Maximum Energy Criterion Research Articles

Application of Point-by-Point Vector Synthesis in Walkaway VSP Logging Data Processing

At present, it is necessary to use Walkaway VSP logging imaging data to drill horizontal shale gas wells in exploration areas lacking three-dimensional seismic data. Walkaway VSP logging imaging profile can delineate the formation structure around wells, obtain detailed information of dip, inclination and fault around wells, and guide the trajectory design of horizontal wells. But VSP logging is richer and more complex than conventional seismic data. The precondition of up-going wave imaging is to separate up-going P-wave or converted S-wave from complex wave field. Nowadays, most vector synthesis techniques can not completely separate up-going P-wave from up-going converted wave, which affects the accuracy of final imaging results. In order to achieve the best wave field separation effect of VSP logging data, the point-by-point vector synthesis technique is adopted. Firstly, the directional rotation synthesis of horizontal components is carried out according to the maximum energy criterion. Then the rotational synthesis of horizontal and vertical components uses ray tracing based on velocity model to estimate the polarization angle of time-varying upward reflected P-wave or converted wave. The method of “velocity fine-tuning scanning” is applied to search for the best synthesis angle, and the point-by-point vector synthesis is carried out by calculating the time-varying polarization angle. Finally, the best separation effect data are selected as the final vector synthesis result. This technique solves the problem that conventional vector synthesis cannot completely separate up-going P-wave from up-going converted S-wave. Upward P-waves acquired after separation has clear characteristics, more continuous phase axis and good fidelity processing effect, which lays a solid foundation for fine imaging of target formation in the study area and has become an indispensable key supporting technology for optimizing the trajectory of horizontal wells in shale gas development in Sichuan Basin.

Wavelet analysis of coherent structures and intermittency in forced homogeneous isotropic turbulence with polymer additives

Large eddy simulation was performed for forced homogeneous isotropic turbulence with/without polymer additives. Wavelet transform in one dimension and two dimensions were performed to investigate the multi-resolution features of coherent structures and intermittency in forced homogeneous isotropic turbulence based on large eddy simulation database. Using wavelet decomposition in one dimension and two dimension, it is found that polymer additives behave inhibitive effect on the intermittent pulse and the amount of coherent structures in forced homogeneous isotropic turbulence. The reconstructions of velocity waveform for coherent structures with strongest intermittence were surveyed at the scale a=26 obtained by maximum energy criterion, showing that the quasi-periodicity and intermittence for coherent structures in polymer solutions are not as distinct as that in the Newtonian fluid. To detect intermittency, the flatness factor and local intermittency measure for velocity fluctuation signals were calculat...

Research Progress of Wavelet Analysis in Flow Structure Characterization

The wavelet analysis is a time-frequency analysis method, which plays an important role in processing non-stationary signals obtained by Particle Image Velocimetry (PIV) to measure turbulent flow fields. Current research status for wavelet analysis in the flow field structure was reviewed: eduction of coherent structures and multi-scale structures(the large-, intermediate- and relatively small-scale structures)by wavelet transform and combine with the maximum energy criterion, extraction of coherent vortical structures and analysis of multi-scale turbulent structures information from the time–frequency diagram. Application of wavelet analysis in the flow structures was also prospected.

Optimum selection combining using the maximum energy criterion for M-ary NCFSK in Rician fading channels

Optimum selection combining using the maximum energy (OSC-ME) criterion for M-ary noncoherent frequency shift keying signaling in independent and nonidentically distributed fading channels is examined. A weighted maximum energy selection combining (WMESC) scheme is proposed and found to provide virtually the same symbol error probability as OSC-ME in Rician fading channels. The WMESC always provides power gain over the classical selection combining regardless of diversity order and signal-to-noise ratio.

Phase-averaged waveforms of Reynolds stress in wall turbulence during the burst events of coherent structures

The time sequence signals of instantaneous longitudinal and normal velocity components at different vertical locations in the turbulent boundary layer over a smooth flat plate have been finely measured by constant temperature anemometry of model IFA-300 and X-shaped hot-wire sensor probe in a wind tunnel. The longitudinal and normal velocity components have been decomposed into multi-scales by wavelet transform. The upward eject and downward sweep motions in a burst process of coherent structure have been detected by the maximum energy criterion of identifying burst event in wall turbulence through wavelet analysis. The relationships of phase-averaged waveforms among longitudinal velocity component, normal velocity component and Reynolds stress component have been studied through a correlation function method. The dynamics course of coherent structures and their effects on statistical characteristics of turbulent flows are analyzed.

The wavelet analysis on the relation of the wall pressure fluctuating and turbulent coherent structures

Abstract Measurements of the wall pressure have been carried out by high-resolution pressure transducers in a wind tunnel and a flume respectively. The characteristics of time scales of the wall pressure signal can be obtained by the non-traditional wavelet analysis with the maximum energy criterion for identifying burst events in wall turbulence.

