18,688 research outputs found
Optimized Solar Photovoltaic Generation in a Real Local Distribution Network
Remarkable penetration of renewable energy in electric networks, despite its
valuable opportunities, such as power loss reduction and loadability
improvements, has raised concerns for system operators. Such huge penetration
can lead to a violation of the grid requirements, such as voltage and current
limits and reverse power flow. Optimal placement and sizing of Distributed
Generation (DG) are one of the best ways to strengthen the efficiency of the
power systems. This paper builds a simulation model for the local distribution
network based on obtained load profiles, GIS information, solar insolation,
feeder and voltage settings, and define the optimization problem of solar PVDG
installation to determine the optimal siting and sizing for different
penetration levels with different objective functions. The objective functions
include voltage profile improvement and energy loss minimization and the
considered constraints include the physical distribution network constraints
(AC power flow), the PV capacity constraint, and the voltage and reverse power
flow constraints.Comment: To be published (Accepted) in: Proceedings of the IEEE PES Innovative
Smart Grid Technologies Conference (ISGT), Washington D.C., USA, 201
Analysis and implementation of the Large Scale Video-on-Demand System
Next Generation Network (NGN) provides multimedia services over broadband
based networks, which supports high definition TV (HDTV), and DVD quality
video-on-demand content. The video services are thus seen as merging mainly
three areas such as computing, communication, and broadcasting. It has numerous
advantages and more exploration for the large-scale deployment of
video-on-demand system is still needed. This is due to its economic and design
constraints. It's need significant initial investments for full service
provision. This paper presents different estimation for the different
topologies and it require efficient planning for a VOD system network. The
methodology investigates the network bandwidth requirements of a VOD system
based on centralized servers, and distributed local proxies. Network traffic
models are developed to evaluate the VOD system's operational bandwidth
requirements for these two network architectures. This paper present an
efficient estimation of the of the bandwidth requirement for the different
architectures.Comment: 9 pages, 8 figure
Methodology for modeling high performance distributed and parallel systems
Performance modeling of distributed and parallel systems is of considerable importance to the high performance computing community. To achieve high performance, proper task or process assignment and data or file allocation among processing sites is essential. This dissertation describes an elegant approach to model distributed and parallel systems, which combines the optimal static solutions for data allocation with dynamic policies for task assignment. A performance-efficient system model is developed using analytical tools and techniques.
The system model is accomplished in three steps. First, the basic client-server model which allows only data transfer is evaluated. A prediction and evaluation method is developed to examine the system behavior and estimate performance measures. The method is based on known product form queueing networks. The next step extends the model so that each site of the system behaves as both client and server. A data-allocation strategy is designed at this stage which optimally assigns the data to the processing sites. The strategy is based on flow deviation technique in queueing models. The third stage considers process-migration policies. A novel on-line adaptive load-balancing algorithm is proposed which dynamically migrates processes and transfers data among different sites to minimize the job execution cost. The gradient-descent rule is used to optimize the cost function, which expresses the cost of process execution at different processing sites.
The accuracy of the prediction method and the effectiveness of the analytical techniques is established by the simulations. The modeling procedure described here is general and applicable to any message-passing distributed and parallel system. The proposed techniques and tools can be easily utilized in other related areas such as networking and operating systems. This work contributes significantly towards the design of distributed and parallel systems where performance is critical
Numerical aerodynamic simulation facility preliminary study: Executive study
A computing system was designed with the capability of providing an effective throughput of one billion floating point operations per second for three dimensional Navier-Stokes codes. The methodology used in defining the baseline design, and the major elements of the numerical aerodynamic simulation facility are described
Optimal Caching and Routing in Hybrid Networks
Hybrid networks consisting of MANET nodes and cellular infrastructure have
been recently proposed to improve the performance of military networks. Prior
work has demonstrated the benefits of in-network content caching in a wired,
Internet context. We investigate the problem of developing optimal routing and
caching policies in a hybrid network supporting in-network caching with the
goal of minimizing overall content-access delay. Here, needed content may
always be accessed at a back-end server via the cellular infrastructure;
alternatively, content may also be accessed via cache-equipped "cluster" nodes
within the MANET. To access content, MANET nodes must thus decide whether to
route to in-MANET cluster nodes or to back-end servers via the cellular
infrastructure; the in-MANET cluster nodes must additionally decide which
content to cache. We model the cellular path as either i) a
congestion-insensitive fixed-delay path or ii) a congestion-sensitive path
modeled as an M/M/1 queue. We demonstrate that under the assumption of
stationary, independent requests, it is optimal to adopt static caching (i.e.,
to keep a cache's content fixed over time) based on content popularity. We also
show that it is optimal to route to in-MANET caches for content cached there,
but to route requests for remaining content via the cellular infrastructure for
the congestion-insensitive case and to split traffic between the in-MANET
caches and cellular infrastructure for the congestion-sensitive case. We
develop a simple distributed algorithm for the joint routing/caching problem
and demonstrate its efficacy via simulation.Comment: submitted to Milcom 201
A Low-Complexity Approach to Distributed Cooperative Caching with Geographic Constraints
We consider caching in cellular networks in which each base station is
equipped with a cache that can store a limited number of files. The popularity
of the files is known and the goal is to place files in the caches such that
the probability that a user at an arbitrary location in the plane will find the
file that she requires in one of the covering caches is maximized.
