منو
بروندادهای پژوهشی
مرتب سازی بر اساس: سال انتشار
(نزولی)
Conference: 1 December 2014
Chemical Engineering and Technology (09307516) 37(12)pp. 2175-2184
A rate-based mathematical model was developed for the reactive absorption of H2S in NaOH, with NaOCl or H2O2 as the chemical oxidant solutions in a packed column. A modified mass transfer coefficient in the gas phase was obtained by genetic algorithm and implemented in the model to correct the assumption of instantaneous reactions. The effects of different operating variables including the inlet H2S concentration, inlet gas mass flux, initial NaOH, concentrations of the chemical oxidants in the scrubbing solutions, and liquid-to-gas ratio on the H2S removal efficiency were studied. A genetic algorithm was employed to optimize the operating variables in order to obtain maximum removal efficiency of H2S. The model results were in good agreement with the experimental data. A modified rate-based mathematical model was developed and evaluated in order to predict the removal efficiency of H2S in a packed-bed column with NaOH and chemical oxidant solutions as absorbents. Results of the validated model were adapted to a genetic algorithm to calculate optimal operating variables. Among the most effective operation parameters the initial pH of the alkaline solution was determined. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
This paper presents a new method for coordinately tuning the parameters of UPFC controller and power system stabilizer (PSS) as well as determining the PSS location to enhance the stability of power system by using a new hybrid particle swarm optimization based co-evolutionary cultural algorithm, so called culture-PSO-co evolutionary (CPCE). Nonlinear simulations are implemented on the IEEE 39-bus power system. The results imply the effectiveness of the proposed method for damping out power system oscillations. © 2016 IEEE.
Etahadtavakol, M. ,
Ng e.y.k., ,
Lucas, C. ,
Ataei, M. Publication Date: 0
pp. 255-274
Publication Date: 0
pp. 155-160
A new control scheme, based on Artificial Neuro-Fuzzy Inference System (ANFIS) is used to design a robust Proportional Integral Derivative (PID) controller for Load Frequency Control (LFC). The controller algorithm is trained by the results of off-line studies obtained by using particle swarm optimization. The controller gains are optimized and updated in real-time according to load and parameters variations. Simulation results of this method on a multi-machine system in comparison with conventional fuzzy controller show the satisfactory results, especially where the parameters of the system change. © 2019 ICAI 2015 - WORLDCOMP 2015. All rights reserved.
Publication Date: 0
pp. 429-463
Most of the weight of the proton exchange membrane (PEM) fuel cell stack is in the bipolar plates. The main function of bipolar plates is uniform distribution of gas reactants as well as distribution of cooling fluid (water or air) inside the fuel cell. Therefore, the plate design and the characteristics of the gas and cooling channels inside them are essential to the operation of the PEM. Although reactive gas channels and cooling channels perform separately, there are many similarities between them. For example, gas channels should be designed so that distribution of reactive gases on the electrode surfaces is uniform. Also, cooling channels should be designed so that temperature distribution inside the fuel cell is uniform. Further, pressure drop of reactive gases inside the gas channels and the fluid inside the cooling channels must be minimal. In this chapter, initially the characteristics, functions and making materials of bipolar plates along with the to make channels inside of them are investigated. Afterwards, gas channels, cooling channels and effects of the shape and size of channels on the PEM fuel cell performance are studied. Finally, different configurations of gas and cooling channel with emphasizing on the new configurations of these channel are researched simultaneously. © 2022 Elsevier Inc. All rights reserved.
Publication Date: 0
pp. 742-747
In this paper, a saturated PD based Fault Tolerant Control is proposed for a quadrotor suffering a severe fault in one of its actuators, on top of a new control scheme assuming the fault has been already detected by the system. Whenever a severe fault occurs in system, the PD control is reconfigured by adding relevant trirotor control equations to the control laws. To tune the optimal parameters of the controllers, a Particle Swarm Optimization algorithm (PSO) is used. The stability of the upgraded PD is proved by using Lyapunov theorem. Simulation Results with some induced disturbance demonstrated the effectiveness of the proposed controller in controlling the damaged quadrotor until it finishes its path. © 2017 IEEE.
