A self-organization formation configuration based assignment probability and collision detection

The formation control of multiple unmanned aerial vehicles(multi-UAVs)has always been a research hotspot.Based on the straight line trajectory,a multi-UAVs target point assignment algorithm based on the assignment probability is proposed to achieve the shortest overall formation path of multi-UAVs with low complexity and reduce the energy consumption.In order to avoid the collision between UAVs in the formation process,the concept of safety ball is introduced,and the collision detection based on continuous motion of two time slots and the lane occupation detection after motion is proposed to avoid collision between UAVs.Based on the idea of game theory,a method of UAV motion form setting based on the maximization of interests is proposed,including the maximization of self-interest and the maximization of formation interest is proposed,so that multi-UAVs can complete the formation task quickly and reasonably with the linear trajectory assigned in advance.Finally,through simulation verification,the multi-UAVs target assignment algorithm based on the assignment probability proposed in this paper can effectively reduce the total path length,and the UAV motion selection method based on the maximization interests can effectively complete the task formation.

Assessment of Similitude Behavior in Natural Frequencies of Printed Turbine Blade

Improving structures involves comparing old and new designs on a key parameter.Calculating the percent change in performance is a method to assess.This paper proposes a cost-effective analogy by generating replicas of additive manufactured aluminum alloy(Al Si10Mg)body-centered cubic lattice(BCC)based turbine blade(T106C)with the same in poly-lactic acid(PLA)material and their comparison in the context of percent change for natural frequencies.Initially,a cavity is created inside the turbine blade(hollow blade).Natural frequencies are obtained experimentally and numerically by incorporating BCC at 50%and 80%of the cavity length into the hollow blade for both materials.The cost of manufacturing the metal blades is 90%more than that of the PLA blades.The two material blade designs show a similar percentage variation,as the first-order mode enhancs more than 5%and the second-order mode more than 4%.To observe the behavior in another material,both blades are analyzed numerically with a nickel-based U-500 material,and the same result is achieved,describing that percent change between designs can be verified using the PLA material.

Increment-Dimensional Scaled Boundary Finite Element Method for Solving Transient Heat Conduction Problem

An increment-dimensional scaled boundary finite element method (ID-SBFEM) is developed to solve the transient temperature field.To improve the accuracy of SBFEM,the effect of high frequency factor on dynamic stiffness is considered,and the first-order continued fraction technique is used.After the derivation,the SBFE equations are obtained,and the dimensions of thermal conduction,the thermal capacity matrix and the vector of the right side term in the equations are doubled.An example is presented to illustrate the feasibility and good accuracy of the proposed method.

Controllable preparation of vertically standing graphene sheets and their wettability and supercapacitive properties

Vertically standing graphene（VSG） sheets have been fabricated by using plasma enhanced chemical vapor deposition（PECVD） method.The lateral size of VSG nanosheets could be well controlled by varying the substrate temperature.The higher temperature usually gives rise to a smaller sheet size.The wettability of VSG films was tuned between hydrophobicity and hydrophilicity by means of oxygen and hydrogen plasma treatment.The supercapacitor electrode made of VSG sheets exhibited an ideal double-layer-capacitor feature and the specific capacitance reached a value up to 9.62 F·m^（-2）.

Magnetoelectric memory effect in the Y-type hexaferrite BaSrZnMgFe_(12)O_(22)

We report on the magnetic and magnetoelectric properties of the Y-type hexaferrite BaSrZnMgFe12O22,which undergoes transitions from a collinear ferrimagnetic phase to a proper screw phase at 310 K and to a longitudinal conical phase at 45 K.Magnetic and electric measurements revealed that the magnetic structure with spiral spin order can be modified by applying a magnetic field,resulting in magnetically controllable electric polarization.It was observed that BaSrZnMgFe12O22 exhibits an anomalous magnetoelectric memory effect：the ferroelectric state can be partially recovered from the paraelectric phase with collinear spin structure by reducing magnetic field at 20 K.We ascribe this memory effect to the pinning of multiferroic domain walls,where spin chirality and structure are preserved even in the nonpolar collinear spin state.

