Theory of transient streaming potentials associated with axial-symmetric flow in unconfined aquifers

We present a semi-analytical solution for the transient streaming potential response of an unconfined aquifer to continuous constant rate pumping. We assume that flow occurs without leakage from the unit below a transverse anisotropic aquifer and neglect flow in the unsaturated zone by treating the water-table as a moving material boundary. In the development of the solution to the streaming potential problem, we impose insulating boundary conditions at land surface and the lower boundary of the lower confining unit. We solve the problem exactly in the double Laplace—Hankel transform space and obtain the inverse transforms numerically. The solution is used to analyse transient streaming potential data collected during dipole hydraulic tests conducted at the Boise Hydrogeophysical Research Site in 2007 June. This analysis yields estimates of aquifer hydraulic parameters. The estimated hydraulic parameters, namely, hydraulic conductivity, transverse hydraulic anisotropy, specific storage and specific yield, compare well to published estimates obtained by inverting drawdown data collected at the field site

Global Inversion of Grounded Electric Source Time-domain Electromagnetic Data Using Particle Swarm Optimization

Global optimization inversion of grounded wire time-domain electromagnetic (TDEM) data was implemented through application of the particle swarm optimization (PSO) algorithm. This probabilistic approach is an alternative to the widely used deterministic local-optimization approach. In the PSO algorithm, each particle that constitutes the swarm epitomizes a probable geophysical model comprised by subsurface resistivity values at several layers and layer thicknesses. The forward formulation of the TDEM problem for calculating the vertical component of the induced magnetic field is first expressed in the Laplace domain. Transformation of the magnetic field from the Laplace domain into the time domain is performed by applying the Gaver-Stehfest numerical method. The implementation of PSO inversion to the TDEM problem is straightforward. It only requires adjustment of a few inversion parameters such as inertia, acceleration coefficients and numbers of iteration and particles. The PSO inversion scheme was tested on synthetic noise-free data and noisy synthetic data as well as to field data recorded in a volcanic-geothermal area. The results suggest that the PSO inversion scheme can effectively solve the TDEM 1D stratified earth problem.

Direct and Inverse Computational Methods for Electromagnetic Scattering in Biological Diagnostics

Scattering theory has had a major roll in twentieth century mathematical physics. Mathematical modeling and algorithms of direct,- and inverse electromagnetic scattering formulation due to biological tissues are investigated. The algorithms are used for a model based illustration technique within the microwave range. A number of methods is given to solve the inverse electromagnetic scattering problem in which the nonlinear and ill-posed nature of the problem are acknowledged.Comment: 61 pages, 5 figure

Development of Time-Domain Green’s Functions and Boundary Element Techniques for Transient Elastodynamics of Multi-Layered Media

Time-domain boundary element method (TD-BEM) is a powerful tool for transient elastodynamic modeling of soil and structures especially for unbounded domain problems. Aimed to add to the advancement of this class of methods and facilitate its coupling with other numerical approaches, a number of new analytical and computational formulations are developed and explored in this study. The work includes the development of a regularized convolution-type boundary integral equation in the time domain for 3-D elastodynamics, the formulation of a rigorous stability analysis via a hybrid amplification matrix of direct TD-BEMs, an extension of a displacement potential-integral transform method from the frequency- to the time-domain, a generalization of the classical Cagniard-de Hoop method in wave propagation theory for Laplace transform's inversion, and the derivation of exact as well as asymptotic forms of the time-domain point-load Green's functions for a homogeneous and a multi-layered half-space. The theoretical developments are employed to develop new computational algorithms such as the new variable-weight multi-step collocation TD-BEM scheme with higher-order time projections and a new numerical contour integration method to compute the fundamental integrals in exact half-space time-domain Green's functions. The efficacy and performance of these developments are evaluated with respect to benchmark elastodynamic problems for both bounded and unbounded domains. The formulation and effectiveness of coupling the proposed TD-BEM approach with a local finite element zone for dynamic soil-structure interaction problems as a rigorous form of wave-absorbing boundary are also investigated

Fuel consumption excess prediction on a flexible pavement

Lo studio riportato in questa tesi valuta l'effetto del comportamento viscoelastico degli strati di una pavimentazione flessibile sul consumo di carburante dei veicoli. L'approccio utilizzato per stimare questo effetto è diviso in due fasi: (1) Calcolare gli stati tensionali, deformativi e gli spostamenti dei punti di una pavimentazione soggetta ad un carico in movimento, (2) valutare l'energia dissipata nella pavimentazione, che è uguale all'energia necessaria al veicolo per superare la forze di trazione addizionali causate dalla risposta della pavimentazione. Durante la prima fase, una soluzione viscoelastica nel dominio del tempo (fornita dal programma ViscoWave II-M) viene utilizzata per calcolare la risposta della pavimentazione. Il programma è stato modificato in modo che calcoli le tensioni e le deformazioni in qualsiasi punto della struttura della pavimentazione. I risultati sono stati validati attraverso il confronto con altre soluzioni di comprovata affidabilità, come ViscoRoute, 3D-Move e SAPSI-M. La dissipazione di energia dovuta alla viscosità degli strati in conglomerato bituminoso è calcolata e utilizzata per stimare il consumo di carburante di un camion del peso di 18 tonnellate a diverse velocità e temperature. E' inoltre stata studiata l'influenza degli spessori dei vari strati sulla dissipazione di energia. Come previsto, l'eccesso del consumo di carburante causato dall'energia dissipata ha un valore significativo solo a velocità basse, o nel caso la temperatura dell'asfalto raggiunga valori elevati. The study reported in this thesis evaluates the effect of the viscoelastic behavior of asphalt layers in a flexible pavement on fuel consumption of vehicles. The approach used to estimate this effect is in two folds: (1) Compute the asphalt pavement response (i.e., stresses and strains) due to a moving load, (2) Estimate the dissipated energy into the pavement which is equal to the energy needed by the vehicle to overcome the additional traction forces caused by the pavement response. During the first step, a time domain dynamic viscoelastic solution (ViscoWave II-M) is used to calculate the asphalt pavement response due to a moving load. The program was modified so that it calculate stresses and strains at any point in the pavement structure. The results were validated through a comparison with other solution of proven reliability, such as ViscoRoute, 3D-Move and SAPSI-M. The dissipation of energy due to the viscosity of the conglomerate bituminous layers is calculated and used to estimate the fuel consumption of an 18t truck at different speeds and temperatures. The influence of the base course thickness is also investigated. As expected, the excess of fuel consumption due to the energy dissipated has a significant value only at low speeds, or in the case the temperature of the asphalt reaches high values

Forced time-harmonic vertical vibration of a rigid disk embedded in a transversely isotropic full-space medium

This research is concerned with the investigation of forced time-harmonic vertical vibration of a rigid disk enclosed in a transversely isotropic full space medium. By properties of integral transform methods, the generalized mixed boundary-value problem is formulated as a set of dual integral equations, which in turn, are reduced to a Fredholm equation of the second kind. The obtained Fredholm integral equation is solved by well-known numerical methods. Selected results for the load distribution on the disk and complex compliance are presented for various ranges of frequency periments