Sharif Digital Repository

Energy hubs that incorporate a variety of energy generation and energy transformation technologies can be used to provide the energy storage needed to enable the efficient operation of a ‘smart energy network’. When these hubs are combined as a network and allowed to exchange energy, they create efficiency advantages in both financial and environmental performance. Further, the interconnectedness of the energy network design provides an added layer of reliability. In this paper, a complex network of energy hubs is modeled and optimized under different scenarios to examine both the financial viability and potential reduction of greenhouse gas emissions. Two case studies consisting of two and... 

In this study, hybrid renewable energy system based on wind/electrolyzer/PEM fuel cell are conceptually modeled, and also, exergy and energy analysis are performed. The energy and exergy flows are investigated by the proposed model for Khaf region-Iran with high average wind speed and monsoon. Exergy and energy analysis framework is made based on thermodynamic, electro-chemical and mechanical model of the different component of hybrid system. Also, the effects of various operating parameters in exergy efficiency are calculated. The results show an optimum wind speed where the exergy efficiency and power coefficient is at maximum level, and also, when the ambient temperature start to be... 

Wireless sensor networks (WSNs) comprise a large number of small sensor nodes scattered across limited geographical areas. The nodes in such networks carry sources of limited and mainly unchangeable energy. Therefore, it is necessary that these networks operate under energy efficient protocols and structures. Energy efficient clustering algorithms have been developed to reduce the networks energy consumption and extend its lifetime. This paper presents an innovative cluster-based communication protocol for WSNs. In order to reduce communication overhead, the authors propose an Energy Aware Clustering Hierarchy Protocol that creates a multi-level hierarchical structure to adequately route and... 

In this paper, we present an energy-efficient manycast routing and spectrum assignment (EEM-RSA) algorithm in elastic optical networks supporting cloud computing applications. The proposed EEM-RSA is adapted for both static and dynamic scenarios. First, an integer linear programing formulation is derived for energy-efficient manycasting and spectrum assignment; then, the corresponding heuristic methods are proposed. To reduce the energy consumption, inactive (idle) elements are turned off, and in the proposed energy-efficient manycasting heuristic, the number of activated elements are minimized. The power consumption of network elements is modeled by considering a constant overhead for the... 

Minimizing energy consumption is the most important concern in wireless sensor networks (WSNs). To achieve this, clustering and prediction methods can enjoy the inherent redundancy of raw data and reduce transmissions more effectively. In this paper, we focus on designing a prediction-based approach, named PDC, to mainly contribute in data-aware clustering. It exploits both spatial and temporal correlations to form highly stable clusters of nodes sensing similar values. Here, the sink node uses only the local prediction models of cluster heads to forecast all readings in the network without direct communication. To the best of our knowledge, PDC is a novel energy efficient approach which... 

This paper presents a reconfigurable network-on-chip (NoC) for many-core chip multiprocessors (CMPs) in the dark silicon era, where a considerable part of high-end chips cannot be powered up due to the power and bandwidth walls. Core specialization, which trades off the cheaper silicon area with energy-efficiency, is a promising solution to the dark silicon challenge. This approach integrates a selection of many diverse application-specific cores into a single many-core chip. Each application then activates those cores that best match its processing requirements. Since active cores may not always form a contiguous active region in the chip, such a partially active many-core CMP requires some... 

The necessity and significance of improving the energy efficiency of cloud implementations have increased due to the rapid growth and proliferation of cloud computing services around the world. Virtual machines (VMs) comprise the backend of most, if not all, cloud computing services. Several VMs are often consolidated on a physical machine to efficiently utilize its resources. In this paper, we take into account the cooling and network structure of the datacenter host ing the physical machines when consolidating the VMs so that fewer racks and routers are employed, without compromising the service-level agreements; consequently, idle routing and cooling equipment can be turned off in order... 

Energy reduction in embedded processors is a must since most embedded systems run on batteries and processor energy reduction helps increase usage time before needing a recharge. Register files are among the most power consuming parts of a processor core. Register file power consumption mainly depends on its size (height as well as width), especially in newer technologies where leakage power is increasing. We provide a register file architecture that, depending on the application behavior, dynamically (i) adapts the width of individual registers, and (ii) puts partitions of temporarily unused registers into low-power mode, so as to save both static and dynamic power. We show that our scheme... 

The hydrodynamics and energetics of bioinspired oscillating mechanisms have received significant attentions by engineers and biologists to develop the underwater and air vehicles. Undulating and pure heaving (or plunging) motions are two significant mechanisms which are utilized in nature to provide propulsive, maneuvering, and stabilization forces.This study aims to elucidate and compare the propulsive vortical signature and performance of these two important natural mechanisms through a systematic numerical study. Navier-Stokes equations are solved, by a pressure-based finite volume method solver, in an arbitrary Lagrangian- Eulerian (ALE) framework domain containing a 2D NACA0012 foil... 

We propose a new optical reconfigurable Network-on-Chip (NoC), named ReFaT ONoC (Reconfigurable Flat and Tree Optical NoC). ReFaT is a dynamically reconfigurable architecture, which customizes the topology and routing paths based on the application characteristics. ReFaT, as an all-optical NoC, routes optical packets based on their wavelengths. For this purpose, we propose a novel architecture for the optical switch, which eliminates the need for optical resource reservation, and thus avoids the corresponding latency and area overheads. As a key idea for dynamic reconfiguration, each application is mapped to a specific set of wavelengths and utilizes its dedicated routing algorithm. We... 

