Digital Commons Network^™

Mobilization Of A Hydrophobic Organic Compound Using Surfactant For Soil Washing., Minwen Liu

LSU Historical Dissertations and Theses

Soil washing using surfactants is a promising alternative for the conventional pump-and-treat method of removing hydrophobic organic compounds. The interactions and the transport of the chemicals have been studied by batch and column experiments. Sodium dodecylsulfate (SDS), an anionic surfactant, and anthracene, a hydrophobic organic, were chosen as the representative surfactant and contaminant, respectively. Fine sand and native soil were used as formation media. The experimental results indicated that the maximum loss of SDS on native soil from the solution was observed when the aqueous SDS concentration was in the region of the critical micelle concentration, and this loss was …

Automatic Tool Path Generation For Numerically Controlled Machining Of Sculptured Surfaces, Xiaoxia Li

Doctoral Dissertations

This dissertation presents four new tool path generation approaches for numerically controlled machining of sculptured surfaces: TRI$\sb-$XYINDEX, FINISH, FIVEX$\sb-$INDEX, FIX$\sb-$AXIS$\sb-$INDEX. All of the above systems index the tool across the object surface in the Cartesian space so that evenly distributed tool paths are accomplished.

TRI$\sb-$XYINDEX is a three-axis tool path generation system which uses a surface triangle set (STS) representation of the surface for tool position calculations. Surface edges are detected with local searching algorithms. Quick tool positioning is achieved by selecting candidate elements of polygons. Test results show that TRI$\sb-$XYINDEX is more efficient when machining surfaces which are relatively …

A Non-Proportional Cyclic Plasticity Model For Metals With Ratchetting Effects., Srinivasan Madras Sivakumar

LSU Historical Dissertations and Theses

The path-dependent and nonlinear behavior of metallic materials subjected to cyclic loading is modelled using the proposed hardening rule. It uses mainly two surfaces, a yield and a limit surface and includes the memory effects through a separate surface called the memory surface which is obtained from a maximum stress criterion. The model considers the facts that the motion of the center of the yield surface in the stress space is mainly governed by the direction of the deviatoric stress rate and that the uniqueness of the solution requires nesting of the two surfaces. The model proposed satisfies both conditions …

A Study Of Heat Transfer In Rotary Desorbers Used To Remediate Contaminated Soils., Charles Alan Cook

LSU Historical Dissertations and Theses

A comprehensive heat transfer model is developed which describes heat transfer phenomena in rotary desorbers. This model predicts the temperatures of the solids bed and gases in the desorber and the rate of water evaporation from the solids. Emphasis is placed on describing the heat transfer process between the rotating wall of a desorber and the adjacent bed of solids. A heat-balance integral method is used to model heat conduction from the wall to adjacent wet bed particles. This solution includes the effects of water evaporation near the wall and a thermal contact resistance between the wall and the first …

Optimal Design Of A Fully Parallel Robot Manipulator., Chan Soo Kim

LSU Historical Dissertations and Theses

Optimal design of a six degrees-of-freedom, fully parallel manipulator, called a Stewart platform is investigated. In order to optimize the mechanism, new performance measures are introduced since use of the previous methods suffer from lack of physical meaning due to dimensional inhomogeneity. To overcome the dimensional inhomogeneity problem, an Euclidean norm definition of each output space with homogeneous dimension is used to find input-output norm relation. As a result, four sets of eigenvalues are obtained which characterize translational and rotational velocity, force and torque, and position and orientation accuracy. From the four sets of eigenvalues, four determinant measures are defined, …

Synergistic Control Of N-Body Computer Generated Robots., Don Alan Iglehart

LSU Historical Dissertations and Theses

This project uses N-Body computer generated robots to investigate the fundamental problem of synergistic control of robots. This facility is important in an automated manufacturing environment and relates directly to the expanding field of study involving nonlinear systems. Experiments are performed utilizing this force controlled model to investigate nonlinear control problems using one of the techniques advanced. The principal results of this work are summarized: (1) A new simulation package is developed which uses Lagrange equations with multipliers to model two dimensional user defined robots. Three dimensionalization and parallelization are discussed and a dynamic optimization algorithm is introduced for regulating …

