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Schematic representation of the relationship between lateral and roll accelerations and displacements during (a) low frequency casting maneuvers (helicopter model) and (b) while high frequency buffeting in unsteady winds (sailboat model). The red and green arrows in (a,b) respectively represent the self-initiated and wind-induced forces and torques respectively. Here fc (<10 Hz) and fv (≈23 Hz) are casting and von Kármán frequencies respectively and t is time. The schematic drawings exaggerate the amplitudes of all motions for the purpose of clearly showing the phase relationship between roll and lateral displacement. For in-scale visualization of the casting and buffeting motions, see Supplementary Videos S3 and S4, respectively. In low frequency casting (a), the lateral force is produced by tilt of the stroke plane, self-initiated by the bee. Therefore, lateral acceleration is of the same sign as the roll angle. In high frequency buffeting (b), the wind induces drag-based force and torque. Therefore, the lateral acceleration is of the same sign as the torque, i.e., opposite to the roll angle. See Supplementary Material S2 for mathematical derivation of the phase relationship between roll and lateral motions.
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The natural wind environment that volant insects encounter is unsteady and highly complex, posing significant flight control and stability challenges. Unsteady airflows can range from structured chains of discrete vortices shed in the wake of an object to fully developed chaotic turbulence. It is critical to understand the flight control strategies...
Citations
... Typical methods to measure the key biological characteristics is to use invasively tranquilized animals which is dangerous and risky for the animals and investigators. Alternatively, post-mortem [28] or museum specimens [29] can be used. ...
Understanding and monitoring wildlife behavior is crucial in ecology and biomechanics, yet challenging due to the limitations of current methods. To address this issue, we introduce WildPose, a novel long-range motion capture system specifically tailored for free-ranging wildlife observation. This system combines a electronically controllable zoom-lens camera with a solid-state LiDAR to capture both 2D videos and 3D point cloud data, thereby allowing researchers to observe high-fidelity animal morphometrics, behavior and interactions in a completely remote manner. Field trials conducted in Kgalagadi Transfrontier Park have successfully demonstrated WildPose’s ability to quantify morphological features of different species, accurately track the 3D movements of a springbok herd over time, and observe the respiratory patterns of a distant lion. By facilitating non-intrusive, long-range 3D data collection, WildPose marks a significant leap forward in ecological and biomechanical studies, offering new possibilities for conservation efforts and animal welfare, and enriching the prospects for interdisciplinary research.
... [8][9][10][11]13 While this success partly results from their sensorimotor feedback control, it is also assisted by inherent aerodynamic properties of flapping wings. 14 For example, flapping wings are able to effectively alleviate freestream gust fluctuation and turbulence in the absence of feedback control; 15 the structure of the leading-edge vortex (LEV), and the average aerodynamic force of flapping wings remain robust under strong ambient flow turbulence, 16 which, on the other hand, would greatly affect the performance of streamlined airfoils. 17 Although these results suggest that MAVs with nature-inspired flapping wings could fly with higher performance in unsteady environments, 5 previous efforts are considerably scarce as to establish the fundamental science underlying the performance and the flow physics of flapping wings in mitigating the adverse effects of unsteady ambient flow. ...
Inspired by the stability achieved by biological flapping-winged fliers in gusty environments, we conducted particle image velocimetry studies on the interactions between plunging wings and large-scale vortex gusts. Our experiments involved a flat plate wing performing sinusoidal plunging motions at various frequencies, resulting in Strouhal numbers (St) ranging from 0 to 0.5 within which biological fliers commonly operate. This range of St corresponded to reduced frequencies (k) between 0 and 0.79 at a chord Reynolds number of 2000. The gust structures, generated periodically by pitching vanes, traveled downstream to the wing. We observed the vortex interactions between wing-induced vortices [particularly the boundary layer and the leading-edge vortex (LEV)] and the gusts. Additionally, we quantified the gusts' effects on the local flow around the wing by calculating the circulation within a control region attached to the plunging wing. The wing-induced vorticity merged momentarily with gusts of the same-sign vorticity. In contrast, opposite-sign gusts not only increased the circulation of the wing-induced vortices but also led to the LEV detaching faster. While gusts had the potential to significantly alter the flow around the wings, the plunging wings sometimes managed to avoid the gusts due to their transverse motion. Furthermore, the prolonged presence of the stronger LEVs near the wing, which are characteristic of plunging wings at higher St and k, could deflect the gusts away, reducing their impact on the vorticity and circulation within the control region. These findings illustrate how robust flapping kinematics can mitigate the effects of vortex gusts.
