فهرست مطالب

  • Volume:3 Issue: 1, 2011
  • تاریخ انتشار: 1391/07/18
  • تعداد عناوین: 7
  • Moslem Akbari, Karim Solaimani, Mohammad Mahdavi, Mahmod Habibnejhad Page 1
    Ecosystem of arid and semiarid regions of the world, much of the country lies in the sensitive and fragile environment Canvases are that factors in the extinction and destruction are easily destroyed in this paper, artificial neural networks (ANNs) are introduced to obtain improved regional low-flow estimates at ungauged sites. A multilayer perceptron (MLP) network is used to identify the functional relationship between low-flow quantiles and the physiographic variables. Each ANN is trained using the Levenberg-Marquardt algorithm. To improve the generalization ability of a single ANN, several ANNs trained for the same task are used as an ensemble. The bootstrap aggregation (or bagging) approach is used to generate individual networks in the ensemble. The stacked generalization (or stacking) technique is adopted to combine the member networks of an ANN ensemble. The proposed approaches are applied to selected catchments in the Lorestan province, Iran, to obtain estimates for several representative low-flow quantiles of summer and winter time. The jackknife validation procedure is used to evaluate the performance of the proposed models. The ANN-based approaches are compared with the traditional parametric regression models. The results indicate that both the single and ensemble ANN models provide superior estimates than these of the traditional regression models. The ANN ensemble approaches provide better generalization ability than the single ANN models.
  • The Effect of Pollutants Dissolved Oxygen and Temperature Change (Case Study:Ghezel-Ozen River)
    Siamak Boudaghpour Page 3
    Rivers can absorb certain amounts of contamination relying on different factors such as: river discharge, the primary conditions of the river, the river depth, discharge and the river viscosity of the offloaded wastes in the river. From parameters of water quality point of view, it is recom-mended to determine some parts of the river which are lower than the standard level in order to find out the critical parts and suitable alternatives for simplifying the critical points. According to the above- mentioned topics, it is essential to identify the parts of the river which do not have standard conditions and also to determine the sources of pollutions that highly influence such conditions and to explore appropriate solutions. This essay provides the effect of polluting sources on the changes of dissolved oxygen and temperature in Ghezel-Ozen River based on the gathered qnalitative and qnalititative data. Since the required information is extensive for being modeled by QUAL2E software and the main effect of temperature parameters on line creatures and the influence of the dissolved oxygen on water quality originating from variety of pollutions. The results of simulating Ghezel-Ozen River imply the suitable oxygen condition and tempera-ture along the modeled river and Shahrud River is its auxiliary branch. Furthermore the fluctua-tions of water temperature in the discharge crossing the river and its effects on the temperature variations and finally dissolved oxygen and discusses the managing and controlling methods of river contamination.
  • Hooman Hajikandi Page 19
    Sudden pipe expansions have been known as efficient hydraulic energy dissipaters for a long time. The complex phenomenon of flow separation and velocity discontinuity at the interface of incoming jet and the recirculation flow, results in intensive shear and tensile rupture of the fluid and the associated destructive phenomenon of cavitation. This paper focuses on aeration in sudden pipe expansion as a remedy to recover the effects of cavitation. The experimental setup consists of a sudden pipe expansion with an expansion to inflow diameter ratio of 3.675. Variation of air content ratio with respect to the Reynolds number and effect of air entrainment on time averaged velocity and pressure distribution is investigated. Finally a combination of sudden pipe expansion and aeration is recommended for energy dissipation at bottom outlets and tunnel spillways.
