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 Mechanical & Aerospace Engineering Faculty Publications (10)
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Articles 1  30 of 31
FullText Articles in Engineering Science and Materials
CurrentDriven Production Of VortexAntivortex Pairs In Planar Josephson Junction Arrays And Phase Cracks In LongRange Order, Francisco EstellésDuart, Miguel Ortuño, Andrés M. Somoza, Valerii M. Vinokur, Alex Gurevich
CurrentDriven Production Of VortexAntivortex Pairs In Planar Josephson Junction Arrays And Phase Cracks In LongRange Order, Francisco EstellésDuart, Miguel Ortuño, Andrés M. Somoza, Valerii M. Vinokur, Alex Gurevich
Physics Faculty Publications
Proliferation of topological defects like vortices and dislocations plays a key role in the physics of systems with longrange order, particularly, superconductivity and superfluidity in thin films, plasticity of solids, and melting of atomic monolayers. Topological defects are characterized by their topological charge reflecting fundamental symmetries and conservation laws of the system. Conservation of topological charge manifests itself in extreme stability of static topological defects because destruction of a single defect requires overcoming a huge energy barrier proportional to the system size. However, the stability of driven topological defects remains largely unexplored. Here we address this issue and investigate numerically ...
Evaluation Of Procurement Scenarios In OneDimensional Cutting Stock Problem With A Random Demand Mix, Hüseyin Sarper, Nebojsa I. Jaksic
Evaluation Of Procurement Scenarios In OneDimensional Cutting Stock Problem With A Random Demand Mix, Hüseyin Sarper, Nebojsa I. Jaksic
Electrical & Computer Engineering Faculty Publications
The onedimensional cutting stock problem describes the problem of cutting standard length stock material into various specified sizes while minimizing the material wasted (the remnant or drop as manufacturing terms). This computationally complex optimization problem has many manufacturing applications. Onedimensional cutting stock problems arise in many domains such as metal, paper, textile, and wood. To solve it, the problem is formulated as an integer linear model first, and then solved using a common optimizer software. This paper revisits the stochastic version of the problem and proposes a prioritybased goal programming approach. Monte Carlo simulation is used to simulate several likely ...
Manufacturing Applications Of The OneDimensional Cutting Stock Problem As A Team Project, Hüseyin Sarper, Nebojsa I. Jaksic
Manufacturing Applications Of The OneDimensional Cutting Stock Problem As A Team Project, Hüseyin Sarper, Nebojsa I. Jaksic
Electrical & Computer Engineering Faculty Publications
This paper explains the beneficial and practical impact of operations research in two real manufacturing settings. Two manufacturing examples used in student projects were (1) cutting rails (80‘ or 40‘) to manufacture railroad frogs of many sizes and (2) cutting round metal rolls (12‘ to 20‘) to meet customer demands for various lengths of cuts. Student teams in Engineering of Manufacturing Processes and Operations Research courses wrote computer programs. The program first identified all possible patterns that can be cut out of a given stock length. Next, the program created a mathematical model (a text file) as an output. This ...
Preface To Special Topic: A Tribute To John Lumley, Kiran Bhaganagar, Thomas B. Gatski, William K. George
Preface To Special Topic: A Tribute To John Lumley, Kiran Bhaganagar, Thomas B. Gatski, William K. George
CCPO Publications
This Special Topic Section is dedicated to the life and memory of John Leask Lumley(19302015), professor and scientist extraordinaire.
Comment On "Roles Of Bulk Viscosity On RayleighTaylor Instability: NonEquilibrium Thermodynamics Due To SpatioTemporal Pressure Fronts" Phys. Fluids 28, 094102 (2016), Robert L. Ash
Mechanical & Aerospace Engineering Faculty Publications
No abstract provided.
Error Aggregation In The Reengineering Process From 3d Scanning To Printing, Jennifer G. Michaeli, Matthew C. Degroff, Roman C. Roxas
Error Aggregation In The Reengineering Process From 3d Scanning To Printing, Jennifer G. Michaeli, Matthew C. Degroff, Roman C. Roxas
Engineering Technology Faculty Publications
This work aims to study the aggregation of dimensional errors in the reengineering processes using 3D scanning and printing without initial design drawings. A 57tooth spur gear is used as an example to facilitate the discussion. Two approaches are investigated. The first one builds the gear model based upon measurement taken from a caliper, and the second approach uses a 3D scanner to collect geometry data. Dimensional errors in each stage of these two approaches are investigated. Particular attention is paid to the geometry data flow in the reengineering process from data acquisition and editing to model construction. Recommendations are ...
