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optimal-timing
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Simulation of endurance time excitations via wavelet transform
, Article Iranian Journal of Science and Technology - Transactions of Civil Engineering ; Volume 43, Issue 3 , 2019 , Pages 429-443 ; 22286160 (ISSN) ; Estekanchi, H. E ; Vafai, H ; Sharif University of Technology
Springer International Publishing
2019
Abstract
This paper puts forth a wavelet-based methodology for generating endurance time (ET) excitations. Conventional simulating practice expresses signals by acceleration values which are then computed via unconstrained nonlinear optimization. Dynamic characteristics of signals, including frequency content, are not represented directly in this type of variable definition. In this study, a new algorithm is developed to generate ET excitations in discrete wavelet transform (DWT) space. In this algorithm, signals are represented by transform coefficients. In addition, objective functions are modified in order to obtain transform coefficients and return the objective function values. The proposed...
Enhanced time-expanded decision network: The original TDN and more
, Article Systems Engineering ; Volume 18, Issue 4 , 2015 , Pages 415-429 ; 10981241 (ISSN) ; Sharif University of Technology
John Wiley and Sons Inc
2015
Abstract
This paper suggests several improvements over the original Time-expanded Decision Network (TDN; a powerful and generic methodology introduced by Silver and de Weck for designing evolvable complex systems) in order to leverage its ease, flexibility, and scope of use. A more accurate model of the switching process, a simpler network representation, and the ability to address systems with unknown lifetime are some of the improvements. However, the most important added feature is the ability to account for other design requirements within the process, which enables the designers to embed the TDN methodology into their general concept exploration phase. As a result, the enhanced TDN (ETDN)...
Analysis and Improvement of Transients and Stability of Electric Shipboards Against Load Disturbances
, M.Sc. Thesis Sharif University of Technology ; Parniani, Mostafa (Supervisor)
Abstract
Nowadays, According to the improvement of technology, especially in power electronics, electric shipboards are preferred over traditional ones. Better maneuverability, lower emission, higher efficiency and reliability are the most conspicuous merits of this type of ships. Notwithstanding the fact that electric shipboards have many advantages, some serious problems may arise in these ships. Since the thruster motors of these ships are usually induction motors and they are fed by the microgrid of the ship, and taking into ACcount that thruster motors consume a huge amount of the generated power by the synchronous generators, the concept of infinite bus is inexistent in these microgrids. Hence,...
Spectral controllability of some singular hyperbolic equations on networks
, Article Journal of Dynamical and Control Systems ; 2016 , Pages 1-22 ; 10792724 (ISSN) ; Salimi, L ; Sharif University of Technology
Springer New York LLC
2016
Abstract
The purpose of this paper is to address the question of well-posedness and spectral controllability of the wave equation perturbed by potential on networks which may contain unbounded potentials in the external edges. It has been shown before that in the absence of any potential, there exists an optimal time T∗ (which turns out to be simply twice the sum of all length of the strings of the network) that describes the spectral controllability of the system. We will show that this holds in our case too, i.e., the potentials have no effect on the value of the optimal time T∗. The proof is based on the famous Beurling-Malliavin’s Theorem on the completeness interval of real exponentials and on a...
Spectral controllability of some singular hyperbolic equations on networks
, Article Journal of Dynamical and Control Systems ; Volume 23, Issue 3 , 2017 , Pages 459-480 ; 10792724 (ISSN) ; Salimi, L ; Sharif University of Technology
Abstract
The purpose of this paper is to address the question of well-posedness and spectral controllability of the wave equation perturbed by potential on networks which may contain unbounded potentials in the external edges. It has been shown before that in the absence of any potential, there exists an optimal time T∗ (which turns out to be simply twice the sum of all length of the strings of the network) that describes the spectral controllability of the system. We will show that this holds in our case too, i.e., the potentials have no effect on the value of the optimal time T∗. The proof is based on the famous Beurling-Malliavin’s Theorem on the completeness interval of real exponentials and on a...
