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Volume 14, Issue 5, 2007
Civil and Mechanical Engineering


Dynamic Responses of Railway Suspension Bridges Under Moving Trains
 
        H. Xia (PhD.)
  • Y.L. Xu [PhD.]
  • T.H.T. Chan [PhD.]
  • J.A. Zakeri [PhD.]

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This paper describes a numerical simulation technique that is used to investigate a dynamic train-long suspension bridge interaction. A three-dimensional finite element model is used to represent a long suspension bridge. Each vehicle of the train is modeled by a 27-degrees-of freedom dynamic system, including two bogies with four wheel-sets. By applying a mode superposition technique to the bridge and taking the measured wheel and track irregularities as known quantities, the degrees of freedom of the bridge-train system are significantly reduced and the coupled equations of motion are efficiently solved. The proposed formulation and the associated computer program are then applied to a real long suspension bridge. The dynamic responses of the bridge and the train vehicles are computed and compared with the limited measured data and the results are satisfactory.


Effects of Density Currents on Sedimentation in Reservoirs
 
        A. Shamsai (PhD.)
  • B.A. Mohammadnezhad [PhD.]

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The development of density or turbidity currents causes serious problems for environmental hydraulics in reservoirs. The stream entered to a reservoir can carry sediments, nutrients and chemicals as density or turbidity currents. The fate of sediment and other substances transported by the current depends on the characteristics of the turbidity current itself, i.e. the velocity of fluid, the amount of mixing with reservoir water and the rates of sediment deposition and re-suspension. These are important factors for water quality in reservoirs. A two-dimensional, depth-averaged, finite-volume numerical model is developed to study density currents, driven by non-cohesive sediments. The model has been, then, run with variant input conditions, which could be assessed for their effects on the development of bed and sediment deposits. The amount of sediment deposition and the grain size of deposits have been found to decrease uniformly with their distance from the inlet. The numerical results are compared with some experimental data of turbidity currents and a favorable general agreement is observed.


Strengthening Design Limitations of an RC Frames Using FRP Column Wrapping Considering Column-to-Beam Strength Ratio
 
        A.R. Khaloo (PhD.)
  • A. Esmaili [PhD.]

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The aim of this paper is to study the influence of the column-to beam strength ratio on the seismic strengthening of a column with a Fiber Reinforced Plastic (FRP) wrapping system. FRP wrapped Reinforced Concrete (RC) columns are analyzed to obtain moment-curvature curves using FRP confined concrete characteristics. A pushover analysis of a 2D model was performed on one and three-story moment-resisting frames, with different column-to-beam strength ratios. The results indicate that FRP strengthening is more efficient in frames with a low ratio of column-to-beam strength, due to the type of lateral failure mechanism of the frame. Also, high values of the column-to-beam strength ratio can be benefited by low values of the confining pressure. In case of a column strength greater than a beam strength, beyond a certain confining pressure ratio, further enhancement in performance will not be achieved. Therefore, the level of effective wrapping on frame performance enhancement is controlled by the column-to-beam strength ratio.


First Order Perturbation Solution for Axial Vibration of Tension Leg Platforms
 
        M.R. Tabeshpour (PhD.)
  • A.A. Golafshani [PhD.]
  • M.S. Seif [PhD.]

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The dynamic response of the leg (tether) of a Tension Leg Platform(TLP), subjected to axial load at the top of the leg, is presented. The structural model is very simple, but several complicated factors, such as foundation effect, buoyancy and simulated ocean wave load, are considered. As an application, the effect of added mass fluctuation on the dynamic response of the leg subjected to such a load is presented. This effect is important in the fatigue life study of tethers. A first order perturbation method is used, in order to formulate and solve the problem. The differential equation is solved by means of non-harmonic Fourier expansion, in terms of eigenfunctions obtained from a non-regular Sturm-Liouville system.


Further Analysis and Developments of the Eshragh-Modarres (E-M) Algorithm on Statistical Estimation
 
        M.A.S. Monfared (PhD.)
  • F. Ranaiefar [PhD.]

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In this paper, the seminal work of Eshragh and Modarres has been discussed in a statistical estimation problem called the Decision on Belief (DoB). The proposed approach has been thoroughly investigated and presented in a novel way, called the 3-phase approach. New instructive examples and detailed calculations are presented to illustrate the logic behind the algorithm in a clear way. The original work has further been developed into new directions, leading to new results.


Approximate Method for Evaluation of the J-Integral for Circumferentially Semi-Elliptical-Cracked Pipes Subjected to Combined Bending and Tension
 
        A. Barani (PhD.)
  • G.H. Rahimi [PhD.]

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In this study, an approximate evaluation method for ductile fracture analysis of a circumferentially semi-elliptical-cracked pipe, subjected to combined bending and tension, was newly developed. This method can explicitly incorporate the contribution of both tension and bending and, also, based on an analytical procedure, put no limit on the crack shape. The effect of a growing crack is neglected and only the J-integral is evaluated. These methods were then verified by full-scale pipe fracture tests. For comparison purposes, a finite element method was employed. The results obtained from the present method are in good agreement with FEM results.


