Aerodynamic Characteristics,Power Requirements and Camber Effects of the Pitching-Down Flapping Hovering

The pitching-down flapping is a new type of bionic flapping,which was invented by the author based on previous studies on the aerodynamic mechanisms of fruit fly(pitching-up)flapping.The motivation of this invention is to improve the aerodynamic characteristics of flapping Micro Air Vehicles(MAVs).In this paper the pitching-down flapping is briefly introduced.The major works include:(1)Computing the power requirements of pitching-down flapping in three modes(advanced,symmetrical, delayed),which were compared with those of pitching-up flapping;(2)Investigating the effects of translational acceleration time,Δτ_t,and rotational time,Δτ_r,at the end of a stroke,and the angle of attack,α,in the middle of a stroke on the aerodynamic characteristics in symmetrical mode;(3)Investigating the effect of camber on pitching-down flapping.From the above works, conclusions can be drawn that:(1)Compared with the pitching-up flapping,the pitching-down flapping can greatly reduce the time-averaged power requirements;(2)The increase in Δτt and the decrease in Δτ_r can increase both the lift and drag coefficients, but the time-averaged ratio of lift to drag changes a little.And α has significant effect on the aerodynamic characteristics of the pitching-down flapping;(3)The positive camber can effectively increase the lift coefficient and the ratio of lift to drag.

CONSTANT AMPLITUDE FATIGUE STRENGTH AND P-S_a-S_m-N CAMBER FAMILY

Functions of the P-Sa-Sm-N camber family in constant amplitude cyclic loading are established by combining the P-S-N curve family and constant life diagrams, which is feasible in engineering application. Meanwhile, the preconditions of mechanics and probability-statistics are clearly presented. According to Weibull's assumptions i.e., monotone decreasing and nonintersecting about individual S-N curves, the relation of isostructural measure preserving transformation (IMPT) between the probability spaces of constant amplitude fatigue life and constant amplitude fatigue strength is proved based on the measure theory. Therefore, an individual specimen possesses the same percentile value in different probability spaces of fatigue life and fatigue strength under constant amplitude loading. The P-Sa -Sm-N cambers of individual, population and sample are also distinguished.

A Comparative Study on Hydrodynamic Performance of Double Deflector Rectangular Cambered Otter Board

In the present work,the hydrodynamic performance of the double deflector rectangular cambered otter board was studied using wind tunnel experiment,flume tank experiment and numerical simulation.Results showed that the otter board had a good hydrodynamic performance with the maximum lift-to-drag ratio(K_(MAX) = 3.70).The flow separation occurred when the angle of attack(AOA) was at 45?,which revealed that the double deflector structure of the otter board can delay the flow separation.Numerical simulation results showed a good agreement with experiment ones,and could predict the critical AOA,which showed that it can be used to study the hydrodynamic performance of the otter board with the advantage of flow visualization.However,the drag coefficient in flume tank was much higher than that in wind tunnel,which resulted in a lower lift-to-drag ratio.These may be due to different fluid media between flume tank and wind tunnel,which result in the big difference of the vortexes around the otter board.Given the otter boards are operated in water,it was suggested to apply both flume tank experiment and numerical simulation to study the hydrodynamic performance of otter board.

Effect of Cambering on the Aerodynamic Performance of Heaving Airfoils

In the present work,a parametric numerical study is conducted in order to assess the effect of airfoil cambering on the aerodynamic performance of rigid heaving airfoils.The incompressible Navier-Stokes equations are solved in their velocity-pressure formulation using a second-order accurate in space and time finite-difference scheme.To tackle the problem of moving boundaries,the governing equations are solved on overlapping structured grids.The numerical simulations are performed at a Reynolds number of Re=1100 and at different values of Strouhal number and reduced frequency.The results obtained show that the airfoil cambering geometric parameter has a strong influence on the average lift coefficient,while it has a smaller impact on the average thrust coefficient and propulsive efficiency of heaving airfoils.

A Bio-Inspired Flapping-Wing Robot With Cambered Wings and Its Application in Autonomous Airdrop

Flapping-wing flight, as the distinctive flight method retained by natural flying creatures, contains profound aerodynamic principles and brings great inspirations and encouragements to drone developers. Though some ingenious flapping-wing robots have been designed during the past two decades, development and application of autonomous flapping-wing robots are less successful and still require further research. Here, we report the development of a servo-driven bird-like flapping-wing robot named USTBird-I and its application in autonomous airdrop.Inspired by birds, a camber structure and a dihedral angle adjustment mechanism are introduced into the airfoil design and motion control of the wings, respectively. Computational fluid dynamics simulations and actual flight tests show that this bionic design can significantly improve the gliding performance of the robot, which is beneficial to the execution of the airdrop mission.Finally, a vision-based airdrop experiment has been successfully implemented on USTBird-I, which is the first demonstration of a bird-like flapping-wing robot conducting an outdoor airdrop mission.

