SIMULATION OF LARGE CIVIL AIRCRAFT LANDING RESPONSE UNDER CONSIDERATIONS OF FLEXIBLE AIRFRAME

To evaluate the landing response of the large civil aircraft in the conceptual design phase , a method for simulating aircraft landing is given.The model for the shock absorber is investigated.The flexible airframe model is established using finite element model ( FEM ) to analyze its modes.Then , the whole aircraft model with flexible airframe is made for the multibody simulation.Tail-down , two-point , three-point and sideslip landing scenarios are studied.The influence on the landing performance considering mode superposition of the flexible airframe is analyzed.Both longitudinal and spanwise positions of the main landing gear are changed to research the influence on the landing performance.Results show that the method is feasible.The shock absorber axial force of the main landing gear with the flexible airframe is smaller than that of rigid airframe.The number of mode superposition and the position of main landing gear can influence the landing response.

Multi-dimensional and Multi-threshold Airframe Damage Region Division Method Based on Correlation Optimization

In order to obtain the image of airframe damage region and provide the input data for aircraft intelligent maintenance,a multi-dimensional and multi-threshold airframe damage region division method based on correlation optimization is proposed.On the basis of airframe damage feature analysis,the multi-dimensional feature entropy is defined to realize the full fusion of multiple feature information of the image,and the division method is extended to multi-threshold to refine the damage division and reduce the impact of the damage adjacent region’s morphological changes on the division.Through the correlation parameter optimization algorithm,the problem of low efficiency of multi-dimensional multi-threshold division method is solved.Finally,the proposed method is compared and verified by instances of airframe damage image.The results show that compared with the traditional threshold division method,the damage region divided by the proposed method is complete and accurate,and the boundary is clear and coherent,which can effectively reduce the interference of many factors such as uneven luminance,chromaticity deviation,dirt attachment,image compression,and so on.The correlation optimization algorithm has high efficiency and stable convergence,and can meet the requirements of aircraft intelligent maintenance.

诺基亚增强AirFrame数据中心产品组合融入OCP设计

诺基亚近日宣布将在Air Frame数据中心产品组合中融入OCP设计（OCP：开放计算项目）。在OCP的帮助下,Air Frame能够提供更高的效率、密度、散热能力和能效,这些关键改进已经帮助Facebook在近3年内节省了超过20亿美元的基础设施成本。这些改进将显著降低运营成本,增强可维护性,并能够在开放式IT平台上提供运营商级的服务质量。

Control strategies for aircraft airframe noise reduction

With the development of low-noise aircraft engine, airframe noise now represents a major noise source during the commercial aircraft＇s approach to landing phase. Noise control efforts have therefore been extensively focused on the airframe noise problems in order to further reduce aircraft overall noise. In this review, various control methods explored in the last decades for noise reduction on airframe components including high-lift devices and landing gears are summarized. We introduce recent major achievements in airframe noise reduction with passive control methods such as fairings, deceleration plates, splitter plates, acoustic liners, slat cove cover and side-edge replacements, and then discuss the potential and control mechanism of some promising active flow control strategies for airframe noise reduction, such as plasma technique and air blowing/suction devices. Based on the knowledge gained throughout the extensively noise control testing, a few design concepts on the landing gear, high-lift devices and whole aircraft are provided for advanced aircraft low-noise design. Finally, discussions and suggestions are given for future research on airframe noise reduction.

An artificial neural network approach for aerodynamic performance retention in airframe noise reduction design of a 3D swept wing model

With the progress of high-bypass turbofan and the innovation of silencing nacelle in engine noise reduction, airframe noise has now become another important sound source besides the engine noise. Thus, reducing airframe noise makes a great contribution to the overall noise reduction of a civil aircraft. However, reducing airframe noise often leads to aerodynamic performance loss in the meantime. In this case, an approach based on artificial neural network is introduced. An established database serves as a basis and the training sample of a back propagation （BP） artificial neural network, which uses confidence coefficient reasoning method for optimization later on. Then the most satisfactory configuration is selected for validating computations through the trained BP network. On the basis of the artificial neural network approach, an optimization pro- cess of slat cove filler （SCF） for high lift devices （HLD） on the Trap Wing is presented. Aerody- namic performance of both the baseline and optimized configurations is investigated through unsteady detached eddy simulations （DES）, and a hybrid method, which combines unsteady DES method with acoustic analogy theory, is employed to validate the noise reduction effect. The numerical results indicate not merely a significant airframe noise reduction effect but also excellent aerodynamic performance retention simultaneously.

