Journal of Advanced Materials in Engineering (Esteghlal)

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Current innovative lateral load carrying systems for tall buildings are those in which the lateral drift is limited to an allowable value without considerable influence on economy. This aim is achieved by using special systems capable of using maximum stiffness and strength capacity of individual structural elements. An effective structural solution in this respect is the use of outrigger braced systems. In the present investigation, a simple compatible structural model is proposed to analyze these systems. Constant or variable stiffness can be considered for the core which is connected to a flexible belt structure via the outrigger braced system. Several conditions including the optimum number and positions for the outrigger braced systems to minimize the drift under different loads are examined

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Most Codes such as API and BSI recommend Morison’s equation to estimate hydrodynamic forces on offshore structures. Significant differences exist among these Codes due to using different methods of analysis and estimation of force coefficients. In this paper, data from full scale tests have been used to evaluate random waves and uniform current actions on the smooth piles. Four time and frequency domain analysis methods were used to estimate Cd & Cm. Force Time Series Fitting Method (LS-TS) has given better results than the others. Furthermore, the errors from estimating hydrodynamic forces on smooth piles are more than those on rough piles.

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This paper is about experimental results for partial reduction of vortex at vertical pipe intakes. One of the easiest and practical ways of reducing vortex effect is to use anti-vortex plates or baffles. These plates can be used to avoid the vortex completely or partially. This paper will concentrate on the latter case. Rectangular plates with different dimensions have been placed at different positions to the intake pipe. Three different pipe diameters (D), 50, 75 and 100 mm, have been used. Vortex reduction percentages have been measured for each case at a constant discharge in such a way that at a given discharge, three water heads on intake pipe, namely, the water head without plate (Hn.p.), water head with plate (H), and water head with complete vortex voidance (Hn.v.), have been measured and analyzed. Plate dimensions and positions have been chosen as a multiple of pipe diameter in order to analyze and introduce the results in nondimensional form. The results of more than 6000 data points show that a plate as small as DX1.5D at the right position can reduce the vortex effect and, hence, increase, the discharge for the same head by 80%. Finally the results are presented in graph and tables format for each plate, showing the effect at best plate positions.

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Tuned Liquid Dampers (TLD) are among passive control devices that have been used to suppress the vibration of structures in recent years. These structures must be adequately presentable as an equivalent single degree of freedom system with long fundamental period. The TLD, located at the top floors of the structure, can dissipate the external input energy into the system through the sloshing effect of the liquid inside the partially filled small containers. The proportions of the TLD are determined such that the liquid’s sloshing frequency is tuned to the vibration frequency of the structure. That will result in optimal performance of the TLD. The interaction between the TLD and the structure takes place through a shear force produced by the difference in hydrodynamic pressure acted upon the TLD walls. In this paper, the application of the TLD in reducing the seismic-induced vibration of the shear buildings will be considered. In this regard, first the governing differential equations of the sloshing liquid are adapted using the nonlinear shallow water wave theory (two-dimensional Navier Stokes equations) for the rectangular tanks subjected to ground acceleration. Using some coefficients obtained for the case of harmonic base excitation, these equations are generalized to consider the different liquid dampings and the wave breaking issue. Then, the equations of the motion of a MDOF shear building is derived taking into account the interaction of the TLD. Numerical simulations were performed to investigate the performance of the TLD for the harmonic base excitations with and without wave breaking and for the earthquake input. Finally, to extend the application of the TLD for the short or intermediate building structures with short period of vibration, a combination of TLD and base isolation system (LRB) is proposed. The performance of the TLD for the base isolated structures under full-scale earthquake loading is studied.

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CA2 (Continuum Analysis, 2- dimensional) is a computer program developed by the author. CA2 can solve a variety of complex geotechnical problems using explicit finite difference method. In this paper, an introduction will be given to the theoretical and numerical basis of the program and the capability of the code will be shown by solving a few interesting nonlinear and transient problems. Finally, a new technique in finding earthquake induced displacement of slopes is proposed.

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A nonlinear model consisting “yaw, roll, longitudinal, lateral and pitch” has been developed in which, tire and suspension characteristics have been considered. Tire model is based on the elliptic concept and tire Calspan data. According to this tire model, cornering force and aligning moment are computed as a function of slip and camber (inclination) angles, normal load, tire adhesion characteristics and skid number. The effects of suspension systems and the component of lateral and longitudinal weight transfers, are considered. Finally the equations of motion are droven, vehicle handling behavior and effect of anti roll stiffness on handling characteristics are shown.