Structural Design and Control of Variable Camber Wing Driven by Ultrasonic Motors

A novel variable camber wing driven by ultrasonic motors is proposed.Key techniques of distributed layout of drive mechanisms,coordination control of distributed ultrasonic motors as well as novel flexible skin undergoing one-dimensional morphing are studied.The system integration of small variable camber wing is achieved.Distributed layout of parallelogram linkages driven by geared ultrasonic motors is adopted for morphing,aimed at reducing the load for each motor and producing various aerodynamic configurations suitable for different flying states.Programmable system-on-chip(PSoC)is used to realize the coordination control of the distributed ultrasonic motors.All the morphing driving systems are assembled in the interior of the wing.The wing surface is covered with a novel smooth flexible skin in order to maintain wing shape and decrease the aerodynamic drag during morphing.Wind tunnel test shows that the variable camber wing can realize morphing under low speed flight condition.Lift and drag characteristics and aerodynamic efficiency of the wing are improved.Appropriate configurations can be selected to satisfy aerodynamic requirements of different flight conditions.The study provides a practical application of piezoelectric precision driving technology in flow control.

Design and test of pneumatic artificial muscle driven variable trailing-edge camber wing

A variable camber wing driven by pneumatic artificial muscles is developed in this paper. Firstly, the experimental setup to measure the static output force of pneumatic artificial muscle is designed and the relationship between the static output force and the air pressure is investigated. Experimental results show that the static output force of pneumatic artificial muscle decreases nonlinearly with the increase of contraction ratio. Secondly, the model of variable camber wing driven by pneumatic artificial muscles is manufactured to validate the variable camber concept. Finally, wind tunnel tests are conducted in the low speed wind tunnel. It is found that the wing camber increases with the increase of air pressure. When the air pressure of PAMs is 0.4 MPa and 0.5 MPa, the tip displacement of the trailing-edge is 3 mm and 5 mm, respectively. The lift of aerofoil with flexible trailing-edge increases by 87% at AOA of 5°.

Measurement on Camber Deformation of Wings of Free-flying Dragonflies and Beating-flying Dragonflies

The knowledge of wing orientation and deformation during flapping flight is necessary for a complete aerodynamic analysis, but to date those kinematic features have not been simultaneously quantified for free-flying insects. A projected comb-fringe (PCF) method has been developed for measuring spanwise camber changes on free-flying dragonflies and on beating-flying dragonflies through the course of a wingbeat, which bases on projecting a fringe pattern over the whole measurement area and then measuring the wing deformation from the distorted fringe pattern. Experimental results demonstrate substantial camber changes both along the wingspan and through the course of a wingbeat. The ratio of camber deformation to chord length for hind wing is up to 0.11 at 75% spanwise with a flapping angle of -0.66 degree for a free-flying dragonfly.

Theoretical Study on Non-transmission High Efficient Parallel Camber Grinding Machine

Be directed against the development trend of modern CNC grinding machine towards high precision and high efficiency, some general weaknesses of existing camber grinding machine are analyzed in detail. In order to develop new type CNC camber grinding machine that can grind complex die, and genuinely achieved accurate feed and high efficient grinding, a new type camber grinding machine is put forward, called non-transmission virtual-shaft CNC camber grinding machine. Its feed system is a parallel mechanism that is directly driven by linear step motor. Therefore, traditional transmission types, such as the ball lead-screw mechanisms, the gears, the hydraulic transmission system, etc. are cancelled, and the feed system of new type CNC camber grinding machine can truly possess non-creep, good accuracy retentiveness a wide range of feed-speed change, high kinematical accuracy and positioning precision, etc. In order to realize that the cutting motion is provided with high grinding speed, step-less speed variation, high rotational accuracy, good dynamic performance, and non-transmission, the driving technology of hollow rotor motor is applied to drive the spindle of new type grinding machine,thus leading to the elimination of the transmission parts of cutting motion. The principle structure model of new type camber grinding machine is advanced. The selection, control gist and driving circuit line of the linear step motor are expounded. The main technology characteristics and application advantages of non-transmission virtual-shaft CNC camber grinding machine are introduced.

