Spelling suggestions: "subject:"piecewise linear"" "subject:"piecewaise linear""
81 |
Modelagem híbrida para o planejamento da operação de sistemas hidrotérmicos considerando as não linearidades das usinas hidráulicasRamos, Tales Pulinho 23 February 2015 (has links)
Submitted by Renata Lopes (renatasil82@gmail.com) on 2015-12-16T11:02:24Z
No. of bitstreams: 1
talespulinhoramos.pdf: 6134665 bytes, checksum: 349537ae72f568271488022944942fb6 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2015-12-16T11:20:33Z (GMT) No. of bitstreams: 1
talespulinhoramos.pdf: 6134665 bytes, checksum: 349537ae72f568271488022944942fb6 (MD5) / Made available in DSpace on 2015-12-16T11:20:33Z (GMT). No. of bitstreams: 1
talespulinhoramos.pdf: 6134665 bytes, checksum: 349537ae72f568271488022944942fb6 (MD5)
Previous issue date: 2015-02-23 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O Sistema Interligado Nacional (SIN) apresenta cerca de 150 usinas hidráulicas e o
planejamento de médio prazo contempla entre 5 e 10 anos de estudo, a representação
do sistema à usinas individualizadas faz com que a resolução do problema seja muito
custoso computacionalmente. Para isso, o sistema é representado a partir de sistemas
equivalentes de energia. Existe um trabalho anterior onde foi realizado a flexibilização
da modelagem do sistema, denominada modelagem híbrida, em que parte do sistema é
representado através de sistemas equivalentes de energia e outra é representada à usinas
individualizadas com a produtibilidade constante. Desta forma, consegue-se um maior
detalhamento nos estudos de médio prazo mantendo a complexidade do sistema em um
nível adequado computacionalmente. Este trabalho apresenta a modelagem híbrida entre
sistemas equivalentes de energia e à usinas individualizadas, porém, considerando as não
linearidades das usinas hidráulicas. As não linearidades das usinas basicamente se dão em
relação a variação do nível do reservatório e da vazão defluente (vazão turbinada acrescida
da vazão vertida), o que implica diretamente na geração hidráulica. A proposta consiste
em modelar a geração hidráulica das usinas (Função de Produção Hidráulica - FPH), que
é uma função analítica não linear e não convexa, por uma função linear por partes convexa
que represente adequadamente a função de produção hidráulica analítica. Há um trabalho
anterior onde a FPH é aproximada por uma função linear por partes em duas etapas,
inicialmente a função é aproximada nas dimensões do armazenamento e do turbinamento
e, em uma segunda etapa, é adicionado a contribuição do vertimento. Já neste trabalho, a
FPH é aproximada por uma função linear por partes obtida em apenas uma etapa para as
três dimensões a partir do algoritmo Convex Hull. Assim, é possível resolver o problema
de médio prazo considerando parte do sistema representado de forma equivalente e outra
parte de forma individualizada considerando a variação da geração hidráulica em função
do volume armazenado, vazão turbinada e vertida (se houver influência no canal de fuga). / The National Interconnected Power System (NIPS) presents around 150 hydraulic plants
and the medium term planning contemplates between 5 to 10 years of study, the representation
of the system to individualized plants makes the problem impracticable in
computing; then the system is represented from equivalent systems of energy. There is an
alternative of modeling flexibility of the system named hybrid modeling, in which part of
the system is represented through equivalent systems of energy and the other is represented
to individualized plants with constant productivity. As a consequence, it is obtained greater
detail in the long term studies, maintaining the complexity of the system in an adequate
level in computing. This paper presents the hybrid modeling between equivalent systems
of energy and individualized plants. However, it considers non-linearities on generation
of hydraulic plants. The non-linear characteristic on generation function basically comes
from the influence of the reservoir level (head term) and the release term (turbinated
outflow added to spilled outflow). The suggestion is to model the hydraulic generation of
the plants (Hydraulic Production Function - HPF), which is a non-linear and non-convex
analytical function, into a convex piecewise linear function that represents appropriately
the function of the analytical hydraulic production. It will be described in detail in this
paper the technique used to obtain this piecewise linear function by applying the Convex
Hull algorithm to guarantee the convexity of this function. To conclude, it is possible to
solve the problem of long term considering part of the system represented by equivalent
form and the other part in individualized manner considering the variation of the hydraulic
generation in relation to the volume stored, turbaned and spilled outflow.
|
82 |
Anomaly Detection in RFID NetworksAlkadi, Alaa 01 January 2017 (has links)
Available security standards for RFID networks (e.g. ISO/IEC 29167) are designed to secure individual tag-reader sessions and do not protect against active attacks that could also compromise the system as a whole (e.g. tag cloning or replay attacks). Proper traffic characterization models of the communication within an RFID network can lead to better understanding of operation under “normal” system state conditions and can consequently help identify security breaches not addressed by current standards. This study of RFID traffic characterization considers two piecewise-constant data smoothing techniques, namely Bayesian blocks and Knuth’s algorithms, over time-tagged events and compares them in the context of rate-based anomaly detection.