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In this paper, a new algorithm for system identification based on frequency response is presented. In this method, given a set of magnitudes and phases of the system transfer function in a set of discrete frequencies, a system of linear equations is derived which has a unique and exact solution for the coefficients of the transfer function provided that the data is noise-free and the degrees of the numerator and denominator are selected correctly. If the data is corrupted with (bounded) noise, then the answer is no longer unique and an acceptable transfer function is one that has a frequency response with a noise bound that covers the noisy data. To find one of these acceptable results, a new performance index is defined as “the least squares distance in the coefficient space”. By minimizing this index, an initial transfer function is obtained which passes optimally through the noisy data. Then, using the so-called dynamic programming technique, the noise is reduced in such a way that at each step the resulting transfer function is pushed toward one of the acceptable noise free systems. An illustrative example shows the effectiveness of the proposed algorithm.

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Sponge iron (DRI) due to the high surface area, often shows a high tendency to re-oxidation and at some cases spontaneous combustion (autoignition). In this work, re-oxidation behavior and autoignition of sponge iron, produced from different types of iron ore has been investigated. Isothermal and non-isothermal re-oxidation experiments were carried out on each type of DRI and their autoignition temperature was determined. Microscopic examination and porosimetric measurements also were used to elucidate the relationship between the DRI specification and its re-oxidation behavior. The type and chemical analysis of the iron ore, used for the production of DRI, had a strong influence on the microstructure of sponge iron and, in turn, on its sensitivity to re-oxidation and autoignition.

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In this study, a relationship between scanner response (RGB) and CIE tristimulus values (XYZ) is established by regression technique with different polynomials for colored polyester fabrics. The results showed that the transformation process is material dependent and higher order polynomials will fit the experimental data better than lower polynomials. The results also showed that the way the colors are chosen for primary calibration samples is more important than the number of samples. Using calibration samples with color characteristics closer to unknown samples leads to better results.

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Various methods have been used to economically design wastewater and stormwater collection systems. In this article, Discrete Differential Dynamic Programming (DDDP) which is a subsection of dynamic programming (DP) was used. For each pipe network, various alternatives such as depth and slope of pipe laying and various diameters could be considered to satisfy hydraulic and engineering constraints. From an economic viewpoint, however there are few alternatives to minimize the costs. Planning algorithm for DDDP is based on determination of one initial answer for network and modifying the answers in continous trials which satisfy economic and engineering considerations. To limit the range of answers in each trial, a corridor of solutions was defined. This range in each trial will converge to an optimum solution. In this regard, a computer program called SNOP (Sewer Network Optimization) has been developed. Several design examples have been run with this program. The results show the suitability of the program.

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The basic structure of a reactor physics laboratory environment simulation software, developed using object modeling technique (OMT), and based on the reactor point kinetic equation, is presented. Also, various capabilities of the simulator in teaching the fundamental concepts of reactor physics are discussed. In this virtual laboratory, student can perform seven different experiments, namely, reactor start up and control, critical mass measurement, critical thermal power measurement, control rod reactivity worth measurement, fuel poisons effects, reactor core void effects, and fine control rod drop. The user-friendly software and the technical instructions embedded provide a convenient environment for performing the experiments. The result presentation, in text and graphical format, both during and after the experiments, is another facility making the software powerful and an easy-to-use educational software.

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In this paper we introduce a simple, computationally inxepentsive, adaptive recursive structure for enhancing bandpass signals highly corrupted by broad-band noise. This adaptive algorithm, enhancing input signals, enables us to estimate the center frequency and the bandwidth of the input signal. In addition, an important feature of the proposed structure is that the conventional bias existing in the estimated frequency and bandwidth of the previously proposed structure will be canceled using an appropriate postfilter. Besides, the enhancement of multiple adjacent sinusoids can be obtained by adaptive adjustment of the bandwidth of the simple bandpass filter. The effects of the proposed postfilter in canceling the bias of the center frequency and bandwidth will be demonstrated through computer simulation.

