27,583 research outputs found
Slope Instability of the Earthen Levee in Boston, UK: Numerical Simulation and Sensor Data Analysis
The paper presents a slope stability analysis for a heterogeneous earthen
levee in Boston, UK, which is prone to occasional slope failures under tidal
loads. Dynamic behavior of the levee under tidal fluctuations was simulated
using a finite element model of variably saturated linear elastic perfectly
plastic soil. Hydraulic conductivities of the soil strata have been calibrated
according to piezometers readings, in order to obtain correct range of
hydraulic loads in tidal mode. Finite element simulation was complemented with
series of limit equilibrium analyses. Stability analyses have shown that slope
failure occurs with the development of a circular slip surface located in the
soft clay layer. Both models (FEM and LEM) confirm that the least stable
hydraulic condition is the combination of the minimum river levels at low tide
with the maximal saturation of soil layers. FEM results indicate that in winter
time the levee is almost at its limit state, at the margin of safety (strength
reduction factor values are 1.03 and 1.04 for the low-tide and high-tide
phases, respectively); these results agree with real-life observations. The
stability analyses have been implemented as real-time components integrated
into the UrbanFlood early warning system for flood protection
Path planning for reconfigurable rovers in planetary exploration
This paper introduces a path planning algorithm that
takes into consideration different locomotion modes in
a wheeled reconfigurable rover. Such algorithm, based
on Fast Marching, calculates the optimal path in terms
of power consumption between two positions, providing
the most appropriate locomotion mode to be used
at each position. Finally, the path planning algorithm is
validated on a virtual Martian scene created within the
V-REP simulation platform, where a virtual model of a
planetary rover prototype is controlled by the same software
that is used on the real one. Results of this contribution
also demonstrate how the use of two locomotion
modes, wheel-walking and normal-driving, can reduce
the power consumption for a particular area.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech
Development and calibration of discrete element method inputs to mechanical responses of granular materials
Simulation of soil excavation is difficult. Tools which manipulate soil are difficult to evaluate in a virtual environment prior to prototype or manufacture. Soil behaves as a discontinuous material in normal excavation activities. Therefore, numerical methods which naturally model discontinuous media, such as the Discrete Element Method (DEM), can be used to perform simulations of soil excavation. However, DEM input parameters must be calibrated to accurately model the mechanical behavior of soil. The goal of this research was
to develop intelligent methodologies to calibrate DEM input parameters to reproduce the mechanical responses of soil and other granular materials subject to traditional laboratory tests, such as triaxial and direct shear tests. A mechanistic understanding of the interaction between sliding and rolling friction was developed and correlated with the critical state strength of drained granular media. In addition, the fundamental soil mechanics concept of relative density was successfully applied to the DEM calibration methodology to predict peak granular strength and dilatancy. Sensitivity analyses of DEM input parameters were used to enhance the characterization of mechanical behavior of DEM specimens. A calibration algorithm was developed to quickly and mechanistically relate DEM input parameters to laboratory measured mechanical behavior of soils. The algorithm eliminates unnecessary iterations during the DEM parameter calibration by enforcing a sophisticated understanding of the mechanisms of granular shear strength. The outcomes of this research greatly simplify the calibration of DEM parameters of soil for use in industrial excavation problems
Multiscale Analysis of the Stress State in a Granular Slope in Transition to Failure
By means of contact dynamics simulations, we analyze the stress state in a
granular bed slowly tilted towards its angle of repose. An increasingly large
number of grains are overloaded in the sense that they are found to carry a
stress ratio above the Coulomb yield threshold of the whole packing. Using this
property, we introduce a coarse-graining length scale at which all stress
ratios are below the packing yield threshold. We show that this length
increases with the slope angle and jumps to a length comparable to the depth of
the granular bed at an angle below the angle of repose. This transition
coincides with the onset of dilatation in the packing. We map this transition
into a percolation transition of the overloaded grains, and we argue that in
the presence of long-range correlations above the transition angle, the
granular slope is metastable.Comment: 11 pages, 14 Fig, submitted to PR
40 Years Theory and Model at Wageningen UR
"Theorie en model" zo luidde de titel van de inaugurele rede van CT de Wit (1968). Reden genoeg voor een (theoretische) terugblik op zijn wer
Dynamic modelling of the behaviour of the quarkiss earthen dam under seismic loads
The dynamic modelling of the behaviour of the Ouarkiss earthen dam under seismic loads was performed using the finite elements method (FEM), with an approach in effective stresses. The soil behaviour is described by the Mohr-Coulomb criterion. A numerical method and a procedure of analysis are presented in this work. The seismic response of an earthen dam was evaluated. Particular emphasis is placed on the calculation of stresses, displacements, deformations and interstitial overpressures recorded during the seismic solicitation. It has been shown that numerical simulation is able to highlight the fundamental aspects of the displacements and deformations processes experienced by the structure ofdam and to produce preliminary results for the evaluation of the seismic behaviour of the structure taking into account the physical non-linearity of the materials constituting the body of the dam and the effect of the rigidity of the different zones of the dam and the foundation
Dynamic problems for metamaterials: Review of existing models and ideas for further research
Metamaterials are materials especially engineered to have a peculiar physical behaviour, to be exploited for some well-specified technological application. In this context we focus on the conception of general micro-structured continua, with particular attention to piezoelectromechanical structures, having a strong coupling between macroscopic motion and some internal degrees of freedom, which may be electric or, more generally, related to some micro-motion. An interesting class of problems in this context regards the design of wave-guides aimed to control wave propagation. The description of the state of the art is followed by some hints addressed to describe some possible research developments and in particular to design optimal design techniques for bone reconstruction or systems which may block wave propagation in some frequency ranges, in both linear and non-linear fields. (C) 2014 Elsevier Ltd. All rights reserved
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Image based simulation of one-dimensional compression tests on carbonate sand
High factors of safety and conservative methods are commonly used on foundation design on shelly carbonate soils. A better understanding of the behavior of this material is, thus, critical for more sustainable approaches for the design of a number of offshore structures and submarine pipelines. In particular, understanding the physical phenomena taking place at the microscale has the potential to spur the development of robust computational methods. In this study, a one-dimensional compression test was performed inside an X-ray scanner to obtain 3D images of the evolving internal structure of a shelly carbonate sand. A preliminary inspection of the images through five loading increments has shown that the grains rearrange under loading and in some cases cracks develop at the contacts. In order to replicate of the experiments in the numerical domain, the 3D image of the soil prior to loading was imported into a micro Finite Element (µFE) framework. This image-based modelling tool enables measurements of the contact force and stress map inside the grains while making use of the real microstructure of the soil. The potential of the µFE model to contribute insights into yield initiation within the grain is demonstrated here. This is of particular interest to better understand the breakage of shelly grains underpinning their highly compressive behavior
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