Practice to improve the plate camber during hot rolling by optimizing rolling schedule

Plate camber is one of the most important problems in hot rolling process which not only lead to lower output caused by increasing of crop loss,but also influence on the efficiency of follow-up shear processes,in severe cases damages of side guides or stands also occurred.In terms of reversible four-high hot rolling mills,the main causes of this problem exist in the following areas,reasons of stands,such as the stiffness difference between the drive side and operation side;reasons of slabs,such as the original wedge or the temperature difference along the width direction;reasons of side guides,such as the error of work pieces centerin.In their essence,it can be concluded that the initial deviation of deformation on both sides will increase as the processing,and then the work piece will deviate the center line of the stand,which will form camber defects in the end. The attempt of improving the plate camber was carried out by design the optimized schedules on the bases of theory of the steady rolling conditions during hot rolling process.In presizing and broadsizing sequence,according to the biting conditions and maximum torque restrictions,the rolling reduction of every pass should be as large as possible for the propose of increasing the negative convexity of load-gap through increasing the rolling force. When rolling process goes to finishing stage,it will be impossible to correct rolling centerline in last serval passes because the work pieces will be too long and thin,while considering the bad impact on plate profile which brought by increasing force.Therefore,the main purpose of finishing sequence should be profile control,and slowing down the speed of camber extension as much as possible by gap tilt adjustment automatically. The results show that in hot rolling process,the degree of final camber is impacted by all the three sequences. It is suggested that the control or even eliminating the defect is expectable by a well designed rolling schedule fundamentally.

Optimum design of camber line shape in a transonic axial fan cascade with splitter

Genetic algorithms and artificial neural networks method were adopted to optimize the camber line shape of splitter cascade in a transonic axial fan. For a certain type of transonic axial fan, the isentropie efficiency was improved by 0. 6% with the modification of splitter cascade rotor. Numerical simulation studies show that the curvature of the optimum splitter cascade with larger suction side is increased, the static pressure gradient is reduced, the process of flow expansion on suction surface is controlled and the separation near hub is eliminated by changing the shock wave structure. The efficiency near hub is improved by 1.3%.

A Study on Relationship among Blade Camber Direction and Pitch Angle and Performance of a Small Straight-Blade Darrieus Wind Turbine by Using Scale Test Model and Gurney Flap

Straight-blade Darrieus vertical axis wind turbines are used as medium and small size wind turbine because of higher power output in vertical axis wind turbine (VAWT). In our previous study, the relationship between the performance and Reynolds number based on airfoil chord length had been investigated by using small-scale test models of lift-type VAWT, and the results showed that the performance of tested wind turbine models with small diameter was clearly lower than that of the large-scale field test machine, and its performance also varies significantly with the blade pitch angle. In this study, we focused on the performance of a small-scale straight-blade Darrieus VAWT, the relationship among the blade airfoil camber direction and the pitch angle, and the performance of the small-scale VAWT was examined experimentally by using a small-scale VAWT test model with Gurney flap which was a small flat plate. Gurney flaps with its height h, as a ratio to the blade chord length c, h/c = 0.036 to 0.055, were attached to the blades of the VAWT test model, in addition, the attaching direction of the Gurney flap on the blade was examined for both inward and outward of the rotor, and the pitch angle was also examined for a range of −5 to 10 degrees. These results are discussed comparing with the result of the VAWT without Gurney flap and considering the numerical results for the single blade with/without the Gurney flap. The results showed that the performance of the tested VAWT was reversed between the inward and outward Gurney flaps around a pitch angle of 10 degrees. That is, the inward Gurney flap was superior at a pitch angle of less than 10 degrees, while the outward Gurney flap was effective at a pitch angle of more than 10 degrees. Furthermore, for the tested small-scale VAWT model, the optimum pitch angle was about 5 degrees, and the inward and shorter Gurney flap showed higher power performance of the VAWT under this pitch angle condition.

Effect of concrete creep on pre-camber of continuous rigid-frame bridge

The effect of concrete creep on the pre-camber of a long-span pre-stressed concrete continuous rigid-frame bridge constructed by cantilever casting method was investigated.The difference of creep coefficients calculated with two Chinese codes was discussed.Based on the calculations,the pre-camber of a pre-stressed concrete continuous rigid-frame box bridge was computed for construction control purpose.The results show that the short-term creep coefficient and long-term creep coefficient calculated with the CC-1985 are larger than those calculated with the CC-2004,while the medium-term creep coefficient calculated with the CC-1985 is smaller than that calculated with the CC-2004.The difference of creep deformation calculated with these two codes is small,and the influences of concrete creep on the pre-camber for most of the segments are negligible.The deflections and stresses of the box girder measured during the construction stages agree very well with the predictions.

CAMBER高速提花圆机

Camber Mellor Bromley公司的RJ/72型针织圆机进一步扩大了提花织物的设计范围和产品种类.RJ/72型圆机对于生产多色、平针或花式双面乔赛针织物十分理想.

