Obtaining and Using Cumulative Bounds of Network Reliability

In this chapter, we study the task of obtaining and using the exact cumulative bounds of various network reliability indices. A network is modeled by a non-directed random graph with reliable nodes and unreliable edges that fail independently. The approach based on cumulative updating of the network reliability bounds was introduced by Won and Karray in 2010. Using this method, we can find out whether the network is reliable enough with respect to a given threshold. The cumulative updating continues until either the lower reliability bound becomes greater than the threshold or the threshold becomes greater than the upper reliability bound. In the first case, we decide that a network is reliable enough; in the second case, we decide that a network is unreliable. We show how to speed up cumulative bounds obtaining by using partial sums and how to update bounds when applying different methods of reduction and decomposition. Various reliability indices are considered: k-terminal probabilistic connectivity, diameter constrained reliability, average pairwise connectivity, and the expected size of a subnetwork that contains a special node. Expected values can be used for unambiguous decision-making about network reliability, development of evolutionary algorithms for network topology optimization, and obtaining approximate reliability values

Visual and Contextual Modeling for the Detection of Repeated Mild Traumatic Brain Injury.

Currently, there is a lack of computational methods for the evaluation of mild traumatic brain injury (mTBI) from magnetic resonance imaging (MRI). Further, the development of automated analyses has been hindered by the subtle nature of mTBI abnormalities, which appear as low contrast MR regions. This paper proposes an approach that is able to detect mTBI lesions by combining both the high-level context and low-level visual information. The contextual model estimates the progression of the disease using subject information, such as the time since injury and the knowledge about the location of mTBI. The visual model utilizes texture features in MRI along with a probabilistic support vector machine to maximize the discrimination in unimodal MR images. These two models are fused to obtain a final estimate of the locations of the mTBI lesion. The models are tested using a novel rodent model of repeated mTBI dataset. The experimental results demonstrate that the fusion of both contextual and visual textural features outperforms other state-of-the-art approaches. Clinically, our approach has the potential to benefit both clinicians by speeding diagnosis and patients by improving clinical care

Optimal reliability-based design of bulk water supply systems

Includes bibliographical references.Bulk water supply systems are usually designed according to deterministic design guidelines. In South Africa, design guidelines specify that a bulk storage reservoir should have a storage capacity of 48 hours of annual average daily demand (AADD), and the feeder pipe a capacity of 1.5 times AADD (CSIR, 2000). Nel & Haarhoff (1996) proposed a stochastic analysis method that allowed the reliability of a reservoir to be estimated based on a Monte Carlo analysis of consumer demand, fire water demand and pipe failures. Van Zyl et al. (2008) developed this method further and proposed a design criterion of one failure in ten years under seasonal peak conditions. In this study, a method for the optimal design of bulk water supply systems is proposed with the design variables being the configuration of the feeder pipe system, the feeder pipe diameters (i.e. capacity), and the size of the bulk storage reservoir. The stochastic analysis method is applied to determine a trade-off curve between system cost and reliability, from which the designer can select a suitable solution. Optimisation of the bulk system was performed using the multi-objective genetic algorithm, NSGA-II. As Monte Carlo sampling can be computationally expensive, especially when large numbers of simulations are required in an optimisation exercise, a compression heuristic was implemented and refined to reduce the computational effort required of the stochastic simulation. Use of the compression heuristic instead of full Monte Carlo simulation in the reliability analysis achieved computational time savings of around 75% for the optimisation of a typical system. Application of the optimisation model showed that it was able to successfully produce a set of Pareto-optimal solutions ranging from low reliability, low cost solutions to high reliability, high cost solutions. The proposed method was first applied to a typical system, resulting in an optimal reservoir size of approximately 22 h AADD and feeder pipe capacity of 2 times AADD. This solution achieved 9% savings in total system cost compared to the South African design guidelines. In addition, the optimal solution proved to have better reliability that one designed according to South African guidelines. A sensitivity analysis demonstrated the effects of changing various system and stochastic parameters from typical to low and high values. The sensitivity results revealed that the length of the feeder pipe system has the greatest impact on both the cost and reliability of the bulk system. It was also found that a single feeder pipe is optimal in most cases, and that parallel feeder pipes are only optimal for short feeder pipe lengths. The optimisation model is capable of narrowing down the search region to a handful of possible design solutions, and can thus be used by the engineer as a tool to assist with the design of the final system

