Resumo em Inglês:

ABSTRACT This paper deals with robust control of underactuated manipulator robots. It presents a comparative study of four combined controllers H2, H∞ , H2/H∞ and µ-synthesis, pluscomputed torque method. These controllers are applied in an actual underactuated manipulator robot with 3 degrees of freedom, of which joints can be configured as active or passive ones. The study performed in this paper compares the robustness of each controller when different disturbances are considered.

Resumo em Inglês:

This paper presents a manipulation planning approach for robot hands that enables the generation of finger trajectories. The planner is based on a hybrid approach that combines discrete-continuous kinematics using a fully discrete transition system. One of the main contributions of this work consists in the representation of the universe of different submodel combinations, as states in a discrete transition system. The manipulated object geometry is taken into account and the system composed by the object and the hand is modeled as a set of closed kinematical chains. The methodology enables the synthesis of complex manipulation trajectories, when one or more fingers change the contact condition with the object. Contact condition changes include rolling contact, sliding contact, contact loss and contact establishment. Tests were carried out employing a three finger manipulation task in computer simulations and with an experimental setup.

Resumo em Inglês:

The available technology for tunnel kilns in Brazil is practically empirical and there is a lack of fundamental studies developed as an aid for the design of new kilns or for the retrofit of old ones. Here, a thermal model of a tunnel kiln is developed allowing the numerical simulation of kilns and dryers aiming toward a more efficient and less energy consuming design. The model is then systematically applied in the design of a new kiln to be used for firing clay tiles, bricks and similar products, with natural gas and sawdust as fuels. The results include the three-dimensional temperature distribution within the walls, gas and load along the kiln and a complete thermal energy balance including all energy fluxes related to the process. The strategies for kiln design are discussed and the advantages of combining the low cost of the wood sawdust and the ease of adjustment and quality of the natural gas combustion are evidenced.

Resumo em Inglês:

Lower limb orthoses are often plagued by a high rejection rate, due both to the excessive effort demanded from their users and to the lack of aesthetics of the resulting gait. These factors are caused, to a great extent, by the fact that orthoses force the whole gait to be performed with the knee articulation in full extension. This work presents a light and compact device, with a low energy consumption, that can improve the performance and the gait aesthetics of knee-ankle-foot orthoses (known as KAFO). To do so, we explore the natural dynamics of the lower limb through a spring that is attached to a standard orthosis system. We also add control circuitry, a small electric motor, sensors and microprocessors to the standard orthosis, so that we can control the whole gait in a relatively natural manner. We have designed the system through a large set of simulations and have shown that the passive dynamics of the lower limb, driven by a burst of energy from a spring at the beginning of the swing phase, is sufficient to reduce the compensation mechanisms required during the gait with orthosis. Thus, this strategy is an alternative to existing solutions relying on functional electrical stimulation (FES), which suffers from limitations such as rapid muscle fatigue and difficult motion control. We describe the design of the device, the model adopted for the swing phase of the gait, the numerical simulations performed and the tests we have conducted.

Resumo em Inglês:

Some power ultrasonic transducers, such as Tonpilz transducers, require high-power transmitting capability as well as broadband performance. Optimized vibrational modes can achieve these requirements. This work compares the resonant characteristics and the surface vibration modes between a homogeneous piezoelectric ring and a 1-3 piezocomposite ring, both used in power ultrasonic transducers. This is the first step in the design of power transducers. Analytical models and finite element results are validated by electrical impedance measurements and the surface acoustic spectroscopy method. Excellent agreement between theoretical and experimental results was obtained. Results show that using piezocomposite ceramics minimize superposition of undesirable modes and increase the bandwidth, as shown in sonograms.

Resumo em Inglês:

Steel sheet coated with zinc or 55%Al-Zn is widely used at the civil construction, mainly for roofing and cladding applications. The 55%Al-Zn coated steel shows mechanical properties slightly different from zinc coated steel, even under the same heat cycle processing, due to the higher molten metal temperature and also to the higher strength of the 55%Al-Zn coating. The knowledge of those differences can be used by the final users to evaluate if some of those products are not suitable for any specific application. Although those two coated products are widely used at the civil construction in Brazil, only a limited literature is available on the difference between the mechanical properties of those products. Through tensile tests of commercial grade samples - as coated and after removing the coating - the aim of this paper is to evaluate the mechanical properties (tensile strength, yield strength, total elongation and hardening coefficient) and also how much the coating influences the mechanical properties of the zinc and 55%Al-Zn coated steel. The 55%Al-Zn coated steel showed higher yield and tensile strength and lower total elongation and hardening coefficient compared to zinc coated steel and the coating showed a significant influence on the mechanical properties of both products.