Publication Date: 0
IEEE Transactions on Vehicular Technology (00189545) 55pp. 1725-1730
Antilock braking systems (ABS) have been developed to improve vehicle control during sudden braking especially on slippery road surfaces. The objective of such control is to increase wheel tractive force in the desired direction while maintaining adequate vehicle stability and steerability and also reducing the vehicle stopping distance. In this paper, an optimized Fuzzy controller is proposed for antilock braking systems. The objective function is defined to maintain wheel slip to a desired level so that maximum wheel tractive force and maximum vehicle deceleration are obtained. All components of fuzzy system are optimized using genetic algorithms. The error based global optimization approach is used for fast convergence near optimum point. Simulation results show fast convergence and good performance of the controller for different road conditions. ©2005 IEEE.
Publication Date: 0
pp. 211-216
This paper proposes an active disturbance rejection control (ADRC) method based on generalized proportional integral (GPI) observer to control of a biped robot while considering its complicated structure and possible disturbances. These observers are used to estimate time-varying disturbances and possible uncertainties. Generally, implying GPI observer on robotic systems is accompanied by a PD-controller in feedback, which is not efficient enough due to abrupt velocity changes of the biped in impact phase, and consequently, a higher level of input torque is required. Thus, applying the back-stepping technique to the mentioned method is suggested. In this study, a two-nested control loop is designed for a 3D biped robot. The back-stepping method with a GPI observer is used in the inner control loop to improve the custom method. Joint trajectories are designed by an offline method and modified by an online method in the outer loop to maintain the stability of the biped. The efficiency of the proposed control strategy is depicted for the biped in the presence of time-varying disturbances through MATLAB simulation. © 2019 IEEE.
Anti-lock braking systems (ABS) have been developed to reduce tendency for wheel lock and improve vehicle control during sudden braking especially on slippery road surfaces. The objective of such control is to increase wheel tractive force in the desired direction while maintaining adequate vehicle stability and steerability and also reducing the vehicle stopping distance. In this paper, a genetic-fuzzy ABS controller is designed. The objective function is defined to maintain wheel slip to a desired level so that maximum wheel tractive force and maximum vehicle deceleration are obtained. All components of the fuzzy system that is Takagi-Sugeno-Kang (TSK) type are obtained using a genetic algorithm. Simulation results show very good performance of the controller for different road conditions. © 2005 IEEE.
Publication Date: 0
2pp. 1343-1352
The ultra-fast charging capability, distinct properties, fine performance and high capacity of nickel cadmium (Ni-Cd) and nickel metal hydride (Ni-MH) batteries along with their limited weight and size are very attractive for use in many applications including cordless and portable devices, emergency and standby power, telecommunication equipments, photovoltaic systems, electric vehicle, satellite and space craft and power plant supporting equipments. However, the limitation on their temperature requires a detail thermal analysis of these batteries. Thermal behavior of batteries are effected by their boundary conditions, type and construction, and more importantly by their chemical reaction. The purpose of this study is to investigate the effect of temperature on thermal behavior of the Ni-Cd and Ni-MH batteries. The governing equation is the transient and non-linear differential energy equation subjected to non linear radiation boundary conditions and source term. To solve the transient and non-linear governing differential energy equation a control volume based finite difference code is utilized. In formulation of the governing differential energy equation, the Ni-Cd and Ni-MH properties (K, C, ρ) are not constant and the chemical characteristic of the Ni-Cd and Ni-MH batteries, source term, vary with location and time. Calculated thermal characteristic of each battery is then compared to experimental results. The result shows that Ni-MH battery is thermally more suitable for space application and satellite. Copyright © 2004 by ASME.
Ataei, M. ,
Khaki-sedigh, A. ,
Lohmann b., ,
Lucas, C. Publication Date: 0
pp. 3106-3111
In this paper, the problem of Lyapunov Exponents (LEs) computation from chaotic time series based on Jacobian approach by using polynomial modelling is considered. The embedding dimension which is an important reconstruction parameter, is interpreted as the most suitable order of model. Based on a global polynomial model fitting to the given data, a novel criterion for selecting the suitable embedding dimension is presented. By considering this dimension as the model order, by evaluating the prediction error of different models, the best nonlinearity degree of polynomial model is estimated. This selected structure is used in each point of the reconstructed state space to model the system dynamics locally and calculate the Jacobian matrices which are used in QR factorization method in the LEs estimation. This procedure is also applied to multivariate time series to include information from other time series and resolve probable shortcoming of the univariate case. Finally, simulation results are presented for some well-known chaotic systems to show the effectiveness of the proposed methodology. © 2003 EUCA.
