Comparative aerodynamic performance of flapping flight in two bat species using time-resolved wake visualization

Bats are unique among extant actively flying animals in having very flexible wings, controlled by multi-jointed fingers. This gives the potential for fine-tuned active control to optimize aerodynamic performance throughout the wingbeat and thus a more efficient flight. But how bat wing performance scales with size, morphology and ecology is not yet known. Here, we present time-resolved fluid wake data of two species of bats flying freely across a range of flight speeds using stereoscopic digital particle image velocimetry in a wind tunnel. From these data, we construct an average wake for each bat species and speed combination, which is used to estimate the flight forces throughout the wingbeat and resulting flight performance properties such as lift-to-drag ratio (L/D). The results show that the wake dynamics and flight performance of both bat species are similar, as was expected since both species operate at similar Reynolds numbers (Re) and Strouhal numbers (St). However, maximum L/D is achieved at a significant higher flight speed for the larger, highly mobile and migratory bat species than for the smaller non-migratory species. Although the flight performance of these bats may depend on a range of morphological and ecological factors, the differences in optimal flight speeds between the species could at least partly be explained by differences in their movement ecology.     

A quantitative comparison of bird and bat wakes

Qualitative comparison of bird and bat wakes has demonstrated significant differences in the structure of the far wake. Birds have been found to have a unified vortex wake of the two wings, while bats have a more complex wake with gradients in the circulation along the wingspan, and with each wing generating its own vortex structure. Here, we compare quantitative measures of the circulation in the far wake of three bird and one bat species. We find that bats have a significantly stronger normalized circulation of the start vortex than birds. We also find differences in how the circulation develops during the wingbeat as demonstrated by the ratio of the circulation of the dominant start vortex and the total circulation of the same sense. Birds show a more prominent change with changing flight speed and a relatively weaker start vortex at minimum power speed than bats. We also find that bats have a higher normalized wake loading based on the start vortex, indicating higher relative induced drag and therefore less efficient lift generation than birds. Our results thus indicate fundamental differences in the aerodynamics of bird and bat flight that will further our understanding of the evolution of vertebrate flight.     

Changes in kinematics and aerodynamics over a range of speeds in Tadarida brasiliensis,the Brazilian free-tailed bat

To date, wake measurements using particle image velocimetry (PIV) of bats in flight have studied only three bat species, all fruit and nectar feeders. In this study, we present the first wake structure analysis for an insectivorous bat. Tadarida brasiliensis, the Brazilian free-tailed bat, is an aerial hunter that annually migrates long distances and also differs strikingly from the previously investigated species morphologically. We compare the aerodynamics of T. brasiliensis with those of other, frugivorous bats and with common swifts, Apus apus, a bird with wing morphology, kinematics and flight ecology similar to that of these bats. The comparison reveals that, for the range of speeds evaluated, the cyclical pattern of aerodynamic forces associated with a wingbeat shows more similarities between T. brasiliensis and A. apus than between T. brasiliensis and other frugivorous bats.     

八轴连通式油气悬架车辆行驶性能和通过性能研究

行驶性能和通过性能是评估车辆越野性能的基本指标.为得到八轴连通式油气悬架车辆的越野性能,分别对行驶性能和通过性能开展了研究.简化了整车的物理模型,根据拉格朗日方程推导了车辆的振动方程,建立了白噪声路面输入方程;通过仿真结果与实验结果的对比,验证了柔性模型的合理性.基于柔性模型,以路面不平度系数为输入变量,得到了车辆在较...     

Soccer ball anisotropy modelling

The work presented in this paper details the development of a finite element (FE) model of a soccer ball, allowing for a greater understanding of the performance of soccer balls under dynamic conditions that are representative of play. The model consists of composite shell elements that include a hyperelastic strain energy potential equation to define the latex bladder layer and a plane stress orthotropic elastic material model to define the anisotropic woven fabric outer panels. The model was validated through a series of experimental impact tests whereby the ball was impacted normal to a rigid plate at an inbound velocity of approximately 34 ms⁻¹ (76 mph), with each impact recorded using high speed video (HSV) techniques. It was found that the combined effects of ball design and panel material anisotropy resulted in impact properties such as coefficient of restitution, contact time, deformation and the 2D shape taken up by the ball at maximum deformation, to vary with pre-impact ball orientation. The model showed good agreement with the measurements, and its ability to represent the effects of anisotropy in ball design.     

The dynamic buckling of sheet steel

The Euler buckling load for end-loaded strips of three types of sheet steel with different mechanical properties was measured at various impact rates up to 13 m/s. At quasi-static load application rates, the Euler buckling load was found to be approximately the same for all three types of steel, but under dynamic loading conditions, the buckling load depended upon the tensile strength of the steel as well as the impact rate. A finite element model predicted an increase in buckling load, with both an increase in impact rate and an increase in the tensile mechanical properties, which was in good agreement with the experimental observations.     

