粘弹性管路液流动态特性分析

本文着重介绍利用三要素和四要素模型分析粘弹性管路液流的动特性问题,推导出压力波传播速度的计算式,通过实验曲线求得实际传播速度的几种方法.并初步探讨应用电回路模型研究粘弹性管路液流动特性的可能性.     

病毒-植物互作对同翅目媒介昆虫生物学及其传毒机制的影响

植物病毒会直接或间接地对媒介昆虫造成影响,它既可以感染媒介昆虫从而改变昆虫的生理生化性质,也可以通过侵染寄主植物并改变植物营养成分来影响媒介昆虫.被影响的媒介昆虫表现出某些生物学特性(包括发育、寿命、繁殖力、表现型等)的变化.该文综述了同翅目蚜虫、飞虱和粉虱等媒介昆虫所传播的植物病毒、昆虫对病毒的获取、传播和保留等特性以及媒介昆虫的传毒机制.     

基于分数导数模型的粘弹性桩振动分析

研究成果表明混凝土桩具有粘弹性性质,为了准确分析粘弹性桩的振动特性,必须建立准确的粘弹性本构模型.在分数导数理论、粘弹性理论、应力波理论的基础上建立了基于分数导数模型的粘弹性桩的振动方程,利用Zhang-Shimizu分数导数数值积分法得到了基于分数导数模型的粘弹性桩的振动方程数值解.分析结果表明,分数导数微分算子的阶数和粘弹比对粘弹性桩桩端速度衰减的快慢和衰减周期等有很大的影响.     

基于XFlow的仿生扑翼飞行器机翼气动特性分析

通过空间曲柄摇杆结构产生的急回特性来实现仿生飞行器扑翼运动.为了探究仿生扑翼飞行器的气动特性的影响因素,采用玻尔兹曼模型的粒子跟踪方法模拟扑动过程中气动特性,基于计算流体力学仿真软件XFlow对不同翼型、翼展、翼平面形状进行仿真分析并探究对升力和推力的影响.结果表明:翼型弯度和翼展的增大能够增加扑翼飞行器的升力系数,推力系数随着弯度的增大而变小;通过综合分析得到翼展长度在2.5倍弦长时,气动特性最佳;不同翼面形状的机翼具有不同的气动性能,相对于机翼后缘几何形状,前缘对气动特性的影响较大.研究结果为扑翼飞行器机翼的系统设计提供了有益的指导.     

地效翼空气动力风洞试验

为深入研究地面效应机理及地面附近粘性流动对地效翼空气动力的影响,在同济大学上海地面交通工具风洞中心的空气动力-气动声学风洞内对地效翼模型进行了风洞吹风试验.风洞试验中利用移动带路面模拟系统模拟了机翼和地面的相对运动;通过改变地效翼展长、装配端板,研究了地效翼的三维效应和端板对空气动力的影响;分析了地效翼的失速特性及其影响因素.通过地效翼风洞试验研究揭示了地面效应机理及移动地面模拟的重要性,并深入分析了地效翼空气动力特性,为地效飞行器空气动力设计和研究提供了参考.     

襟缝翼对民用飞机失速特性的影响

从外侧缝翼缝道参数、内侧缝翼分离面、缝翼与挂架间隙以及后缘襟翼缝道参数等方面考虑,分析了民用飞机失速特性和失稳特性的影响因素.结果表明,前缘缝翼根部和梢部细节对力矩特性有较大影响,缝翼挂架堵缝可提高升力,不影响力矩特性,调整襟翼偏角,可改变机翼有效弯度,不改变主翼分离特性.     

含蜡原油低温粘弹性研究的现状与分析

我国盛产含蜡原油,在低温(凝点温度附近)条件下,含蜡原油具有一定的粘弹性。概述了国内外含蜡原油低温粘弹性研究的主要进展。含蜡原油粘弹性起因于其内部形成的蜡晶结构。振荡剪切实验方法最适合于含蜡原油的粘弹性测量。粘弹性与胶凝温度、胶凝强度、屈服应力和触变性等参数有关。含蜡原油经历的热历史、剪切历史以及析蜡特性是影响粘弹性的主要因素。分析了在含蜡原油低温粘弹性认识上和研究中存在的问题。建议进一步研究含蜡原油粘弹性与屈服应力、触变性的关系,在机理研究方面加大力度;通过研究粘弹性与热历史、剪切历史的关系,建立管道运行和停输期间含蜡原油胶凝特性的预测模型,以更加有效地指导管道的安全运行。     

