Resumo em Inglês:

This work proposes an experimental technique for the simultaneous estimation of temperature-dependent thermal diffusivity, α, and thermal conductivity, λ, of insulation materials. The thermal model used considers a transient one-dimensional heat transfer problem. The determination of these properties is done by using the principle of the Mixed technique. In this technique two objective functions are defined, one in the frequency domain and the other in the time domain. The objective function in the frequency domain is based on the square difference between experimental and calculated values of the phase angle, while the other objective function is the least square error function of experimental and calculated signals of temperature. The properties α and λ are obtained by using an experimental apparatus that basically consists of a Polyvinyl Chloride (PVC) sample exposed to different temperatures inside an oven. The temperature inside the oven is controlled by a PID temperature controller. The properties α and λ were estimated for 7 (seven) points of average temperature in a range from 20 ºC to 66 ºC. The properties were determined with an additional heating of approximately 4.5 K on the frontal surface. Analyses of sensitivity, sensors location and sample dimensions were also made.

Resumo em Inglês:

This paper studies the linear feedback control strategies for nonlinear systems. Asymptotic stability of the closed-loop nonlinear system is guaranteed by means of a Lyapunov function, which can clearly be seen to be the solution of the Hamilton-Jacobi-Bellman equation thus guaranteeing both stability and optimality. The formulated Theorem expresses explicitly the form of minimized functional and gives the sufficient conditions that allow using the linear feedback control for nonlinear system. The numerical simulations the Duffing oscillator and the nonlinear automotive active suspension system are provided to show the effectiveness of this method.

Resumo em Inglês:

Coolants are widely used in industries for metal cutting operations. Though there are varieties of coolants available, the most widely used are water-soluble coolants because of their low cost and better heat dissipation compared to straight cutting oils. In the present investigation, amongst the various causes, which deteriorate the coolant, the role of hardness of water is primarily studied. Accordingly, water from different sources with varying hardness is considered and coolants are prepared from the same. The extent to which hardness can affect the performance of coolants is studied as a function of coolant lubricity in a reciprocating tribometer. Further, the effect of entry of coolants into lubricated machine tool slideways is also assessed by evaluating the mixture of coolant and lubricating oil for its frictional behavior. This is important from assessing the impact of the mixing of coolant and lubricating oil on machine tool slideways with regard to positioning exactness and stick slip behavior of slideways in terms of coolant-lube compatibility.

Resumo em Inglês:

In sheet metal stamping, several variables must be taken into account such as the material's mechanical properties, the tool's geometry, interface lubrication between punch and sheet metal and deformation rate, among others. This paper reports on a study of the lubricant's influence on the stretching forming process. The lubricants used ranged from liquid, such as mineral and vegetable oils with extreme pressure additives and synthetic fluids to solid PVC (polyvinyl chloride) and polyurethane films. In this work, the main objective was to study a minor strain profile as an alternative method to analyze the influence of solid and liquid lubricants on stretching forming of high stampability steels (DC 06). The minor true strain distribution profile was obtained, from the die radius to the punch pole, from stamping tests with stretching characteristics. Analyses of the strain distribution profile and of the fracture position allow an evaluation of the lubrication efficiency. Of the five lubricants studied, the results indicated that the solid polyurethane film yielded the best performance, promoting a more homogeneous distribution profile of the minor true strain (ε2), increasing from the die radius to the punch pole, where tearing of the metal sheet occurred.

Resumo em Inglês:

In mechanical system modeling, uncertainties are present and, to improve the predictability of the models, they should be taken into account. This work discusses uncertainties present in boundary conditions using the model of a vibrating Timoshenko beam, free in one end and pinned with rotation constrained by a linear elastic torsional spring in the other end. The Finite Element Method is used to discretize the system and two probabilistic approaches are considered to model the uncertainties: (1) the stiffness of the torsional spring is taken as uncertain and a random variable is associated to it (parametric probabilistic approach); (2) the whole stiffness matrix is considered as uncertain and a probabilistic model is constructed for the associated random matrix (nonparametric probabilistic approach). In both approaches, the probability density functions are deduced from the Maximum Entropy Principle. In the first approach only the uncertainty of a parameter is taken into account, and in the second approach, the uncertainties of the model are taken into account, globally. Both approaches are compared and their capability to improve the predictability of the system response is discussed.

