IRANIAN JOURNAL OF SCIENCE AND TECHNOLOGY TRANSACTION B- ENGINEERING
Year:2004 | Volume:28 | Issue:B5|Papers Count:12

In order to reach an optimum analysis and design for airport aprons variables such as the area and dimensions of the apron considering the passenger and cargo, the number and dimensions of the gates depending on the different type of aircraft, parking configuration and the arrangement of aircraft in different time periods at the airport has been looked into carefully. In this research a mathematical model for the optimum analysis and design of airport aprons based on minimum transportation cost has been developed. The main parameters considered for transportation cost are user capital and operational costs. Based on these parameters, a mathematical model as well as computerized simulation software have been developed taking into consideration the actual variables of design and analysis of airport aprons. The results obtained from the computerized simulation software indicate that the policies of the airport authorities and air carriers within the context of flight scheduling, gate use strategy, planning and analyzing the operational condition of the aircraft fleet have a significant impact on the planning and design of airport aprons.

An efficient algorithm is presented for the formation of suboptimal cycle bases of graphs corresponding to sparse cycle adjacency matrices, leading to the formation of highly sparse flexibility matrices. The algorithm presented employs concepts from the algebraic graph theory, together with a Greedy type algorithm to select cycles with small overlaps and uses a simple graphtheoretical method for controlling the independence of the selected cycles. Application of the present algorithm is extended to the formation of cycle bases corresponding to well conditioned flexibility matrices.

Although different methods for estimating the discharge capacity of compound channels have been developed, no entirely satisfactory method exists. However, a large body of experimental data has now been acquired covering small scale and large scale laboratory compound channels. In this paper, discharge characteristics in straight compound channels having homogeneous roughness are studied, and a method for discharge calculation in these channels is presented by analysing some experimental results from a United Kingdom flood channel facility (UK-FCF). The approach presented uses two correction coefficients, a and b, which are applied to the component mean velocities predicted by the traditional vertical division method in order to find more accurate values of the mean velocities in the main channel and floodplains. It has been found that a and b can be expressed in terms of two dimensionless parameters of the channel, coherence and the relative depth (ratio of the floodplain depth to the total depth). Although the procedure developed in this study is based on data from UK-FCF, it is simple and shows satisfactory results when compared to the recently developed method by Lambert and Myers, termed the weighted divided channel method, and when applied to the independent data set collected by others.

Uniqueness of the relationship between the return periods of the annual maximum series (AMS) and the partial duration series (PDS) are evaluated in light of the actual data. Rainfall intensities with durations of 15, 30, 60, and 360 minutes are calculated for seven stations representing a variety of climatic conditions (humid, cold, desert, and hot desert), and the corresponding AMS and PDS values are considered. PDS values are evaluated in view of annual exceedance series (AES), up to the minimum one observation (MOO). The two-parameter gamma distribution is found to be the most suitable to provide various return periods for the calculated rainfall intensities. A comparison of the results suggests that a unique relationship does not exist between return periods of AMS and PDS. Indeed, length ratio (ratio of record length of PDS series to that of AMS) should be considered as an additional independent variable. Therefore, any further attempts to extend the uniqueness of the relationship between AMS and PDS for the computation of hydrological variables such as rainfall depth are shown to be inappropriate. Finally, it is concluded that any relationship between AMS and PDS return periods is actually a function of rainfall duration as well as station location.

Downward and upward (hydraulic trap) advective-diffusive transport of chloride was modeled in two and three layer soil laboratory systems with Darcy velocities ranging from 3×10-9 m/s to 5.7×10-8 m/s. Two layer soil models simulated a compacted clayey layer over a sandy layer, underlying a landfill. Three layer soil models simulated an unsaturated secondary leachate collection system in a landfill with overlying and underlying saturated compacted silty liners. The effect of the hydarulic trap in minimizing diffusive downward chloride movement was investigated in both models. The agreement between the experimental results and theoretical predictions suggests that existing solute transport theory can adequately predict chloride migration through two saturated layers of clay over sand and also three layer soil systems consisting of two saturated silt layers with an unsaturated sand drainage layer in between. The comparison of the downward and upward advective-diffusive transport in two and three layer soil models, having two different Darcy velocities and soil density, showed that the upward flow (hydraulic trap) could reduce the concentrations in the underlying receptor reservoirs in both models. The rate of the Darcy velocity (or soil density) played a controlling role in chloride movement in both systems.

A complete second-order closure model of turbulence has been used to predict the behaviour of fully developed turbulent flow in a square river harbour. For the two dimensional, this closure model entails the solution of five differential equations for the turbulence parameters, excluding the three general equations of motion. The turbulent flow was driven by a stationary current in an adjacent model river. Emphasis has been focused on comparing the simple and more sophisticated turbulence models, including the Reynolds and algebraic stress models to predict accurately the velocity patterns within such basins. The governing equations have been discretized using the finite difference method. The advective acceleration terms in the hydrodynamics equations were treated using the third order upwind scheme, whereas the counterpart terms in the k-ه equations were treated using the exquisite scheme. Experimental data from the model river harbour were used to check the numerical model results, which found that both of the closure models of turbulence generally produced accurate results for the tests considered within the harbour.

