Engineering Commons^™

On Velocity-Conditioned Scalar Mixing In Homogeneous Turbulence, Rodney O. Fox

Rodney O. Fox

Scalar mixing models are required to modelturbulent molecular mixing in full probability density function (pdf) simulations of turbulent reacting flows. Despite the existence of direct numerical simulation (DNS) data suggesting the contrary, most scalar mixing models assume that molecular mixing is independent of the instantaneous velocity, i.e., 〈D∇2φ|V,ψ〉=〈D∇2φ|ψ〉. Since in a joint velocity, composition pdf calculation the velocity is known, this assumption is unnecessary and leads to a lack of local isotropy in the scalar field. Moreover, since velocity conditioning offers a numerically tractable approach for including the effects of local anisotropy and mean velocity gradients on scalar mixing, it …

Построение Редуцированного Физического Гамильтониана Для Сферически-Симметричной Гравитации, Николай Заркевич

Nikolai A. Zarkevich

No abstract provided.

Electronic Origins Of Ordering In Multicomponent Metallic Alloys: Application To The Cu-Ni-Zn System, J. D. Althoff, Duane D. Johnson, F. J. Pinski, J. B. Staunton

Duane D. Johnson

We investigate the ordering tendencies of the fcc Cu-Ni-Zn system using a recently developed first-principles, density-functional-based theory of atomic short-range order (ASRO) in disordered substitutional alloys of an arbitrary number of components. We find for the binary alloys a variety of effects which should lead to competition in the ternaries: commensurate ordering (Ni-Zn), long-period ordering (Cu-rich Cu-Zn), and clustering (Cu-Ni), in agreement with experiment. We calculate the ASRO of various disordered ternary alloys (as described by the Warren-Cowley pair-correlation function) and discuss its relationship to the electronic structure of the binary and ternary disordered alloys. We find [100]-type ASRO over …

Oscillatory Dynamics In A Heterogeneous Surface Reaction: Breakdown Of The Mean-Field Approximation, R. Dennis Vigil, Frank T. Willmore

R. Dennis Vigil

Hierarchical mean-field rate equations and lattice-gas simulations were developed to elucidate the effects of the breakdown of the mean-field approximation for a model heterogeneous chemical oscillator that represents a simple extension of the well-known monomer-dimer surface reaction model. The bifurcation structure of the reaction kinetics depends sensitively on the details of surface transport processes, and the oscillatory behavior exhibited by the site approximation rate equations is not generally robust with respect to spatial correlations.

Comparison Of Sensors And Techniques For Crop Yield Mapping, Stuart J. Birrell, Kenneth A. Sudduth, Steven C. Borgett

Stuart J. Birrell

The implementation of site-specific crop management is dependent on the variations in yield and yield potential within a field. Crop yield maps are important for both the implementation and evaluation of site-specific crop management strategies. Management decisions and evaluations based on yield maps must take into consideration the accuracy and resolution of the maps.

An impact-based yield monitor and a volumetric yield monitor were compared. The effect of different dynamic models of combine grain flow on the calculated instantaneous yields were investigated. Both simple time delay models and first order models could be used to model the grain flow. In …

A Mixing Model To Improve The Pdf Simulation Of Turbulent Diffusion Flames, A. R. Masri, Shankar Subramaniam, S. B. Pope

Shankar Subramaniam

A new mixing model based on Euclidean minimum spanning trees (EMST), which has been developed by Subramaniam and Pope, is used in the PDF simulation of pilot-stabilized turbulent non-premixed flames. a model equation is solved for the joint PDF of velocity composition and turbulence frequency using a particle mesh method.