... Thus, these candidate loci may be involved in adaptation to novel environments in B. terrestris, where precipitation or other linked environmental factors might be drivers of selection.Average summer wind speed had the highest number of associated outlier SNPs (i.e. in RDA2;Table 3). Wind influences several aspects of bumblebee behaviour, such as landing performance(Chang et al., 2016), stability during flight(Ravi et al., 2016), energetic costs | 13 KARDUM HJORT et al. ...
Invasive species are predicted to adjust their morphological, physiological and life‐history traits to adapt to their non‐native environments. Although a loss of genetic variation during invasion may restrict local adaptation, introduced species often thrive in novel environments. Despite being founded by just a few individuals, Bombus terrestris (Hymenoptera: Apidae) has in less than 30 years successfully spread across the island of Tasmania (Australia), becoming abundant and competitive with native pollinators. We use RADseq to investigate what neutral and adaptive genetic processes associated with environmental and morphological variation allow B. terrestris to thrive as an invasive species in Tasmania. Given the widespread abundance of B. terrestris , we expected little genetic structure across Tasmania and weak signatures of environmental and morphological selection. We found high gene flow with low genetic diversity, although with significant isolation‐by‐distance and spatial variation in effective migration rates. Restricted migration was evident across the mid‐central region of Tasmania, corresponding to higher elevations, pastural land, low wind speeds and low precipitation seasonality. Tajima's D indicated a recent population expansion extending from the south to the north of the island. Selection signatures were found for loci in relation to precipitation, wind speed and wing loading. Candidate loci were annotated to genes with functions related to cuticle water retention and insect flight muscle stability. Understanding how a genetically impoverished invasive bumblebee has rapidly adapted to a novel island environment provides further understanding about the evolutionary processes that determine successful insect invasions, and the potential for invasive hymenopteran pollinators to spread globally.
... After hundreds of millions of years of evolution, insects in nature not only possess amazing flying skills [1][2][3][4] but also can climb and adhere to surfaces made of various materials [5][6][7]. The complex flapping movement of insects during flight is the key to generating high lift and maintaining efficient and agile flight. ...
Insects that can perform flapping-wing flight, climb on a wall, and switch smoothly between the 2 locomotion regimes provide us with excellent biomimetic models. However, very few biomimetic robots can perform complex locomotion tasks that combine the 2 abilities of climbing and flying. Here, we describe an aerial–wall amphibious robot that is self-contained for flying and climbing, and that can seamlessly move between the air and wall. It adopts a flapping/rotor hybrid power layout, which realizes not only efficient and controllable flight in the air but also attachment to, and climbing on, the vertical wall through a synergistic combination of the aerodynamic negative pressure adsorption of the rotor power and a climbing mechanism with bionic adhesion performance. On the basis of the attachment mechanism of insect foot pads, the prepared biomimetic adhesive materials of the robot can be applied to various types of wall surfaces to achieve stable climbing. The longitudinal axis layout design of the rotor dynamics and control strategy realize a unique cross-domain movement during the flying–climbing transition, which has important implications in understanding the takeoff and landing of insects. Moreover, it enables the robot to cross the air–wall boundary in 0.4 s (landing), and cross the wall–air boundary in 0.7 s (taking off). The aerial–wall amphibious robot expands the working space of traditional flying and climbing robots, which can pave the way for future robots that can perform autonomous visual monitoring, human search and rescue, and tracking tasks in complex air–wall environments.
