排序方式： 共有13条查询结果，搜索用时 390 毫秒
1.
2.
Natural Hazards - Recent tsunami disasters caused devastating damage to non-engineered as well as engineered coastal infrastructure. In fact, previous design guidelines containing provisions for... 相似文献
3.
The complex stream bank profiles in alluvial channels and rivers that are formed after reaching equilibrium has been a popular topic of research for many geomorphologists and river engineers. The entropy theory has recently been successfully applied to this problem. However, the existing methods restrict the further application of the entropy parameter to determine the cross-section slope of the river banks. To solve this limitation, we introduce a novel approach in the extraction of the equation based on the calculation of the entropy parameter (λ) and the transverse slope of the bank profile at threshold channel conditions. The effects of different hydraulic and geometric parameters are evaluated on a variation of the entropy parameter. Sensitivity analysis on the parameters affecting the entropy parameter shows that the most effective parameter on the λ-slope multiplier is the maximum slope of the bank profile and the dimensionless lateral distance of the river banks. 相似文献
4.
The objective of this study is to evaluate the performance of a large eddy simulation (LES) numerical model to assess the influence of mitigation walls with various cross sections on the tsunami-induced loading exerted on a freestanding structure. The validation of the model was performed using laboratory experiment results previously conducted by the second author. The employed experiments simulated a tsunami-like bore at two different impoundment depths, including 55 and 85 cm. The results showed that the one-equation subgrid-scale energy transport LES approach performs better than RANS models such as k-ε, k-ω and LRR and can accurately reproduce experimental data obtained for a wide range of experimental conditions. 相似文献
5.
Seyed Ahmad Meshkani Behzad Mehrabi Abdolmajid Yaghubpur Younes Fadakar Alghalandis 《Journal of Geochemical Exploration》2011
In regional exploration programs, the distribution of elements in known mineral deposits can be used as a guide for the classification of deposits, search for new prospects and modeling ore deposit patterns. The Sanandaj–Sirjan Zone (SSZ) is a major metallogenic zone in Iran, containing lead and zinc, iron, gold, copper deposits. In the central part of the SSZ, lead and zinc mineralization is widespread and hitherto exploration has been based on geological criteria. In this study, we used clustering techniques applied to element distribution for classification lead and zinc deposits in the central part of the SSZ. The hierarchical clustering technique was used to characterize the elemental pattern. Elements associated with lead and zinc deposits were separated into four clusters, encompassing both ore elements and their host rock-forming elements. It is shown that lead and zinc deposits in the central SSZ belong to two genetic groups: a MVT type hosted by limestone and dolomites and a SEDEX type hosted by shale, volcanic rocks and sandstone. The results of elemental clustering were used for pattern recognition by the K-means method and the respective deposits were classified into four distinct categories. K-means clustering also reveals that the elemental associations and spatial distribution of the lead and zinc deposits exhibit zoning in the central part of the SSZ. The ratios of ore-forming elements (Sb, Cd, and Zn) vs. (Pb and Ag) show zoning along an E–W trend, while host rock-forming elements (Mn, Ca, and Mg) vs. (Ba and Sr) show a zoning along a SE–NW trend. Large and medium deposits occur mainly in the center of the studied area, which justify further exploration around occurrences and abandoned mines in this area. The application of a pattern recognition method based on geochemical data from known mineralization in the central SSZ, and the classification derived from it, uncover elemental zoning, identify key elemental associations for further geochemical exploration and the potential to discover possible target areas for large to medium size ore deposits. This methodology can be applied in a similar way to search for new ore deposits in a wide range of known metallogenic zones. 相似文献
6.
C. P. Rajendran Kusala Rajendran Majid Shah-hosseini Abdolmajid Naderi Beni C. M. Nautiyal Ronia Andrews 《Natural Hazards》2013,65(1):219-239
Evaluating the hazard potential of the Makran subduction zone requires understanding the previous records of the large earthquakes and tsunamis. We address this problem by searching for earthquake and tectonic proxies along the Makran Coast and linking those observations with the available constraints on historical seismicity and the tell-tale characteristics of sea floor morphology. The earthquake of Mw 8.1 of 1945 and the consequent tsunami that originated on the eastern part of the Makran are the only historically known hazardous events in this region. The seismic status of the western part of the subduction zone outside the rupture area of the 1945 earthquake remains an enigma. The near-shore shallow stratigraphy of the central part of Makran near Chabahar shows evidence of seismically induced liquefaction that we attribute to the distant effects of the 1945 earthquake. The coastal sites further westward around Jask are remarkable for the absence of liquefaction features, at least at the shallow level. Although a negative evidence, this possibly implies that the western part of Makran Coast region may not have been impacted by near-field large earthquakes in the recent past??a fact also supported by the analysis of historical data. On the other hand, the elevated marine terraces on the western Makran and their uplift rates are indicative of comparable degree of long-term tectonic activity, at least around Chabahar. The offshore data suggest occurrences of recently active submarine slumps on the eastern part of the Makran, reflective of shaking events, owing to the great 1945 earthquake. The ocean floor morphologic features on the western segment, on the contrary, are much subdued and the prograding delta lobes on the shelf edge also remain intact. The coast on the western Makran, in general, shows indications of progradation and uplift. The various lines of evidence thus suggest that although the western segment is potentially seismogenic, large earthquakes have not occurred there in the recent past, at least during the last 600?years. The recurrence period of earthquakes may range up to 1,000?years or more, an assessment based on the age of the youngest dated coastal ridge. The long elapsed time points to the fact that the western segment may have accumulated sufficient slip to produce a major earthquake. 相似文献
7.
