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Articles 1 - 14 of 14

Full-Text Articles in Mechanical Engineering

Coherent Solid/Liquid Interface With Stress Relaxation In A Phase-Field Approach To The Melting/Solidification Transition, Valery I. Levitas, Kamran Samani Oct 2011

Coherent Solid/Liquid Interface With Stress Relaxation In A Phase-Field Approach To The Melting/Solidification Transition, Valery I. Levitas, Kamran Samani

Aerospace Engineering Publications

An advanced Ginzburg-Landau (GL) approach to melting and solidification coupled with mechanics is developed. It is based on the concept of a coherent solid-liquid 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 size-dependent melting temperature and temperature-dependent thickness of the surface molten layer. All types of interface stress distributions ...


Surface-Induced Phase Transformations: Multiple Scale And Mechanics Effects And Morphological Transitions, Valery I. Levitas, Mahdi Javanbakht Oct 2011

Surface-Induced 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 Δξ and internal stresses on surface-induced pretransformation and phase transformations (PTs) are revealed. Using our further developed phase-field approach, we found that above some critical Δξ*, a morphological transition from fully transformed layer to lack of surface pretransformation occurs for any transformation strain εt. It corresponds to a sharp transition to the universal (independent of εt), strongly increasing the master relationship of the critical thermodynamic driving force for PT Xc on Δξ. For large εt, with increasing Δξ, X ...


3d Simulation Of Wind Turbine Rotors At Full Scale. Part Ii: Fluid–Structure Interaction Modeling With Composite Blades, Y. Bazilevs, Ming-Chen Hsu, J. Kiendel, R. Wuchner, K. U. Bletzigner Oct 2011

3d Simulation Of Wind Turbine Rotors At Full Scale. Part Ii: Fluid–Structure Interaction Modeling With Composite Blades, Y. Bazilevs, Ming-Chen Hsu, J. Kiendel, R. Wuchner, K. U. Bletzigner

Ming-Chen Hsu

In this two-part 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 analysis-suitable 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 ...


High-Performance Computing Of Wind Turbine Aerodynamics Using Isogeometric Analysis, Ming-Chen Hsu, Ido Akkerman, Yuri Bazilevs Oct 2011

High-Performance Computing Of Wind Turbine Aerodynamics Using Isogeometric Analysis, Ming-Chen Hsu, Ido Akkerman, Yuri Bazilevs

Ming-Chen Hsu

In this article we present a high-performance computing framework for advanced flow simulation and its application to wind energy based on the residual-based 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 Electric-Field Imprinting For Micron And Sub-Micron Patterns On Wavy Or Planar Surfaces, Abhijit Chandra, Ashraf F. Bastawros, Ambar K. Mitra, Charles A. Lemaire Aug 2011

Apparatus For Focused Electric-Field Imprinting For Micron And Sub-Micron 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 fine-pitched 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 proton-exchange membrane whose shape is varied using suction on a backing fluid through a support mask. Other ...


Phase-Field Modeling Of Fracture In Liquid, Valery I. Levitas, Alexander V. Idesman, Ameeth K. Palakala Aug 2011

Phase-Field Modeling Of Fracture In Liquid, Valery I. Levitas, Alexander V. Idesman, Ameeth K. Palakala

Aerospace Engineering Publications

Phase-field 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 phase-field approaches for any material instability. Analytical analysis of the equations is performed. Problems relevant to the melt-dispersion mechanism of the reaction ...


Single-Shot Gas-Phase Thermometry Using Purerotational Hybrid Femtosecond/Picosecond Coherent Anti-Stokes Raman Scattering, Joseph D. Miller, Sukesh Roy, Mikhail N. Slipchenko, James R. Gord, Terrence R. Meyer Aug 2011

Single-Shot Gas-Phase Thermometry Using Purerotational Hybrid Femtosecond/Picosecond Coherent Anti-Stokes Raman Scattering, Joseph D. Miller, Sukesh Roy, Mikhail N. Slipchenko, James R. Gord, Terrence R. Meyer

Mechanical Engineering Publications

High-repetition-rate, single-laser-shot measurements are important for the investigation of unsteady flows where temperature and species concentrations can vary significantly. Here, we demonstrate singleshot, pure-rotational, hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (fs/ps RCARS) thermometry based on a kHz-rate 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 100-fs pump/Stokes pulses and the pulse-shaped 8.4-ps probe. A time- and frequency-domain theoretical model is introduced to account for rotational-level dependent collisional dephasing and indicates that the optimal probe-pulse 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 Jul 2011

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 second-order orthorhombic-to-tetragonal 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 4-4 (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, N1 at 4d, and N2 at 8h Wyckoff positions. Both of ...


Abstracts, Review Of Progress In Quantitative Nondestructive Evaluation (Burlington, Vermont, July 17-22, 2011), Center For Nondestructive Evaluation, Iowa State University Jul 2011

Abstracts, Review Of Progress In Quantitative Nondestructive Evaluation (Burlington, Vermont, July 17-22, 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 Quadrature-Based Kinetic Model For Dilute Non-Isothermal Granular Flows, Alberto Passalacqua, Janine E. Galvin, Prakash Vedula, Christine M. Hrenya, Rodney O. Fox Jul 2011

A Quadrature-Based Kinetic Model For Dilute Non-Isothermal 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 hard-sphere collision kernel for mono-dispersed particles. Different orders of accuracy in terms of the moments of the velocity distribution function are considered, accounting for moments up to seventh order. Quadrature-based closures for four different models for inelastic collisionthe Bhatnagar-Gross-Krook, ES-BGK, the Maxwell model for hard-sphere collisions, and the full Boltzmann hard-sphere collision integral-are derived and compared. The approach is validated studying a dilute non-isothermal granular flow of inelastic particles between two stationary Maxwellian walls. Results obtained from the kinetic models ...


Model-Assisted Development Of A Laminography Inspection System, Robert J. Grandin, Joseph N. Gray Jul 2011

Model-Assisted 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 non-destructive 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 geometrically-simple analytical models, such as the Shepp-Logan phantom, for the development of their algorithms. Recent work at the Center for Non-Destructive Evaluation makes extensive use of a forward model, XRSIM, to study artifacts ...


Mhz-Rate Nitric Oxide Planar Laser-Induced 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 Feb 2011

Mhz-Rate Nitric Oxide Planar Laser-Induced 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 laser-induced 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 high-speed image sequences captured a variety ...


3d Simulation Of Wind Turbine Rotors At Full Scale. Part I: Geometry Modeling And Aerodynamics, Y. Bazilevs, Ming-Chen Hsu, I. Akkerman, S. Wright, K. Takizawa, B. Henicke, T. Spielman, T. E. Tezduyar Jan 2011

3d Simulation Of Wind Turbine Rotors At Full Scale. Part I: Geometry Modeling And Aerodynamics, Y. Bazilevs, Ming-Chen Hsu, I. Akkerman, S. Wright, K. Takizawa, B. Henicke, T. Spielman, T. E. Tezduyar

Ming-Chen Hsu

In this two-part 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 analysis-suitable 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 Surface-Induced Melting Of Nanoparticles, Valery I. Levitas, Kamran Samani Jan 2011

Size And Mechanics Effects In Surface-Induced Melting Of Nanoparticles, Valery I. Levitas, Kamran Samani

Aerospace Engineering Publications

Various melting-related phenomena (like surface melting, size dependence of melting temperature, melting of few nm-size 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 phase-field 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 solid-melt interface with uniaxial transformation strain, is demonstrated. A crossover in temperature dependence of interface energy for radii below 20 nm is found. Surface-induced premelting and ...