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Articles 1 - 10 of 10
Full-Text Articles in Engineering
A Fast Three-Step Phase-Shifting Algorithm, Peisen S. Huang, Song Zhang
A Fast Three-Step Phase-Shifting Algorithm, Peisen S. Huang, Song Zhang
Song Zhang
We propose a new three-step phase-shifting algorithm, which is much faster than the traditional three-step algorithm. We achieve the speed advantage by using a simple intensity ratio function to replace the arctangent function in the traditional algorithm. The phase error caused by this new algorithm is compensated for by use of a look-up-table (LUT). Our experimental results show that both the new algorithm and the traditional algorithm generate similar results, but the new algorithm is 3.4 times faster. By implementing this new algorithm in a high-resolution, real-time 3D shape measurement system, we were able to achieve a measurement speed of …
3-D Optical Measurement Using Phase Shifting Based Methods, Peisen S. Huang, Song Zhang
3-D Optical Measurement Using Phase Shifting Based Methods, Peisen S. Huang, Song Zhang
Song Zhang
We review some of our most recent works on 3-D shape measurement using the digital fringe projection and phase-shifting method. First, we introduce the measurement principle and phase-shifting algorithms. Then we discuss an effective method for phase error compensation and a novel idea for system calibration. Finally, we describe a 3-D shape measurement system for high-resolution, real-time 3-D shape acquisition, reconstruction and display.
Phase Error Compensation For A 3-D Shape Measurement System Based On The Phase-Shifting Method, Song Zhang, Peisen S. Huang
Phase Error Compensation For A 3-D Shape Measurement System Based On The Phase-Shifting Method, Song Zhang, Peisen S. Huang
Song Zhang
This paper describes a novel phase error compensation method for reducing the measurement error caused by non-sinusoidal waveforms in the phase-shifting method. For 3D shape measurement systems using commercial video projectors, the non-sinusoidal nature of the projected fringe patterns as a result of the nonlinear gamma curve of the projectors causes significant phase measurement error and therefore shape measurement error. The proposed phase error compensation method is based on our finding that the phase error due to the non-sinusoidal waveform of the fringe patterns depends only on the nonlinearity of the projector's gamma curve. Therefore, if the projector's gamma curve …
Crystal-Amorphous And Crystal-Crystal Phase Transformations Via Virtual Melting, Valery I. Levitas
Crystal-Amorphous And Crystal-Crystal Phase Transformations Via Virtual Melting, Valery I. Levitas
Valery I. Levitas
A new mechanism of crystal (c)–amorphous (a) and c-c phase transformations (PTs) and internal stress relaxation via virtual melting (VM) induced by internal stresses was justified thermodynamically and kinetically. VM removes interface friction, reduces kinetic barrier, increases atomic mobility, and can reduce thermodynamic melting temperature. We combine VM and nonequilibrium PT diagrams to develop new scenarios of c-a and c-c PTs. Results are applied for a new interpretation of c-c and c-a PT mechanisms in ice Ih and are also applicable for other materials.
Inverse Design Of And Experimental Measurements In A Double-Passage Transonic Turbine Cascade Model, G. M. Laskowski, A. Vicharelli, G. Medic, C. J. Elkins, J. K. Eaton, Paul A. Durbin
Inverse Design Of And Experimental Measurements In A Double-Passage Transonic Turbine Cascade Model, G. M. Laskowski, A. Vicharelli, G. Medic, C. J. Elkins, J. K. Eaton, Paul A. Durbin
Paul A. Durbin
A new transonic turbine cascade model that accurately produces infinite cascade flow conditions with minimal compressor requirements is presented. An inverse design procedure using the Favre-averaged Navier-Stokes equations and k-ε turbulence model based on the method of steepest descent was applied to a geometry consisting of a single turbine blade in a passage. For a fixed blade geometry, the passage walls were designed such that the surface isentropic Mach number (SIMN) distribution on the blade in the passage matched the SIMN distribution on the blade in an infinite cascade, while maintaining attached flow along both passage walls. An experimental rig …
Unsteady Effects On Trailing Edge Cooling, G. Medic, Paul A. Durbin
Unsteady Effects On Trailing Edge Cooling, G. Medic, Paul A. Durbin
Paul A. Durbin
It is shown how natural and forced unsteadiness play a major role in turbine blade trailing edge cooling flows. Reynolds averaged simulations are presented for a surface jet in coflow, resembling the geometry of the pressure side breakout on a turbine blade. Steady computations show very effective cooling; however when natural-or even moreso, forced-unsteadiness is allowed, the adiabatic effectiveness decreases substantially. Streamwise vortices in the mean flow are found to be the cause of the increased heat transfer.
