SCIENTIA IRANICA
Year:2003 | Volume:10 | Issue:2|Papers Count:15

In this paper, an attempt to identify and characterize minor road traffic behaviorat unsignalized urban intersections in a city situated in a developingcountry is described. Information about the particular traffic behavior was collected using video cameras placed at 12 unsignalized intersections connecting minor to major roadways in Tehran. Stop signs and/or blinking red signals provided the stopping message at the minor approaches of the selected intersections. Relevant information about the behavior of more than 2400 vehicles was extracted from the video displays and the database records consisted of 31 variables reflecting driver, pedestrian, passenger, vehicle and intersection characteristics. Four key driver behavior characteristics, including observation of the stop message,departure distance and time from the stopping position and stopping distance from the pavement markings stopping line, were studied and evaluated. Univariateand multivariate statistical analyses of the database were carried out. Inappropriate and proper drivingbehavior, as related to 4 keycharacteristics, wereidentified and modeled. The applied mode Jingtechniques consisted of regression analysis, artificial neural network modeling and discriminant analysis. Although the study findings are based on a rather limited database and are location specific, the same methodology can be applied to any unsignalizedinter section.

A Boundary Element Method (BEM) for the calculation of hydrodynamic characteristics and Flow analysis, including cavitation, is presented. The effectivenessof the method is demonstrated with results for a partially cavitating, three-dimensional hydrofoiland a marine propeller. The method employs source and dipole singularities, which give an integral equation on body and cavity surfaces, to obtain the cavity shape and hydrodynamic characteristics of the cavitating hydrofoils.A nonlinearformula of the dynamic boundary condition was applied for determining the potential on the cavity surface. The effect of the cross-flow was considered when calculating the velocityon the cavity surface. The lift and drag coefficients, pressure distribution and cavity shape of the hydrofoil were calculated and compared with experimental results for a cavitating hydrofoil. The calculated results show good agreement with the experimental values. Flow velocity fields around the cavitating hydrofoils were also investigated by the present method. The method was extended to a marine propeller(with cavitation) and, again. good comparisons Were found. However, further improvement can. be made if the definitionof the cavity separation and cavity trailing edge is improved in order to achieveexact cavity area.

The backbone of any successful Integrated Traffic Management System (ITMS) for a metropolis is the availability of reliable, accurate and real-time data. Travel time, speed and delay are three of the most important factors used in ITMS for onitoring, quantifying and controlling congestion. A global positioning system has recently become available for civil applications and, as it provides real-time spatial and time measurements, it has an increasing use in conducting different transportation studies. This paper presents the application of GPS in collecting travel time, speed and delay information on 64 major roads all over the State of Delaware. A comparative statistical analysis was performed between data collected by the GPS method and data collected simultaneously by the conventional method. The GPS data proved to be at least as accurate as the data collected by the conventional method and was 50% more efficient in terms of manpower. Moreover, the sample-size requirement was determined to maintain a 95%confidence level throughout the controlled test. Benefiting from the Geographic Information System's Dynamic Segmentation tool, our travel time, delay and speed information was integrated with other relevant traffic data and presented graphically on the internet for public use. Statistical trend analysis for the data collected in 1997, 1998 and 1999 are also presented and applications in the overall ITMS are discussed.

Rainfall characteristics, which include spatial variability, exert a major influence on runoff properties. Many techniques have been proposed for determining the spatial distribution of daily rainfall. One of these techniques is spatial modeling, based on rainfall data measured by rain-gauge networks. In this study, application of different interpolation methods in the GIS environment, for estimating the spatial distribution of daily rainfall in the southwest of Iran with low rain-gauge density, have been compared on a regional scale. The cross validation technique was selected as an accuracy index and statistical parameters, such as MAE (Mean Absolute Error) and MBE (Mean Bias Error), were used for comparing the results of cross validation. The ranking of MAE and MBE values was used for determining the best interpolation method. The interpolation methods that were studied for mappingthe spatial distribution of daily rainfall include nearest point, moving average, moving surface, trend surface and kriging. Since the spatial pattern of daily rainfall is random, the moving average method, with inverse distance weight function, was determined as the best method for interpolating daily rainfall data in the region of study.