Resumo em Inglês:

This work analyses the performance of the TiN/TiCN, TiAlN, TiN/TiAlN and TiN/TiAlN/WCC coatings on HSS M2 drills used in the drilling of the aluminium-silicon alloy ISO 3522 AlSi8Cu3Fe, correlating the life of the tools to the coating adhesion characterization experiments. Coating adhesion was characterized using Rockwell C indentation tests and scratch tests with progressive load. The performance of the coatings in the life experiments was the following, in decreasing order: TiN/TiCN, TiAlN, TiN/TiAlN/WCC and TiN/TiAlN. In the adhesion characterization experiments with TiN/TiCN there were no cracks or delamination of the coatings, which justifies its best performance in the life experiments.

Resumo em Inglês:

In this experimental study, the pulsed ultrasonic Doppler velocimetry was used to measure simultaneously the local velocity and the local concentration in a flow of solid-liquid suspension in a horizontal pipe. In order to distinguish between the Doppler signals coming from the continuous phase, water and those of the glass bead particles larger than the Kolmogorov length scale and the wavelength of the ultrasonic wave, a threshold is imposed on the integral of the power spectral density of the Doppler signal. The new approach measurement of the local concentration was used. It consists of counting a number NP of the Doppler signals of the solid particles crossing the measurement volume and a number NPt of the Doppler signals of the solid particles crossing the control volume. The concentration profile is then represented by the ration NP / NPt. The results obtained show that the suspension of fine particles, which represents a tracer, behaves as a homogenous fluid. For large particles, we confirmed the existence of the slip velocity and the effects of both concentration and size particle on the turbulence. The use of two distinct measurement volumes allows the direct determination of the turbulent length scales. The results show that the turbulence characteristics of the carried fluid are modified by the presence of the solid particles.

Resumo em Inglês:

This paper presents an immersed boundary formulation for three-dimensional incompressible flows that uses the momentum equation to calculate the Lagrangian force field indirectly imposing the no-slip condition on solid interfaces. In order to test the performance of this methodology the flow past a sphere for Reynolds numbers up to 1,000 have been calculated. Results are compared with numerical data from other authors and empirical correlations available in the literature. The agreement is found to be very good.

Resumo em Inglês:

This work presents a comparative study among three linearization schemes widely used in petroleum reservoir simulation, namely the Implicit Pressure Explicit Saturation (IMPES), Fully Implicit (FI) and Adaptive Implicit Method (AIM). Attention is given to the criterion used for switching from IMPES to FI and vice-versa. The black-oil model considering the oil-water flow is employed. The equations are discretized using an unstructured Voronoi mesh in a finite-volume framework. The numerical results are analyzed based on the number of iterations in the Newton and solver procedures, number of implicit volumes, and mass balance error of components. The effect of the stopping criterion on Newton's iterations is also investigated. The outcome of the study reveals that adaptive implicit methodologies can be a good choice when unstructured grids are present, allowing the use of time steps with the same order of magnitude as the ones used in FI procedures, but with reduction in the computational effort.

Resumo em Inglês:

This text is a snapshot of the last four years of the Journal of the Brazilian Society of Mechanical Sciences and Engineering (JBSMSE). The last four years is related to the period of the current editorial team which is coming to an end. At first, we present the evolution of the paper manuscript submission and peer review system towards an online electronic system, the SciELO system. This resulted on a much more reliable and efficient solution. After, a brief summary of the current peer review process is presented together with statistics of paper manuscripts submitted and approved for publication in each section. A qualitatively analysis of time duration for a peer review process is realized while trying to identify drawbacks and possible improvements. An analysis of the paper download requests via the SciELO system, during the past 4 years, is presented. Some of the most downloaded papers are listed together with their statistics. It is claimed here that number of downloads could be a possible Scientometrics index. At the end, we draw some conclusions on the current importance of the JBSMSE.