A cost driven predictive maintenance policy for structural airframe maintenance

Airframe maintenance is traditionally performed at scheduled maintenance stops.The decision to repair a fuselage panel is based on a fixed crack size threshold,which allows to ensure the aircraft safety until the next scheduled maintenance stop.With progress in sensor technology and data processing techniques,structural health monitoring（SHM） systems are increasingly being considered in the aviation industry.SHM systems track the aircraft health state continuously,leading to the possibility of planning maintenance based on an actual state of aircraft rather than on a fixed schedule.This paper builds upon a model-based prognostics framework that the authors developed in their previous work,which couples the Extended Kalman filter（EKF） with a firstorder perturbation（FOP） method.By using the information given by this prognostics method,a novel cost driven predictive maintenance（CDPM） policy is proposed,which ensures the aircraft safety while minimizing the maintenance cost.The proposed policy is formally derived based on the trade-off between probabilities of occurrence of scheduled and unscheduled maintenance.A numerical case study simulating the maintenance process of an entire fleet of aircrafts is implemented.Under the condition of assuring the same safety level,the CDPM is compared in terms of cost with two other maintenance policies：scheduled maintenance and threshold based SHM maintenance.The comparison results show CDPM could lead to significant cost savings.

Airframe Damage Region Division Method Based on Structure Tensor Dynamic Operator

In order to improve the accuracy of damage region division and eliminate the interference of damage adjacent region,the airframe damage region division method based on the structure tensor dynamic operator is proposed in this paper.The structure tensor feature space is established to represent the local features of damage images.It makes different damage images have the same feature distribution,and transform varied damage region division into consistent process of feature space division.On this basis,the structure tensor dynamic operator generation method is designed.It integrates with bacteria foraging optimization algorithm improved by defining double fitness function and chemotaxis rules,in order to calculate the parameters of dynamic operator generation method and realize the structure tensor feature space division.And then the airframe damage region division is realized.The experimental results on different airframe structure damage images show that compared with traditional threshold division method,the proposed method can improve the division quality.The interference of damage adjacent region is eliminated.The information loss caused by over-segmentation is avoided.And it is efficient in operation,and consistent in process.It also has the applicability to different types of structural damage.

Theoretical fundamentals of airframe/ propulsion integration for high-speed aircraft

Fundamental features of aerodynamic interference and integration of airframes and air-breathing jet engines for high-speed flight vehicles are studied within the framework of supersonic small perturbation theory.Both the influence of airframe components on air intakes performance and influence of intakes on vehicle external aerodynamics are under consideration.Analytical relations and specific examples show that significant favorable interference between airframes and air intakes can be realized by using preliminary compression of the flow in front of intakes at flight Mach numbers exceeding approximately 3.

Analytical Model of Elastomeric Lag Damper Kinematic Coupling and Its Effect on Helicopter Air Resonance in Hover

For an elastomeric lag damper with nonlinear properties and kinematic couplings, its differential equation about equilibrium position was derived in a rotating frame. The equation was then transformed into a non-rotating frame by multi-blade transformation and incorporated into the rotor/airframe differential equations for eigen analysis. The effects of damper steady displacement and kinematic couplings on helicopter air resonance in hover were analyzed. The results demonstrate that the elastomeric damper can increase helicopter dynamic stability; however, its available damping will decrease as its steady displacement increased. For the notional rotor system, the damper steady displacement will decrease when kinematic couplings are introduced, and hence the regressive lag modal damping can be increased.

Application of the titanium alloy in civil aviation

Titanium and titanium alloys have been widely used in civil aviation due to their high strength-to-weight ratio and excellent corrosion resistance. A brief history of the development of titanium for aerospace application, including application areas and reasons why aviation manufacturing uses titanium, is introduced in this study. Its future trend is analyzed and discussed as well, including information on trends of the alloy development, melting technologies, present and emerging manufacturing technologies, new alloys and some new techniques for producing low cost titanium.

