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Numerical Analysis of Initialization of a Nanosecond-Pulsed Dielectric Barrier Discharge Actuator

AIAA JOURNAL 2024年第10期62卷 3591-3603页

作者： Murzionak, Aliaksandr Mullane, Katrina Etele, J. Carleton Univ Dept Mech & Aerosp Engn Ottawa ON K1S 5B6 Canada

In this work a nanosecond-pulsed dielectric barrier discharge actuator is simulated to investigate the plasma and surface charge behavior during the startup phases of a given pulse sequence. A potential of plus/minus 1.2 kV is applied sinusoidally with a total pulse width of 100 ns over five full pulses. These results show that plasma development changes substantially between the first three pulses, where the distribution of free electrons resulting from the previous pulse influences the development of the plasma sheath and hence the downstream extent of the bulk plasma. Between the third and fifth pulses, a negative surface charge region persists at the downstream extent of the plasma, which generates an electron void, thus inhibiting the development of a strongly ionizing plasma sheath. These results show that by five pulses the plasma has reached its maximum extent and that for the purposes of establishing average values the first two pulses should not be considered representative of the longer-term plasma behavior.

关键词： Actuators Numerical Simulation Dielectric Barrier Discharge Electron Temperature Electric Field Strength Low Pressure Turbine Conservation of Momentum Equations Lumped Element Modeling High Speed Flows computing and informatics

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Leveraging Large Language Models for Tradespace Exploration

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JOURNAL OF SPACECRAFT AND ROCKETS 2024年第5期61卷 1165-1183页

作者： Apaza, Gabriel Selva, Daniel Texas A&M Univ College Stn TX 77843 USA Aerosp Engn Dept 710 Ross St College Stn TX USA

This paper proposes a method for leveraging large language models (LLMs) to improve the question-answering capabilities of artificial intelligence (AI) assistants for tradespace exploration. The method operates by querying an information space composed of fused data sources encompassing the tradespace exploration process and responding based on the gathered information. The information retrieval process is modeled as an internal dialog where an LLM-based dialog agent converses with a subquery answering agent. A case study is conducted on a next-generation soil moisture mission (SM-NG), and a generative AI assistant (named Daphne-G) is configured on it. The effect of the dialog agent and the choice of LLM are assessed by comparing the performance of three different system configurations on a validation question set. A second validation effort is conducted, comparing Daphne-G's responses to those of a baseline template-based AI assistant, Daphne-VA. Results show that the dialog-based system is necessary for answering complex questions requiring multiple documents. Furthermore, results show that Daphne-G can correctly answer all the questions Daphne-VA can answer, while simultaneously being able to answer a greater number of questions than Daphne-VA. The results suggest that LLMs could significantly improve the outcomes of the tradespace exploration process, which may result in better and more cost-effective mission concepts being implemented.

关键词： Natural Language Processing Attitude Determination and Control System Satellite Bus Tropical Rainfall Measuring Mission Renewable Energy Model Based System Engineering Synthetic Aperture Radar Sun Synchronous Orbit Data Products computing and informatics

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Fixed- and Free-Mode Flutter Derivatives During Aeroelastic Optimization

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AIAA JOURNAL 2024年第12期62卷 4645-4653页

作者： Stanford, Bret K. Thelen, Andrew S. Jacobson, Kevin E. NASA Langley Res Ctr Aeroelasticity Branch Res Aerosp Engineer Hampton VA 23681 USA

Aeroelastic flutter design derivatives may be approximated by ignoring the sensitivity of the structural mode shapes. This fixed-mode derivative is less expensive to compute than the exact free-mode derivative (which accommodates the mode shape dependency) but also may provide inaccurate sensitivities for optimization. This work formulates both fixed- and free-mode flutter derivatives and demonstrates the conditions under which they are equivalent. Two different types of fixed-mode derivatives are also developed in this work. Using a cantilevered-plate demonstration problem with both shape and sizing design parameters, the accuracy of the free-mode derivative and the two fixed-mode derivatives is demonstrated via gradient-based optimization.

