IRANIAN JOURNAL OF SCIENCE AND TECHNOLOGY TRANSACTION B- ENGINEERING
Year:2004 | Volume:28 | Issue:B1|Papers Count:15

In hydraulically well-connected groundwater and surface water systems, stream-aquifer interaction has been simulated using a MODFLOW model developed by USGS, which couples hydraulic behavior of groundwater and surface water subsystems. It assumes a constant stream-stage during each stress period, employing a stream flow routing module which is limited to steady flow in rectangular, prismatic channels. One of the challenges in understanding the interaction of surface water and groundwater systems lies in their different time scales. In this paper, the INTRACT model is developed and incorporated into MODFLOW. INTRACT simulates unsteady, nonuniform flow by solving St. Venant equations. Terms that describe leakage between stream and aquifer as a function of streambed conductance and differences in water table and stream stage were incorporated into the continuity equation. INTRACT calculates new stream stages for each time step in a transient simulation based on upstream boundary conditions, stream properties, and estimated head distribution. Next, MODFLOW calculates head distribution using aquifer properties, stresses, and stream stages calculated by INTRACT. This process is repeated until convergence criteria are met for aquifer head distribution and stream stages. Because the time steps used in groundwater modeling can be much longer than time intervals used in surface water simulation, a provision has been made for handling multiple INTRACT time intervals within one MODFLOW time step. Performance of the coupled model was validated using an analytical solution from the previous studies.

In this study, the nonsymmetrical two dimensional elasticity problem of an elastic layer which is supported by two elastic quarter planes has been carried out. It is assumed that the contact between the layer and the supports is frictionless and only compressive tractions can be transmitted along the contact area. The problem is handled by using integral transform and singular integral equations techniques, and a computer program has been developed for solving the problem. Some numerical examples have been solved and the pertinent results were compared with those found by two other methods. The three methods, namely, the integral transform technique jointly used with a numerical solution technique for singular integral equations, the finite element method, and the boundary element method, being dependent on completely different mathematical concepts, show a very close match among their results and is a perfect sign of their reliability.

A control algorithm based on the instantaneous optimal control method is presented for on-line control of structures subjected to earthquake excitations. This algorithm employs the digital state-space equation to discretize the continuous dynamical equation of motion, and named discrete instantaneous optimal control method. Based on the Lyapunov stability method, a procedure to obtain a discrete stable weighting matrix is developed. To demonstrate the precision and the efficiency of the proposed control algorithm an 8-story shear-type building frame equipped with one active mass damper/driver (AMD) mechanism is used. Behavior of different weighting matrices is also examined.

An analysis of buckling for thick anisotropic plates subjected to arbitrary loading is presented. The analysis employs the complex finite strip method which utilizes complex harmonic functions in the longitudinal direction, a cubic polynomial in the transverse direction and a parabolic distribution of the transverse shear strains through the thickness of the thick plate based on the higher-order shear deformation theory. The method is programmed to investigate local buckling of square and long thick plates subjected to compression bending and shear stresses. Examples of the accuracy of the method with an increasing number of strips are presented. The method is then applied to study the local instability of thick orthotropic plates under compression and shear with different boundary conditions. Local instability interaction between compression and shear, and bending and shear in thick orthotropic plates is investigated

Smart systems in general, and specifically neural networks, are expected to be of great assistance in large scale matrix computation. However it was necessary to work with smaller problems at first step. To this end, a method based on using perceptrons and Kohonen networks for determining the first three modal frequencies of frames of up to 20 stories high and two bays wide from their stiffness and mass matrices, was developed. This paper introduces this modular network as a preferable alternative for designing smart systems for learning large scale mapping problems in structural engineering, and in addition, reports the successful application of this modular network to the eigenvalue and modal frequency determination of shear frame structures.

