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The feasibility of detecting and quantifying delamination at the interface between steel (or GFRP) bar and concrete using ultrasonic guided waves is investigated in this study. These waves can propagate a long distance along the reinforcing steel (or GFRP) bar or concrete beam as guided waves and are sensitive to the interface bonding condition between the steel (or GFRP) bar and concrete. The traditional ultrasonic methods are good for detecting large voids in concrete but not very efficient for detecting delamination at the interface between concrete and steel (GFRP) bar since they use reflection, transmission and scattering of longitudinal waves by internal defects. In this study, special solid couplers between the steel/GFRP bar (or concrete beam) and ultrasonic transducers have been used to launch cylindrical guided waves (or Lamb waves) in the steel/GFRP bar (or concrete). This investigation shows that the guided wave inspection technique is an efficient and effective tool for health monitoring of concrete structures.

High sensitivity grating interferometry has become an important method in experimental mechanics to measure, with submicron sensitivity, the in-plane displacements of nearly flat objects under load. This study looks to extend the use of this interferometric setup through specific modifications to the interferometric setup, focusing specifically on developing the system's ability to register simultaneously both the in-plane and out-of-plane displacements so that dynamic events may be examined with great precision and speed. First presented is the author's approach for mapping in- and out-of-plane displacements through modifications to a conventional grating interferometer. Then, the author extends the method to the analysis of dynamic events, proposing a few workable solutions for registering two interferograms at the same time. Included in this discussion are suggestions for acquiring the orthogonal in-plane displacements u and v and the out-of-plane displacement w simultaneously. The second part of the work details the analysis of different phase measurement techniques, focusing on the error sources inherent in each approach. New, error-reducing algorithms are presented and the influence of the intensity sample weighting (window function) on phase errors is described. A spatial, phase measurement technique advanced by the author, the M-point technique, is chosen as the best choice for achieving fast analysis and high accuracy in displacement testing in the modified grating interferometric setup.

The Disturbed State Concepts (DSC) model, with simplified unloading/reloading formulation, is implemented in a nonlinear dynamic finite element program for porous media named DSC-DYN2D. It can perform static, two phase dynamic and consolidation analysis of soils and soil-structure interaction problems with the DSC model. The model and the computer procedure are verified by back predictions of laboratory tests of clay, steel-clay interfaces as well as a simulation of pile-soil interaction problem. The Disturbed State Concepts have been developed recently as a constitutive modeling approach. In the DSC, the material is assumed to transform continuously and randomly from the relatively intact state to the fully adjusted state under loading. Hence, the observed response of the material is expressed in terms of the response of relatively intact and fully adjusted states. In this dissertation, the Disturbed State Concept constitutive model is developed by using the HiSS model for the relative intact part and the critical state model for the fully adjusted part in the material. The general formulation for implementation is developed. New and simplified unloading/reloading schemes are proposed for cyclic loading. Then the DSC model with the unloading/reloading scheme are implemented in the dynamic finite element program based on the generalized Biot's theory. The procedure for determining the parameters of the DSC model and the unloading/reloading is discussed. The parameters for the steel-clay interface are found from the tests and used for the prediction of the tests. Consolidation and cyclic loading tests from the field load tests on a pile segment were numerically simulated using the finite element program DSC-DYN2D and compared with field measurements and those from the previous analysis with the HiSS model. The DSC predictions show improved agreement with the field behavior of the pile compared to those from the HiSS model. The unloading/reloading models proposed in the study are simple yet give the realistic prediction of unloading and reloading behavior of the geomaterials under cyclic loading. Overall, the computer procedure with the DSC allows improved and realistic simulation of the complex dynamic soil-structure interaction problems.

The linear Boltzmann equation for the transport of neutral particles is investigated with the objective of generating benchmark-quality calculations for homogeneous infinite media. In all cases, the problems are stationary, of one energy group, and the scattering is both isotropic and anisotropic. In the transport problems considered, the Green's function is generally the quantity of interest. The solution is obtained through the use of the Fourier transform method. The numerical inversions use standard numerical techniques, such as Gauss-Legendre quadrature, summation of infinite series, and Euler-Knopp acceleration. The most basic source of neutral particles is the point-beam source, or Green's function source. The Green's function in an infinite medium with isotropic scattering is treated as explained in chapter two. The Green's function in an infinite medium with anisotropic scattering is treated using two different mathematical methods as explained in chapters three and four. The results for both cases is shown in chapter 5.

