排序方式： 共有37条查询结果，搜索用时 31 毫秒
1.
Arthur C. R. Gleason Diego Lirman Dana Williams Nuno R. Gracias Brooke E. Gintert Hossein Madjidi R. Pamela Reid G. Chris Boynton Shahriar Negahdaripour Margaret Miller & Philip Kramer 《Marine Ecology》2007,28(2):254-258
Four hurricanes impacted the reefs of Florida in 2005. In this study, we evaluate the combined impacts of hurricanes Dennis, Katrina, Rita, and Wilma on a population of Acropora palmata using a newly developed video‐mosaic methodology that provides a high‐resolution, spatially accurate landscape view of the reef benthos. Storm damage to A. palmata was surprisingly limited; only 2 out of 19 colonies were removed from the study plot at Molasses Reef. The net tissue losses for those colonies that remained were only 10% and mean diameter of colonies decreased slightly from 88.4 to 79.6 cm. In contrast, the damage to the reef framework was more severe, and a large section (6 m in diameter) was dislodged, overturned, and transported to the bottom of the reef spur. The data presented here show that two‐dimensional video‐mosaic technology is well‐suited to assess the impacts of physical disturbance on coral reefs and can be used to complement existing survey methodologies. 相似文献
2.
Hussain Abid Rasul Golam Mahapatra Bidhubhusan Wahid Shahriar Tuladhar Sabarnee 《Natural Hazards》2018,91(3):1365-1383
Natural Hazards - Changes in climate, associated hazards, local adaptations in agriculture, and socioeconomic factors affecting adaptation were investigated using data from a large survey of 2310... 相似文献
3.
Shahriar M. Wahid Mukand S. Babel Ashim Das Gupta Roberto S. Clemente 《Hydrogeology Journal》2007,15(2):365-382
In Bangladesh, development of the groundwater resource for irrigation is a vital component of the government’s agricultural
strategy to attain food self-sufficiency. Amidst reports of falling groundwater levels in many parts of Bangladesh, the potential
of groundwater use has been investigated in the Teesta Barrage Project (TBP) in which large-scale groundwater development
for dry-season irrigation has taken place in the recent past. Several techniques and tools have been applied such as the combination
of analysis of groundwater hydrographs and mathematical modelling to derive key hydrogeological variables, calculation of
net irrigation requirement and the use of geographical information systems. The results show that the economically attractive
high-yielding variety (HYV) Boro (dry season) rice cultivation during the groundwater irrigation season may not be sustained in large parts of the project
area if the current trends in abstraction are continued. However, due to spatial variation in abstraction, nine thanas (sub-districts)—out of a total of 21 in the project area—may still be able to expand groundwater-irrigated cropland and a
groundwater-use potential of 40 mm/year may be created if deep-set shallow tubewells are used by the farmers to abstract groundwater.
A structured approach, based on zoning of potential areas, is recommended for groundwater development and use.
Resumen En Bangladesh, el desarrollo de las aguas subterráneas para riego es un componente vital del la estrategia agrícola del Gobierno para obtener la auto-suficiencia alimentaria. Un informe intermedio evidencia un descenso de los niveles de aguas subterráneas en muchas partes de Bangladesh, el uso potencial de aguas subterránea ha sido investigado en el Proyecto Tessta Barrage (TBP) en el cual ha tenido lugar el desarrollo de las aguas subterráneas a gran escala para el riego en la estación seca en un pasado reciente. Se ha aplicado algunas técnicas y herramientas, como la combinación del análisis de datos gráficos de aguas subterráneas y modelización matemática para obtener variables hidrogeológicas clave, el cálculo de la necesidad neta de riego y el uso de Sistemas de Información Geográfica. El resultado muestra que el cultivo, económicamente atractivo, de arroz HYV Boro (estación seca) durante la estación de riego con aguas subterráneas puede no ser sostenible en gran parte del área del proyecto si continúan las tendencias actuales en las extracciones. Sin embargo, debido a la variación espacial en la extracción, nueve thanas (subdistritos)—de un total de 21 en el área del Proyecto—pueden todavía sufrir un aumento de la tierra cultivable regada con aguas subterráneas y que se puede asumir un uso potencial de agua subterránea de 40 mm/estación si los granjeros utilizan sondeos someros instalados en fosas para la extracción. Se recomienda una aproximación estructurada para el desarrollo y uso de las aguas subterráneas, basada en la zonificación de áreas potenciales.