Resumo em Inglês:

This paper concerns the numerical simulation of the flow around an oscillating circular cylinder, which moves with constant velocity in a quiescent Newtonian fluid with constant properties. For each time step of the simulation a number of discrete Lamb vortices is placed close to the body surface; the intensity of each of these is determined such as to satisfy the no-slip boundary condition. The aerodynamic loads acting on the surface of cylinder are computed using the integral formulation derived from the pressure Poisson equation. The influence of the frequency and amplitude oscillation on the aerodynamic loads and on the Strouhal number is presented and discussed.

Resumo em Inglês:

The steady flow of incompressible and electrically conducting micropolar fluid flow through a rectangular channel is considered taking Hall and ionic effects into consideration. An external uniform magnetic field is applied which is directed arbitrary in a plane perpendicular to the flow direction. The governing partial differential equations are solved numerically using finite difference method, and the effects of micropolar parameters, magnetic parameter, Hall parameter and ion slip parameter on the velocity and microrotation are discussed.

Resumo em Inglês:

The traditional welding flux development has been by cost, material, time and labour intensive experiments. The extensive and expensive trial and error experimentation is needed because it is often difficult to know a priori how the flux ingredients interact to determine the operational characteristics of the flux and the final performance of the welded structure. The limitation of the traditional approach includes: (1) long lead-time (2) expensive experiments in terms of materials and energy consumption and labour requirements (3) the flux developed can not be guaranteed to be optimal and (4) inability to identify and quantify direct and interaction effects of flux ingredients. These constraints are due to the paucity of statistical modelling tools in welding flux technology. Since prediction models are derived from designed experiments, flux researchers need other methods by which flux experiments may be designed. This paper discusses a statistical modelling tool known as mixture experiment which has the potential to revolutionize welding flux development technology. Mixture design is discussed but not fully developed. The procedure of mixture experiment, analytical model forms and the sequence of model fitting are discussed. Areas of welding flux research where the various mixture designs may be useful are suggested.

Resumo em Inglês:

Trajectory planning strategy is proposed to jump over an obstacle integrated three various dynamics in one-legged multi-joint hopping robot. A concept of inertia matching ellipsoid and directional manipulability are extended to optimize take-off postures. Optimized results have been used to plan hopping trajectory. Aimed at the sensitivity of motion trajectory to constraint conditions, a 6th polynomial function is proposed to plan hopping motion and it has a better robustness to the parameters change of constraint conditions than traditional 5th polynomial function. During flight phase, an iterative method and angular momentum theory are used to control posture to a desired configuration. In order to lift foot over an obstacle, correction functions are constructed under unchanged boundary constraint conditions. During stance phase, robot trajectories are planned based on internal motion dynamics and steady-state consecutive hopping motion principle. A prototype model is designed, and the effectiveness of the proposed method is confirmed via simulations and experiments.

Resumo em Inglês:

Most of the works accomplished in the optimization area in the cement industry are addressed to solve problems just considering only one variable, forgetting that it includes too many variables and they act at the same time. Among the main variables it can be mentioned the quality of the final product, the environmental ones, the costs along the process and the reduction of the fossil fuels (primary) employed through the use of alternative fuels (secondary), among others. The present work intends to build a mathematical model using optimization tools seeking to improve the cement production process foreseeing what can happen with the clinker and the emissions when the industrial residues co-processing technology is used as alternative or secondary fuel. In the optimization process a new approach called Particle Swarm Optimization (PSO) is employed, which is based on the Cauchy and Gauss distribution considering several process restrictions such as the specific fuel consumption, the cement quality and the environmental impact. The results obtained with PSO were precise and promising and they were compared with the classical Sequential Quadratic Programming (SQP). It was also possible to evaluate the levels of primary fuels substitution through the alternative or secondary ones.

Resumo em Inglês:

This work presents a methodology for self-adaptive finite element analysis of two-dimensional elastic-plastic structures. The self-adaptive process is based on an h-type refinement, with a posteriori error estimation. Two types of error estimators are available. The first is based on effective stress (Lee and Bathe, 1994) and the second is based on a ratio of plastic work (Peric et al., 1994). In the non-linear adaptive process for incremental plasticity analysis, a technique for interpolating analysis variables across distinct meshes (Lee and Bathe, 1994) is adopted. The von Mises yield criterion, with isotropic hardening, is adopted. Fracture problems are used to evaluate the performance of the adaptive process.