The Flapping Flight of Birds. II

1927 ◽  
Vol 31 (196) ◽  
pp. 337-342 ◽  
Author(s):  
Gilbert T. Walker
Keyword(s):  
Mechanical Model ◽  
High Efficiency ◽  
Flapping Flight ◽  
Angle Of Incidence ◽  
Negative Work ◽  
Outer Portion ◽  
Pectoralis Minor ◽  
Standard Section ◽  
Large Muscle

In a paper in the number of this journal for November, 1925, it was shown that if a flying machine were fitted with wings of standard section and these were flapped in a rhythmical manner, the machine would be supported and propelled, its weight, dimensions and velocity being those of a typical bird; the degree of accuracy attempted in the analysis did not exceed five per cent.A subsequent examination of the power involved established a high efficiency; but this was due to a large amount of negative work during up–beats; and although such conditions might be maintained in a mechanical model they were unlikely in a bird, which has a large muscle, the pectoralis minor, for lifting its wings. In a bird efficiency seemed to require that the angle of incidence of the outer portion during an up–beat should be negative (see §7, p. 593, of the previous paper); the angle was however made zero (see §9) in order to secure adequate lift, and it is this feature which gives rise to the negative work.

High-angle Kikuchi patterns

1954 ◽  
Vol 221 (1145) ◽  
pp. 224-242 ◽  
Keyword(s):  
Lithium Fluoride ◽  
High Efficiency ◽  
Cylindrical Specimen ◽  
Angle Of Incidence ◽  
High Angle ◽  
Lead Sulphide ◽  
Marked Contrast ◽  
Experimental Conditions ◽  
Low Intensity ◽  
Glancing Angle

A cylindrical specimen chamber and camera have been used to study the high-angle Kikuchi patterns obtained by reflexion of electrons, of energy 6 to 50 keV, from the cleavage surfaces of crystals with the sodium chloride structure. Angles of scattering ranging from 0 to 164° were covered. The relative intensity of the pattern at different scattering angles was measured using a photographic technique. The intensity distribution was found to become less steep as the energy of the incident electrons decreased. In photographs taken with a large value of the glancing angle of incidence, defect bands were found, starting near the shadow edge of the pattern; these changed to excess bands at higher angles of scattering. The most striking feature of the results is the remarkable intensity and clarity at the highest scattering angles of the pattern produced by crystals such as lead sulphide and potassium iodide, the constituents of which have a relatively high elastic scattering cross-section. In marked contrast, a relatively low intensity and low clarity was found at these angles for lithium fluoride under the same experimental conditions. An investigation of the width of Kikuchi bands, visible over the whole available angular range, showed that the electrons forming these bands had the same energy as that of the incident electrons within the experimental error of 10%. A possible mechanism is discussed by means of which electrons can be diffused through large angles with high efficiency, relative to small angles, and with relatively little loss of energy.

The influence of negative work on optimal flapping flight

2010 ◽  
Vol 24 (12) ◽  
pp. 2441-2449 ◽  
Author(s):  
Christopher O. Johnston ◽  
William H. Mason ◽  
Cheolheui Han
Keyword(s):  
Flapping Flight ◽  
Negative Work

scholarly journals Transparent Surface Lens Of Low-Temperature Solar Devices

2020 ◽  
Vol 02 (10) ◽  
pp. 145-149
Author(s):  
Jo'raev M.Q ◽  
◽  
Muzaffarov F.F ◽  
Rustamov S.Sh ◽  
Timirov H.N ◽  
...  
Keyword(s):  
Solar Cells ◽  
Low Temperature ◽  
Mathematical Analysis ◽  
Light Absorption ◽  
High Efficiency ◽  
Angle Of Incidence ◽  
Light Penetration ◽  
Efficient Operation ◽  
Work Related ◽  
Transparent Surface

The transparent surface of low-temperature solar devices is insulated with glass or polyethylene. Ensuring more light penetration from such surfaces ensures efficient operation of the device, in other words, the device has a high efficiency. Selecting the device design to allow most of the sunlight falling on the transparent surface to enter the device, keeping the transparent surface clean, reducing the angle of incidence of the light to small values, and so on. In most cases, it depends on the parameters. In this article, we analyze the theoretical and practical solutions of work related to the selection and optimization of the angle of incidence of light on the transparent surface of the device to increase the incidence of sunlight during the day. Light absorption, rotation and absorotion of light into low- temperature solar cells. Mathematical analysis and formulas are given.