混合蝙蝠算法在包装件配送中的应用研究

目的使蝙蝠算法(BA)适应包装件配送车辆路径问题(VRP)的求解,并提高该算法的求解性能。方法在标准BA算法的基础上提出混合蝙蝠算法(HBA)。首先,设计改进的蝙蝠算法(IBA),使其能够适用于包装件配送VRP问题的求解。其次,引入混沌系统,对IBA算法进行混沌初始化。然后,设计裂变算子和变异算子。在IBA算法迭代前半段,将蝙蝠种群中较差的一半蝙蝠重新混沌初始化,以提高种群多样性。在IBA算法迭代后半段,对陷入局部最优解的蝙蝠进行鲶鱼扰动。最后,提出HBA算法并对企业实例进行仿真测试。结果 HBA算法求得的最优配送距离为773.01 km,相对于GA算法(781.25 km)和IBA算法(786.04 km)分别节约了8.24 km和13.03 km。结论与IBA算法和GA算法相比,HBA算法求解包装件配送VRP问题的全局优化能力更强、收敛速度更快。     

State-of-the-Art Finite Element Modeling of Rotorcraft Main Rotor Blade for Bird Strike Damage Analysis

This paper demonstrates the state-of-the-art composite modeling methodology to investigate the bird strike phenomenon using available numerical bird models through experimental tests and simulation tools. The present work is based on the application of nonlinear explicit finite element analysis to simulate the response of rotorcraft main rotor blade root end under high velocity impact load. The damage behavior of blade made of composites under soft body impact depends upon bird size, blade size, blade span-wise location of impact and bird orientation with respect to hitting location, blade rotational speed and rotorcraft cruise speed. Bird model is considered as hydrodynamic with length-to-diameter ratio of 2. A bird strike event is characterized by loads of high intensity and short duration. A transient explicit nonlinear finite element-based impact analysis using Autodyn has been carried out to predict bird strike resistance to withstand 1.0 kg bird at critical flight condition. Numerical analysis indicates that blades do not tear which agrees well with the physical test conducted.     

新型打桩锤电液控制系统研究

为提高打桩锤的打桩质量和工作效率,提出一种基于插装阀设计的新型大流量液压打桩锤。通过分析该打桩锤电液控制系统的结构组成和工作原理,建立了液压系统驱动桩锤打桩的动力学模型。基于AMESim平台构建了打桩锤电液仿真系统,同时搭建了实验平台,对桩锤锤击过程动态特性进行仿真和实验研究。仿真和实验结果表明该系统在满足液压打桩锤基本性能的前提下,还具有实现打击能的无级调节、打桩锤控制效率高、换向压力波动小,以及能保证打桩能量和打击重复精度等优点,为优化桩锤参数和开发新型液压打桩锤产品提供了重要依据。     

Relation between shear banding and penetration characteristics of conventional tungsten alloys

The dynamic compression failure and ballistic penetration characteristics of conventional tungsten alloys similar in strength were investigated. Dynamic compression failure properties were generated with a symmetric Taylor test technique and penetration characteristics were obtained with 44 mm kinetic penetrators against an 300 HB hardness steel target at 1400 m/s. From shear crack length data generated with Taylor specimens impacted at different impact speeds a critical speed characterizing shear band initiation was deduced. The critical equivalent plastic strain at shear band initiation sites, obtained from the numerical simulation of the Taylor test at the critical impact speed, was found to decrease with the increase of the penetration performance. These results reinforce the argument that shear band formation is a failure mechanism associated with the erosion process for conventional tungsten alloys.     

Sliding along frictionally held incoherent interfaces in homogeneous systems subjected to dynamic shear loading: a photoelastic study

An experimental investigation was conducted to study dynamic sliding at high strain rates along incoherent (frictional) interfaces between two identical plates. The plates were held together by a uniform compressive stress, while dynamic sliding was initiated by an impact-induced shear loading. The case of freely-standing plates with no external pressure was also investigated. The dynamic stress fields that developed during the events were recorded in a microsecond time scale by high-speed photography in conjunction with classical dynamic photoelasticity. Depending on the choice of experimental parameters (impact speed and superimposed static pressure), pulse-like and crack-like sliding modes were observed. Visual evidence of sub-Rayleigh, intersonic and even supersonically propagating pulses were discovered and recorded. Unlike classical shear cracks in coherent interfaces of finite strength, sliding areas in frictional interfaces seem to grow at various discrete speeds without noticeable acceleration phases. A relatively broad loading wave caused by the interference between the impact wave and the preexisting static stress field was observed emanating from the interface. There was a cusp in the stress contours at the interface, indicating that the propagation speed was slightly faster along the interface than in the bulk. The observed propagation speeds of the sliding tips were dependent on the projectile speed. They spanned almost the whole interval from sub-Rayleigh speeds to nearly the sonic speed of the material, with the exception of a forbidden gap between the Rayleigh wave speed and the shear wave speed. Supersonic trailing pulses generating Mach lines of different inclination angles, emanating from the sliding zone tips, were discovered. In addition, behind the sliding tip, wrinkle-like opening pulses were observed for a wide range of impact speeds and confining stresses. They always traveled at speeds between the Rayleigh wave speed and the shear wave speed of the material. Symposium on Physics and Scaling in Fracture held during the ICF11 (2005) in Turin.     

