Non-linear dynamics of a drill-string with uncertain model of the bit–rock interaction

The drill-string dynamics is difficult to predict due to the non-linearities and uncertainties involved in the problem. In this paper a stochastic computational model is proposed to model uncertainties in the bit–rock interaction model. To do so, a new strategy that uses the non-parametric probabilistic approach is developed to take into account model uncertainties in the bit–rock non-linear interaction model. The mean model considers the main forces applied to the column such as the bit–rock interaction, the fluid–structure interaction and the impact forces. The non-linear Timoshenko beam theory is used and the non-linear dynamical equations are discretized by means of the finite element method.     

Simulation of free and forced convection incompressible flows using an adaptive parallel/vector finite element procedure

The numerical simulation of complex flows demands efficient algorithms and fast computer platforms. The use of adaptive techniques permits adjusting the discretisation according to the analysis requirements, but creates variable computational loads that are difficult to manage in a parallel/vector program. This paper describes the approach adopted to implement an adaptive finite element incompressible Navier–Stokes solver on the Cray J90 machine. Performance measurements for the simulation of free and forced convection incompressible flows indicate that the techniques employed result in a fast parallel/vector code. Copyright © 1999 John Wiley & Sons, Ltd.     

Sedimentation rate and accumulation of nutrients in the Upper Paraná river floodplain

Journal of Radioanalytical and Nuclear Chemistry - The objective was to rebuild the history of sedimentation and accumulation of nutrients rate in the Upper Paraná River floodplain. Two corers...     

Investigation of ground- and excited-state photophysical properties of 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphyrin with ruthenium outlying complexes

The present work employs a set of complementary techniques to investigate the influence of outlying Ru(II) groups on the ground- and excited-state photophysical properties of free-base tetrapyridyl porphyrin (H(2)TPyP). Single pulse and pulse train Z-scan techniques used in association with laser flash photolysis, absorbance and fluorescence spectroscopy, and fluorescence decay measurements, allowed us to conclude that the presence of outlying Ru(II) groups causes significant changes on both electronic structure and vibrational properties of porphyrin. Such modifications take place mainly due to the activation of nonradiative decay channels responsible for the emission quenching, as well as by favoring some vibrational modes in the light absorption process. It is also observed that, differently from what happens when the Ru(II) is placed at the center of the macrocycle, the peripheral groups cause an increase of the intersystem crossing processes, probably due to the structural distortion of the ring that implies a worse spin-orbit coupling, responsible for the intersystem crossing mechanism.     

Smooth decomposition of random fields

The Smooth Decomposition (SD) method was introduced to analyze discrete-time signals and generalized to continuous-time vector-valued random processes. The SD is obtained solving a generalized eigenproblem defined from the covariance matrix of the random process and the covariance matrix of the associated time-derivative random process which defines the decomposition basis. This paper presents a new extension of the SD to continuous-time and continuous-space vector-valued random processes, classically named random fields. This generalization is a major step since one now deals with operators in infinite-dimensional spaces and not matrices. It is shown that in this new context the main properties of the SD are preserved. Applied to the responses of randomly excited continuous mechanical systems, the SD can be considered as an output-only analysis tool. Moreover, two natural orderings are defined to classify the decomposition terms which permit to interpret the SD in terms of modal analysis or in terms of Karhunen–Loève analysis.