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Formal Framework For Safety, Security, And Availability Of Aircraft Communication Networks, Rohit Dureja, Kristin Yvonne Rozier
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 shortrange wireless network for aircraft onboard communications is outlined using the common ZigBee protocol and privacypreserving 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 BugFinding, Rohit Dureja, Jianwen Li, Geguang Pu, Moshe Y. Vardi, Kristin Yvonne Rozier
Intersection And Rotation Of Assumption Literals Boosts BugFinding, Rohit Dureja, Jianwen Li, Geguang Pu, Moshe Y. Vardi, Kristin Yvonne Rozier
Aerospace Engineering Publications
SATbased techniques comprise the stateoftheart in functional verification of safetycritical hardware and software, including IC3/PDRbased model checking and Bounded Model Checking (BMC). BMC is the incontrovertible best method for unsafety checking, aka bugfinding. Complementary Approximate Reachability (CAR) and IC3/PDR complement BMC for bugfinding 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 ExponentialLogarithmic Transformation Stretches In A Multiphase Phase Field Approach To Martensitic Transformations, Anup Basak, Valery I. Levitas
An Exact Formulation For ExponentialLogarithmic 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 exponentiallogarithmic 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 variantvariant 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, BerndHolger Schlingloff, Michael Winikoff, Neil YorkeSmith
Towards A Framework For Certification Of Reliable Autonomous Systems, Michael Fisher, Viviana Mascardi, Kristin Yvonne Rozier, BerndHolger Schlingloff, Michael Winikoff, Neil YorkeSmith
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 stateoftheart in automated verification ...
FifthDegree Elastic Potential For Predictive StressStrain 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
FifthDegree Elastic Potential For Predictive StressStrain 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 5thorder elastic potential found by minimizing error relative to density functional theory (DFT) results. The Cauchy stressLagrangian 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 PreStressing NanoAluminum Particles, Michael N. Bello, Alan M. Williams, Valery I. Levitas, Nobumichi Tamura, Daniel K. Unruh, Juliusz Warzywoda, Michelle L. Pantoya
Highly Reactive Energetic Films By PreStressing NanoAluminum 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 nanoaluminum particles (nAl). The nAl powder was prestressed to examine how modified mechanical properties of the fuel particles influenced film reactivity. Prestressing conditions varied by quenching rate. Slow and rapid quenching rates induced elevated dilatational strain within the nAl particles that was measured using synchrotron Xray 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
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 = C_{P,av}, where C_{P,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 (C_{P}) 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
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 phasefield approach (PFA) to martensitic phase transformation (PT) are presented. Finite elastic and transformational strains are considered using a fully geometricallynonlinear 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
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 straininduced anisotropy, strain hardening, and pathdependent ...
Satisfiability Checking For MissionTime Ltl, Jianwen Li, Moshe Y. Vardi, Kristin Y. Rozier
Satisfiability Checking For MissionTime Ltl, Jianwen Li, Moshe Y. Vardi, Kristin Y. Rozier
Aerospace Engineering Publications
Missiontime LTL (MLTL) is a bounded variant of MTL over naturals designed to generically specify requirements for missionbased 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 NEXPTIMEcomplete and that satisfiability checking MLTL_{0 }, the variant of MLTL where all intervals start at 0, is PSPACEcomplete. We introduce translations for MLTLtoLTL, MLTLtoLTL_{f} , MLTLtoSMV, and MLTLtoSMT, creating four ...
Numerical Investigation Of The Effect Of Airfoil Thickness On Onset Of Dynamic Stall, Anupam Sharma, Miguel Visbal
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 chordbased Reynolds number of 200 000. Four symmetric NACA airfoils of thicknesstochord ratios of 9 %, 12 %, 15 % and 18 % are studied. The threedimensional Navier–Stokes solver, FDL3DI is used with a sixthorder compact finite difference scheme for spatial discretization, secondorder implicit time integration and discriminating filters to remove unresolved wavenumbers. A constantrate pitchup 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 ...
LargeEddy Simulation Of Turbulent Flow Over A Parametric Set Of Bumps, Racheet Matai, Paul A. Durbin
LargeEddy 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, twodimensional bumps is studied by wellresolved largeeddy 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 nearwall 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, ChienPing Chou, Leonard J. Bond
A Methodology For Sorting Haploid And Diploid Corn Seed Using Terahertz Time Domain Spectroscopy And Machine Learning, Jared Taylor, ChienPing 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 InProcess For Metal Parts Fabricated Using Powder Based Additive Manufacturing, Leonard J. Bond, Lucas W. Koester, Hossein Taheri
Nde InProcess 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 online 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 online measurement for monitoring and characterization during the build. Inprocess, 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
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
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 oneatatime. Stateofthe 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 interproperty 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 NitramineOctahydro1,3,5,7Tetranitro1,3,5,7Tetrazocine, P. Bowlan, B. F. Henson, L. Smilowitz, Valery I. Levitas, N. Suvorova, D. Oschwald
Kinetics Of The Γ–Δ Phase Transition In Energetic NitramineOctahydro1,3,5,7Tetranitro1,3,5,7Tetrazocine, P. Bowlan, B. F. Henson, L. Smilowitz, Valery I. Levitas, N. Suvorova, D. Oschwald
Aerospace Engineering Publications
The solid, secondary explosive nitramineoctahydro1,3,5,7tetranitro1,3,5,7 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 β–δ 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 MatrixVariateT Distribution, Geoffrey Z. Thompson, Ranjan Maitra, William Q. Meeker, Ashraf Bastawros
Classification With The MatrixVariateT Distribution, Geoffrey Z. Thompson, Ranjan Maitra, William Q. Meeker, Ashraf Bastawros
Aerospace Engineering Publications
Matrixvariate distributions can intuitively model the dependence structure of matrixvalued observations that arise in applications with multivariate time series, spatiotemporal or repeated measures. This paper develops an ExpectationMaximization algorithm for discriminant analysis and classification with matrixvariate tdistributions. 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 StrainInduced Phase Transformations Under High Pressure: Example For UltraPure Zr, K. K. Pandey, Valery I. Levitas
In Situ Quantitative Study Of Plastic StrainInduced Phase Transformations Under High Pressure: Example For UltraPure Zr, K. K. Pandey, Valery I. Levitas
Aerospace Engineering Publications
First in situ quantitative synchrotron Xray diffraction (XRD) study of plastic straininduced phase transformation (PT) has been performed on α−ω PT in ultrapure Zr as an example under different compressionshear pathways in rotational diamond anvil cell (RDAC). Radial distributions of pressure in each phase and in the mixture, and concentration of ωZr, 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 straininduced α−ω PT, 1.2 GPa, is smaller by a ...
