生物运动仿生力学与智能微型飞行器

概述了微型飞行器研究与发展现状,分析了实用化面临的主要技术关键,重点讨论了低雷诺数空气动力学、高升阻比气动布局、智能控制等问题．已有的经验和理论分析表明：主尺度小于15cm以后,用常规方法已经很难设计出具有良好飞行性能的微型飞行器,而必须采用仿生学方法．对微型飞行器仿生学设计中的一些主要问题,包括高升力、高机动性、抗干扰稳定性以及飞行过程的力能学分析等问题分别进行了讨论。     

微电子机械系统中构件的基本力学量检测

本文就近几年在ＭＥＭＳ（ＭｉｃｒｏＥｌｅｃｔｒｏＭｅｃｈａｎｉｃａｌＳｙｓｔｅｍｓ）基本力学量测量技术的最新发展及其特点、意义、进行了较全面的综述。内容包括：ＭＥＭＳ所用材料的基本力学参数测量（如Ｅ、Ｇ、μ），材料的摩擦与摩损的测量，ＭＥＭＳ结构内应力、应变的测量，结构的动态参数和机构运动速度的测量等，为ＭＥＭＳ的研究提供有益的参考。     

拦截高超声速飞行器的三维有限时间制导律设计

由于高超声速飞行器具有飞行速度快、机动能力强等特点,因此,传统的制导方式难以保证拦截弹拦截高超声速飞行器时的制导精度。为了减小弹目相对速度,降低对拦截弹的过载能力要求,按照前向制导方式,设计了有限时间收敛的三维前向滑模制导律。该制导律采用了连续的快速双幂次趋近律,不仅保证收敛速度快,同时削弱了传统制导律中存在的抖振现象。在此基础上为了处理系统扰动的上界未知的问题,又设计了自适应滑模制导律,该制导律既可以处理未知上界的外部扰动又可以保证第一种制导律所具有的良好特性。运用李雅普诺夫稳定性理论对所设计的滑模制导律进行了理论证明,最后,通过数值仿真验证了所设计制导律的有效性及优越性。     

生物与仿生材料表面微纳力学行为

评述了国内外在生物材料表面微纳力学行为研究方面的若干分支,包括:生物材料的疏水特性、水面昆虫的浮水力学、生物材料表面的减阴特性、生物材料吸附与脱附微纳力学行为、以及表面疏水和吸附仿生材料的制备与应用,并注重分析了在微纳尺度上生物结构、生物材料、生物生存技能与生存需求等方面的多功能自然协同进化和优化.     

A numerical study for three-dimensional viscoelastic flow inspired by non-linear radiative heat flux

Present article examines the three-dimensional flow of upper-convected Maxwell (UCM) fluid over a radiative bi-directional stretching surface. Novel non-linear Rosseland formula for thermal radiation is utilized in the formulation of energy equation. The conventional transformations lead to a strongly non-linear differential system which is treated numerically through Runge–Kutta integration procedure together with the shooting approach. We found that heat transfer rate from the sheet has inverse as well as non-linear relationship with wall to ambient temperature ratio. Moreover an increase in viscoelastic fluid parameter (Deborah number) corresponds to a decrease in the fluid velocity and the boundary layer thickness.     

On the destabilization of a periodically driven three-dimensional torus

We report experimental evidence of the destabilization of a 3D torus obtained when a small subharmonic perturbation is added to a 2D torus characteristic of a driven relaxation oscillator. The Poincaré sections indicate that the torus breakup is sensitive to the phase difference between the main driving frequency and its first subharmonic perturbing component. The observed transition confirms the Newhouse, Ruelle and Takens quasiperiodic transition to chaos on a 3D torus. Numerical results on a sinusoidally perturbed circle map mirror the experimental results and confirm the key role of the phase difference in the transition between distinct dynamical regimes.

     

Auxetic frameworks inspired by cubic crystals

In this work we show that a structure consisting of a network of bending beams can exhibit a negative Poisson’s ratio. We have shown that the negative Poisson’s ratio behaviour is driven by the (bcc analogous) type III beams, the type II (fcc like) beams result in a structure with a Poisson’s ratio of around zero and type I (simple cubic configuration) beams result in a Poisson’s ratio of nearly +1. The tensile and shear strengths of the type III beams are augmented by addition of type II and type III beams. By tailoring the relative stiffness of the component beams within the structure it is possible to design an auxetic truss structure with specific Poisson’s ratio, tensile and shear moduli.This validates the hypothesis that crystal structures can provide inspiration for macro structures with tailored mechanical properties where the mechanism for negative Poisson’s ratio (auxetic) behaviour at the atomic scale in cubic crystals is replicated by bending beams.     