Power-gating is a promising method for reducing the leakage power of digital systems. In this paper, we propose a novel power-gating scheme for virtual channels in on-chip networks that uses an adaptive method to dynamically adjust the number of active VCs based on the on-chip traffic characteristics. Since virtual channels are used to provide higher throughput under high traffic loads, our method sets the number of virtual channel at each port selectively based on the workload demand, thereby do not negatively affect performance. Evaluation results show that by using this scheme, about 40% average reduction in static power consumption can be achieved with negligible performance overhead  

Summary Increasing interest in smart grids exhibits its potential benefits for providing reliable, secure, efficient, environmental friendly and sustainable electricity from renewable energy resources. Here, reliability models of four types of renewable and hybrid distributed generation were developed. A fuzzy multi-objective function was suggested for simultaneous optimization of reliability, electricity generation cost, grid loss and voltage profile. This not only considers uncertainty of renewable energy resources but also provides smart generation dispatching. An efficient reliability index consisting of energy and interruption frequency terms was also defined. A novel hybrid heuristic... 

Aggregation services play an important role in the domain of Wireless Sensor Networks (WSNs) because they significantly reduce the number of required data transmissions, and improve energy efficiency on those networks. In most of the existing aggregation methods that have been developed based on the mathematical models or functions, the user of the WSN has not access to the original observations. In this paper, we propose an algorithm which let the base station access the observations by introducing a distributed method for computing the Principal Component Analysis (PCA). The proposed algorithm is based on transmission workload of the intermediate nodes. By using PCA, we aggregate the... 

Energy constraint is the most critical problem in wireless sensor networks (WSNs). To address this issue, clustering has been introduced as an efficient way for routing. However, the available clustering algorithms do not efficiently consider the geographical information of nodes in cluster-head election. This leads to uneven distribution of cluster-heads and unbalanced cluster sizes that brings about uneven energy dissipation in clusters. In this paper, an Efficient Distributed Cluster-head Election technique for Load balancing (EDCEL) is proposed. The main criterion of the algorithm, dispersal of cluster-heads, is achieved by increasing the Euclidian distance between cluster-heads.... 

Wireless networks with the shared media require Medium Access Control (MAC) protocol that provides contention resolution mechanism. The design of MAC protocol in underwater sensor networks is a challenging issue because of limited energy source and high propagation delay. The most important goal of the MAC design for underwater sensor networks is to resolve data packet collision efficiently with respect to energy consumption. So, selection of MAC protocol is an important task because it has significant impact on the system efficiency. A suitable MAC protocol must consider some factors such as fairness, energy consumption, latency and throughput based on various applications. The bandwidth in... 

In this work we introduce Heterogeneous Interconnect for Low Resolution Cache Access (Helia). Helia improves energy efficiency in snoop-based chip multiprocessors as it eliminates unnecessary activities in both interconnect and cache. This is achieved by using innovative snoop filtering mechanisms coupled with wire management techniques. Our optimizations rely on the observation that a high percentage of cache mismatches could be detected by utilizing a small subset but highly informative portion of the tag bits. Helia relies on the snoop controller to detect possible remote tag mismatches prior to tag array lookup. Power is reduced as a) our wire management techniques permit slow... 

In this paper a novel refractive structure for increasing the performance of photovoltaic cells1 is proposed. This structure which is named back-to-back-Fresnel lens is similar to conventional Fresnel lens used for energy concentration on PV cells while comprising some superior features. Among these features is its thinness, just like Fresnel lens, and lower loss of energy and simpler structure and design compared to a Fresnel lens with similar properties. The proposed lens is experimentally tested with a PV cell while the obtained results confirm its superior features  

Wireless sensor networks are tiny devices with limited computation and energy capacities. For such devices, data transmission is a very energy-consuming operation. It thus becomes essential to increase the lifetime of a WSN by minimizing the number of bits sent by each device. One well known approach is to aggregate sensor data. Data aggregation is used to eliminate redundancy and minimize the number of transmissions in order to save energy. Most energy efficient aggregation protocols have focused on cluster-based structure approaches. In this paper, we investigate the efficiency of data aggregation by focusing on two aspects of the problem: first how to improve cluster-based routing... 

Error control is an important mechanism for providing robust multimedia communication in wireless sensor networks. Although there have been several research works in analysis of error control mechanisms in wireless multimedia networks and wireless sensor networks, but none of them are directly applicable to the wireless multimedia sensor networks (WMSNs) which has resource and performance constraints of WSNs as well as QoS requirements of multimedia communications. In this paper, we comprehensively evaluate the performance of several error control mechanisms in WMSNs. The results of our analysis provide an extensive comparison between automatic repeat request (ARQ), forward error correction... 

Charge recovery is a promising concept to design (cryptographic) VLSI circuits with low energy dissipation. However, unsatisfactory designs of proposed logic cells degrade its theoretical efficiency significantly both in its energy consumption and the resistance against differential power analysis attacks (DPA-attacks). Short circuit dissipation and non-adiabatic discharging of capacitance loads are the two major sources of this degradation which are addressed in this paper. In order to reduce these dissipation significantly, we manipulate threshold voltage of circuits transistors by body biasing. To evaluate the efficiency of our method we select a common charge recovery logic called 2N2N2P...