M. Rabbani, K. Rezaie, M. M. Lotfi and M. Abadi,
Volume 23, Issue 1 (7-2004)
Abstract
In this paper, a new method for developing a lower bound on exact completion time distribution function of stochastic PERT networks is provided that is based on simplifying the structure of this type of network. The designed mechanism simplifies network structure by arc duplication so that network distribution function can be calculated only with convolution and multiplication. The selection of duplicable arcs in this method differs from that of Dodin’s so that it must be considered a different method. In this method, best duplicable arcs are adopted using a new mechanism. It is proved that duplicating numbers is minimized by this method. The distribution function of this method is a lower bound on exact network distribution function and an upper bound on distribution function of Dodin’s and Kleindorfer’s methods. After the algorithm for the method is presented, its efficiency is discussed and illustration examples will be used to Compare numerical results from this method with those from exact network distribution and Dodin’s method.
K. Eshgee and M. Kazemi,
Volume 23, Issue 1 (7-2004)
Abstract
In this paper, a new algorithm for solving the single loop routing problem is presented. The purpose of the single loop routing problem(SLRP) is to find the shortest loop for an automated guided vehicle covering at least one edge of each department of a block layout. First it shown that this problem can be represented as a graph model. Then a meta-heuristic algorithm based on and colony system is developed for ALRP by using the properties of the graph model. Computational results show the efficiency of the proposed algorithm in comparison with other techniques for solving SLRP.
M. A. Lotfollahi Yaghin, K. Farzad and M. Naghipour,
Volume 23, Issue 1 (7-2004)
Abstract
Similar to random sea waves, forces on the offshore structures due to waves are random. These forces can be mainly divided into two components, namely, inline forces and transverse or lift forces. The random nature of lift forces is more complicated than that of inline forces and both should be combined for design purposes. In the present paper, two different approaches have been used to determine time series of lift forces. Along these lines, the determination of lift coefficients is discussed which have then been used to obtain transverse forces and compared with experimental data. The experimental data used in this study were collected at Delft Hydraulics Laboratory on a full-scale rough vertical cylinder.
D. Mostofinejad, O. R. Barani and M. Saadatpour,
Volume 23, Issue 1 (7-2004)
Abstract
In the Present study, attempt will be made to propose a new method for prediction of long-term essential creep of concrete utilizing some short-term creep tests under high temperature. To do so, regarding the similarities between essential creep of concrete and creep in viscoelastic materials, the time–temperature equivalence relation in viscoelastic materials is evaluated for concrete. This relation states that experimental curves of creep at different temperatures fit into a single curve when shifted along the axis of logaritmic time. To develop the model, an
equation was first developed taking into account the effect of temperature and the maturity of concrete. Then, an appropriate method was proposed for transmission of the creep curve of concrete under a specific temperature to fit in the creep curve of the same concrete under a temperature. The proposed model was verified using existing experimental data which very good agreement was observed.
A. Ardeshir, F. Bahadori and A. Tahershamsi,
Volume 23, Issue 1 (7-2004)
Abstract
In this paper, development of a semi-two- dimensional mathematical model called SDAR is introduced. The model is composed of two principal modules of hydraulics and sediment transport. The newly developed SDAR model has a number of capabilities including determination of sediment transport rate, aggradation - degradation
calculation, longitudinal profile and lateral cross–sectional variation simulation, and tracing armor layer development phenomena. SDAR is a semi- two dimensional ( S-2D) model, in the sense that the lateral variation of velocity, shear stress, and rate of sediment transport are achieved by subdividing the channel course into several stream tubes carrying equal discharges. Sediment routing and bed variation calculations are accomplished along each stream tube designated by virtual interfaces.
