Sharif Digital Repository

In directional drilling, the most important thing that leads to pulling out the drill string is end of mud motor working life. Considering the working conditions of down hole mud motors; increasing the mechanical properties of their stator’s elastomer is crucial. Some attempts were done to increase the motor performance through geometrical changes but lack of material improvement is significant in previous studies. In this study, NBR/nanoclay composite samples were prepared through melt intercalation in an internal mixer and tested with regard to the temperature and drilling mud of down hole. Hardness, tear, fatigue and tensile test results of neat NBR elastomer and nanocomposite of NBR and... 

Regarding the increasing number of electrical devices in the smart homes that leads to increase in total electricity consumption and cost, it is essential to use energy management methods to reduce the electricity cost. However, this can cause resident's dissatisfaction. Hence, it is important to define a method in which cost and dissatisfaction be optimized simultaneously. Among different services, an electric vehicle is the one that can be used as an energy storage system, so it can reduce the daily cost despite of increasing the total energy consumption. In this paper, we study the effect of the EV on the cost and dissatisfaction in our proposed method. © 2018 IEEE  

An adaptive approach for distribution system reconfiguration and charging management of plug-in electric vehicles (PEV) is presented in this study. A stochastic model predictive control is applied to stochastically, adaptively, and dynamically reconfigure the system, manage the incidental charging pattern of PEVs, and deal with the variable and uncertain power of renewable energy sources. The objective function of problem is minimizing daily operation cost of system. Herein, the geography of area is considered and the behavior of PEVs' drivers (based on their income level) is modeled with respect to the value of incentive and their hourly distance from each charging station. It is shown that... 

Spin-Transfer Torque Random Access Memories (STT-RAMs) are a promising alternative to SRAMs in on-chip caches. STT-RAMs face with a high error rate in write operations due to stochastic switching. To alleviate this problem, Error-Correcting Codes (ECCs) are commonly used, which results in a significant area and energy consumption overhead. This paper proposes an efficient technique, so-called Adaptive Way Allocation for Reconfigurable ECCs (AWARE), to correct write errors in STT-RAM caches. AWARE exploits the asymmetric error rate in cell switching directions, which leads to data-dependent write error rates, to reduce the ECC overheads without compromising the reliability of the cache. To... 

For the purposes of lowering environmental emission cost and increasing economic profit, energy efficient combined heat and power (CHP) units can be integrated with conventional separate heat and power production units to meet heat and power demands. The goal of this study is to develop and examine a novel heuristic and deterministic optimization algorithm for solving the profit-based unit commitment (PBUC) problem for a generation company with integrated CHP-thermal-heat only system for (i) satisfying demands for heat and power, (ii) selling spinning reserve for power, (iii) reducing environmental CO2 emission cost, and (iv) accounting for valve-point effects for steam turbines. For... 

The present study conducts a comprehensive comparative techno-economic analysis of some near-term sensible thermal energy storage (TES) alternatives to the ‘standard’ two-tank molten salt system for concentrated solar power (CSP) plants. As such, we conducted detailed, relative annual transient simulations for single-medium thermocline (SMT), dual-media thermocline (DMT), and shell-and-tube (ST) systems. To be consistent with recent literature, the DMT and ST systems use concrete with a porosity of 0.2 (e.g. where concrete occupies 80% of the system) as their low cost filler material. The systems were integrated into a validated 19.9 MWe Gemasolar CSP model, which has a solar multiple of... 

Recent developments in improving lighting efficiency and cost reduction of LEDs have made them suitable alternatives to the current lighting systems. In this paper, a novel offline structure is proposed to drive LEDs. The proposed circuit has a high-input power factor, high efficiency, a long lifetime, and it produces no flicker. To increase the lifetime of the converter, the proposed circuit does not include any electrolytic capacitors in the power stage. The proposed circuit consists of a transition mode flyback converter in order to improve power factor. Additionally, a buck converter is added to the third winding of the flyback transformer in order to create two parallel paths for the... 

Refrigerators have considerable share of residential consumption. They can be, however, flexible loads because their operating time and consumption patterns can be changed to some extent. Accordingly, they can be selected as a target for the study of Demand Side Management plans. In this paper, two experimental models for a refrigerator are derived. In obtaining the first model, following assumptions are made: the ambient temperature of refrigerator is assumed to be constant and the refrigerator door is remained closed. However, in the second model the variation of ambient temperature and door-opening effects are considered according to some general patterns. Further, two strategies are... 

For a simple polygon P of size n, we define weak visibility counting problem (WVCP) as finding the number of visible segments of P from a query line segment pq. We present different algorithms to compute WVCP in sub-linear time. In our first algorithm, we spend O(n7) time to preprocess the polygon and build a data structure of size O(n6), so that we can optimally answer WVCP in O(logn) time. Then, we reduce the preprocessing costs to O(n4+ε) time and space at the expense of more query time of O(log5n). We also obtain a trade-off between preprocessing and query time costs. Finally, we propose an approximation method to reduce the preprocessing costs to O(n2) time and space and O(n1/2+ε) query... 

