tolles-Lawson magnetic calibration method continues to be the industry standard and was developed when airborne magnetic survey aircraft were first employed over 70 years ago. In this paper, we present a magnetic calibration algorithm based on a factor graph optimization using inertial measurements as well as inputs from both a vector and scalar magnetometer. The factor graph is well suited for combining multiple sensor inputs; allowing accurate calibrations in the presence of large permanent moments and a time-varying external magnetic field, two problems that are difficult to solve with previous approaches. The ability to accurately calibrate a magnetic sensor in flight (i.e. with the presence of a large platform field and a varying Earth field due to movement) will allow greater flexibility in sensor mounting locations for magnetic anomaly navigation
Validating Multi-Resolution Aircraft Models with Probabilities of Agreement
No full textModeling and simulation capabilities help the Department of Defense to organize, train, education, equip, and employ current and future forces for the full range of operations. Within the military analytic domain, validation activities and the study of the appropriateness of modeling and simulation is a growing area of professional concern. In this article, a recent functional response validation metric, the probability-of-agreement validation metric, is detailed, which enables informed comparisons between military simulation models and the real-world systems or processes they emulate. The metric is the probability that the difference between functional responses at the same design point fall within a range deemed acceptable. The corresponding probability-of-agreement plot summarizes agreement transparently and directly across typical measured values while accounting for potentially complicated bias and variability structures. We demonstrate its applicability in the military analytic domain using a validation exercise involving the comparison of two multi-resolution, high-fidelity F-16 aircraft simulation models
Deep Selenium Donors in ZnGeP\u3csub\u3e2\u3c/sub\u3e Crystals: An Electron Paramagnetic Resonance Study of a Nonlinear Optical Material
Get PDFZinc germanium diphosphide (ZnGeP2) is a ternary semiconductor best known for its nonlinear optical properties. A primary application is optical parametric oscillators operating in the mid-infrared region. Controlled donor doping provides a method to minimize the acceptor-related absorption bands that limit the output power of these devices. In the present study, a ZnGeP2 crystal is doped with selenium during growth. Selenium substitutes for phosphorus and serves as a deep donor. Significant concentrations of native defects (zinc vacancies, germanium-on-zinc antisites, and phosphorous vacancies) are also present in the crystal. Electron paramagnetic resonance (EPR) is used to establish the atomic-level model for the neutral charge state of the selenium donor. The S = 1/2 signal from the neutral donors is produced at 6 K by illuminating with 633 nm light (electrons excited from doubly ionized Zn vacancies convert Se+p donors to Se0p donors). A g matrix, with principal values of 2.088, 2.203, and 1.904, is extracted from the angular dependence of the EPR spectrum. The principal-axis direction associated with the 1.904 principal value is close to a Se–Ge bond. This indicates an asymmetric distribution of unpaired spin density around the selenium ion and thus predicts the deep donor behavior
Residual Stress Generation in Additive Manufacturing of Complex Lattice Geometries
Get PDFResidual stresses developed during additive manufacturing (AM) can influence the mechanical performance of structural components in their intended applications. In this study, thermomechanical residual stress simulations of the laser powder bed fusion (LPBF) process are conducted for both simplified (plate and cube-shaped) geometries as well as five complex lattice geometries fabricated with Inconel 718. These simulations are conducted with the commercial software package Simufact Additive©, which uses a nonlinear finite element analysis and layer-by-layer averaging approach in determining residual stresses. To verify the efficacy of the Simufact Additive© simulations, numerical results for the plate and cube-shape geometries are analyzed for convergence and compared to experimental residual stress results available in the literature. Numerical residual stress results are subsequently compared for five complex lattice geometries. Results suggest that lattice geometry can play a significant role in the distribution and magnitude of residual stresses, which are significant in some applications
High Elevation Radiation Array (HERA) Detectors for Airborne Thunderstorm Investigations
