Nondimensional frequency scaling of aerodynamically-tensioned membranes

Membrane wings have applications that involve low Reynolds number flyers such as micro air vehicles. The time-averaged and time-dependent deformations of the membrane affect the aerodynamic characteristics of the wing, primarily in the region beyond the maximum aerodynamic efficiency of the wing. This paper investigates an appropriate nondimensional vibration frequency scaling of a spanwise tensioned membrane with free (unattached) leading and trailing edges at low Reynolds numbers relative to nondimensional aeroelastic parameters. Silicone rubber membranes with varying spanwise pre-tension, aerodynamic tension (due to wing angle-of-attack and flow dynamic pressure), modulus of elasticity, span, and thickness are studied. Experimental results are compared to a proposed scaling that simplifies the aerodynamic loading as a uniform pressure distribution acting on the membrane. Data is further compared and discussed relative to previous published results of membrane wings with finite wing spans (three-dimensional flow) and fixed (rigid) leading edges.     

高升力外形下机翼的位流计算

本文采用第二代低阶面元法给出了一种高升力外形外机翼位流计算方法。     

Research on the Raman properties of NiFe/cicada wing composite SERS platform modified by silver nanoparticles

Composite structures have been widely concerned in the preparation of surface enhanced Raman scattering (SERS) substrates. In this paper, by solving the problem that the magnetic material was difficult to glow in magnetron sputtering, ferro-nickel (NiFe) alloy was deposited on the cicada wing (CW) and the NiFe/CW substrate was obtained. The results of sliver nanoparticles (Ag NPs) modified on the substrate were subsequently compared, and the SERS properties of the new Ag/NiFe/CW substrate were analyzed. Obviously, the intensity of SERS signals has been greatly improved after the modification of Ag NPs, and the substrate exhibits excellent reproducibility. The Ag NPs modified substrates were also applied to the detection of toxic crystal violet (CV) solution, which showed remarkable SERS activity. It has been proved that the strategy of modifying Ag NPs on the substrate to form a composite structure has great potential for improving the SERS performance of the substrate.     

Aerodynamic force and flow structures of two airfoils in flapping motions

Aerodynamic force and flow structures of two airfoils in a tandem configuration in flapping motions are studied, by solving the Navier-Stokes equations in moving overset grids. Three typical phase differences between the fore- and aftairfoil flapping cycles are considered. It is shown that: (1) in the case of no interaction (single airfoil), the time average of the vertical force coefficient over the downstroke is 2.74, which is about 3 times as large as the maximum steady-state lift coefficient of a dragonfly wing; the time average of the horizontal force coefficient is 1.97, which is also large. The reasons for the large force coefficients are the acceleration at the beginning of a stroke, the delayed stall and the “pitching-up” motion near the end of the stroke. (2) In the cases of two-airfoils, the time-variations of the force and moment coefficients on each airfoil are broadly similar to that of the single airfoil in that the vertical force is mainly produced in downstroke and the horizontal force in upstroke, but very large differences exist due to the interaction. (3) For in-phase stroking, the major differences caused by the interaction are that the vertical force on FA in downstroke is increased and the horizontal force on FA in upstroke decreased. As a result, the magnitude of the resultant force is almost unchanged but it inclines less forward. (4) For counter stroking, the major differences are that the vertical force on AA in downstroke and the horizontal force on FA in upstroke are decreased. As a result, the magnitude of the resultant force is decreased by about 20 percent but its direction is almost unchanged. (5) For 90°-phase-difference stroking, the major differences are that the vertical force on AA in downstroke and the horizontal force on FA in upstroke are decreased greatly and the horizontal force on AA in upstroke increased. As a result, the magnitude of the resultant force is decreased by about 28% and it inclines more forward. (6) Among the three cases of phase angles, inphase flapping produces the largest vertical force (also the largest resultant force); the 90°-phase-difference flapping results in the largest horizontal force, but the smallest resultant force.     

A spectroscopic investigation of turbulence in magnetized plasmas

We present a spectroscopic investigation of turbulence in the Tore-Supra edge plasma, where deuterium spectral lines are found to exhibit a power-law behavior in their wings. Such a feature is not predicted by the equilibrium line broadening theory in the conditions of the edge plasma, where the thermal Stark effect is negligible. Therefore, the possible role of turbulence is investigated along two separate paths. Indeed, both the Stark and the Doppler profiles may differ significantly from the equilibrium profiles.     