Résumé Au Bangladesh, l’exploitation des ressources en eau souterraines pour l’irrigation est une composante vitale de la stratégie agricole gouvernementale pour atteindre l’auto-suffisance alimentaire. Parmi les baisses de niveaux piézométriques rapportées sur de nombreuses régions du Bangladesh, le potentiel d’utilisation des eaux souterraines a été étudié sur le Projet de Barrage de Teesta (TBP), où, dans un passé récent, les eaux souterraines ont été massivement exploitées pour l’irrigation en saison sèche. De nombreux outils et techniques ont été utilisés, comme l’analyse combinée des chroniques piézométriques et des modèles mathématiques pour dégager les variables hydrogéologiques clés, le calcul des besoins nets pour l’irrigation, et l’utilisation des systèmes d’information géographique. Les résultats démontrent que la culture en saison d’irrigation de la variété de riz HYV Boro (saison sèche), économiquement attrayante, n’est potentiellement pas viable sur de nombreux secteurs de la zone étudiée si les prélèvements perdurent selon la tendance actuelle. Cependant, du fait de la variation spatiale des prélèvements, neuf thanas (sous-districts)—sur un total de 21 sur le secteur d’étude—pourraient encore augmenter les surfaces irriguées, et une disponibilité en eau de 40 mm/saison pourrait être générée si les agriculteurs utilisaient des puits peu profonds pour exploiter les ressources souterraines. Une approche structurée, basée sur le zonage des secteurs potentiels, est recommandée pour l’exploitation et l’utilisation des eaux souterraines.相似文献
4.
This study presents a thermo-hydro-mechanical (THM) model of unsaturated soils using isogeometric analysis (IGA). The framework employs Bézier extraction to connect IGA to the conventional finite element analysis (FEA), featuring the current study as one of the first attempts to develop an IGA-FEA framework for solving THM problems in unsaturated soils. IGA offers higher levels of interelement continuity making it an attractive method for solving highly nonlinear problems. The governing equations of linear momentum, mass, and energy balance are coupled based on the averaging procedure within the hybrid mixture theory. The Drucker-Prager yield surface is used to limit the modified effective stress where the model follows small strain, quasi-static loading conditions. Temperature dependency of the surface tension is implemented in the soil-water retention curve. Nonuniform rational B-splines (NURBS) basis functions are used in the standard Galerkin method and weak formulations of the balance equations. Displacement, capillary pressure, gas pressure, and temperature are four independent quantities that are approximated by NURBS in spatial discretization. The framework is used to simulate strain localization in an undrained dense sand subjected to plane strain biaxial compression under different temperatures and displacement velocities. Results show that an increase in the displacement rate leads to reduction in the equivalent plastic strain while an increase in the temperature leads to an increase in the equivalent plastic strain. The findings suggest that the proposed IGA-based framework offers a viable alternative for solving THM problems in unsaturated soils. 相似文献
5.
A geomechanical model can reveal the mechanical behavior of rocks and be used to manage the reservoir programs in a better mode. Fluid pressure will be reduced during hydrocarbon production from a reservoir. This reduction of pressure will increase the effective stress due to overburden sediments and will cause porous media compaction and surface subsidence. In some oil fields, the compacting reservoir can support oil and gas production. However, the phenomena can also cause the loss of wells and reduced production and also cause irreparable damage to the surface structures and affect the surrounding environment. For a detailed study of the geomechanical behavior of a hydrocarbon field, a 3D numerical model to describe the reservoir geomechanical characteristics is essential. During this study, using available data and information, a coupled fluid flow-geomechanic model of Fahlian reservoir formation in X-field in SW of Iran was constructed to estimate the amount of land subsidence. According to the prepared model, in this field, the maximum amount of the vertical stress is 110 MPa and the maximum amount of the horizontal stress is 94 MPa. At last, this model is used for the prediction of reservoir compaction and subsidence of the surface. The maximum value of estimated ground subsidence in the study equals to 29 mm. It is considered that according to the obtained values of horizontal and vertical movement in the wall of different wells, those movements are not problematic for casing and well production and also the surrounding environment. 相似文献
6.