Models For Steady State Flow Past A Cylinder, Sergio J. D'Alessio

Digitized Theses

Three steady state models for determining the flow of a viscous incompressible Newtonian isothermal fluid past a two-dimensional cylindrical object are proposed. These models offer numerical methods of solving the governing Navier-Stokes equations as well as a mathematical understanding of the nature of the flow.;In the first model, the behaviour of the vorticity is patterned for both large and small distances by expressing the vorticity as {dollar}\zeta\ =\ \Phi\rm e\sp{lcub}\rm F{rcub}{dollar} with F chosen to accommodate both boundary-layer and wake theory. The resulting equations are then solved by finite differences and by the method of Dennis and Chang (1970).;The second …

The Free Vibration Of Plates, Shallow Shells And Solids, Philippe Georges Young

Digitized Theses

The Ritz approach is used in this thesis to study the free structural vibration problem of a wide class of plates, shallow shells and solids. The boundaries and/or internal supports of the systems considered are described by polynomials in Cartesian coordinates. The geometric boundary conditions at these boundaries or internal supports are enforced by including in a simple polynomial trial series the polynomial equation describing the position of the support raised to the appropriate power. For plates and shallow shells, in some instances, the displacement field is discretized into several domains or elements, as in the standard finite element method, …

Response Statistics Of Shell Structures With Geometrical And Material Nonlinearities, Meilan Liu

Digitized Theses

The investigation in this thesis is concerned with response statistics of shell structures with geometrical and material nonlinearities under stationary and non-stationary Gaussian random excitations.;A series of hybrid strain based three node flat triangular shell elements is developed for linear and nonlinear shell structural analyses. In the former the Hellinger-Reissner variational principle is employed. The elements are obtained by combining a triangular bending element and a plane stress element, and incorporating the drilling degrees-of-freedom. For the nonlinear analysis the updated Lagrangian formulation and the incremental Hellinger-Reissner variational principle are applied, with incremental displacements and strains being the independently assumed fields. …

Hydrodynamic And Electrohydrodynamic Instability Of Shear Flows And The Numerical Simulation Of Viscous Droplets, Kenzu Abdella

Digitized Theses

In this thesis, we investigate three fluid dynamic problems involving various physical mechanisms which exhibit interfacial instability. These problems have wide ranging industrial, scientific and engineering applications.;In the first problem, we investigate the linear stability of the unbounded Couette flow of two fluids separated by a plane interface. The exact dispersion relation is solved asymptotically and numerically to analyze the effects of the four stability parameters of the flow; the ratio of the viscosities, the ratio of the density, the surface tension and gravity. While our results confirm most of the earlier reported theories involving shear flows of fluids of …

Multibond Graph Method For Flexible Multibody System Dynamics, Simon Xun-Nan He

Digitized Theses

In this thesis, a general method for the modelling and simulation of the dynamics of flexible multibody systems undergoing special motion is developed using the multiband graph approach. Until now, bond graph was mostly used to model rigid multibody system dynamics and two dimensional flexible bodies. The multibond graph approach developed in this thesis for the computer-aided modelling and simulation of flexible multibody system dynamics provides an alternative to current computer-aided modelling and simulation of 3-D flexible multibody system dynamics with the added advantage of including a mixed energy domain. The flexible multibody system considered consists of a number of …

Ground Motion Spatial Incoherence, Its Modelling And Effects On Long Gravity Dams, Osman Mohamed Ramadan

Digitized Theses

Seismic design of concrete gravity dams is usually based on a two-dimensional analysis of one monolith, or slice. This analysis provides the basic information but neglects the interaction between adjacent dam monoliths and assumes uniformity of dam section, foundation properties and ground motions along the dam longitudinal axis. While the seismic response of gravity dams has been investigated in considerable detail, the effects of ground motion spatial incoherence on dam response have not been investigated to any great detail.;In this study, dam response to spatially variable seismic excitations is theoretically investigated. Deterministic and random representations of the space-time random field …