An Approach For The Development Of Complex Systems Archetypes, Walter Lee Akers
An Approach For The Development Of Complex Systems Archetypes, Walter Lee Akers
Engineering Management & Systems Engineering Theses & Dissertations
The purpose of this research is to explore the principles and concepts of systems theory in pursuit of a collection of complex systems archetypes that can be used for system exploration and diagnostics. The study begins with an examination of the archetypes and classification systems that already exist in the domain of systems theory. This review includes a critique of their purpose, structure, and general applicability. The research then develops and employs a new approach to grounded theory, using a visual coding model to explore the origins, relationships, and meanings of the principles of systems theory. The goal of the ...
The Effect Of Noise On The Response Of A Vertical Cantilever Beam Energy Harvester, Michael I. Friswell, Onur Bilgen, S. Faruque Ali, Grzegorz Litak, Sondipon Adhikari
The Effect Of Noise On The Response Of A Vertical Cantilever Beam Energy Harvester, Michael I. Friswell, Onur Bilgen, S. Faruque Ali, Grzegorz Litak, Sondipon Adhikari
Mechanical & Aerospace Engineering Faculty Publications
An energy harvesting concept has been proposed comprising a piezoelectric patch on a vertical cantilever beam with a tip mass. The cantilever beam is excited in the transverse direction at its base. This device is highly nonlinear with two potential wells for large tip masses, when the beam is buckled. For the prebuckled case considered here, the stiffness is low and hence the displacement response is large, leading to multiple solutions to harmonic excitation that are exploited in the harvesting device. To maximise the energy harvested in systems with multiple solutions the higher amplitude response should be preferred. This paper ...
An Agent Based Approach For Simulating Demo Enterprise Models, Mamadou Seck, Joseph Barjis
An Agent Based Approach For Simulating Demo Enterprise Models, Mamadou Seck, Joseph Barjis
Engineering Management & Systems Engineering Faculty Publications
DEMO (design and engineering methodology for organization) is a theoretically grounded methodology for rigorous enterprise modeling. It provides relevant concepts from a construction perspective. As the methodology gains a wider audience, there is a growing interest in simulating DEMO models. Most attempts to develop a simulation approach for enterprise models in general, and the DEMO methodology in particular, are based on process oriented conceptualizations that are typically implementation in a discrete event paradigm. In this paper, we propose a conceptual framework for the translation of DEMO models into an agent based simulation. We will describe the DEMO methodology in some ...
Effects Of Gravity On The Acceleration And Pair Statistics Of Inertial Particles In Homogeneous Isotropic Turbulence, H. Parishani, O. Ayala, B. Rosa, L.P. Wang, W. W. Grabowski
Effects Of Gravity On The Acceleration And Pair Statistics Of Inertial Particles In Homogeneous Isotropic Turbulence, H. Parishani, O. Ayala, B. Rosa, L.P. Wang, W. W. Grabowski
Engineering Technology Faculty Publications
Within the context of heavy particles suspended in a turbulent airflow, we study the effects of gravity on acceleration statistics and radial relative velocity (RRV) of inertial particles. The turbulent flow is simulated by direct numerical simulation (DNS) on a 256^{3} grid and the dynamics of O(10^{6}) inertial particles by the pointparticle approach. For particles/droplets with radius from 10 to 60 µm, we found that the gravity plays an important role in particle acceleration statistics: (a) a peak value of particle acceleration variance appears in both the horizontal and vertical directions at a particle Stokes number ...