Publication Date: 0
2018pp. 1-7
One of the main problems in the islanded microgrids is the frequency regulation. Moreover, there are several uncertainties and disturbances in the islanded microgrids that may lead to the instability. To solve this problem, this paper proposes the design of a multi-objective Linear Matrix Inequalities (LMIs) based regulator. It considers the LMI conditions in such a way that the design criterion holds. It also considers the disturbances, including solar radiation, wind speed, and load demand variations. With extracting microgrid state space model, it builds a framework to synthesize the controller. Next, it presents the mixed robust design criteria to set up the multi-objective function. The controller design process includes two steps: state feedback and observer designs. With considering weighing functions in the design process, it determines the optimal solution of the objective function. The obtained solution is the state feedback matrix, and it forms the controller by combining the state feedback matrix with a state observer. We have applied the designed controller to the islanded microgrid, and the effect of disturbances is evaluated together with parametric uncertainties. The proposed regulator is compared with the traditional PI method. The results show that the designed regulator has robust performance as well as robust stability. © 2017 IEEE.
This paper presents an analysis on electrolytic capacitor-less inverter and proposes a strategy for resonance suppression control for a DC-link voltage and input current in electrolytic capacitor-less inverter. The proposed electrolytic capacitor-less inverter can operate both in the motoring mode and regenerating mode owing to its inherent bidirectional power flow capability of the active front-end rectifier whose switching frequency is equal to the input line frequency. However, in the electrolytic capacitor-less inverter, the DC-link voltage is fluctuating with six times of the frequency of input three phase source due to its small DC link capacitance. Also, an input filter should be employed to remove the high frequency component generated by PWM inverter. By the input filter, the DC-link voltage can be resonant, and a specific resonance suppression control is required when the input line-to-line voltage is low and the demanded power is large. In this paper, a novel resonance suppression strategy is proposed for a stable operation of the electrolytic capacitor-less inverter. The experimental results show the effectiveness of proposed strategy. ©2009 IEEE.
In this entry, photo-reactors for catalytic solar hydrogen production are introduced and explained. To be an economical environmentally benign and sustainable pathway, hydrogen should be produced from a renewable energy source, i.e., solar energy. Solar driven water splitting combines several attractive features for sustainable energy utilization. The conversion of solar energy to a type of storable energy has crucial importance. In the first part of the entry, background information is presented regarding different photo-reactor configurations for water dissociation with light energy to generate hydrogen. The photo-electrochemistry of water splitting is discussed, as well as photo-catalytic reaction mechanisms. The design and scale-up of photo-reactors for photo-catalytic water splitting are explained by classification of light-based hydrogen production systems. At the end, a new photo-catalytic energy conversion system is analyzed for continuous production of hydrogen at a pilot-plant scale. Two methods of photo-catalytic water splitting and solar methanol steam reforming are investigated as two potential solar-based methods of catalytic hydrogen production. The exergy efficiency, exergy destruction, environmental impact, and sustainability index are investigated for these systems. The light intensity is found to be one of the key parameters in design and optimization of the photo-reactors, in conjunction with light absorptivity of the catalyst. © Springer Science+Business Media New York 2013. All rights reserved.
