ABSTRACT This study aimed to model nutrient losses in an Oxisol under varied soil properties and vegetation cover. The experimental area was located at the Paraná Rural Development Institute, in Santa Tereza do Oeste, Paraná, Brazil. The treatments consisted of six cover crops in summer, six cover crops in winter, and management systems no-tillage (NT) traditional (control), NT with gypsum, and NT with scarification. Nutrient data were collected at each natural rainfall through sample collection from collection troughs. The design was completely randomized, and the data were adjusted using an exponential function of two variables, as a function of soil density, macroporosity, straw dry mass, green cover, and rainfall. Greater losses of Mg and Ca was related to higher soil density and lower macroporosity. Lower losses of Mg, Ca, K, and P were associated with lower straw dry mass and higher green cover. K and P losses were stable for all soil density values, but they decreased with an increase in macroporosity.

Este trabalho apresenta uma abordagem para a solução de problemas de escoamento tridimensional de fluidos com aplicação no problema da cavidade cúbica com tampa deslizante. A quantidade de movimento é modelada pelas equações de Navier-Stokes, as quais são discretizadas utilizando o método de diferenças finitas. A solução para o problema foi obtida utilizando o método SOR (Successive Over Relaxation) para resolver a equação de Poisson para pressão para cada passo de tempo. Apresentam-se os resultados de simulações numéricas na forma de gráficos da velocidade, pressão e superfícies de corrente. É observada a formação vórtices a partir do cantos da cavidade próximo à tampa deslizante. Os resultados generalizam a solução do problema da caixa bidimensional e mostram que as estratégias numérico-computacionais empregadas são válidas e possuem boa qualidade numérica.

This paper presents an approach to solving problems of three-dimensional fluid flow with application to the problem cubic cavity with sliding covering. The fluid flow is modeled by the Navier-Stokes equations which are discretized using the finite difference method. The solution to the problem was obtained using the SOR method (Successive Over Relaxation) to solve the Poisson equation for pressure for each time step. The results of numerical simulations are presented as graphs of velocity, pressure and surface current. It is observed the formation of tridimensional vortices rising from the corners of the cavity near the covering. The results generalize the solution of the two-dimensional case and show the numerical-computational strategies employed are appropriated and exhibit good numerical quality.