This was accomplished using data from experimental RFID readings and comparing (1) the event counts versus time if using the smoothed curves versus empirical histograms of the raw data and (2) the threshold-dependent alert-rates based on inter-arrival times obtained if using the smoothed curves versus that of the raw data itself. Results indicate that both algorithms adequately model RFID traffic in which inter-event time statistics are stationary but that Bayesian blocks become superior for traffic in which such statistics experience abrupt changes.
|
83 |
Development of High-order CENO Finite-volume Schemes with Block-based Adaptive Mesh Refinement (AMR)Ivan, Lucian 31 August 2011 (has links)
A high-order central essentially non-oscillatory (CENO) finite-volume scheme in combination with a block-based adaptive mesh refinement (AMR) algorithm is proposed for solution of hyperbolic and elliptic systems of conservation laws on body- fitted multi-block mesh. The spatial discretization of the hyperbolic (inviscid) terms is based on a hybrid solution reconstruction procedure that combines an unlimited high-order k-exact least-squares
reconstruction technique following from a fixed central stencil with a monotonicity preserving limited piecewise linear reconstruction algorithm. The limited reconstruction is applied to computational cells with under-resolved solution content and the unlimited k-exact reconstruction
procedure is used for cells in which the solution is fully resolved. Switching in the
hybrid procedure is determined by a solution smoothness indicator. The hybrid approach
avoids the complexity associated with other ENO schemes that require reconstruction on
multiple stencils and therefore, would seem very well suited for extension to unstructured meshes. The high-order elliptic (viscous) fluxes are computed based on a k-order accurate average gradient derived from a (k+1)-order accurate reconstruction. A novel h-refinement criterion based on the solution smoothness indicator is used to direct the steady and unsteady refinement of the AMR mesh. The predictive capabilities of the proposed high-order AMR scheme are demonstrated for the Euler and Navier-Stokes equations governing two-dimensional
compressible gaseous flows as well as for advection-diffusion problems characterized
by the full range of Peclet numbers, Pe. The ability of the scheme to accurately represent
solutions with smooth extrema and yet robustly handle under-resolved and/or non-smooth solution content (i.e., shocks and other discontinuities) is shown for a range of problems. Moreover, the ability to perform mesh refinement in regions of smooth but under-resolved and/or non-smooth solution content to achieve the desired resolution is also demonstrated.
|
84 |
Development of High-order CENO Finite-volume Schemes with Block-based Adaptive Mesh Refinement (AMR)Ivan, Lucian 31 August 2011 (has links)
A high-order central essentially non-oscillatory (CENO) finite-volume scheme in combination with a block-based adaptive mesh refinement (AMR) algorithm is proposed for solution of hyperbolic and elliptic systems of conservation laws on body- fitted multi-block mesh. The spatial discretization of the hyperbolic (inviscid) terms is based on a hybrid solution reconstruction procedure that combines an unlimited high-order k-exact least-squares
reconstruction technique following from a fixed central stencil with a monotonicity preserving limited piecewise linear reconstruction algorithm. The limited reconstruction is applied to computational cells with under-resolved solution content and the unlimited k-exact reconstruction
procedure is used for cells in which the solution is fully resolved. Switching in the
hybrid procedure is determined by a solution smoothness indicator. The hybrid approach
avoids the complexity associated with other ENO schemes that require reconstruction on
multiple stencils and therefore, would seem very well suited for extension to unstructured meshes. The high-order elliptic (viscous) fluxes are computed based on a k-order accurate average gradient derived from a (k+1)-order accurate reconstruction. A novel h-refinement criterion based on the solution smoothness indicator is used to direct the steady and unsteady refinement of the AMR mesh. The predictive capabilities of the proposed high-order AMR scheme are demonstrated for the Euler and Navier-Stokes equations governing two-dimensional
compressible gaseous flows as well as for advection-diffusion problems characterized
by the full range of Peclet numbers, Pe. The ability of the scheme to accurately represent
solutions with smooth extrema and yet robustly handle under-resolved and/or non-smooth solution content (i.e., shocks and other discontinuities) is shown for a range of problems. Moreover, the ability to perform mesh refinement in regions of smooth but under-resolved and/or non-smooth solution content to achieve the desired resolution is also demonstrated.
|
Page generated in 0.0388 seconds