No full textA high-energy atmospheric physics phenomenon, referred to as a terrestrial gamma ray flash (TGF), is associated with lightning and produces large bursts of energetic photon radiation. TGFs will be investigated using a suite of gamma-ray instruments designed and constructed to fly on ten United States Air Force (USAF) WC-130J Hurricane Hunter aircraft as part of an aircrew ionization study led by the Air Force Institute of Technology (AFIT) and the United States Air Force School of Aerospace Medicine (USAFSAM), in cooperation with the 53rd Weather Reconnaissance Squadron (WRS). Each instrument consists of one NaI and one plastic detector, a GPS timing device, and an instrument computer that performs data acquisition. High Elevation Radiation Array (HERA) detectors will be employed to maximize the chances of observing TGFs near their source and to gain a better understanding of their origin, mechanism, ubiquity, and to assess potential hazards posed to military and commercial aircrew and passengers. The HERA program, deployed on 10 separate Air Force aircraft over a multi-year campaign, will result in thousands of observational flight hours and be the largest concerted effort to date to observe TGFs in situ through aircraft observations. In this paper, we give an overview of the scientific goals of this campaign and how the HERA instruments have been designed to meet those goals. We include a detailed description of the HERA instrument, along with mass model and signal processing simulations
Monte Carlo Simulation of Spacecraft Breakup Events in Low Lunar Orbit
No full textMonte Carlo simulations of spacecraft breakup events in Low Lunar Orbit are conducted to study the behavior of artificial debris across all orbit types in this environment. 2000 breakup events at random initial states in lunar orbit are simulated, and the resulting nearly 500,000 particles are propagated for five years using a high-fidelity lunar trajectory model. Debris from a smaller sample of 200 breakup events is also propagated for ten years. Trends in the rate of decay of debris from lunar orbit are analyzed to investigate the longevity of debris in lunar orbit, and the locations of lunar surface impacts are plotted to determine if some regions of the Moon would be at greater risk than others from an orbital breakup event. Across all orbits, about 38% of the debris remained in lunar orbit after five years, and the longevity of debris was found to depend significantly on the pre-breakup perilune and inclination. Debris generally remained in lunar orbit for less time as the pre-breakup perilune decreased, although an average of 19% the debris remained in lunar orbit after five years even for pre-breakup perilune altitudes below 50 km. Debris was also found to be highly unstable in certain inclinations. The rates of decay across all orbit types tended to slow greatly after two years, suggesting that a portion of the debris can often remain in lunar orbit for at least a decade. Finally, clusters of lunar surface debris impacts were identified, which could have applications for lunar satellite disposal after mission completion. The results of this study provide novel insights into the consequences of lunar breakup events, helping support the development of debris mitigation recommendations for lunar orbit as international interest in exploration of the Moon grows
Twisted Vortex Gaussian Schell-model Beams, Generalized ABCD Systems, and Multidimensional Hermite Polynomials
No full textWe derive the cross-spectral density (CSD) function for a twisted vortex partially coherent beam at the output of a general ABCD system in terms of multidimensional Hermite polynomials (MDHPs). MDHPs offer notational and computational advantages over prior CSD function representations that use common (one-dimensional) Hermite polynomials. We explain how to compute MDHPs using the recurrence relation given in the literature and include MATLAB code to generate MDHPs of any order. Lastly, we validate our work experimentally by comparing the measured spectral density of a twisted vortex beam at the output of an asymmetric optical system to predictions from our theoretical CSD function
A Stochastic Drag Model for Improved Uncertainty Realism of Select LEO Orbit Predictions
No full textThe Dimension of an orbitope based on a solution to the Legendre pair problem
No full textThe Legendre pair problem is a particular case of a rank-1 semidefinite description problem that seeks to find a pair of vectors (u,v) each of length ℓ such that the vector (u⊤,v⊤)⊤ satisfies the rank-1 semidefinite description. The group (Zℓ×Zℓ)⋊Z×ℓ acts on the solutions satisfying the rank-1 semidefinite description by ((i,j),k)(u,v)=((i,k)u,(j,k)v) for each ((i,j),k)∈(Zℓ×Zℓ)⋊Z×ℓ. By applying the methods based on representation theory in Bulutoglu [Discrete Optim. 45 (2022)], and results in Ingleton [Journal of the London Mathematical Society s(1-31) (1956), 445-460] and Lam and Leung [Journal of Algebra 224 (2000), 91-109], for a given solution (u⊤,v⊤)⊤ satisfying the rank-1 semidefinite description, we show that the dimension of the convex hull of the orbit of u under the action of Zℓ or Zℓ⋊Z×ℓ is ℓ−1 provided that ℓ=pn or ℓ=pqi for i=1,2, any positive integer n, and any two odd primes p,q. Our results lead to the conjecture that this dimension is ℓ−1 in both cases. We also show that the dimension of the convex hull of all feasible points of the Legendre pair problem of length ℓ is 2ℓ−2 provided that it has at least one feasible point