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2019

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Aerospace Engineering Publications

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Highly Reactive Energetic Films By Pre-Stressing Nano-Aluminum Particles, Michael N. Bello, Alan M. Williams, Valery I. Levitas, Nobumichi Tamura, Daniel K. Unruh, Juliusz Warzywoda, Michelle L. Pantoya Dec 2019

Highly Reactive Energetic Films By Pre-Stressing Nano-Aluminum Particles, Michael N. Bello, Alan M. Williams, Valery I. Levitas, Nobumichi Tamura, Daniel K. Unruh, Juliusz Warzywoda, Michelle L. Pantoya

Aerospace Engineering Publications

Energetic films were synthesized using stress altered nano-aluminum particles (nAl). The nAl powder was pre-stressed to examine how modified mechanical properties of the fuel particles influenced film reactivity. Pre-stressing conditions varied by quenching rate. Slow and rapid quenching rates induced elevated dilatational strain within the nAl particles that was measured using synchrotron X-ray diffraction (XRD). An analytical model for stress and strain in a nAl core–Al2O3 shell particle that includes creep in the shell and delamination at the core–shell boundary, was developed and used for interpretation of strain measurements. Results show rapid quenching induced 81% delamination at the ...


Designing Wind Turbine Rotor Blades To Enhance Energy Capture In Turbine Arrays, Benham Moghadassian, Anupam Sharma Nov 2019

Designing Wind Turbine Rotor Blades To Enhance Energy Capture In Turbine Arrays, Benham Moghadassian, Anupam Sharma

Aerospace Engineering Publications

An inverse design approach is proposed to compute wind turbine blade geometries which maximize the aggregate power output from a wind farm. An iterative inverse algorithm is used to solve the optimization problem. The algorithm seeks to minimize the target function, f = -CP,av, where CP,av is the average normalized mechanical power of all the turbines in the wind farm. An upper bound on the blade planform area, representative of the blade weight, is imposed to demonstrate how to incorporate constraints in the design process. The power coefficients (CP) of the turbines in the farm are ...


Algorithmic Aspects And Finite Element Solutions For Advanced Phase Field Approach To Martensitic Phase Transformation Under Large Strains, Hamed Babaei, Anup Basak, Valery I. Levitas Oct 2019

Algorithmic Aspects And Finite Element Solutions For Advanced Phase Field Approach To Martensitic Phase Transformation Under Large Strains, Hamed Babaei, Anup Basak, Valery I. Levitas

Aerospace Engineering Publications

A new problem formulation and numerical algorithm for an advanced phase-field approach (PFA) to martensitic phase transformation (PT) are presented. Finite elastic and transformational strains are considered using a fully geometrically-nonlinear formulation, which includes different anisotropic elastic properties of phases. The requirements for the thermodynamic potentials and transformation deformation gradient tensor are advanced to reproduce crystal lattice instability conditions under a general stress tensor obtained by molecular dynamics (MD) simulations. The PFA parameters are calibrated, in particular, based on the results of MD simulations for PTs between semiconducting Si I and metallic Si II phases under complex action of all ...


Tensorial Stress−Strain Fields And Large Elastoplasticity As Well As Friction In Diamond Anvil Cell Up To 400 Gpa, Valery I. Levitas, Mehdi Kamrani, Biao Feng Oct 2019

Tensorial Stress−Strain Fields And Large Elastoplasticity As Well As Friction In Diamond Anvil Cell Up To 400 Gpa, Valery I. Levitas, Mehdi Kamrani, Biao Feng

Aerospace Engineering Publications

Various phenomena (fracture, phase transformations, and chemical reactions) studied under extreme pressures in diamond anvil cell are strongly affected by fields of all components of stress and plastic strain tensors. However, they could not be measured. Here, we suggest a coupled experimental−theoretical−computational approach that allowed us (using published experimental data) to refine, calibrate, and verify models for elastoplastic behavior and contact friction for tungsten (W) and diamond up to 400 GPa and reconstruct fields of all components of stress and large plastic strain tensors in W and diamond. Despite the generally accepted strain-induced anisotropy, strain hardening, and path-dependent ...


Satisfiability Checking For Mission-Time Ltl, Jianwen Li, Moshe Y. Vardi, Kristin Y. Rozier Jul 2019

Satisfiability Checking For Mission-Time Ltl, Jianwen Li, Moshe Y. Vardi, Kristin Y. Rozier

Aerospace Engineering Publications

Mission-time LTL (MLTL) is a bounded variant of MTL over naturals designed to generically specify requirements for mission-based system operation common to aircraft, spacecraft, vehicles, and robots. Despite the utility of MLTL as a specification logic, major gaps remain in analyzing MLTL, e.g., for specification debugging or model checking, centering on the absence of any complete MLTL satisfiability checker. We prove that the MLTL satisfiability checking problem is NEXPTIME-complete and that satisfiability checking MLTL0 , the variant of MLTL where all intervals start at 0, is PSPACE-complete. We introduce translations for MLTL-to-LTL, MLTL-to-LTLf , MLTL-to-SMV, and MLTL-to-SMT, creating four ...