软质面层抑制高阶模态降低地板结构撞击声研究

为了研究并降低地板结构受到激励时产生的撞击声响应,利用振动模态叠加思想,将地板结构受到激励时空间中一点接收到的声信号表示为各阶振动模态的叠加,若某一阶振动模态受到抑制或不被激发则可降低、消除对应频率处的辐射噪声。通过在结构表面铺设软质面层并用标准撞击器激励的方法进行实验研究,结果表明,通过在地板结构表面引入软质面层的方法,可以有效降低地板结构的规范化撞击声压级,因为随着频率的增加,当激励力不足以激发高阶模态时,地板结构不辐射对应频率处的噪声,由此可以达到降噪的目的。     

电液可变气门高速开关阀用电磁铁设计与研究

采用经验公式与有限元分析相结合的方法对高速电磁铁进行设计以提高其电磁吸力和动态性能.建立了高速电磁铁的数学模型,利用Ansoft电磁场分析软件对隔磁角、衔铁长度、隔磁长度等按照经验公式无法获得的结构参数对高速电磁铁的静、动态特性影响进行了分析.在此基础上研制了高速电磁铁,并对其静、动态性能进行了测试,试验结果与仿真结果吻合,表明采用经验公式与有限元分析相结合的方法可以有效提高电磁铁的设计精度,而优化隔磁角、衔铁长度、隔磁长度等结构参数可以有效提高高速电磁铁静、动态性能.     

围压下岩石的冲击力学行为及动态统计损伤本构模型研究

采用改进后具有主动围压加载装置的f100mm 分离式Hopkinson压杆(SHPB)试验装置,研究了斜长角闪岩在不同围压等级(0MPa~6MPa)和不同应变率(50s^-1~170s^-1)下的冲击压缩力学性能。试验结果表明：在相同围压下,斜长角闪岩的动态抗压强度随应变率的增加而近似线性增加,动态增长因子与应变率的对数呈近似线性关系,体现了显著的应变率相关性;在同等级应变率范围内,随着围压的增加,岩石的增强效果逐渐增强,显现出较强的围压效应。采用组合建模的方法,将统计损伤模型和粘弹性模型相结合,建立了基于Weibull 分布的动态损伤本构模型。验证发现,修正后的模型曲线和试验曲线吻合较好,表明所构建本构模型是合理的,可为进一步研究和工程应用提供一定的参考。     

混凝土圆柱体试件在低速冲击下动力效应的研究

为研究混凝土圆柱体试件在冲击荷载作用下的动力效应,利用落锤冲击试验机,对混凝土圆柱体试件在应变率100~101/s范围内进行轴向冲击试验,并采用混凝土连续面盖帽模型（CSCM）对试验过程进行数值模拟。试验中测量不同冲击速度及冲击边界下的锤头冲击力、试件轴向应变时程曲线,获取了试件破坏形态及破坏过程的高速影像,比较分析了不同冲击速度及边界条件下,试件应力、应变峰值,应变率及动力增强系数（DIF）的变化规律。结果表明：随冲击速度的增加,试件的应力、应变峰值,应变率及动力增强系数都呈增加的趋势,冲击力作用时间则减小。混凝土平均强度与冲击速度呈抛物线关系,应变率则与冲击速度呈线性关系。模拟结果表明,CSCM混凝土本构模型在低速冲击范围内,有很好的计算精度,模拟破坏形态与试验结果吻合良好。     

碳纤维/环氧树脂复合材料高速冲击性能

采用树脂传递模塑(RTM)工艺制备碳纤维/环氧树脂复合材料,通过空气炮冲击实验研究树脂韧性和碳纤维类型对复合材料抗高速冲击性能的影响,并对高速冲击后的试样进行压缩性能测试,研究高速冲击损伤对复合材料剩余压缩性能的影响。结果表明:树脂的韧性可以降低复合材料遭受高速冲击时的内部损伤程度,大幅提高复合材料的抗高速冲击性能和冲击后剩余压缩性能;T700S碳纤维增强复合材料抗高速冲击性能优于T800H碳纤维增强复合材料;复合材料的破坏模式与冲击速率有关,冲击速率较低时,复合材料弹击面出现圆形凹坑,背弹面出现鼓包;冲击速率较高时,复合材料弹击面出现圆形通孔,背弹面出现沿纤维方向撕裂断口。     