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The six-degree equations of flight in their classic form do not provide a proper physical perception due to a number of interferences. Nor do they render visible the important role of attack angles. In this study, attempts have been made to develop a complete set of 3D acceleration equations from the equations of normal and tangential acceleration αN=vωv, αt=v ̇. For this purpose, a coordinate set stuck to the velocity vector is introduced such that the angles of attack act as a bridge between the coordinate introduced and that of the body. Thus, αNy=vωz and αNz=vωvy, are obtained, where ωvz and ωvy are the components of angular velocity vector given in terms of attack angles and p, q, r (the angular velocity of body in the body coordinate). It is also known that momentum equations are written in terms of p, q, r. Thus, the angles of attack play the role of a bridge between the force equations (now written in velocity coordinate) and the momentum equations (already written in the body coordinate). For symmetric missiles without roll, these equations become simpler and nearly linear. The undesired and nonlinear effects also become easier to analyze. The dynamic behavior among the momentum, the rotation of the body and the rotation of the velocity vector become completely visible. Thus, the aerodynamic coefficients appear directly in the dynamic equations. It follows that this new approach should help not only the auto pilot designer but also the aerodynamic body designer.

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Load modeling is widely used in power system studies. Two types of modeling, namely, static and dynamic, are employed. The current industrial practice is the static modeling. Static modelss are algebraic equations of active and reactive power changes in terms of voltage and frequency deviations. In this paper, a component based on static modeling is employed in which the aggregate model is derived based on the sensitivity coefficients and participation factors of load components. As an induction motor comprises a significant portion of industrial loads, Artificial Neural Network (ANN) is employed to derive its static model readily from nameplate data as accurately as possible.

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This paper describes a new method for the evaluation of non-utility generation impacts on preventive-corrective control of power systems. The proposed method relies on a mixed integer nonlinear optimization and is capable of recognizing the effectiveness of demand side preventive-corrective actions. A number of cases are presented to illustrate the consequences of introducing demand side actions. In particular, it is shown that using the proposed method can significantly reduce total security cost. This algorithm provides a basis for negotiations between the power system operators and potential providers of demand side preventive-corrective actions.

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The present study is intended to develop a Preventive Maintenance (PM) policy for industrial applications, while considering two different objectives: the first objective is to optimize the total maintenance costs, i.e., the Preventive Maintenance (PM) and Emergency Maintenance (EM) Costs Per Unit Time. (CPUT). The second objective is to design the policy in such a way that the simplicity of its application in a production industry environment is improved. A simulation model is constructed and, using a Monte Carlo simulation, the model is run for a sufficient number of cycles in order to determine the optimum value of a decision parameter (TX). The TX value provides the PM planning section with the possibility of economically postponing the PM action to its next scheduled date. Numerical examples are given to show the validity of the model and comparisons are made with existing PM policies in industry and in the literature to evaluate the cost reduction values that can be obtained through the adoption of the policy, while the implementation simplicity is also maintained

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Bilevel programming, a tool for modeling decentralized decision problems, consists of the objective of the leader at its first level and that of the follower at the second level. Bilevel programming has been proved to be an Np-hard problem. Numerous algorithms have been developed for solving bilevel programming problems. These algorithms lack the required efficiency for solving a real problem. In this paper, attempts have been made to develop an algorithm based on Simulated Annealing (SA) Approach. This algorithm is efficient enough to find a near optimal solution. The proposed method is compared with the one developed by Mathieu et al [1] through application of both to a number of different problems.

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Arch dams are generally built in cantilvever monoliths. Vertical contraction joints between monoliths control the stresses due to concrete shrinkage and temperature variations. Past studies in earthquake safety evaluation of the system often show the tensile fracture and local nonlinear deformation of joints. In this paper, some nonlinear joint element constitutive models are presented to examine the tensile and shear fractures of joints. Reservoir hydrodynamic interaction and water compressibility are considered in the finite element analysis of the system. Some primary examples were calculated. Regarding the numerical results, efficiency of the proposed models is promising for safety evaluation of arch dams under static and dynamic loads

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Many studies have been conducted on the characteristics of hydraulic jumps over horizontal basins. On sloping basins, however, few such studies have been performed so that the issue requires more investigation. A significant number of studies has also been conducted on basins with positive slopes but comparatively few have been carried out on basins with negative slopes. This study was carried out to determine the characteristics of hydraulic jumps over negative slopes with negative steps. The results revealed that negative steps have significant effects on the stability of hydraulic jumps, while also increasing their length and conjugated depth.

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2-D and axisymmetric Navier-Stokes equations are solved using Reiman-Roe solver with different limiters for second-order accurate schemes. The results were obtained for supersonic viscous flows over semi-infinite axisymmetric and 2-D bodies. The free stream Mach numbers were 7.78 and 16.34. The stability of Roe method with different limiters and entropy conditions were considered. The results show that the limiters greatly affect the stability and accuracy of the numerical solution while the entropy conditions do not.