Optimal state-feedback design for non-linear feedback-linearisable systems
, Article IET Control Theory and Applications ; Volume 5, Issue 2 , 2011 , Pages 323-333 ; 17518644 (ISSN) ; Farokhi, F ; Karimi-Ghartemani, M ; Sharif University of Technology
2011
Abstract
This paper addresses the problem of optimal state-feedback design for a class of non-linear systems. The method is applicable to all non-linear systems which can be linearised using the method of state-feedback linearisation. The alternative is to use linear optimisation techniques for the linearised equations, but then there is no guarantee that the original non-linear system behaves optimally. The authors use feedback linearisation technique to linearise the system and then design a state feedback for the feedback-linearised system in such a way that it ensures optimal performance of the original non-linear system. The method cannot ensure global optimality of the solution but the global...
One-for-one period policy in a two-echelon inventory system with commoncycle and poisson demand rate for retailers
, Article 2009 International Conference on Computers and Industrial Engineering, CIE 2009 ; 2009 , Pages 831-834 ; 9781424441365 (ISBN) ; Tayebi, H ; Haji, B ; Sharif University of Technology
Abstract
This paper deals with a two-echelon inventory system consisting of onesupplier and N retailers. Each retailer faces an independent Poisson demand withthe same rate and applies a new ordering policy called one-for-one- periodordering policy for its inventory control. In this ordering policy the ordersize is equal to one and the time interval between any two consecutive ordersforms a common fixed cycle. Thus, the supplier faces a deterministic demand andadopts a deterministic inventory policy. At each cycle he orders a batch of sizeN to his own supplier. Upon receipt of each batch he sends 1 unit of theproduct to each retailer with a transportation cost. In this paper, for theabove system we...
One-for-one period policy in a two-echelon inventory system with poisson demand and constraint on total lost sales
, Article 2009 IEEE/INFORMS International Conference on Service Operations, Logistics and Informatics, SOLI 2009, Chicago, IL, 22 July 2009 through 24 July 2009 ; 2009 , Pages 74-77 ; 9781424435418 (ISBN) ; Haji, B ; Sharif University of Technology
2009
Abstract
In this paper we consider a two- echelon inventory system consisting of one supplier and a number of retailers with independent Poisson demand. Unsatisfied demands in retailers are lost and it is assumed that there is a constraint on total lost sales for the system. Each retailer applies a new ordering policy called one-fer-one-peried ordering policy for its inventory control. In this ordering policy the order size is equal to one and the time interval between any two consecutive orders is fixed. Thus, the supplier faces a uniform and deterministic demand originated from each retailer and applies one for one ordering policy in response to orders received from all retailers. For this system...
A model for the time dependent vehicle routing problem with time windows under traffic conditions with intelligent travel times
, Article RAIRO - Operations Research ; Volume 55, Issue 4 , 2021 , Pages 2203-2222 ; 03990559 (ISSN) ; Shahmizad, M ; Mahdavi, I ; Mahdavi Amiri, N ; Ghasemi, P ; Sharif University of Technology
EDP Sciences
2021
Abstract
A new mixed-integer nonlinear programming model is presented for the time-dependent vehicle routing problem with time windows and intelligent travel times. The aim is to minimize fixed and variable costs, with the assumption that the travel time between any two nodes depends on traffic conditions and is considered to be a function of vehicle departure time. Depending on working hours, the route between any two nodes has a unique traffic parameter. We consider each working day to be divided into several equal and large intervals, termed as a time interval of traffic. Here, allowing for long distances between some of the nodes, travel time may take more than one time interval of traffic,...
