Álvaro Luiz De Bortoli

Development of reduced reaction mechanisms for hydrogen and methanol diffusion flames

Abstract Biofuels, such as biohydrogen, biomethanol, bioethanol and biodiesel may be the future of energy for transportation. The methanol can be used directly for powering Otto engines or fuel cells; it is commonly used in biodiesel production for its reactivity. Biohydrogen is a replacement for fossil and biorenewable liquid fuels. Based on a mechanism composed by 20 reversible elementary reactions among 8 reactive species, we propose a reduction process to obtain the mechanism of hydrogen, and from 129 reversible elementary reactions among 23 reactive species, we obtain a reduced mechanism for the methanol. Therefore, the aim of this work is the development of an algorithm consisting of 7 steps, which eliminates the fastest reactions of the reaction mechanism since the slowest reactions are rate-determining. The main advantage of the strategy is the decrease of the work needed to solve the system of chemical equations.

A parallel Navier–Stokes solver for the rotating flow problem

In this paper, we investigate the parallel solution of rotating internal flow problems, using the Navier–Stokes equations as proposed by Speziale and Thangam (in 1983) and Speziale (in 1985). A Runge–Kutta time-stepping scheme was applied to the equations and both sequential and message-passing implementations were developed, the latter using MPI, and were tested on a four-processor SGI Origin200 distributed, global shared memory parallel computer and on a 32-processor IBM 9076 SP/2 distributed memory parallel computer. The results show that our approach to parallelize the sequential implementation requires little effort whilst providing good results even for medium-sized problems. Copyright

Equations of Fluid Dynamics

This chapter presents the basic equations of fluid dynamics for reactive and nonreactive flows in Cartesian coordinates. The equations are based on the balance obtained for mass, momentum, and energy. It also presents the derivation of the equation for the mass fraction of the chemical species, and shows the terms to be added to the equations of momentum and energy. The reactive term is proportional to the species concentration and follows the Arrhenius kinetics. The set of equations is presented using Einstein notation, which allows simplification of writing the equations system, in order to facilitate the numerical implementation.

A new formalism for the dynamic modelling of cables

This article proposes a new formalism for the dynamic modelling of cables that can even be applied when they are submitted to cross flow of water or air. An important application is the case of umbilical cables used in remotely operated vehicles. The primary basis for the formulation is to assume that the continuous flexibility is represented by a discrete approach, consisting of rigid links connected by elastic joints, allowing movement in three dimensions. Each elastic joint allows three independent movements, called elevation, azimuth and torsion (twist). A significant contribution of the proposed formalism is the development of a compact equation that allows obtaining the Lagrangian of the system directly and automatically, regardless of the number of links chosen to form a chain of rigid bodies connected by flexible joints to represent the continuous flexibility of the cable. This formulation allows the construction of an algorithm for obtaining the equations of the dynamic model of flexible cables.

Um novo algoritmo para a modelagem dinâmica de manipuladores flexíveis

Active control law development of flexible structures is still an open problem. It has been the object of many researches, mainly starting from the eighties. In spite of many works dedicated to the dynamic modeling of such structures, the obtaining of a realistic dynamic model is of fundamental importance for the control law development. In the present work it is introduced a new algorithm to determinate in a quite simple way, the dynamic differential equations of a one flexible link manipulator. It is still developed analytic transfer functions for this specific problem, which are important for the validation of the lumped mass approach model proposed in the form of an algorithm.

Reduction of Reacting Flow Models by the Reaction-Diffusion Manifolds Method for Methane/Air Turbulent Jet Diffusion Flames

Combustion processes are usually described using detailed chemical kinetic mechanisms. Sometimes, in the modeling of the complex burner systems is necessary to use chemical reduction techniques to decrease the stiffness of the system of differential equations. The principal difference among the existing reduction methods appears in the tactics to distinguish between slow and fast processes. In the present work the Reaction-Diffusion Manifolds method is applied to the methane/air reaction mechanism, in order to reduce the chemical kinetic model, depending on transport properties. The approach allows incorpora ting the effect of the coupling of reaction and diffusion processes. The methodology applied, based on slow manifolds of low dimension, allows decreasing the computational time needed to obtain results for confined turbulent jet diffusion flame. The Large-Eddy Simulation is required to represent the turbulent flow. The numerical results compare favorably with the experimental data available in the literature.

Implications of time adjustments at micro, macro and meso levels in undergraduate and graduate piano students’ performance

ABSTRACT A short piano piece was prepared by undergraduate and graduate piano students (N = 15) without guidance from their piano teachers. Temporal parameters were analyzed in several time frames, from a phrase-to-phrase level to an interonset interval. At a macro level, local tempo was shown to be a crucial parameter that divided the students into two groups that differed in their approach to a particular phrase, revealing the degree of proficiency in terms of interpretive decisions. The mathematical modeling of this phrase was further analyzed in terms of the mean squared error in comparison to the nominal (technical, strict tempo) and pianist (artistic) performance. This approach was employed to classify the students’ performance in categories that were shown to be more related to their proficiency level than to their academic level. From the instrument pedagogy point of view, this research suggests fomenting in students a critical conscious about rhythm structure and its implications for coherence within the limits set by stylistic conventions of western classical music.

Numerical analysis of the acoustics of a diffusion flame

The aim of this work is to obtain an analytical-numerical solution for a jet diffusion flame in a closed domain and analyze its acoustic field. The combustion chamber is a closed three-dimensional region in which a jet of methane is injected separated from the jet of air. To analyze the influence of the flame under the acoustic field, two tests are performed: in the first test occurs only the mixing, and in the second test occurs the mixing and the chemical reactions. The proposed model uses the Navier-Stokes, mass conservation and wave equations, which are solved numerically. The flow equations are coupled with the equations for the mass fraction of chemical species and temperature, which are solved analytically based on the flamelet model. The numerical scheme follows the finite difference method and the Runge-Kutta multistage scheme is employed for the integration in time. An estimate for the error is presented based on the solution of three grids using the error estimator of Richardson. The results show good agreement with data from the literature. The proposed model is a quick and less expensive option to investigate the acoustic field of reactive flows in a closed region.

Mathematical Techniques in Obtaining Reduced Kinetic Mechanisms With Illustration for Methane Flames

The computational treatment of detailed kinetic reaction mechanisms of combustion is very expensive, especially when the objective is the implementation of CFD (Computational Fluid Dynamics) models; therefore, major effort in searching for methods of mechanisms reduction has been observed. In the pursuit of efficient techniques, various ideas and theories have emerged in recent years. Sensitivity analysis, lumping and DRG (Directed Relation Graph) are some of these techniques, which seem to be powerful tools that can assist in this challenge. This paper shows these strategies, objectively describing their applications on reduction of reaction mechanisms. A reduced mechanism for methane flames consisting of six-step among nine reactive species is obtained from the skeletal mechanism, which consists of 25 reactions.

Mixing and Turbulent Flows

This chapter presents the basics of mixing in turbulent flow, starting with the notion of mixture fraction. This formulation can be extended to flows with various mixture fractions, when the number of reactions is small. Following is presented the basics of turbulent flows, such as turbulence scales, and the averages of Reynolds and Favre, which are useful for writing the reactive Navier equations. Notions of turbulence and models for the turbulent viscosity to be used with large-eddy simulation (LES) are presented. LES is the preferred technique, because there are no conditions for solving realistic Reynolds numbers, encountered in practice, using direct numerical simulation techniques.