The Flapping Flight of Birds

1925 ◽  
Vol 29 (179) ◽  
pp. 590-594 ◽  
Author(s):  
Gilbert T. Walker
Keyword(s):  
Wind Tunnel ◽  
Flapping Flight ◽  
Present Writer ◽  
Previous Issue ◽  
Gliding Flight ◽  
It Support ◽  
Standard Section ◽  
Lift And Drag

In connection with gliding flight enough measurements of “ lift ” and “ drag ” have been made to enable us to calculate the conditions for success of an aeroplane fitted with wings of standard sections; but no attempt has been made, as far as the present writer is aware, to ascertain what would happen if a flying machine were fitted with wings of standard section and these were flapped in a rhythmical manner. Would it support and propel itself? Several authors, including M. F. Fitzgerald and Colonel J. D. Fullerton in the previous issue of this journal, have discussed various portions of this problem; but instead of appealing to wind-tunnel determinations the latter has used such expressions as pSUV or pSUV2 for the pressure on a wing of area S, where p is the density of the air and V, U are the component velocities along and at right angles to its surface.

scholarly journals An Ultrathin, Triple-Band Metamaterial Absorber with Wide-Incident-Angle Stability for Conformal Applications at X and Ku Frequency Band

2020 ◽  
Vol 15 (1) ◽  
Author(s):  
Guangsheng Deng ◽  
Kun Lv ◽  
Hanxiao Sun ◽  
Jun Yang ◽  
Zhiping Yin ◽  
...  
Keyword(s):  
Free Space ◽  
High Efficiency ◽  
Incident Angle ◽  
Surface Current ◽  
Normal Incidence ◽  
Metamaterial Absorber ◽  
Angle Of Incidence ◽  
Perfect Absorption ◽  
Absorption Frequency ◽  
Unit Cells

AbstractAn ultrathin and flexible metamaterial absorber (MA) with triple absorption peaks is presented in this paper. The proposed absorber has been designed in such a way that three absorption peaks are located at 8.5, 13.5, and 17 GHz (X and Ku bands) with absorption of 99.9%, 99.5%, and 99.9%, respectively. The proposed structure is only 0.4 mm thick, which is approximately 1/88, 1/55, and 1/44 for the respective free space wavelengths of absorption frequency in various bands. The MA is also insensitive due to its symmetric geometry. In addition, the proposed structure exhibits minimum 86% absorption (TE incidence) within 60° angle of incidence. For TM incidence, the proposed absorber exhibits more than 99% absorptivity up to 60° incidence. Surface current and electric field distributions were investigated to analyze the mechanism governing absorption. Parameter analyses were performed for absorption optimization. Moreover, the performance of the MA was experimentally demonstrated in free space on a sample under test with 20 × 30 unit cells fabricated on a flexible dielectric. Under normal incidence, the fabricated MA exhibits near perfect absorption at each absorption peak for all polarization angles, and the experimental results were found to be consistent with simulation results. Due to its advantages of high-efficiency absorption over a broad range of incidence angles, the proposed absorber can be used in energy harvesting and electromagnetic shielding.

scholarly journals Phasing of dragonfly wings can improve aerodynamic efficiency by removing swirl

2008 ◽  
Vol 5 (28) ◽  
pp. 1303-1307 ◽  
Author(s):  
James R Usherwood ◽  
Fritz-Olaf Lehmann
Keyword(s):  
Mechanical Model ◽  
Hind Wing ◽  
Micro Air Vehicles ◽  
Flapping Flight ◽  
Single Pair ◽  
Helicopter Rotors ◽  
Aerodynamic Efficiency ◽  
Winged Form ◽  
Low Speed ◽  
Dragonfly Wings

Dragonflies are dramatic, successful aerial predators, notable for their flight agility and endurance. Further, they are highly capable of low-speed, hovering and even backwards flight. While insects have repeatedly modified or reduced one pair of wings, or mechanically coupled their fore and hind wings, dragonflies and damselflies have maintained their distinctive, independently controllable, four-winged form for over 300 Myr. Despite efforts at understanding the implications of flapping flight with two pairs of wings, previous studies have generally painted a rather disappointing picture: interaction between fore and hind wings reduces the lift compared with two pairs of wings operating in isolation. Here, we demonstrate with a mechanical model dragonfly that, despite presenting no advantage in terms of lift, flying with two pairs of wings can be highly effective at improving aerodynamic efficiency. This is achieved by recovering energy from the wake wasted as swirl in a manner analogous to coaxial contra-rotating helicopter rotors. With the appropriate fore–hind wing phasing, aerodynamic power requirements can be reduced up to 22 per cent compared with a single pair of wings, indicating one advantage of four-winged flying that may apply to both dragonflies and, in the future, biomimetic micro air vehicles.

Substrate and DLARC Layers Selection for High Efficiency Solar Cell

2019 ◽  
Vol 18 (01) ◽  
pp. 1850012 ◽  
Author(s):  
M. Ismail Fathima ◽  
K. S. Joseph Wilson
Keyword(s):  
Solar Cell ◽  
High Efficiency ◽  
Light Trapping ◽  
Substrate Material ◽  
Antireflective Coating ◽  
Angle Of Incidence ◽  
Si Substrate ◽  
Optical Losses ◽  
Near Ir ◽  
Selection For