An Intelligent Search Technique for Solving Train Scheduling Problems:Simulated Annealing and Constraint Satisfaction
 
        M.T. Isaai (PhD.)

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This paper presents a hybrid scheduling technique for generating the predictive schedules of passenger trains. The algorithm, which represents a combination of simulated annealing and a constraint-based heuristic, has been designed using an object-oriented methodology and is suitable for a primarily single-track railway with some double-track sections. The search process gets started from a good initial solution created by the scheduling heuristic and continues, according to the simulated annealing search control strategy. The heuristic is also used in the neighborhood exploration process. This hybrid approach solves the problem in a short span of time. Simulation experiments, with the real data of manual timetables and two corridors of Iran's railway, show the superiority of the hybrid method to the heuristic designed and the manual system, in terms of the three performance measures used.


An Energy-Based Paradigm for Reliability Assessment Caused by Creep Damage in Axisymmetric Components
 
        K. Zarrabi (PhD.)
  • L. Ng Kiam Yam [PhD.]

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The creep of materials is a research topic of major significance in the life assessment and design of many pressure components used in various industries, such as power generation plants and chemical plant refineries. Often, these components are axisymmetric, both in terms of geometry and loading. To predict the creep life of such components, one necessary ingredient is a creep damage paradigm. The current creep damage paradigms are either too cumbersome to be readily employed and/or not sufficiently accurate for practical applications. This paper describes a creep damage paradigm that alleviates the major shortcomings of the existing paradigms, yet is simple enough to be readily applicable to industrial cases. Comparison with experimental data shows that the paradigm is capable of predicting creep life with an accuracy of 14% or better.


A New Set of Conservation Equations Based on the Kinetic Theory Applied to Gas Mixture Problems
 
        M.M. Alishahi (PhD.)
  • R. Kamali [PhD.]
  • H. Emdad [PhD.]

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In this work, the hydrodynamics of multicomponent ideal gas mixtures have been studied. Starting from kinetic equations, the Eulerian approach is used to derive equations of motion for a multicomponent system, where each component may have a different velocity and kinetic temperature. The equations are based on Grad's method of moment derived from the kinetic model, in a Relaxation Time Approximation (RTA). Based on this model, a computer code has been developed for numerical computation of compressible flows of a binary gas mixture in generalized curvilinear boundary conforming coordinates. Since these equations are similar to the Navier-Stokes equations for the single fluid systems, the same numerical methods are applied to these new equations. The Roe's numerical scheme is used to discretize the convective terms of governing fluid flow equations. The prepared algorithm and the computer code are capable of computing and presenting the flow fields of each component of the system separately, as well as the average flow field of the multicomponent gas system as a whole. A comparison between the present code results and those of a more common algorithm based on the mixture theory in a supersonic converging-diverging nozzle provides the validation of the present formulation. Afterwards, a more involved nozzle cooling problem with a binary ideal gas (Helium-Xenon) is chosen to compare the present results with those of the ordinary mixture theory. The present model provides the details of the flow fields of each component separately which is not available otherwise.


Data Acquisition and Resistance Measurements Using a Simple Program
 
        H. Golnabi (PhD.)
  • P. Azimi [PhD.]
  • G.H. Poseh [PhD.]

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The goal of this paper is to describe a simple method for the automated data acquisition and analysis of data taken by programmable instruments. Device controls and communication method are explained and some typical illustrative examples showing the potential applications of the method in real experiments are presented. This method offers a quick and flexible way to control many instruments by using a multi-device arrangement of a stacking method in a parallel operation. The General-Purpose Interface Bus (GPIB) is used here for remote control of the devices. By using Excel and Visa interactive programs and using GPIB interface, easy communication and data transfer between instruments and a PC is accomplished. A special probe system is devised for the small resistant measuring experiments and the DC resistance measurements are performed by using the four-probe method. The related temperatures are measured by using a silicone diode as a resistance thermometer detector. Using this data acquisition method, short circuit voltage measurement, resistance measurements and the temperature dependence of resistance for a thin platinum wire are reported.