R. Naghdabadi and A. Saeedi,
Volume 23, Issue 1 (7-2004)
Abstract
In this paper, an elastic constitutive model based on the Eulerian corotational rate of the logarithmic strain tensor is proposed. Using this model, the large deformation of a closed cycle containing tension, shear, compression and inverse shear is analyzed. Since the deformation path includes a closed cycle and the material is considered as an isotropic elastic material, the normal and shear components of the stress at the end of the cycle must vanish. Using conventional constitutive models, the non-zero solution for the stress components is obtained. Using the proposed constitutive model, the normal and shear components of stress at the end of the cycle are obtained to be exactly equal to zero.
M. Mani, M. R.soltani, and A. Haghiri,
Volume 23, Issue 1 (7-2004)
Abstract
Several experiments involving two-dimensional and axisymmetric bodies have been carried out in a Trisonic wind tunnel at supersonic speeds to investigate and analyse the measured values of base pressure and to compare them with those from the theoretical methods. The objective of the experiments was to obtain an appropriate method for processing the results of wind tunnel tests on rockets or aircraft having base area, hence, base drag. Among numerous semi-empirical methods available for two-dimensional and axisymmetric geometry, the methods presented by Chapman, Korst and Tanner have been utilized to calculate values of base pressure for comparison with the experimental findings for the same model. The results indicate that the pressure increase for the 2-D model with a steplike base is greater that of the axisymmetric model with the same conditions. The experimental results for all cases considered in this investigation compare well with those from existing the theoretical method developed by Tanner
M. F. Najafabadi and M. A. Golozar,
Volume 23, Issue 1 (7-2004)
Abstract
In this research work, the possibility of semi industrial production of Al-TiB2 and Al-ZrB2 composites, using reactive slag in a flame furnace have been investigated. For this purpose, commercial pure aluminum and powder mixture of TiO2 (ZrO2) , KBF4 and Na3AlF6 were used. The results showed that using a proper ratio of slag forming materials as well as proper amounts of the above-mentioned compounds make it possible to produce good quality Al-TiB2 and Al-ZrB2 compounds employing the conventional melting equipment such as a flame furnace.
K. Farmanesh and A. Najafi-Zadeh,
Volume 23, Issue 1 (7-2004)
Abstract
Among the titanium alloys, Ti-6Al-4V is the most widely used. In the present work, the uniaxial hot compressive behavior of Ti-6Al-4V has been investigated under constant strain rates. A series of dilatometery experiments were carried out to determine the transformation temperatures at different cooling rates. Specimens were homogenized at 1050 °C for 10 minutes followed by fast cooling to different straining temperatures from 1050 to 850°C. The cooling rate was chosen fast enough to prevent high temperature transformation during cooling. A series of isothermal compression tests were conducted at different temperatures of 850, 900, 950, 1000, 1050°C at constant true strain rates of 0.1, 0.01 and 0.001 s-1, respectively. Samples were uniaxialy compressed to a true strain of 0.55 followed by water quenching to room temperature. The apparent activation energy for compression in two phase regions was calculated at 840 KJmol-1. The partial globularization of a-phase was observed in the specimens deformed at low strain rates and at temperatures near the transformation zone followed by annealing.
S. A. Hosseini, G. Afkhami, A. Tabibi and A. Sadeghi,
Volume 23, Issue 1 (7-2004)
Abstract
Physical properties of cotton yarns are affected by the characteristics of cotton fibers such as fineness, length, maturity and strength. This relationship has been worked out by means of multivariable regression and stepwise method for an open-end spun (NeC 20) cotton yarn. Moreover, with the help of linear programming, it was made possible to determine the percentage of different cottons in the blend with the aim of reducing the yarn price to a minimum while keeping the yarn quality to a certain level.
S. Z. Shafaie, S. Banisi, M. Karamozian and A. Islami,
Volume 23, Issue 1 (7-2004)
Abstract
Process optimization is one of the most important activities in today's competitive industries. the rather high cost of research and development has necessitated the development of experimental methods by which the factors affecting processes
could be determined with minimum number of experiments. Over the last two decades, various types of experimental designs have been used. Among the different methods of experimental design such as complete and partial factorial and Latin squares design, the Taguchi method has found wide applications in some industrial divisions because of its comprehensive nature. In this paper, the laboratory scale flotation of the Sarcheshmeh copper ore which mainly consists of chalcocite was studied using the Taguchi method. The effects of seven factors namely collectors, Z11 (Xanthate) and R407 (Methyl isoboutyl carbonyl), frothers, pine oil and A65 (Polypropylene glycol), particle size, pH and flotation time were investigated. In addition to a significant reduction in cost and time of experimentation, the results indicated that a 5% increase in copper recovery could be obtained if all the factors are tested at their high experimental levels, as suggested by the Taguchi method. The optimal flotation time was also found to be 11 minutes.
