Optimization of a plate with holes

We consider a simply supported plate with constant thickness, defined on an unknown multiply connected domain. We optimize its shape according to some given performance functional. Our method is of fixed domain type, easy to be implemented, based on a fictitious domain approach and the control variational method. The algorithm that we introduce is of gradient type and performs simultaneous topological and boundary variations. Numerical experiments are also included and show its efficiency.     

Fast estimation of outage probabilities in MIMO channels

Fast estimation methods for small outage probabilities of signaling in fading multiple-input multiple-output (MIMO) channels are developed. Communication over such channels is of much current interest, and quick and accurate methods for estimating outage capacities are needed. The methods described herein use adaptive importance sampling (IS) techniques as developed in a series of recent publications. Fast algorithms are provided for evaluating "nonergodic" capacities of Rayleigh fading MIMO channels. The methodology can be extended to more general models. Numerical results on outage capacity are provided, and these extend and complement known results in the literature.     

Brazilian Solar Resource Atlas CD-ROM

The Brazilian Solar Resource Atlas CD-ROM is intended to be a tool for solar system design, delivering information that relies on a large interactive database, including, also, a modern device for calculating the solar radiation collected by planes inclined at different tilt angles or tracking the sun around one or two axes. The spatial distribution of the daily solar radiation, monthly and yearly averaged, that hits Brazil is presented in 13 colored maps, together with the methodological procedures used for harmonizing the information and designing the maps. A map containing the location of pyranometric and actinographic terrestrial stations, the information which was used for designing the maps, is also presented. The period of collected data runs from 1978 to 1990. Similarly, the atlas contains 13 colored maps, including daily insolation, monthly and yearly averaged, in addition to the map containing the location of the heliographic stations. The CD-ROM stores a database that includes over 500 stations located in Brazil and on the borders of its neighboring countries. The information is given either as daily, monthly average global solar radiation, or daily, monthly average insolation. A search device is included in the database, allowing to navigate over the maps or to select a desired location. The information may be printed as a report. The CD-ROM also includes a software to perform the following calculations: solar radiation estimates on a fixed plane at any inclination on North-South orientation; estimates of solar radiation collected by a plane tracking the sun about one or two axes; generation of synthetic series based on Markov’s Transition Matrixes.     

A stochastic approach to handle resource constraints as knapsack problems in ensemble pruning

Machine Learning - Ensemble-based methods are highly popular approaches that increase the accuracy of a decision by aggregating the opinions of individual voters. The common point is to maximize...     

Solar radiation in the Brazilian Northeast

The significant increase in recent years of the number of rural electrification systems (some thousands of them do exist) using photovoltaic technology installed in the Northeast of Brazil (1,500,000 km², approximately 42 million people) used for illumination or water pumping, calls for an improvement on the design procedures in order to reduce the burden of capital costs per unit of generated power. Such objective can be accomplished as long as a better knowledge about the solar resource is achieved, considering how much these applications depend on it.The sources of information on solar radiation in Brazil are quite varied at both institutional and publication level. At institutional level, among others, we can find the National Institute of Meteorology (INMET), State Departments of Agriculture, research institutes, universities and electric power generation and distribution utilities. Progress reports or scientific and technical journals are the main publishing vehicles where this information can be found. This way, data quality varies considerably, showing spatial and temporal discontinuities, in addition to the fact that measurement instruments and physical units of registered data are not standardized. The Solarimetric Atlas of Brazil was recently published [Brazilian Solarimetric Atlas, Final Technical Report I–IV (1997); Renewable Energy 18 (1998) 393] contains that information, which is grouped, evaluated, qualified, and presented in a standardized way. It is one of the best currently existing sources of information, and it certainly consists of almost the entirety of the existing information on the solar resource (data on solar radiation and sunshine hours) in Brazil.By using this database, simultaneous records of solar radiation (measured with pyranographs or pyranometers) and sunshine hours with heliographs were obtained in 35 different places in the Northeast region. Coefficients a and b were calculated for those different places using Angstrom's correlation. Using the geostatistical interpolation method known as ‘kriging’, the values of a and b were placed on contour maps, the coverage of which is the Northeast region. The relevant kriging estimate error maps were also obtained.The general objective of this paper is to improve the amount of the currently existing information on the solar radiation in the Northeast of Brazil. Regarding this, the contour maps of coefficients a and b have made possible estimating solar radiation in 82 additional locations, were only sunshine hours data were available.     