Optimizing Vibration Isolation Of Flex Circuits In Hard Disk Drives, M. R. Brake, Jonathan A. Wickert
Optimizing Vibration Isolation Of Flex Circuits In Hard Disk Drives, M. R. Brake, Jonathan A. Wickert
Jonathan A. Wickert
A "flex circuit" is a laminate of polyimide substrate, adhesive, and copper conductors that is used to connect the stationary electronic components in a computer hard disk drive to the rotating arm that positions read/write heads above the disks. The flex circuit's transverse and longitudinal vibrations couple with the arm, and those motions, although seemingly small, degrade performance during seek operations from one data track to another. The flex circuit and arm mechanism is defined by a number of geometric parameters, and some latitude is available at the design stage for choosing dimensions and angles so as to minimize vibration …
Solid-Solid Phase Transformation Via Internal Stress-Induced Virtual Melting: Additional Confirmations, Valery I. Levitas, Laura B. Smilowitz, Bryan F. Henson, Blaine W. Asay
Solid-Solid Phase Transformation Via Internal Stress-Induced Virtual Melting: Additional Confirmations, Valery I. Levitas, Laura B. Smilowitz, Bryan F. Henson, Blaine W. Asay
Valery I. Levitas
Recently, we predicted a mechanism of solid-solid phase transformation (PT) via virtual melting at 121K below the melting temperature. We report additional experimental and theoretical results for PTs among three polymorphs of the energetic material HMX, α, β, and δ that support this mechanism. In particular: (a) the predicted velocity of interface propagation for β→δ PT and overall kinetics of δ→β PT are in agreement with experiment; (b) the energy of internal stresses is sufficient to reduce the melting temperature from 520to400K for δ→β PT; (c) the nanocracking that appears during solidification does not change the PT thermodynamics and kinetics …
A Lagrangian Stochastic Model For Dispersion In Stratified Turbulence, S. K. Das, Paul A. Durbin
A Lagrangian Stochastic Model For Dispersion In Stratified Turbulence, S. K. Das, Paul A. Durbin
Paul A. Durbin
In this paper we discuss the development of a Lagrangian stochastic model (LSM) for turbulent dispersion of a scalar (species). Given any tensorally linear second-moment closure (SMC) turbulence model we show how to derive a mathematically equivalent set of stochastic differential equations (SDEs), i.e., the second-moment equations constructed from these SDEs are exactly the same (within a realizability constraint) as the given SMC. This set of equations forms the LSM. Both turbulence anisotropy and buoyancy effects are incorporated by this method. In order to achieve the correct critical Richardson number and to obtain the simplest Lagrangian formulation, a revised set …
Transformation-Induced Plasticity And Cascading Structural Changes In Hexagonal Boron Nitride Under High Pressure And Shear, Valery I. Levitas, Yanzhang Ma, Javad Hashemi
Transformation-Induced Plasticity And Cascading Structural Changes In Hexagonal Boron Nitride Under High Pressure And Shear, Valery I. Levitas, Yanzhang Ma, Javad Hashemi
Valery I. Levitas
In situx-ray diffraction study and modeling of the degree of disorder, s, and phase transformation (PT) in hexagonal hBN were performed. It was proven that changes in s are strain-induced and that s can be used to quantify plastic strain. During the strain-induced hBN→wurtzitic wBN PT, the transformation-induced plasticity (TRIP) was exposed and quantified. TRIP exceeds conventional plasticity by a factor of 20. Cascading structural changes were revealed. Strain-induced disorder explains why PT under hydrostatic and nonhydrostatic conditions started at the same pressure∼10GPa. For the same disorder, plastic shear reduces PT pressure by a factor of 3–4.