Towards a more accurate characterization of granular media 2.0: Involving AI in the process

publishedVersio

Decision Support Algorithms for Sectorization of Water Distribution Networks

Many water utilities, especially ones in developing countries, continue to operate low efficient water distribution networks (WDNs) and are consequently faced with significant amount of water (e.g. leakage) and revenue losses (i.e. non-revenue water – NRW). First step in reducing the NRW is assessment of water balance in WDN aimed to establish the baseline level of water losses. Then, water utilities can plan NRW reduction activities according to this baseline. Sectorization of WDN into District Metered Areas (DMAs) is the most cost-effective strategy used for active leakage (i.e. water loss) control, achieved by monitoring the flow data on DMAs’ boundaries. Sectorization of WDN has to be designed carefully, as required network interventions can endanger network’s water supply and pressure distribution. In this thesis new methods and algorithms, aimed to support making more effective and objective decisions regarding the WDN sectorization procedure, are presented, tested and validated. Presented methods and algorithms are part of proposed decision support methodology compensating for disadvantages in available methods, valuable to practicing engineers commencing implementation of sectorization strategy in WDN. Main sectorization objective adopted in methodology presented in this thesis is to design layout of DMAs that will allow efficient tracking of water balance in the network. Least investment for field implementation and maintaining the same level of WDN’s operational efficiency are adopted as main design criteria. New sectorization algorithm, named DeNSE (Distribution Network SEctorization), is developed and presented, adopting above-named objective and design criteria. DeNSE algorithm utilizes newly developed uniformity index which drives the sectorization process and identifies clusters. New engineering heuristic is developed and used for placing the flow-meters and isolation valves on clusters’ boundary edges, making them DMAs. Post sectorization operational efficiency of WDN is evaluated using adopted performance indicators (PIs). Top-down approach to hierarchical sectorization of WDN, particulary convenient for water utilities constrained with limited funding and insufficient reliable input data, is also implemented in DeNSE algorithm. New method for hydraulic simulation, named TRIBAL-DQ is developed to address the issue of low computational efficiency, recognized in available sectorization methodologies employing optimization. TRIBAL-DQ is a loop-flow based method which combines the novel TRIangulation Based ALgorithm (TRIBAL) for loop identification with efficient implementation of the loop-flow hydraulic solver (DQ). TRIBAL-DQ method is tested on various networks of different complexities and topologies. This thesis reports only results of testing on literature benchmark networks, used to validate methods’ performance. TRIBAL-DQ method based hydraulic solver is compared to the node based solver implemented in EPANET, most prominent software for hydraulic calculation of WDN. New TRIBAL-DQ solver showed significant dominance in computational efficiency, with stable numerical performance and same level of prediction accuracy. DeNSE algorithm is benchmarked against other available sectorization methodologies on real-sized WDN. Obtained results demonstrate the ability of DeNSE algorithm to identify good set of feasible solutions, without worsening operational status of the WDN compared to its baseline condition. Reported computational efficiency of the algorithm is one of its strong points, as it allows generation of feasible solutions for large WDN in reasonable time. In this field, algorithm particularly outperforms methods employing multi-objective optimization (e.g. minutes compared to hours).Комунална предузећа која управљају водоводним системима, нарочита она у земљама у развоју, суочена су са проблемима дотрајале и лоше одржаване дистрибутивне мрже који за последицу имају значајне количине воде која се губи у дистрибуцији. Први корак ка смањењу губитака у водоводном систему је процена водног биланса у дистрибутивној мрежи како би се утврдило почетно стање система, а затим и приступило планирању и предузимању мера за смањење губитака како би се то стање поправило. Најисплативија, и опште прихваћена, стратегија за остваривање овог циља је подела дистрибутивне мреже, односно њена секторизација, на тзв. основне зоне билансирања (ОЗБ). ОЗБ се у мрежи успостављају јасним дефинисањем њихових граница, на којима се инсталирају изолациони затварачи и мерачи протока. Избор ОЗБ није једнозначан, и приликом њиховог