  • Hossein Ghasemi, Abbas Ali Gholami, Gholamreza Hadarbadi, Hossein Ebrahimi Page 37
    Of the many climatic events that influence the Earth’s environment, drought is perhaps the one that is most linked with desertification. Drought is the consequence of a natural reduction in the amount of precipitation received over an extended period, usually a season or more in length. Drought monitoring is an essential component of drought risk management. It is normally performed using various drought indices that are effectively continuous functions of rainfall and other climatic variables. A number of drought indices have been introduced and applied in different countries to date. This paper compares the performance of two indices for drought monitoring in Hossein Abad Plain which includes several catchments and villages. The indices used include deciles and standard precipitation indexes. The comparison of indices is based on drought cases and classes that were detected in the12 synoptic stations over the 11 years of data, as well as over the latest 1998–2001 drought spell. Then by using ArcGIS 9.2 software were planned drought and wetness maps. The method of interpolate was Kriging (one of suitable Geo statistical methods).The results show that SPI respond slowly to drought onset. DI appears to be very responsive to rainfall events of a particular year, but it has inconsistent spatial and temporal variation. The SPI was found to be able to detect the onset of drought, its spatial and temporal variation consistently, and it may be recommended for operational drought monitoring in the country and SPI was found to be more responsive to the emerging drought and performed better.
  • Jalal Bazargan, Hamed Zamanisabzi, Hassan Hashemi, Alireza Moazami Page 45
    According to the former researcher’s presented relations for flow through rock-fill porous media, the effects of physical characteristics was not studied separately. Hence, due to the application of these relations, physical characteristics of porous materials effect must be investigated separately. In various constructed physical models of porous media, the effect of several variables such as unified coefficient of materials, kind of materials, material gradation and material figures on the parameters such as void ratio, raggedness and specified surface area of materials have been studied. These parameters have a significant effect on the flow discharge coefficient through rock-fill porous materials. In the defined research during this paper, using artificial unique spherical materials with diameters of 10, 37 and 75 mm with the same configuration, the effect of parameters including specified area of rock-fill materials, figure of rock-fill materials and the size of rock-fill materials on the hydraulic characteristics of discharge flow through rock-fill porous media in rock-fill dam models with inbuilt spillway and spillways on the upstream face, have been studied. Also, using the data of these experiments in combination with the data of experiments of the former researches on the natural rock-fill materials, dimensionless relations of Bazargan have been investigated. Finally, using statistical multi variable analysis, a dimensionless relation with maximum correlation coefficient and acceptable accuracy based on the physical characteristics has been presented.
  • Mojtaba Saneie, Bahare Sadat Mosavi Page 59
    River banks are exposed to bank erosion and destruction. One of the river engineering goals is to provide human life requirements and reduce river danger. So spreading extent of this phenomenon, whose risk and other important factors must be recognized. Using groins is one of the control ways that by accurate design and accurate performance, bank erosion control and field reclamation would be possible. In addition, groin placement has important effect on bank erosion control. The purposes of this research were to survey groin placement on river protection and reduce bank erosion by experimental model. Tests were done by 3 different intervals and 5 discharges. Results showed that in 30 cm with erodible stuff, groin reduced bank erosion, destruction in river bank protection was almost 24-55% and with 15-25 l/s of discharge, bank erosion reduction was about 16.6%. By adding groin at river bank the water surface changes, with increasing discharge water surface first decreases and then increases by adding discharge.
  • Taymaz Esmaeili, Amir Ahmad Dehghani, Mohammad Reza Pirestani, Tetsuya Sumi Page 69
    Local scouring around bridge piers is a natural phenomenon caused by the erosive process of flowing stream on alluvial beds. The 3D flow field around bridge piers interacting with the bed materials increases complexity of local scour process. The local scour depth develops in accelerated flows and if it is not predicted correctly, the bottom level of local scour hole will exceed the original level of pier foundation. In this case the failure of bridge will occur. Using different methods of local scour countermeasure for reducing the magnitude of local scouring depth and retrofitting costs would be economically efficient. As a local scour countermeasure method, applying slots in the piers could reduce the local scour depth around circular piers. Since in natural streams the piers are skewed to flow in most cases, it is more feasible to evaluate the skew slots effects on scour reduction. The present study focuses on numerical simulation of maximum depth of scour due to the installing of slots in various angles of flow attacks by employing a 3D numerical model (SSIIM program). The results show the ability of SSIIM for modeling the local scouring around bridge piers with slots.