Esmaili, M.R. ,
Khodabakhshian, A. ,
Heydarian-forushani e., ,
Shafie-khah, M. ,
Hafezi h., ,
Faranda r., ,
Catalao, J.P.S. Publication Date: 0
Installation of new power generating units as backup black-start (BBS) sources is a vital issue to improve the acceleration of power network restoration, especially when a serious problem is occurred in main BS units (BSUs) and leads to fail in operation. Accordingly, this work address a new design for the optimal locating of the Gas-based Turbine (GT) as BBS to improve the smart grid performance during both restoration and normal conditions. To this end, there will be incompatible fitness functions to be minimized. Therefore, a multi-objective problem (MOP) including a mixed integer Non-linear programming (MINLP), is formulated. The Pareto answers of the proposed MOP as the best solutions are modified and extracted by utilizing a meta-heuristic method, called crow search algorithm (CSA). A typical test system is employed for evaluation of the given plan. The extracted outcomes reveal that the network can desirably operate from this design not only to favorably enhance the capability of BSUs, but also to improve the power system performance in normal conditions. It also provides the better start-up program of non-black-start (NBS) power sources with the optimal paths during the restoration process. © 2019 IEEE.
Publication Date: 0
pp. 13-18
We study the diversity-multiplexing trade-off (DMT) of diamond relay channels. A diamond network contains a transmitter, two relays and a receiver. DMT of a network represents a fundamental trade-off between the reliability and rate of transmission with the diversity and multiplexing gains for wireless networks with fading channels. In this paper, we compute the DMT of full-duplex diamond relay channels and find the DMT of QMF communication strategy for half-duplex diamond relay channels. Also, a new genetic algorithm is introduced to solve the DMT of static QMF strategy for half-duplex diamond relay channels. By simulation, it is shown than the running time of the genetic algorithm is much better than the running time of finding the DMT of SQMF using grid based optimization techniques. The novelty of the proposed genetic algorithm is in using creative crossover and mutation operators in the algorithm which improved the results. © 2016 IEEE.
The diversity-multiplexing trade-off (DMT) expresses the optimal trade-off between the transmission rate and the error probability for communications at high signal to noise ratios (SNR) in wireless networks with fading channels. For half-duplex single relay networks with quasi-static fading channels, if the average signal to noise ratio (SNR) of the source-relay (S-R) link is equal to the average SNR of the relay-destination (RD) link, quantize-map-and-forward (QMF) and dynamic decode-and-forward (DDF) strategies are DMT optimal at high and low multiplexing gains, respectively. In this paper, we show that DDF and SQMF strategies are not generally DMT optimal in half-duplex single relay networks when the average SNR of the S-R link and R-D link are not equal. We show that DMT of dynamic QMF strategy is strictly greater than DMT of DDF and static QMF strategies for a specific half-duplex single relay network at certain multiplexing gains. © 2015 IEEE.
In this paper, an exergy-economic model is developed to analyze the performance of a direct steam solar tower - steam turbine - organic Rankine cycle (ORC) power plant under different working conditions. The solar power plant is connected to a power grid, and it is integrated with a hydrogen storage system. The hydrogen storage system is composed of an electrolyser, fuel cell, steam turbine and organic Rankine cycle. When solar energy is not available, electrical power is generated by the fuel cell, steam turbine and ORC using the hydrogen produced by the electrolyzer. The analyses are made for the maximum solar irradiation that is available in the city of YAZD in Iran. The effects of the current density and operating temperature on the performance of the solid oxide electrolyzer cell (SOEC) and solid oxide fuel cell (SOFC) are investigated. The effect of solar irradiation on the energy and exergy efficiencies of the cycle is investigated. The results indicate that increase of the solar irradiation leads to an increase of the energy and exergy efficiencies of the cycle. The solar tower has the highest exergy destruction and capital investment cost. © 2022 Proceedings of WHEC 2022 - 23rd World Hydrogen Energy Conference: Bridging Continents by H2. All rights reserved.
The problem of recovering a sparse L-ary signal from magnitudes of its Fourier transform or equivalently its autocorrelation function is considered. Although, one can show that solving the phase retrieval problem for L-ary signals is possible in time that is polynomial in L and length of the signal, however, the current algorithms are still not practical. We introduce a backtracking algorithm on a tree which solves the phase retrieval problem. By simulations, we show that the average number of nodes visited on the tree by the backtracking algorithm grows polynomially in L and signal length, although the search tree has an exponential size. © 2014 IEEE.
