acase@tulane.edu

The purpose of this research project was to improve the accuracy of the predictions for the solubility of hydrocarbon solids in supercritical fluids. The role of size and energy asymmetries of solid-supercritical fluid systems on the attractive and repulsive pressure terms of various equations of state was determined. Modifications to improve the accuracy of the solubility predictions can be made based on the role of these pressure terms in the model The Peng-Robinson equation of state, with different random fluid mixing rules, was used to predict the solubility of a solid in a supercritical solvent. Discrepancies in accurately predicting the solubility appear to be due to the random fluid assumption rather than the form of the particular mixing rule. A modification of the van der Waals one-fluid mixing rule which includes both temperature and density dependence for the attractive parameter of the equation of state was developed based on a probabilistic approach. With the proposed modification, the Peng-Robinson equation of state can provide good solubility predictions Discrepancies in accurately predicting the solubility of solids in supercritical fluids with the more complex Boublik-Alder-Chen-Kreglewski equation of state are again due to the random fluid approximation in the mixing rule. The Perturbed-Hard-Chain equation of state, using rigorously derived mixing rules and eliminating the random fluid assumption (a nonrandomness concept), yields good results for solubility predictions. Importantly, the Perturbed-Hard-Chain approach offers the ability of extrapolative calculations, since the binary interaction coefficient can be obtained from previously compiled data. To give a more theoretical basis for the dependence of the attractive term of the equation of state on density, Local Composition Theory was used with the three equations of state, but its application yielded poor results for solubility predictions To determine the role of the repulsive force contribution to the equation of state, the combinatorial entropy of mixing for the system was calculated using the repulsive term of the three equations of state. Results suggest that the repulsive term of the Perturbed-Hard-Chain equation of state is the most correct form / acase@tulane.edu

Until recently, predicting the increase in soil resistance during pile driving due to short or lengthy delays was unfeasible. It has often relied on experience and judgement Estimating the hammer efficiency for theoretical wave equation studies was disputable. Dynamic measurements performed on piles during pile driving produced a wide varying range of unexplainable efficiency correlations From fifteen actual platform case studies comprising over eighty piles, design curves to estimate the average increase in unit friction and the ratio of average increase in unit skin friction to average unit adhesion at the resumption of pile driving as a function of time and depth are provided A new concept that explains the variation in dynamic measurement results is also provided A new theoretical method to construct the soil resistance during pile driving versus blows/foot curve is included It is hoped that the work included in this study will be an incentive for further research work / acase@tulane.edu

acase@tulane.edu

The transportation costs of low value per unit volume materials can become a major portion of the total distribution cost. A stochastic dynamic mixed-integer linear program of a transportation model containing intermediate processing stations between suppliers and demand centers has been developed which has been found to reduce total transportation costs by 39 percent over standard models. The model selects the optimal locations for the intermediate processing stations and the primary demand center from a given set of possible candidates. It includes costs of environmental constraints and includes the stochastic (e.g., seasonal) nature of the supply / acase@tulane.edu

acase@tulane.edu

The purpose of this doctoral research was to pursue a better understanding of heterocoagulation When fine particles are placed in an ionic fluid medium, a two-phase system may be formed. This type of two-phase system is called colloidal dispersion. In most cases, a colloidal dispersion is thermodynamically unstable due to the tendency of the dispersed phase to minimize its surface area. Thermodynamic equilibrium between the two phases is established when the suspended particles coalesce and form a precipitate. When suspended particles are similar in surface chemical characteristics, the aggregation process is known as homocoagulation, whereas if the suspended particles are dissimilar in surface chemical nature, the process may be more accurately termed as heterocoagulation Particle encounters which may or may not result in coagulation occur due to Brownian motion and external forces. Whether coagulation takes place or not depends on the magnitude of the forces which particles exert on each other as they interact. These forces need to be understood and quantified for the purpose of explaining a macroscopic phenomenon of colloidal stability and coagulation. Since particles in a colloidal dispersion may be dissimilar in surface chemical nature, the forces of heterointeracting particles need to be understood as the forces of heterointeracting particles. Investigations were made on the forces between dissimilar particles to assess a heterocoagulation process quantitatively An algorithm to calculate the electrostatic repulsion energy between dissimilar spheres was developed. This algorithm solves the Poisson-Boltzmann equation between dissimilar plates by de-coupling the equation and estimates the spherical interaction energy using the Derjaguin method. Since a colloidal dispersion may consist of particles with different sizes, the effect of particle size distribution on the dispersion stability was investigated. The stability of polydisperse colloidal dispersion was experimentally investigated using an acoustically created n-pentadecane-in-water emulsion by a Coulter Counter. In addition, the effect of surface potential distribution was theoretically studied. Because the experimental data available on the stability of colloidal dispersion in most cases are concerned with only the onset of coagulation, viz. formation of secondary particles, an investigation was conducted on the advanced stages of coagulation of monodisperse polystyrene latices. (Abstract shortened with permission of author.) / acase@tulane.edu

A study on the static stresses developed by granular materials in storage containers is presented here in two parts. The first part of this work was initiated by the improvements provided by Cowin on the classical Janssen's formulas for bin static stresses. Janssen assumed that the horizontal and vertical stresses inside the bin at a particular depth were uniform. He also assumed that full frictional force is mobilized at the bin wall. Cowin replaced these stronger assumptions with less restrictive assumptions and rederived the essence of Janssen's results. In his improved formulas Cowin also included the effect of material consolidation upon the bin stresses, an aspect, which was not considered in the original Janssen's formulas. In the first part of this dissertation, a reassessment of most of the experimental investigation, based on Cowin's improved formulas is presented. Also, an experimental investigation on the granular material consolidation is reported and the results of this investigation show that the improved formulas are reasonable and practical In the second part, a concept from classical Janssen's theory is incorporated into an equilibrium continuum theory and applied to two dimensional bin and hopper problems. The method of characteristics is used to obtain the bin and hopper static stress solutions and the results are compared with solutions obtained from limiting static equilibrium (LSE) theory. The LSE theory also uses the method of characteristics and the solutions involve cumbersome numerical procedures. But, the method based on equilibrium continuum theory presents analytical solutions and gives bounds on bin and hopper static stresses / acase@tulane.edu

acase@tulane.edu

In the analysis of piles supporting offshore structures under lateral loading conditions, the key element is predicting the lateral load-deformation relationship (P-Y curves) for the soil. The present practice of constructing P-Y curves is based on the results of lateral load tests on instrumented piles and strength-deformation characteristics of the soil The research described in this paper was sponsored by Texaco U.S.A. It narrates a procedure for estimating the uncertainties in the computed deflections and bending moments in a pile subjected to lateral loads. In this procedure, the uncertainties in the soil properties and soil response are first estimated; then, employing the finite difference equations governing the pile behavior, estimates are made of the uncertainties in the computed curves which describe the lateral behavior of the pile The investigation utilizes three different computer programs: STRUDL, COM624, and BMCOL76. Since the present version of the INTRA program is not configured properly for the Texaco CDC computer, it is not included in this report Five example studies are presented in which an instrumented pile is embedded in different types of soil and subjected to static and cyclic loading. A study was carried out to compare the results from the three different computer programs to the instrumented pile test data Using the COM624 program results as the base case, the results from the other two programs are compared and evaluated Two special problems, mudslide and pile groups, are discussed based on an engineering approach / acase@tulane.edu