Mechanical properties and simulated thermal conductivity of biomimetic structured PS-PVD(Gd_(0.9)Yb_(0.1))_(2)Zr_(2)O_(7) thermal barrier coatings

Plasma spray physical vapor deposition(PS-PVD)(Gd_(0.9)Yb_(0.1))_(2)Zr_(2)O_(7)(GYbZ)thermal barrier coatings(TBCs)exhibited better silicate-phobicity than coatings produced by electron beam physical vapor depo-sition.In combination with PS-PVD and ultrafast laser direct writing technology,biomimetic structured GYbZ TBCs,with a triple-scale micro/nano surface microstructure,were obtained.Laser ablating on the PS-PVD GYbZ coating enhanced the surface roughness,improving its wear resistance without increasing the surface hardness.Furthermore,during the laser ablation processing,numerous nanoparticles were deposited in-situ in the gaps between columns of the coating,reducing the coating Young’s modulus.The simulated temperature field and heat flux field demonstrated that the presence of numerous interfaces between small columns of the PS-PVD coatings is beneficial to thermal insulation.However,laser ablation decreased the coating thickness,reducing the thermal insulation by around 20%-30%as compared to its PS-PVD counterpart,suggesting that a moderate increase in the coating thickness should be considered when designing an efficient TBC system.

Unmanned autonomous air-to-air refueling intelligent docking technology

Unmanned autonomous Air-to-Air Refueling(AAR)capability is the key guarantee to support the distant-field,high-intensity and durable operations of the penetration counterair combat system.In the future,the long-range unmanned reconnaissance and attack platform can reach the maximum flight range requirement through AAR.At present,large transport aircraft platforms in China are still equipped with probe-and-drogue systems,and the refueling mode is gradually changing from manned to unmanned autonomous operation.The docking process is the riskiest and most important part,and there are strict safety,precision,and efficiency requirements for refueling operation,especially during close-distance docking and formation maintenance phases.In this paper,five issues that need to be solved to achieve autonomous AAR docking are summarized.On this basis,five key technology development needs are proposed to solve these engineering issues.Finally,some prospects are given.

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.

Active flutter suppression of nonlinear fin-actuator system via inverse system and immersion and invariance method

Structural nonlinearities such as freeplay will affect the stability and even flight safety of the fin-actuator system.There is a lack of a practical method for designing Active Flutter Suppression (AFS) control laws for nonlinear fin-actuator systems.A design method for the AFS controller of the nonlinear all-movable fin-electromechanical actuator system is established by combining the inverse system and the Immersion and Invariance (I&I) theory.First,the composite control law combining the inverse system principle and internal model control is used to offset the nonlinearity and dynamics of the actuator,so that its driving torque can follow the ideal signal.Then,the ideal torque of the actuator is designed employing the I&I theory.The unfavorable oscillation of the fin is suppressed by making the output torque of the actuator track the ideal signal.The simulation results reveal that the proposed AFS method can increase the flutter speed of the nonlinear finactuator system with freeplay,and a set of controller parameters is also applicable for wider freeplay within a certain range.The power required for the actuator does not exceed the power that can be provided by the commonly used aviation actuator.This method can also resist a certain level of noise and external disturbance.

Single image defogging via multi-exposure image fusion and detail enhancement

Outdoor cameras play an important role in monitoring security and social governance.As a common weather phenomenon,haze can easily affect the quality of camera shooting,resulting in loss and distortion of image details.This paper proposes an improved multi-exposure image fusion defogging technique based on the artificial multi-exposure image fusion(AMEF)algorithm.First,the foggy image is adaptively exposed,and the fused image is subsequently obtained via multiple exposures.The fusion weight is determined by the saturation,contrast,and brightness.Finally,the image fused by a multi-scale Laplacian algorithm is enhanced with simple adaptive details to obtain a clearer defogging image.It is subjectively and objectively verified that this algorithm can obtain more image details and distinct picture colors without a priori information,effectively improving the defogging ability.

