Aerospace Engineering

Aerospace Engineering

ID

aere

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URI

https://dr.lib.iastate.edu/handle/20.500.12876/98928

Publication Search Results

Now showing 1 - 10 of 37

Publication

Dynamic subgrid-scale scalar-flux model based on the exact rate of production of turbulent fluxes

2020-11 , Bader, Shujaut H. , Durbin, Paul , Aerospace Engineering

A dynamic subgrid-scale (SGS) scalar-flux model, based on the exact rate of production of turbulent scalar fluxes, is proposed. The model is derived from an assumption that the pressure-scalar correlation in the equation for turbulent scalar flux is a vector that is approximately aligned with the scalar flux itself. The formulation then yields a tensor diffusivity which allows nonalignment of the SGS scalar fluxes with respect to the resolved scalar gradient. In contrast to eddy diffusivity models and to general gradient diffusion hypothesis models, for which the diffusivity tensor is symmetric, the present formulation produces an asymmetric diffusion tensor; for theoretical and experimental reasons, that tensor is known to be very asymmetric. The model contains a single coefficient, which is determined dynamically. The model is validated in fully developed turbulent channel flow and in separated and reattaching flow over a backstep.

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Publication

Quantitative matching of forensic evidence fragments utilizing 3D microscopy analysis of fracture surface replicas

2022-05 , Dawood, Bishoy , Llosa-Vite, Carlos , Thompson, Geoffrey Z. , Lograsso, Barbara K. , Claytor, Lauren K. , Vanderkolk, John , Meeker, William , Maitra, Ranjan , Bastawros, Ashraf , Aerospace Engineering , Statistics , Mechanical Engineering

Silicone casts are widely used by practitioners in the comparative analysis of forensic items. Fractured surfaces carry unique details that can provide accurate quantitative comparisons of forensic fragments. In this study, a statistical analysis comparison protocol was applied to a set of 3D topological images of fractured surface pairs and their replicas to provide confidence in the quantitative statistical comparison between fractured items and their silicone cast replicas. A set of 10 fractured stainless steel samples were fractured from the same metal rod under controlled conditions and were replicated using a standard forensic casting technique. Six 3D topological maps with 50% overlap were acquired for each fractured pair. Spectral analyses were utilized to identify the correlation between topological surface features at different length scales of the surface topology. We selected two frequency bands over the critical wavelength (greater than two-grain diameters) for statistical comparison. Our statistical model utilized a matrix-variate t-distribution that accounts for overlap between images to model match and non-match population densities. A decision rule identified the probability of matched and unmatched pairs of surfaces. The proposed methodology correctly classified the fractured steel surfaces and their replicas with a posterior probability of match exceeding 99.96%. Moreover, the replication technique shows potential in accurately replicating fracture surface topological details with a wavelength greater than 20 μm, which far exceeds the feature comparison range on most metallic alloy surfaces. Our framework establishes the basis and limits for forensic comparison of fractured articles and their replicas while providing a reliable fracture mechanics-based quantitative statistical forensic comparison.

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Publication

Real-Time Personalized Physiologically Based Stress Detection for Hazardous Operations

2023-03-08 , Finseth, Tor , Dorneich, Michael , Vardeman, Stephen , Keren, Nir , Franke, Warren , Industrial and Manufacturing Systems Engineering , Aerospace Engineering , Agricultural and Biosystems Engineering , Kinesiology , Virtual Reality Applications Center

When training for hazardous operations, real-time stress detection is an asset for optimizing task performance and reducing stress. Stress detection systems train a machine-learning model with physiological signals to classify stress levels of unseen data. Unfortunately, individual differences and the time-series nature of physiological signals limit the effectiveness of generalized models and hinder both post-hoc stress detection and real-time monitoring. This study evaluated a personalized stress detection system that selects a personalized subset of features for model training. The system was evaluated post-hoc for real-time deployment. Further, traditional classifiers were assessed for error caused by indirect approximations against a benchmark, optimal probability classifier (Approximate Bayes; ABayes). Healthy participants completed a task with three levels of stressors (low, medium, high), either a complex task in virtual reality (responding to spaceflight emergency fires, n =27) or a simple laboratory-based task (N-back, n =14). Heart rate, blood pressure, electrodermal activity, and respiration were assessed. Personalized features and window sizes were compared. Classification performance was compared for ABayes, support vector machine, decision tree, and random forest. The results demonstrate that a personalized model with time series intervals can classify three stress levels with higher accuracy than a generalized model. However, cross-validation and holdout performance varied for traditional classifiers vs. ABayes, suggesting error from indirect approximations. The selected features changed with window size and tasks, but found blood pressure was most prominent. The capability to account for individual difference is an advantage of personalized models and will likely have a growing presence in future detection systems.