Numerical Investigation Of The Effect Of Airfoil Thickness On Onset Of Dynamic Stall, Anupam Sharma, Miguel Visbal Jul 2019

Numerical Investigation Of The Effect Of Airfoil Thickness On Onset Of Dynamic Stall, Anupam Sharma, Miguel Visbal

Aerospace Engineering Publications

Effect of airfoil thickness on onset of dynamic stall is investigated using large eddy simulations at chord-based Reynolds number of 200 000. Four symmetric NACA airfoils of thickness-to-chord ratios of 9 %, 12 %, 15 % and 18 % are studied. The three-dimensional Navier–Stokes solver, FDL3DI is used with a sixth-order compact finite difference scheme for spatial discretization, second-order implicit time integration and discriminating filters to remove unresolved wavenumbers. A constant-rate pitch-up manoeuver is studied with the pitching axis located at the airfoil quarter chord. Simulations are performed in two steps. In the first step, the airfoil is kept static at a prescribed ...


Large-Eddy Simulation Of Turbulent Flow Over A Parametric Set Of Bumps, Racheet Matai, Paul A. Durbin May 2019

Large-Eddy Simulation Of Turbulent Flow Over A Parametric Set Of Bumps, Racheet Matai, Paul A. Durbin

Aerospace Engineering Publications

Turbulent flow over a series of increasingly high, two-dimensional bumps is studied by well-resolved large-eddy simulation. The mean flow and Reynolds stresses for the lowest bump are in good agreement with experimental data. The flow encounters a favourable pressure gradient over the windward side of the bump, but does not relaminarize, as is evident from near-wall fluctuations. A patch of high turbulent kinetic energy forms in the lee of the bump and extends into the wake. It originates near the surface, before flow separation, and has a significant influence on flow development. The highest bumps create a small separation bubble ...


A Methodology For Sorting Haploid And Diploid Corn Seed Using Terahertz Time Domain Spectroscopy And Machine Learning, Jared Taylor, Chien-Ping Chou, Leonard J. Bond May 2019

A Methodology For Sorting Haploid And Diploid Corn Seed Using Terahertz Time Domain Spectroscopy And Machine Learning, Jared Taylor, Chien-Ping Chou, Leonard J. Bond

Aerospace Engineering Publications

The ability of terahertz (THz) electromagnetic waves to penetrate a wide range of materials gives potential for diverse applications in nondestructive evaluation, biomed, and agriculture and there has been rapid expanding both in its use. One possible application is in relation to corn breeding, specifically when the doubled haploid method is used as a process that greatly speeds up plant breeding, and this requires seed sorting. Haploid kernels are induced in corn plants in order to decrease the time to reach homozygous genetic corn lines. These haploid kernels must be separated from the surrounding diploid kernels; presently this is labor ...


Nde In-Process For Metal Parts Fabricated Using Powder Based Additive Manufacturing, Leonard J. Bond, Lucas W. Koester, Hossein Taheri Mar 2019

Nde In-Process For Metal Parts Fabricated Using Powder Based Additive Manufacturing, Leonard J. Bond, Lucas W. Koester, Hossein Taheri

Aerospace Engineering Publications

Ensuring adequate quality for additive manufactured (AM) materials presents unique metrology challenges to the on-line process measurement and nondestructive evaluation (NDE) communities. AM parts now have complex forms that are not possible using subtractive manufacturing and there are moves for their use in safety criticality components. This paper briefly reviews the status, challenges and metrology opportunities throughout the AM process from powder to finished parts. The primary focus is on new acoustic signatures that have been demonstrated to correlate process parameters with on-line measurement for monitoring and characterization during the build. In-process, quantitative characterization and monitoring of material state is ...


Slip Of Shuffle Screw Dislocations Through Tilt Grain Boundaries In Silicon, Hao Chen, Valery Levitas, Liming Xiong Feb 2019

Slip Of Shuffle Screw Dislocations Through Tilt Grain Boundaries In Silicon, Hao Chen, Valery Levitas, Liming Xiong

Aerospace Engineering Publications

In this paper, molecular dynamics (MD) simulations of the interaction between tilt grain boundaries (GBs) and a shuffle screw dislocation in silicon are performed. Results show that dislocations transmit into the neighboring grain for all GBs in silicon. For Σ3, Σ9 and Σ19 GBs, when a dislocation interacts with a heptagon site, it transmits the GB directly. In contrast, when interacting with a pentagon site, it first cross slips to a plane on the heptagon site and then transmits the GB. The energy barrier is also quantified using the climbing image nudged elastic band (CINEB) method. Results show that Σ3 ...