In this study, the static analysis of a multi-bay coupled shear wall on an elastic foundation, having any number of stiffening beams is studied using the continuous connection method (CCM). The shear wall is considered to be made up of a finite number of sections in the vertical direction, with or without stiffening beams between each pair of consecutive sections. This method of analysis, which accounts for thickness variation and elastic beam-wall connections, treats the discrete connecting beams as a continuous layered medium. To implement the foregoing analysis a computer program has been developed in the MATHEMATICA computer algebra system. To support the validity of the present method comparisons have been carried out with the results of SAP2000 structural analysis program and those in some references.

A one point quadrature pentahedral solid element with hourglass stabilization is developed for large deformation analysis of elastoplastic solids. This type of element is particularly suited for analysis of shell-like structures where multiple fracturing without any predefined direction takes place in the shell surface. Thus, the element design is motivated by requirements of the analysis of delamination and fracture in multilayered composite shells. The element formulation and the hourglass control procedure are based on the standard assumed strain method for stabilization of solid elements previously developed by other researchers. Several numerical tests, from simple beam bending to fracture analysis of laminated plates have been carried out to assess the performance of the element.

Cone penetration test (CPT) allows for the soil type to be determined from the measured values of cone resistance (qt) and sleeve friction (fs). Since the cone penetrometer progressed from the mechanical cone to the electrical piezocone (CPTu), the reliability of the determination of soil type also improved by pore pressure (u) measurement. This paper references several published methods of soil profiling. All but two of these apply cone resistance plotted against the friction ratio (Rf). A new method for soil profiling has been developed by plotting effective cone resistance (qE) versus sleeve friction with a compiled database from 20 sites in 5 countries. This paper presents two soil profiling methods based on the piezocone and compares them with three specific cases containing sand, normally consolidated clay and overconsolidated clay. Both methods result in an accurate soil type determination.

The difference between effective reflectance from sub sea objects and water suspended materials is a function of attenuation coefficient (k) of light intensity in bodies of water. The amount of C-Cmin (here C is digital number) identifies the effective reflectance and it is possible to differentiate the effective reflectance from sub sea objects and water suspended loads using a specific display image of band ratios. In a ratio display image of Landsat TM band pairs, this difference is a function of (1- e ki)/(1 – ekj). This value for Khark and Kharkoo sub sea objects (Coral reefs and sandy beds) in the Landsat TM image of 1998 is always positive and less than one. Thus a RGB false color of the atmospherically corrected ratio image of effective reflectance (C-Cmin) display image as (C – Cmin)b2/(C – Cmin)b1 ; (C – Cmin)b3/(C – Cmin)b2 ; (C – Cmin)b4/(C – Cmin)b3 : (RGB) shows the best separation of the sub sea objects. The proposed model has been used for detecting coral reefs and sandy beds around two Iranian islands in the Persian Gulf, Khark and Kharkoo. The results have been checked by field studies and draft maps, which show a good correlation with a high overall accuracy of about 90%.

Rock masses supporting a tunnel often have natural cracks and joints which must be detected and analyzed at excavation to assess tunnel stability. Mathematically, these are discontinuities that must be embedded in the finite element model of the excavation to improve reliability. Because direct consideration of cracks as mathematical discontinuities in excavation models presents considerable computational and analytical challenge, a simple discrete element model (DEM) has been used to analyze the stability of tunnels in jointed rocks. This model, which is a member of the DEM group, has the advantage of being able to model large displacements and behavior of highly fractured rock masses. The low volume of numerical computing and high speed in analysis are other advantages of the used model.A new algorithm for detecting contact points between blocks has been used to improve the model. Different examples and case studies have been solved successfully using this modified discrete element model.

The effect of the upward flow (the hydraulic trap effect) on advective-diffusive migration of chloride through silt under two different soil densities and Darcy velocity conditions was examined. Comparison on chloride concentrations in the receptor reservoirs beneath the silt samples in downward and upward flow tests showed that the hydraulic trap system could significantly reduce the concentrations in the soil and underlying receptor reservoirs and hence, the system could be used in solid waste landfill designs to minimize the contamination potential from landfill leachate. Effective chloride diffusion coefficients were measured on clay and silt samples from Urmia City landfill site in Iran, using the solid waste leachate from the same landfill. The experimental results were in good agreement with theoretical predictions in diffusive and advective-diffusive tests.