... Passive dynamics is difficult to measure experimentally because it requires turning off the insect's flight controller in mid-air, while the animal keeps its nominal hovering wing kinematics. Hence, passive flight stability is typically analyzed numerically, 10 using computational fluid dynamics (CFD) methods [11][12][13][14][15][16][17][18][19][20][21][22][23] or quasi-steady aerodynamic models. [24][25][26][27][28] Briefly, these methods are used to calculate wingbeataveraged aerodynamic forces and torques, and, relying on the separation of timescales between the fast wing kinematics and slow body dynamics, these forces and torques are then used to calculate the insect's aerodynamic derivatives. ...
... Such nonlinear analysis can inform us on the system's passive response to specific large perturbations and assist in testing a control system in particular cases. 21,30,31 CFD-based linear stability analysis has been applied to several insect species in various Reynolds (Re) numbers: bumblebee [11][12][13] (Re ¼ 1326), honeybee 14 (Re % 900), hoverfly [14][15][16] (Re % 400), dronefly [17][18][19] (Re ¼ 782), hawkmoth 18 (Re ¼ 3315), dragonfly 20 (Re % 660), mosquito 22 (Re % 100), and vegetable leaf miner and gall midge 23 ðRe < 100). Among these, earlier works typically assumed simplified wing kinematics, where the wing stroke angle kinematics are sinusoidal, with zero elevation angle and a simplified profile of the angle of attack. ...
... and a center-of-pressure situated above the center-of-mass results in a qualitatively similar negative sideways-roll coupling. 21 The next level of model complexity considers simplified wing kinematics. Such kinematics typically consist of a sinusoidal stroke angle kinematics, synthetic pitch, and zero elevation angle and have been used in several stability analyses. ...
Understanding the uncontrolled passive dynamics of flying insects is important for evaluating the constraints under which the insect flight control system operates and for developing biomimetic robots. Passive dynamics is typically analyzed using computational fluid dynamics (CFD) methods, relying on the separation of the linearized hovering dynamics into longitudinal and lateral parts. While the longitudinal dynamics are relatively understood across several insect models, our current understanding of the lateral dynamics is lacking, with a nontrivial dependence on wing–wing interaction and on the details of wing kinematics. Particularly, the passive stability of the fruit fly, D. melanogaster, which is a central model in insect flight research, has so far been analyzed using simplified quasi-steady aerodynamics and synthetic wing kinematics. Here, we perform a CFD-based lateral stability analysis of a hovering fruit fly, using accurately measured wing kinematics, and considering wing–wing interaction. Lateral dynamics are unstable due to an oscillating–diverging mode with a doubling time of 17 wingbeats. These dynamics are determined by wing–wing interaction and the wing elevation kinematics. Finally, we show that the fly's roll controller, with its one wingbeat latency, is consistent with the lateral instability. This work highlights the importance of accurate wing kinematics and wing–wing interactions in stability analyses and forms a link between such passive instability and the insects' controller.
... The dexterity of natural flight often surpasses that of engineering flight vehicles in highly unsteady flows. In many such instances, engineering flights spin out of control, whereas birds and insects maintain stability [10,11]. For example, during rapid pitching of the wing, the flow becomes highly unsteady, affecting aerodynamic performances. ...
Many marine animals can dynamically twist their pectoral fins while swimming. The effects of such dynamic twisting on the unsteady forces on the fin and its surrounding flow field are yet to be understood in detail. In this paper, a flat plate executing a heaving maneuver is subjected to a similar dynamic twisting. In particular, the effects of the direction of twist, non-dimensional heaving amplitude, and reduced frequency are studied using a force sensor and Particle Image Velocimetry (PIV) measurements. Two reduced frequencies, Γ = 0.105, and 0.209, and two twisting modes are investigated. In the first twisting mode, the plate is twisted in the direction of the heave (forward-twist), and in the second mode, the plate is twisted opposite to the direction of the heave (backward-twist). Force sensor measurements show that the forward-twist recovers some of the lift that is usually lost during the upstroke of flapping locomotion. Additionally, the forward-twist maintains a near-constant lift coefficient during the transition between downstroke and upstroke, suggesting a more stable form of locomotion. PIV results show that forward-twist limits circulation and leading-edge vortex (LEV) growth during the downstroke, keeping ΓΓ ≈ 0 at the cost of the reduced lift. By contrast, backward-twist increases the circulation during the downstroke, resulting in large increases in both lift and drag coefficients. Force sensor data also showed that this effect on the lift is reversed during the upstroke, where the backward-twist causes a negative lift. The effects of each twisting mode are mainly caused by the changes in the shear layer velocity that occur as a result of spanwise twisting.
