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Articles 1  14 of 14
FullText Articles in Mechanical Engineering
Coherent Solid/Liquid Interface With Stress Relaxation In A PhaseField Approach To The Melting/Solidification Transition, Valery I. Levitas, Kamran Samani
Coherent Solid/Liquid Interface With Stress Relaxation In A PhaseField Approach To The Melting/Solidification Transition, Valery I. Levitas, Kamran Samani
Aerospace Engineering Publications
An advanced GinzburgLandau (GL) approach to melting and solidification coupled with mechanics is developed. It is based on the concept of a coherent solidliquid interface with a transformation strain tensor, the deviatoric part of which is described by a thermodynamically consistent kinetic equation. Due to the relaxation of the elastic energy, a promoting contribution to the driving force for phase transformation in the GL equation appears, both for melting and solidification. Good agreement with known experiments is obtained for Al nanoparticles for the sizedependent melting temperature and temperaturedependent thickness of the surface molten layer. All types of interface stress distributions ...
SurfaceInduced Phase Transformations: Multiple Scale And Mechanics Effects And Morphological Transitions, Valery I. Levitas, Mahdi Javanbakht
SurfaceInduced Phase Transformations: Multiple Scale And Mechanics Effects And Morphological Transitions, Valery I. Levitas, Mahdi Javanbakht
Aerospace Engineering Publications
Strong, surprising, and multifaceted effects of the width of the external surface layer Δ_{ξ} and internal stresses on surfaceinduced pretransformation and phase transformations (PTs) are revealed. Using our further developed phasefield approach, we found that above some critical Δ_{ξ}*, a morphological transition from fully transformed layer to lack of surface pretransformation occurs for any transformation strain ε_{t}. It corresponds to a sharp transition to the universal (independent of ε_{t}), strongly increasing the master relationship of the critical thermodynamic driving force for PT X_{c} on Δ_{ξ}. For large ε_{t}, with increasing Δ_{ξ}, X ...
3d Simulation Of Wind Turbine Rotors At Full Scale. Part Ii: Fluid–Structure Interaction Modeling With Composite Blades, Y. Bazilevs, MingChen Hsu, J. Kiendel, R. Wuchner, K. U. Bletzigner
3d Simulation Of Wind Turbine Rotors At Full Scale. Part Ii: Fluid–Structure Interaction Modeling With Composite Blades, Y. Bazilevs, MingChen Hsu, J. Kiendel, R. Wuchner, K. U. Bletzigner
MingChen Hsu
In this twopart paper, we present a collection of numerical methods combined into a single framework, which has the potential for a successful application to wind turbine rotor modeling and simulation. In Part 1 of this paper we focus on: 1. The basics of geometry modeling and analysissuitable geometry construction for wind turbine rotors; 2. The fluid mechanics formulation and its suitability and accuracy for rotating turbulent flows; 3. The coupling of air flow and a rotating rigid body. In Part 2, we focus on the structural discretization for wind turbine blades and the details of the fluid–structure interaction ...
HighPerformance Computing Of Wind Turbine Aerodynamics Using Isogeometric Analysis, MingChen Hsu, Ido Akkerman, Yuri Bazilevs
HighPerformance Computing Of Wind Turbine Aerodynamics Using Isogeometric Analysis, MingChen Hsu, Ido Akkerman, Yuri Bazilevs
MingChen Hsu
In this article we present a highperformance computing framework for advanced flow simulation and its application to wind energy based on the residualbased variational multiscale (RBVMS) method and isogeometric analysis. The RBVMS formulation and its suitability and accuracy for turbulent flow in a moving domain are presented. Particular emphasis is placed on the parallel implementation of the methodology and its scalability. Two challenging flow cases were considered: the turbulent Taylor–Couette flow and the NREL 5 MW offshore baseline wind turbine rotor at full scale. In both cases, flow quantities of interest from the simulation results compare favorably with the ...
Apparatus For Focused ElectricField Imprinting For Micron And SubMicron Patterns On Wavy Or Planar Surfaces, Abhijit Chandra, Ashraf F. Bastawros, Ambar K. Mitra, Charles A. Lemaire
Apparatus For Focused ElectricField Imprinting For Micron And SubMicron Patterns On Wavy Or Planar Surfaces, Abhijit Chandra, Ashraf F. Bastawros, Ambar K. Mitra, Charles A. Lemaire
Aerospace Engineering Patents
A Focused Electric Field Imprinting (FEFI) process and apparatus provides a focused electric field to guide an unplating operation and/or a plating operation to form very finepitched metal patterns on a substrate. The process is a variation of the electrochemical unplating process, wherein the process is modified for imprinting range of patterns of around 2000 microns to 20 microns or less in width, and from about 0.1 microns or less to 10 microns or more in depth. Some embodiments curve a protonexchange membrane whose shape is varied using suction on a backing fluid through a support mask. Other ...