M. Latifi, M. Amani, S. M. Etrati and A. H. Sadri,
Volume 23, Issue 1 (7-2004)
Abstract
Quality control of textile products is an important stage in textile industries. To this end, the conventional method in fault detection is human inspection. In the present work, Wavelet transform was applied on images of simple circular knitted fabrics to diagnose five regular defects. The results showed that the method applied was accurate and fast in addition to being capable of determining fault position and dimensions. Therefore, the Wavelet transform method is suitable for online fault detection
A. Sayadiyan, K. Badi, M. Moin and N. Moghadam,
Volume 23, Issue 2 (1-2005)
Abstract
Hidden Markov Model is a popular statisical method that is used in continious and discrete speech recognition. The probability density function of observation vectors in each state is estimated with discrete density or continious density modeling. The performance (in correct word recognition rate) of continious density is higher than discrete density HMM, but its computation complexity is very high, especially in very large discrete utterance recognition problems. For real time implementation of very large discrete utterance recognition, we must use discrete density HMM (DDHMM). To increase the performance of DDHMM, one usual solution is fuzzy interpolation. In this study, we present a new method named Gaussian interpolation. We implemented and compared the performance of two types of interpolation methods for 1500 Persian speech command words. Results show that precision and flexibility of Gaussian interpolation is better thanthose of the fuzzy interpolation.
M. Eidiani, M. H. Modir Shanechi and E. Vaahedi,
Volume 23, Issue 2 (1-2005)
Abstract
Methods for calculating Available Transfer Capability (ATC) of the transmission systems may be grouped under Static and Dynamic methods. This paper presents a fast dynamic method for ATC calculations, which considers both Transient Stability Limits and Voltage Stability Limits as terminating criteria. A variation of Energy Function Method is used to determine the transient stability limit and the determinant of the Jacobian matrix of the system is used as an index to determine the voltage stability limit. A novel method is used to approximately calculate this determinant. Combining these two methods, an algorithm that calculates ATC, based on both voltage and angle dynamic stability is presented. The advantage of this algorithm, besides considering both voltage and angle dynamic stability, is its high speed. This speed of calculation makes the algorithm a perfect
candidate to be used in screening contingencies and to determine those cases that need to be further analyzed. To demonstrate the validity, efficiency, and the speed of the new method, it is employed in the calculation of ATC for numerical examples with 2, 3, 7 (CIGREE), 10, 30 (IEEE) and 145 (Iowa State) buses.
H. Farzanehfard, S. R. Motahari and M.m. Tavasoulkhamseh,
Volume 23, Issue 2 (1-2005)
Abstract
One of the difficulties with PWM switching converters is high switching loss and electromagnetic interference due to switching at non-zero voltage and current, which limits the operating frequency. In order to reduce the converter volume and weight (by increasing the frequency) and reducing switching losses, zero voltage and current switching methods are recommended. In this paper, four main zero voltage switching (ZVS) methods in full bridge converters are introduced and compared. These four methods are compared on dead times required to obtain the ZVS, load range at ZVS condition, circulating energy in the switch anti parallel diodes during freewheeling periods and voltage oscillations on rectifying diodes. Finally, the results of a 3 KW prototype full bridge ZVS converter with a clamp circuit for rectifier diodes oscillations are presented and analyzed
S. Sharifian and S. M. Ahadi,
Volume 23, Issue 2 (1-2005)
Abstract
A variety of methods are used for speaker adaptation in speech recognition. In some techniques, such as MAP estimation, only the models with available training data are updated. Hence, large amounts of training data are required in order to have significant recognition improvements. In some others, such as MLLR, where several general transformations are applied to model clusters, the results are desirable for small training data, but with increasing training data, the performance improvement reaches the saturation lvel. In this paper, a new approach is introduced that makes use of the advantages of both mentioned techniques to improve the recognition rate. Here, the models with available training data are trained using MAP while
for those with insufficient training data, appropriate prior parameters for MAP estimation are found using MLLR. This technique has yielded better performance in comparison to either MAP or MLLR, in a system based on FARSDAT speech corpus.
