Resumo em Inglês:

The objective of this paper is to study the problem of orbital maneuvers for an artificial satellite moving in a Keplerian Force Field. Analytical equations are derived to solve this problem. Several cases are studied to validate the algorithm developed. The results show that the theory developed here are suitable for real simulations and mission analysis.

Resumo em Inglês:

The main objective of this work is to contribute to the development of a new tomographic reconstruction method well suited for processing signals obtained from electrical or other soft sensing field probes. The adopted approach consists in formulating the reconstruction problem in terms of an error function, which assesses the difference between a prospective and the actual internal contrast distribution (3D image), and searching for its minimum with the help of a specialized genetic algorithm (GA). Numerical simulations have been performed to demonstrate the feasibility of the proposed reconstruction method, as well as to emphasize the relation between the ill-posed nature of the problem and the topology of the minimization hyper-surface, and the importance of considering this relation when designing the numerical solution procedure. Results show that convergence is greatly enhanced when a priori information is introduced in the error function.

Resumo em Inglês:

This paper presents an experimental investigation of the mineral oil ISO VG10-refrigerant R12 mixture flow with foam formation in a straight horizontal 3.22 mm ID, 6.0 m long tube. An experimental apparatus was designed to allow the measurement of both pressure and temperature profiles along the tube as well as the visualization of the flow patterns. Tests were performed at different mass flow rates, several refrigerant mass fractions at the inlet of the flow, and inlet mixture temperatures around 29.0 °C. At the inlet of the tube a liquid mixture flow was visualized. In this region, both temperature and pressure gradient were constant. As the flow proceeded towards the exit of the tube the pressure drop produced a reduction of the refrigerant solubility in the oil yielding to the formation of the first bubbles. Initially, small and few bubbles could be noticed and the flow behaved as a bubbly flow. Eventually, the bubble population increased and foam flow pattern was observed at the exit of the tube. Due to the large formation of bubbles, both the temperature and the pressure of the mixture were substantially reduced in this region. Visualization results also showed that both flow regimes (bubbly and foam) were intermittent.

Resumo em Inglês:

This paper describes a versatile computational program for automatic two-dimensional mesh generation and remeshing adaptation of triangular, quadrilateral and mixed meshes. The system is flexible to be incorporated into an adaptive global or local remeshing procedure and for generating both, iso and anisotropic meshes. The main contribution of this work is to extend well established procedures for the generation and adaptation of both, iso and anisotropic triangular meshes, such as local and global remeshing as well as boundary layer mesh generation, to deal with iso and anisotropic quadrilateral and mixed meshes. Several examples are presented to illustrate the quality of the meshes produced, and the flexibilities of the computational system.

Resumo em Inglês:

A steady-state model is presented of the operation of a water-ammonia absorption system for production of scale ice. The model involves relations of thermodynamics, heat transfer, and fluid mechanics, and uses simplifying assumptions for the internal mass transfer processes, leading to a non-linear system with more than 100 unknowns and equations, that are reduced to a dimension-10 Newton-Raphson problem by means of the Substitution-Newton-Raphson approach. The model was validated against experimental data with good agreement.

Resumo em Inglês:

Wire electrical discharge machining (WEDM) is a specialized thermal machining process capable of accurately machining parts of hard materials with complex shapes. Parts having sharp edges that pose difficulties to be machined by the main stream machining processes can be easily machined by WEDM process. Technology of the WEDM process is based on the conventional EDM sparking phenomenon utilizing the widely accepted non-contact technique of material removal with a difference that spark is generated at wire and work piece gap. Since the introduction of the process, WEDM has evolved as a simple means of making tools and dies to the best alternative of producing micro-scale parts with the highest degree of dimensional accuracy and surface finish. This paper outlines the development of a model and its application to optimize WEDM machining parameters. Experiments are conducted to test the model and satisfactory results are obtained. The methodology described here is expected to be highly beneficial to manufacturing industries, and also other areas such as aerospace, automobile and tool making industries.

Resumo em Inglês:

Computer simulations have become very popular in the automotive industry. In order to achieve a good conformity with field test, sophisticated vehicle models are needed. A real vehicle incorporates many complex dynamic systems, such as the drive train, the steering system and the wheel/axle suspension. On closer inspection some force elements such as shock absorbers and hydro-mounts turn out to be dynamic systems too. Modern vehicle models consist of different subsystems. Then, each subsystem may be modeled differently and can be tested independently. If some subsystems are available as a set of nested models of different complexity it will be even possible to generate overall vehicle models which are well tailored to particular applications. But, the numerical solution of coupled subsystems is not straight forward. This paper shows that the overall vehicle model can be solved very effectively by suitable interfaces and an implicit integration algorithm. The presented concept is realized in the product ve-DYNA, applied worldwide by automotive companies and suppliers.