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Publication

Nontrivial nanostructure, stress relaxation mechanisms, and crystallography for pressure-induced Si-I → Si-II phase transformation

2022-02-21 , Levitas, Valery , Levitas, Valery I. , Popov, Dmitry , Velisavljevic, Nenad , Aerospace Engineering , Mechanical Engineering , Ames Laboratory

Crystallographic theory based on energy minimization suggests austenite-twinned martensite interfaces with specific orientation, which are confirmed experimentally for various materials. Pressure-induced phase transformation (PT) from semiconducting Si-I to metallic Si-II, due to very large and anisotropic transformation strain, may challenge this theory. Here, unexpected nanostructure evolution during Si-I → Si-II PT is revealed by combining molecular dynamics (MD), crystallographic theory, generalized for strained crystals, and in situ real-time Laue X-ray diffraction (XRD). Twinned Si-II, consisting of two martensitic variants, and unexpected nanobands, consisting of alternating strongly deformed and rotated residual Si-I and third variant of Si-II, form {111} interface with Si-I and produce almost self-accommodated nanostructure despite the large transformation volumetric strain of −0.237. The interfacial bands arrest the {111} interfaces, leading to repeating nucleation-growth-arrest process and to growth by propagating {110} interface, which (as well as {111} interface) do not appear in traditional crystallographic theory.

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Publication

Impact and Influence of Cyber-Physical Systems Research on Autonomous Aerospace Systems

2023 , Bradley, Justin , Fleming, Cody , Rozier, Kristin Yvonne , Pritchett, Amy , Aerospace Engineering , Computer Science , Mathematics , Electrical and Computer Engineering , Virtual Reality Applications Center , Mechanical Engineering

Cyber-Physical Systems, as a discipline, is relatively new, appearing prominently between 2000-2010, but has rapidly made contributions in many disciplines. The aerospace industry has been a primary application domain for CPS from the beginning, with much focus on autonomous systems, particularly Unmanned Aircraft Systems. Aerospace systems provide an opportune, complex, safety-critical system on which to prove out CPS research, techniques, and strategies where robustness, agility, and provable performance guarantees are important. In this paper we survey and discuss the synthesis of core CPS research areas into four key areas of autonomous aerospace systems. We illuminate how these have been applied across aviation and space systems that interface with human operators and/or bystanders. We also discuss how computing and select CPS concepts more prominently applied in other applications could be applied in aerospace systems. Finally, we elaborate on existing shortcomings in cyber-physical aerospace systems and propose future avenues of exploration and application to pursue.

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Publication

On the occasion of the anniversary of Professor Vladimir An. Levin

2022-08-08 , Dell’Isola, Francesco , Levitas, Valery , Matveenko, Valery P. , Aerospace Engineering , Mechanical Engineering , Ames Laboratory

Vladimir An. Levin is a Distinguished Professor of the Department of Computational Mechanics at the Faculty of Mechanics and Mathematics at Lomonosov Moscow State University. He is an active, persistent, and productive scientist, who made significant contributions to both fundamental and applied continuum mechanics science.

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Publication

A finite-temperature coarse-grained atomistic approach for understanding the kink-controlled dynamics of micrometer-long dislocations in high-Peierls-barrier materials

2022-09-06 , Ji, Rigelesaiyin , Phan, Thanh , Chen, Youping , McDowell, David L. , Xiong, Liming , Aerospace Engineering

We present a phonon dynamics-based finite-temperature coarse-grained (FT-CG) atomistic approach for characterizing the kink-controlled dislocation dynamics in high-Peierls-barrier materials. The applicability of it is demonstrated through simulating the motion of a ~ 3 µm-long dislocation in a bcc iron sample containing ~ 230 million atoms. Cross-kink and debris are found on a µm-long dislocation at a lower stress than that on a nm-long dislocation. They are largely promoted by high-frequency/short-wavelength phonons. FT-CG is shown to be a first model of its kind that can predict the mobility of a µm-long dislocation without smearing out the atomic-level kink dynamics on it.