Time-varying dual accelerated gradient ascent: A fast network optimization algorithm
, Article Journal of Parallel and Distributed Computing ; Volume 165 , 2022 , Pages 130-141 ; 07437315 (ISSN) ; Mahdavi Amiri, N ; Sharif University of Technology
Academic Press Inc
2022
Abstract
We propose a time-varying dual accelerated gradient method for minimizing the average of n strongly convex and smooth functions over a time-varying network with n nodes. We prove that the time-varying dual accelerated gradient ascent method converges at an R-linear rate with the time to reach an ϵ-neighborhood of the solution being of O([Formula presented]ln[Formula presented]), where c is a constant depending on the graph and objective function parameters and M is a constant depending on the initial values. We test the proposed method on two classes of problems: L2-regularized least squares and logistic classification problems. For each class, we generate 1000 problems and use the...
Soil-buried wave barriers for vibration control of structures subjected to vertically incident shear waves
, Article Soil Dynamics and Earthquake Engineering ; Volume 109 , 2018 , Pages 312-323 ; 02677261 (ISSN) ; Rafiee dehkharghani, R ; Mohtasham dolatshahi, K ; Mirghaderi, R ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
Traditionally, the effects of seismic forces on structures have been mitigated by installing supplemental energy dissipation systems. In this paper, a new approach is explored for the mitigation of earthquake-induced vibrations by obstructing the entrance of seismic energy to the structure through the insertion of some concrete wave barriers within the soil domain. To do so, genetic algorithm (GA) based adaptive optimization methodology is utilized that is capable of finding the efficient layout of the concrete barriers in a manipulated soil zone around the structure. The optimization methodology is coupled with finite element (FE) method for analyzing the complex wave propagation phenomenon...
Stochastic modeling of the energy supply system with uncertain fuel price - A case of emerging technologies for distributed power generation
, Article Applied Energy ; Volume 93 , 2012 , Pages 668-674 ; 03062619 (ISSN) ; Saboohi, Y ; Sharif University of Technology
2012
Abstract
A deterministic energy supply model with bottom-up structure has limited capability in handling the uncertainties. To enhance the applicability of such a model in an uncertain environment two main issues have been investigated in the present paper. First, a binomial lattice is generated based on the stochastic nature of the source of uncertainty. Second, an energy system model (ESM) has been reformulated as a multistage stochastic problem. The result of the application of the modified energy model encompasses all uncertain outcomes together and enables optimal timing of capacity expansion. The performance of the model has been demonstrated with the help of a case study. The case study has...
Design Optimization of a Ladder Secondary Single-Sided Linear Induction Motor for Improved Performance
, Article IEEE Transactions on Energy Conversion ; Volume 30, Issue 4 , 2015 , Pages 1595-1603 ; 08858969 (ISSN) ; Nasiri Gheidari, Z ; Sharif University of Technology
Abstract
In this paper, design and optimization of a ladder-type single-sided linear induction motor (Ladder SLIM) for machine tool applications is investigated. High-speed linear induction machines suffer from the end-effect phenomenon, which can reduce the thrust and result in declined output characteristics. Although it is common to consider this phenomenon in high-speed applications, it is essential to take it into account in the design and analysis of low-speed low-air-gap linear machines. In addition, Ladder SLIMs have significant flux density ripples, and using skewed bars for secondary of the machine is a common solution for it. Therefore, providing required equations, an algorithm for...
Performance limits of optical clock recovery systems based on two-photon absorption detection scheme
, Article IEEE Journal on Selected Topics in Quantum Electronics ; Volume 14, Issue 3 , 2008 , Pages 963-971 ; 1077260X (ISSN) ; Salehi, J. A ; Sharif University of Technology
2008
Abstract
In this paper, we analyze and discuss the performance limits of optical clock recovery systems using a phase-locked loop (PLL) structure with nonlinear two-photon absorption (TPA) phase detection scheme. The motivation in analyzing the aforementioned optical PLL with TPA receiver structure is due to a recent successful experiment reported in [8]. We characterize the mathematical structure of PLLs with TPA, so as to evaluate the performance limits on optical clock recovery mechanism. More specifically, we identify two intrinsic sources of phase noise in the system namely, the ON-OFF nature of the incoming data pulses and the detector's shot noise that ultimately limit the performance of the...