Kinetics Of The Γ–Δ Phase Transition In Energetic Nitramine-Octahydro-1,3,5,7-Tetranitro-1,3,5,7-Tetrazocine, P. Bowlan, B. F. Henson, L. Smilowitz, Valery I. Levitas, N. Suvorova, D. Oschwald Jan 2019

Kinetics Of The Γ–Δ Phase Transition In Energetic Nitramine-Octahydro-1,3,5,7-Tetranitro-1,3,5,7-Tetrazocine, P. Bowlan, B. F. Henson, L. Smilowitz, Valery I. Levitas, N. Suvorova, D. Oschwald

Aerospace Engineering Publications

The solid, secondary explosive nitramine-octahydro-1,3,5,7-tetranitro-1,3,5,7 or HMX has four different stable polymorphs which have different molecular conformations, crystalline structures, and densities, making structural phase transitions between these nontrivial. Previous studies of the kinetics of the βδ HMX structural transition found this to happen by a nucleation and growth mechanism, where growth was governed by the heat of fusion, or melting, even though the phase transition temperature is more than 100 K below the melting point. A theory known as virtual melting could easily justify this since the large volume difference in the two ...


High-Pressure Phase Transformations Under Severe Plastic Deformation By Torsion In Rotational Anvils, Valery I. Levitas Jan 2019

High-Pressure Phase Transformations Under Severe Plastic Deformation By Torsion In Rotational Anvils, Valery I. Levitas

Aerospace Engineering Publications

Numerous experiments have documented that combination of severe plastic deformation and high mean pressure during high-pressure torsion in rotational metallic, ceramic, or diamond anvils produces various important mechanochemical effects. We will focus here on four of these: plastic deformation (a) significantly reduces pressure for initiation and completion of phase transformations (PTs), (b) leads to discovery of hidden metastable phases and compounds, (c) reduces PT pressure hysteresis, and (d) substitutes a reversible PT with irreversible PT. The goal of this review is to summarize our current understanding of the underlying phenomena based on multiscale atomistic and continuum theories and computational modeling ...


Classification With The Matrix-Variate-T Distribution, Geoffrey Z. Thompson, Ranjan Maitra, William Q. Meeker, Ashraf Bastawros Jan 2019

Classification With The Matrix-Variate-T Distribution, Geoffrey Z. Thompson, Ranjan Maitra, William Q. Meeker, Ashraf Bastawros

Aerospace Engineering Publications

Matrix-variate distributions can intuitively model the dependence structure of matrix-valued observations that arise in applications with multivariate time series, spatio-temporal or repeated measures. This paper develops an Expectation-Maximization algorithm for discriminant analysis and classification with matrix-variate t-distributions. The methodology shows promise on simulated datasets or when applied to the forensic matching of fractured surfaces or the classification of functional Magnetic Resonance, satellite or hand gestures images.


Intersection And Rotation Of Assumption Literals Boosts Bug-Finding, Rohit Dureja, Jianwen Li, Geguang Pu, Moshe Y. Vardi, Kristin Yvonne Rozier Jan 2019

Intersection And Rotation Of Assumption Literals Boosts Bug-Finding, Rohit Dureja, Jianwen Li, Geguang Pu, Moshe Y. Vardi, Kristin Yvonne Rozier

Aerospace Engineering Publications

SAT-based techniques comprise the state-of-the-art in functional verification of safety-critical hardware and software, including IC3/PDR-based model checking and Bounded Model Checking (BMC). BMC is the incontrovertible best method for unsafety checking, aka bug-finding. Complementary Approximate Reachability (CAR) and IC3/PDR complement BMC for bug-finding by detecting different sets of bugs. To boost the efficiency of formal verification, we introduce heuristics involving intersection and rotation of the assumption literals used in the SAT encodings of these techniques. The heuristics generate smaller unsat cores and diverse satisfying assignments that help in faster convergence of these techniques, and have negligible runtime overhead ...


In Situ Quantitative Study Of Plastic Strain-Induced Phase Transformations Under High Pressure: Example For Ultra-Pure Zr, K. K. Pandey, Valery I. Levitas Jan 2019

In Situ Quantitative Study Of Plastic Strain-Induced Phase Transformations Under High Pressure: Example For Ultra-Pure Zr, K. K. Pandey, Valery I. Levitas

Aerospace Engineering Publications

First in situ quantitative synchrotron X-ray diffraction (XRD) study of plastic strain-induced phase transformation (PT) has been performed on α−ω PT in ultra-pure Zr as an example under different compression-shear pathways in rotational diamond anvil cell (RDAC). Radial distributions of pressure in each phase and in the mixture, and concentration of ω-Zr, all averaged over the sample thickness, as well as thickness profile were measured. The yield strength of both phases is estimated to be practically the same, in strong contrast to known estimates. Minimum pressure for the strain-induced α−ω PT, 1.2 GPa, is smaller by a ...


Scalable Verification Of Designs With Multiple Properties, Rohit Dureja, Kristin Yvonne Rozier Jan 2019

Scalable Verification Of Designs With Multiple Properties, Rohit Dureja, Kristin Yvonne Rozier

Aerospace Engineering Publications

Many industrial verification tasks entail checking a large number of properties on the same design. Formal verification techniques, such as model checking, can verify multiple properties concurrently, or sequentially one-at-a-time. State-of-the- art verification tools do not optimally exploit subproblem sharing between properties, leaving an opportunity to save considerable verification resources. A significant need therefore exists to develop efficient and scalable techniques that intelligently check multiple properties by utilizing implicit inter-property logical dependencies and subproblem sharing, and improve tool orchestration. We report on our investigation of the multiproperty model checking problem, and discuss research results, and highlight future research directions.