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(a) Digital reconstruction of the hindwing of Sympetrum vulgatum. Dark areas are thick, light areas are thin (linear scale from dark to light). (b-e) Crosssectional micro-CT image near the wing root showing the highly corrugated wing architecture build up by the wings veins and membrane. Cross sections more distant of the root (c-e) show less corrugation and the cross section near the wing tip (e) reveils the hollow pterostigma. The main difference between this figure and 3 are the much thinner veins and membrane
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Dragonfly wings are highly corrugated, which increases the stiffness and strength of the wing significantly, and results in
a lightweight structure with good aerodynamic performance. How insect wings carry aerodynamic and inertial loads, and how
the resonant frequency of the flapping wings is tuned for carrying these loads, is however not fully und...
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... digitally smooth the cross-sections and subsequently recon- struct the wings (Figs. 3 and 4). The gray-values in Figs. 3 and 4 represent wing thickness. Dark indicates thick areas whereas light areas are thin. Although we used a state of the art micro-CT scanner, dragonfly wings still proved to be challenging thin. Especially for the hindwing in Fig. 4; 56% of its membrane area has a thickness less than the resolution of the scan. Fortunately, roughly 96% of the area of the forewing proved thick enough for a three- dimensional scan. We therefore focus our study on the forewing and assume that the area with a thickness smaller than the scan resolution (approximately 4%) has a ...
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Citations
... The power consumption of a flexible wing was 25% less than that of a rigid wing in the same external conditions [24]. The deformation properties of insect wings are critical for improving the flight ability of insects [25][26][27]. ...
Locust Locusta migratoria exhibits remarkable aerial performances, relying predominantly on its hind wings that generate most of lift and thrust for flight. The mechanical properties of the cross-veins determine the deformation of the hind wing, which greatly affect the aerodynamic performance of flapping flight. However, whether the mechanical behaviours of the locust cross-veins change with loading rate is still unknown. In this study, cross-veins in four physiological regions (anterior–medial, anterior–lateral, posterior–medial and posterior–lateral) of the hind wing from adult locusts were investigated using uniaxial tensile test, stress relaxation test and fluorescence microscopy. It was found that the cross-veins were a type of viscoelastic material (including rate-independent elastic modulus and obvious stress relaxation). The cross-veins in the two anterior regions of the hind wing had significantly higher elastic moduli and higher ultimate tensile stress than those of its two posterior regions. This difference might be attributed to different resilin distribution patterns in the cross-veins. These findings furnish new insights into the mechanical characteristics of the locust cross-veins, which might deepen our understanding of the aerodynamic mechanisms of locust flapping flight.
... The detailed arrangement and corresponding layouts are presented in Figures 7-11, where the plain and isometric view of lattice-infilled optimized wing structures with and without skin are shown. It can be seen from these figures that at the maximum bending load, more material distribution is noted in the form of compact lattices at the area near the root of the wing, where the lattice structure is distributed as per the strength requirements in the form of branches, playing a structural role by making the wing stiffer [81]. The summary of weight saving compared to the base-wing model is presented in Figure 16. ...
... Materials 2024, 17, x FOR PEER REVIEW 13 [81]. The summary of weight saving compared to the base-wing model is presented Figure 16. ...
Lightweight structures with a high stiffness-to-weight ratio always play a significant role in weight reduction in the aerospace sector. The exploration of non-conventional structures for aerospace applications has been a point of interest over the past few decades. The adaptation of lattice structure and additive manufacturing in the design can lead to improvement in mechanical properties and significant weight reduction. The practicality of the non-conventional wing structure with lattices infilled as a replacement for the conventional spar–ribs wing is determined through finite element analysis. The optimal lattice-infilled wing structures are obtained via an automated iterative method using the commercial implicit modeling tool nTop and an ANSYS workbench. Among five different types of optimized lattice-infilled structures, the Kelvin lattice structure is considered the best choice for current applications, with comparatively minimal wing-tip deflection, weight, and stress. Furthermore, the stress distribution dependency on the lattice-unit cell type and arrangement is also established. Conclusively, the lattice-infilled structures have shown an alternative innovative design approach for lightweight wing structures.
... The wing outline is affected by aerodynamics, but the aerodynamic restraints on the cross-section are low as long as the mechanisms for the Λ-vortex generation, collapse, and maintaining the groove's subsequent turbulent structure remain functional. Figure 10 implies that structural factors [37], including wing torsion [38], will presumably intervene in defining the dragonfly wing geometry. Figure 11(a) shows that the wing's upper surface, where the pressure was low at = 0°, is even lower at = 8°. ...