дефинисања мора се водити рачуна о планираним интервенцијама у мрежи које могу имати негативан утицај на водоснабдевање потрошача и распоред притисака у мрежи. У овој дисератацији су приказане и тестиране нове методе и алгоритми намењени за подршку одлучивању приликом секторизације водоводне дистрибутивне мреже на ОЗБ. Презентоване методе и алгоритми надомешћују недостатке постојећих метода и могу бити од користи инжењерима који се у пракси баве задатком секторизације дистрибутивних мрежа. Основни циљ методологије за секторизацију приказане у овој дисертацији је дефинисање распореда ОЗБ који ће омогућити ефикасно праћење водног биланса у дистрибутивној мрежи. Основни критеријуми за вредновање и избор оптималног решења су минимална улагања у неопходне интервенције у мрежи и очување поузданости система. У дисертацији је приказан нови алгоритам за секторизацију водоводне мреже, назван DeNSE (Distribution Network SEctorization), заснован на претходно наведеном основном циљу и критеријумима. Секторизација применом DeNSE алгоритма је базирана на употреби новог индекса униформности мреже, који омогућава идентификацију зона у мрежи уједначених према потрошњи. За дефинисање ОЗБ, на границе претходно идентификованих зона потребно је поставити мераче протока и изолационе затвараче. За ове потребе развијена је и приказана методлогија засновна на практичним инжењерским принципима. За процену поузданости система након секторизације коришћени су усвојени индикатори перформанси (PIs – Performance Indicators). Предвиђена је и могућност за хијерархијску секторизацију дистрибутивне мреже, нарочито привлачна за комунална предузећа која располажу ограниченим финансијским средствима и имају потребу да процес секторизације изведу у неколико фаза. Услед проблема са значајним рачунарским временом који имају постојеће методе за секторизацију које користе оптимизацију, у оквиру истраживања је развијен и нови метод за хидраулички прорачун мрежа под притиском, назван TRIBAL-DQ. TRIBAL-DQ метод је заснован на примени новог алгоритма за идентификацију прстенова у мрежи базираног на триангулацији (TRIBAL – TRIangulation Based ALgorithm) и ефикасној имплементацији нумеричког модела хидрауличког прорачуна базираног на методи прстенова (DQ). TRIBAL-DQ метод је тестиран на бројним дистрибутивним мрежама различите сложености. У овој дисертацији су приказани само резултати добијени применом на тест-мрежама познатим из литературе, како би се потврдила њихова ваљаност. TRIBAL-DQ метод је упоређен са методом коју користи најпознатији софтвер за хидраулички прорачун мрежа под притиском – EPANET. Резултати приказују значајну предност новог метода у погледу рачунарске ефикаснонсти, уз очување нумеричке стабилности и тачности решења хидрауличког прорачуна. DeNSE алгоритам је упоређен са постојећим методама за секторизацију дистрибутивних мрежа. Резултати потврђују да је нови алгоритам у стању да идентификује скуп могућих решења, која не угрожавају поузданост система и снабдевање потрошача. Рачунарска ефикаснонст DeNSE алгоритма је једна од његових најзначајнијих предности јер омогућава идентификацију не једног, већ скупа могућих решења за реалне дистрибутивне мреже у релативно кратком рачунарском времену. Ова чињеница посебно долази до изражаја када се рачунарско време DeNSE алгоритма упореди са рачунарским временом метода које користе оптимизационе алгоритме (минути у поређењу са сатима).Belgrade: University of Belgrade-Faculty of Civil Engineerin

Index to 1984 NASA Tech Briefs, volume 9, numbers 1-4

Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1984 Tech B Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences

Comparative evaluation of approaches in T.4.1-4.3 and working definition of adaptive module

The goal of this deliverable is two-fold: (1) to present and compare different approaches towards learning and encoding movements us- ing dynamical systems that have been developed by the AMARSi partners (in the past during the first 6 months of the project), and (2) to analyze their suitability to be used as adaptive modules, i.e. as building blocks for the complete architecture that will be devel- oped in the project. The document presents a total of eight approaches, in two groups: modules for discrete movements (i.e. with a clear goal where the movement stops) and for rhythmic movements (i.e. which exhibit periodicity). The basic formulation of each approach is presented together with some illustrative simulation results. Key character- istics such as the type of dynamical behavior, learning algorithm, generalization properties, stability analysis are then discussed for each approach. We then make a comparative analysis of the different approaches by comparing these characteristics and discussing their suitability for the AMARSi project