Finite difference 3D common-shot migration of data from the West Delta area of the Gulf of Mexico

The advent of the network, or “cluster,” of modern personal computers has enabled prestack 3D “wave equation” methods, such as common-shot migration, to become practical alternatives to standard Kirchhoff depth migration. Clusters have overcome hardware limitations (cost-effective memory and speed) that previously limited the widespread use of these wave equation algorithms. Prestack Kirchhoff migration is efficient and easily adapts to various data acquisition geometries, while its steep-dip and high-resolution imaging capabilities are unparalleled. Traveltime calculations, typically by ray tracing, are fundamental to conventional Kirchhoff migration. However, propagating wavefronts become complicated when traveling through complex geology; for example, a simple spherical wave propagating near its source eventually separates into several (or many) distinct “branches” as the wave encounters large lateral velocity variations. Computing 3D traveltime fields that faithfully represent such wave propagation and actually using these in 3D Kirchhoff migration is difficult and computationally expensive. Conventional Kirchhoff migration instead uses simplified, single-valued traveltime fields produced by criteria such as first arrival or maximum energy. Where several raypaths encounter a grid node, for example, the maximum-energy criterion selects the traveltime from the raypath with largest amplitude. The single-valued traveltime approximation may be poor in complex geology, where the traveltime fields really are multibranched or multivalued. Prestack wave equation imaging, on the other hand, such as finite difference common-shot migration, uses numerical modeling of the one-way wave equation instead of ray tracing. These wave equation methods can be more accurate than ray methods for modeling wave propagation in complex media. The result can be a superior image in areas of complex geology, such as beneath salt bodies. The most serious limitation of these one-way wave equation methods is that they are dip-limited relative to Kirchhoff methods, especially for strong lateral velocity variations. Most of today's prestack wave equation methods use accurate “dual-domain” techniques …

Tensile properties of randomly oriented short δ-Al2O3 fiber reinforced aluminum alloy composites. I. Microstructure characteristics, fracture mechanisms and strength prediction

The tensile properties of short δ-Al2O3 fiber randomly reinforced aluminum alloy composites were characterized. Systems based on three matrix alloys, Al–5.5Zn, Al–5.5Mg and Al–12Si, were prepared to observe and measure the microstructural and mechanical characteristics of squeeze cast short fiber composites, including the orientation and length of short fiber, interfacial bond and micro-hardness of the reinforced matrix. It was found that the orientation and length of the short fibers satisfied the Weibull's and normal distribution, respectively. The micro-hardness values of the reinforced matrix alloys were higher than that of the unreinforced alloys. The interfacial bond differed with the variation of matrix alloy. Based on the microstructural characteristics and in situ tensile observation by scanning electronic microscopy, the fracture mechanisms of the three composite systems were discussed and related to the microstructural characterization. Finally, the tensile strengths of the composites were predicted by the statistical integration average method, based on using the maximum energy criterion for the composite strength. In this way, the prediction accounts for the practical distributions of the fiber orientation and length. The predicted results agree well with the experimental data.

Application of the Maximum Energy Criterion to Describe the Strength of the Motion Segment Under Axial Compression

A simulation study of compression of vertebral motion segments to failure was performed. The aim of this study was to determine whether damage of the motion segment under axial compression can be predicted when the load is quantified by means of the elastic energy storage it causes in the segment. Although in one-cycle loading, motion segment strength can be described by the relationship between the product of the bone density and cross-sectional area of the vertebrae and the maximum force, no single criterion has been found to describe strength in both one-cycle and cyclic compressional loading protocols. Input data were derived from in vitro studies by Hansson et al, Keller et al, and by Brinckmann et al. Elastic energy storage at failure was computed using a three-parameter model for a viscoelastic solid with a nonlinear initial response, and related to the product of the bone density and cross-sectional area. The relationship of the product of density and area with the elastic energy appeared to be accurately described by a curvilinear equation. This relationship accounted for 65-93% of the variance in maximum energy. Generalizability of the relationship from cyclic axial loading to one-cycle axial loading was successfully tested. The results of the present study have shown that one criterion suffices to describe the strength of the motion segment in different compressional loading modes.

Turbulent breakage of filamentous microorganisms in submerged culture in mechanically stirred bioreactors

A discussion is presented suggesting that hyphal breakage in mechanically stirred fermenters is likely to occur by direct tensile stresses acting on the opposite ends of the hypha of filamentous microorganisms. These stresses originate from the dynamic pressure fluctuations of eddies with scales in the inertial convection subrange of the turbulent energy spectrum. The maximum strain energy theory of failure of an elastic material under this mode of stress is used to set up a relationship between the stable length of hyphae and some of the physical parameters affecting it, including the mean energy dissipation rate in the bioreactor. Experimental data are reported for the rate of breakage of hyphae obtained under different operating conditions during the fermentation of Penicillium chrysogenum in a 7 and 150 1 mechanically stirred bioreactor. Data on the stable size of hyphae agree well with the model based on the maximum energy criterion. The experimental data further suggest that hyphal breakage is approximately a first-order kinetic process with a rate constant which appears to be moderately dependent on the product of the mean energy dissipation rate and the reciprocal of the impeller circulation time.

Variational transition state theory. Primary kinetic isotope effects for atom transfer reactions

The effect of variational determination of the location of the generalized transition state on the prediction of kinetic isotope effects for atom transfer reactions is considered. Instead of choosing the transition state dividing surface on the basis of the conventional maximum energy criterion, a maximum free energy criterion in which entropic effects compete with energetic effects is used. Several reactions with symmetric and nearly symmetric saddle points, loose saddle points, and intermediate cases are considered. Numerical examples are based on model potential energy surfaces for three-body systems. The model potential energy surfaces are based on a modified and extended bond-energy, bond-order method that have been presented previously. Examples involving isotopic substitution by /sup 2/H, /sup 3/H, /sup 14/C, and /sup 37/Cl for a wide range of temperatures are presented. In some cases the results of the variational calculations essentially confirm the more readily used conventional transition state theory. However, this is not always the case. It is shown that the location of the variationally best transition state dividing surface is sometimes very sensitive to isotopic substitution. Furthermore, this sometimes leads to a large change in the predicted kinetic isotope effect.