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Formal Framework For Safety, Security, And Availability Of Aircraft Communication Networks, Rohit Dureja, Kristin Yvonne Rozier May 2020

Formal Framework For Safety, Security, And Availability Of Aircraft Communication Networks, Rohit Dureja, Kristin Yvonne Rozier

Aerospace Engineering Publications

As the costs of fuel and maintenance increase and regulations on weight and environmental impact tighten, there is an increasing push to transition onboard aircraft networks to wireless, reducing weight, fuel, maintenance time, and pollution. A candidate short-range wireless network for aircraft onboard communications is outlined using the common ZigBee protocol and privacy-preserving search implemented as a secure publish/subscribe system using specially coded metadata. Formally specifying safety and security properties and modeling the network in New e(X)tensible Model Verifier enable verification and fault analysis via model checking and lay the groundwork for future certification avenues. Experiments formally ...


Intersection And Rotation Of Assumption Literals Boosts Bug-Finding, Rohit Dureja, Jianwen Li, Geguang Pu, Moshe Y. Vardi, Kristin Yvonne Rozier Mar 2020

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 ...


An Exact Formulation For Exponential-Logarithmic Transformation Stretches In A Multiphase Phase Field Approach To Martensitic Transformations, Anup Basak, Valery I. Levitas Jan 2020

An Exact Formulation For Exponential-Logarithmic Transformation Stretches In A Multiphase Phase Field Approach To Martensitic Transformations, Anup Basak, Valery I. Levitas

Aerospace Engineering Publications

A general theoretical and computational procedure for dealing with an exponential-logarithmic kinematic model for transformation stretch tensor in a multiphase phase field approach to stress- and temperature- induced martensitic transformations with N martensitic variants is developed for transformations between all possible crystal lattices. This kinematic model, where the natural logarithm of transformation stretch tensor is a linear combination of natural logarithm of the Bain tensors, yields isochoric variant-variant transformations for the entire transformation path. Such a condition is plausible and cannot be satisfied by the widely used kinematic model where the transformation stretch tensor is linear in Bain tensors. Earlier ...


Towards A Framework For Certification Of Reliable Autonomous Systems, Michael Fisher, Viviana Mascardi, Kristin Yvonne Rozier, Bernd-Holger Schlingloff, Michael Winikoff, Neil Yorke-Smith Jan 2020

Towards A Framework For Certification Of Reliable Autonomous Systems, Michael Fisher, Viviana Mascardi, Kristin Yvonne Rozier, Bernd-Holger Schlingloff, Michael Winikoff, Neil Yorke-Smith

Aerospace Engineering Publications

A computational system is called autonomous if it is able to make its own decisions, or take its own actions, without human supervision or control. The capability and spread of such systems have reached the point where they are beginning to touch much of everyday life. However, regulators grapple with how to deal with autonomous systems, for example how could we certify an Unmanned Aerial System for autonomous use in civilian airspace? We here analyse what is needed in order to provide verified reliable behaviour of an autonomous system, analyse what can be done as the state-of-the-art in automated verification ...


Fifth-Degree Elastic Potential For Predictive Stress-Strain Relations And Elastic Instabilities Under Large Strain And Complex Loading In Si, Hao Chen, Nikolai A. Zarkevich, Valery I. Levitas, Duane D. Johnson, Xiancheng Zhang Jan 2020

Fifth-Degree Elastic Potential For Predictive Stress-Strain Relations And Elastic Instabilities Under Large Strain And Complex Loading In Si, Hao Chen, Nikolai A. Zarkevich, Valery I. Levitas, Duane D. Johnson, Xiancheng Zhang

Aerospace Engineering Publications

Materials under complex loading develop large strains and often transition via an elastic instability, as observed in both simple and complex systems. Here, we present Si I under large strain in terms of Lagrangian strain by an 5th-order elastic potential found by minimizing error relative to density functional theory (DFT) results. The Cauchy stress-Lagrangian strain curves for arbitrary complex loadings are in excellent correspondence with DFT results, including elastic instability driving Si I→II phase transformation (PT) and the shear instabilities. PT conditions for Si I→II under action of cubic axial stresses are linear in Cauchy stresses in agreement ...


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 ...


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.


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 ...


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.


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 ...


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 ...


Imaging Stress And Magnetism At High Pressures Using A Nanoscale Quantum Sensor, S. Hsieh, P. Bhattacharyya, C. Zu, T. Mittiga, T. J. Smart, F. Machado, B. Kobrin, T. O. Hohn, N. Z. Rui, Mehdi Kamrani, S. Chatterjee, S. Choi, M. Zaletel, V. V. Struzhkin, J. E. Moore, Valery I. Levitas, R. Jeanloz, N. Y. Yao Dec 2018

Imaging Stress And Magnetism At High Pressures Using A Nanoscale Quantum Sensor, S. Hsieh, P. Bhattacharyya, C. Zu, T. Mittiga, T. J. Smart, F. Machado, B. Kobrin, T. O. Hohn, N. Z. Rui, Mehdi Kamrani, S. Chatterjee, S. Choi, M. Zaletel, V. V. Struzhkin, J. E. Moore, Valery I. Levitas, R. Jeanloz, N. Y. Yao

