Smooth particle hydrodynamics studies of wet granular column collapses

Acta Geotechnica - Dry granular materials have been the subject of many investigations, while wet granular materials, which widely exist in many real-world applications, have only received limited...     

Assessment of Various Fuzzy c-Mean Clustering Validation Indices for Mapping Mineral Prospectivity: Combination of Multifractal Geochemical Model and Mineralization Processes

This paper describes the application of an unsupervised clustering method, fuzzy c-means (FCM), to generate mineral prospectivity models for Cu?±?Au?±?Fe mineralization in the Feizabad District of NE Iran. Various evidence layers relevant to indicators or potential controls on mineralization, including geochemical data, geological–structural maps and remote sensing data, were used. The FCM clustering approach was employed to reduce the dimensions of nine key attribute vectors derived from different exploration criteria. Multifractal inverse distance weighting interpolation coupled with factor analysis was used to generate enhanced multi-element geochemical signatures of areas with Cu?±?Au?±?Fe mineralization. The GIS-based fuzzy membership function MSLarge was used to transform values of the different evidence layers, including geological–structural controls as well as alteration, into a [0–1] range. Four FCM-based validation indices, including Bezdek’s partition coefficient (V_Pc) and partition entropy (V_Pe) indices, the Fukuyama and Sugeno (V_FS) index and the Xie and Beni (V_XB) index, were employed to derive the optimum number of clusters and subsequently generate prospectivity maps. Normalized density indices were applied for quantitative evaluation of the classes of the FCM prospectivity maps. The quantitative evaluation of the results demonstrates that the higher favorability classes derived from V_FS and V_XB (N_d?=?9.19) appear more reliable than those derived from V_Pc and V_Pe (N_d?=?6.12) in detecting existing mineral deposits and defining new zones of potential Cu?±?Au?±?Fe mineralization in the study area.

     

Spatial Modeling of Geotechnical Information Using GML

Geotechnical data characterizes the geometry and physical properties of soil deposits, which are determined from field observations, in-situ and laboratory tests, and engineering analyses. Until now, geotechnical information was mainly described and exchanged as relational data, which occasionally included spatial characteristics. Hereafter, the spatial features of geotechnical data are investigated by invoking the geotechnical data model of the Association of Geotechnical and Geoenvironmental Specialists (AGS), which is widely used in the United Kingdom to exchange geotechnical data in engineering practice. The basic geometric objects in AGS geotechnical data are first identified. These geometric objects are mapped to basic geometric features of the Geography Markup Language (GML). AGS data can therefore be fully rendered using GML-conformant schemas, which make geotechnical data readily importable into GML-aware applications. The data can be also imported to mainstream GIS applications using Extensible Markup Language (XML) transformations. This article demonstrates the rendition of AGS data format to a GML-conformant schema and illustrates the implementation of the new format through a few geotechnical examples.     

Estimating wave crest distributions using the method of L-moments

The design of fixed or floating offshore structures requires accurate information of the met-ocean data at the intended offshore site. In the design process it is recognized that this environmental data is modified in the near-field by the interaction with the particular geometrical configuration of the offshore structure. This transformation of the incident wave field around and beneath an offshore structure presents a challenge for ocean engineers when specifying the wave gap elevation to avoid impact loads on the underside of the deck and inundation of the topsides. Thus, the accurate estimation of the wave crest distributions from measurements at various locations near and under the offshore structure during model test studies is essential. A semi-empirical approach is presented herein that builds upon the findings of previous studies and introduces the Method of L-moments. A three parameter model for a wave crest probability distribution function is presented and explicit relationships between the parameters of the distribution and its’ first three L-Moments are established. Furthermore, three narrow-band models from earlier research studies are reviewed and compared with the new model. Wave measurements from a mini-TLP model test program are used as the basis for comparison of the four distributions. The root-mean-square error is used as a metric to quantify the overall fit of the data and its accuracy in the high end tail of the data. The L-Moment model is shown to be more robust in representing the data in both the far-field and beneath the deck of the mini-TLP where the wave field demonstrates increased non-linear behavior.     

