Umberto Rizza

On an Analytical Model for the Radioactive Contaminant Release in the Atmosphere from Nuclear Power Plants

While the renaissance of nuclear power was motivated by the increasing energy demand and the related climate problem, the recent history of nuclear power, more specifically two disastrous accidents have forced focus on nuclear safety. Although, experience gathered along nuclear reactor developments has sharpened the rules and regulations that lead to the commissioning of latest generation nuclear technology, an issue of crucial concern is the environmental monitoring around nuclear power plants. These measures consider principally the dispersion of radioactive material that either may be released in control actions or in accidents, where in the latter knowledge from simulations guide the planning of emergency actions. In this line the following contribution focuses on the question of radioactive material dispersion after discharge from a nuclear power plant.

WRF-chem Simulation of a Saharan dust Outbreak over the Mediterranean Regions

A fully coupled meteorology-chemistry-aerosol model (WRF-Chem) is applied to simulate the Saharan dust outbreak over the Mediterranean regions. Two dust emission schemes, namely, those of Jones et al., (2010), and Shao (2001) are evaluated using the the GOCART aerosol model. To investigate the performance of each dust emission scheme, a case study was carried out for a Mediterranean dust event that took place between 21 and 23 May 2014. Considering the time average Aerosol Optical Depth, simulation results reproduced satisfactorily the outbreak and transport pattern of dust plumes. However, the estimated dust emission amounts in each scheme differ greatly due to the presence of several tuning parameters, that must be adjusted considering satellite and ground based experimental data.

EVALUATION OF WIND POTENTIAL IN A REGION OF SOUTHERN BRAZIL

Knowledge of wind behavior plays a key role in the production of wind energy, in ambient ventilation and in air quality. In thisxa0study the wind speed behavior in Cachoeira do Sul (RS) is analyzed. Wind speed data was measured by a sonic anemometerxa0and it was used to estimate the potential for power generation in the period from 2010 to 2014 . One of the methodologies usedxa0for the study of wind was the statistical analysis using functions of probability density. There are several models of probability distribution in the literature for time series of data. For wind data, the most commonly used distribution is the Weibull function. This distribution is considered to be the most adequate for wind characterization and is also applied in the analysis of rainfall data, clarity index, water level prediction, among other applications. Thus, the objective of the present study is to obtain preliminaryxa0estimates of the wind potential of Cachoeira do Sul (RS) using the Weibull probability distribution to estimate the wind power. Thexa0results show that wind power is below 500 W=m 2 (in 50 m) which indicates low wind potential.

ANALYSIS OF THE PROPAGATION AND MAINTENANCE OF VORTICES GENERATED BY A STATIC AND ISOLATED MICROBURST

The Southern Brazilian region is specially affected by extreme weather events, very often intense wind gusts coming from deep convection may develop itself as a microburst producing winds higher than 100 km/h. In order to understand the physical and dynamical process evolved in this phenomena, a static and isolated microburst is produced through a Large Eddy Simulation. A quantitative analysis of propagation an maintenance of the microburst vortex ring is performed in order to understand its evolution.

DEVELOPMENT OF A MATHEMATICAL MODEL TO DESCRIBE THE CONTAMINANT DISPERSION IN MEANDERING CONDITIONS

In this work it’s derived a mathematical model to describe the meandering contaminants dispersion in the planetary boundary layer.xa0 The model employs a heuristic functional form for the velocity autocorrelation function which describes the negatives lobes observed in meandering data. Furthermore, the model is derived from the linearization of the Langevin equation. The mathematical equations, that represent the longitudinal and lateral wind components describe the bi-dimensional pattern of the meandering flow and can be utilized to calculate the contaminant concentrations occurring in situations in which the meandering phenomenon plays a decisive role.

MICROBURST FRONT DETECTION WITH FINITE TIME LYAPUNOV EXPONENTS

A microburst is a phenomena that occurs in the atmosphere which consist on a very intense downdraft that, after impinging on the ground surface, leads to strongly divergent winds at and just above the ground level. Such winds can reach more than 30 m/s -1 and are associated with high shear forces, representing a serious threat to aircrafts and buildings. The detection and tracking of the front of the microburst expansion at the ground level becomes an important and interesting field for researchers. Previous works show the detection of the vortex core but not for the vortex front. From velocity fields obtained from a LES simulation, we utilize Finite Time Lyapunov Exponents (FTLE) which measures the exponential divergence between particle trajectories. Then we identify manifolds which acts as separatrices of the flow and represent the edge or front of the vortex. By tracking the vortex front we also measure its displacement through time. xa0Find the front of the vortex using only vorticity and velocity fields is complicated and imprecise. Therefore, the combination of these two methods represents a new approach in this particular problem.

Eddy diffusivities for the convective boundary layer derived from LES spectral data

Large Eddy Simulation (LES) spectral data and Taylor statistical diffusion theory are used to obtain Eddy diffusivities in a convective boundary layer. The derivation employs a fitting expression obtained from LES data for the vertical peak frequency. The vertical Eddy diffusivities are well behaved and show similar patterns and magnitudes as those derived from experimental spectral peak frequency data. In addition, this new vertical Eddy diffusivity was introduced into an advection diffusion equation which was solved by Generalized Integral Laplace Transform Technique (GILLT) method and validated with observed contaminant concentration data of the Copenhagen experiment. The results of this new approach are shown to agree with the measurements of Copenhagen.

UMA NOVA EXPRESSÃO PARA A VARIÂNCIA DA VELOCIDADE TURBULENTA CONVECTIVA DERIVADA DE UM MODELO LES

The aim of this study is to derive a new expression for the vertical turbulent velocity variance using LES data in a convective boundary layer.

APLICAÇÃO DO MODELO WRF-ARW PARA DESENVOLVIMENTO DE PROJETOS EÓLICOS

O estudo consiste na comparacao dos resultados das simulacoes do WRF com medicoes de vento realizadas por uma torre anemometrica e dados fornecidos pelo Banco de Dados Meteorologicos para Ensino e Pesquisa (BDMEP) do Instituto Nacional de Meteorologia (INMET) por um periodo de 24 meses. Os resultados mostraram uma boa concordância entre os observados e os preditos pelo modelo, validando a metodologia aplicada na representacao de ventos da regiao. Isso permitira desenvolver series historicas sinteticas de longo prazo com a metodologia de mesoescala, ajudando no conhecimento da climatologia local e reduzindo as incertezas dos projetos eolicos.

INVESTIGATION WITH LARGE-EDDY SIMULATION OF THE SEA BREEZE REGIMES

Neste trabalho, investigam-se as interacoes entre a brisa maritima e a turbulencia sobre a Terra empregando uma simulacao dos grandes turbilhoes (LES). Os resultados mostram que o modelo LES e capaz de similar um regime de brisa Mar-Terra-Mar.