Aerospace Engineering Publications

Pressure alters the physical, chemical and electronic properties of matter. The development of the diamond anvil cell (DAC) enables tabletop experiments to investigate a diverse landscape of high-pressure phenomena ranging from the properties of planetary interiors to transitions between quantum mechanical phases. In this work, we introduce and utilize a novel nanoscale sensing platform, which integrates nitrogen-vacancy (NV) color centers directly into the culet (tip) of diamond anvils. We demonstrate the versatility of this platform by performing diffraction-limited imaging (~600 nm) of both stress fields and magnetism, up to pressures ~30 GPa and for temperatures ranging from 25-340 K. For ...


Numerical Investigation Of Low-Noise Airfoils Inspired By The Down Coat Of Owls, Andrew Bodling, Anupam Sharma Dec 2018

Numerical Investigation Of Low-Noise Airfoils Inspired By The Down Coat Of Owls, Andrew Bodling, Anupam Sharma

Aerospace Engineering Publications

Numerical analysis of airfoil geometries inspired by the down coat of the night owl is presented. The bioinspired geometry consists of an array of 'finlet fences', which is placed near the trailing edge of the baseline (NACA 0012) airfoil. Two fences with maximum nondimensional heights, H/delta* = 1 and 2.26 are investigated, where delta* is the displacement thickness at 2.9% chord upstream of the airfoil trailing edge. Wall-resolved large eddy simulations are performed at chord-based Reynolds number, Re-c = 5 x 10(5), flow Mach number, M = 0.2, and angle of attack, alpha = 0 degrees. The simulation results ...


Sat-Based Explicit Ltlf Satisfiability Checking, Jianwen Li, Kristin Y. Rozier, Geguang Pu, Yueling Zhang, Moshe Y. Vardi Nov 2018

Sat-Based Explicit Ltlf Satisfiability Checking, Jianwen Li, Kristin Y. Rozier, Geguang Pu, Yueling Zhang, Moshe Y. Vardi

Aerospace Engineering Publications

We present here a SAT-based framework for LTLf (Linear Temporal Logic on Finite Traces) satisfiability checking. We use propositional SAT-solving techniques to construct a transition system for the input LTLf formula; satisfiability checking is then reduced to a path-search problem over this transition system. Furthermore, we introduce CDLSC (Conflict-Driven LTLf Satisfiability Checking), a novel algorithm that leverages information produced by propositional SAT solvers from both satisfiability and unsatisfiability results. Experimental evaluations show that CDLSC outperforms all other existing approaches for LTLf satisfiability checking, by demonstrating an approximate four-fold speedup compared to the second-best solver.


Lattice Instability During Solid-Solid Structural Transformations Under A General Applied Stress Tensor: Example Of Si I → Si Ii With Metallization, Nikolai A. Zarkevich, Hao Chen, Valery I. Levitas, Duane D. Johnson Oct 2018

Lattice Instability During Solid-Solid Structural Transformations Under A General Applied Stress Tensor: Example Of Si I → Si Ii With Metallization, Nikolai A. Zarkevich, Hao Chen, Valery I. Levitas, Duane D. Johnson

Aerospace Engineering Publications

The density functional theory was employed to study the stress-strain behavior and elastic instabilities during the solid-solid phase transformation (PT) when subjected to a general stress tensor, as exemplified for semiconducting Si I and metallic Si II, where metallization precedes the PT, so stressed Si I can be a metal. The hydrostatic PT occurs at 76 GPa, while under uniaxial loading it is 11 GPa (3.7 GPa mean pressure), 21 times lower. The Si I → Si II PT is described by a critical value of the phase-field’s modified transformation work, and the PT criterion has only two parameters ...


Morphology And Stress Evolution During The Initial Stages Of Intergranular Corrosion Of X70 Steel, Denizhan Yavas, Abdullah Alshehri, Pratyush Mishra, Pranav Shrotriya, Ashraf F. Bastawros, Kurt R. Hebert Sep 2018

Morphology And Stress Evolution During The Initial Stages Of Intergranular Corrosion Of X70 Steel, Denizhan Yavas, Abdullah Alshehri, Pratyush Mishra, Pranav Shrotriya, Ashraf F. Bastawros, Kurt R. Hebert

Aerospace Engineering Publications

Pipeline steels are vulnerable to stress corrosion cracking (SCC) during intergranular corrosion (IGC) at potentials of active dissolution in moderately alkaline carbonate-bicarbonate solutions. Morphology evolution accompanying IGC has not been fully described, despite the relevance of the corrosion geometry to crack initiation. The present article reports a characterization of concurrent morphology and mechanical stress development during the initial stages of IGC of X70 steel in sodium bicarbonate solution, in the potential range of high SCC susceptibility. Morphology was revealed by scanning electron microscope examination of cross sections through the IGC layer, and stress evolution was monitored by curvature interferometry. At ...


