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Distribution network expansion planning considering distribution automation system
, Article IET Conference Publications ; Vol. 2013, issue. 615 CP , 2013 ; Fotuhi-Firuzabad, M ; Kazemi, S ; Maslehati, V ; Sharif University of Technology
Abstract
Planning of distribution networks is usually accomplished using a cost-based conventional model that minimizes the total cost of construction and reinforcement of substations and feeders. The resulted expansion plan designed by this cost-based model is not necessarily the best choice for an electrical distribution company (DISCO) in the nowadays deregulated structure. This happening is mainly due to the fact that the utility seeks to maximize its profit in this competitive environment. On the other hand, this model does not consider the upcoming new challenges ahead of distribution systems, such as smart grid and distribution automation technologies. This paper presents a novel profit-based...
Robust H∞ hybrid observer-controller design with application to attitude control of 2-DOF helicopter
, Article ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE) ; Vol. 4A , 2014 ; ISBN: 9780791846476 ; Merat, K ; Salarieh, H ; Alasty, A ; Meghdari, A ; Sharif University of Technology
Abstract
In this paper, a class of uncertain piecewise affine (PWA) systems, subject to system and measurement external disturbances are studied. The uncertainties are assumed to be norm bounded and the external disturbance signals belong to the L2 space. The problem of optimizing the system response in the H?sense, by means of a piecewise affine observer-controller, is formulated as an optimization problem subject to a number of constraints in the form of matrix inequalities. The derived constraints are obtained by considering a partially piecewise quadratic Lyapunov function in combination with the general conditions for H?stability. Then the uncertain PWA approximation of the nonlinear attitude...
Shape optimization of concrete arch dams considering abutment stability
, Article Scientia Iranica ; Vol. 21, issue. 4 , 2014 , p. 1297-1308 ; 10263098 ; Ghaemian, M ; Sharif University of Technology
Abstract
A novel and robust approach is proposed to find the optimum shape of concrete arch dams located on any unsymmetrical shape of a valley. The approach is capable of finding the optimum shape for any given valley type in suitable time, based on abutment stability analysis, against thrust forces from an arch dam. The behavior and stability of a concrete arch dam is strongly dependent on the bedrock on which the dam rests. The stability of the abutment is considered a constraint in the proposed approach. In addition, a new objective function is introduced to decrease the final volume of the arch dam. Furthermore, a computer program was developed, which takes the effect of the dam foundation...
Comparison between different multi-objective approaches to distribution network planning
, Article IET Conference Publications ; Volume 2013, Issue 615 CP , 2013 ; 9781849197328 (ISBN) ; Eini, B. J ; Mirvazand, M ; Safari, M ; Sharif University of Technology
2013
Abstract
Distribution companies try to meet different goals such as increasing profitability, reducing investment and improving reliability indices. Therefore, distribution network planning has converted into complex multi-objective optimization problems. Mathematicians and operation research experts have developed many methods which can be used for solving these problems. Despite all efforts to develop applicable approaches for these problems, there is still no general consensus on project selection policy. Evaluating the strengths and weaknesses of each network optimization strategy selection in pragmatic manner is the objective of current research. In this paper, many methods used in network...
Optimal placement of fast charging station in a typical microgrid in Iran
, Article International Conference on the European Energy Market, EEM ; 2013 ; 21654077 (ISSN); 9781479920082 (ISBN) ; Kashanizadeh, B ; Vakilian, M ; Barband, S. A ; Sharif University of Technology
2013
Abstract
In this work a microgrid is established within the geographical perspective of interest. The characteristics of the grid and its urban are employed to determine the candidate points for establishment of EV charging stations. The investment costs and operation costs are calculated for each station realizing the required constraints. This process resulted in optimum selection of EV stations. The optimization is achieved based on two different types of preliminary assumptions. In the first one, it is assumed to have only one station, while in the second one possibility of having multi-stations is considered. Using the total investment and operation costs as the objective function of...
