Showing papers by "King Fahd University of Petroleum and Minerals published in 2002"

Optimal des'ign of Power System Stabilizers Using Particle Swarm Opt'imization

Abstract: In this paper, a novel evolutionary algorithm-based approach to optimal design of multimachine power system stabilizers (PSSs) is proposed. The proposed approach employs the particle swarm optimization (PSO) technique to search for optimal settings of PSS parameters. Two elgenvalue-based objective functions to enhance system damping of electromechanical modes are considered. The robustness of the proposed approach to the initial guess is demonstrated. The performance of the proposed PSO-based PSS (PSOPSS) under different disturbances, loading conditions, and system configurations is tested and examined for different multimachine power systems. Eigenvalue analysis and nonlinear simulation results show the effectiveness of the proposed PSOPSSs to damp out the local as well as the interarea modes of oscillations and work effectively over a wide range of loading conditions and system configurations. In addition, the potential and superiority of the proposed approach over the conventional approaches are demonstrated.

Attack on plain and blended cements exposed to aggressive sulfate environments

Abstract: The recent modifications in the cement manufacturing technology and the extensive use of mineral admixtures have introduced changes in the chemical and mineralogical composition of the present-day cements. These changes may significantly affect the durability of concrete, particularly the sulfate attack. Due to these modifications, the need for understanding the mechanisms of sulfate attack through laboratory and field exposure studies becomes all the more important. This paper reviews the studies conducted at King Fahd University of Petroleum and Minerals (KFUPM) to assess sulfate attack on plain and blended cements exposed to aggressive environments in the laboratory and the field. Based on this review, the mechanisms of sulfate attack are discussed. The effect of cation type associated with the sulfate anions on concrete deterioration due to sulfate attack and the role of chloride ions on sulfate attack in plain and blended cements are also elucidated.

Solutions of the nonrelativistic wave equation with position-dependent effective mass

Abstract: Given a spatially dependent mass distribution, we obtain potential functions for exactly solvable nonrelativistic problems. The energy spectrum of the bound states and their wave functions are written down explicitly. This is accomplished by mapping the wave equation for these systems into well-known exactly solvable Schrodinger equations with constant mass using point canonical transformation. The Oscillator, Coulomb, and Morse class of potentials are considered.

Testing the Random Walk Behavior and Efficiency of the Gulf Stock Markets

Abstract: Inferences drawn from tests of market efficiency are rendered imprecise in the presence of infrequent trading. As the observed index in thinly traded markets may not represent the true underlying index value, there is a systematic bias toward rejecting the efficient market hypothesis. For the three emerging Gulf markets examined in this paper, correction for infrequent trading significantly alters the results of market efficiency and random walk tests. The Beveridge–Nelson (1981) decomposition of index returns is done to estimate the underlying index.

Development of heavy oil hydrocracking catalysts using amorphous silica-alumina and zeolites as catalyst supports

Abstract: The overall objective of this research work was to prepare hydrocracking catalysts using amorphous silica-alumina (ASA) supports in combination with USY and β-zeolites. Three supports: namely silica-alumina, USY and β-zeolites were selected to prepare the extrudates using AP-1 as a binder, while two metal pairs: namely Ni–W and Ni–Mo were loaded on the extrudates through co-impregnation using incipient wetness technique. The catalysts were then calcined at 550 °C for 2 h. The catalysts were tested in a fixed-bed flow reaction system for their activity, using desulfurized vacuum gas oil (DS-VGO) as a feedstock. The catalytic evaluation results of the catalysts showed that β-zeolite alone and in combination with the ASA used in this study, has a potential as a support for developing heavy oil hydrocracking catalysts. A balance of weak and strong acidities of β-zeolite provides control cracking, while high surface area and bigger pores of silica-alumina may be useful for producing stable hydrocracking and hydrotreating catalysts.

Support vector machines for short-term electrical load forecasting

Abstract: Short-term electrical load forecasting plays a vital role in the electric power industries. It ensures the availability of supply of electricity, as well as providing the means of avoiding over- and under-utilization of generating capacity and therefore optimizes energy prices. Several methods have been applied to short-term load forecasting, including statistical, regression and neural networks methods. This paper introduces support vector machines, the latest neural network algorithm, to short-term electrical load forecasting and compares its performance with the auto-regression model. The results indicate that support vector machines compare favourably against the auto-regressive model using the same data for building and testing both models based on the root-mean-square errors between the actual and the predicted data. Support vector machines allow the training data set to be increased beyond what is possible using the auto-regressive model or other neural networks methods. Increasing the training data further improves the performance of support vector machines method. Copyright © 2002 John Wiley & Sons, Ltd.

