Investigation of lake drying attributed to climate change   总被引：1，自引：1，他引：0  

M. Abbaspour  A. H. Javid  S. A. Mirbagheri  F. Ahmadi Givi  P. Moghimi 《International Journal of Environmental Science and Technology》2012,9(2):257-266

In recent decades, climate change has been of great concern due to its effect on water level and its impact on aquatic ecosystems. Urmia Lake, the largest inland wetland in Iran, has been shrinking. There is a great concern whether it will dry up like the Aral Sea. Therefore, a hydrodynamic model has been developed to simulate the condition of Urmia Lake. The model has been validated using the known annual data on precipitation, evaporation, run off, river discharges and water level which are available for the last 35?years. Different hydrological conditions regarding lake input and output data were tested and water depth was calculated using bathymetry to predict water-level fluctuations in the future. The results predict that the water level will decrease continuously. The lake will be dried up in about 10?years if very dry conditions continue in the region. The drought speed cannot be reduced and there is no potential to develop a water-usage program. Besides, the lake water depth decrease is more slightly, applying alternate wet and dry-period conditions. In some hydrological conditions there is a good potential to consider water development projects. The sensitivity analysis of different parameters indicates that the lake is highly sensitive to river discharges, which implies that the water development project plans will disturb the lake ecosystem if implemented up to 2021 and integrated watershed management plan for the lake can change the condition by regulating the dam output.  相似文献   

Comparison of artificial neural network and multivariate linear regression methods for estimation of daily soil temperature in an arid region   总被引：5，自引：0，他引：5  

Hossein Tabari  Ali-Akbar Sabziparvar  Mohammad Ahmadi 《Meteorology and Atmospheric Physics》2011,110(3-4):135-142

Soil temperature (T _S) strongly influences a wide range of biotic and abiotic processes. As an alternative to direct measurement, indirect determination of T _S from meteorological parameters has been the focus of attention of environmental researchers. The main purpose of this study was to estimate daily T _S at six depths (5, 10, 20, 30, 50 and 100?cm) by using a multilayer perceptron (MLP) artificial neural network (ANN) model and a multivariate linear regression (MLR) method in an arid region of Iran. Mean daily meteorological parameters including air temperature (T _a), solar radiation (R _S), relative humidity (RH) and precipitation (P) were used as input data to the ANN and MLR models. The model results of the MLR model were compared to those of ANN. The accuracy of the predictions was evaluated by the correlation coefficient (r), the root mean-square error (RMSE) and the mean absolute error (MAE) between the measured and predicted T _S values. The results showed that the ANN method forecasts were superior to the corresponding values obtained by the MLR model. The regression analysis indicated that T _a, RH, R _S and P were reasonably correlated with T _S at various depths, but the most effective parameters influencing T _S at different depths were T _a and RH.  相似文献   

A hybrid distinct element–boundary element approach for seismic analysis of cracked concrete gravity dam–reservoir systems     

M. Mirzayee  N. KhajiM.T. Ahmadi 《Soil Dynamics and Earthquake Engineering》2011

This paper proposes a new algorithm for modeling the nonlinear seismic behavior of fractured concrete gravity dams considering dam–reservoir interaction effects. In this algorithm, the cracked concrete gravity dam is modeled by distinct element (DE) method, which has been widely used for the analysis of blocky media. Dynamic response of the reservoir is obtained using boundary element (BE) method. Formulation and various computational aspects of the proposed staggered hybrid approach are thoroughly discussed. To the authors' knowledge, this is the first study of a hybrid DE–BE approach for seismic analysis of cracked gravity dam–reservoir systems. The validity of the algorithm is discussed by developing a two-dimensional computer code and comparing results obtained from the proposed hybrid DE–BE approach with those reported in the literature. For this purpose, a few problems of seismic excitations in frequency- and time-domains, are presented using the proposed approach. Present results agree well with the results from other numerical methods. Furthermore, the cracked Koyna Dam is analyzed, including dam–reservoir interaction effects with focus on the nonlinear behavior due to its top profile crack. Results of the present study are compared to available results in the literature in which the dam–reservoir interaction were simplified by added masses. It is shown that the nonlinear analysis that includes dam–reservoir interaction gives downstream sliding and rocking response patterns that are somehow different from that of the case when the dam–reservoir interaction is approximated employing added masses.  相似文献   

The application of geochemical pattern recognition to regional prospecting: A case study of the Sanandaj–Sirjan metallogenic zone,Iran     

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   

State of stress in the northern Tabas block, east-central Iran, as inferred from focal mechanisms of the 1978 Tabas earthquake sequence     

G. Behzad Zamani 《Central European Journal of Geosciences》2011,3(1):77-89

In this paper, the state of stress in the northern Tabas block in east-central Iran is analyzed based on the systematic inversion of aftershock focal mechanisms from the 1978.09.16 Tabas earthquake, to characterise the stress regime that controls most earthquakes in this area. Here, stress inversions of double-couple focal mechanisms of earthquakes recorded during the 30 days following the main shock have been carried out. The calculated average stress regime indicates dominant major 226° to 237° trending compression for the Tabas region. The dominating regime in east-central Iran is thrusting with a minimum stress axis, σ ₃, close to vertical. The reconstruction of the main seismotectonic stress in east-central Iran with a NE-SW compression is consistent with independent information of the active plate convergence related to Arabia-Eurasia convergence. Most earthquakes in the mentioned area occur near or around concealed Quaternary thrust faults with their activity being controlled by the NE-SW compression. Where ?, the ratio of principal stress differences, is 0.5, a small difference between σ ₂; σ ₃ and σ ₁ and small amounts of deviatoric stress is indicated. Therefore, for small deviatoric horizontal σ ₁ it is not possible to increase and reactivate small sections of basement thrust faults and create secondary basement aftershocks. Reconstructed stress regimes in this study for sedimentary cover (237) and basement (226) of Tabas are similar. Therefore, it seems that the basement and cover were coupled together, possibly along the 2–4 km of upper Precambrian low-grade metamorphic rocks. Then these segments of the fold-and-thrust belt were involved in similar seismic activity under a similar stress regime.  相似文献   