Experimental and numerical investigations of low velocity impact behavior of high-performance fiber-reinforced cement based composite

Fiber-reinforced concrete (FRC) has been used in structural applications in order to enhance the structural performance under dynamic loading and reduce cracking and spalling phenomena by increasing toughness, ductility, and tensile strength of the concrete. High-performance fiber-reinforced cement based composite (HPFRC) is a high-strength FRC with enhanced high-performance characteristics. Recent studies have shown that HPFRC has higher impact resistance than other types of concrete. Therefore, it has been widely considered as a promising material for the construction of important and strategic structures. HPFRC panels are tested by drop projectiles up to an impact at which failure occurs. Mechanical properties of HPFRC are obtained to define material parameters in the MAT_SOIL_CONCRETE model in LS-DYNA, which is used to simulate the behavior of HPFRC panel under impact loading and perform parametric studies. Predicted crack and failure patterns on both sides of the HPFRC panel based on finite element simulation are in good agreement with their corresponding experimental results.     

Effects of process parameters on periodic impact force exerting on cutting tool in ultrasonic vibration-assisted oblique turning

During ultrasonic vibration-assisted machining, the large impact force induced by tool-workpiece reengagement (TWR) is an important factor that affects tool chipping. However, mechanical analysis into process factors that affect the impact force and their influencing mechanisms are insufficient. Herein, a prediction model for the instantaneous cutting force during both TWR and the stable turning process, which depends on the process parameters and material properties, is firstly proposed based on the kinematic and dynamic analysis of ultrasonic vibration-assisted oblique turning (UVAOT). The results calculated using the developed cutting force model agree well with the experimental results presented in the literature. Next, the linear change law of the instantaneous cutting force with cutting time during the actual TWR is clarified using the proposed model. The effect of the UVAOT process parameters on the average impact force during the periodic TWR process is discussed, and the influence mechanism is analyzed from the perspective of mechanics. A positive linear correlation is discovered between the feed speed and average impact force. The ultrasonic amplitude and cutting speed do not significantly affect the average impact force of the new sharp cutting tools. These findings are consistent with the experimental observations of tool chipping and are applicable to select process parameters for reducing tool chipping during UVAOT.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-022-00398-x     

Force propagation speed in a bed of particles due to an incident particle impact

The force propagation speed in granular matter is a very difficult property to be measured. A new technique has been developed to calculate the force propagation speed in granular matter based on measuring experimentally the contact time. The contact time for a particle hitting a bed of particles is estimated as the time taken for a particle to strike a bed of particles till the time of its ejection, and it is calculated using the discrete element method. The speed of force propagation in a bed of particles is estimated by plotting the dependence of the path length of the contact force on the contact time and finding the gradient of such dependence. Such approach leads to accurate results if the impact speed is below the yield velocity, i.e. no plastic deformations. It is found that the force propagation speed in spherical granular matter is proportional to the impact speed of the incident particle, which is different from force propagation in continuum matter. It is also found that the propagation speed is dependent on the material and diameters ratio of the interacting particles, but it is not dependent on the number of bed layers. The propagation speed in granular matter is normalized by dividing it by a reference propagation speed, i.e. the propagation speed at an impact speed of 1 m/s. It is found that the normalized propagation speed is independent of the material and diameter of the interacting particles, but it is logarithmically proportional to the impact speed. The proportionality constant is equal to 0.16, which can be taken as a universal constant for force propagation in spherical granular matter.     

Data-driven modelling of group formation in the fission–fusion dynamics of Bechstein’s bats

Communal roosting in Bechstein’s bat colonies is characterized by the formation of several groups that use different day roosts and that regularly dissolve and re-merge (fission–fusion dynamics). Analysing data from two colonies of different sizes over many years, we find that (i) the number of days that bats stay in the same roost before changing follows an exponential distribution that is independent of the colony size and (ii) the number and size of groups that bats formed for roosting depend on the size of the colony, such that above a critical colony size two to six groups of different sizes are formed. To model these two observations, we propose an agent-based model in which agents make their decisions about roosts based on both random and social influences. For the latter, they copy the roost preference of another agent which models the transfer of the respective information. Our model is able to reproduce both the distribution of stay length in the same roost and the emergence of groups of different sizes dependent on the colony size. Moreover, we are able to predict the critical system size at which the formation of different groups emerges without global coordination. We further comment on dynamics that bridge the roosting decisions on short time scales (less than 1 day) with the social structures observed at long time scales (more than 1 year).