Numerical analysis and optimization of boundary layer suction on airfoils

Numerical approach of hybrid laminar flow control （HLFC） is investigated for the suc- tion hole with a width between 0.5 mm and 7 mm. The accuracy of Menter and Langtry＇s transition model applied for simulating the flow with boundary layer suction is validated. The experiment data are compared with the computational results. The solutions show that this transition model can pre- dict the transition position with suction control accurately. A well designed laminar airfoil is selected in the present research. For suction control with a single hole, the physical mechanism of suction control, including the impact of suction coefficient and the width and position of the suc- tion hole on control results, is analyzed. The single hole simulation results indicate that it is favor- able for transition delay and drag reduction to increase the suction coefficient and set the hole position closer to the trailing edge properly. The modified radial basis function （RBF） neural net- work and the modified differential evolution algorithm are used to optimize the design for suction control with three holes. The design variables are suction coefficient, hole width, hole position and hole spacing. The optimization target is to obtain the minimum drag coefficient. After optimization, the transition delay can be up to 17% and the aerodynamic drag coefficient can decrease by 12.1%.

Recent development of a CFD-wind tunnel correlation study based on CAE-AVM investigation

This paper starts with brief introduction to the open topic of the CFD and wing tunnel correlation study, followed by a description of the Chinese Aeronautical Establishment（CAE） –Aerodynamic Validation Model（AVM） and its wind tunnel test in the German-Dutch Wind tunnels（DNW）. The features of the aerodynamic design, the CFD approach, the wind tunnel model fabrication and the experimental techniques are discussed along with the motivation of the CAEDNW workshop on CFD-wind tunnel correlation study. The workshop objective is focused on the interference from the aero-elastic deformation of the wind tunnel model and the model support system to the aerodynamic performance and CFD validations. The four study cases, geometry and mesh preparation of the workshop are introduced. A comprehensive summary of the CFD results from the organizer and the participants is provided. Major observations, both CFD to CFD and CFD to wind tunnel, are identified and summarized. The CFD results of the participants are in good agreement with each other, and with the wind tunnel test data when the wing deformation and a Z-sting system are included in the CFD, indicating the importance of considering such interference at high subsonic Mach number of 0.85.

High-speed wind tunnel test of the CAE aerodynamic validation model

For the purpose of establishing and validating aerodynamic performance predictions at transonic Mach numbers, a wind tunnel test was conducted in the High-Speed Tunnel（HST） of the German-Dutch Wind Tunnels. The test article is the aerodynamic validation model from the Chinese Aeronautical Establishment, which is a full-span scale model representation of a business jet aircraft. The wind tunnel test comprised of parallel deployments of balance, pressures, infrared thermography, and model marker measurement techniques. Dedicated investigations with a dummy support were conducted as well, in order to derive and correct for the interference that the support system imposed on the overall model loads. This enabled the establishment of a comprehensive dataset in which the steady overall model loads, the wing load distribution, the state of the wing boundary layer, and the aeroelastic wing shape were quantified for conditions up to and beyond the cruise Mach number of 0.85.

Correlation analysis of combined and separated effects of wing deformation and support system in the CAE-AVM study

The Chinese Aeronautical Establishment（CAE） Aerodynamic Validation Model（AVM）is a dual-purpose test geometry dedicated to verify the aerodynamic performance of a conceptual intercontinental jet aircraft and to provide a dataset for CFD software validation. To this end, a scaled model of the AVM was tested in the High-Speed Tunnel（HST） of the German-Dutch Wind-tunnels（DNW） with special test consideration and instrumentation. For complementary analysis of experimental results, specific CAE-AVM geometries are analyzed using a CAE inhouse CFD code. The specific geometries consist of a baseline aircraft, an aircraft with a deformed wing shape, and an aircraft with both a deformed wing shape and a representation of the model support system used in the wind tunnel. Detailed analysis of numerical and experimental results is presented; both the combined and individual attributions of wing deformation and support system interference on wing pressure distributions and longitudinal aerodynamic characteristics are summarized.

EQUIVALENCY THEOREM FOR “SADDLE-POINT” FINITE ELEMENT SCHEMES AND TWO CRITERIA OF STRONG BABUSKA-BREZZI CONDITION

This paper is concerned with the general study in the existence,uniqueness and error estimationof finite element solutions for a larger class of 'saddle-point' schemes. The established theory inthe form of Lax-like equivalency theorem includes Brezzi’s theory that has been treated as a specialcase.Two criteria are presented so as to help the practical verification of S-Babuska condition.

