Applied Mechanics and Materials Vol. 775

Abstract: This study explores the curvature and mechanical sensitivity of a pre-stressed layered plate embedded with a piezoelectric layer in large deflection. Piezoelectric effect was included in deriving the nonlinear governing equations but the arising nonlinear terms are neglected, yielding a standard Bessel equation or a modified Bessel equation for the lateral slope. Analytical solutions are developed and further manipulated to obtain lateral curvature and mechanical sensitivity. The results for a nearly monolithic plate under low pretension and low voltage applied across the piezoelectric layer agree well with those of CPT for a single-layered plate under pure mechanical loading. For typical symmetric 3-layered piezoelectric plates, the solutions show that, piezoelectric effect is apparent only up to a moderate initial tension. Beyond a moderate threshold value, the pretension turns to be dominant, resulting in nearly zero curvature and uniform mechanical sensitivity throughout the entire plate.

Abstract: Energy is vital to machines and equipment basic functioning. On the other hand, it has an ambiguity determined by its detrimental side under other circumstances. This paper aims to present a review of simple laws of physics / mechanics in order to understand some benefits of using such energies (kinetic and potential energies), in order to process products or generating movement (mechanical energy). However, also shows its damaging side for driving systems, where such energies may generate catastrophes, usually due to high impacts. This last, which destroys complete or partial systems due to the absence of any robust / preventive protection. There is a safety manner (solution) to protect the systems, described along the text.

Abstract: According to the law of energy conservation and the second law of Kepler, this paper obtains the spacecraft velocity in perilune and apolune. Based on trajectory inversion thought, this paper obtains position and velocity direction in the perilune and apolune. For the five sub stages of soft landing, this paper discusses the optimal control strategy: establishing optimization model of genetic algorithm for the main deceleration section, the terminal constraint condition is reflected on the fitness function through the penalty function, combined with linear iterative thought, the winner engine thrust and direction angle are obtained. Aiming at the rapid adjustment period, the spacecraft angle change is done equivalent decomposition and discrete linear, so the thrust can be obtained through the angle change provided by adjusting attitude engine and combined with rigid body motion law.

Abstract: This paper considers the problem of stabilizing an integral process with time delay by a PID controller. As the proportional gain reaches the extreme value, the closed-loop system contains a double pole on the non-negative imaginary axis. Using this property, the admissible range of the proportional gain is derived, also the corresponding integral gain and derivative gain are obtained. For a fixed value of the proportional gain, the stability region in the plane of the integral and derivative gains is determined analytically. Moreover, the admissible ranges of the integral and derivative gains are computed and found to be non-convex. A numerical example illustrates the method presented.

Abstract: The pareto optimal controller design on a two-track vehicle dynamic model with 8-degrees of freedom considering two simultaneous conflicting objective functions has been made in order to prevent the rollover phenomena. In this regard, the requisiteness of trading off among the conflicting requirements of vehicle dynamic control results in utilizing multi-objective optimization techniques. More effectively, a multi-objective uniform-diversity genetic algorithm (MUGA) with a diversity preserving mechanism known as the ε-elimination algorithm has been used to optimize multi input multi output (MIMO) sliding mode controller. The most important conflicting objective functions that have been considered for minimization in this study are, control effort and vehicle roll angle, correspondingly. Finally, The comparison of the obtained results with those in the literature demonstrates that the strategy employed cause remarkable improvement in rollover prevention and maneuverability.

Abstract: Progress in the field of microelectronics and micromechanics has created new opportunities for the development of fluid power microsystems and microhydraulics. Miniaturization of hydraulic elements allows replacing the classical hydraulics with microhydraulics, where due to size or weight the former cannot be applied. Gear pumps are common use due to their reliability, resistance to working medium impurities, high efficiency, small size in comparison with other pumps and simple and compact design. Therefore micropumps often associate with a gear pump type. A micropump entails microbearings production. This requirement leads to cost increasing due to requirements to high accuracy of manufacturing. The paper focuses on a method for micropumps production without bearings. The idea based on application of materials with satisfactory friction coefficient in pairs. Friction pairs analysis made from different polymer and composite materials was carried out. As a result a gear micropump was designed and produced.

Abstract: With the increasing complexity of the space mission, the ability of fast reconstruction of manipulator is more and more important. To solve the problem of space manipulator’s fast reconstruction, this paper designs a novel manipulator that contains mechatronics modular joints and a connecting mechanism. Compared to the traditional manipulator, the manipulator in this paper have the advantage of great convenience of assembling and replacement of the modular joint. In this paper, we analyze the relationship between tolerance ability and structural parameters and computed the tolerance ability after optimization of the connecting mechanism; Using the perturbation method, we conducted the simulation of analysis error. Results show that relationship between the end position error and the error of the modular joints is approximate linear, which providing a theory instruction for the design of manipulator.

Abstract: This article focuses on the complicated dynamics behavior of the nonlinear vibrations of the bistable cantilevered piezoelectric beam. The base excitation on the beam is the harmonic load. We studied the jump phenomenon of the system by sweeping the voltage and displacement, the experimental results show that the bistable piezoelectric cantilever beam reflects the obvious hard spring characteristics. In addition, the influence of the distance between the magnets and the thickness of the piezoelectric layer on the dynamic behavior also being studied. Experimental results show that the distance between the magnets is closely impact on the nonlinear dynamic responses of the system, there is an optimal distance between the magnets causes the most complex dynamic behavior in frequency domain. System appears period doubling bifurcation into chaos many times when the distance between magnets is appropriate.

Abstract: It is well known that lightning strokes produce mal-operation of transmission line protection relays. Where, protection devices cannot identify correctly between lightning stroke that generates or not permanent faults. Thus, when a flash produces a permanent fault, the protection relay sends a trip order, and the Transmission Line (TL) is disconnected correctly. However, when a lightning stroke does not produce a permanent fault, the protection devices also send the trip order, and the TL is disconnected unnecessary. In this context, these phenomena can produce unnecessary electric power outages, producing damage for the society and economic. Therefore, it is necessary to correctly identify between these lightning stroke signals. Besides that, direct lightning strokes, which hit directly on TLs or transmission towers, have usually been analyzed. However, induced lightning strokes, which hit on ground, have not been considered in previous analyzed. In this paper, in order to identify these induced lightning strokes, an algorithm based on a deterministic focus is proposed.

Abstract: It is clear that lightning strokes produce overvoltages on Transmission Lines (TLs), which can be higher that the Basic Insulator Level (BIL), generating a fault or short circuit. Thus, in order to adequately analyze when a lightning hits on a TL, it is necessary to simulate different elements corresponding to Electric Power Systems (EPSs) as real as possible. In this context, transmission towers are considered crucial parameters in lightning studies, which must be correctly selected and simulated in order to consider reflected voltage waveforms from cross arms. Based on the above said, this paper presents a comparative study corresponding to the transmission tower simulation using two models. The first uses inductances, and the second uses distributed parameters impedances characterized by their impedance and travel time. This paper presents voltage variations that exist in each phase, using different lightning features. Alternative Transients Program (ATP) is used to simulate the TL model considering different lightning currents and the two tower models. Results show that the impedance model analyze reflected waveforms, while that the inductance model does not analyze this issue.