As natural and man-made disasters have been increasing, interest in preventing crises and/or mitigating the associated consequences has been growing as well. When dealing with predictable disasters, there is a limited time for effective response, and people should be evacuated in a short time to minimize the fatalities. In such extraordinary situations, attention should be given to making better use of existing infrastructure. The aim of this study is to present a model for optimizing street directions in order to increase the outbound capacity of the network. However, because of the magnitude of the problem, an optimal solution cannot be reached through ordinary methods. Hence, the simulated annealing algorithm, which is a meta-heuristic technique, is used. Computational results on a case study demonstrate that this technique yields considerable improvement in the objective function of the problem which is total travel time of road network users.
相似文献7.
Exceptionally high ground motions (horizontal peak ground acceleration (PGA) of 1.82g) were recorded at the Tarzana Station during the main shock of the 1994 Northridge earthquake (moment magnitude 6.7 at an epicentral distance of 6 km). At the time of the main shock, the instrument was located near the edge of a 21 m-high ridge with side slopes ranging from 3H:1V to 15H:1V. The ridge is underlain by shallow fill and soft rocks of Medelo Formation.
The objectives of this study were to (1) identify the relative contributions of various factors such as local geology, topography, source mechanism, and travel path on the large ground motions recorded at Tarzana Station and (2) develop an analytical model that could adequately predict observed ground motions at the Tarzana site during the Northridge earthquake and at similar sites during future earthquakes. This study is an integral part of a series of inter-related studies referred to as the ROSRINE research (Resolution of Site Response Issues during Northridge Earthquake) project.
The PGA at the surface of competent bedrock (1 km/s shear wave velocity found about 100 m below ground surface) is estimated by Silva [ROSRINE Study (2000)] at 0.46 gravity (g). To identify the source of ground motion amplification, one-dimensional ( ), two-dimensional (TELDYN and SASSI), and three-dimensional (SASSI) analyses were conducted using both recorded aftershock data and an estimated ground acceleration time histories at a 100 m depth.
The results of the analyses indicate that (1) local geology and topography could only partially account for the observed ground motion amplification, and (2) the PGA and response spectra at a point near the edge of the ridge (the location of the instrument at the time of the main shock) is in good agreement with recorded values when the angle of incident of shear waves (SV waves) at 100 m depth is assumed at 30° from vertical. Considering the local geology and variation of shear wave velocity with depth, the 30° incident angle at 100 m depth corresponds to an 8° incident angle of shear waves at the ground surface. This observation is, in general, consistent with the incident angles of shear waves reported from study of the recorded aftershock data. 相似文献
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Ship hulls, as well as bridges, port dock pilings, dams, and various underwater structures need to be inspected for periodic maintenance. Additionally, there is a critical need to provide protection against sabotage activities, and to establish effective countermeasures against illegal smuggling activities. Unmanned underwater vehicles are suitable platforms for the development of automated inspection systems, but require integration with appropriate sensor technologies. This paper describes a vision system for automated ship-hull inspection, based on computing the necessary information for positioning, navigation, and mapping of the hull from stereo images. Binocular cues are critical in resolving a number of complex visual artifacts that hamper monocular vision in shallow-water conditions. Furthermore, they simplify the estimation of vehicle pose and motion, which is fundamental for successful automatic operation. The system has been implemented on a commercial remotely operated vehicle (ROV), and tested in pool and dock tests. Results from various trials are presented to demonstrate the system capabilities 相似文献
10.
Md. Sumon Shahriar Mohammad Kamruzzaman John McCulloch Simon Beecham 《Earth Science Informatics》2016,9(3):271-279
We develop multiple step ahead prediction models of river flow for locations in Tasmania (Australia) for decision support in aquaculture. In predicting river flows for multiple days ahead, we first statistically determine the maximum input lags of rainfall and river flow. We then use machine learning techniques in building models. In multiple step ahead prediction, we consider both static and dynamic approaches. In dynamic approach, one day prediction is served as input to two days ahead prediction. The experimental results demonstrate that, in general, a dynamic approach provides better accuracy in multiple day’s ahead prediction. For Duck Bay location using dynamic approach, support vector regression performs best over linear regression, M5P and multilayer perceptron. However, at Montagu Bay location, we find that M5P performs best over methods. We find that multiple step ahead prediction of river flow for each location requires modelling of lags with associated machine learning techniques. 相似文献