سال:1386 | دوره: | شماره: |تعداد مقالات:12

Despite the importance of the effects of inadmissible loads in the reduction of the life cycle and operation time of bridges, there is no scientific and systematic procedure for the deterioration analysis of bridges under overloaded vehicles. The main objective of this article is to outline a methodology for determining the damage effects of inadmissible loads on concrete bridge decks, considering the fatigue effect. With recourse to the fatigue phenomenon, the relationships between the passing loads and the number of allowable load cycles were determined. These relationships were the bases for constructing models by which the deterioration ratios of concrete bridges could be assessed and, consequently, the amount of fines for vehicles can be calculated.

In the present paper, a mixed, shear-flexural (VM) hinge element, with zero or nonzero length, for using in frames, has been introduced, where shear-flexural interaction has been considered.The element has the capability of modeling flexural yielding, shear yielding and their interaction in frames, subjected to all kinds of monotonic or cyclic loadings. The inelastic shear and flexural deformations and tangential stiff nesses are considered by using the multi-surfaces approach with dissimilar yield surfaces and by a stiffness matrix with nonzero off-diagonal components. A new kinematics hardening rule and, also, a new non-associated flow rule are introduced. The mixed hinge element can be used in the arbitrary location of beam-column elements, where shear effect is significant. The model is examined for some link beams in eccentrically braced steel frames (EBFs) and it is shown that the analytical and experimental results have excellent agreement.Some reduced web section beams are investigated, too. It is shown that the mixed hinge results are in good agreement with the finite element results.

Every year, many deaths, injuries and much economic loss due to falling rocks and boulders occur to the people who live in and pass through mountainous regions worldwide. Closed transportation corridors and damage to infrastructures, like rock sheds, due to rock falls, are common phenomena in some countries, especially during rainfall or earthquake. Realistic simulation of rock falls, along with defining their most vulnerable fall trajectories, can result in providing mitigation measures in the right places with the least cost. While many numerical approaches have been developed to predict the trajectory of falling rocks, none of them consider the interaction between the blocks of falling objects. In this paper, a common discrete element software (i.e., Working Model 3D) has been employed as a new tool to model rock fall. The interaction between falling masses, i.e., the impact between falling rock blocks, is considered.The results are compared to those obtained from traditional rock fall simulations. While the recent approach gives a more realistic result, its drawback is the enormous time needed to perform calculations, i.e. more than ten to a hundred fold, depending on the number of falling objects involved. The results show that existing simulation techniques give a lower bound for the hazard zone scattering and, consequently, the measuring structures will not be very efficient. On the other hand, designers should over-design to cover unseen hazard zones, which lead to heavy project costs.

One of the most important concerns in designing an embankment dam is seepage analysis.Conventional seepage analyses of embankment dams are performed in two-dimensional (2D) space, in which the impacts of water flow lines seeping from the side abutments are ignored.This fact is especially important if the dam is constructed in a narrow valley. In addition, if the effects of existing underlain faults in the reservoir water discharge rate, under different loading conditions, are to be scrutinized, three-dimensional (3D) modeling of the dam for seepage analysis is inevitable. In this paper, the significance of three-dimensional seepage analyses is emphasized by making a 3D model of a real dam site. The assumed 3D model contains all details of the rock-fill dam body and its foundation and abutments. Also, all ground improving methods for the water tightening of the underlain faults have been considered. The 3D steady state seepage analysis results were compared to those of a 2D analysis, from different points of view. Indicating that when a dam is designed for a narrow valley, performing a 3D seepage analysis is vital, due to the widthwise water flow from the side abutments. Several sensitivity analyses were also performed to show the effect of uncertainty in evaluating the characteristics of side abutment grouting curtains in seepage analysis results.

A decision for selection of a target market is one of the most important issues in strategic marketing. To tackle this issue, an appropriate segmentation of the "available market", as well as the determination of market attractiveness criteria, is defined in the marketing process.Therefore, determining the best position in the market can be decided through the process of segmenting, targeting and positioning analysis. By using the market attractiveness criteria market targeting can be supported by multi-criteria decision-making methods. The objective of this research his to introduce the application of PROMETHEE as a multi-criteria decision making approach for ranking preferential alternatives and for determining the best target market. The proposed approach is examined in a case study on the TV market in Iran. To do this, the ideas of consultants, specialists and experts in the TV market, as well as existing research and statistical analyses on the TV market, have been gathered to determine market attractiveness criteria, in order to evaluate possible alternatives in the target market. Then, the Preference Ranking Organization Method for Enrichment Evaluations (PROMETHEE), which is one of the most efficient methods for solving the problems of multi attribute decision-making, has been used, in order to rank alternatives and to determine the target market. This paper focuses on the application of PROMETHEE in determining the target market, which also supports the marketers in their decision for optimum allocation of organizational resources to the marketing mix. A bridge from an important problem area in marketing management to a quantitative approach for solving the problem, using a multi-criteria decision making method, is the main contribution of this research to the area of marketing science.

