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In this paper, on the basis of the micropolar (Cosserat) continua approach, a constitutive model for simulation of granular material (e.g., sand) response in the elastoplastic range has been presented. Numerical analyses on strain localization in this type of material are carried out in the last part of this paper. The influence of the evolution of the internal length-scale micropolar parameters on the formation of strain localization is investigated. [ABSTRACT FROM AUTHOR]

In a companion paper, experimental evidence was elaborated to confirm that in particular circumstances the performance of level-furrow irrigation can exceed that of level-basin irrigation. The application of a single furrow simulation model to an irrigation event in a level-furrow field resulted in large estimation errors. To overcome them, the development and validation of a numerical model of level-furrow irrigation is reported in this work. The model is based on the interconnection of a number of one-dimensional channels. The individual channels are connected using confluence or bifurcation points. Furrow infiltration is modelled through a Kostiakov infiltration equation including the furrow discharge as an independent variable. The proposed model is validated using the experimental level furrow evaluation presented in the companion paper. Finally, the model is applied to explore the conditions in which level furrow irrigation can outperform level basin irrigation. The proposed model stands as a valuable tool in the design and management of level furrow irrigation systems. [ABSTRACT FROM AUTHOR]

The paper deals with transverse resistance problems occurring in railway ballast bed viewed from the standpoint of construction, maintenance, and safety of the railway track in use. Various ways of an analytical approach to the phenomenon tested using illustrative examples of mathematical models found in literature have been analyzed. A survey has been made into the current state of experimental works related to transverse resistances, and different methods of conducting such experiments in railway track during operation have been discussed. Furthermore, the idea of undertaking research, by a group of scientists from the Gdansk University of Technology, on the application of the tamping machine, is considered. Attention is focused on the process of preparing and carrying out the experimental works on transverse resistances, inclusive of an appropriate measuring system. The results of the experiments were analyzed and are included in the paper. The topic on how to deal with the time signals obtained from measurements and how to interpret them is discussed. The basic part of the paper is related to the theory of modeling the railway track structure paying special attention to the presented experimental work. An explanation has been provided to the mathematical description of the adopted model. The presented algorithm makes allowance for running simulation of the phenomenon on computer. The results obtained from simulation and experiments were aimed at convergence. Finally the results of such a simulation to enable a numerical description of the transverse resistance to the rail track ballast bed are tested. [ABSTRACT FROM AUTHOR]

Calibration, on the basis of data from centrifuge and shake table experiments, continues to promote the development of more accurate computational models. Capabilities such as coupled solid-fluid formulations and nonlinear incremental-plasticity approaches allow for more realistic representations of the involved static and dynamic/seismic responses. In addition, contemporary high-performance parallel computing environments are permitting new insights, gained from analyses of entire ground-foundation-structural systems. On this basis, the horizon is expanding for large-scale numerical simulations to further contribute toward the evolution of more accurate analysis and design strategies. The studies presented in this paper address this issue through recently conducted three-dimensional (3D) representative research efforts that simulate the seismic response of (1) a shallow-foundation liquefaction countermeasure, (2) a pile-supported wharf, and (3) a full bridge-ground system. A discussion of enabling tools for routine usage of such 3D simulation environments is also presented, as an important element in support of wider adoption and practical applications. In this regard, graphical user interfaces and visualization approaches can play a critical role. [ABSTRACT FROM AUTHOR]

Discontinuous gravity currents in rectangular channels are modeled numerically by solving the 3D unsteady Reynolds-averaged Navier-Stokes (URANS) equations closed with a buoyancy corrected low-Reynolds number (LRN) k-[variant_greek_epsilon] model using second-order accurate finite-volume numerics. It is shown that, on moderately fine computational meshes (with ∼106 grid nodes) and with careful modeling of the near-wall flow, the URANS model can capture the essential large-scale 3D dynamics of gravity current flows, which previously had been resolved only by DNS and/or large-eddy simulation (LES) on very fine computational meshes. These 3D dynamics include the onset of the well-known lobe-and-cleft instability at the current head, the onset of large-scale Kelvin-Helmholtz billows at the head of the gravity current, and the breakdown of the interfacial billows in the rear part of the current head due to intense three-dimensional mixing. The computed results underscore the importance of careful modeling of the near wall flow in URANS simulations. The standard k-[variant_greek_epsilon] model with wall functions fails to capture the aforementioned complex 3D dynamics, which are only resolved by the LRN k-[variant_greek_epsilon] model on grids that resolve the near-wall region. Furthermore, numerical experiments show that including in the simulation the lateral no-slip end walls of the channel has a profound effect on the accuracy of the computed solutions. End-wall effects enhance the three-dimensionality of the flow, result in increased mixing of the dense and the ambient fluids behind the head of gravity currents, and yield results in good agreement with measurements. On the other hand, when end-wall effects are omitted, by imposing periodicity in the spanwise direction, three-dimensional mixing is suppressed and the breakdown of interfacial billows is significantly underestimated. Grid sensitivity studies are also carried out using three successively refined meshes and show that the URANS LRN model yields grid-converged solutions at affordable computational resources. As URANS modeling requires only a fraction of the computational cost of DNS or LES with near-wall resolution, the present results underscore the potential of unsteady statistical turbulence models for predicting and elucidating the physics of gravity current flows in complex geometries and at Reynolds numbers of engineering relevance. [ABSTRACT FROM AUTHOR]