关键词： High Aspect Ratio Finite Element Analysis Low Aspect Ratio Wings Structural Dynamics and Characterization Aerodynamic Force Aircraft Design Software Computational Fluid Dynamics Subsonic Flow Aircraft Wing Design computing and informatics

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Evaluation of Uncertainties of Pressure Gain Measurements in Rotating Detonation Combustor

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AIAA JOURNAL 2024年第1期62卷 108-126页

作者： Feleo, Alexander D. Gamba, Mirko Univ Michigan Dept Aerosp Engn Ann Arbor MI 48109 USA

Experimentally measuring the pressure gain of a rotating detonation combustor through the method of equivalent available pressure is prone to many experimental uncertainties. A detailed analysis of sources of random and systematic uncertainties in the thrust and pressure gain is performed using data from a hydrogen/air-operated rotating detonation combustor. The combustor had an axial air inlet and a 50% exit constriction. The measured (negative) pressure gain values agree with the results in the literature for similar inlet-to-exit area ratios. The base drag correction on the centerbody was found to be the greatest source of uncertainty for the thrust. While thrust is the predominant source of random uncertainty in the pressure gain calculation, significant systematic errors can be committed due to the assumed exit Mach number. The impact of this assumption becomes more detrimental the closer to positive the measured pressure gain is. By experimentally evaluating the exit Mach number, the random and systematic uncertainty in pressure gain both decreased, indicating that this should be an essential step. A definitive demonstration of gain is challenging, given the assessed uncertainties, and recommendations are provided to increase the precision of the equivalent available pressure methodology.

关键词： Rotating Detonation Combustor Choking Mach Number Equivalent Available Pressure Mass Flow Rate Combustion Efficiency Fluid Mechanics computing and informatics Pressure Transducers Detonation Waves Gas Constant

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Reachability Analysis for Atmospheric Reentry Vehicle

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2024年第1期47卷 133-142页

作者： Patel, Jinaykumar Subbarao, Kamesh Univ Texas Arlington Dept Mech & Aerosp Engn Arlington TX 76019 USA

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Decentralized Observation Allocation for a Large-Scale Constellation

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JOURNAL OF AEROSPACE INFORMATION SYSTEMS 2023年第8期20卷 447-461页

作者： Parjan, Shreya Chien, Steve A. CALTECH Jet Prop Lab Pasadena CA 91109 USA

Increased space sensing enables new measurements of a wide range of Earth science phenomena including volcanism, flooding, wildfires, and weather. Large-scale observation constellations of hundreds of assets have already been deployed (for example, Planet Labs's Dove satellites), and several constellations of tens of thousands of assets are planned. New challenges exist to rapidly assimilate available data and to optimize measurements by directing spacecraft assets to best observe complex Earth science phenomena. Centralized approaches to managing request allocation in these large constellations are constrained by 1) the need to assign/elect a central node to assign requests to spacecraft and 2) reliance on a single agent communicating with potentially thousands of dependent agents. On the other hand, entirely decentralized approaches to request allocation and observation are prone to oversatisfaction of some requests and undersatisfaction of others due to a lack of communication among agents. In large constellations, an intermediary method is necessary to solve the request allocation problem in a distributed manner. We present distributed artificial intelligence/multiagent methods that leverage existing work on distributed constraint optimization to allocate observations in a satellite constellation. We compare their performance to centralized and highly decentralized approaches using realistic orbits and observation request distributions. Our distributed algorithms can find approximate solutions to the large-scale constellation request allocation problem with low data volume for agent coordination and extend to continuous planning problems with varying request sets and availability of spacecraft agents.