HighPressure Phase Transformations Under Severe Plastic Deformation By Torsion In Rotational Anvils, Valery I. Levitas
HighPressure 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 highpressure 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
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 highpressure 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 nitrogenvacancy (NV) color centers directly into the culet (tip) of diamond anvils. We demonstrate the versatility of this platform by performing diffractionlimited imaging (~600 nm) of both stress fields and magnetism, up to pressures ~30 GPa and for temperatures ranging from 25340 K. For ...
Numerical Investigation Of LowNoise Airfoils Inspired By The Down Coat Of Owls, Andrew Bodling, Anupam Sharma
Numerical Investigation Of LowNoise 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. Wallresolved large eddy simulations are performed at chordbased Reynolds number, Rec = 5 x 10(5), flow Mach number, M = 0.2, and angle of attack, alpha = 0 degrees. The simulation results ...
SatBased Explicit Ltlf Satisfiability Checking, Jianwen Li, Kristin Y. Rozier, Geguang Pu, Yueling Zhang, Moshe Y. Vardi
SatBased Explicit Ltlf Satisfiability Checking, Jianwen Li, Kristin Y. Rozier, Geguang Pu, Yueling Zhang, Moshe Y. Vardi
Aerospace Engineering Publications
We present here a SATbased framework for LTLf (Linear Temporal Logic on Finite Traces) satisfiability checking. We use propositional SATsolving techniques to construct a transition system for the input LTLf formula; satisfiability checking is then reduced to a pathsearch problem over this transition system. Furthermore, we introduce CDLSC (ConflictDriven 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 fourfold speedup compared to the secondbest solver.
Lattice Instability During SolidSolid 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
Lattice Instability During SolidSolid 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 stressstrain behavior and elastic instabilities during the solidsolid 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 phasefield’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
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 carbonatebicarbonate 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 ...
PhaseField Approach For Stress And TemperatureInduced Phase Transformations That Satisfies Lattice Instability Conditions. Part 2. Simulations Of Phase Transformations Si I↔Si Ii, Hamed Babaei, Valery I. Levitas
PhaseField Approach For Stress And TemperatureInduced 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 phasefield 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 compressiontension 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
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 petrochemical industries. Design, fabrication and optimization of such transducers using piezoelectric materials remains a challenge. In this work, experimental databased 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 temperaturedependent 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 RibRoughened RoughToSmooth Turbulent Channel Flows, Umair Ismail, Tamer A. Zaki, Paul A. Durbin
Simulations Of RibRoughened RoughToSmooth Turbulent Channel Flows, Umair Ismail, Tamer A. Zaki, Paul A. Durbin
Aerospace Engineering Publications
Highfidelity simulations of turbulent flow through a channel with a rough wall, followed by a smooth wall, demonstrate a high degree of nonequilibrium 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, smoothwall levels persist in the developing region. Within the thin wall layer, the profile shapes for turbulence stresses recover very quickly and wallnormal locations of characteristic peaks are established. However, even in this thin layer, complete recovery of magnitudes of turbulence ...
Instability Waves And Transition In AdversePressureGradient Boundary Layers, Rikhi Bose, Tamer A. Zaki, Paul A. Durbin
Instability Waves And Transition In AdversePressureGradient Boundary Layers, Rikhi Bose, Tamer A. Zaki, Paul A. Durbin
Aerospace Engineering Publications
Transition to turbulence in incompressible adversepressuregradient (APG) boundary layers is investigated by direct numerical simulations. Purely twodimensional 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 freestream 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 freestream turbulence (∼0.1%), transition onset is highly sensitive to ...
Nanoscale Multiphase Phase Field Approach For Stress And TemperatureInduced Martensitic Phase Transformations With Interfacial Stresses At Finite Strains, Anup Basak, Valery I. Levitas
Nanoscale Multiphase Phase Field Approach For Stress And TemperatureInduced 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 temperatureinduced 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 Ndimensional 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 variantvariant transformation path from a straight line have been penalized. Some shortcomings of the existing models are resolved. Three different kinematic ...