Resumo em Inglês:

The use of MEMS-based technologies for producing scanning mirrors enables its batch production with a consequent increase in the throughput and a decrease in the manufacturing costs per device. However, the use of Silicon as a structural material could introduce non-linearities in the device behavior due to the variation of its mechanical properties according to the crystalline orientation. The orthotropic properties when taken into account in the finite element model of the device could enhance the accuracy in the design of micromachined scanning mirrors. The model used in this paper does not take into account the orthotropic behavior, however, satisfactory results were obtained. To validate the finite element model, a modal analysis of the device was performed using the Laser Doppler Vibrometry method. The normal modes of the structure were identified and the results agree well with the finite element model. This work presents the FE model and experimental modal analysis results of a Silicon micromachined double-rotor scanning mirror.

Resumo em Inglês:

For linear time-invariant (LTI) state space systems it is well-known that its asymptotic stability can be related to solution properties of the Lyapunov matrix equation according to so-called inertia theorems. The question now arises how analogous results can be obtained for LTI descriptor systems (singular systems, differential-algebraic equations). The stability behaviour of a LTI descriptor system is characterized by the eigenvalues of the related matrix pencil. Additionally, by a quadratic Lyapunov function the stability problem can be discussed by solution properties of a generalized Lyapunov matrix equation including a singular coefficient matrix. To overcome this difficult problem of singularity, the Lyapunov matrix equation will be modified such that a regular Lyapunov matrix equation appears and asymptotic stability is preserved. This aim can be reached by shifting the system matrices in a well defined manner. For that the a priori knowledge of an upper bound of the eigenvalues is assumed. It will be discussed how to get such bound. The paper ends with an inertia theorem where the solution properties of a regular modified Lyapunov matrix equation are uniquely related to the asymptotic stability of the LTI descriptor system.

Resumo em Inglês:

The main objective of this work is to present and discuss some results of an integrated control system for a biped robot machine in the dynamic gait. We divided the integrated control system in two sub-systems: a control of the trajectories for the legs and the Automatic Generator of Trajectory. We designed the Automatic Generator of Trajectory by employing a neural network, which updates online the conditions of trajectory for the trunk, from the evolution of the gait, with the objective to reduce the magnitude of the resultant force and moment. We consider that this scheme is a new and interesting approach to generate online the trajectory for the trunk, giving so reflexes for the biped-walking robot.

Resumo em Inglês:

The process of voiced sounds production can be described as follows: air coming from the lungs is forced through the narrow space between the two vocal folds, which are set in motion in a frequency governed by the tension of their tissues. The vocal folds change the continuous flow that comes from the lungs into a series of pulses. Then, as the flow passes through the oral and nasal cavities it is amplified and changed until it is finally radiated from the mouth. This complex process can be modeled by a system of integral-differential equations. In spite of such complexity, this paper shows that it is possible to obtain synthetic voice sounds of satisfactory realism using simple mathematical models. The perception of a synthetic sound as natural is increased by choosing suitable waveforms for the time-varying subglottal pressure, rather than by augmenting the number of degrees of freedom of the mechanical model. This paper also shows possible ways to adapt the models to voices of men, women and children.

Resumo em Inglês:

The aim of this paper is to evaluate forces and torques in flexible joints of a flexible multi-body system (FMS). To represent such a FMS a 2D non-linear model based on finite element method is built. Its numerical form solution based on a stable integration scheme and on the non-linear Newton-Raphson method is described. As the evaluation procedure first requires that some model physical properties are obtained as identified parameters, two procedures are used: direct and indirect identification. They are respectively based on dynamic equilibrium verification and on comparison between simulated and measured kinematics of the proposed model. The development of the two procedures and a performance comparison between them is carried out.

Resumo em Inglês:

The present work is part of an effort for developing a methodology for the aeroelastic analysis of two-dimensional lifting surfaces using an unsteady, Euler-based, CFD tool for the calculation of the aerodynamic operator. The CFD tool solves the flow problem with the finite-volume method applied to an unstructured grid context. The proposed methodology is based on the determination of the aerodynamic operator with the transfer function technique, which is given, in the frequency domain, by the analysis of the system response to an exponentially-shaped pulse in the time domain. The response in the frequency domain is achieved with the Fast Fourier Transform (FFT) technique available in any mathematical manipulation tool, such as Matlab©. Some numerical experiments are performed involving unsteady subsonic and transonic flows around a flat plate and a NACA 0012 airfoil, and the results are presented as curves of generalized aerodynamic forces. The unsteady simulations start from a converged steady state solution obtained by the same CFD tool. Some unsteady validation results are compared with available data in the literature and the initial steps of the methodology are tested. The frequency domain results obtained agree very well with other numerical solutions given in the literature, which validates the present approach for the evaluation of the generalized aerodynamic forces for use in efficient, frequency domain, aeroelastic analyses.