PhaseField Modeling Of Fracture In Liquid, Valery I. Levitas, Alexander V. Idesman, Ameeth K. Palakala
PhaseField Modeling Of Fracture In Liquid, Valery I. Levitas, Alexander V. Idesman, Ameeth K. Palakala
Aerospace Engineering Publications
Phasefield theory for the description of the overdriven fracture in liquid (cavitation) in tensile pressure wave is developed. Various results from solid mechanics are transferred into mechanics of fluids. Thermodynamic potential is formulated that describes the desired tensile pressure–volumetric strain curve and for which the infinitesimal damage produces infinitesimal change in the equilibrium bulk modulus. It is shown that the gradient of the order parameter should not be included in the energy, in contrast to all known phasefield approaches for any material instability. Analytical analysis of the equations is performed. Problems relevant to the meltdispersion mechanism of the reaction ...
SingleShot GasPhase Thermometry Using Purerotational Hybrid Femtosecond/Picosecond Coherent AntiStokes Raman Scattering, Joseph D. Miller, Sukesh Roy, Mikhail N. Slipchenko, James R. Gord, Terrence R. Meyer
SingleShot GasPhase Thermometry Using Purerotational Hybrid Femtosecond/Picosecond Coherent AntiStokes Raman Scattering, Joseph D. Miller, Sukesh Roy, Mikhail N. Slipchenko, James R. Gord, Terrence R. Meyer
Mechanical Engineering Publications
Highrepetitionrate, singlelasershot measurements are important for the investigation of unsteady flows where temperature and species concentrations can vary significantly. Here, we demonstrate singleshot, purerotational, hybrid femtosecond/picosecond coherent antiStokes Raman scattering (fs/ps RCARS) thermometry based on a kHzrate fs laser source. Interferences that can affect nanosecond (ns) and ps CARS, such as nonresonant background and collisional dephasing, are eliminated by selecting an appropriate time delay between the 100fs pump/Stokes pulses and the pulseshaped 8.4ps probe. A time and frequencydomain theoretical model is introduced to account for rotationallevel dependent collisional dephasing and indicates that the optimal probepulse time ...
Phase Transition And Structure Of Silver Azide At High Pressure, Dongbin Hou, Fuxiang Zhang, Cheng Ji, Trevor Hannon, Hongyang Zhu, Jianzhe Wu, Valery I. Levitas, Yanzhang Ma
Phase Transition And Structure Of Silver Azide At High Pressure, Dongbin Hou, Fuxiang Zhang, Cheng Ji, Trevor Hannon, Hongyang Zhu, Jianzhe Wu, Valery I. Levitas, Yanzhang Ma
Aerospace Engineering Publications
ilver azide (AgN _{3}) was compressed up to 51.3 GPa. The results reveal a reversible secondorder orthorhombictotetragonal phase transformation starting from ambient pressure and completing at 2.7 GPa. The phase transition is accompanied by a proximity of cell parameters aand b, a 3° rotation of azide anions, and a change of coordination number from 44 (four short, four long) to eight fold. The crystal structure of the high pressure phase is determined to be inI4/mcm space group, with Ag at 4a, N_{1} at 4d, and N_{2} at 8h Wyckoff positions. Both of ...
Abstracts, Review Of Progress In Quantitative Nondestructive Evaluation (Burlington, Vermont, July 1722, 2011), Center For Nondestructive Evaluation, Iowa State University
Abstracts, Review Of Progress In Quantitative Nondestructive Evaluation (Burlington, Vermont, July 1722, 2011), Center For Nondestructive Evaluation, Iowa State University
Review of Progress in Quantitative Nondestructive Evaluation
Abstracts of papers presented at the 2011 Review of Progress in Quantitative Nondestructive Evaluation (QNDE) conference held in Burlington, Vermont from July 17–22, 2011.