环境条件下沥青路面热粘弹性温度应力计算

利用热粘弹性力学理论和有限元方法 ,以广义Maxwell模型模拟沥青混合料的粘弹特性 ,通过试验研究和理论推导得到其增量型热粘弹性本构关系 ,建立了环境条件下沥青路面的温度应力场有限元计算方法 .并给出一个计算实例     

非饱和土粘弹性地基一维固结特性分析

基于Fredlund的非饱和土一维固结理论,采用李氏比拟法,研究有限厚度粘弹性非饱和土层在大面积均布瞬时加荷时的一维固结问题.针对Merchant粘弹性模型,采用Laplace 变换及Cayley-Hamilton等数学方法,引入边界及初始条件,得到Laplace变换域内顶面排气不排水、底面不渗透情况下粘弹性非饱和土地基一维固结时的超孔隙水压力、超孔隙气压力以及土层沉降的解,采用Crump及Durbin方法实现Laplace逆变换, 获得半解析解;分析在不同气、水渗透系数比k_a/k_w下,Merchant粘弹性模型的Kelvin体中弹性模量E₁和粘滞系数η等对粘弹性非饱和土地基一维固结特性的影响,揭示粘弹性非饱和土地基的固结特性;最后通过与弹性解析解的对比,验证了半解析解方法的正确性.     

昆虫飞行高升力的一种新解释——柔性楔形效应

以探索仿生扑翼飞行机器人研制为目的,在研究"柔性楔形效应"的基础上,将昆翅视为柔性翅,提出用"柔性楔形效应"解释昆虫飞行高升力的观点.指出了用"柔性楔形效应"解释昆虫飞行高升力的仿生学意义.根据该观点,翅翼在自适应变形状态下施以简单的节律运动将是未来仿生扑翼飞行机器人翅翼驱动方式的发展趋势.仿生运动的模拟越简单越容易稳定地实现,实验小组已设计制作了仿生扑翼飞行机器人样机,并成功进行了多次室外放飞.     

昆虫飞行特性的视觉测量方法

该文提出了一种应用立体视觉技术测量昆虫飞行特性的方法。针对昆虫飞行的图像,尤其是对翅脉,进行预处理、分割和特征提取。指出采用区域匹配和特征匹配相结合的匹配方法,对图像进行立体匹配。最后提出对二维图像进行三维重构,计算昆虫空间坐标。通过这些步骤,可以获得描述昆虫飞行特性的信息。该文对方案进行了初步的仿真验证。使用立体视觉这种非接触性测量手段,可以不需要翅膀截面只有一次变形的假设,测量得到昆虫自由飞行时的飞行特性。     

Unconventional lift-generating mechanisms in free-flying butterflies

Flying insects generate forces that are too large to be accounted for by conventional steady-state aerodynamics. To investigate these mechanisms of force generation, we trained red admiral butterflies, Vanessa atalanta, to fly freely to and from artificial flowers in a wind tunnel, and used high-resolution, smoke-wire flow visualizations to obtain qualitative, high-speed digital images of the air flow around their wings. The images show that free-flying butterflies use a variety of unconventional aerodynamic mechanisms to generate force: wake capture, two different types of leading-edge vortex, active and inactive upstrokes, in addition to the use of rotational mechanisms and the Weis-Fogh 'clap-and-fling' mechanism. Free-flying butterflies often used different aerodynamic mechanisms in successive strokes. There seems to be no one 'key' to insect flight, instead insects rely on a wide array of aerodynamic mechanisms to take off, manoeuvre, maintain steady flight, and for landing.     

Optimizing the success of random searches.

We address the general question of what is the best statistical strategy to adapt in order to search efficiently for randomly located objects ('target sites'). It is often assumed in foraging theory that the flight lengths of a forager have a characteristic scale: from this assumption gaussian, Rayleigh and other classical distributions with well-defined variances have arisen. However, such theories cannot explain the long-tailed power-law distributions of flight lengths or flight times that are observed experimentally. Here we study how the search efficiency depends on the probability distribution of flight lengths taken by a forager that can detect target sites only in its limited vicinity. We show that, when the target sites are sparse and can be visited any number of times, an inverse square power-law distribution of flight lengths, corresponding to Lévy flight motion, is an optimal strategy. We test the theory by analysing experimental foraging data on selected insect, mammal and bird species, and find that they are consistent with the predicted inverse square power-law distributions.     