We develop distributed asynchronous algorithms for deciding which contents to
store in which cache. Such cooperative algorithms require communication only
between caches with overlapping coverage areas and can operate in asynchronous
manner. The development of the algorithms is principally based on an
observation that the problem can be viewed as a potential game. Our basic
algorithm is derived from the best response dynamics. We demonstrate that the
complexity of each best response step is independent of the number of files,
linear in the cache capacity and linear in the maximum number of base stations
that cover a certain area. Then, we show that the overall algorithm complexity
for a discrete cache placement is polynomial in both network size and catalog
size. In practical examples, the algorithm converges in just a few iterations.
Also, in most cases of interest, the basic algorithm finds the best Nash
equilibrium corresponding to the global optimum. We provide two extensions of
our basic algorithm based on stochastic and deterministic simulated annealing
which find the global optimum.
Finally, we demonstrate the hit probability evolution on real and synthetic
networks numerically and show that our distributed caching algorithm performs
significantly better than storing the most popular content, probabilistic
content placement policy and Multi-LRU caching policies.Comment: 24 pages, 9 figures, presented at SIGMETRICS'1
Phytoplankton temporal strategies increase entropy production in a marine food web model
We develop a trait-based model founded on the hypothesis that biological
systems evolve and organize to maximize entropy production by dissipating
chemical and electromagnetic potentials over longer time scales than abiotic
processes by implementing temporal strategies. A marine food web consisting of
phytoplankton, bacteria and consumer functional groups is used to explore how
temporal strategies, or the lack there of, change entropy production in a
shallow pond that receives a continuous flow of reduced organic carbon plus
inorganic nitrogen and illumination from solar radiation with diel and seasonal
dynamics. Results show that a temporal strategy that employs an explicit
circadian clock produces more entropy than a passive strategy that uses
internal carbon storage or a balanced growth strategy that requires
phytoplankton to grow with fixed stoichiometry. When the community is forced to
operate at high specific growth rates near 2 d-1, the optimization-guided model
selects for phytoplankton ecotypes that exhibit complementary for winter versus
summer environmental conditions to increase entropy production. We also present
a new type of trait-based modeling where trait values are determined by
maximizing entropy production rather than by random selection.Comment: 39 pp. including Supplementary Material, 6 Figure
Power quality and electromagnetic compatibility: special report, session 2
The scope of Session 2 (S2) has been defined as follows by the Session Advisory Group and the Technical Committee: Power Quality (PQ), with the more general concept of electromagnetic compatibility (EMC) and with some related safety problems in electricity distribution systems.
Special focus is put on voltage continuity (supply reliability, problem of outages) and voltage quality (voltage level, flicker, unbalance, harmonics). This session will also look at electromagnetic compatibility (mains frequency to 150 kHz), electromagnetic interferences and electric and magnetic fields issues. Also addressed in this session are electrical safety and immunity concerns (lightning issues, step, touch and transferred voltages).
The aim of this special report is to present a synthesis of the present concerns in PQ&EMC, based on all selected papers of session 2 and related papers from other sessions, (152 papers in total). The report is divided in the following 4 blocks:
Block 1: Electric and Magnetic Fields, EMC, Earthing systems
Block 2: Harmonics
Block 3: Voltage Variation
Block 4: Power Quality Monitoring
Two Round Tables will be organised:
- Power quality and EMC in the Future Grid (CIGRE/CIRED WG C4.24, RT 13)
- Reliability Benchmarking - why we should do it? What should be done in future? (RT 15
- …