排序方式： 共有69条查询结果，搜索用时 35 毫秒
51.
Mohammad Tahsin Karimi Nezhad Manijeh Ghahroudi Tali Mohammad Hashemi Mahmoudi Ebrahim Pazira 《Environmental Earth Sciences》2011,64(5):1203-1213
The aim of this study was to investigate the influences of land use, parent materials (rock types) and soil properties on total arsenic and cadmium concentrations in the agricultural soils. A total of 87 surface (0–20 cm) soil samples were collected from four types of land use: irrigated farming, rangeland, dry farming and orchard. The average concentrations of the analyzed elements in topsoil were 84.426 mg As/kg and 3.289 mg Cd/kg. In addition, the pH, organic matter (OM), cation exchange capacity (CEC), soil grain sizes and CaCO3 were measured for each sample. The results indicated that land use had no significant effect on As and Cd concentrations. Our findings indicated that the Cd concentrations were influenced by bedrock composition, but for As there were no significant differences between various soil parent materials (bedrocks). Soil pollution was assessed on the basis of pollution index (PI), comprehensive pollution index (P n ) and geoaccumulation index (I geo). Calculated indices showed high-pollution levels for As and low- to moderate-pollution levels for Cd. 相似文献
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Hamideh Rouhani Tazangi Ataallah Soltani Goharrizi Ebrahim Jahanshahi Javaran 《国际泥沙研究》2021,36(5):637-655
In the current study, the settling, interaction, drafting, kissing, and tumbling of two identical and non-identical circular particles were simulated in a two-dimensional box in shear-thinning, Newtonian, and shear-thickening fluids by using the combined lattice Boltzmann-smoothed profile methods. Furthermore, the drag coefficient of one particle settling for different power-law indexes and Archimedes numbers was calculated. Also, the effect of the diameter ratio of the two particle pairs was considered during settling. The developed method was validated by simulating the settling of one particle and two identical particles in a Newtonian fluid. To consider two non-identical particles, two cases were examined. In Case A, the larger particle was above the smaller one and in the Case B, the smaller particle was above the larger one. The results showed that the two non-identical particles were separated more easily than the identical ones. In the settling of two particles under the same Archimedes number, the drafting and kissing time considerably increased by changing the non-Newtonian fluid behavior from a shear-thinning one to a shear-thickening one. Also, when the larger particle was above the smaller one, the time duration of the kissing stage increased with the decrease in the diameter ratio. 相似文献
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ABSTRACTPrediction of design hydrographs is key in floodplain mapping using hydraulic models, which are either steady state or unsteady. The former, which require only an input peak, substantially overestimate the volume of water entering the floodplain compared to the more realistic dynamic case simulated by the unsteady models that require the full hydrograph. Past efforts to account for the uncertainty of boundary conditions using unsteady hydraulic modeling have been based largely on a joint flood frequency–shape analysis, with only a very limited number of studies using hydrological modeling to produce the design hydrographs. This study therefore presents a generic probabilistic framework that couples a hydrological model with an unsteady hydraulic model to estimate the uncertainty of flood characteristics. The framework is demonstrated on the Swannanoa River watershed in North Carolina, USA. Given its flexibility, the framework can be applied to study other sources of uncertainty in other hydrological models and watersheds. 相似文献
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Mohammad Azarafza Akbar Ghazifard Haluk Akgün Ebrahim Asghari-Kaljahi 《Environmental Earth Sciences》2018,77(24):805
This study assesses the landslide susceptibility of the South Pars Special Zone (SPSZ) region that is located in southwest Iran. For this purpose, a combinatorial method containing multi-criteria decision-making, likelihood ratio and fuzzy logic was applied in two levels (regional and local) at three critical zones (northwest, middle and southeast of the project area). The analysis parameters were categorised in seven main triggering factors such as climatology, geomorphology, geology, geo-structure, seismic activity, landslide prone areas and man-made activities which have different classes with multi-agent partnership correlations. Landslide susceptibility maps were prepared for these levels and zones after purified and enriched fuzzy trending runs were performed. According to the results of the risk-ability assessment of the landslide occurrences for SPSZ, the north part of the study area which includes the south edge of the Assalouyeh anticline and the southern part of the Kangan anticline were estimated as high-risk potential areas that were used in landslide hazard mitigation assessment and in land-use planning. 相似文献