Molecular dynamics of cyclically contracting insect flight muscle in vivo

Flight in insects--which constitute the largest group of species in the animal kingdom--is powered by specialized muscles located within the thorax. In most insects each contraction is triggered not by a motor neuron spike but by mechanical stretch imposed by antagonistic muscles. Whereas 'stretch activation' and its reciprocal phenomenon 'shortening deactivation' are observed to varying extents in all striated muscles, both are particularly prominent in the indirect flight muscles of insects. Here we show changes in thick-filament structure and actin-myosin interactions in living, flying Drosophila with the use of synchrotron small-angle X-ray diffraction. To elicit stable flight behaviour and permit the capture of images at specific phases within the 5-ms wingbeat cycle, we tethered flies within a visual flight simulator. We recorded images of 340 micros duration every 625 micros to create an eight-frame diffraction movie, with each frame reflecting the instantaneous structure of the contractile apparatus. These time-resolved measurements of molecular-level structure provide new insight into the unique ability of insect flight muscle to generate elevated power at high frequency.     

压电粘弹性微梁的粘附分析

以处于粘附状态下的压电粘弹性微梁为研究对象，通过引入参数剥离数表示其粘附特征，分析了压电电压、粘弹性参数和几何参数对处于粘附状态下压电粘弹性微梁剥离数的影响.结果表明，压电电压能有效提高微梁的剥离数，这给通过压电电压修复已处于粘附状态的压电微梁提供了理论依据和参考.同时，微梁的几何参数对微梁的剥离数也有着重要影响，这对微梁的设计造成了一定的限制.     

昆虫病毒对脊椎动物体细胞的致突变性研究

用微核测定法,检测3种昆虫病毒包涵体及其降解物对小白鼠骨髓多染红细胞染色体的损伤程度。证明对脊椎动物体细胞是否具有致突变性。结果表明,3种昆虫病毒对小白鼠骨髓嗜多染红细胞没有损伤作用。可以认为3种昆虫病毒对哺乳动物体细胞无致突变作用。     

Characterization of viscoelastic properties of hydrolyzed polyacrylamide using the stress recovery experiment

Polymer solutions have very important applications in the enhanced oil recovery due to their unique viscoelastic properties increasing microscale displacement efficiency. In this paper, the viscoelastic properties of partially hydrolyzed polyacrylamide (HPAM) solution have been investigated. Results show that the viscoelastic properties of HPAM increase with HPAM concentration increasing, and decrease with the increase of sodium dodecyl sulfate (SDS).Meanwhile, adding NaCI can destroy the viscoelastic properties.     

扑翼飞行二维情形数值分析

基于计算流体力学(CFD)方法对微扑翼飞行的非定常空气动力学问题进行研究,已被大多数学者所认可.在对昆虫飞行运动仿真模拟的基础上,建立了扑翼运动二维简化模型及运动方程,并利用FLUENT软件及其嵌入用户自定义函数(UDF)和动网格技术,分析了二维翼型在不同控制飞行参数(包括扑翼频率、最大转动幅值、平动和转动相位差等)下的平均升力和阻力系数.数值模拟所得结果为微扑翼飞行器的设计提供了参考依据.     

Loss and recovery of wings in stick insects

The evolution of wings was the central adaptation allowing insects to escape predators, exploit scattered resources, and disperse into new niches, resulting in radiations into vast numbers of species. Despite the presumed evolutionary advantages associated with full-sized wings (macroptery), nearly all pterygote (winged) orders have many partially winged (brachypterous) or wingless (apterous) lineages, and some entire orders are secondarily wingless (for example, fleas, lice, grylloblattids and mantophasmatids), with about 5% of extant pterygote species being flightless. Thousands of independent transitions from a winged form to winglessness have occurred during the course of insect evolution; however, an evolutionary reversal from a flightless to a volant form has never been demonstrated clearly for any pterygote lineage. Such a reversal is considered highly unlikely because complex interactions between nerves, muscles, sclerites and wing foils are required to accommodate flight. Here we show that stick insects (order Phasmatodea) diversified as wingless insects and that wings were derived secondarily, perhaps on many occasions. These results suggest that wing developmental pathways are conserved in wingless phasmids, and that 're-evolution' of wings has had an unrecognized role in insect diversification.