Although it is one of the most difficult tasks in hydrology, delineation of aquifer heterogeneity is essential for accurate simulation of groundwater flow and transport. There are various approaches used to delineate aquifer heterogeneity from a limited data set, and each has its own difficulties and drawbacks. The inverse problem is usually used for estimating different hydraulic properties (e.g. transmissivity) from scattered measurements of these properties, as well as hydraulic head. Difficulties associated with this approach are issues of indentifiability, uniqueness, and stability. The Iterative Conditional Simulation (ICS) approach uses kriging (or cokriging), to provide estimates of the property at unsampled locations while retaining the measured values at the sampled locations. Although the relation between transmissivity (T) and head (h) in the governing flow equation is nonlinear, the cross covariance function and the covariance of h are derived from a first-order-linearized version of the equation. Even if the log transformation of T is adopted, the nonlinear nature between f (mean removed Ln[T]) and h still remains. The linearized relations then, based on small perturbation theory, are valid only if the unconditional variance of f is less than 1.0. Inconsistent transmissivity and head fields may occur as a result of using a linear relation between T and h. In this dissertation, Artificial Neural Networks (ANN) is investigated as a means for delineating aquifer heterogeneity. Unlike ICS, this new computational tool does not rely on a prescribed relation, but seeks its own. Neural Networks are able to learn arbitrary non-linear input-output mapping directly from training data and have the very advantageous property of generalization. For this study, a random field generator was used to generate transmissivity fields from known geostatistical parameters. The corresponding head fields were obtained using the governing flow equation. Both T and h at sampled locations were used as input vectors for two different back-propagation neural networks designed for this research. The corresponding values of transmissivities at unsampled location (unknown), constituting the output vector, were estimated by the neural networks. Results from the ANN were compared to those obtained from the (ICS) approach for different degrees of heterogeneity. The degree of heterogeneity was quantified using the variance of the transmissivity field, where values of 1.0, 2.0, and 5.0 were used. It was found that ANN overcomes the limitations of ICS at high variances. Thus, ANN was better able to accurately map the highly heterogeneous fields using limited sample points.

Gas flow behavior from a spherical source is explored by using linear and nonlinear models, not only in terms of pressure but also in terms of flux. The approach considers dimensionless parameters scaling both radius and time. Specific observations are made for large, moderate, and small time conditions. At large time, the nonlinear model becomes a linear ordinary differential equation with pressure solution independent of the material. However, for moderate and small scaled times this is not the case. The nonlinear model must be solved by using either linear approximations, semi-analytical, or numerical procedures. This model is nonlinear in the primary variable (pressure). However, appropriate mathematical manipulations allow one to change the nonlinearity into a single coefficient, depending on pressure. Focusing on the effects of this coefficient, the nonlinear solution can be confined between two linear solutions obtained by using atmospheric and boundary pressures. Appendix A is an exploration of the errors arising between the nonlinear solution and these two solutions. In Appendix B, a nonlinear model is used to find solutions for large, moderate, and small times. For large time, the case corresponds to the steady state case, and coincides with the solution presented in Appendix A. For moderate and small times the quasi-analytical approximation and the asymptotic solutions of linear and quadratic normalizations of pressure are presented. In Appendix C, simulations of gas flows in linear and nonlinear situations are made. The problem is to determine the change of air pressure in a tank when it is connected to a spherical cavity embedded in a porous medium. These changes in pressure occur when the air moves through the porous media, either for gas extraction or air injection. Both linear and nonlinear analyses require calculations of the pressure and the mass in the tank when the initial and boundary conditions change with time. For each case, gas extraction or air injection, the differences between the linear and the nonlinear models are examined to determine the suitability of the linear model.

A new algorithm for coupling boundary and finite element methods is developed for transient two dimensional heat conduction and thermoelastic analyses of regions with dissimilar materials and geometric discontinuities. Such regions are susceptible to failure initiation in electronic devices. As the component size decreases while enhancing performance, the accurate prediction of thermal and thermoelastic response of such devices is critical for achieving acceptable design. This study concerns both the conduction heat transfer and thermoelasticity. Solution to transient heat conduction equation provides the non-uniform thermal field for the thermoelastic analysis. Although the finite element method (FEM) is highly efficient and commonly used, its application with conventional elements to complex layered structures with length parameters varying in order of magnitudes leads to inaccurate and mesh dependent results. The accuracy of the results from the boundary element method (BEM) formulation, which requires computationally intensive integration schemes, is much higher than that of the FEM. This new algorithm combines the advantages of both methods while not requiring the commonly accepted iterations along the interfaces between BEM and FEM domains. The BEM part of the solution, acting as a global element, captures the singular nature of the solution variables arising from geometrical and material discontinuities and, eliminates the mesh dependency.