SUMMARYNumerical solutions for problems in coupled poromechanics suffer from spurious pressure oscillations when small time increments are used. This has prompted many researchers to develop methods to overcome these oscillations. In this paper, we present an overview of the methods that in our view are most promising. In particular we investigate several stabilized procedures, namely the fluid pressure Laplacian stabilization (FPL), a stabilization that uses bubble functions to resolve the fine-scale solution within elements, and a method derived by using finite increment calculus (FIC). On a simple one-dimensional test problem, we investigate stability of the three methods and show that the approach using bubble functions does not remove oscillations for all time step sizes. On the other hand, the analysis reveals that FIC stabilizes the pressure for all time step sizes, and it leads to a definition of the stabilization parameter in the case of the FPL-stabilization. Numerical tests in one and two dimensions on 4-noded bilinear and linear triangular elements confirm the effectiveness of both the FPL-and the FIC-stabilizations schemes for linear and nonlinear problems.
SUMMARYPresented here is a numerical investigation of the influence of non-uniform soil conditions on a prototype concrete bridge with three bents (four span) where soil beneath bridge bents are varied between stiff sands and soft clay. A series of high-fidelity models of the soil-foundation-structure system were developed and described in some details. Development of a series of high-fidelity models was required to properly simulate seismic wave propagation (frequency up to 10 Hz) through highly nonlinear, elastic plastic soil, piles and bridge structure. Eight specific cases representing combinations of different soil conditions beneath each of the bents are simulated. It is shown that variability of soil beneath bridge bents has significant influence on bridge system (soil-foundation-structure) seismic behavior. Results also indicate that free field motions differ quite a bit from what is observed (simulated) under at the base of the bridge columns indicating that use of free field motions as input for only structural models might not be appropriate. In addition to that, it is also shown that usually assumed beneficial effect of stiff soils underneath a structure (bridge) cannot be generalized and that such stiff soils do not necessarily help seismic performance of structures. Moreover, it is shown that dynamic characteristics of all three components of a triad made up of earthquake, soil and structure play crucial role in determining the seismic performance of the infrastructure (bridge) system.
SUMMARYThe dynamic sti ness of a foundation embedded in a multiple-layered halfspace is calculated postulating one-dimensional wave propagation in cone segments. In this strength-of-materials approach the sectional property of the cone segment increases in the direction of wave propagation. Re ections and refractions with waves propagating in corresponding cone segments occur at layer interfaces. Compared to rigorous procedures the novel method based on cone segments is easy to apply, provides conceptual clarity and physical insight in the wave propagation mechanisms.This method postulating one-dimensional wave propagation in cone segments with re ections and refractions at layer interfaces is evaluated, calculating the dynamic sti ness of a foundation embedded in a multiple-layered halfspace. For sites resting on a exible halfspace and ÿxed at the base, engineering accuracy (deviation of ±20%) is achieved for all degrees of freedom with a vast parameter variation. The behaviour below the cut-o frequency in an undamped site ÿxed at its base is also reliably predicted. The accuracy is, in general, better than for the method based on cone frustums, which can lead to negative damping.
SUMMARYA complete and accurate simulation of two-phase flow in porous media requires knowledge of all the controlling physics (and values of physical parameters) that play a relevant role and an understanding of the effects of each one on the solution. Of particular concern here is the effect of capillary pressure and the length scale over which it is relevant. The goal of this paper is to provide guidance onto when to include the effects of capillary pressure in the model, and onto what are the resulting length scale restrictions if those effects are to be included.
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