International Journal of Engineering
Volume:16 Issue: 3, Oct 2003

Drought is an inevitable part of the world’s climate. It occurs in wet as well as in dry regions. Therefore, planning for drought and mitigating its impacts is essential. In this study, a hedging rule is developed using the zero/one mixed integer-programming approach. Furthermore, some procedures are introduced to ease the computational burden inherent in integer programming. Hedging rules are developed using three, two, and one-year historical droughts. Moreover, yield model (YM) along with the standard operating policy (SOP) are also formulated for comparison purposes. Simulations are carried out using 40 years of monthly historical data along with 20 series of synthetically generated inflows of the same length. The Karadj reservoir located in the northwest of Tehran is the major source of the capital’s municipal water supply. It also provides a substantial portion of the irrigation demand of the Karadj Valley. Synthetic data are generated using single and multi-variate autoregressive modeling approaches. Models are compared using important reservoir operation criteria including reliability, resiliency, and vulnerability. As compared to the well-known SOP model, it is noticed that the application of the hedging rule and the yield model substantially reduces the system reliability as well as it’s vulnerability, however it increases the resiliency. Moreover, hedging rules developed using longer drought periods tend to have lower vulnerability and reliability, and higher resiliency.

In this article a brief review of the literature on the subject is cited. The method of analysis by a finite element program is discussed in which the effect of different influential parameters are examined. The results of these computations are then compared to the corresponding empirical data and two other existing formulae for two dimensional cases. The comparisons show quite reliable and acceptable agreement between the results of the present computations and the results obtained by other recently published formulae, and also with the existing observational data. Finally some prepared design diagrams are presented for predicting the maximum values of surface settlement and the maximum settlement of the tunnel crown.

This paper describes the application of static var compensators, (SVC) on an electrical distribution network containing two large synchronous motors, one of which is excited via a three-phase thyristor bridge rectifier. The second machine is excited via a diode bridge rectifier. Based on linear optimization control (LOC), the measurable feedback signals are applied to the control system loops of SVC and the excitation control loop of the first synchronous motor. The phase equations method was used to develop a computer program to model the distribution network. Computer results were obtained to demonstrate the system performance for some abnormal modes of operation. These results show that employing SVC based on the LOC design for electrical distribution networks containing large synchronous motors is beneficial and may be considered a first stage of the system design.

This paper describes an application of Artificial Neural Networks (ANN) to Load Frequency Control (LFC) of nonlinear power systems. Power systems, such as other industrial processes, have parametric uncertainties that for controller design had to take the uncertainties in to account. For this reason, in the design of LFC controller the idea of robust control theories are being used. To improve the stability of nonlinear power system, in the various operating point and under different disturbances this controller has been reconstructed with the use of neural network capability based on Radial Basis Function (RBF). The motivation of using the robust control for training of the RBF neural networks controller is taking the large parametric uncertainties into account in such away that both stability of the overall system and good performance have been achieved for all admissibleuncertainties. The simulation results on interconnected power system show that the proposed Nonlinear Neural Controller (NNC) not only is robust to increasing of load perturbations and operating point variations, but also the NNC gives good dynamic response compared with conventional PI and robust controllers. It guarantees the stability of the overall system even in the presence of generation rate constraint (GRC).

A numerical study on Nox emission from an industrial furnace utilizing high temperature air combustion (HTAC) technology was done. The basic concept of the regenerative burner including heating a diluting of fresh air by flue gas was implemented in a two-dimensional furnace model. Governing equations in conjunction with a turbulence model and an overall chemistry model were solved using an implicit numerical scheme. Effect of temperature and O2 concentration of preheated airflow on Nox emission from a furnace were investigated. Numerical results show a drastic increase in Nox emission when temperature or O2 concentration of preheated airflow increases. High combustion efficiency and low Nox emission can be achieved when the inlet airflow is preheated up to a high temperature, for instance, about 1500 ºK, and O2 reduced to about 5%.

The influence of benzoate anions on the corrosion inhibition effect of benzotriazole (BTA) for mild steel in sulfuric acid has been investigated. The investigation was carried out by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. The addition of benzoate ions greatly enhances the inhibition efficiency of BTA in a synergistic manner. This effect has been attributed to co-adsorption of benzoate and protonated benzotriazole ions. While inhibition property of BTA has been attributed to adsorption of the molecules on the metal surface, through interaction of lone pair electrons on nitrogen atoms or π electrons of the aromatic ring, followed by polymeric complex formation. In acid solution, in presence of benzoate anions, protonated BTA molecules are adsorbed mostly by columbic attractions on the surface partially covered with benzoate anions.

Mathematical model for a pilot scale iron ore pellet induration furnace has been developed which considers the process of induration including the reactions of limestone, magnetite and coke. The differential equations of energy, mass and momentum are solved simultaneously. The profiles of temperature, pressure and concentration are obtained. Performing separate experiments on sub processes; drying, firing and cooling have checked the validity of the model. At first, a mixture of iron ore is selected and then the percentage of limestone is changed. The maximum metallization and fired pellet strength with minimum sticking vs. basicity is obtained. In the next stage the percentage of coke in iron ore is altered and all of physical and chemical property of the pellets are measured. Finally, the optimum percentage of coke in the iron ore is determined. By using different percentage of coke in the pellet the experiments are performed in three conditions. In the first condition, inlet gas temperature is decreased alone. In the second condition, inlet gas temperature and total indurtion time are decreased together and in the third condition, in addition to above conditions, oxygen injection to the furnace is carried out. Energy savings in all three conditions have been obtained.

The size and length effects of an inclusion on multi-pass copper shaped-wire drawing were investigated. For this purpose, an experimental investigation on optimal die half-angle was conducted. Based on experimental data of optimal die half-angle, wire and inclusion deformations, drawing and hydrostatic stress of copper shaped-wires that contain an inclusion were calculated by two-dimensional finite element analysis. As a result, during drawing of a wire containing an inclusion, necking occurred. The effects of inclusion size and length on drawing stress and maximum hydrostatic tensile stress in front of inclusion during multi-pass copper shaped-wire drawing were carried out. The maximum hydrostatic tensile stress occurred on wire centerline in front of inclusion for single-pass drawing. When the wire was repeatedly drawn, the maximum hydrostatic tensile stress regions symmetrically separated out and were at both side of wire centerline in front of inclusion. Symmetrical double crack easily occurred in those regions.

The dissolution kinetics of pandermite and hydroboracite, present in an Iranian borate ore, in sulfuric acid has been comparatively studied. The effect of particle size, temperature, and acid concentration on their dissolution rate was investigated. Dissolution rates of both minerals increased by reducing the particle size and by raising the temperature. Although, an increase in the acid concentration from 0.5 to 1 N accompanied an increase in the dissolution rate, the concentration beyond 1N did not produce any significant change. The dissolution of hydroboracite occurred appreciably faster than pandermite, which was attributed to its lower calcium content. This could be due to the formation of a product layer namely, CaSO4.2H2O, acting as a diffusion barrier, which in the case of hydroboracite was less effective. The rate data obtained was in agreement with a kinetic model proposed for diffusion- controlled heterogeneous reactions.