Utilization of cathodic protection for transmission towers through photovoltaic generation

In this study, we analyzed the application of photovoltaic solar energy as a source of cathodic protection in metallic structures foundations on transmission lines towers. As preliminary studies concerning the need for cathodic protection of the structure, we have measured the resistivity of the soil, the pH and the natural corrosion potential. After the verification of the need for protection against corrosion, the cathodic protection system (CPS) was designed calculating the current to be injected, the PV system and a monitoring system.For analyzing the efficacy of the CPS, a comparison was made between the measurements done in two towers very close to each other, one with a CPS and the other acting as a witness. By comparing the loss in masses of the carbon steel coupons installed around the base of both towers and the measurements of the potentials reached due to the injected current, the efficacy of this system was experimentally demonstrated. In the protected tower, the rate of mass loss experienced a decrease by a factor equal to 2.5.Finally, the economical analysis using the LCC, showed that the usage of CPS has a significant and clear advantage regarding traditional methods.     

Generation of daily solar irradiation by means of artificial neural net works

The present study proposes the utilization of Artificial Neural Networks (ANN) as an alternative for generating synthetic series of daily solar irradiation. The sequences were generated from the use of daily temporal series of a group of meteorological variables that were measured simultaneously. The data used were measured between the years of 1998 and 2006 in two temperate climate localities of Brazil, Ilha Solteira (São Paulo) and Pelotas (Rio Grande do Sul). The estimates were taken for the months of January, April, July and October, through two models which are distinguished regarding the use or nonuse of measured bright sunshine hours as an input variable. An evaluation of the performance of the 56 months of solar irradiation generated by way of ANN showed that by using the measured bright sunshine hours as an input variable (model 1), the RMSE obtained were less or equal to 23.2% being that of those, although 43 of those months presented RMSE less or equal to 12.3%. In the case of the model that did not use the measured bright sunshine hours but used a daylight length (model 2), RMSE were obtained that varied from 8.5% to 37.5%, although 38 of those months presented RMSE less or equal to 20.0%.A comparison of the monthly series for all of the years, achieved by means of the Kolmogorov–Smirnov test (to a confidence level of 99%), demonstrated that of the 16 series generated by ANN model only two, obtained by model 2 for the months of April and July in Pelotas, presented significant difference in relation to the distributions of the measured series and that all mean deviations obtained were inferior to 0.39 MJ/m².It was also verified that the two ANN models were able to reproduce the principal statistical characteristics of the frequency distributions of the measured series such as: mean, mode, asymmetry and Kurtosis.     

Softwares for designing, simulating or providing diagnosis of photovoltaic water-pumping systems

This paper identifies and evaluates software programs for designing, simulating and providing diagnosis of photovoltaic water-pumping systems available in the world market. The identified software programs were evaluated according to the following general criteria:

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Results for several commercial software programs analyzed according to these criteria are given.     

Analysis of monthly time series of solar radiation and sunshine hours in tropical climates

This paper analyses the interannual variability of solar radiation and sunshine hours for a large tropical region (Brazil), located between latitude 0°S and 30°S, in order to improve knowledge on solar resources, generate statistical parameters for model checking or to be used as input data of synthetic time series generation. The statistics for the daily, monthly average solar radiation deviations, and daily, monthly average sunshine hours, for the various localities in Brazil, tested with the Kolmogorov–Smirnov method, show that they are random variables, normally distributed. On the other hand, the sequential properties analysis shows that the auto-correlation coefficients with lag 1 are statistically significant only for a few locals: Fortaleza, São Luís, Manaus and Belém. But it is necessary to emphasize that the auto-correlation coefficients with lag 1, though not usually statistically significant, are positive for almost all the locals. The AR-1 is the suggested procedure for monthly solar radiation synthetic time series generation, with auto-correlation coefficients varying from 0.30 to 0.47 for the localities in the north of Brazil and zero for other regions.     

Technical note On the development of spatialtemporal solar radiation maps: a Brazilian case study

This work summarizes recently published information on the solar resource of Brazil. We describe the spatial distribution of solar radiation and its relationship with climatic and geographical conditions. In order to harmonize the information in terms of type of instruments, time recording period and data processing methods, a careful selection of records from the data base was made. Density of recording stations is reasonable in the south, southeast and northeast regions of the country, while in the west center and north regions the density of stations is rather poor. The procedure to elaborate the maps of daily solar radiation, monthly and annual average is described. Consideration of the measuring period of the monthly averages, used to elaborate the contour maps, shows that they meet the requirement that 90% of averages are inside the strip of ±7.5%, centralized on the average of very long period measurements. We present one map with the localization of the recording stations and one annual and 12 monthly contour maps, describing daily solar radiation levels over the whole territory. Spacing among the contour lines is (±2 MJm² day). Annual average of solar radiation lies within the interval of ((18±2) MJm² day), except in the northeast region where values higher than (20 MJm² day) are found. Two regions with levels of (16 MJm² day) are also observed. The highest monthly average values (24 MJm² day) are observed in the state of Rio Grande do Sul, southern end of the country, in the summer season (December and January). The lowest values in the country (8 MJm² day) are observed in June and July (winter in the southern hemisphere), on the extreme south coastline of the same state, Rio Grande do Sul, below 32° south latitude.