ESTEGHLAL
Year:2000 | Volume:19 | Issue:1|Papers Count:17

In a detection network, the final decision is made by fusing the decisions from local detectors.The objective of that decision is to minimize the final error probability. To implement an optimal fusion rule, the performance of each detector, i.e. its probability of false alarm and its probability of missed detection as well as the a priori probabilities of the hypotheses, must be known. However, these statistics are usually unknown or may vary with time. In this paper, we develop a recursive algorithm that adapts the fusion center.This approach is based on the time-averaging of local decisions and on using the analytic solutions that guarantee the asymptotic convergence. Also a simple method is proposed that enables the algorithm to track changes faster. Simulation results are presented to demonstrate the efficiency and convergence properties of the algorithm.

The start up dynamics of a one-million and two-hundred-thousand liter anaerobic digester of municipal waste treatment sluge was studied. In the digester, mixing was accomplished by circulation of the produced biogas at a rate of 0.13 m3 per m3 of the digester volume per hour. During the nine-month study, no serious phenomena of foaming, getting sour, temperature fall, etc. were observed despite the fact that there were problems including gas leakage, sludge leakage, heating system shortcomings and weak mixing system. In the process of digestion of a 3:1 mixture of primary and secondary sludge at a rate of 25 m3 / day, 25oC and a residence time of 48 days, volatile content removal was as high as 60%. The experimental data collected in this study was checked against a theoretical model already published in the literature and a good comparison was observed between the measured values and those calculated based on the model.

In this paper, the effect of curing time and temperature as well as various primers on durability of high density polyethylene on plain carbon steel has been investigated. The aim is to increase adhesion, improve durability and aim to produce a defect-free coating in order to improve the corrosion resistance of steel substrate. For this purpose, after surface preparation and applying a primer (zinc phosphate, polyvinylalcohol, resol, stearic acid, and polyurethane) polymer coating was applied using electrostatic powder coating system. Coatings having 300 m thicknesses were produced and then subjected to primary and secondary curing treatments. In addition to adhesion, ductility, and corrosion tests, quality of coatings were studied using scanning electron microscopy. The results obtained revealed that, surface porosity and uniformity of metal/coating interface is a function of curing time and temperature, as well as of the primers used. The best results obtained after curing for 45 min at 230oC. The effects of primers were as followes: no primers < Stearic acid, < resol, < polyvinylalcohol, < polyurethane. Results of corrosion tests showed no sign of corrosion on the steel substrate after 60 days immersion in sulfuric acid, ferric chloride, distilled water, and salt spray.

The problem of determining the sequence of a set of jobs with the objective function of minimizing the maximum earliness and tardiness in one machine is studied.Production systems like JIT are one of the many applications of the problem. This problem is studied in special cases and their optimal solutions are introduced with simple orders. In general, some effective conditions for neighboring jobs have been developed and the dominant set for the optimal solution is determined. Branch and Bound (BB) method is also used for this problem. The strong upper and lower limits are introduced in BB, resulting in optimal solutions to a lot of problems in short time periods. To show the effectiveness of the suggested solution method:" as many as 720 problems in different sizes, with 5 to 100 jobs, have been randomly generated and solved.

In this research, a new method for market-product strategic planning is presented. In this method, an expert system is designed on the basis of identifying important factors that are effective in a firm and analyzing the logical relations between them. The objective is to develop a decision support system (DSS) for helping managers to make strategic decisions. DDS can serve as suitable replacement for the existing methods which are mostly qualitative. The output of the system is software, which takes as input simple information on independent factors to provide a final strategy as output. To verify the system, it has been tested with the real data from an industrial firm.

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.

Most Code such as API and BSI recommend Morison's equation to estimate hydrodynamic forces on offshore structures. Significant difference exists 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.

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 avoidance (Hn.v.), have been measured and analyzed. Plate dimension and positions have been chosen as a multiple of pipe diameter in order to analyze and introduce the results in nondimensional form. The resul1sof 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 resul1sare presented in graph and tables format for each plate, showing the effect at best plate positions.

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.

Tuned Liquid Dampers (TLD) is 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.

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 system and the component of lateral and longitudinal weight transfers are considered.Finally the equations of motion are driven; vehicle handling behavior and effect of anti roll stiffness on handling characteristics are shown.

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 noisefree systems. An illustrative example shows the effectiveness of the proposed algorithm.

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.

In this study, a relationship between scanner response (RGB) and CIE tristimulus values (XYZ) is established by regression technique with different polynomial 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.

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 al1ernativessuch as depth and slope of pipe lying 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 continuous 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.

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.