Two- and three-dimensional flows in nearly rectangular cavities driven by collinear motion of two facing walls

Two- and three-dimensional flows in nearly cuboidal cavities are investigated experimentally. A tight cavity is formed in the gap between two long and parallel cylinders of large radii by adding rigid top, bottom, and end walls. The cross-section perpendicular to the axes of the cylinders is nearly rectangular with aspect ratio Γ. The axial aspect ratio Λ > 10 is large to suppress end-wall effects. The fluid motion is driven by independent and steady rotation of the cylinders about their axes which defines two Reynolds numbers Re _1,2. Stability boundaries of the nearly two-dimensional steady flow have been determined as functions of Re _1,2 for Γ = 0.76 and Γ = 1. Up to six different three-dimensional supercritical modes have been identified. The critical thresholds for the onset of most of the three-dimensional modes, three of which have been observed for the first time, agree well with corresponding linear-stability calculations. Particular attention is paid to the flow for Γ = 1 under symmetric and parallel wall motion. In that case the basic flow consists of two mirror symmetric counter-rotating parallel vortices. They become modulated in span-wise direction as the driving increases. Detailed LDV measurements of the supercritical three-dimensional velocity field and the bifurcation show an excellent agreement with numerical simulations.

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GPU accelerated simulations of three-dimensional flow of power-law fluids in a driven cube

Newtonian fluid flow in two- and three-dimensional cavities with a moving wall has been studied extensively in a number of previous works. However, relatively a fewer number of studies have considered the motion of non-Newtonian fluids such as shear thinning and shear thickening power law fluids. In this paper, we have simulated the three-dimensional, non-Newtonian flow of a power law fluid in a cubic cavity driven by shear from the top wall. We have used an in-house developed fractional step code, implemented on a Graphics Processor Unit. Three Reynolds numbers have been studied with power law index set to 0.5, 1.0 and 1.5. The flow patterns, viscosity distributions and velocity profiles are presented for Reynolds numbers of 100, 400 and 1000. All three Reynolds numbers are found to yield steady state flows. Tabulated values of velocity are given for the nine cases studied, including the Newtonian cases.     

Sound absorbing properties of spiral metasurfaces inspired by micro-perforated plates

As a kind of classical low-frequency sound-absorbing material, the microperforated plate (MPP) has been widely used. Here, we inspired by the sound absorption mechanism of the MPP, a spiral metasurface (SM) is designed and the analytical solution of acoustic impedance and sound absorption coefficient are obtained. The relationship between the sound absorption properties of the MPP and the SM with their own structures is systematically studied, and the analytical solutions are used to optimise the structure. It is concluded that the MPP and the SM of the same thickness achieve effective absorption in the frequency range between 390-900 Hz and 1920-4266 Hz, with a total thickness less than 1/6 of the wavelength. Meanwhile, the numerical calculation shows that the MPP and SM can match well with the background medium in the effective rang. Our study provides new insights into the design methods of sound-absorbing materials and is potentially suitable for many acoustic engineering applications.     

Cascaded quasi-zero stiffness nonlinear low-frequency vibration isolator inspired by human spine

Human motion induced vibration has very low frequency, ranging from 2 Hz to 5 Hz. Traditional vibration isolators are not effective in low-frequency regions due to the trade-off between the low natural frequency and the high load capacity. In this paper, inspired by the human spine, we propose a novel bionic human spine inspired quasi-zero stiffness (QZS) vibration isolator which consists of a cascaded multi-stage negative stiffness structure. The force and stiffness characteristics are investigated first, the dynamic model is established by Newton’s second law, and the isolation performance is analyzed by the harmonic balance method (HBM). Numerical results show that the bionic isolator can obtain better low-frequency isolation performance by increasing the number of negative structure stages, and reducing the damping values and external force values can obtain better low-frequency isolation performance. In comparison with the linear structure and existing traditional QZS isolator, the bionic spine isolator has better vibration isolation performance in low-frequency regions. It paves the way for the design of bionic ultra-low-frequency isolators and shows potential in many engineering applications.

     

Decentralized coordination of autonomous swarms inspired by chaotic behavior of ants

In this paper, we propose a decentralized coordination algorithm for a group of mobile nodes, called an autonomous swarm, on a finite two-dimensional space, which can efficiently coordinate cooperatively the autonomous swarm to the optimal solution. Our algorithm is inspired by chaotic behavior of a single ant and self-organization behavior of the whole ant colony. To construct this algorithm, we firstly assume that each agent is a nonlinear oscillator presenting the chaotic behavior of a single ant. Then we establish a self-organization mechanism according to the self-organization behavior of the whole ant colony. Moreover, we analyze the convergence of the proposed algorithm. Finally, we experimentally evaluate the performance of our algorithm with the clustering and dispersion operations of a swarm. Comparison results of the proposed algorithm and the gradient-type one are also presented to illustrate the effectiveness of the proposed scheme in approximately global optimization for swarms.     

Large-scale vortex generation driven by nonequilibrium turbulence

The development of large-scale perturbations in a heated layer of rotating fluid is studied within the framework of the nonequilibrium turbulence model with asymmetric Reynolds stress tensor. It is shown that, as in spiral turbulence, when there is no equilibrium on one of the boundaries of the layer large-scale structures develop. Conditions under which both perfect intrinsic matching of turbulence and convection and internal resonance development exist are determined. It is shown that the manifestation in a turbulent medium of properties of the convective vector field such as spirality may be caused by constraints imposed by the angular momentum conservation law.Novosibirsk. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 47–55, January–February, 1996.