Thermal energy storage systems as a key technology in energy conservation

Abstract: In this study we deal with the methods and applications of describing, assessing and using thermal energy storage systems, as well as economical, energy conservation and environmental aspects of such systems. The energetic and environmental impacts of thermal energy storage (TES) systems are discussed and highlighted with a number of illustrative examples. The main emphasis is laid on sensible TES, since it is internationally accepted as the most economical and practical energy storage technique. An energy and exergy modelling is presented for TES systems as a key component in the above-mentioned aspects. Illustrative examples are also given to practically demonstrate how exergy analysis provides a more realistic and meaningful assessment than the conventional energy analysis of the efficiency and performance of a sensible heat storage system. It is believed that the results will be useful to engineers and designers seeking to improve and optimize TES systems. Copyright © 2002 John Wiley & Sons, Ltd.

International Brand-Name Standardization/Adaptation: Antecedents and Consequences

Abstract: Using the structure-conduct-performance paradigm along with Porter’s international factor conditions, the authors propose and empirically test a conceptual framework to explain the antecedents and consequences of a firm’s brand-name standardization/adaptation strategy. Survey research and structural equation modeling results show that firms adapt (vary) their brand names when market structure factors measured by competitive, buyer, and distribution intensity increase. Furthermore, the authors find that the more standardized the brand name worldwide, the higher are the firm’s cost savings and the higher is the product’s sales volume as perceived by marketing executives.

Tracking performance limitations in LTI multivariable discrete-time systems

Abstract: In this paper, we investigate tracking properties of linear shift-invariant feedback control systems. We consider the standard unity feedback configuration, and use the energy of an error signal as a measure of tracking ability. Our main goal is to understand the fundamental limitation on tracking performance, which can arise due to the nonminimum phase zeros, unstable poles, and time delays in the plant, and which varies with input reference signals. We consider step, ramp, and sinusoidal signals, and for each type of the signals we derive a closed form expression for the minimum tracking error attainable by any stabilizing controller. Our results display an explicit dependence of the tracking error on nonminimum phase zeros, unstable poles, and in particular the coupling between the directions of the poles and zeros, and those of the input reference signal, upon which a number of useful conclusions can be drawn. One interesting outcome is that not only zero and pole locations affect tracking performance, but their directional properties also play an important role. The paper provides a nontrivial extension of the previously available results to discrete-time systems, with a consideration on broader classes of reference inputs.

Long-term effect of sulfate ions and associated cation type on chloride-induced reinforcement corrosion in Portland cement concretes

Abstract: This paper reports the influence of sulfate concentration on chloride-induced reinforcement corrosion in Portland cement concretes (with C3A varying from 3.6% to 9.65%). The concrete specimens were exposed to mixed chloride and sulfate solutions for a period of 1200 days. The chloride was fixed at 5% NaCl for all solutions, while the sulfate concentration was varied to represent that noted in the sulfate-bearing soil and ground water. The study included an assessment of the effect of cation type associated with sulfate ions, namely Na+ and Mg2+, on chloride-induced reinforcement corrosion, an important factor that has received little attention. Reinforcement corrosion was evaluated by measuring corrosion potentials and corrosion current density at regular intervals. The results indicate that the presence of sulfate ions in the chloride solution did not influence the time to initiation of chloride-induced reinforcement corrosion, but the rate of corrosion increased with increasing sulfate concentration. Further, the rate of chloride-induced reinforcement corrosion in the concrete specimens exposed to sodium chloride plus magnesium sulfate solutions was more than that in the concrete specimens exposed to sodium chloride plus sodium sulfate solutions.

Optimal design of power system stabilizers using evolutionary programming

Abstract: The optimal design of power system stabilizers (PSSs) using evolutionary programming (EP) optimization technique is presented in this paper. The proposed approach employs EP to search for optimal settings of PSS parameters that shift the system eigenvalues associated with the electromechanical modes to the left in the s-plane. Incorporation of EP algorithm in the design of PSSs significantly reduces the computational burden. The performance of the proposed PSSs under different disturbances, loading conditions, and system configurations is investigated for a multimachine power system. The eigenvalue analysis and the nonlinear simulation results show the effectiveness and robustness of the proposed PSSs to damp out the local as well as the interarea modes of oscillations and work effectively over a wide range of loading conditions and system configurations.

