Semi-analytical and numerical methods for computing transient waves in 2D acoustic / poroelastic stratified media

Wave propagation in a stratified fluid / porous medium is studied here using analytical and numerical methods. The semi-analytical method is based on an exact stiffness matrix method coupled with a matrix conditioning procedure, preventing the occurrence of poorly conditioned numerical systems. Special attention is paid to calculating the Fourier integrals. The numerical method is based on a high order finite-difference time-domain scheme. Mesh refinement is applied near the interfaces to discretize the slow compressional diffusive wave predicted by Biot's theory. Lastly, an immersed interface method is used to discretize the boundary conditions. The numerical benchmarks are based on realistic soil parameters and on various degrees of hydraulic contact at the fluid / porous boundary. The time evolution of the acoustic pressure and the porous velocity is plotted in the case of one and four interfaces. The excellent level of agreement found to exist between the two approaches confirms the validity of both methods, which cross-checks them and provides useful tools for future researches.Comment: Wave Motion (2012) XX

A model for railway induced ground vibrations in the frame of preliminary assessment studies

This thesis focuses on the development of an analytical model for the generation and propagation parts of a global model of ground induced vibrations to be used in preliminary assessment studies for the case of at-grade railway infrastructures. The model is designed prioritising its speed, simplicity and usability ahead its accuracy modelling the real railway system. This model takes into account the subgrade as a viscoelastic and homogeneous half-space, the superstructure as a 2-layer supporting model and the vehicle as 1DOF system. With the aim of simplify the model, the superstructure/subgrade interaction is studied in terms of the wheel/rail contact dynamics, bounding in what cases this interaction can be neglected. The adaptation of this model when a far eld semi-analytical model is desired to be used as the propagation model is fully developed, by means of the dimensioning of the near eld and far eld regions