Determination of forming limit in sheet metal forming processes is very important and can reduce the number of costly trials. Therefore numerous numerical and experimental analyses have been reported. In this paper, 3D model of hydro-forming process of T-shape tube was simulated by finite element method. An integral ductile damage model, coupled with von Mises plastic criterion, has been applied to predict where and when onset of ductile rupture occurs in the process. Model is based on damage evolution and accounts nonlinear strain paths. Results have been compared with experimental tests and empirical observations. Because of bending effects and nonlinear strain paths assumptions, the ductile damage model showed good agreement with experimental tests and empirical observations. The results were satisfactory and acceptable. Hence ductile damage model can be used as a reliable criterion in prediction of ductile fracture in sheet metal forming processes.
Afshari, E. ,
Asghari, S. ,
Jahantigh, N. ,
Shamsizadeh, P. Publication Date: 0
pp. 417-440
Work production systems cannot convert all input energy into useful work, and in these systems, always a part of the input energy is rejected to the environment in the form of heat. Therefore, the efficiency of work production systems is limited. In these systems, one of the limiting factors of the work production rate is the disposal of the produced heat during the process. The lack of proper heat dissipation increases the temperature of the system and its various parts of damages. Cooling system is an inseparable part of work production systems. The cooling system can be very simple (a natural circulation air-cooling system) or very complex (a nuclear facility cooling system). Simple cooling systems are usually used for low energy production rates (a few watts) and complex systems for high production rates (several hundred megawatts). The polymer electrolyte membrane (PEM) fuel cell is not excluded from this issue. In addition to the production of electric power, heat is produced in the PEM fuel cell, which is even slightly more than the production power. Therefore, one of the most important challenges that affects the use of this fuel cell is the issue of heat removal from the cell and heat management in it, which is done by a cooling system. © 2023 Elsevier Inc. All rights reserved.
Publication Date: 1997
1pp. 375-378
In the gradient based learning algorithms, the momentum has usually an improving effect in convergence rate and decreasing the zigzagging phenomena but sometimes it causes the convergence rate to decrease. The Parallel tangent (Partan) gradient is used as deflecting method to improve the convergence. In this paper, we modify the gradient Partan algorithm for learning the neural networks by using two different learning rates, one for gradient search and the other for accelerating through parallel tangent, respectively. Moreover, the dynamic self adaptation of learning rate is used to improve the performance. In dynamic self adaptation, each learning rate is adapted locally to the cost function landscape and the previous learning rate. Finally we test the proposed algorithm, called accelerated Partan on various problems such as xor and encoders. We compare the results with those of the dynamic self adaptation of learning rate and momentum.
Publication Date: 1997
2pp. 951-954
Throughout the history of power system protection, improvements have continuously been made to most aspects of the protection system. However the choice of the protection function and the type selection are still carried out by specialist based on their personal experience. Since the applied design methods are strongly impacted by the personal philosophy of the designer, most of the existing protection system are not always optimal. In this paper a new method will be presented which is based on exact rules of the graph theory to achieve (at least near to) an optimum protection system for an arbitrary network configuration.
Publication Date: 1997
IEE Conference Publication (05379989) (434)pp. 70-73
Up to now the design of power system protection is done by experts. Despite using software tools like relay coordination program, the design process is mostly based on personal experience. Therefore the design of the most existing protection systems are not always optimal. In this paper a new method will be presented which is based on exact rules for obtaining an optimal design.
Publication Date: 1998
Journal of Intelligent and Fuzzy Systems (18758967) 6pp. 419-434
In this article, an effective method to control a power system during emergency conditions is presented. Based on Fuzzy Linear Programming (FLP), a new technique is developed to solve the Load Shedding and Generation Reallocation (LSGR) optimization problem. The objective function consists of terms of load curtailments and deviations in generation schedules. The constraints are power system variables limitations. The objective function and constraints coefficients are uncertain, which are represented by fuzzy numbers. Thus a fuzzy environment is prepared and a FLP approach is developed to solve more realistically and successfully the LSGR optimization problem. The method is successfully applied on a test system, where the load curtailments and deviations from the nominal states are to be minimized. The results of various cases of fuzzy and crisp modes of the problem are demonstrated. © 1998, IOS Press.