Wing rock motion can be described as an oscillatory bank angle buildup to a constant amplitude rocking motion. This phenomenon is realized for delta wings with more than 74 degrees leading edge sweep angles. where asymmetric vortex shedding occurs before vortex breakdown. For wings with sweep angles less than 74 degrees. rocking motion occurs if the wing is in a yawed situation. In this paper, a new and simple method has been presented to predict the amplitude and frequency of oscillation of delta wings undergoing rocking motion at high angles of attack. The predicted data are in excellent agreement with those obtained by experimental studies for wings with sweep angles of 76 and 80 degrees.

Natural convection flow on a vertical cylinder is considered here when the Prandtl number is large. Little work has been done in this field apart from some experimental studies which are for lower Prandtl numbers. Here. the singular perturbation technique is used to solve this problem. The method adopted is to split the flow into a thin layer close to the surface of the cylinder, surrounded by a much thicker layer where the velocity is reduced to zero. It is shown that at high Prandtl numbers, the velocity boundary layer tends to be somewhat larger due to large kinematic viscosity relative to thermal diffusivity. The motion of the outer layer, however, seems to be caused by the drag force exerted by the inner layer, not due to the buoyancy itself.The basic properties of the flow are evaluated. The heat transfer coefficient is shown to give good prediction for all ranges of Prandtl numbers.

Motion and torque control of flexible joint robots is difficult, due to the inherent characteristics of such systems. The joint flexibility may generate resonant frequencies within the range of control bandwidth that may destabilize the system. The joint flexibility should be considered in motion control of high performance robots. This paper presents a new H¥- based torque control design method for flexible joint robots. First, a nominal torque transfer function of the joint is identified from input-output experimental tests. Second, by varying the input signal amplitude, a set of models describing the effect of nonlinearities in the system is extracted. The difference between this set and the nominal transfer function defines the uncertainty bounds for control design purposes. Third, an H - based torque control law is designed to minimize the ¥-norm of the torque transfer function. Finally, the effectiveness of the proposed torque control design method is experimentally verified on the IRIS-facility (a versatile, modular and reconfigurable prototype robot developed at the robotics and Automation Laboratory of the University of Toronto).

In this paper, a theory regarding the zeroextension line method for axial symmetry has been developed. The method assumes that the soil will yield progressively in accordance with the Mohr-Coulomb failure criterion. A simple approach has been employed for the derivation of equations, which is completely different from the method of characteristics. Equations satisfying equilibrium and yield have been directly written along the zero extension lines to allow the calculation of stresses and displacements at the same points in the soil mass. The governing equations have been shown to be more general in the axi-symmetriccase so that those for plane strain cases can be deduced from them. The mobilized strength in soil is related to shear strain. The finite difference form of the equations has also been put forward and the steps towards calculation of the fields have been presented. The most important application of the theory is the prediction of the load-deflection curves for structures in contact with soil. This has been shown using examples of circular footings on clay and sand. It has been concluded that the :zero extension line theory provides a relatively simple analytical method for the prediction of the load-deflection curves in both axi-symmetric and plane strain problems in soil mechanics.

In this paper, the measurements and evolution of a 3-D numerical solution procedure are Described for prediction and valuation the production of carbon black in the course of turbulent incomplete combustion and thermal decomposition of natural gas in a gas carbon black furnace.A particle collection system is used to measure the carbon black concentrations in the furnace. In the numerical technique. a combination of a two-step soot model and a chemical reaction Formulation relates the production of the carbon black to the incomplete combustion and pyrolysis of natural gas as the parent fuel. The chemical reaction model, which involvessolid carbon and other precursorspecies for formation of carbon black, based on an assumed Probability Density Function (PDF) is parameterized by the mean and variance of the mixture fraction and,  b-PDF shape. The effect of feedstock flow rate, equivalence ratio and radiation on carbon black furnace parameters are investigated. The comparison between numerical predictions and experimental measurements show good agreement. The results show that for relatively low feedstock flow rates, most feedstock hydrocarbon burns to CO while, for higher feedstock flow rates, the decomposition of feedstock and formation of solid carbon is the dominant process and has an important role in the production of carbon black. The results also show that radiation has a major influenceon the precombustor where most soot combustion takes place, causing a reduction of about 10% in the precombustor temperature.