Input data selection for solar radiation estimation   总被引：1，自引：0，他引：1  

Azadeh Ahmadi  Dawei Han  Mohammad Karamouz  Renji Remesan 《水文研究》2009,23(19):2754-2764

Model input data selection is a complicated process, especially for non‐linear dynamic systems. The questions on which inputs should be used and how long the training data should be for model development have been hard to solve in practice. Despite the importance of this subject, there have been insufficient reports in the published literature about inter‐comparison between different model input data selection techniques. In this study, several methods (i.e. the Gamma test, entropy theory, AIC (Akaike's information criterion)/BIC (Bayesian information criterion) have been explored with the aid of non‐linear models of LLR (local linear regression) and ANN (artificial neural networks). The methodology is tested in estimation of solar radiation in the Brue Catchment of England. It has been found that the conventional model selection tools such as AIC/BIC failed to demonstrate their functionality. Although the entropy theory is quite powerful and efficient to compute, it failed to pick up the best input combinations. On the other hand, it is very encouraging to find that the new Gamma test was able to choose the best input selection. However, it is surprising to note that the Gamma test significantly underestimated the required training data while the entropy theory did a better job in this aspect. This is the first study to compare the performance of those techniques for model input selections and still there are many unsolved puzzles. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Stochastic earthquake response of secondary systems in base-isolated structures     

Yu Chen  Goodarz Ahmadi 《地震工程与结构动力学》1992,21(12):1039-1057

This paper studies the stochastic responses of secondary systems in base-isolated shear beam structures. A number of base isolation systems such as the laminated rubber bearing (LRB), the resilient-friction base isolator (R-FBI) with or without sliding upper plate, and the EDF system are considered. The stochastic models for the El Centro 1940 and the Mexico City 1985 earthquakes which preserve the non-stationary evolutions of amplitude and frequency content of ground accelerations are used as earthquake excitations. The technique of equivalent linearization is utilized and the mean-square response statistics of secondary systems and primary structure are evaluated. The accuracy of the linearization scheme is verified by comparison with the Monte Carlo simulation results. Statistically estimated peak responses of the secondary system are evaluated and the results are compared with the response spectra for actual earthquake accelerograms. It is shown that the use of base isolation systems, generally, provides considerable protection for structural contents. In particular, the LRB system is remarkably effective in reducing responses of secondary systems. Results for the Mexico City earthquake show that the base-isolated structures are sensitive to long period ground excitations.  相似文献   

A model for dilatation, densification, and static liquefaction of loose sands     

V. B. DeGregorio  G. Ahmadi 《Mathematical Geology》1990,22(1):1-13

Utilizing basic balance laws of saturated granular media, a theoretical model for describing the phenomena of dilatation and densification of dry sand, as well as the increase of pore water pressure of saturated sand during shear loading, is developed. An expression for the free-energy function of loose sands is postulated, and the problem of static shearing of a sand sample is analyzed. Predictions of the model for pore water pressure are compared with those obtained experimentally for dry pluviated and moist vibrated samples of fine Ottawa sand and solid-glass beads and discussed.  相似文献   

A Geometric Computational Model for Calculation of Longwall Face Effect on Gate Roadways     

Hamid Mohammadi  Mohammad Ali Ebrahimi Farsangi  Hossein Jalalifar  Ali Reza Ahmadi 《Rock Mechanics and Rock Engineering》2016,49(1):303-314

In this paper a geometric computational model (GCM) has been developed for calculating the effect of longwall face on the extension of excavation-damaged zone (EDZ) above the gate roadways (main and tail gates), considering the advance longwall mining method. In this model, the stability of gate roadways are investigated based on loading effects due to EDZ and caving zone (CZ) above the longwall face, which can extend the EDZ size. The structure of GCM depends on four important factors: (1) geomechanical properties of hanging wall, (2) dip and thickness of coal seam, (3) CZ characteristics, and (4) pillar width. The investigations demonstrated that the extension of EDZ is a function of pillar width. Considering the effect of pillar width, new mathematical relationships were presented to calculate the face influence coefficient and characteristics of extended EDZ. Furthermore, taking GCM into account, a computational algorithm for stability analysis of gate roadways was suggested. Validation was carried out through instrumentation and monitoring results of a longwall face at Parvade-2 coal mine in Tabas, Iran, demonstrating good agreement between the new model and measured results. Finally, a sensitivity analysis was carried out on the effect of pillar width, bearing capacity of support system and coal seam dip.  相似文献   

Groundwater travel time computation for two-layer islands     

Hamed?KetabchiEmail author  Davood?Mahmoodzadeh  Behzad?Ataie-Ashtiani 《Hydrogeology Journal》2016,24(4):1045-1055

A closed-form analytical computation of groundwater travel time (GWTT) for two-layer oceanic small island aquifers is developed assuming steady-state and sharp-interface conditions. The two-layer geology impacts on the GWTT are investigated using the developed analytical solution to achieve a greater transparency of such conceptualizations. The results demonstrate that the inclusion of geologic layering leads to large changes in the GWTT. Sensitivity analyses, using specified dimensionless parameters, are employed to assess the influences of hydraulic conductivity, recharge rate, upper layer thickness, and seawater/freshwater density difference parameters, which influence the GWTT. These evaluations reveal that the GWTT is mainly influenced by the recharge rate and the upper layer thickness compared to the other influential parameters when the typical parameter ranges are considered.  相似文献