A spongy icing model for aircraft icing

Researches have indicated that impinging droplets can be entrapped as liquid in the ice matrix and the temperature of accreting ice surface is below the freezing point. When liquid entrapment by ice matrix happens, this kind of ice is called spongy ice. A new spongy icing model for the ice accretion problem on airfoil or aircraft has been developed to account for entrapped liquid within accreted ice and to improve the determination of the surface temperature when enter- ing clouds with supercooled droplets. Different with conventional icing model, this model identifies icing conditions in four regimes： rime, spongy without water film, spongy with water film and glaze. By using the Eulerian method based on two-phase flow theory, the impinging droplet flow was investigated numerically. The accuracy of the Eulerian method for computing the water collection efficiency was assessed, and icing shapes and surface temperature distributions predicted with this spongy icing model agree with experimental results well.

Numerical study of compression corner flowfield using Gao-Yong turbulence model

A numerical simulation of shock wave turbulent boundary layer interaction induced by a 24° compression corner based on Gao-Yong compressible turbulence model was presented.The convection terms and the diffusion terms were calculated using the second-order AUSM(advection upstream splitting method) scheme and the second-order central difference scheme,respectively.The Runge-Kutta time marching method was employed to solve the governing equations for steady state solutions.Significant flow separation-region which indicates highly non-isotropic turbulence structure has been found in the present work due to intensity interaction under the 24° compression corner.Comparisons between the calculated results and experimental data have been carried out,including surface pressure distribution,boundary-layer static pressure profiles and mean velocity profiles.The numerical results agree well with the experimental values,which indicate Gao-Yong compressible turbulence model is suitable for the prediction of shock wave turbulent boundary layer interaction in two-dimensional compression corner flows.

Interaction formulae for buckling and failure of orthotropic plates under combined axial compression/tension and shear

An interaction function was constructed based on the axial compression/tension and shear loads of orthotropic plates.The coefficients of the polynomial function were determined by uniaxial test results.Buckling interaction and failure interaction formulae under combined axial tension/compression and shear loads were established.Based on the uniaxial load test results of orthotropic plates,the buckling load and bearing capacity under any proportion of the combined loads could be predicted by using the proposed interaction formulae.The buckling interaction curves and failure envelopes predicted by the proposed interaction formulae were in excellent agreement with the test results.

Preliminary study on heat flux measurement data of TT-0 flight test

With the explosive development of aerospace science,the design of the new generation airliner at higher speeds is attracting more attentions.To achieve this goal,it is necessary to achieve accurate prediction of the aerodynamic heating/force loads and successful reduction of drag and heat flux.As a remedy for the existing studies which are based upon the CFD and wind tunnel tests,this study presents a flight test for the drag and heat reduction spike technology.The principal goals of this flight test were to provide reference for verifying the accuracy of the prediction technology on ground and promote the development of the drag and heat reduction technology.By adopting the OS-X rocket,the TT-0 test vehicle designed by Shenyang Aircraft Design&Research Institute reached a maximum Mach number of 5.8 and a maximum altitude of 38 km.Hypersonic and supersonic pressure data by pressure scanning valves and heat fluxes by gauges at different locations were obtained successfully.Also,heat fluxes obtained by in-house CFD code are illustrated in comparison with the flight data.The results indicate that the numerical errors are large in most cases.More technologies,such as more CFD codes and more numerical procedures,should be adopted to conduct studies on this issue in the future.

Flutter analysis of an airfoil with multiple nonlinearities and uncertainties

An original method for calculating the limit cycle oscillations of nonlinear aeroelastic system is presented.The problem of detemining the maximum vibration amplitude of limit cycle is transfomed into a nonlinear optimization problem.The hamonic balance method and the Floquet theory are selected to construct the general nonlinear equality and inequality constraints.The resulting constrained maximization problem is then solved by using the MultiStart algorithm.Finally,the proposed approach is validated and used to analyse the limit cycle oscillations of an airfoil with multiple nonlinearities and uncertainties.Numerical examples show that the coexistence of multiple nonlinearities may lead to low amplitude limit cycle oscillation.