In this paper, a simple and efficient method is developed for evaluating the eigenvalues of matrices having special patterns. This is achieved by decomposing the matrices into specific forms. The application is extended to calculate the eigenvalues of the Laplacian of graphs having special connectivity properties.

In this paper, a new model to obtain the Energy Release Rate (ERR) for pull-out test specimens, based on a variational approach, is introduced. To include radial dependency, due to axial deformations of a matrix, in an efficient and accurate way,.a continuous displacement function is introduced which satisfies the required geometrical as well as kinetical boundary conditions. The displacement function includes the shear deformation. While obtaining the parameters of displacement function from the principle of total potential energy, two distinct solutions are recognized which have different physical interpretations. One solution demonstrates shear deformation and radial dependency, whereas the other solution represents a constant normal strain. Employing the proposed modeling, the effects of various geometrical and material parameters on ERR were studied. Numerical results are presented to show the accuracy and efficiencyof this model in comparison with other such modelings.

This article describes the results of experimental observations in pulsating Simple Shear Flows (SSF). A uniform-mean-gradient shear flow was generated within the test section of an open circuit wind tunnel. Transverse arrays of honeycomb channels with differing resistances were used to generate shear flow at low shear rates (less than 20 S-1). A set of rotating vanes pulsated the flow field at 8.5 Hz and 18 Hz. Instantaneous velocitywas measured by employing a two-component hot wire anemometry technique. The experimental credibility of the facility was established in stationary SSF. In pulsating flows the pulsation effects on mean shear rate, the kinetic energy of turbulence, Reynolds stresses and the probability density of stream-wise velocity fluctuations were studied. It was found that deviation from stationary turbulence with pulsation at 8.5 Hz was more significant than that at 18 Hz. The modified form of the governing equations for pulsating flows was derived. The emphasis of the analysis was placed on the production and dissipation mechanisms in pulsating SSF. The results are discussed in connection with the modified equations and physically plausible explanations are offered to interpret the laboratory observations. It is concluded that the anisotropic dissipation mechanism may be responsible for the observed experimental results.

In this paper, pulsating grid-generated turbulence is studied. A two-component hot wire anemometry technique is used. The pulsation effects on characterizing length scales and the statistical description of fluctuations are studied in comparison with their stationary counterparts. No significant change in the character of the turbulent flow with pulsation is observed.

In this paper, the results of a study comparing the performance of two types of interchange, i.e.,  Conventional Diamond Interchange and Single Point Urban Diamond Interchange, are reported. The analysis is based on simulation of a Single Point Urban Diamond Interchange. The real data that is collected from two different existing Conventional Diamond Interchanges during peak hours is used as input for analysis. Highway capacity software is used to analyze the performance of the Conventional Diamond Interchanges while a simulation model is used for analyzing the performance of the Single Point Urban Diamond Interchanges. The results indicate that the performance of the Single Point Urban Diamond Interchange is superior to that of the Conventional Diamond Interchange.

The implementation of new techniques and design of new elements have been an important issues among finite element researchers. In this regard, a designed super element has been applied to analyze a series of dynamic problems. Findings indicate that in large structure analysis the same results as the conventional method can be obtained when applying a few super elements. The time required for dynamic analysis using a super element is significantly smaller than the regular finite element. In this paper, the forced vibration of laminated composite rectangular plates is analyzed. The dynamic response of the plate, using a four-super element, is obtained. In-plane deformation, as well as bending deformation, is included in the model. The current computational model is a simple and efficient way to predict the dynamic behavior of the laminated composite plate.