In this study, we examined the aerodynamics around the hindwing of a faithfully reproduced Pantala Flavescens (globe wanderer) under gliding conditions. The dragonfly wing is corrugated, with numerous veins running through the entire wing. This convexoconcave geometry improves the lift-to-drag ratio under low Reynolds number conditions. However, until now, aerodynamic analyses have only been performed on 2D chordwise cross-sections of the wing and pseudo-3D shapes extending the profiles spanwise. The aerodynamic performance of a 3D geometry that faithfully replicates all wing veins has yet to be investigated. Therefore, we prepared a faithful analytical model by 3D scanning the hindwing of a Pantala Flavescens specimen; as a migratory dragonfly, it is capable of long-duration and long-distance flight. In our simulation results, the V-shaped groove formed by the large wing veins was covered by separation vortices, resulting in a pseudo-smooth wing surface. The role of the differently-sized wing veins is supposedly to inhibit separation. The faithful reproduction of the wings provides a better understanding of the 3D flow structure and directly leads to a precise estimation of the underlying aerodynamic characteristics. Accurate performance must be evaluated by simulating a faithful geometry in low angle of attacks, where aerodynamic efficiency is required for long-distance flight.
... The Voronoi pattern is also based on topology optimization results but is applied based on the voids appearing in the extracted load lines; see Figure 9. The Voronoi option was selected based on its similarity to the dragonfly wing structure which flaps its wings at 32.3 Hz during hover flight and has a first vibration mode of 154 Hz-4.8 times higherpotentially providing greater stiffness and raising the first vibrational mode [43]. In this design, reinforcement was achieved through the incorporation of skeleton-based features, which were strategically aligned with the internal load lines of the structure for optimal stability. ...
... hancements in deformation behavior are observed across both scenarios-the first eigenfrequency and various load cases-distinguishing it as the second-best performer in the latter and the optimal choice under resonance, with the exception of the reference design, as can be observed in Figure 11 and Figure 12. This finding suggests that, analogous to the structural attributes observed in dragonfly wings [43], Voronoi structures-as the results demonstrate-show a remarkable stiffness, surpassing even designs explicitly tailored to fulfill precise vibrational criteria. Figure 11. ...
... Significative enhancements in deformation behavior are observed across both scenarios-the first eigenfrequency and various load cases-distinguishing it as the second-best performer in the latter and the optimal choice under resonance, with the exception of the reference design, as can be observed in Figures 11 and 12. This finding suggests that, analogous to the structural attributes observed in dragonfly wings [43], Voronoi structures-as the results demonstrateshow a remarkable stiffness, surpassing even designs explicitly tailored to fulfill precise vibrational criteria. In the realm of bioinspired design, understanding the long-term durability and resilience of structures under repetitive stress conditions is of great importance. ...
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... Compared to structures with periodically arranged layouts, lattice structures with spatial-varying microstructures generally exhibit superior performance. This notion can be supported by the observations of common microstructures in nature, such as the veins of the dragonfly's wings (see Fig. 1(a) [27] for reference), which serve the dual functions of maintaining biological and physiological circulatory function while also providing stiffening effects that enhance the wings' resilience to local damages [28,29]. A similar radial structure in the stems of the Amazon water lily (see Fig. 1(b) [30]), in which the network of branching stems provides significant bending stiffness to support even the weight of an adult [31]. ...
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Adult Odonatoptera are among the most efficient flying predators. They have retained many physical characteristics over an immense period stretching from the Carboniferous to the present. Over this time they have greatly varied in size and mass, as shown in the fossil record and in particular by the length, shape, and structure of their wings. A fossil of Meganeurites gracilipes indicates that this large ‘griffenfly’ had a ‘hawker’ hunting behavior similar to certain extant species, with long periods of flight in which power, thermoregulation, and respiration would therefore tend to a ‘steady state’ equilibrium, allowing oxygen requirements and tracheole volumes to be projected and compared to extant ‘hawkers’. Comparing these values with standard pO2 models allows paleo-atmospheric density estimates to be derived. The results suggest that paleo-air pressure has varied from over two bars in the Late Carboniferous, Late Permian, and Middle to Late Jurassic, with lower values in the Early Triassic and Early Jurassic.