Effects Of Forcing Time Scale On The Simulated Turbulent Flows And Turbulent Collision Statistics Of Inertial Particles, B. Rosa, H. Parishani, O. Ayala, L.P. Wang
Effects Of Forcing Time Scale On The Simulated Turbulent Flows And Turbulent Collision Statistics Of Inertial Particles, B. Rosa, H. Parishani, O. Ayala, L.P. Wang
Engineering Technology Faculty Publications
In this paper, we study systematically the effects of forcing time scale in the largescale stochastic forcing scheme of Eswaran and Pope ["An examination of forcing in direct numerical simulations of turbulence," Comput. Fluids 16, 257 (1988)] on the simulated flow structures and statistics of forced turbulence. Using direct numerical simulations, we find that the forcing time scale affects the flow dissipation rate and flow Reynolds number. Other flow statistics can be predicted using the altered flow dissipation rate and flow Reynolds number, except when the forcing time scale is made unrealistically large to yield a Taylor microscale flow Reynolds ...
Complementarities Of Probabilistic And Evidence Approaches: An Uncertainty Assessment For Selection Of Composite Material, Stella B. Bondi, Resit Unal, Patrick T. Hester, Trina M. Chytka
Complementarities Of Probabilistic And Evidence Approaches: An Uncertainty Assessment For Selection Of Composite Material, Stella B. Bondi, Resit Unal, Patrick T. Hester, Trina M. Chytka
Engineering Technology Faculty Publications
A complimentary probabilistic and evidence theory approach is utilized to enhance uncertainty assessments in the area of critical safety characteristics for conceptual design. This research provides additional exploration into the failure modes necessary to utilize Fiber Reinforced Polymer (FRP) and various composites to their fullest potential and to minimize uncertainty by comparing probability and evidence theories. This combined approach has been applied to a selection of composite material that could provide uncertainty assessment design for a space transportation system. Uncertainty estimates presented are bounded by belief and plausibility functions. The results may provide additional information to the decision makers in ...
NonEquilibrium Pressure Control Of The Height Of A LargeScale, GroundCoupled, Rotating Fluid Column, R. L. Ash, I. R. Zardadhkan
NonEquilibrium Pressure Control Of The Height Of A LargeScale, GroundCoupled, Rotating Fluid Column, R. L. Ash, I. R. Zardadhkan
Mechanical & Aerospace Engineering Faculty Publications
When a groundcoupled, rotating fluid column is modeled incorporating nonequilibrium pressure forces in the NavierStokes equations, a new exact solution results. The solution has been obtained in a similar manner to the classical equilibrium solution. Unlike the infiniteheight, classical solution, the nonequilibrium pressure solution yields a groundcoupled rotating fluid column of finite height. A viscous, nonequilibrium Rankine vortex velocity distribution, developed previously, was used to demonstrate how the viscous and nonequilibrium pressure gradient forces, arising in the vicinity of the velocity gradient discontinuity that is present in the classical Rankine vortex model, effectively isolate the rotating central fluid column from ...
Optical Detection Of Melting Point Depression For Silver Nanoparticles Via In Situ Real Time Spectroscopic Ellipsometry, S. A. Little, T. Begou, R. W. Collins, S. Marsillac
Optical Detection Of Melting Point Depression For Silver Nanoparticles Via In Situ Real Time Spectroscopic Ellipsometry, S. A. Little, T. Begou, R. W. Collins, S. Marsillac
Electrical & Computer Engineering Faculty Publications
Silver nanoparticle films were deposited by sputtering at room temperature and were annealed while monitoring by real time spectroscopic ellipsometry (SE). The nanoparticle dielectric functions (0.75 eV6.5 eV) obtained by SE were modeled using Lorentz and generalized oscillators for the nanoparticle plasmon polariton (NPP) and interband transitions, respectively. The nanoparticle melting point could be identified from variations in the oscillator parameters during annealing, and this identification was further confirmed after cooling through significant, irreversible changes in these parameters relative to the asdeposited film. The variation in melting point with physical thickness, and thus average nanoparticle diameter, as measured ...
The Influence Of Pressure Relaxation On The Structure Of An Axial Vortex, Robert L. Ash, Irfan Zardadkhan, Allan J. Zuckerwar
The Influence Of Pressure Relaxation On The Structure Of An Axial Vortex, Robert L. Ash, Irfan Zardadkhan, Allan J. Zuckerwar
Mechanical & Aerospace Engineering Faculty Publications
Governing equations including the effects of pressure relaxation have been utilized to study an incompressible, steadystate viscous axial vortex with specified farfield circulation. When sound generation is attributed to a velocity gradient tensorpressure gradient product, the modified conservation of momentum equations that result yield an exact solution for a steady, incompressible axial vortex. The vortex velocity profile has been shown to closely approximate experimental vortex measurements in air and water over a wide range of circulationbased Reynolds numbers. The influence of temperature and humidity on the pressure relaxation coefficient in air has been examined using theoretical and empirical approaches, and ...