Resumo em Inglês:

Fluid film forces are generated in multirecess journal bearings by two types of lubrication mechanism: the hydrostatic lubrication in the bearing recesses and hydrodynamic lubrication in the bearing lands, when operating in rotation. The combination of both lubrication mechanism leads to hybrid journal bearings (HJB). When part of hydrostatic pressure is also dynamically modified by means of hydraulic control systems, one refers to the active lubrication, resulting in the active hybrid journal bearing (AHJB). The AHJB is mathematically modeled based on the Reynolds' equations in land regions and a set of modified continuity equations for the lubricant flow in the bearing recesses, coupled to equations describing pressure and flow in the servovalves. The solution of such a set o equations allows the determination of fluid film stiffness and damping coefficients of the hybrid and/or active lubricated bearing. Such coefficients are a function of design and operational parameters, characterized by the Sommerfeld number as well by the gains of the feedback control system. The main contribution of the present theoretical work is to analyze the stability characteristics of a flexible rotor-bearing system by using passively and actively lubricated hybrid journal bearing. The dynamic of a flexible rotor is modeled by using finite element method and, after coupling the bearing dynamic coefficients to the rotor model, the feedback control law is defined and a suitable set of control gains is calculated for the active lubrication, leading to a rotor with a wider and more safety operational frequency range.

Resumo em Inglês:

The usual Lagrange equations of motion cannot be directly applied to systems with mass varying explicitly with position. In this particular context, a naive application, without any special consideration on non-conservative generalized forces, leads to equations of motions which lack (or exceed) terms of the form 1/2(<FONT FACE=Symbol>¶</font>m/<FONT FACE=Symbol>¶</FONT>q.2), where q is a generalized coordinate. This paper intends to discuss the issue a little further, by treating some applications in offshore engineering under the analytic mechanics point of view.

Resumo em Inglês:

This paper shows the design and analysis of a parallel three-dimensional linkage, conceived to work as the ankle and hip joints of an anthropometric biped robot. This kind of mechanism architecture provides low-weight, highly stable assemblies, and allows the use of actuator synergies. On the other hand, the mechanical transmission ratio is not usually favorable, and a non-linear kinematic model has to be derived and solved. The mechanism proposed here is driven by two rotational servo-actuators, and allows the joint to follow a specified angular trajectory determined by the gait pattern. Namely, the joint linkage can generate dorsi/plantar flexion and inversion/eversion of the ankle, and hip flexion/extension and adduction/abduction movements. Several approaches to the direct and inverse kinematical modeling of the linkage are presented and compared, regarding their accuracy and computational cost, where the last performance parameter is closely related to on-line computer implementing of the controller. Strategies to fit current gait angular amplitudes into the linkage workspace, as well as singularity analysis, are discussed. An optimization method was applied to find some geometrical design parameters of the linkage that minimizes a cost function. This function is the mean transmission ratio between the motor inputs and the joint output torques over a predefined dominion. The minimization is constrained to a minimum workspace area value and to minimum and maximum values of the design parameters. Several design solutions were generated. The chosen was one where the workspace is compatible to the gait amplitude requirements and that exhibits the lowest cost function. A biped robot using the linkage geometry designed in this paper has been built and tested with real human gait data acquired in a gait lab.

Resumo em Inglês:

The philosophy of the extremal disturbance analysis for dynamical systems with uncertain inputs is described. This analysis involves solving optimal control problems in which the time histories of the inputs (external disturbances) are regarded as the control functions and a response measure of the system serves as the performance index. The performance index should be maximized or minimized over the disturbances within a prescribed class. Often this class is specified by lower and upper bounds (a corridor) between which the values of the disturbance must lie. The maximization and minimization problems are referred to as the worst disturbance and best disturbance problems, respectively. The solutions of these problems provide the extreme values between which the response measure lies for any disturbance from the specified class. The extremal disturbance analysis is important, in particular, when designing standards for testing devices for the protection of fragile objects from impact loads. This approach is illustrated for a single-degree-of-freedom system that can be regarded as a simplified model of the equipment for sled tests of automobile restraint systems.

Resumo em Inglês:

This paper introduces practically important concept of local non-smoothness where any dynamical system can be considered as smooth in a finite size subspace of global hyperspaceomega. Global solution is generated by matching local solutions obtained by standard methods. If the dynamical system is linear in all subspaces then an implicit global analytical solution can be given, as the times when non-smoothness occurs have to be determined first. This leads to the necessity of solving a set of nonlinear algebraic equations. To illustrate the non-smooth dynamical systems and the methodology of solving them, three mechanical engineering problems have been studied. Firstly the vibro-impact system in a form of moling device was modelled and analysed to understand how the progression rates can be maximised. Periodic trajectories can be reconstructed as they go through three linear subspaces (no contact, contact with progression and contact without progression). In the second application frictional chatter occurring during metal cutting has been examined via numerical simulation method. The analysis has shown that the bifurcation analysis can be very useful to make an appropriate choice of the system parameters to avoid chatter. The last problem comes from rotordynamics, where nonlinear interaction between the rotor and the snubber ring are studied. The results obtained from the developed mathematical model confronted with the experiment have shown a good degree of correlation.