On The Importance Of Chain Reptation In Models Of Dissolution Of Glassy Polymers, Balaji Narasimhan, Nikolaos A. Peppas

Balaji Narasimhan

Polymer dissolution was described by chain reptation incorporated into penetrant transport. The penetrant concentration field was divided into three regimes which delineate three different transport processes. Solvent penetration through the polymer was modeled to occur as a consequence of a diffusional flux and an osmotic pressure contribution. Species momentum balances were written that coupled the polymer viscoelastic behavior with the transport mechanism. Transport in the second penetrant concentration regime was modeled to occur in a diffusion boundary layer adjacent to the rubbery-solvent interface, where a Smoluchowski type diffusion equation was obtained. The disentanglement rate of the polymer is given by …

An Efficient Fast‐Multipole Algorithm Based On An Expansion In The Solid Harmonics, H.Y. Wang, Richard Alan Lesar

Richard Alan Lesar

We present an efficient variant of the fast‐multipole method for calculating long‐range interactions in three‐dimensional Coulombic systems. Using a multipole expansion based on the solid harmonics instead of the more common spherical harmonics leads to a greater increase in computational efficiency than a recently‐reported fast‐Fourier transform method, with none of the overhead associated with that approach.

Subband Absolute Moment Block Truncation Coding, Kai-Kuang Ma, Sarah A. Rajala

Sarah A. Rajala

In this paper, a new subband coding system called subband absolute moment block truncation coding (SAMBTC) is introduced to compress monochrome images and color images recorded in YIQ and L*u*v* uniform color spaces. The SAMBTC incorporates full‐band absolute moment block truncation coding (AMBTC) into subbands along with a new subband dynamic bit allocation algorithm which is derived from the Shannon rate‐distortion bound. Simulation results show that the proposed Shannon/bound‐based bit allocation algorithm outperforms the commonly used standard‐deviation‐based bit allocation scheme. Compared with ABMTC, SAMBTC achieves superior imaging without blocking artifacts at low bit rates

Low‐Frequency Perturbation Theory In Eddy‐Current Non‐Destructive Evaluation, Nicola Harfield, Y. Yoshida, John R. Bowler

Nicola Bowler

A method is presented by which series solutions for the impedance change in an eddy‐current test probe due to closed cracks in a non‐magnetic, conducting half‐space can be derived at low frequency. The series solution is applicable for flaws whose dimensions are much smaller than the electromagnetic skin‐depth. The problem is formulated using an approach in which the flaw is represented by an equivalent distribution of current dipoles. The electric field scattered by the flaw is then written as an integral, over the flaw, of the product of the dipole density distribution and an appropriate Green’s function. Terms in the …

Evaluation Of Gps For Applications In Precision Agriculture, Steven C. Borgelt, John D. Harrison, Kenneth A. Sudduth, Stuart J. Birrell

Stuart J. Birrell

Location coordinate information is needed in precision agriculture to map in-field variability, and to serve as a control input for variable rate application. Differential global positioning system (DGPS) measurement techniques were compared with other independent data sources for sample point location and combine yield mapping operations. Sample point location could be determined to within 1 m (3 ft) 2dRMS using C/A code processing techniques and data from a high-performance GPS receiver. Higher accuracies could be obtained with carrier phase kinematic positioning methods, but this required more time and was a less robust technique with a greater potential for data acquisition …

Nutrient Mapping Implications Of Short-Range Variability, Stuart J. Birrell

Stuart J. Birrell

Successful site specific nutrient application depends on accurate soil nutrient maps, which are generally developed from grid samples. The implication of short range variability for soil nutrient mapping is investigated. Interpretation of soil nutrient maps must consider the level of confidence associated with estimated values.

Analysis Of Spatial Factors Influencing Crop Yield, K. A. Sudduth, S. T. Drummond, Stuart J. Birrell, N. R. Kitchen

Stuart J. Birrell

The spatial relationship between crop yields and soil and site parameters was modeled using several methods. Yield maps estimated by projection pursuit regression and neural network analysis agreed well with measured yields. These methods also allowed generation of response curves for estimated yield as a function of each of the input parameters. These response curves were useful for investigating the relationship between yields and individual soil and site parameters.

Missouri Precision Agriculture, N. R. Kitchen, K. A. Sudduth, Stuart J. Birrell, S. C. Borgelt

Stuart J. Birrell

A number of projects related to different facets of precision agriculture are being carried out by an interdisciplinary team of scientists and engineers with the University of Missouri and the USDA Agricultural Research Service. This paper provides an overview of those projects.