Design of a Zone Refiner for Optimization Studies
 
        S. Dost (PhD.)
  • J. Haas [PhD.]
  • Y.C. Liu [PhD.]

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Many of the physical properties of semiconductor materials depend on the presence of imperfections. A significant source of lattice imperfections is the inclusion of foreign atoms, or impurities. Since most semiconductor devices require accurate and repeatable results, highly pure materials are desired. In order to obtain high purity semiconductor metals, zone purification is commonly utilized as the final purification stage. The University of Victoria Crystal Growth Lab (CGL) Group is carrying out an optimization study of the zone refining process. To provide the required experimental platform for this study, a zone refining test bench (``CGL zone refiner'') was developed. The apparatus will be used to study the effects of zone geometry and mixing on the efficiency of the zone refining process. It also has the capability of zone refining, under an applied rotating magnetic field and an electric current, in order to examine their effect. A series of preliminary experiments were carried out with the CGL zone refiner prior to optimization testing. Samples were removed from the processed ingots and sent for glow discharge mass spectrometry (GDMS) analysis. The GDMS results indicated that the system operates efficiently and that, even with as few as three zone passes, the CGL zone refiner purified the material. A numerical thermal analysis for the zone refining of Te is also presented. In general, the numerical results were in agreement with experimental observations

    the solid/liquid interface was convex(toward liquid) for small liquid zones, concave for large liquid zones and the system was thermally stable.


Intrinsic Expressions for Arbitrary Stress Tensors Conjugate to General Strain Tensors
 
        R. Naghdabadi (PhD.)
  • S. Sohrabpour [PhD.]
  • M. Asghari [PhD.]

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In this paper, a unified explicit tensorial relation is sought between two stress tensors conjugate to arbitrary and general Hill strains. The approach used for deriving the tensorial relation is based on the eigenprojection method. The result is, indeed, a generalization of the relations that were derived by Farahani and Naghadabadi [1] in 2003 from a component to intrinsic form. The result is unified in the sense that it is valid for all cases of distinct and coalescent principal stretches. Also, in the case of three dimensional Euclidean inner product space, using the derived unified relation, some expressions for the conjugate stress tensors are presented.


A Fuzzy Efficient Frontier Method for Resource Allocation with Different Time Cycles
 
        S.J. Sadjadi (PhD.)
  • A. Eskandarpour [PhD.]

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The primary assumption, in many resource allocation problems, is that every asset has a unique length of return. However, this simple assumption may create some chaos when different investment alternatives may return in various time cycles and resources cannot be allocated at any given time. This paper presents a new extended efficient frontier problem. The new method assumes that all risky assets have different time cycles for their returns. The primary assumption is that the return for each asset is fuzzy in nature. The problem is solved and the results discussed, with some numerical examples.


Two-Objective Stacking Sequence Optimization of a Cylindrical Shell Using Genetic Algorithm
 
        M. Shakeri (PhD.)
  • M.H. Yas [PhD.]
  • M. Ghasemi-Gol [PhD.]

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In this paper, the stacking sequence optimization of a laminated cylindrical shell has been studied for obtaining maximum natural frequency and buckling stress, simultaneously. An anisotropic cylindrical shell has a finite length with simply supported conditions at both ends. Three-dimensional elasticity approaches are used for free vibration analysis and the buckling stress function is based on the theory of classic shells. A genetic algorithm is used for optimization and, regarding the two-objective problem, a Pareto optimally curve is used to help determine the best way to simultaneously satisfy all objectives. Finally, numerical results are presented for the optimization of a six-layer cylindrical shell.


Energy of the Crystalline Lattice and Sound Velocity of Lanthanide Chlorides in Aqueous T-Butanol
 
        S.H. Mousavi (PhD.)

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The ultrasonic velocity of lanthanide chlorides in aqueous t-butanol has been determined, using a single-crystal interferometer at 25, 30, 35 and 40\degree C. The velocities are accurate to ± 0.003 %. The velocity data are correlated with lattice energies of the substances on the basis of Kudriavtsev's theory. The agreement between the calculated and experimental values is good at low concentration (C = 0.03 mole/liter) of electrolytes containing structure-breaking ions, while it becomes poor with a further increase in concentration. The discrepancy is believed to be due to the invalidity of the theory in the case of higher valance electrolytes, such as rare-earth chlorides. It has been observed that, almost at any concentration, the apparent lowering of velocity is in the order of gadolinium chloride > samarium chloride > neodymium chloride, while lanthanum chloride > neodymium chloride at low concentration and is reversed as the concentration increases. The results are discussed in the light of the structure breaking property of the ions studied.


Effect of Quantum Interference on the Absorption Spectrum of a Four-Level Atom in Photonic Crystals
 
        H. Tajalli (PhD.)
  • S. Roshan Entezar [PhD.]

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In this paper, the probe absorption spectrum of a four-level atom in photonic crystals has been investigated. A model is used, which assumes the transitions from the two upper levels to one of the lower levels coupled to the modes of the modified reservoir (photonic band gap) and transitions from the two upper levels to the other lower level coupled to the free vacuum modes. The effect of quantum interference in spontaneous emissions from the two upper levels to the lower levels on the absorption spectrum of an atom is investigated in detail. Most interestingly, it is shown that the atom becomes transparent to a probe laser field coupled to the free space transition only in situations where complete quantum interference takes place in both the free space transitions and the modified reservoir transitions.