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The least-squares wavelet analysis, an alternative to the classical wavelet analysis, was introduced in order to analyze unequally spaced and non-stationary time series exhibiting components with variable amplitude and frequency over time. There are a few methods such as cross-wavelet transform and wavelet coherence that can analyze two time series together. However, these methods cannot generally be used to analyze unequally spaced and non-stationary time series with associated covariance matrices that may have trends and/or datum shifts. A new method of analyzing two time series together, namely the least-squares cross-wavelet analysis, is developed and applied to study the disturbances in the gravitational gradients observed by GOCE satellite that arise from plasma flow in the ionosphere represented by Poynting flux. The proposed method also shows its outstanding performance on the Westford–Wettzell very long baseline interferometry baseline length and temperature series. 相似文献
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A numerical simulation algorithm based on the finite volume discretisation is presented for analyzing ship motions. The algorithm employs a fractional step method to deal with the coupling between the pressure and velocity fields. The free surface capturing is fulfilled by using a volume of fluid method in which the interface between the liquid (water) and gas (air) phases are computed by solving a scalar transport equation for the volume fraction of the liquid phase. The computed velocity field is employed to evaluate the acting forces and moments on the vessel. Using the strategy of boundary-fitted body-attached mesh and calculating all six degrees-of-freedom of motion in each time step, time history of ship motions including displacements, velocities and accelerations are evaluated.To verify the proposed algorithm, a series of verification tests are conducted. First, a two-dimensional asymmetrical wedge slamming is simulated as a simple type of a common case for high-speed vessels. Then, the steady-state forward motion of a high-speed planing catamaran is investigated. Results of both test cases show good agreement with experimental data. It is concluded that the proposed algorithm can be a promising strategy for both performance prediction and design of high-speed vessels. 相似文献
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Girma Yimer Ebrahim Kelly Hamonts Ann van Griensven Andreja Jonoski Winnie Dejonghe Arthur Mynett 《水文研究》2013,27(11):1634-1645
Groundwater interacts with surface water features nearly in all types of landscapes. Understanding these interactions has practical consequences on the quantity and quality of water in either system, because the depletion or contamination of one of the systems will eventually affect the other one. Many studies have shown that the use of heat as natural tracer in conjunction with water level measurements is an effective method for estimating water flow (fluxes) between groundwater and surface water. A number of studies have explored the effects of spatial and temporal variability of groundwater–surface water flux exchanges using temperature and water level measurements; however, the effect of temporal resolution of water level and temperature data on estimating flux remains unexplored. Therefore, this study investigated the effect of temporal resolution of input data on temporal variation of groundwater–surface water flux exchanges. To this end, we calibrated a variably saturated two‐dimensional groundwater flow and heat transport model (VS2DH) at hourly and daily time scales using temperatures measured at multiple depths below the riverbed of the Zenne River, located at a well‐known Belgian brownfield site. Results of the study showed that the computed water flux through the streambed ranged between ?32 mm/day and +25 mm/day using the hourly model and from ?10 mm/day to ?37 mm/day using the daily model. The hourly model resulted in detecting reversal of flow direction inducing short‐term surface water flow into the streambed. However, such events were not captured if daily temperature and water level measurements were used as input. These findings have important implications for understanding contaminant mass flux and their attenuation in the mixing zone of groundwater and surface water. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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Mohammad Saeed SEIF Ebrahim JAHANBAKHSH Roozbeh PANAHI Mohammad Hossein KARIMI 《中国海洋工程》2009,23(3):517-528
High speed planing hulls have complex hydrodynamic behaviors. The trim angle and drafts are very sensitive to speed and location of the center of gravity. Therefore, motion simulation for such vessels needs a strong coupling between rigid body motions and hydrodynamic analysis. In addition, free surface should be predicted with good accuracy for each time step. In this paper, velocity and pressure fields are coupled by use of the fractional step method. On the basis of integration of the two-phase viscous f... 相似文献