Modeling relationships between the network distance and travel time dynamics for assessing equity of accessibility to urban parks

Static models of accessibility are usually based on the fixed distance or Average Travel Time (ATT) models. Because of ignoring the traffic as a dynamic process affecting the accessibility through the change of Travel Time (TT), these models lead to unperceived temporal inequities. In contrast to the consideration of the temporal Variation of TT (VTT) in the previous studies, the variation of traffic- related TT and its relations with network distance has not been considered. In this study, relations between VTT and network distance to access urban parks in Tehran megacity has been modeled. Traffic maps at five times of day are used to produce TT maps of Traffic Analysis Zones (TAZs) to their 3-closest parks. Comparison of the Gini coefficients of accessibility show significant inequities of accessibility at different times of day. Relations between the distance, ATT, and TTmax are modeled by statistical analysis. Results show both TT and TTmax have significant positive relations with distance and traffic and reach their maximum at 6 p.m. Observation of significant relations between distance, ATT, TTmax, and VTT provides interesting knowledge for the conversion of temporal measures of equity (TT) to a physical measure of equity (distance). A simple application of these findings for effective management of the spatiotemporal inequities is the definition of critical distances from public services. As an example, to decrease the TTmax of TAZs to less than 12 min, their maximum distance to the closest parks should be less than 4 km. The developed approach can be adopted for the accessibility evaluation of the other public services, particularly the health and education centers.     

Development of water management strategies in southern Mesopotamia during the fourth and third millennium B.C.E.

The last two decades witnessed increasing scholarly interest in the history of water management in southern Mesopotamia. Thanks to many geoarchaeological research projects conducted throughout the central and southern Iraqi floodplains, a general understanding of the macrophases of anthropogenic manipulation of this vast hydraulic landscape has been achieved. However, current narratives mostly rely on studies at a regional scale and are based on excessively long chronological phases (often spanning a whole millennium). A finer-tuned analysis at a submillennial scale is needed to better appreciate the dynamics that led to the development of artificial canals and irrigation systems and the creation of harbours in cities and other navigation-related facilities. The Iraqi-Italian QADIS project is addressing this issue through a systematic geoarchaeological investigation in the south-eastern area of the Qadisiyah province. We aim to update the current narrative by analysing case studies involving specific periods of occupation. We performed 17 boreholes to propose a date on the functioning period of the hydraulic works in five selected archaeological sites of this region. This approach allowed us to understand changes in water management strategies in both the short and the medium term (i.e., on a scale of centuries). In this paper, we present the results for the fourth and third millennia B.C.E. This period witnessed a crucial passage from the basic exploitation of natural watercourses for irrigation and occasional navigation to the emergence of the first system of artificial canals and intraurban harbours.     

Prediction and validation of traffic vibration reduction due to cement column stabilization

The transmission and reduction of vibrations in the far-field of the surface of the ground due to a surface load is investigated theoretically and validated with given field measurement data. The performance of a given stabilization column, located directly underneath the load, at a number of receiver positions is studied and measured in terms of insertion loss. A numerical model is presented, which enables the wave-field in the region of the column to be determined, based on an integral equation formulation of the problem which is solved using a boundary element approach. It is shown that the column has a beneficial effect at low frequencies especially in certain frequency bandwidths and is validated with field data. However, when the Rayleigh wavelength becomes short compared with the depth and width of the column adverse effects occur at some frequencies which are also observed in the far-field. Various depths of columns and material properties of the surrounding soil medium are studied and results presented so that some preliminary physical conclusions may be derived.     

Unstable modes of non-axisymmetric gaseous discs

We present a perturbation theory for studying the instabilities of non-axisymmetric gaseous discs. We perturb the dynamical equations of self-gravitating fluids in the vicinity of a non-axisymmetric equilibrium, and expand the perturbed physical quantities in terms of a complete basis set and a small non-axisymmetry parameter ε. We then derive a linear eigenvalue problem in matrix form, and determine the pattern speed, growth rate and mode shapes of the first three unstable modes. In non-axisymmetric discs, the amplitude and the phase angle of travelling waves are functions of both the radius R and the azimuthal angle φ. This is due to the interaction of different wave components in the response spectrum. We demonstrate that wave interaction in unstable discs, with small initial asymmetries, can develop dense clumps during the phase of exponential growth. Local clumps, which occur on the major spiral arms, can constitute seeds of gas giant planets in accretion discs.     

Vertical eddy diffusivity estimations in Swan river estuary

A field experiment is described in which diapycnal diffusivity is estimated by direct and indirect methods in Swan river estuary, Perth, Western Australia. The microstructure profiles were collected in a narrow and straight part of this estuary using a portable flux profiler (PFP). The profiles were segmented into stationary parts and the rate of vertical eddy diffusivity was estimated for the segments within the pycnocline. The direct measurement showed that instantaneous flux could be positive or negative with a low net rate of vertical eddy diffusivity for mass of about 6.5 × 10⁻⁸ m² s⁻¹. All the indirect methods overestimated this rate. However, within the indirect methods, the method of Osborn yielded the poorest estimate while the method of Osborn and Cox gave the closest estimate.     

喀纳斯自然保护区地衣生态地理分布的研究

根据1985年以来实地考察的基础上,对保护区自然地理条件和地衣生长发育的地理背景进行了分析,对地衣植被的生态地理分布规律进行了初步探讨.并对地衣植被进行了生态分类.