Publication Date: 1998
IEEE Power Engineering Review (02721724) 18(6)pp. 43-45
The coordination of protective relays of multiloop networks is a tedious and time consuming process. The complicated part of this process is the determination of a set of relays referred to as the break-point set (BPS), with a minimal size to start the coordination procedure. This letter introduces a new graph-theoretical approach to determine the BPS. This method reduces the complexity of the problem, by exploiting the available sparsity of the dependencies among relays in protection systems.
Publication Date: 1998
EUT Report, Eindhoven University of Technology, Faculty of Electrical Engineering (09298525) (98 -E-309)
The basic task of a electrical power system protection is to detect faults in system components, and to rapidly isolate them by opening all incoming current paths. On the other hand, in the case of any fault, the protection system should disconnect only a minimum number of components, to minimize interruptions to consumers. Therefore, relays of a protection system should be adjusted for the minimum possible operation time, while maintaining coordination among all relays. Modern power system networks are often multi-loop structured. Coordinated setting of protective relays in such networks is tedious and time consuming. The complicated part of this problem is the determination of a minimum set of relays, the so-called minimum Break Point Set (BPS), to start the coordination procedure. This report presents a new graph-theoretical method to determine a minimum or a near-to-minimum BPS. Using the rules of this method, the determination of a minimum BPS can be reduced and decomposed into sub-problems. Owing to the efficiency of these rules, the presented method quickly achieves the result, even for large networks. Moreover, due to the simplicity of the method, it can be manually applied to the graph of each network. Since the presented rules are general, they can be applied to improve any method dealing with BPS determination.
Publication Date: 1998
1pp. 245-250
Throughout the history of power system protection' improvements have continuously been made to most aspects of the protection system. However' the selection of type and characteristics of the protective relay are still carried out by specialists based on their experience. Since the applied design methods are strongly impacted by the personal philosophy of the designer' most of the existing protection systems are not optimal. In this paper' a new method will be presented to achieve an optimal protection system for an arbitrary network configuration' based on graph-Theoretical tools.an example. In this simple case' a selective protection only requires an overcurrent definite-time function for each relay location. In this case' relays rj' rj and r4 do not backup any relays' and can be adjusted for the shortest operation time (without delay). But relay r3 must take over the function of backup for r^ and rj-Therefore to achieve selectivity' r^ must operate after rj and r'. This can be realized by adding a time delay (i.e. zc=0.3 sec.) to ry In the same way' r^ should operate after ry and needs an additional delay of at least 2. © 1998 Institute of Electrical and Electronics Engineers Inc. All Rights Reserved.
Publication Date: 1998
IEE Proceedings: Generation, Transmission and Distribution (13502360) 145(6)pp. 717-721
Modern power system networks are often multiloop structured. Co-ordinated setting of overcurrent and distance protective relays in such networks is tedious and time consuming. The complicated part of this problem is the determination of a proper minimum set of relays, the so-called minimum break-point set (BPS), to start the co-ordination procedure. The paper presents a new graph-theoretical method to determine a near-to-minimum or a minimum BPS. Using the lemmas of this method, the determination of a minimum BPS can be reduced and decomposed into subproblems. Owing to the efficiency of these lemmas, the presented method quickly achieves the result, even for large networks. Moreover, due to the simplicity of the method, it can be manually applied to the graph of each network. Since the presented lemmas are general, they can be applied to improve any method dealing with BPS determination. © IEE, 1998.
Publication Date: 1999
IRANIAN JOURNAL OF SCIENCE AND TECHNOLOGY (03601307) 23(3)pp. 180-181
Madder (Rubia tinctrum) is a plant growing in areas such as south east Asia, and Europe. Over the ages its root has been used for dyeing wool and natural silk fibers, but the traditional methods of dyeing suffer from some disadvantages such as the long time required for dyeing, low brightness of fibers, etc. For this reason, the extraction of coloring matters of madder root has been performed and the parameters have been experimentally optimized. In the present article, a brief explanation of the methods, and the design procedure for the extraction unit, along with other extraction conditions have been thoroughly investigated. Equilibrium data for solid-liquid in the leaching process at different temperatures as well as different solvents have been experimentally obtained. © Shiraz University.
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University of Isfahan
Address: Isfahan, Azadi Square, University of Isfahan