Development and implementation of a hybrid intelligent controller for interior permanent-magnet synchronous motor drives

Abstract: A hybrid neuro-fuzzy scheme for online tuning of a genetic-based proportional-integral (PI) controller for an interior permanent-magnet synchronous motor (IPMSM) drive is presented in this paper. The proposed controller is developed for accurate speed control of the IPMSM drive under various system disturbances. In this work, initially different operating conditions are obtained based on motor dynamics incorporating uncertainties. At each operating condition a genetic algorithm is used to optimize the PI controller parameters in a closed-loop vector control scheme. In the optimization procedure a performance index is developed to reflect the minimum speed deviation, minimum settling time and zero steady-state error. A fuzzy basis function network (FBFN) is utilized for online tuning of the PI controller parameters to ensure optimum drive performance under different disturbances. The proposed FBFN-based PI controller provides a natural framework for combining numerical and linguistic information in a uniform fashion. The proposed controller is successfully implemented in real time using a digital signal processor board DS 1102 for a laboratory 1-hp IPMSM. The effectiveness of the proposed controller is verified by simulation as well as experimental results at different dynamic operating conditions. The proposed controller is found to be robust for applications in an IPMSM drive.

On energetic, exergetic and environmental aspects of drying systems†

Abstract: In this study, a comprehensive discussion of energetic, exergetic and environmental aspects of drying systems is presented. Some theoretical and practical limitations on increased energy and exergy efficiencies and discussions of the relations between energy and exergy, and the environment, along with two illustrative examples are presented. A number of issues relating to energy, exergy and the environment are examined from the drying industry perspectives. It is pointed out that exergy is a suitable technique for furthering the goal of more efficient energy-resource use and it is a key tool to determine the locations, types, and true magnitudes of wastes and losses in the drying systems. It is believed that this paper will provide some guidance to drying industry people in attaining optimum system design and operation. Copyright © 2002 John Wiley & Sons, Ltd.

Effect of waterproofing coatings on steel reinforcement corrosion and physical properties of concrete

Abstract: This paper reports the results of a study conducted to evaluate steel reinforcement corrosion and some physical properties of concrete specimens coated with two polymer-based, a cement-based polymer-modified, and a cement-based waterproofing coatings The coated and uncoated concrete specimens were subjected to accelerated corrosion to determine the time-to- corrosion initiation The physical properties were also evaluated by subjecting the concrete specimens to wetting/drying cycles and heating/cooling cycles for five months The physical properties evaluated were water absorption, water permeability, chloride permeability, and adhesion The accelerated corrosion test results clearly showed that the specimens coated with the polyurethane elastomer-based waterproofing material performed better than concrete specimens coated with other waterproofing materials This was followed by the specimens coated with cement-based polymer modified, epoxy-based, and cement-based coatings in descending order The two polymer-based coatings showed better performance than the cement-based polymer-modified and cement-based coatings in terms of the evaluated physical properties

The role of diffusion in alkyl-benzenes catalytic cracking

Abstract: The present study reports the catalytic cracking of three hydrocarbon model compounds: cumene, 1,3-di- iso -propyl-benzene (1,3-DIPB) and 1,3,5-tri- iso -propyl-benzene (1,3,5-TIPB). Experiments were developed in a novel CREC Riser Simulator, a catalytic reactor that mimics the operating conditions of large-scale fluid catalytic cracking (FCC) units. Reaction testing involved different reaction times and temperatures, using Y-zeolites of different crystal sizes (0.4 and 0.9 μm). It was shown that cumene cracking and the cumene cracking products are unaffected by the zeolite crystal size. It was proven that 1,3-DIPB cracking; it remains unaltered with changes in crystal size with however, crystal dimensions affecting product selectivities. Regarding the 1,3,5-TIPB cracking, at 350–450 °C using the 0.4 μm Y-zeolites, higher 1,3,5-TIPB conversions were obtained. Differences on 1,3,5-TIPB conversions were however, less significant at 500–550 °C. It is postulated that the 1,3,5-TIPB conversion differences are caused by constrained diffusional transport in the Y-zeolite crystals and that the increase of temperature changes the catalytic cracking of 1,3,5-TIPB from the diffusionally controlled regime to the kinetically controlled regime.