Optical losses are one of the important parameters that affect the efficiency of solar cell. Various light-trapping techniques are used to reduce the optical losses, especially reflectivity loss. Antireflective coating (ARC) is used to reduce the reflectivity losses in the solar cell. In this paper, we have analyzed the reflectivity of double layer ARC (DLARC) in the solar cell using transfer matrix method. The reflectivity of various combinations of DLARC materials with a suitable substrate material is analyzed in the visible and near IR region. It is found that ZnS/Ge DLARC on Si substrate solar cell provides minimum reflectance in the range of wavelength 550–950[Formula: see text]nm. It is also found that zero reflectance occurs at 550[Formula: see text]nm. This minimum reflectance also depends on the angle of incidence. Here it is continuously maintained up to the angle of incidence from 0[Formula: see text] to 20[Formula: see text]. From these investigations, it is concluded that ZnS/Ge DLARC is one of the suitable DLARCs on Si substrate in 550–950[Formula: see text]nm range of wavelength.

scholarly journals Study on New Bolted T-Stub Connection with Inserted Plates under Axial and Cyclic Loads

2020 ◽  
Vol 10 (7) ◽  
pp. 2631
Author(s):  
Xiaoming Zhu ◽  
Zhaoqi Wu
Keyword(s):  
Energy Dissipation ◽  
Mechanical Model ◽  
Experimental Tests ◽  
Rectangular Plates ◽  
Reasonable Range ◽  
Compressive Loads ◽  
Standard Section ◽  
Energy Dissipation Capacity ◽  
Energy Dissipated ◽  
Optimum Width

The bolted T-stub connection joining beam with column is being widely applied. To enhance the energy dissipation capacity of conventional T-stub connections, two rectangular plates are proposed to be inserted between the T-stub and column, so that the T-stub flange can yield both under tensile and compressive loads. This study put forward a mechanical model of a new T-stub connection with inserted plates and investigated important factors that could affect its mechanical behavior through experimental tests. Thirty specimens were designed with different configurations that differed according to the existence or absence of inserted plates, the fabrication method and the width of inserted plates. These configurations were tested under axial and cyclic loading conditions, and results showed that the proposal aiming to improve the energy dissipation capacity was feasible. The mechanical model presented coincided with the test observation and data. The advent of two inserted plates elevated the load bearing capacity, stiffness and ductility of connections under compression, whereas in tension the properties were not substantially enhanced. The welded T-stub connections outperformed those cut from standard section steel. The energy dissipated by connections with inserted plates was about 150% of that by traditional connections without inserted plates. Only within a reasonable range can the increment of plate width promote the energy dissipation capacity of T-stub connections. The optimum width of plates in terms of energy consumption accounted for around 31% of the overall width of connections.

scholarly journals Ellipsometry of thin films of biological objects under conditions of total internal reflection

2022 ◽  
Vol 24 (4) ◽  
pp. 7-12
Author(s):  
Valeriy V. Yatsishen
Keyword(s):  
Thin Films ◽  
Total Internal Reflection ◽  
Critical Angle ◽  
High Efficiency ◽  
Polarized Light ◽  
Internal Reflection ◽  
Test Material ◽  
Angle Of Incidence ◽  
Film Material ◽  
Circularly Polarized

An analysis of the ellipsometric parameters of the reflected light from the prism test material air system is carried out when circularly polarized light is incident on it under the conditions of the onset of the phenomenon of total internal reflection. At the onset of total internal reflection, the ellipsometry parameter shows high variability with the angle of incidence, in contrast to the parameter r0. It is shown that TIR occurs when the angle of incidence is not equal to the critical angle of the adjacent media for two different materials, these angles differ from each other. In the case of a film, the TIR phenomenon occurs at an angle equal to the critical angle at the prism-air interface and does not depend on the film material. The results obtained show the high efficiency of using the ellipsometric method together with circularly polarized incident radiation for diagnostics of thin films made of biological material.

scholarly journals Application of Absolute Nodal Coordinate Formulation in Calculation of Space Elevator System

2021 ◽  
Vol 11 (23) ◽  
pp. 11576
Author(s):  
Shihao Luo ◽  
Youhua Fan ◽  
Naigang Cui
Keyword(s):  
Mechanical Model ◽  
High Efficiency ◽  
Absolute Nodal Coordinate Formulation ◽  
Low Cost ◽  
Axial Loading ◽  
Lumped Mass ◽  
Absolute Nodal Coordinate ◽  
Calculation Results ◽  
Mechanical Models ◽  
Flexible Deformation

The space elevator system is a space tether system used to solve low-cost space transportation. Its high efficiency, large load, reusability and other characteristics have broad application prospects in the aerospace field. Most of the existing mechanical models are based on “chain-bar” and a lumped mass tether model, which cannot effectively reflect the flexible behaviour of the rope of space elevator system. To establish an accurate mechanical model, the gradient deficient beam elements of the absolute nodal coordinate formulation (ANCF) are used to build the mechanical model of the space elevator system. The universal gravitation and centrifugal force in the model are derived. The calculation results of the ANCF model are compared with the results of the finite element method (FEM) and lumped mass (LM) models. The results show that the calculation results of the ANCF method are not very different from the results of the FEM and LM models in the case of axial loading. In the case of lateral loading, the calculation results of the ANCF method are basically the same as the results of the FEM and LM models, but can better reflect the local flexible deformation of the space elevator rope, and have a better calculation stability than FEM. Under the same calculation accuracy, the ANCF method can use fewer elements, and the speed of convergence is faster than the FEM and LM models.

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