About 1% of the total storage capacity in the world’s reservoirs is lost annually due to sedimentation. Sediments can also block intakes in reservoirs and damage tunnels or turbines. One of the most effective techniques to remove these sediments is flushing, whereby water level is lowered sufficiently to re-erode deposits and flush them through the intakes. Outflow sediment discharge may well be related to the parameters such as the sediment characteristics in the reservoir, during flushing and geometry of flushing channel. In this study, laboratory experiments were performed on a 1-D reservoir model in a flume in the hydraulics laboratory of Shiraz University to investigate the flushing operation processes by using polymer particles. The polymer particles were lightweight and non-cohesive with an average grain size of about 2.40 mm and density of 1065.3 (kg/m3). The model was installed in a flume; 30 m long, 1 m wide and 0.75 m height. The length of the test section was 11.5 m, and sediments were placed at a length of 4.8 m long upstream from the dam position. Experimental runs have been performed for two flow conditions; 0.0004678 m3/s and 0.000628 m3/s. The very low inflow discharge helped for better monitoring and measuring of the effective parameters. A sluice gate was placed at the central bottom of the dam (as the bottom outlet) and was opened at a constant rate to make the complete drawdown. Results showed that the rate of sediment flushing is strongly associated with outflow rate, water surface gradient with the dam section and the width of the flushing channel. The results from this study were in agreement with that in the literature. It is considered that the low density of the particles causes them to behave as very fine and non-cohesive sediment particles, like loess sediments.

Estimates of soil erosion and sediment yield from watersheds are needed to select the best management practices for sediment yield abatement and protection of water quality. The ‘ANSWERS’ model predicts sediment yield from agricultural watersheds for individual rainfall events. Conventional values of the soil erodibility factor, K, for soils containing rock fragments may result in an overestimation of sediment concentration present in the runoff. In this study, the effect of K factor adjustment to predict a more accurate sediment yield by the ANSWERS model was investigated. The value of the K factor was adjusted for the volumetric fraction of rock fragment. This resulted in a higher level of agreement between the predicted and observed values of sediment concentration in the watershed runoff. Therefore, it is concluded that the volumetric fraction of rock fragment should be determined for watershed soils containing rock fragments and be applied for modification of published K values.

The determination of hydraulic properties of open-channels and rivers is very important in water resources management and engineering. Geostatistical estimation methods in comparison with direct measurements and/or using mathematical models can be more cost and time effective. The objective of this study is to evaluate the possibility of applying cokriging and residual kriging methods to estimate some hydraulic parameters of rivers or open-channels. The results indicate that cokriging can be used to estimate flow cross-sectional area, flow velocity and hydraulic radius, while residual kriging can be used to estimate flow cross-sectional area, flow velocity and water surface level elevation. It is concluded that water surface width is preferable to water depth as an auxiliary variable in the cokriging method. The relative error of estimation for geostatistical estimators was about 0.87 to 22%. Thus, these methods can be considered appropriate and the user’s expected accuracy is important in choosing the geostatistical estimators for estimation of hydraulic parameters in open-channels or rivers. In general, cokriging and residual kriging can be used to estimate openchannel hydraulic parameters by using 25% (29 data) of measured data instead of 115 measured cross-sections along the channel or river with minimal cost and the least amount of time.

Most parts of southern Iran have frequently experienced drought and flooding events. The occurrence of these natural disasters is common in Fars province which supplies about 25% of the national wheat product. Shiraz (capital city of the province) is studied as a representative of the province. Estimating rainfall and temperature can help in agricultural water management, protection from water shortages, and flood damage, thus having significant economic impacts. The prediction is, however, a complicated procedure and conventional mathematical methods are not able to easily capture such a relationship. To overcome the problem, neural network-based models were used for forecasting temperature and rainfall in Shiraz (Iran). Various simulation results based on the real data are presented. The results suggest that the applied methodology is suitable and more practical than the previous approaches for the prediction of rainfall and temperature. The developed model is able to predict rainfall and temperature one season ahead with reasonable error.