Camber Angle Control Method Corresponding to the Electric Vehicle Age

In recent years, the conversion of vehicles to electric power has been accelerating, and if a full conversion to electric power is achieved, further advancements in vehicle kinematic control technology are expected. Therefore, it is thought that kinematic performance in the critical cornering range could be further improved by significantly controlling not only the steering angle but also the camber angle of the tires through the use of electromagnetic actuators. This research focused on a method of ground negative camber angle control that is proportional to the steering angle as a technique to improve maneuverability and stability to support the new era of electric vehicles, and the effectiveness thereof was clarified. As a result, it was found that in the critical cornering range as well, camber angle control can control both the yaw moment and lateral acceleration at the turning limit. It was also confirmed that both stability and the steering effect in the critical cornering range are improved by implementing ground negative camber angle control that is proportional to the steering angle using actuators. Dramatic improvements in cornering limit performance can be achieved by implementing ground negative camber angle control that is proportional to the steering angle.

CAMBER针织圆机变频调速改造

扬州红星针织总厂于1985年起,先后引进英国CAMBER公司生产的H_3F型针织圆机8台,使用直流电机进行调速。经长期使用,直流电机已逐渐损坏。直流电机的维修技术较为复杂,维修时间长,费用高。改造其调速部分,尽可能发挥设备价值,是保证生产正常进行的条件之一。

Design and validation of a variable camber wing structure

Variable camber wing technology is one of the important development trends of green aviation at present.Through smooth,seamless,continuous and adaptive change of wing camber,the aerodynamic performance is improved in achieving increase in lift and reduction in resistance and noise.Based on the aerodynamic validation model CAE-AVM,Chinese Aeronautical Establishment(CAE)has carried out the design and validation of a variable camber wing,proposed an aerodynamic deformation matrix for the leading and trailing edges of aircraft wings in takeoff,landing and cruise conditions.Various structures and driving schemes are compared,and several key technology problems of leading and trailing edge deformation are solved.A full-size leading edge wind tunnel test piece with a span of 2.7 m and a trailing edge ground function test piece are developed.The deformation and shape maintenance capabilities of the leading edge is verified under real wind load conditions,and the load bearing and deformation capabilities of the trailing edge is verified under simulated follow-on load.The results indicate that the leading and trailing edges of the variable camber wing can achieve the required deformation angle and have a certain load-bearing capacity.Our study can provide some insights into the application of variable camber wing technology for civil aircraft.

A novel mechanism fusion data control method for slab camber in hot rolling

For asymmetric plate shape,control over the hot rolling process mainly depends on the subjective judgement and personal experience of the operator as there are great deviations and much instability in hot rolling.Unfortunately,the intrinsic mechanisms and sensitivity affecting characteristic parameters and variables in the asymmetric rolling process remain understudied.Therefore,a novel mechanism fusion data control method for slab camber in hot rolling using dimensional analysis and data-driven technique was proposed.The approach of dimensional analysis was used to establish a mathematical model and analyse the main parameters affecting the slab camber of the rough rolling.Subsequently,the established mathematical model combined with the data-driven techniques was employed to accurately predict the slab bending value.Furthermore,the superiority and effectiveness of the proposed model were demonstrated by a comparison with three regression models.Finally,the proposed control strategy was successfully applied in a 1580 mm hot rolling industrial process.The automatic control results show that the hit rate of slab cambers in different sizes from 10 to 30 mm is improved,and the quality stability of intermediate slab is significantly improved.

Hysteretic behavior of cambered surface steel tube damper:Theoretical and experimental research

A novel cambered surface steel tube damper(CSTD)with a cambered surface steel tube and two concave connecting plates is proposed herein.The steel tube is the main energy dissipation component and comprises a weakened segment in the middle,a transition segment,and an embedded segment.It is believed that during an earthquake,the middle weakened segment of the CSTD will be damaged,whereas the reliability of the end connection is ensured.Theoretical and experimental studies are conducted to verify the effectiveness of the proposed CSTD.Formulas for the initial stiffness and yield force of the CSTD are proposed.Subsequently,two CSTD specimens with different steel tube thicknesses are fabricated and tested under cyclic quasi-static loads.The result shows that the CSTD yields a stable hysteretic response and affords excellent energy dissipation.A parametric study is conducted to investigate the effects of the steel tube height,diameter,and thickness on the seismic performance of the CSTD.Compared with equalstiffness design steel tube dampers,the CSTD exhibits better energy dissipation performance,more stable hysteretic response,and better uniformity in plastic deformation distributions.