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1.
In this paper the steady lateral growth of three-dimensional turbulent inclined turbidity current is investigated. To simulate the current, an experimental setup is developed to analyze the turbidity current for different regimes in the particle laden density currents environment. The Buckingham's π theorem together with a dimensional analysis is implemented to derive the appropriate non-dimensional variables. The experimental results were normalized and plotted in the form of non-dimensional graphs from which a theoretical model is developed and analyzed. Based on the results obtained for the steady lateral growth, three different regimes, namely, inertia-viscous one as the first regime, buoyancy-viscous and gravity-viscous as the second and third regimes are distinguished within the current.In these regimes, the force balance is between the driving and resisting forces. Namely, in the first regime, the force balance is between the inertia and viscous forces, in the second regime, the buoyancy and viscous forces, and in the third regime, gravity and viscous forces are balanced. The experimental results indicate that the lateral growth rate in the first regime is smaller than that in the second and third regimes due to the magnitude and type of the forces involved in those regimes. According to the graphical results, the three different lateral growth rates appear when the normalized current length is smaller than about 3, between about 3 and 10, and larger than about 10. In those regions,the slopes of the data are different with respect to one another. 相似文献
2.
In this paper, we search the existence of Bianchi type I cosmological model in f(R,T) gravity, where the gravitational Lagrangian is given by an arbitrary function of the Ricci scalar R and of the trace of the stress-energy tensor T. We obtain the gravitational field equations in the metric formalism, and reconstruct the corresponding f(R,T) functions. Attention is attached to the special case, f(R,T)=f 1(R)+f 2(T) and two examples are assumed for this model. In the first example, we consider the unification of matter dominated and accelerated phases with f(R) gravity in anisotropic universe, and in the second instance, model of f(R,T) gravity with transition of matter dominated phase to the acceleration phase is obtained. In both cases, f(R,T) is proportional to a power of R with exponents depending on the input parameters. 相似文献
3.
Identification, analysis and prediction of the erosion and sedimentation or the increase and decrease in river bed level are among the most complex and yet up-to-date topics of deposit hydraulics and river engineering. If cross structures in rivers and canals are also to be considered the complexity of flow pattern and deposit transfer increases. In this research using the one-dimensional mathematical model HEC-RAS 4.1 the effect of short dikes on flow hydraulic and the trend of sedimentation and erosion in the Karun River were simulated and analyzed within the boundaries of Ahwaz City. The area introduced into the model started from the Ghir dike to Khoramshahr. Moreover, the Mollathani, Farsiat and Ahwaz hydrometric stations were used as the upper limit, lower limit and calibration limit of the model, respectively. The flow was assumed to be quasi-unsteady and based on the existing knowledge of different methods and experiences with the methods in other studies the Toffaleti method was used to solve the deposit equations. The model was prepared and applied in the following four states: without dike and with dikes 0.7, 1.2 and 1.7 m above the average level in the desired areas. Finally, results of the model applied with and without short dikes revealed that the short dikes and dikes 1.2 m above the average floor level of modeled areas were significantly ineffective under hydraulic conditions and morphological changes. Moreover, the majority of changes in the river bed and all the morphological changes, in general, were the result of other factors. Dikes with heights of 1.7 m above the average floor level significantly caused sedimentation in the upstream and affected the hydraulics of flow. 相似文献
4.
Assessing the uncertainties of hydrologic model selection in climate change impact studies 总被引：3，自引：0，他引：3
The uncertainties associated with atmosphere‐ocean General Circulation Models (GCMs) and hydrologic models are assessed by means of multi‐modelling and using the statistically downscaled outputs from eight GCM simulations and two emission scenarios. The statistically downscaled atmospheric forcing is used to drive four hydrologic models, three lumped and one distributed, of differing complexity: the Sacramento Soil Moisture Accounting (SAC‐SMA) model, Conceptual HYdrologic MODel (HYMOD), Thornthwaite‐Mather model (TM) and the Precipitation Runoff Modelling System (PRMS). The models are calibrated based on three objective functions to create more plausible models for the study. The hydrologic model simulations are then combined using the Bayesian Model Averaging (BMA) method according to the performance of each models in the observed period, and the total variance of the models. The study is conducted over the rainfall‐dominated Tualatin River Basin (TRB) in Oregon, USA. This study shows that the hydrologic model uncertainty is considerably smaller than GCM uncertainty, except during the dry season, suggesting that the hydrologic model selection‐combination is critical when assessing the hydrologic climate change impact. The implementation of the BMA in analysing the ensemble results is found to be useful in integrating the projected runoff estimations from different models, while enabling to assess the model structural uncertainty. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
5.
