Search for: planning-horizons
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    Planning of multi-hub energy system by considering competition issue

    , Article International Journal of Sustainable Energy Planning and Management ; Volume 30 , 2021 , Pages 5-20 ; 22462929 (ISSN) Farshidian, B ; Rajabi Ghahnavieh, A ; Haghi, E ; Sharif University of Technology
    Aalborg University press  2021
    Energy hub concept has been emerged as a suitable tool to analyze multi-carrier energy systems. Deregulation and increasing competition in the energy industry have provided a suitable platform for developing the multi-agent energy systems. Planning of energy hubs considering the competition between the hubs has not been sufficiently addressed, yet. A model has been proposed in this study for planning of a multi-hub energy system considering the competition between the hubs. The hubs are interconnected via an electric transmission system. A linear model has been developed to determine the optimal planning/operation strategy for energy hubs in a multi-period planning horizon to meet the heat... 

    A new order splitting model with stochastic lead times for deterioration items

    , Article International Journal of Systems Science ; Vol. 45, Issue. 9 , 2014 , pp. 1936-1954 ; ISSN: 00207721 Sazvar, Z ; Jokar, M. R. A ; Baboli, A ; Sharif University of Technology
    In unreliable supply environments, the strategy of pooling lead time risks by splitting replenishment orders among multiple suppliers simultaneously is an attractive sourcing policy that has captured the attention of academic researchers and corporate managers alike. While various assumptions are considered in the models developed, researchers tend to overlook an important inventory category in order splitting models: deteriorating items. In this paper, we study an order splitting policy for a retailer that sells a deteriorating product. The inventory system is modelled as a continuous review system (s, Q) under stochastic lead time. Demand rate per unit time is assumed to be constant over... 

    A novel deterministic model for simultaneous weekly assignment and scheduling decision-making in operating theaters

    , Article Scientia Iranica ; Volume 24, Issue 4 , 2017 , Pages 2035-2049 ; 10263098 (ISSN) Haghi, M ; Fatemi Ghomi, S. M. T ; Hooshangi Tabrizi, P ; Sharif University of Technology
    This paper studies a simultaneous weekly assignment and scheduling decisionmaking problem in operating theaters with elective patients. Because of limited recourses in hospitals, considering assignment and scheduling decisions simultaneously can help mangers exploit the available resources more efficiently and make the work-load uniformly distributed during the planning horizon. This procedure can significantly reduce hospital costs and increase satisfaction of patients and personnel. This paper formulates the mentioned problem as a Mixed Integer Linear Program (MILP) considering applicable assumptions like finite recovery beds and limitation of equipment. Since the problem is NP-hard, in... 

    A replenishment policy for perishable products with non-linear holding cost under stochastic supply lead time

    , Article International Journal of Advanced Manufacturing Technology ; Volume 64, Issue 5-8 , 2013 , Pages 1087-1098 ; 02683768 (ISSN) Sazvar, Z ; Baboli, A ; Akbari Jokar, M. R ; Sharif University of Technology
    The development and application of inventory models for deteriorating items is one of the main concerns of subject matter experts. The inventory models developed in this field have focused mainly on supply chains under the assumption of constant lead time. In this study, we develop an inventory model for a main class of deteriorating items, namely perishable products, under stochastic lead time assumption. The inventory system is modeled as a continuous review system (r, Q). Demand rate per unit time is assumed to be constant over an infinite planning horizon and the shortages could be backordered completely. For modeling the deterioration process, a non-linear holding cost is considered.... 

    A hybrid polynomial-time algorithm for the dynamic quantity discount lot size model with resale

    , Article Computers and Operations Research ; Volume 39, Issue 7 , 2012 , Pages 1771-1778 ; 03050548 (ISSN) Mirmohammadi, H. S ; Eshghi, K ; Sharif University of Technology
    We propose an efficient optimal algorithm for determining the lot sizes for purchase component in Material Requirement Planning (MRP) environments with deterministic time-phased demand and zero lead time. In this model, backlog is not permitted, the unit purchasing price is based on the all-units discount system with single price break point and resale of the excess units is acceptable at the ordering time. The problem is divided into the sub-plans with specific properties by the dynamic programming (DP) method already presented. By modifying the main structure of the DP method, we present a branch-and-bound algorithm to obtain the optimal ordering policy for each sub-plans. Furthermore, we... 