K. Mohamed-Pour and M. Noorbakhsh,
Volume 23, Issue 2 (1-2005)
Abstract
In this paper, the combination of equalization and turbo decoding is studied. In the iterative decoding of a product code in block turbo coding system, the equalization process is performed within the iteration loop. The present study aims to investigate the decision feedback equalizer (DFE) incorporated in the iterative decoding. Simulation results show that the more severe the channel interference, the more the gain of the combination of DFE and turbo decoder performance compared with the case in which each is used individually
Gh. Moslehi and A. R. Rezaie,
Volume 23, Issue 2 (1-2005)
Abstract
In this paper, two-dimensional cutting stock problem with demand has been studied.In this problem, cutting of large rectangular sheets into specific small pieces should be carried out hence, the waste will be minimized. Solving this problem is important to decrease waste materials in any industry that requires cutting of sheets. In most previus studies, the demand of pieces has not been usually considered. The cutting problems belong to the category of Np-hard problems. So finding a desirable solution in a suitable time is practically impossible and heuristic methods must be used. A meta-heuristic algorithm using SA approach is presented.Then attempt will be made to regulate the SAs parameters. Initial solutions are produced with a rule based
algorithm and two internal and main SAs are used that lead to better performance of the algorithm. Due to lack of benchmark or test problems, two procedures for generating random problems is presented and are used to study efficiency of the algorithm. For this purpose, problems about 10 to 50 types of pieces with maximum demands of 2400 are generated and solved using the proposed algorithm. The results indicate that the algorithm capable of finding a solution with less than 6% of waste for problems with 30 types of pieces and total demands of 500.
K. Badv,
Volume 23, Issue 2 (1-2005)
Abstract
This study is an attempt to introduce scientific fundamentals and available methods for wellhead protection area (capture zone) delineation for drinking water wells in cities. The results of this study could obviate some demands of the national water and wastewater company in quality control of the drinking water resources by delineation and application of the wellhead protection areas. For this purpose, the available literaturer reviewed to extract, criteria and methods of wellhead protection delineation, Then, (1) fixed radius method, (2) simplified variable shape methods, and (3) flow-transport analytical methods implemented in the computer code WHPA are introduced. The applicability of these methods is shown by some sample calculations for Urmia drinking water wells. Samples of the calculated wellhead protection areas for 36 wells in Urmia City will be shown using three analytical modules in WHPA. The effects of the hydrogeologic parameters on the wellhead areas will be discussed. When reliable hydrogeologic parameters are available in the region where wells are located, the analytical methods and WHPA code produce accurate results for wellhead protection areas.
A.heidari, B. Saghfian and R. Maknoon,
Volume 23, Issue 2 (1-2005)
Abstract
Flood hydrograph simulation is affected by uncertainty in Rainfall – Runoff )RR( parameters. Uncertainty of RR parameters in Gharasoo catchment, part of the great Karkheh river basin, is evaluated by Monte–Carlo (MC) approach. A conceptual-distributed model, called ModClark, was used for basin simulation, in which the basin’s hydrograph was determined using the superposition of runoff generated by individual cells dividing the catchment in a raster–based discretization. A narrow parameter range was obtained through application of the MC method. Parameter range depended on goodness of fit measures. The results of various goodness-of-fit measures are discussed in this paper. The selected goodness-of-fit measures gave high weight to peak discharge to reduce peak discharge error.