Robust decentralized voltage control of an islanded microgrid under unbalanced and nonlinear load conditions
, Article Proceedings of the IEEE International Conference on Industrial Technology, Cape Town, South Africa ; Feb , 2013 , Pages 1825-1830 ; 9781467345699 (ISBN) ; Hamzeh, M ; Paridari, K ; Karimi, H ; Bakhshai, A ; Sharif University of Technology
2013
Abstract
This paper presents a new decentralized control strategy for the islanded operation of a microgrid under unknown load conditions. In the islanded mode of operation, the microgrid should provide the load with a set of regulated balanced three-phase voltages. The load which is parametrically and topologically uncertain can also be unbalanced and/or nonlinear. Thus, the use of conventional control strategies results in the poor performance and even instability of the microgrid system. The proposed method assumes that the load current is a measurable disturbance signal. The robust optimal control approaches are used to design a controller to overcome the disturbances resulting from the unknown...
Optimal and suboptimal sensing sequences in multiuser cognitive radio networks
, Article 2012 6th International Symposium on Telecommunications, IST 2012, 6 November 2012 through 8 November 2012 ; November , 2012 , Pages 243-248 ; 9781467320733 (ISBN) ; Nasiri Kenari, M ; Sharif University of Technology
2012
Abstract
Designing proper spectrum decision schemes for cognitive radios (CRs) improves spectral usage efficiency as well as CR network throughput. One of the key effecting factors of the CR network throughput is the spectrum sensing sequences of the secondary users (SUs). In this paper, the SUs throughput maximization through appropriately selecting the sensing sequences of the SUs, called sensing matrix (SM), is investigated. More specifically, first the average throughput of the CR network is evaluated for a given SM in the case of error-free channel sensing. Then, an optimization problem is formulated with the aim to maximize the network throughput by finding the optimal SM. In order to avoid...
Multi-aspect group formation using facility location analysis
, Article Proceedings of the 17th Australasian Document Computing Symposium, ADCS 2012 ; 2012 , Pages 62-71 ; 9781450314114 (ISBN) ; Beigy, H ; Hiemstra, D ; Sharif University of Technology
2012
Abstract
In this paper, we propose an optimization framework to retrieve an optimal group of experts to perform a given multi-aspect task/project. Each task needs a diverse set of skills and the group of assigned experts should be able to collectively cover all required aspects of the task. We consider three types of multiaspect team formation problems and propose a unified framework to solve these problems accurately and efficiently. Our proposed framework is based on Facility Location Analysis (FLA) which is a well known branch of the Operation Research (OR). Our experiments on a real dataset show significant improvement in comparison with the state-of-the art approaches for the team formation...
On Marton's inner bound for broadcast channels
, Article IEEE International Symposium on Information Theory - Proceedings, 1 July 2012 through 6 July 2012 ; July , 2012 , Pages 581-585 ; 9781467325790 (ISBN) ; Nair, C ; Anantharam, V ; Sharif University of Technology
2012
Abstract
Marton's inner bound is the best known achievable region for a general discrete memoryless broadcast channel. To compute Marton's inner bound one has to solve an optimization problem over a set of joint distributions on the input and auxiliary random variables. The optimizers turn out to be structured in many cases. Finding properties of optimizers not only results in efficient evaluation of the region, but it may also help one to prove factorization of Marton's inner bound (and thus its optimality). The first part of this paper formulates this factorization approach explicitly and states some conjectures and results along this line. The second part of this paper focuses primarily on the...
A GES/TS algorithm for the job shop scheduling
, Article Computers and Industrial Engineering ; Volume 62, Issue 4 , 2012 , Pages 946-952 ; 03608352 (ISSN) ; Kianfar, F ; Sharif University of Technology
2012
Abstract
The job shop scheduling problem is a difficult combinatorial optimization problem. This paper presents a hybrid algorithm which combines global equilibrium search, path relinking and tabu search to solve the job shop scheduling problem. The proposed algorithm used biased random sampling to have a better covering of the solution space. In addition, a new version of N6 neighborhood is applied in a tabu search framework. In order to evaluate the algorithm, comprehensive tests are applied to it using various standard benchmark sets. Computational results confirm the effectiveness of the algorithm and its high speed. Besides, 19 new upper bounds among the unsolved problems are found
A filter trust-region algorithm for unconstrained optimization with strong global convergence properties
, Article Computational Optimization and Applications ; Volume 52, Issue 1 , 2012 , Pages 239-266 ; 09266003 (ISSN) ; Mahdavi Amiri, N ; Sharif University of Technology
Abstract
We present a new filter trust-region approach for solving unconstrained nonlinear optimization problems making use of the filter technique introduced by Fletcher and Leyffer to generate non-monotone iterations. We also use the concept of a multidimensional filter used by Gould et al. (SIAM J. Optim. 15(1):17-38, 2004) and introduce a new filter criterion showing good properties. Moreover, we introduce a new technique for reducing the size of the filter. For the algorithm, we present two different convergence analyses. First, we show that at least one of the limit points of the sequence of the iterates is first-order critical. Second, we prove the stronger property that all the limit points...