Numerical modeling of local scour at a submerged weir with a downstream slope using a coupled moving-mesh and maskedelement approach 总被引：2，自引：2，他引：0
This paper presents a model for local scour at submerged weirs with downstream slopes that uses a coupled moving-mesh and masked-element approach.In the developed model,the fluid-sediment interface is tracked using a moving-mesh technique,and the effects of the structure on the hydrodynamics and bed morphology are resolved using a masked-element technique.Compared to traditional sediment scour models,based on the moving-mesh technique,the present model has the advantage of allowing for a simpler setup of the computational grids and a larger-amplitude deformation.Laboratory experiments on local scour at a submerged weir with a downstream slope were conducted,which provided bed profiles at different time instants.The results obtained by the present model are compared to the experimental data.The comparisons demonstrate the performance of the model in satisfactorily predicting local scour at a submerged weir with a downstream slope.The model was further modified and employed to carry out additional computations to investigate the influence of various parameters and sub-models. 相似文献
8.
Cyril Aubert Elodie Brisset Morteza Djamali Arash Sharifi Philippe Ponel Belinda Gambin Tayebeh Akbari Azirani Frédéric Guibal Hamid Lahijani Abdolmajid Naderi Beni Jacques-Louis de Beaulieu Ali Pourmand Valérie Andrieu-Ponel Alain Thiéry Emmanuel Gandouin 《Journal of Paleolimnology》2017,58(2):151-167
We reconstructed the paleohydrologic and climatic history of the Lake Neor region, NW Iran, from the end of the late glacial to the middle Holocene (15,500–7500 cal yr BP). Subfossil chironomid and pollen assemblages in a sediment core from a peatland located south of Lake Neor enabled identification of four main hydrologic phases. The period 15,500–12,700 cal yr BP was characterized by a relatively dry climate with an open landscape, suggested by the abundance of Irano-Turanian steppe plants (e.g. Amaranthaceae, Artemisia and Cousinia). Dominance of several shallow-water and semi-terrestrial chironomid taxa (e.g. Pseudosmittia, Smittia/Parasmittia and Paraphaenocladius/Parametriocnemus) during this period is indicative of lower water tables in the wetland. Between 12,700 and 11,300 cal yr BP, chironomid taxa indicate higher wetland water tables, as suggested by the presence of Zavrelia, Chironomus anthracinus/plumosus-type and Micropsectra, which are inhabitants of open-water, lacustrine areas. The open-steppe vegetation remained dominant in the watershed during this time. Increasing wetland moisture could be explained by: (1) cool summers that reduced the evaporation rate; and/or (2) a decrease in duration of the summer dry season. The period 11,300–8700 cal yr BP was characterized by lower wetland moisture, contemporaneous with a delay in the expansion of deciduous forest, suggesting persistent dry climate conditions throughout the beginning of the Holocene, which may have been related to the intensified seasonality of precipitation. Around 8700 cal yr BP, higher wetland water levels, inferred from chironomids, occurred simultaneously with the onset of regional deciduous forest expansion, probably caused by a shortening of the summer dry period. We concluded that chironomids are appropriate paleoecological proxies to investigate global and local hydrologic variability in the Middle East. 相似文献
9.
Hassan Mohammadian Mosammam Mozaffar Sarrafi Jamileh Tavakoli Nia Ali Mohammadian Mosammam 《The Professional geographer》2017,69(3):455-471
The purpose of this article is to identify food deserts using a geographic information system (GIS)-based multicriteria decision-making (MCDM) approach in the city of Tehran. We have found that, compared to technocratic methods, GIS-based MCDM and taking into account people or their agents' opinions in the food deserts analysis leads to different results. Whereas measuring food deserts based on the distance to large retail food stores indicated that a large part of the northern neighborhoods of Tehran do not have access to large food stores, identifying the food desert through the GIS-based MCDM approach revealed that northern neighborhoods of Tehran have relatively good access to healthy, affordable food. In addition, results indicated that individual factors have a more effective role than environmental factors in food accessibility. Food accessibility analysis revealed that more than 26.6 percent of Tehran's people (2,049,796) are living in very low and low food accessibility areas. Accordingly, to achieve a relatively healthy and inclusive food environment, establishment of a food council, development of mobile food markets and farmers' markets, extension of public transport, enhancement of food literacy, and community-based development of small full-service grocery stores, especially in southern and western sections of Tehran, should be pursued. In addition, addressing Tehran's food desert issues would be incomplete without due attention to the wider political and economic environment. 相似文献
10.
Canonical balanced dynamic equations involving vertically sheared horizontal flow with heat or mass sources have emerged recently in systematic multi-scale modeling of the equatorial wave guide on a wide range of spatio-temporal scales. Here, a new self-contained derivation of these equations is developed briefly in a context for potential applications to the hurricane embryo. These canonical balanced equations are studied through a combination of exact solutions and simple numerics. The results below include elementary exact solutions given by velocity fields that are linear in the spatial coordinates combined with an exact nonlinear stability analysis for vertical vorticity amplification in such a preconditioned environment. Other elementary solutions studied here include the evolution of radial eddies, which represent “hot towers” in the hurricane embryo in a suitable radial preconditioned background environment. 相似文献