Understanding Practical Limits To Heavy Truck Drag Reduction, Drew Landman, Richard Wood, Whitney Seay, John Bledsoe
Understanding Practical Limits To Heavy Truck Drag Reduction, Drew Landman, Richard Wood, Whitney Seay, John Bledsoe
Mechanical & Aerospace Engineering Faculty Publications
A heavy truck wind tunnel test program is currently underway at the Langley Full Scale Tunnel (LFST). Seven passive drag reducing device configurations have been evaluated on a heavy truck model with the objective of understanding the practical limits to drag reduction achievable on a modern tractor trailer through addon devices. The configurations tested include side skirts of varying length, a full gap seal, and tapered rear panels. All configurations were evaluated over a nominal 15 degree yaw sweep to establish wind averaged drag coefficients over a broad speed range using SAE J1252. The tests were conducted by first quantifying ...
Volume Viscosity In Fluids With Multiple Dissipative Processes, Allan J. Zuckerwar, Robert L. Ash
Volume Viscosity In Fluids With Multiple Dissipative Processes, Allan J. Zuckerwar, Robert L. Ash
Mechanical & Aerospace Engineering Faculty Publications
The variational principle of Hamilton is applied to derive the volume viscosity coefficients of a reacting fluid with multiple dissipative processes. The procedure, as in the case of a single dissipative process, yields two dissipative terms in the NavierStokes equation: The first is the traditional volume viscosity term, proportional to the dilatational component of the velocity; the second term is proportional to the material time derivative of the pressure gradient. Each dissipative process is assumed to be independent of the others. In a fluid comprising a single constituent with multiple relaxation processes, the relaxation times of the multiple processes are ...
Electronic And Structural Properties Of Molybdenum Thin Films As Determined By Real Time Spectroscopic Ellipsometry, J. D. Walker, H. Khatri, V. Ranjan, Jian Li, R. W. Collins, S. Marsillac
Electronic And Structural Properties Of Molybdenum Thin Films As Determined By Real Time Spectroscopic Ellipsometry, J. D. Walker, H. Khatri, V. Ranjan, Jian Li, R. W. Collins, S. Marsillac
Electrical & Computer Engineering Faculty Publications
Walker, J.D., Khatri, H., Ranjan, V., Li, J., Collins, R.W., & Marsillac, S. (2009). Electronic and structural properties of molybdenum thin films as determined by realtime spectroscopic ellipsometry. Applied Physics Letters, 94(14). doi: 10.1063/1.3117222
Hypersonic Boundary Layer Receptivity To Acoustic Disturbances Over Cones, Kursat Kara
Hypersonic Boundary Layer Receptivity To Acoustic Disturbances Over Cones, Kursat Kara
Mechanical & Aerospace Engineering Theses & Dissertations
The receptivity mechanisms of hypersonic boundary layers to free stream acoustic disturbances are studied using both linear stability theory (LST) and direct numerical simulations (DNS). A computational code is developed for numerical simulation of steady and unsteady hypersonic flow over cones by combining a fifthorder weighted essentially nonoscillatory (WENO) scheme with thirdorder totalvariationdiminishing (TVD) RungeKutta method. Hypersonic boundary layer receptivity to freestream acoustic disturbances in slow and fast modes over 5degree, halfangle blunt cones and wedges are numerically investigated. The freestream Mach number is 6.0, and the unit Reynolds number is 7.8×106/ft. Both the steady and ...