Optimized compact-support interpolation kernels
, Article IEEE Transactions on Signal Processing ; Volume 60, Issue 2 , November , 2012 , Pages 626-633 ; 1053587X (ISSN) ; Ayremlou, A ; Amini, A ; Marvasti, F ; Sharif University of Technology
2012
Abstract
In this paper, we investigate the problem of designing compact-support interpolation kernels for a given class of signals. By using calculus of variations, we simplify the optimization problem from an nonlinear infinite dimensional problem to a linear finite dimensional case, and then find the optimum compact-support function that best approximates a given filter in the least square sense (ℓ 2 norm). The benefit of compact-support interpolants is the low computational complexity in the interpolation process while the optimum compact-support interpolant guarantees the highest achievable signal-to-noise ratio (SNR). Our simulation results confirm the superior performance of the proposed kernel...
Impacts of controlled and uncontrolled PHEV charging on distribution systems
, Article IET Conference Publications ; Volume 2012, Issue 616 CP , 2012 ; 9781849197434 (ISBN) ; Fotuhi Firuzabad, M ; Rastegar, M ; Sharif University of Technology
Institution of Engineering and Technology
2012
Abstract
Plug-in hybrid electric vehicle (PHEV) technology provides one of the most promising solutions to tackle the threatening challenges such as air pollution in urban areas. Dramatic increases in the number of PHEVs could have major impacts on power system operations because of their high electricity demand. From the distribution system operator facet, distribution system congestion during PHEVs charging is an economic and security concern. It is, therefore, necessary to investigate the effects of widespread using of PHEVs on the performance of distribution networks. In this paper, PHEV characteristics are exactly studied and a comprehensive model for investigation of PHEV impacts is achieved....
Multi-objective optimization of functionally graded hollow cylinders
, Article ASME 2011 International Mechanical Engineering Congress and Exposition, IMECE 2011 ; Volume 8 , 2011 , Pages 583-590 ; 9780791854945 (ISBN) ; Ahmadian, M. T ; ASME ; Sharif University of Technology
Abstract
In this study, two physical properties of simply supported hollow cylinders made of functionally graded materials are investigated. These two properties are mass and first natural frequency which is desirable to be minimized and maximized respectively in mechanical applications. The functionally graded material properties are assumed to vary continuously through the thickness of the cylinder. In this multi-objective optimization problem the first natural frequency of the FGM cylinders as well as its mass are formulated in terms of the volume fraction of the constituents, then by using Genetic algorithm optimization method the continuous volume fraction function of the constituents has been...
CRA based control of fractional order systems subject to control signal constraint
, Article International Conference on Control, Automation and Systems ; 2011 , Pages 268-272 ; 15987833 (ISSN) ; 9781457708350 (ISBN) ; Haeri, M ; Sharif University of Technology
Abstract
An approach is proposed to control transient response of fractional order systems with maximum permissible control signal. This goal is achieved using a newly suggested characteristic ratio assignment method. Based on the proposed method, the generalized time constant τ and the characteristic ratios including their pattern, an adjustable parameter β, and the product of two successive characteristic ratios ρ are determined such that predefined level of overshoot and time specification of closed loop step response are obtained while the control signal is confined to a pre assigned maximum magnitude. The raised issue is solved by defining an optimization problem in which the design parameters...