关键词： Distributed Artificial Intelligence Algorithms and Data Structures computing and informatics Optimization Algorithm Satellite Remote Sensing Earth Observation Satellite Multi-Agent System

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Analytic Gradient Computation and Applications in Multitarget Multi-Impulse Trajectory Optimization

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2024年第2期47卷 347-357页

作者： Zhang, Nan Di, Wu Baoyin, Hexi Tsinghua Univ Sch Aerosp Engn Beijing 100084 Peoples R China

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Regional Constellation Reconfiguration Problem: Integer Linear Programming Formulation and Lagrangian Heuristic Method

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JOURNAL OF SPACECRAFT AND ROCKETS 2023年第6期60卷 1828-1845页

作者： Lee, Hang Woon Ho, Koki West Virginia Univ Dept Mech & Aerosp Engn Morgantown WV 26506 USA Georgia Inst Technol Daniel Guggenheim Sch Aerosp Engn Atlanta GA 30332 USA

A group of satellites, with either homogeneous or heterogeneous orbital characteristics and/or hardware specifications, can undertake a reconfiguration process due to variations in operations pertaining to Earth observation missions. This paper investigates the problem of optimizing a satellite constellation reconfiguration process against two competing mission objectives: 1) the maximization of the total coverage reward, and 2) the minimization of the total cost of the transfer. The decision variables for the reconfiguration process include the design of the new configuration and the assignment of satellites from one configuration to another. We present a novel biobjective integer linear programming formulation that combines constellation design and transfer problems. The formulation lends itself to the use of generic mixed-integer linear programming (MILP) methods such as the branch-and-bound algorithm for the computation of provably optimal solutions;however, these approaches become computationally prohibitive even for moderately sized instances. In response to this challenge, this paper proposes a Lagrangian relaxation-based heuristic method that leverages the assignment problem structure embedded in the problem. The results from the computational experiments attest to the near-optimality of the Lagrangian heuristic solutions and a significant improvement in the computational runtime as compared to a commercial MILP solver.

关键词： Satellite Constellations Earth Observation Mixed Integer Linear Programming Orbital Maneuvers computing and informatics Reconfiguration Lagrangian Relaxation

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Aeroacoustic Source Potential Based on Poisson's Equation

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AIAA JOURNAL 2024年第7期62卷 2772-2782页

作者： Schoder, Stefan Bagheri, Eman Spieser, Etienne Graz Univ Technol Inst Fundamentals & Theory Elect Engn IGTE Inffeldgasse 18 A-8010 Graz Austria Friedrich Alexander Univ Inst Fluid Mech LSTM D-91058 Erlangen Germany Friedrich Alexander Univ Inst Fluid Mech LSTM D-91058 Erlangen Germany Hong Kong Univ Sci & Technol Dept Mech & Aerosp Engn Clear Water Bay Hong Kong Peoples R China

Poisson's equation is an important equation to postprocess the aerodynamic fields into linearized momentum modes and was recently found to be important for the computation of an isotropic pressure-like source for scalar aeroacoustic wave models, like the aeroacoustic wave equation based on Pierce's operator (AWE-PO). Mathematically viable boundary conditions of the Poisson equation, which computes the AWE-PO source, are investigated. For the different source fields, the wave propagation is computed using the AWE-PO, and the details of the sound prediction results are compared to a reference direct numerical simulation of a mixing layer. The different boundary conditions of the Poisson equation were found to have a minor influence on the overall sound prediction characteristics of the AWE-PO equation. The AWE-PO is reformulated into a simplified version of the Phillips's equation, which mitigates the intermediate step of computing an isotropic source potential. By doing so, a previously obtained interference radiation valley in the radiated acoustic intensity of the AWE-PO results is attributed to a missing shear-noise source term.

关键词： Mathematical Analysis Computational Fluid Dynamics Aeroacoustics computing and informatics

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Rapid Determination of Low-Earth-Orbit Occultation-Event Windows

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2024年第5期47卷 979-985页

作者： Yang, Hongwei Zhang, Yu Li, Shuang Bai, Xiaoli Nanjing Univ Aeronaut & Astronaut Coll Astronaut Nanjing 211106 Peoples R China Rutgers State Univ Dept Mech & Aerosp Engn Piscataway NJ 08854 USA

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