... In the field, foraging bumblebees encounter turbulence generated by the vegetation canopy. A typical situation of a bumblebee approaching a flower was modelled in [61] by introducing a vertically oriented cylindrical obstacle in an otherwise unperturbed inflow. By confronting the results of numerical simulations and animal flight experiments in a wind tunnel, it was shown that bumblebees can ride through the small-scale high-frequency turbulence without any assistance from the neural system. ...
... In [61] we studied the bumblebee's motion while flying in the von Karman vortex street generated in the wake of a circular cylinder, at Re = 4200 ( Figure 12). The high resolution numerical simulations with more than 2.2 billion grid points run on 8192 cores allowed to study the free flight dynamics of flapping bumblebees considering two degrees of freedom, lateral displacement and roll rotation about the longitudinal axis of the body. ...
... The velocity field in the horizontal plan of the insect is represented by arrows. From[61]. ...
The state-of-the-art of insect flight research using advanced computational fluid dynamics techniques on supercomputers is reviewed, focusing mostly on the work of the present authors. We present a brief historical overview, discuss numerical challenges and introduce the governing model equations. Two open source codes, one based on Fourier, the other based on wavelet representation, are succinctly presented and a mass-spring flexible wing model is described. Various illustrations of numerical simulations of flapping insects at low, intermediate and high Reynolds numbers are presented. The role of flexible wings, data-driven modeling and fluid–structure interaction issues are likewise discussed.
... Significant biologic system focused research has been conducted on the effects of freestream unsteadiness such as turbulence on flying insects, birds, and fish [17][18][19][20][21][22][23][24][25]. We briefly review previous studies on fish and fishlike swimming in an unsteady environment here as this has inspired our current research on studying the impact of flow environment unsteadiness on the propulsive performance of flapping foils. ...
A numerical study is conducted to understand the impact of an unsteady freestream on the aerodynamic performance of an oscillating airfoil. The unsteady flow environment is generated by placing a stationary inline circular cylinder array upstream of the oscillating airfoil. The dependence of thrust with variation of Reynolds numbers and Strouhal numbers is investigated, and it is revealed that the unsteady flow environment enhances thrust production of a pitching airfoil. This increased thrust production was related to an effective increase in the Reynolds number experienced by the airfoil. With airfoil–vortex interaction analysis, the increase in average thrust coefficient was shown to be caused by constructive interaction of freestream vortex structures and the oscillating airfoil. Drag-inducing interactions were also observed but were less common than thrust-increasing events, resulting in a higher average thrust. A simple scaling law is expanded to include the effects of unsteadiness, where thrust is found to be linearly dependent on turbulence intensity. It is demonstrated that the thrust generated by the pitching airfoil when operating in highly unsteady flow environments is more accurately represented as a function of Reynolds number, Strouhal number, and turbulence intensity.
... Flapping their flexible wings enables insects to carry food (Mountcastle et al., 2015), catch prey, and escape predators (Crall et al., 2017). They can also fly steadily in bad weather by spiraling or rapidly tilting and turning using their wings (Karásek et al., 2018;Ravi et al., 2016). For these unique flying skills, insects require a suitable pair of wings to flap for achieving the lift and driving torque necessary to adjust their attitude and control stability. ...