Transmit beampattern synthesis using eigenvalue decomposition in MIMO radar
, Article ICICS 2011 - 8th International Conference on Information, Communications and Signal Processing, 13 December 2011 through 16 December 2011 ; December , 2011 , Page(s): 1 - 5 ; 9781457700309 (ISBN) ; Behnia, F ; Sharif University of Technology
2011
Abstract
MIMO radar is the next generation radar which transmits arbitrary waveforms at each one of its apertures. It has been shown that design of waveforms for MIMO radars in order to synthesize a desired spatial beampattern is mapped into a waveform correlation matrix (R) design in the narrowband case. Searching for desired R has been modeled as a convex optimization problem which demands considerable processing power. There are also some close form solutions for special cases like rectangular beampatterns. Here we deal with the problem from a matrix eigenvalue theory perspective and show how close form solutions can be found for more general cases relaxing high computational power demand. Our...
Statistical design of genetic algorithms for combinatorial optimization problems
, Article Mathematical Problems in Engineering ; Volume 2011 , 2011 ; 1024123X (ISSN) ; Najafi, A. A ; Niaki, S. T. A ; Sharif University of Technology
2011
Abstract
Many genetic algorithms (GA) have been applied to solve different NP-complete combinatorial optimization problems so far. The striking point of using GA refers to selecting a combination of appropriate patterns in crossover, mutation, and and so forth and fine tuning of some parameters such as crossover probability, mutation probability, and and so forth. One way to design a robust GA is to select an optimal pattern and then to search for its parameter values using a tuning procedure. This paper addresses a methodology to both optimal pattern selection and the tuning phases by taking advantage of design of experiments and response surface methodology. To show the performances of the proposed...
Design of low order dynamic pre-compensators using convex methods
, Article Proceedings of the American Control Conference, 29 June 2011 through 1 July 2011, San Francisco, CA ; 2011 , Pages 3680-3685 ; 07431619 (ISSN) ; 9781457700804 (ISBN) ; Nejati, A ; Nobakhti, A ; Karimi, H ; Sharif University of Technology
2011
Abstract
Pre-compensators are used in multivariable control systems to reduce (or eliminate) open loop system interactions. Classical methods for the design of pre-compensator are traditionally based on static designs. Static pre-compensators are preferred for their simplicity, but are highly unsystematic in the amounts of achievable diagonal dominance. In many applications, only the more powerful dynamic pre-compensators are able to deliver the desired amounts of decoupling. This paper proposes a new method for the design of dynamic pre-compensators which is based on a Quadratic Programming (QP) optimization. Using the proposed approach the total pre-compensator is found through several smaller...
Conditional distribution inverse method in generating uniform random vectors over a simplex
, Article Communications in Statistics: Simulation and Computation ; Volume 40, Issue 5 , Dec , 2011 , Pages 685-693 ; 03610918 (ISSN) ; Abbasi, B ; Mahlooji, H ; Sharif University of Technology
Abstract
Motivated by numerous applications in Monte Carlo techniques and as of late, in deriving non dominated solutions in multi-objective optimization problems, this article addresses generating uniform random variables (λi, λi ≥ 0, i = 1,..., n) over a simplex in ℝ2 (n ≥ 2), i.e., Σi=1 n λi = 1. In this article, first, conditional distribution of λi where Σi=1 n λi = 1 is derived and then inverse method is applied to generate random variables
Streamline-based history matching constrained to reservoir geostatistics using gradual deformation technique
, Article Petroleum Science and Technology ; Volume 29, Issue 17 , 2011 , Pages 1765-1777 ; 10916466 (ISSN) ; Pishvaie, M. R ; Kamali, M. R ; Badakhshan, A ; Sharif University of Technology
Abstract
A new and general procedure for history matching that uses streamline simulation and a gradual deformation technique has been proposed. Streamline trajectories define the major flow paths and help the algorithm to modify the reservoir model only in the regions that cause the mismatch between simulation results and field observations. The use of a gradual deformation technique enables the algorithm to remain constrained to reservoir geostatistics. It also reduces the number of independent variables in the optimization problem. In our algorithm, effective conductivities are defined along each streamline. The effective streamline conductivities are then adjusted using the values of measured and...