    Lot sizing and lead time quotations in assembly systems

    , Article Scientia Iranica ; Volume 16, Issue 2 E , 2009 , Pages 100-113 ; 10263098 (ISSN) Kianfar, F ; Mokhtari, G ; Sharif University of Technology
    In this paper, a simultaneous lead time quotation and lot sizing problem in an assembly system is investigated. We address a production system with a product that has deterministic demand over a T-period planning horizon and is produced in lots because of the economy of scale. If a lot is completed before the demand period, inventory carrying cost is incurred. On shortages, a lead time is quoted to customers and a lead time quotation cost is incurred. Finally, if the order is delivered later than its due date period, a tardiness cost is charged. The components supply lead time is stochastic, which follows a discrete distribution. The problem is to decide on the lot size of products and... 

    Multi objective distributed generation planning using NSGA-II

    , Article 2008 13th International Power Electronics and Motion Control Conference, EPE-PEMC 2008, Poznan, 1 September 2008 through 3 September 2008 ; 2008 , Pages 1847-1851 ; 9781424417421 (ISBN) Ahmadi, M ; Yousefi, A ; Soroudi, A ; Ehsan, M ; Sharif University of Technology
    With the increasing share of distributed generation in electrical energy supply, the proper planning procedure for using these units, has become more vital for power system planners. In this paper, the application of multi-objective optimization techniques for siting, sizing and determination of the proper technology to be used, has been investigated in such a way that, the load demand during the planning horizon is met and the technical and environmental constraints are satisfied. Unlike the traditional optimization methods used in power system optimization, NSGA-II multi-objective optimization algorithm does not consider techno-economical and environmental parameters in the constraints of... 

    Development of a dynamic long-term water allocation model for agriculture and industry water demands

    , Article Water Resources Management ; Volume 24, Issue 9 , 2010 , Pages 1717-1746 ; 09204741 (ISSN) Karimi, A ; Ardakanian, R ; Sharif University of Technology
    Demands growth and water resources limitation, enforce water sector policy makers to integrate water supply-demand interactions in a coherent framework for efficient water allocation. Water supply-demand interaction, changes long-term trend of water demands, which in turn has a substantial influence on water allocation. Researches on water allocation modeling lack adequate projection of relationship between water supply and demand. Socio-economic factors representing water allocation stakeholders' benefits, account for the main share of water supply-demand interaction. Identification, representation and consideration of these factors in a water allocation model, is the main limitation of... 

    Dynamic economic evaluation of distribution automation systems

    , Article 2009 International Conference on Electric Power and Energy Conversion Systems, EPECS 2009 ; 2009 ; 9789948427155 (ISBN) Rahmani, S ; Ehsan, M ; Sharif University of Technology
    In a deregulated environment of power distribution industry, a comprehensive economic evaluation for the implementation of distribution automation (DA) systems is inevitable. Using the presented methodology in this paper and system dynamics approach, it is efficiently possible to deal with variation of the economic parameters such as the interest rate, inflation rate, energy supply cost, load growth, etc. In this paper, economic short-run and long-run impacts of DA systems are evaluated from utility point of view. Also economic benefits from customers' point of view are analyzed. A practical pricing strategy for maximizing the utility profit is suggested depending on the underlying market... 

    Application of a maintenance management model for iranian railways based on the markov chain and probabilistic dynamic programming

    , Article Scientia Iranica ; Volume 16, Issue 1 A , 2009 , Pages 87-97 ; 10263098 (ISSN) Shafahi, Y ; Hakhamaneshi, R ; Sharif University of Technology
    Railway managers have a strong economic incentive to minimize track maintenance costs, while maintaining safety standards and providing adequate service levels to train operators. The objective of this study is to apply a procedure for making optimal maintenance decisions in Iranian Railways. This study consists of two parts. First, a cumulative damage model, based on a Markov process, is applied to model the deterioration of the track. For this reason, tracks are categorized into six classes, so that those tracks with similar traffic loads and geographical location are collected into one class. The track survey data from 215 blocks (4,228 km) of the ten divisions of the Iranian Railway...