A QuadratureBased Kinetic Model For Dilute NonIsothermal Granular Flows, Alberto Passalacqua, Janine E. Galvin, Prakash Vedula, Christine M. Hrenya, Rodney O. Fox
A QuadratureBased Kinetic Model For Dilute NonIsothermal Granular Flows, Alberto Passalacqua, Janine E. Galvin, Prakash Vedula, Christine M. Hrenya, Rodney O. Fox
Chemical and Biological Engineering Publications
A moment method with closures based on Gaussian quadrature formulas is proposed to solve the Boltzmann kinetic equation with a hardsphere collision kernel for monodispersed particles. Different orders of accuracy in terms of the moments of the velocity distribution function are considered, accounting for moments up to seventh order. Quadraturebased closures for four different models for inelastic collisionthe BhatnagarGrossKrook, ESBGK, the Maxwell model for hardsphere collisions, and the full Boltzmann hardsphere collision integralare derived and compared. The approach is validated studying a dilute nonisothermal granular flow of inelastic particles between two stationary Maxwellian walls. Results obtained from the kinetic models ...
ModelAssisted Development Of A Laminography Inspection System, Robert J. Grandin, Joseph N. Gray
ModelAssisted Development Of A Laminography Inspection System, Robert J. Grandin, Joseph N. Gray
Center for Nondestructive Evaluation Conference Papers, Posters and Presentations
Traditional computed tomography (CT) is an effective method of determining the internal structure of an object through nondestructive means; however, inspection of certain objects, such as those with planar geometrics or with limited access, requires an alternate approach. An alternative is laminography and has been the focus of a number of researchers in the past decade for both medical and industrial inspections. Many research efforts rely on geometricallysimple analytical models, such as the SheppLogan phantom, for the development of their algorithms. Recent work at the Center for NonDestructive Evaluation makes extensive use of a forward model, XRSIM, to study artifacts ...
MhzRate Nitric Oxide Planar LaserInduced Fluorescence Imaging In A Mach 10 Hypersonic Wind Tunnel, Naibo Jiang, Matthew Webster, Walter R. Lempert, Joseph D. Miller, Terrence R. Meyer, Christopher B. Ivey, Paul M. Danehy
MhzRate Nitric Oxide Planar LaserInduced Fluorescence Imaging In A Mach 10 Hypersonic Wind Tunnel, Naibo Jiang, Matthew Webster, Walter R. Lempert, Joseph D. Miller, Terrence R. Meyer, Christopher B. Ivey, Paul M. Danehy
Mechanical Engineering Publications
Nitric oxide planar laserinduced fluorescence (NO PLIF) imaging at repetition rates as high as 1 MHz is demonstrated in the NASA Langley 31 in. Mach 10 hypersonic wind tunnel. Approximately 200 timecorrelated image sequences of between 10 and 20 individual frames were obtained over eight days of wind tunnel testing spanning two entries in March and September of 2009. The image sequences presented were obtained from the boundary layer of a 20° flat plate model, in which transition was induced using a variety of different shaped protuberances, including a cylinder and a triangle. The highspeed image sequences captured a variety ...
3d Simulation Of Wind Turbine Rotors At Full Scale. Part I: Geometry Modeling And Aerodynamics, Y. Bazilevs, MingChen Hsu, I. Akkerman, S. Wright, K. Takizawa, B. Henicke, T. Spielman, T. E. Tezduyar
3d Simulation Of Wind Turbine Rotors At Full Scale. Part I: Geometry Modeling And Aerodynamics, Y. Bazilevs, MingChen Hsu, I. Akkerman, S. Wright, K. Takizawa, B. Henicke, T. Spielman, T. E. Tezduyar
MingChen Hsu
In this twopart paper we present a collection of numerical methods combined into a single framework, which has the potential for a successful application to wind turbine rotor modeling and simulation. In Part 1 of this paper we focus on: 1. The basics of geometry modeling and analysissuitable geometry construction for wind turbine rotors; 2. The fluid mechanics formulation and its suitability and accuracy for rotating turbulent flows; 3. The coupling of air flow and a rotating rigid body. In Part 2 we focus on the structural discretization for wind turbine blades and the details of the fluid–structure interaction ...
Size And Mechanics Effects In SurfaceInduced Melting Of Nanoparticles, Valery I. Levitas, Kamran Samani
Size And Mechanics Effects In SurfaceInduced Melting Of Nanoparticles, Valery I. Levitas, Kamran Samani
Aerospace Engineering Publications
Various meltingrelated phenomena (like surface melting, size dependence of melting temperature, melting of few nmsize particles and overheating at a very fast heating rate) are of great fundamental and applied interest, although the corresponding theory is still lacking. Here we develop an advanced phasefield theory of melting coupled to mechanics, which resolves numerous existing contradictions and allowed us to reveal exciting features of melting problems. The necessity of introducing an unexpected concept, namely, coherent solidmelt interface with uniaxial transformation strain, is demonstrated. A crossover in temperature dependence of interface energy for radii below 20 nm is found. Surfaceinduced premelting and ...