The identification and determination of products and their quantities, according to available resources, is an important matter in manufacturing plants, the answer to which is achieved by referring to objectives. This problem is often called the "product mix" decision, which is one of the applications of the Theory of Constraints (TOC). As the number of resources and products in the "product mix" decision, increase, solving the problem becomes much more complex. Therefore, optimization methods are limited to small-scale problem instances and heuristic methods are introduced for large-scale problems. In this research study, while reviewing previous related works, Simulated Annealing (SA) is used to solve the product mix problem.Furthermore, the effect of parameter changes on accuracy and computing time is investigated.The results of SA, in comparison with other heuristic results, show that the efficiency of SA in solving product mix problems is greater than other meta-heuristic methods.

A type II (eoe: extraordinary-ordinary-extraordinary) phase matching condition in a 2nd Harmonic Generation of Nd-YAG laser under a high electric field in a uniaxial KDP crystal has been measured. Type II phase matching takes place when the two mixing waves are of orthogonal polarizations (extraordinary-ordinary) and the 2nd harmonic radiation corresponds to an extraordinary wave. By applying an electric field along the X(Y) axes of the crystal, a new phase-matching angle was measured under the influence of different electric fields. The deflection angle of the SHG beam was measured as a function of the applied voltage. An optical collector will focus the 1st harmonic and a fraction of its 2nd harmonic generation used in surgical operations.

Multiple square cross section jets into a cross flow at three different velocity ratios, namely 0.5, 1.0 and 1.5, have been computationally simulated, using the Large Eddy Simulation (LES) approach.The finite volume method is applied in the computational methodologies, using an unsteady SIMPLE algorithm and employing a non-uniform staggered grid. All spatial and temporal terms in the Navier-Stokes equations have been discretized using the Power-Law and Crank- Nicolson schemes, respectively. Mean velocity profiles at different X-locations are compared with the existing experimental and Reynolds Averaged Navier-Stokes (RANS) computational results. Although the RANS computations require much fewer computational resources than the LES, the authors' results show reasonably good agreement with existing experimental results, rather than the computational ones. It is shown that, by increasing the velocity ratio, the jet penetration into the cross flow is increased, accompanied by a high mixing with the cross flow. In addition, the formation of counter rotating vortex pairs after the jet enters the cross flow is explained and its behavior in different Y Z-planes is investigated.

In this paper, variable confinement parameters were successfully developed for compressible vorticity confinement. Three variable confinement parameters, that have velocity dimension, were defined, based on three artificial dissipation schemes. The resulting confinement parameters are functions of the spectral radii of the Jacobian matrices and the Jacobian matrices themselves.Therefore, the confinement parameter implicitly contains the grid size and other local fluid properties. Preliminary results for moving vortices showed that the new confinement parameters allow the capture of vortical layers that, effectively, do not decay in time, like Hu et al.'s confinement. Calculations of the supersonic base flow and supersonic shear layer showed good agreement with experimental and analytical data, especially for the variable CUSP confinement parameter. When variable confinement parameters are used, the tuning constant is equal to, or larger than, the equivalent value of the constant confinement (Hu et al.). This means that the tuning constant varies in a range smaller than that of the Hu et al. constant confinement, especially for the CUSP confinement parameter.

A computer code for axisymmetric modeling of nano- and micro-particle motions in an aerodynamic particle beam focusing system was developed. The effectiveness of the focusing system, consisting of several lenses, a nozzle and the chamber downstream of the nozzle, was analyzed. The code included an accurate model for the Brownian diffusion of nano-particles in sharply varying pressure fields in the aerodynamic lens system. Assuming an axisymmetric condition, the compressible airflow and thermal field in the lens were evaluated. A Lagrangian particle trajectory analysis was performed, assuming a one-way coupling model. The particle equation of motion used included drag and Brownian forces. Trajectories of different size nano and micro-particles in an aerodynamic lens were analyzed and the particle beam focusing process was studied. The numerical results for particle velocity, collection efficiency and beam diameter were compared with the experimental data and good agreement was observed. The importance of the accuracy of the Brownian diffusion model, for predicting the focusing performance of aerodynamic lenses in the focusing of nano-particles, was discussed. The simulation results showed that for particle diameters less than 30 nm in air, the Brownian force could significantly affect beam focusing and particle collection efficiency.

In this paper, propagation of an electromagnetic beam wrapped around the axis of a thin axisymmetric wave guide embedded in a square law medium, depending on a b2 parameter small enough to make the b2n terms negligible for n  ³ 2 has been analyzed. To solve Maxwell's equations in this wave guide, a paraxial approximation of the wave equations, satisfied by the electric and magnetic components of the electromagnetic field, has been used. The solutions of the corresponding paraxial wave equations describe beam propagation by a series expansion of Gaussian modes.

Coordinate Measuring Machines (CMMs) are designed for precision inspection of complex industrial products. The mechanical accuracy of CMMs depends on both static and dynamic sources of error. In automated CMMs, one of the dynamic error sources is vibration of the probe, due to inertia forces resulting from parts acceleration and deceleration. Modeling of a gantry type CMM, based on the Timoshenko beam theory with moving mass effects, is developed and the dynamic errors of the probe resulting from the acceleration and deceleration of moving parts, are calculated. Findings from analytical solution and dynamic modeling software indicate high accuracy and good agreement between the results.