产生旁瓣的激光波前功率谱密度与焦斑性能分析

讨论了在放置与不放置焦斑形态控制器件 KPP的两种情况下 ,采用功率谱密度模拟分析有旁瓣焦斑的激光束波前分布的特点 ,并由此探讨高功率激光驱动器在无旁瓣的聚焦情形下 ,对入射到打靶透镜的激光束波前畸变量的控制要求。     

Experimental investigations of the functional morphology of dragonfly wings

Nowadays, the importance of identifying the flight mechanisms of the dragonfly, as an inspiration for designing flapping wing vehicles, is well known. An experimental approach to understanding the complexities of insect wings as organs of flight could provide significant outcomes for design purposes. In this paper, a comprehensive investigation is carried out on the morphological and microstructural features of dragonfly wings. Scanning electron microscopy （SEM） and tensile testing are used to experimentally verify the functional roles of different parts of the wings. A number of SEM images of the elements of the wings, such as the nodus, leading edge, trailing edge, and vein sections, which play dominant roles in strengthening the whole structure, are presented. The results from the tensile tests indicate that the nodus might be the critical region of the wing that is subjected to high tensile stresses. Considering the patterns of the longitudinal corrugations of the wings obtained in this paper, it can be supposed that they increase the load-bearing capacity, giving the wings an ability to tolerate dynamic loading conditions. In addition, it is suggested that the longitudinal veins, along with the leading and trailing edges, are structural mechanisms that further improve fatigue resistance by providing higher fracture toughness, preventing crack propagation, and allowing the wings to sustain a significant amount of damage without loss of strength.     

Line shape in far wings and water vapor absorption in a broad temperature interval

Despite the long-term history of extensive studies on water vapor continuum absorption it can hardly be said that an exhaustive consideration has been given to this problem both from experimental and theoretical viewpoints. For instance, deficiency remains concerning the precise data on the absorption coefficient as a function of temperature, especially at reduced temperatures. New experimental data on water vapor continuum absorption in the 800-1250 cm⁻¹ spectral region at temperatures from 311 to 363 K have become available quite recently [15]. Two advanced variants of the line wing theory - asymptotic and quasistatic - are briefly outlined. The asymptotic line wing theory has been used successfully to describe the absorption coefficient both at elevated temperatures of the Baranov study and at the temperatures of earlier experimental data. Comparison is made with the results obtained from the quasistatic line wing theory.     

三角翼上分离及涡流的数值模拟

综述了三角翼(包括双三角翼,边条-三角翼,近距耦合鸭翼)上分离及涡流问题的数值模拟进展,介绍了用Euler方程、N-S方程的数值方法模拟不同三角翼,在不同攻角、不同来流M数等多种条件下的复杂涡流形态和流动结构,研究了控制方程、网格、湍流模型和计算方法等对计算结果的影响。      

Wing wettability of Odonata species as a function of quantity of epicuticular waxes

Dragonflies have gained much attention due to their sophisticated wing surface structure, and their associated superhydrophobic, self-cleaning and bactericidal properties. In this work, we compared and contrasted the chemical composition and surface morphology of the wing membranes of four species of dragonfly and damselfly from the Odonata family collected in 1970s (Diplacodes melanopsis and Xanthagrion erythroneurum) and 2011 (Diplacodes bipunctata, and Ischnura heterosticta). Diplacodes species are dragonflies, whilst Xanthagrion and Ischnura are damselflies. Fourier-transform infrared spectroscopy data obtained from the Australian Synchrotron were used to classify the fundamental components of all four of the insect species’ wings. The spectra of all species were dominated by CH stretching, amide I and amide II and OH stretch absorbance indicating the presence of a similar membrane composition of chitin, protein and wax in all four species. Although the samples were collected 40 years apart, there was no evidence of degradation having taken place during this time. Despite the overall similarities in spectral profile, species-specific differences were observed, most notably in the intensity of the νCH₂ peaks, which in part reflected the amount of waxes present on the wings, which appeared to be different between individual species. The surface topography also contained minor differences in the diameter and the spacial distribution of its nanopillars. It is postulated that the differences in surface wettability of the wings could be attributed to these minor differences in surface chemistry and surface topography. For example, X. erythroneurum presented the highest water contact angle (WCA) of 160° whilst the D. melanopsis wings exhibited the lowest WCA (138°), and the wettability of their wings was found to directly correlate with the intensity of hydrocarbon peaks found in their respective IR specta.