The capability level of rotary as well as first generation drilling operation could not be matched for deeply drilling programs. To reach that deep, the increasing in drill string length could also cause an additional constraint on hydraulic performance. The operation of slim hole drilling has significant potential to reduce well costs. This cost might be savings are especially important with increased demand for reduced capital finance under current economic conditions in the Iranian oil and gas industry. This savings achievement could be caused by use of smaller drilling rigs, work over rigs, reduced casing size, reducing requirement for drilling consumables and other costs associated with... 

Purpose - The purpose of this paper is to analyze the effects of supply chain coordination on inventory management while the retailer inventory cycle consists of a shortage period and the backorder rate linearly decreases as a function of shortage duration. It is intended to consider how on-hand inventory and shortage durations are altered when the decisions are centralized. Design/methodology/approach - Mathematical modelling of inventory costs for the retailer and the vendor is used to formulate objective functions. The vendor sets his inventory period as an integer multiple (n) of the retailer inventory cycle in which the integer multiple is a decision variable. Solution spaces of models... 

Recently, there has been a growing attention in frequent itemset mining in distributed systems. In this paper, we present an algorithm to extract frequent itemsets from large distributed datasets. Our algorithm uses gossip as the communication mechanism and does not rely on any central node. In gossip based communication, nodes repeatedly select other random nodes in the system, and exchange information with them. Our algorithm proceeds in rounds and provides all nodes with the required support counts of itemsets, such that each node is able to extract the global frequent itemsets. For local iteration and generation of candidate itemsets, a trie data structure is used, which facilitates the... 

Nowadays, companies strive to survive in a competitive global environment. Reduction of product development cycle plays a major role in market penetration and cost reduction. To speed up product development/modifications, it is suggested to adopt a collaborative product development approach. Collaborative design and manufacture requires an integrated platform to support related CAx product data models. To integrate CAx product data, a number of solutions are proposed. The most successful solution is adopting the STandard for Exchange of Product Data (STEP). In the course of the STEP standard structure and procedure development, two approaches can be recognised: classical and modular. The... 

Cooperation among supply chain members, both horizontally and vertically, has become the norm in practice. Unlike traditional supply chains with members competing to reduce their individual costs, the overall cost of the entire supply chain is minimized in a cooperative supply chain. The savings from cooperation may be shared among the members, while a lower average cost and a lower cost variation is materialized for individual members. The problem is formulated as an integrated flow network and expanded to multi-period and multi-product, with the possibility of holding inventories in a multi-stage, multi-member cooperative supply chain. Simulation results indicate an approximately 26%... 

Direct steam generation (DSG) in parabolic trough collectors causes an increase to competitiveness of solar thermal power plants (STPP) by substitution of oil with direct steam generation that results in lower investment and operating costs. In this study the integrated solar combined cycle system with DSG technology is introduced and techno-economic assessment of this plant is reported compared with two conventional cases. Three considered cases are: an integrated solar combined cycle system with DSG technology (ISCCS-DSG), a solar electric generating system (SEGS), and an integrated solar combined cycle system with HTF (heat transfer fluid) technology (ISCCS-HTF).This study shows that... 

Nowadays, software product line is an approach to reduce costs of software development, decrease time to market, and increase capabilities of reuse in designing and exploiting software development processes. Moreover, other quality attributes of the project domain should be considered to enhance quality of the product. Meanwhile, taking advantage of software product line makes developers capable of estimating development costs and time to market in a more realistic way. However, old approaches to estimate cost of development and foresee time to market are not suitable enough for software product line. In this paper, some important business parameters and a way to calculate cost and time to... 

Nowadays, product line, as an important topic in software development domain, has been paid attention by software engineering practitioners. Finding suitable components to construct an efficient and comprehensive product line with low costs is one of the critical problems in this domain which demands to be satisfied. In this paper a method is presented which can manage and control complexities of component selection problem, an NP problem, and result in creation of declared product line. By making use of this method, a product line will be constructed with suitably-adopted components to cover up requirements based on architecture; that's why software product line development process will... 

Sensor networks are increasingly employed in many applications ranging from environmental to military cases. The network topology used in many sensor network applications has a kind of geographical structure. A graph weighting method for reducing consensus time in random geographical networks is proposed in this paper. We consider a method based on the mutually coupled oscillators for providing general consensus in the network. In this way, one can relate the consensus time to the properties of the Laplacian matrix of the connection graph, i.e. to the second smallest eigenvalue (algebraic connectivity). Our weighting algorithm is based on the node and edge between centrality measures. The... 

This paper introduces a new framework included mathematical model and a new software package interfacing two powerful softwares (MATLAB and GAMS) for obtaining the optimal distributed generation (DG) capacity sizing and sitting investments with capability to simulate large distribution system planning. The proposed optimization model allows minimizing total system planning costs for DG investment, DG operation and maintenance, purchase of power by the distribution companies (DISCOs) from transmission companies (TRANSCOs) and system power losses. The proposed model provides not only the DG size and site but also the new market price as well. Three different cases depending on system... 

Recent researches have shown the importance of improving the supply chain competitiveness by means of strategic alliances. This study considers the retailer-supplier partnership through a vendor-managed inventory (VMI) system and develops an analytical model to explore the effect of important supply chain parameters on the cost savings realized from collaborative initiatives. This model is developed for a two-level supply chain consisting of a single supplier and a single retailer and examines the inventory management practices before and after implementation of VMI. The results of analytical examination show that VMI implementation in economic order quantity model when shortage is...