Phase-Field Approach For Stress- And Temperature-Induced Phase Transformations That Satisfies Lattice Instability Conditions. Part 2. Simulations Of Phase Transformations Si I↔Si Ii, Hamed Babaei, Valery I. Levitas Aug 2018

Phase-Field Approach For Stress- And Temperature-Induced Phase Transformations That Satisfies Lattice Instability Conditions. Part 2. Simulations Of Phase Transformations Si I↔Si Ii, Hamed Babaei, Valery I. Levitas

Aerospace Engineering Publications

A complete system of equations of the advanced phase-field theory for martensitic phase transformations (PTs) under a general stress tensor is presented. Theory includes a fully geometrically nonlinear formulation for the general case of finite elastic and transformational strains as well as anisotropic and different elastic properties of phases. Material parameters are calibrated, in particular, based on the crystal lattice instability conditions from atomistic simulations for martensitic PTs between cubic Si I and tetragonal Si II phases under complex triaxial compression-tension loading. A finite element algorithm and numerical procedure is developed and implemented in the code deal.II. Various 3D ...


Resonance Analysis Of A High Temperature Piezoelectric Disc For Sensitivity Characterization, Prathamesh N. Bilgunde, Leonard J. Bond Jul 2018

Resonance Analysis Of A High Temperature Piezoelectric Disc For Sensitivity Characterization, Prathamesh N. Bilgunde, Leonard J. Bond

Aerospace Engineering Publications

Ultrasonic transducers for high temperature (200 °C+) applications are a key enabling technology for advanced nuclear power systems and in a range of chemical and petro-chemical industries. Design, fabrication and optimization of such transducers using piezoelectric materials remains a challenge. In this work, experimental data-based analysis is performed to investigate the fundamental causal factors for the resonance characteristics of a piezoelectric disc at elevated temperatures. The effect of all ten temperature-dependent piezoelectric constants (ε33, ε11, d33, d31, d15, s11, s12, s13, s33, s44) is studied numerically on both the radial and thickness mode resonances of a piezoelectric disc. A sensitivity ...


Simulations Of Rib-Roughened Rough-To-Smooth Turbulent Channel Flows, Umair Ismail, Tamer A. Zaki, Paul A. Durbin May 2018

Simulations Of Rib-Roughened Rough-To-Smooth Turbulent Channel Flows, Umair Ismail, Tamer A. Zaki, Paul A. Durbin

Aerospace Engineering Publications

High-fidelity simulations of turbulent flow through a channel with a rough wall, followed by a smooth wall, demonstrate a high degree of non-equilibrium within the recovery region. In fact, the recovery of all the flow statistics studied is incomplete by the streamwise exit of the computational domain. Above a thin wall layer, turbulence intensities significantly higher than fully developed, smooth-wall levels persist in the developing region. Within the thin wall layer, the profile shapes for turbulence stresses recover very quickly and wall-normal locations of characteristic peaks are established. However, even in this thin layer, complete recovery of magnitudes of turbulence ...


Instability Waves And Transition In Adverse-Pressure-Gradient Boundary Layers, Rikhi Bose, Tamer A. Zaki, Paul A. Durbin May 2018

Instability Waves And Transition In Adverse-Pressure-Gradient Boundary Layers, Rikhi Bose, Tamer A. Zaki, Paul A. Durbin

Aerospace Engineering Publications

Transition to turbulence in incompressible adverse-pressure-gradient (APG) boundary layers is investigated by direct numerical simulations. Purely two-dimensional instability waves develop on the inflectional base velocity profile. When the boundary layer is perturbed by isotropic turbulence from the free stream, streamwise elongated streaks form and may interact with the instability waves. Subsequent mechanisms that trigger transition depend on the intensity of the free-stream disturbances. All evidence from the present simulations suggest that the growth rate of instability waves is sufficiently high to couple with the streaks. Under very low levels of free-stream turbulence (∼0.1%), transition onset is highly sensitive to ...


Nanoscale Multiphase Phase Field Approach For Stress- And Temperature-Induced Martensitic Phase Transformations With Interfacial Stresses At Finite Strains, Anup Basak, Valery I. Levitas Apr 2018

Nanoscale Multiphase Phase Field Approach For Stress- And Temperature-Induced Martensitic Phase Transformations With Interfacial Stresses At Finite Strains, Anup Basak, Valery I. Levitas

Aerospace Engineering Publications

A thermodynamically consistent, novel multiphase phase field approach for stress- and temperature-induced martensitic phase transformations at finite strains and with interfacial stresses has been developed. The model considers a single order parameter to describe the austenite↔martensitic transformations, and another N order parameters describing N variants and constrained to a plane in an N-dimensional order parameter space. In the free energy model coexistence of three or more phases at a single material point (multiphase junction), and deviation of each variant-variant transformation path from a straight line have been penalized. Some shortcomings of the existing models are resolved. Three different kinematic ...