Vol. 3, No. 1 (2019): Regular Issue

Displacement limiters also known as stoppers are rigid barriers used to limit the motion or to alleviate the load in mechanical design. This paper identifies conditions under which the stopper causes the motion to be trapped in large amplitude oscillations accompanied by violent impact with the stopper. Special focus is on those parameters for which the stopper was not expected to play any role based on the predicted linear steady-state responses.

Piezoelectric material has been extensively used in energy harvesting technologies. However, most commercially available piezoelectric materials, Pb [ZrxTi1-x] O3 (PZT), contains of more than 60 weight percent lead (Pb) [1]. Because of its extremely hazardous effects of lead elements, there is a strong motive to substitute PZT by new lead-free materials with comparable properties to those of PZT. This paper tested three different piezoelectric bimorphs, one is made by lead-free piezoelectric materials Barium Titanate (BaTiO3) (BT) and the other two are made from traditional Pb [ZrxTi1-x] O3 (PZT). Their output voltage and power were studied and compared when the cantilever bimorphs subjected to a tip or a base excitation. Equivalent circuit models of both lead free Ba-Tio3 and traditional PZT cantilevered piezoelectric energy harvester (Mech-PEH) were built in ANSYS APDL. The Finite Element (FEM) model was validated through comparing the output voltage and power with the experiment results. The energy harvesting performance of the lead free piezoelectric bimorph were compared with the same size high performance PZT bimorph via FEM analysis. The factors contribute to the piezoelectric material’s behavior were described. The output voltage and power were computed with the transient vibrations caused by plucking forces. Due to the complicated fabrication process of lead free piezoelectric samples, a typical quarter size samples were usually produced and examined by researchers before the mass production of formal rectangular shape bimorphs. Therefore, in this work, all bimorphs, including lead free Barium titanate (BaTiO3) (BT) and the other two types of PZTs, were composed of two quarter size circular ceramics and a rectangular substrate plate.

The present paper discusses influence of duct joint on structural dynamic characteristics (modal parameters) of a rectangular duct. An analytical model is developed to consider the effect of duct joint on modal parameters. The joint condition is modeled as a combination of linear and torsional spring’s stiffness. Developed analytical model is validated with experimental results for a rectangular duct with Pittsburgh lock joint. It is observed that both natural frequencies and mode shapes are in good agreement. For further understanding the influence of duct joint on modal parameters, current analytical model results are compared to duct without joints results and noticed that only antisymmetric mode shapes of duct with joint condition are deviating from ideal duct.

The effect of flow interference on the flow-induced vibrations (FIVs) of two staggered circular cylinders at low Reynolds numbers is investigated using fluid-structure interaction (FSI) simulations. The FIV mechanical model of the two staggered circular cylinders in a laminar flow is proposed and the corresponding non-dimensional governing equations are presented. An FSI solution procedure is subsequently developed by combining the modified characteristic-based split (CBS) finite element method, dual-time stepping method, segment spring analogy technique, generalized-α method and loosely-coupled partitioned method. The stability and accuracy of the procedures are validated using a benchmark FSI problem concerning the FIVs of a single circular cylinder in a laminar flow. Finally, using the numerical method proposed, the FIVs of two staggered circular cylinders at Re = 200, T/D (space ratio) = 5∼7 and α (inclined angle of the line connecting the two cylinders centers) = 0°∼ 90° are computed, and the effects of T/D and α on the vortex structure, fluid load and FIVs are discussed in detail.

In this paper, the dynamics of a Duffing oscillatory system are studied through both an experimental method and analytical predictions. A Duffing oscillatory circuit is built and experimental data of various periodic motions are obtained. The semi-analytical method using discrete implicit maps is adopted to determine such periodic trajectories analytically using the same parameters as in the experiments. Finally, illustrations of various periodic motions on both trajectories and harmonic amplitudes are demonstrated between the experimental data and analytical predictions. From the current experimental technology, experimental results may not provide real results in nonlinear dynamical systems.

Oblique impact is a common phenomenon in engineering. The appearance of oblique impact will make the system strongly nonlinear and nonsmooth. In this paper, the period N−n motion of an oblique impact system with single degree of freedom is investigated by the theory of discontinuous dynamical system. The analytical conditions for the existence and local stability of the period N−n motion are obtained. All of these are under the assumption that the mass moved with very small angular amplitude. Once such an assumption was not true, the method above would be invalid. The discrete mapping method is used to solve this problem. The analytical conditions for the existence, the local stability of the period N−n motion are given through the discrete mapping method. The numerical simulation shows that the oblique impact will make the dynamic behavior of a single degree of freedom system more complex.

Firstly, the dynamics model of fixed-wing UAV is given in the paper and an adaptive controller of the mode is designed based on dynamic inversion method, then a compensation strategy called SFNN-RC based on the self-organizing fuzzy neural network techniques and a robust controller is designed to online identify and compensate the modeling uncertainty part of fixed-wing UAV system in trajectory tracking control process. The robust controller in SFNN-RC is presented to optimize the convergence performance of the self-organizing fuzzy neural network. The stability of the SFNN-RC method can be proved based on Lyapunov theory. To demonstrate the effectiveness of the proposed method, some simulation results are illustrated in this paper.