Poroelastic two‐phase material modeling: theoretical formulation and embedded finite element method implementation

This paper presents the formulation of FEMs for the numerical modeling of a poroelastic two‐phase (aggregates/mixture phase) solid. The displacement and pressure fields are decomposed, following the Enhanced Assumed Strain (EAS) method, into a regular part and an enhanced part. This leads to discontinuous strain and pressure gradient fields allowing to capture the jump in mechanical and hydrical properties passing through the interface between the aggregates and the mixture phase. All these enhanced fields are treated in the context of the embedded FEM through a local enhancement of the finite element interpolations as these jumps appear. The local character of these interpolations leads after a static condensation of the enhanced fields to a problem exhibiting the same structure as common poroelastic finite element models but incorporating now the mechanical and hydrical properties of a two‐phase solid. Copyright © 2015 John Wiley & Sons, Ltd.     

A simple method to analyse non-cohesive sediment mobility in coastal environment

This paper presents a method to investigate the relative influence of waves, wind-induced currents and tidal currents on sediment mobility in coastal environment. It is based on the assumption that, knowing high uncertainties linked to sediment dynamics studies, simple sediment mobility indicators are sufficient tools to provide useful information. This method is based on five main steps: (1) assessing hydrodynamic conditions and related errors spatially and temporally for an area; (2) evaluating the bottom shear stress induced by these hydrodynamic conditions; (3) providing simple sediment mobility indicators; (4) analysing the sensitivity of these indicators to the existing hydrodynamic uncertainties; (5) interpreting indicators knowing their limits (identified in the sensitivity analysis). This methodology is applied to a test site on the inner shelf, seaward of the Pertuis Charentais region in France. Using wave (SWAN) and sea-level and currents (MARS-2DH) modelling, we study the spatial distribution of the relative contribution of waves, tides and wind-induced current in the non-cohesive sediment mobility under storm conditions. The deduced sediment dynamics indicators reveal the dominant action of waves in sediment initiation in the offshore area, in water depths of up to 60 m. The sensitivity study, performed in order to evaluate the validity of results, shows that the sediment mobility indicators still provide relevant information, even for hydrodynamic uncertainties of ±20% or furthermore when only a qualitative sedimentological knowledge of the area is available.     

Finite element simulations of the behavior of piled‐raft foundations using a multiphase model

Finite element simulations of the behavior of a piled raft foundation have been carried out using a multiphase model conceived as an improved homogenization approach. According to this model, the ground reinforced by a group of piles is treated as a homogeneous continuous medium. In this approach, no specific interface elements are necessary to account for the mechanical interaction between the piles and the ground: this interaction is described by means of two scalar parameters, one stiffness parameter and one which can easily be derived from the maximum ground‐pile friction. The implementation of the model into a finite element code provides an efficient tool for the analysis of the influence of the pile number or length on the settlement and bearing capacity of a square piled raft foundation and of the way the total applied load is shared between the raft and the piles. Results are compared with a standard 3D finite element analysis. The comparison highlights the fact that the proposed approach remains to be improved to account for tip resistance. Copyright © 2012 John Wiley & Sons, Ltd.     

Meridional transport of HCN from SL9 impacts on Jupiter

In July 1994, the Shoemaker-Levy 9 (SL9) impacts introduced hydrogen cyanide (HCN) to Jupiter at a well confined latitude band around −44°, over a range of specific longitudes corresponding to each of the 21 fragments (Bézard et al. 1997, Icarus 125, 94-120). This newcomer to Jupiter's stratosphere traces jovian dynamics. HCN rapidly mixed with longitude, so that observations recorded later than several months after impact witnessed primarily the meridional transport of HCN north and south of the impact latitude band. We report spatially resolved spectroscopy of HCN emission 10 months and 6 years following the impacts. We detect a total mass of HCN in Jupiter's stratosphere of 1.5±0.7×10¹³ g in 1995 and 1.7±0.4×10¹³ g in 2000, comparable to that observed several days following the impacts (Bézard et al. 1997, Icarus 125, 94-120). In 1995, 10 months after impact, HCN spread to −30° and −65° latitude (half column masses), consistent with a horizontal eddy diffusion coefficient of K_yy=2-3×10¹⁰ cm² s⁻¹. Six years following impact HCN is observed in the northern hemisphere, while still being concentrated at 44° south latitude. Our meridional distribution of HCN suggests that mixing occurred rapidly north of the equator, with K_yy=2-5×10¹¹ cm² s⁻¹, consistent with the findings of Moreno et al. (2003, Planet. Space Sci. 51, 591-611) and Lellouch et al. (2002, Icarus 159, 112-131). These inferred eddy diffusion coefficients for Jupiter's stratosphere at 0.1-0.5 mbar generally exceed those that characterize transport on Earth. The low abundance of HCN detected at high latitudes suggests that, like on Earth, polar regions are dynamically isolated from lower latitudes.     