Variational Approach To The Volume Viscosity Of Fluids, Allan J. Zuckerwar, Robert L. Ash
Variational Approach To The Volume Viscosity Of Fluids, Allan J. Zuckerwar, Robert L. Ash
Mechanical & Aerospace Engineering Faculty Publications
The variational principle of Hamilton is applied to develop an analytical formulation to describe the volume viscosity in fluids. The procedure described here differs from those used in the past in that a dissipative process is represented by the chemical affinity and progress variable (sometimes called "order parameter") of a reacting species. These state variables appear in the variational integral in two places: first, in the expression for the internal energy, and second, in a subsidiary condition accounting for the conservation of the reacting species. As a result of the variational procedure, two dissipative terms appear in the NavierStokes equation ...
Response To "Comment On Variational Approach To The Volume Viscosity Of Fluids" [Phys. Fluids 18, 109101 (2006)], Allen J. Zuckerwar, Robert L. Ash
Response To "Comment On Variational Approach To The Volume Viscosity Of Fluids" [Phys. Fluids 18, 109101 (2006)], Allen J. Zuckerwar, Robert L. Ash
Mechanical & Aerospace Engineering Faculty Publications
We respond to the Comment of Markus Scholle and therewith revise our material entropy constraint to account for the production of entropy. (c) 2006 American Institute of Physics.
Evolution Of The Band Structure Of ΒIn2 S3−3x O3x Buffer Layer With Its Oxygen Content, N. Barreau, S. Marsillac, J. C. Bernède, L. Assmann
Evolution Of The Band Structure Of ΒIn2 S3−3x O3x Buffer Layer With Its Oxygen Content, N. Barreau, S. Marsillac, J. C. Bernède, L. Assmann
Electrical & Computer Engineering Faculty Publications
The evolution of the band structure of βIn2 S3−3x O3x (BISO) thin films grown by physical vapor deposition, with composition x, is investigated using xray photoelectron spectroscopy. It is shown that the energy difference between the valenceband level and the Fermi level remains nearly constant as the optical band gap of the films increases. As a consequence, the difference between the conduction band level and the Fermi level increases as much as the optical band gap of the films. The calculation of the electronic affinity [ ] of the BISO thin films shows that it decreases linearly from 4.65 to ...
Fuzzy System Identification Based Upon A Novel Approach To Nonlinear Optimization, Raymond Scott Starsman
Fuzzy System Identification Based Upon A Novel Approach To Nonlinear Optimization, Raymond Scott Starsman
Electrical & Computer Engineering Theses & Disssertations
Fuzzy systems are often used to model the behavior of nonlinear dynamical systems in process control industries because the model is linguistic in nature, uses a naturallanguage rule set, and because they can be included in control laws that meet the design goals. However, because the rigorous study of fuzzy logic is relatively recent, there is a shortage of welldefined and understood mechanisms for the design of a fuzzy system. One of the greatest challenges in fuzzy modeling is to determine a suitable structure, parameters, and rules that minimize an appropriately chosen error between the fuzzy system, a mathematical model ...
Study Of A Growth Instability Of ΓIn[Sub 2]Se[Sub 3], C. Amory, J. C. Bernede, S. Marsillac
Study Of A Growth Instability Of ΓIn[Sub 2]Se[Sub 3], C. Amory, J. C. Bernede, S. Marsillac
Electrical & Computer Engineering Faculty Publications
γIn[sub 2]Se[sub 3] thin film are deposited for various substrate temperatures in the range of 523–673 K. This study shows that at 573 and 673 K the thin films are well crystallized with grains aligned along the c axis. Between these temperatures, a domain of instability appears where the γIn[sub 2]Se[sub 3] thin films have a randomly orientation and the clattice parameter increases. The presence of the metastable phase κIn[sub 2]Se[sub 3], during the growth, can explain the existence of this domain of instability. The insertion of Zn during the ...
Developing A Methodology To Detect Partial Failures For Dynamic Systems, Anwar A. AlJowder
Developing A Methodology To Detect Partial Failures For Dynamic Systems, Anwar A. AlJowder
Engineering Management & Systems Engineering Theses & Dissertations
The purpose of this research is to develop a decision support system that can assist in detecting partial failures in dynamic systems such as Fire Control System Tracking Radar (TR) onboard Naval Ships. Partial failures do not necessarily shut down the system immediately but cause degradation of operational performance. Previous work has shown that experts in the field of failure detection, test point insertion and BuiltInTest Equipment (BITE) can provide useful input in detecting partial failures. Partial failures affect operational system performance and support costs, which can be significant. Often, however, partial failure detection consists of the estimations and opinions ...