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Publication

Internal defect detection and characterization of samarium-cobalt sintered magnets by ultrasonic testing technique

2023-02-11 , Cui, Baozhi , Cui, Jun , Barnard, Daniel J. , Bond, Leonard , Aerospace Engineering , Critical Materials Institute , Ames Laboratory , Materials Science and Engineering , Center for Nondestructive Evaluation

Excessive quantities of samarium-cobalt (Sm-Co) magnet material are being scrapped needlessly due to a lack of understanding of inhomogeneity distribution and unacceptable internal defects. If there is a way to identify, locate, characterize and when needed separate the defective portions of magnet material, utilization can be increased and product quality improved. Further, the magnets’ magnetic and mechanical performance can be improved by reducing the occurrence of internal defects. This paper reports on a cost-effective and efficient nondestructive evaluation method based on an ultrasonic testing (UT) technique applied for detecting and characterizing internal defects in Sm-Co sintered magnets. Applying the UT technique will allow users to comprehensively analyze internal defects, such as inclusions, porosity, microcracks, and other structural irregularities, check for homogeneity and anomalous regions and give the locations of these internal anomalies and defects within the Sm-Co sintered magnets. The UT technique can also be applied to other rare-earth permanent magnets, such as sintered or die-upset neodymium-iron-boron (Nd-Fe-B) magnets. The UT technique can effectively guide quality control and acceptable product selection, in addition to optimizing the magnet alloy design and production processes. Thus, it can facilitate the improvement of magnet manufacturing efficiency and machinability, reduce scrap, prolong service life, increase the use of what would be post-production waste, and enhance product reuse and recycling at end-of-life disposition.

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Publication

Manipulating Stress Responses during Spaceflight Training with Virtual Stressors

2022-02-22 , Dorneich, Michael , Keren, Nir , Franke, Warren , Vardeman, Stephen , Vardeman, Stephen B. , Industrial and Manufacturing Systems Engineering , Aerospace Engineering , Statistics , Kinesiology , Agricultural and Biosystems Engineering , Virtual Reality Applications Center

Virtual reality (VR) provides the ability to simulate stressors to replicated real-world situations. It allows for the creation and validation of training, therapy, and stress countermeasures in a safe and controlled setting. However, there is still much unknown about the cognitive appraisal of stressors and underlying elements. More research is needed on the creation of stressors and to verify that stress levels can be effectively manipulated by the virtual environment. The objective of this study was to investigate and validate different VR stressor levels from existing emergency spaceflight procedures. Experts in spaceflight procedures and the human stress response helped design a VR spaceflight environment and emergency fire task procedure. A within-subject experiment evaluated three stressor levels. Forty healthy participants each completed three trials (low, medium, high stressor levels) in VR to locate and extinguish a fire on the International Space Station (VR-ISS). Since stress is a complex construct, physiological data (heart rate, heart rate variability, blood pressure, electrodermal activity) and self-assessment (workload, stress, anxiety) were collected for each stressor level. The results suggest that the environmental-based stressors can induce significantly different, distinguishable levels of stress in individuals

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Publication

Roadmap on Measurement Technologies for Next Generation Structural Health Monitoring Systems

2023-04-28 , Laflamme, Simon , Di Matteo, Alberto , Pirrotta, Antonina , Perry, Marcus , Fu, Yuguang , Li, Jian , Wang, Hao , Hoang, Tu , Glisic, Branko , Bond, Leonard , Shu, Yening , Loh, Kenneth J. , Wang, Yang , Ding, Siqi , Wang, Xinyue , Yu, Xun , Han, Baoguo , Goldfeld, Yiska , Ryu, Donghyeon , Napolitano, Rebecca , Moreu, Fernando , Giardina, Giorgia , Milillo, Pietro , Civil, Construction and Environmental Engineering , Aerospace Engineering

Structural Health Monitoring (SHM) is the automation of the condition assessment process of an engineered system. When applied to geometrically large components or structures, such as those found in civil and aerospace infrastructure and systems, a critical challenge is in designing the sensing solution that could yield actionable information. This is a difficult task to conduct cost-effectively, because of the large surfaces under consideration and the localized nature of typical defects and damages. There has been significant research efforts in empowering conventional measurement technologies for applications to SHM in order to improve performance of the condition assessment process. Yet, the field implementation of these SHM solutions is still in its infancy, attributable to various economic and technical challenges. The objective of this Roadmap publication is to discuss modern measurement technologies that were developed for SHM purposes, along with their associated challenges and opportunities, and to provide a path to research and development efforts that could yield impactful field applications.

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