Impact of permafrost development on groundwater flow patterns: a numerical study considering freezing cycles on a two-dimensional vertical cut through a generic river-plain system

The impact of glaciation cycles on groundwater flow was studied within the framework of nuclear waste storage in underground geological formations. The eastern section of the Paris Basin (a layered aquifer with impervious/pervious alternations) in France was considered for the last 120 ka. Cold periods corresponded with arid climates. The issue of talik development below water bodies was addressed. These unfrozen zones can maintain open pathways for aquifer recharge. Transient thermal evolution was simulated on a small-scale generic unit of the landscape including a “river” and “plain”. Coupled thermo-hydraulic modeling and simplified conductive heat transfer were considered for a broad range of scenarios. The results showed that when considering the current limited river dimensions and purely conductive heat transfer, taliks are expected to close within a few centuries. However, including coupled advection for flows from the river to the plain (probably pertinent for the eastern Paris Basin aquifer recharge zones) strongly delays talik closure (millennium scale). The impact on regional underground flows is expected to vary from a complete stop of recharge to a reduced recharge, corresponding to the talik zones. Consequences for future modeling approaches of the Paris Basin are discussed.     

Discrete element modeling of tool‐rock interaction II: rock indentation

The failure mechanisms induced by a wedge‐shaped tool indenting normally against a rock surface are investigated using the discrete element method (DEM). The main focus of this study is to explore the conditions controlling the transition from a ductile to a brittle mode of failure. The development of a damage zone and the initiation and propagation of a brittle fracture is well captured by the DEM simulations. The numerical results support the conjecture that initiation of brittle fractures is governed by a scaled flaw length Λ, a ratio between the flaw size λ and the characteristic length (where K_Ic is the toughness and σ_c the uniaxial compressive strength). The size of the damage zone agrees well with analytical predictions based on the cavity expansion model. The effects of a far‐field confining stress and the existence of a relief surface near the indenter are also examined.Copyright © 2012 John Wiley & Sons, Ltd.     

Paleoenvironmental context of archaeological sites,implications for subsistence strategies under Holocene climate change,northern Kenya

The Holocene was time of dramatic climate change in East Africa, shifting from wetter climate in the Early–Mid Holocene (∼10–5ka) to drier climates in the Late Holocene, followed by a slight reversal at <1ka. The Holocene was a time of cultural change from hunter‐gatherer and fishing to pastoralism. Recent excavations along the eastern shores of Lake Turkana, Kenya (4°N) provide new archaeological materials, a high‐resolution stratigraphic and paleoenvironmental data set, OSL dates, and cultural records in the context of documented environmental change (falling lake levels). Archaeological site FwJj25 (4.20 ± 0.28ka), on the northeastern margin of Lake Turkana, provides one of the earliest records of pastoralism in the region. The palimpsest record of FwJj5 (0.90 ± 0.06ka) was in a small valley containing a groundwater seep located 5km from the lake. FwJj5 reflects occupation by people who may have covered great distances in accessing resources, but were likely drawn to an environmental refugia of freshwater springs during times of regional aridity. © 2011 Wiley Periodicals, Inc.     

Two Approaches of Textural Classification for the Location of the Flows of Lava on the Volcanic Site of the Mountain Cameroon

Abstract

This study presents two approaches of textural classification on a synthetic aperture radar (SAR) ERS‐2 image, with the aim of the location of the flows of lava and of the serviced zones around the volcanic site of the Mountain Cameroon. The first approach is a method of progressive supervised classification, where a single class is extracted at the same moment, by using 7 parameters of texture stemming from the run length method. Three classes of texture were extracted by this method and the images from the three classes were merged by the red green blue coloured composition to produce the final map. For purposes of comparison, a not supervised classification was applied to the same image. The applied not supervised classification uses parameters of texture stemming from the co‐occurrence matrix method, and it lays on the detection of the peaks of a histogram. The results obtained by the two methods are coherent, and the validation of the results was made by observations during a recent mission on the site of study.     

Modelling the history of semi-structured geographical entities

Geographical entities are characterized by rather complex structures. They involve space and thematic information, which is subject to change in time, while history should be maintained. On the other hand, these structures may be irregular (i.e. they do not necessarily conform to a fixed schema), because associated data is usually collected based on different specifications and multiple resolutions. Hence, the representation of geographical entities in traditional data models, such as the relational or object-oriented, is not always feasible. In this respect, this paper investigates the use of semi-structured data (SSD) models—an innovative approach recently developed in Information Technology—for modelling dynamic geographical entities. A framework for the representation of geographic entities in Object Exchange Model (OEM), a popular model for semi-structured data, is introduced. Additionally, it is shown how useful information can be extracted from such a representation using the LOREL query language for SSD. A simplified case study in the application domain of cadastre involving SSD is examined closely.     

A DUAL mission for nuclear astrophysics

DUAL will study the origin and evolution of the elements and explores new frontiers of physics: extreme energies that drive powerful stellar explosions and accelerate particles to macroscopic energies; extreme densities that modify the laws of physics around the most compact objects known; and extreme fields that influence matter in a way that is unknown on Earth. The variability of these extreme objects requires continuous all-sky coverage, while detailed study demands an improvement in sensitivity over previous technologies by at least an order of magnitude. The DUAL payload is composed of an All-Sky Compton Imager (ASCI), and two optical modules, the Laue-Lens Optic (LLO) and the Coded-Mask Optic (CMO). The ASCI serves dual roles simultaneously, both as an optimal focal-plane sensor for deep observations with the optical modules and as a sensitive true all-sky telescope in its own right for all-sky surveys and monitoring. While the optical modules are located on the main satellite, the All-Sky Compton Imager is situated on a deployable structure at a distance of 30?m from the satellite. This configuration not only permits to maintain the less massive payload at the focal distance, it also greatly reduces the spacecraft-induced detector background, and, above all it provides ASCI with a continuous all-sky exposure.