Textured Mos 2 Thin Films Obtained On Tungsten: Electrical Properties Of The W/Mos 2 Contact, E. Gourmelon, J. C. Bernède, J. Pouzet, S. Marsillac
Textured Mos 2 Thin Films Obtained On Tungsten: Electrical Properties Of The W/Mos 2 Contact, E. Gourmelon, J. C. Bernède, J. Pouzet, S. Marsillac
Electrical & Computer Engineering Faculty Publications
Textured films of molybdenum disulfide have been obtained by solid state reaction between the constituents in thin films form when a (200) oriented tungsten sheet is used as substrate. The crystallites have their c axis perpendicular to the plane of the substrate. The annealing conditions are T=1073K and t=30 min. The films are stoichoimetric and p type. Such highly textured films are achieved without foreign atom addition (Ni, Co...). It appears, as shown by xray photoelectron spectroscopy, that a thin WS_{2} layer is present at the interface W/MoS_{2}. The crystallization process is discussed by a ...
Large Amplitude Pitching Of Supermaneuver Delta Wings Including Flow Control, Yahia A. Abdelhamid
Large Amplitude Pitching Of Supermaneuver Delta Wings Including Flow Control, Yahia A. Abdelhamid
Mechanical & Aerospace Engineering Theses & Dissertations
The unsteady, threedimensional NavierStokes equations are solved to simulate and study the aerodynamic response of a delta wing undergoing large amplitude pitching motion up to 90° angle of attack. The primary model under consideration consists of a 76° swept, sharpedged delta wing of zero thickness, initially at zero angle of attack. The freestream Mach number and Reynolds number are 0.3 and 0.45 × 106, respectively. The governing equations are solved timeaccurately using the implicit, upwind, Roe fluxdifference splitting, finitevolume scheme. Both laminar and turbulent flow solutions are investigated. In the laminar flow solutions, validation of the computational results is ...
Efficient Dynamic Unstructured Methods And Applications For Transonic Flows And Hypersonic Stage Separation, Xiaobing Luo
Efficient Dynamic Unstructured Methods And Applications For Transonic Flows And Hypersonic Stage Separation, Xiaobing Luo
Mechanical & Aerospace Engineering Theses & Dissertations
Relativemoving boundary problems have a wide variety of applications. They appear in staging during a launch process, store separation from a military aircraft, rotorstator interaction in turbomachinery, and dynamic aeroelasticity.
The dynamic unstructured technology (DUT) is potentially a strong approach to simulate unsteady flows around relativemoving bodies, by solving timedependent governing equations. The dualtime stepping scheme is implemented to improve its efficiency while not compromising the accuracy of solutions. The validation of the implicit scheme is performed on a pitching NACA0012 airfoil and a rectangular wing with low reduced frequencies in transonic flows. All the matured accelerating techniques, including the ...
Placement Of Piezoelectric Actuators For Active Control Of Vibration Using Modal Parameters, Xuegeng Zhu
Placement Of Piezoelectric Actuators For Active Control Of Vibration Using Modal Parameters, Xuegeng Zhu
Mechanical & Aerospace Engineering Theses & Dissertations
An equation is derived to model the piezoelectric actuators incorporation with flexible structures. This equation permits the comparison of the performance indices over the entire structure for a piezoelectric actuator with constant area, which is unachievable if the Finite Element Method is used for complicated structures.
An index has been developed for placement of piezoelectric actuator for control of vibration of a flexible structure. This index is derived from the definition of H2norm. Computation of the proposed index requires only the natural frequencies and corresponding mode shapes of the structures of interest. The method is well suited to large ...
An Apparatus For Measuring The Thermal Conductivity Of Cast Insulation Materials, Christine A. Wilkins, Robert L. Ash
An Apparatus For Measuring The Thermal Conductivity Of Cast Insulation Materials, Christine A. Wilkins, Robert L. Ash
Mechanical & Aerospace Engineering Faculty Publications
A steadystate apparatus has been developed for measuring the thermal conductivity of cast materials. The design has employed a novel thermal symmetry arrangement which can permit total electrical isolation of the test material from its surroundings. © 1980 American Institute of Physics