In solutions of boundary value problems in soil engineering, it is usually assumed that the stress and velocity fields are coaxial. Some researchers have argued the validity of this assumption. This paper investigates the influence of this simplifying assumption on the solution in these problems. The zero extension line method has been used for this investigation. The theory of the method has first been extended to the more general case of non-coaxial fields of velocity and stress in soils. A computer code has been written which can solve the given boundary value problem assuming coaxiality or non-coaxiality. The rotation of rough and smooth strip footings into loose and dense sands has been provided as an example of a typical boundary value problem. The analyses have been performed once with and the other without assuming coaxiality. A comparison of the results indicates that higher loads are required for the same deflection when coaxiality is assumed. It is therefore recommended to consider the non-coaxiality in the analysis if the soil really behaves so; otherwise the obtained result would not be correct.

Cloud models can play a key role in interpreting observational evidence to estimate the potential for successful cloud seeding experiments. Among different types of cloud models, onedimensional cloud models with bulk water microphysical parameterization are very useful. Therefore in this paper, a one-dimensional Ogura and Takahashi (O-T) cloud model with bulk parameterization has been discussed for studying the possibility of improvement in microphysical processes in applying for cloud seeding experiments. The most important features of the new model could be defined as the inclusion of Kessler Parameterization (PMZ) in a warm rain process, Bigg’s freezing PMZ, and terminal velocities of rain water and hail particles. The model has been run for various cases, Kessler PMZ, Kessler PMZ and Bigg’s freezing, and Kessler PMZ, Bigg’s freezing, and Lin PMZ. Strong modifications were noticed in the rainfall profile, with Kessler PMZ rain started later due to the necessity of cloud droplets to initiate formation. Rainfall became heavier due to the accretion of cloud droplets and raindrops. With Bigg’s freezing, due to the enhancement of the freezing process rate, the second peak of rainfall intensity vanished. With Lin terminal velocities of rain and hail, due to the accumulation of rain water near the surface, the updraft became weaker, while downdraft became stronger. Due to the above mentioned improvements, the rainfall pattern of the improved model became heavier and sharper in a shorter time and is in good agreement with the behavior of occurrence of natural showers.

In this study, a free vibration analysis of flexibly connected, elastically supported, stiffened coupled shear walls is carried out by a simplifying method widely used in the past for the static analysis of similar structures [1]. This method, called the continuous connection technique (CCT), comprises an efficient tool for the predesign computations related to the treatment of highrise buildings. While the discrete structure is formulated as a continuous medium, the continuously distributed mass of the structure is discretized to a system of lumped masses for finding the corresponding flexibility matrix. After obtaining the standard frequency equation of the discrete system, the circular frequencies are determined in a straightforward manner and used to find the modes of vibration. Some comparisons are made between the results of the present method and those of a previous one, resulting in a perfect match of the two.

The post-buckling behavior of rectangular frames in an elastic domain is studied in depth. In analysis, unsymmetrical geometry, sway possibility and support conditions are considered in order to find their influences on load-deflection paths and non-linear deformations. The static perturbation technique is used for analysis and discussion. The first, a second order perturbation problem as an accurate measurement for the frame, is solved and the solutions compared with previously published papers. The results reveal that symmetric frames with a sway movement, due to lack of an axial force in the beam in the first order perturbation analysis, have a symmetric bifurcation point. However, the post-buckling behavior of un-symmetric frames with or without sway is bifurcated in an asymmetric manner.

In most parts of the city of Isfahan, at depths of 5 to 20 meters from the ground surface, schist is the predominant rock. This schist is a layered rock with variable thickness of 3 cm or more. Triaxial tests were conducted on the specimens with various anisotropic angles under confining pressures of 0, 7 and 15 MPa, and axial stress-axial strain were measured and plotted for various conditions. The results obtained reveal the effects of schistosity on the strength and deformability of the rock very clearly. The modulus of deformation of this rock varies with the anisotropic angle. For zero orientation, the modulus of deformation increases to a maximum. The results show that the friction angle and cohesion are affected by the anisotropic orientation, which is more important for the cohesion than the friction angles. It is not possible to apply failure criteria such as Mohr–Coulomb and Hoek–Brown for this rock without consideration of anisotropy orientation.

Most of the water loss in distribution and conveyance earth canals occurs through seepage. This loss should be considered in irrigation network design through conveyance efficiency (ec). It is a common practice for the value of ec to be measured in existing irrigation systems under different soil types, vegetation covers and canal sizes. However, it is a costly and time consuming practice, therefore, empirical models to indicate the relationship between ec and soil texture, canal capacity and vegetation cover in earth canals may be effective in the estimation of ec at different conditions. This research was conducted to measure the conveyance efficiency in earth canals that are well above groundwater level with different soil textures and water weed densities in the northern and north-western areas of Isfahan province, I.R. of Iran. Conveyance efficiency of a km reach in distributary earth canals with a sandy loam soil was 67.3%, and for a clay loam soil in tributary earth canals 95.8%. The vegetation cover in the earth canal did not affect the ec value significantly. Therefore, it is concluded that traditional earth canals with medium to heavy soils in the study area have high ec and the lining may not be economically justified. Furthermore, for earth canals well above the groundwater level a multiple regression model was presented to estimate the ec value based on flow rates smaller than 404 l s-1 in distributary and tributary canals and sand content in soil.