Insects in nature flap their wings to generate lift force and driving torque to adjust their attitude and control stability. An insect wing is a biomaterial composed of flexible membranes and tough veins. In this paper, we study the microscopic structures and mechanical properties of the forewing of the black cicada, Cryptotympana atrata . The thickness of the wing membranes and the diameter of veins varied from the wing root to the tip. The thickness of the wing membranes ranged from 6.0 to 29.9 μm, and the diameter of the wing veins decreased in a gradient from the wing root to the tip, demonstrating that the forewing of the black cicada is a nonuniform biomaterial. The elastic modulus of the membrane near the wing root ranged from 4.45 to 5.03 GPa, which is comparable to that of some industrial membranes. The microstructure of the wing vein exhibited a hollow tubular structure with flocculent structure inside. The “fresh” sample stored more water than the “dry” sample, resulting in a significant difference in the elastic modulus between the fresh and dried veins. The different membrane thicknesses and elastic moduli of the wing veins near the root and tip resulted in varied degrees of deformation on both sides of the flexion line of the forewing during twisting. The measurements of the forewing of the cicada may serve as a guide for selecting airfoil materials for the bionic flapping‐wing aircraft and promote the design and manufacture of more durable bionic wings in the future.
Research Highlights
The distribution of the wing vein diameter and the wing membrane thickness indicated that the forewing of Cryptotympana atrata is composed of heterogeneous materials.
The wing membrane and the outer wall of the wing vein are the layered structure with multilayer fibers, which has a great significance for improving the ability of the forewing to sustain aerodynamic loads.
The elastic modulus of the wing membrane near the wing root is in the range of 4.45–5.03 GPa , which is comparable to that of membranes manufactured by industries. This is a suitable reference for selecting materials for making bionic aircraft wings.
We proved that the elastic moduli of the “fresh” and “dry” wing veins differ greatly compared with those of the wing membrane. Because the wing vein microstructure exhibits an internal hollow tubular structure with flocculent structure inside, the “fresh” sample stores more water than the “dry” sample.
The wing membrane near the wing root is thicker and reinforced by the main wing vein with a high elastic modulus. This renders the region near the wing root difficult to deform. The membrane far from the wing root is thinner and the elastic modulus of the nearby wing veins is smaller, making them more flexible.
... Insects are model systems for this challenge as they achieve robust maneuvers in unpredictable dynamic environment despite relatively limited neural resources (Ravi et al 2016). This performance includes multi-agent behaviors such as cohesion, swarming, and other coordinated motions involving navigation relative to each other. ...
... Larger free flight tunnel (31 × 31 × 86 cm) environments have shown promise to understanding insect decision making algorithms (Maimon et al 2008). There is promise to more transitional environments, including measurement in a gusting wind tunnel (100 mm 3 tracked region, tethered and free flight cases) that have shown that free flight in unsteady conditions features more complex motions, such as high frequency rolling motions and lateral accelerations superimposed on slower casting motions in (Ravi et al 2016). ...
Individual insects flying in crowded assemblies perform complex aerial maneuvers by sensing and feeding back neighbor measurements to small changes in their wing motions. To understand the individual feedback rules that permit these fast, adaptive behaviors in group flight, both experimental preparations inducing crowded flight and high-speed tracking systems capable of tracking both body motions and more subtle wing motion changes for multiple insects in simultaneous flight are needed. This measurement capability extends tracking beyond the previous focus on individual insects to multiple insects. This paper describes an experimental preparation that induces crowded insect flight in more naturalistic conditions (a laboratory-outdoor transition tunnel) and directly compares the resulting flight performance to traditional flight enclosures. Measurements are made possible via the introduction of a multi-agent high speed insect tracker called Hi-VISTA, which provides a capability to track wing and body motions of multiple insects using high speed cameras (9000-12,500 fps). Processing steps consist of automatic background identification, data association, hull reconstruction, segmentation, and feature measurement. To improve the biological relevance of laboratory experiments and develop a platform for interaction studies, this paper applies the Hi-VISTA measurement system to Apis mellifera foragers habituated to transit flights through the transparent transition environment. Binary statistical analysis (Welch's t-test, Cohen's d effect size) of 95 flight trajectories is presented, quantifying the differences between flights in an unobstructed environment and in a confined tunnel volume. The results indicate that body pitch angle, heading rate, flapping frequency, and vertical speed (heave) are each affected by confinement, and other flight variables show minor or statistically insignificant changes. These results form a baseline as swarm tracking and analysis begins to isolate the effects of neighbors from environmental enclosures, and improve the connection of high speed insect laboratory experiments to outdoor field experiments.