... They exhibit intriguingly sophisticated flight thanks to their highly specialised wings [1][2][3][4][5][6][7][8][9] . Many of the wing features, including gradients of material properties 12,13 and thickness 14,15 , venation pattern 2,16,17 , corrugation 18,19 , nodus 16,20 , pterostigma 21 , vein joints and joint-associated spikes 22,23 , resilin patches [24][25][26] , vein ultrastructure 23,27 , flexion lines 28 , and the basal complex 4,29,30 contribute to the automatic deformability of odonatan wings, and in particular, wing camber formation. A widely accepted but not yet explicitly tested hypothesis is that the basal complex-a 3D structure at the wing base with a special arrangement of veins-is key to determining the quality of wing deformations in odonatan species 2,16,29 . ...
Insect wings are adaptive structures that automatically respond to flight forces, surpassing even cutting-edge engineering shape-morphing systems. A widely accepted but not yet explicitly tested hypothesis is that a 3D component in the wing’s proximal region, known as basal complex, determines the quality of wing shape changes in flight. Through our study, we validate this hypothesis, demonstrating that the basal complex plays a crucial role in both the quality and quantity of wing deformations. Systematic variations of geometric parameters of the basal complex in a set of numerical models suggest that the wings have undergone adaptations to reach maximum camber under loading. Inspired by the design of the basal complex, we develop a shape-morphing mechanism that can facilitate the shape change of morphing blades for wind turbines. This research enhances our understanding of insect wing biomechanics and provides insights for the development of simplified engineering shape-morphing systems.
... The structural function of veins is not straightforward, and it coexists with their other roles as transmission conduits of air and hemolymph, and as sensory elements [19]. However, a few main features are recurrent, such as the veins being the thickest closest to the wing root, tapering towards the tip and trailing edge of the wings [22,23]. Another observation is that most insect wings present a zone near the leading edge stiffened by thick veins and relief (see e.g. ...
We study the aerodynamics of a flapping flexible wing with a two-vein pattern that mimics the elastic response of insect wings in a simplified manner. The experiments reveal a non-monotonic variation of the thrust force produced by the wings when the angle between the two veins is varied. An optimal configuration is consistently reached when the two veins are spaced at an angle of about 20 degrees. This value is in the range of what has been measured in the literature for several insect species. The deformation of the wings is monitored during the experiment using video recordings, which allows to pinpoint the physical mechanism behind the non-monotonic behaviour of the force curve and the optimal distribution of the vein network in terms of propulsive force.
... A density ratio ρ * = 20 is selected such that ρ * h * s = 0.4 and a value Π 0 = 0.0984 are obtained. This value is of the same order of magnitude of the effective inertia of insects (Hamamoto et al. 2007;Jongerius & Lentink 2010;Ren et al. 2013;Shyy et al. 2013) and birds (Kodali et al. 2017). The range of the effective stiffness considered here, 10 2 ), is comparable to that considered in previous studies (Fu et al. 2018). ...
We report direct numerical simulations of the flow around a spanwise-flexible wing in forward flight. The simulations were performed at $Re=1000$ for wings of aspect ratio 2 and 4 undergoing a heaving and pitching motion at Strouhal number $St_c\approx 0.5$ . We have varied the effective stiffness of the wing $\varPi _1$ while keeping the effective inertia constant, $\varPi _0=0.1$ . It has been found that there is an optimal aerodynamic performance of the wing linked to a damped resonance phenomenon, that occurs when the imposed frequency of oscillation approaches the first natural frequency of the structure in the fluid, $\omega _{n,f}/\omega \approx 1$ . In that situation, the time-averaged thrust is maximum, increasing by factor 2 with respect to the rigid case with an increase in propulsive efficiency of approximately 15 %. This enhanced aerodynamic performance results from the combination of larger effective angles of attack of the outboard wing sections and a delayed development of the leading edge vortex. With increasing flexibility beyond the resonant frequency, the aerodynamic performance drops significantly, in terms of both thrust production and propulsive efficiency. The cause of this drop lies in the increasing phase lag between the deflection of the wing and the heaving/pitching motion, which results in weaker leading edge vortices, negative effective angles of attack in the outboard sections of the wing, and drag generation in the first half of the stroke. Our results also show that flexible wings with the same $\omega _{n,f}/\omega$ but different aspect ratio have the same aerodynamic performance, emphasizing the importance of the structural properties of the wing for its aerodynamic performance.