M. Najafi F. Mohammad-Hosseinzadeh 《International Journal of Environmental Science and Technology》2013,10(4):665-676
In this study, a one-dimensional transient cumulonimbus cloud is modeled to be seeded by liquid CO2. The model includes microphysical and dynamical processes associated with glaciogenic seeding by homogenous ice nucleation and two thermal terms associated with seeding by ?90 ºC liquid CO2. For this model, the study concentrates on five types of hydrometeors, namely, cloud droplet, cloud ice, snow, hail/graupel, and rain. Point and horizontal seeding methods are implemented to observe their implications for rainfall enhancement, amount of hail/graupel production, vertical cloud extension, and radar’s reflectivity. In addition, the seeding temperature effects on the rainfall and microphysical processes are investigated. The results of the study show that, the rainfall enhancement and rainfall intensity in the point seeding case are more than those in the horizontal seeding. Moreover, the study reveals that, there is a vertical cloud extension enhancement of 0.5 km for clouds with top height of 10.5 km. The most important sources of the rain water production are found to be the accretion of cloud water by rain (P RACW) and by snow (P SACW), and for the graupel production is dry growth of the graupel (P GDRY). The results of this study are confirmed by the results of other investigators and are found to be comparable with the recorded data at rain gauge stations. 相似文献
6.
Seyed Hamidreza Sadeghi Saeed Najafi Alireza Riyahi Bakhtiari Parviz Abdi 《水文科学杂志》2013,58(9):1753-1762
AbstractSoil erosion and eroded sediment are serious threats to sound land management. However, less attention has been given to quantifying the importance of different soil erosion features based on appropriate control measures that could be designated. Accordingly, this research was planned to quantify the contribution of potential sediment sources, i.e. sheet, rill and gully erosion, in Idelo watershed in Zanjan Province, Iran, using composite fingerprinting. Toward this aim, 16 geochemical and organic tracers were detected in sediment sources and sediment deposited at the outlet. The results of applying the composite fingerprinting technique, with a relative error of 16%, showed that sheet, rill and gully sources contributed 56%, 44% and 0%, respectively, to sediment yield. It was also apparent from the results that the composite fingerprinting approach could be successfully utilized to assess the provenance of sediment deposited at the main outlet of the study watershed by soil erosion type.Editor Z.W. Kundzewicz 相似文献
7.
An appropriate, rapid and effective response to extreme precipitation and any potential flood disaster is essential. Providing an accurate estimate of future changes to such extreme events due to climate change are crucial for responsible decision making in flood risk management given the predictive uncertainties. The objective of this article is to provide a comparison of dynamically downscaled climate models simulations from multiple model including 12 different combinations of General Circulation Model (GCM)–regional climate model (RCM), which offers an abundance of additional data sets. The three major aspects of this study include the bias correction of RCM scenarios, the application of a newly developed performance metric and the extreme value analysis of future precipitation. The dynamically downscaled data sets reveal a positive overall bias that is removed through quantile mapping bias correction method. The added value index was calculated to evaluate the models' simulations. Results from this metric reveal that not all of the RCMs outperform their host GCMs in terms of correlation skill. Extreme value theory was applied to both historic, 1980–1998, and future, 2038–2069, daily data sets to provide estimates of changes to 2‐ and 25‐year return level precipitation events. The generalized Pareto distribution was used for this purpose. The Willamette River basin was selected as the study region for analysis because of its topographical variability and tendency for significant precipitation. The extreme value analysis results showed significant differences between model runs for both historical and future periods with considerable spatial variability in precipitation extremes. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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9.
Petr Vaníček Mehdi Najafi Zdeněk Martinec Lars Harrie Lars E. Sjöberg 《Journal of Geodesy》1995,70(3):176-182
In this paper we formulate two corrections that have to be applied to the higher-degree reference spheroid if one wants to use it in conjunction with the Stokes-Helmert scheme for geoid determination. We show that in a precise geoid determination one has to apply the correction for the residual topographical potential and the correction for the earth ellipticity. Both these corrections may reach several decimetres; we show how their magnitudes vary within Canada and we give their global ranges. 相似文献
10.
Amir Mohseni Adel Reyhanitabar Nosratollah Najafi Shahin Oustan Kambiz Bazargan 《Arabian Journal of Geosciences》2018,11(14):384
The aim of this study was to determine the influence of sewage sludge (SLU) amendment on the desorption characteristics of zinc (Zn), lead (Pb), and cadmium (Cd) in contaminated calcareous soils. Three levels of SLU (0, 1, and 3% w/w) were added to the two calcareous contaminated soils. Samples were incubated for 30 days and equilibrated with 0.005 M DTPA for 0.25 to 240 h. The addition of SLU significantly increased the amount of DTPA-extractable Zn in soils. While the amounts of Cd, Pb, dissolved organic carbon (DOC), and pH showed a significant increase only in 3% w/w of SLU, with the exception of Cd desorption in 1% w/w of SLU, kinetics of Zn, Pb, and Cd extraction increased together with an increase in the level of applied SLU. The best models for describing desorption data were explicitly power function and Elovich. The rate constants of Zn and Pb had significant correlations with DTPA-extractable Zn and Pb, DOC and pH, which affect Zn and Pb desorption. Also, the rate constants of Cd had significant correlations with CEC that can be deemed as equivalent to the fact that Cd desorption is controlled by surface adsorption, particularly in the lower sludge application amount. These results can be used for management of sewage sludge application in contaminated calcareous soils. 相似文献