Aerodynamics analysis of a hypersonic electromagnetic gun launched projectile

A hypersonic aerodynamics analysis of an electromagnetic gun(EM gun) launched projectile configuration is undertaken in order to ameliorate the basic aerodynamic characteristics in comparison with the regular projectile layout.Static margin and pendulum motion analysis models have been applied to evaluate the flight stability of a new airframe configuration.With a steady state computational fluid dynamics(CFD) simulation,the basic density,pressure and velocity contours of the EM gun projectile flow field at Mach number 5.0,6.0 and 7.0(angle of attack=0°) have been analyzed.Furthermore,the static margin values are enhanced dramatically for the EM gun projectile with configuration optimization.Drag,lift and pitch property variations are all illustrated with the changes of Mach number and angle of attack.A particle ballistic calculation was completed for the pendulum analysis.The results show that the configuration optimized projectile,launched from the EM gun at Mach number 5.0 to 7.0,acts in a much more stable way than the projectiles with regular aerodynamic layout.

STUDY ON FLAP SIDE-EDGE NOISE BASED ON THE FLY-OVER MEASUREMENTS WITH A PLANAR MICROPHONE ARRAY

A large planar microphone array, which consists of 111 microphones, was successfully applied to measure a two dimensional mapping of the sound sources on landing aircraft. The focus was on the flap side edge noise source in this paper. The spectra, directivity and sound pressure level of flap side edge noise of 10 aircraft were presented in this paper. It is found that the spectrum of flap side edge noise is a broadband noise with some tones in some cases. Two different types of tone sources are found. It is proposed that one type of these tone sources is trailing edge semi baffled dipole source, and another is produced from the shedding of vortex from the wing cusp. The total sound pressure level of flap side edge broadband noise has no obvious directionality. However, the directivity of the tone noise in the flap side edge noise spectrum is obvious. It is demonstrated that the local flow field is the key to controlling the flap side edge noise.

Landing Gear Shimmy and Directional Stability of Aircraft Undergoing Non-Straight Taxiing

A dynamic model of landing gear struts is introduced in a non-inertial coordinate system. Together with a six degrees of freedom model of aircraft ground handling, the model can be applied to investigate the landing gear shimmy and the directional stability of aircraft undergoing non-straight taxiing. Take the K8 aircraft as an example, motions of the strut under both the straight and non-straight taxiing are simulated as well as the directional adjusting procedure of the airframe. Results of the example are reasonable, indicating that the model may have some value in related research.

Assessment on critical technologies for conceptual design of blended-wing-body civil aircraft

Civil aviation faces great challenges because of its robust projected future growth and potential adverse environmental effects. The classical Tube-And-Wing(TAW) configuration following the Cayley’s design principles has been optimized to the architecture’s limit, which can hardly satisfy the further requirements on green aviation. By past decades’ investigations the BlendedWing-Body(BWB) concept has emerged as a potential solution, which can simultaneously fulfill metrics of noise, emission and fuel burn. The purpose of the present work is to analyze the developments of critical technologies for BWB conceptual design from a historical perspective of technology progress. It was found that the high aerodynamic efficiency of BWB aircraft can be well scaled by the mean aerodynamic chord and wetted aspect ratio, and should be realized with the trade-offs among stability and control and low-speed performance. The structure concepts of non-cylinder pressurized cabin are of high risks on weight prediction and weight penalty. A static stability criterion is recommended and further clear and adequate criteria are required by the evaluations of flying and handling qualities. The difficulties of propulsion and airframe integration are analyzed. The energy to revenue work ratios of well-developed BWB configurations are compared,which are 31.5% and 40% better than that of TAW, using state-of-art engine technology and future engine technology, respectively. Finally, further study aspects are advocated.

Recent research progress on airbreathing aero-engine control algorithm

Airbreathing aero-engines are regarded as excellent propulsion devices from ground takeoff to hypersonic flight,and require control systems to ensure their efficient and safe operation.Therefore,the present paper aims to provide a summary report of recent research progress on airbreathing aero-engine control to help researchers working on this topic.First,five control problems of airbreathing aero-engines are classified:uncertainty problem,multiobjective and multivariable control,fault-tolerant control,distributed control system,and airframe/propulsion integrated control system.Subsequently,the research progress of aircraft gas turbine engine modelling,linear control,nonlinear control,and intelligent control is reviewed,and the advantages and disadvantages of various advanced control algorithms in aircraft gas turbine engines is discussed.Third,several typical hypersonic flight tests are investigated,and the modelling and control issues of dual-mode scramjet are examined.Fourth,modelling,mode transition control and thrust pinch control for turbine-based combined cycle engines are introduced.Followed,significant hypersonic airframe/propulsion integrated system control is analysed.Finally,the study provides specific control research topics that require attention on airbreathing aero-engines.