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The force-generation mechanism of a dovelike flapping-wing micro air vehicle was studied by numerical simulation and experiment. To obtain the real deformation pattern of the flapping wing, the digital image correlation technology was used to measure the dynamic deformation of the wing. The dynamic deformation data were subsequently interpolated and embedded into the CFD solver to account for the aeroelastic effects. The dynamic deformation data were further used to calculate the inertial forces by regarding the wing as a system of particles to take into account the wing flexibility. The temporal variation of the forces produced by the flapping wing was measured by a miniature load cell. The numerical results provide more flow details of the unsteady aerodynamics of the flapping wing in terms of vortex formation and evolution. The calculated results of the inertial forces are analyzed and compared with the CFD results which represent the aerodynamic forces. In addition, the total forces, i.e., the sum of the CFD result and inertial result, are compared with the experimental results, and an overall good agreement is obtained.

A flexible flapping wing with a rectangular planform was designed to investigate the influence of flexible deformation. This planform is more convenient and easier to define and analyzed its deforming properties in the direction of spanwise and chordwise. The flapping wings were created from carbon fiber skeleton and polyester membrane with similar size to medium birds. Their flexibility of deformations was tested using a pair of high-speed cameras, and the 3D deformations were reconstructed using the digital image correlation technology. To obtain the relationship between the flexible deformation and aerodynamic forces, a force/torque sensor with 6 components was used to test the corresponding aerodynamic forces. Experimental results indicated that the flexible deformations demonstrate apparent cyclic features, in accordance with the flapping cyclic movements. The deformations in spanwise and chordwise are coupled together; a change of chordwise rib stiffness can cause more change in spanwise deformation. A certain lag in phase was observed between the deformation and the flapping movements. This was because the deformation was caused by both the aerodynamic force and the inertial force. The stiffness had a significant effect on the deformation, which in turn, affected the aerodynamic and power characteristics. In the scope of this study, the wing with medium stiffness consumed the least power. The purpose of this research is to explore some fundamental characteristics, as well as the experimental setup is described in detail, which is helpful to understand the basic aerodynamic characteristics of flapping wings. The results of this study can provide an inspiration to further understand and design flapping-wing micro air vehicles with better performance.

How to conveniently tune the flexibility of the composite anisotropic flapping wing to an optimum level to improve flight efficiency is still an open question. Two simple methods have been ...

Making full use of wind energy can effectively alleviate the global energy shortage and environment contamination problems. Nevertheless, how to significantly improve the performance of the wind turbine airfoil and blade is a crucial issue. As the novel flow control method, the co-flow jet (CFJ) technology is one of the most potential methods to solve this problem. Thus, the effects of the CFJ technology on the performance enhancement of the S809 airfoil and Phase VI wind turbine blade are explored in this study. Furthermore, the effects of the injection location and jet momentum coefficient are studied, and an adaptive jet momentum coefficient strategy of the CFJ technology is proposed. Results demonstrate that the CFJ technology can significantly improve the maximum lift coefficient and maximum corrected lift-to-drag ratio of the S809 airfoil. Moreover, the power coefficient of the Phase VI wind turbine blade at the low tip speed ratio is greatly enhanced as well. In particular, the maximum lift coefficient and maximum corrected lift-to-drag ratio of the typical S809 CFJ airfoil with adaptive Cμ are improved by 119.7% and 36.2%, respectively. The maximum power coefficient of CFJ blade can be increased by 4.5%, and the power coefficient of CFJ blade can be boosted by 226.7% when the tip speed ratio is 1.52.

Due to different requirements of flight tasks, take-off weights vary according to different payloads, which will definitely influence the trim characteristics and flight dynamics of vehicle...

Case ejecting device is one of the most important devices of a tank, whose performance influences the working performance of a tank directly. This study focuses on the failure criteria analysis and reliability assessment of the projecting process of an ejector. Firstly, the failure mechanism of projecting process is studied and the condition of cartridge case can't be thrown out of the window occurs frequently. Secondly, the simulation model of projecting process is established by using the LMS Virtual Lab, then, it is validated by mathematical model. Then, the failure criterion is established by considering the trajectory of cartridge case's mass center and the size of window. The expression of up and down range of cartridge case is got. Finally, reliability is assessed based on the simulation model. The torque generated by torsional springs and the angle of collector are the two main factors which impact the performance of ejector, so the failure boundary and the relationship of the two factors are also calculated by this model. By using the assessment of reliability and failure boundary of main factors, the performance of projecting process of ejector can be improved in practice

In this paper, a bio-inspired monocular vision perception method combined with a learning-based reaction local planner for obstacle avoidance of micro UAVs is presented. The system is more computationally efficient than other vision-based perception and navigation methods such as SLAM and optical flow because it does not need to calculate accurate distances. To improve the robustness of perception against illuminance change, the input image is remapped using image moment which is independent of illuminance variation. After perception, a local planner is trained using deep reinforcement learning for mapless navigation. The proposed perception and navigation methods are evaluated in some realistic simulation environments. The result shows that this light-weight monocular perception and navigation system works well in different complex environments without accurate depth information.

With the purpose to improve the performance of the flexible membrane flapping wing, a kind of flapping wing with an attached airfoil to the root is designed and tested in a wind tunnel. In order to study, the actual performance improvement of the flapping wing, the flight performance is calculated and compared instead of the aerodynamic performance. A method to establish a semi-empirical cycle-averaged mathematical model for the flapping wing with high precision based on the wind tunnel experiment is proposed to calculate the flight performance. The established continuous mathematical model can solve the problem of how to obtain the trimmed state by using discrete experimental data. By attaching the airfoil EPPLER 378 with a thickness of 4.07% chord length to the root, the cruise velocity envelope is expanded, especially with a small cruise velocity. Although the attached airfoil to the root can cause a slight decrease in endurance and range of the flapping wing, it will greatly enhance the climbing performance and effectively reduce the demand for the takeoff sites. Besides, the flapping wing with an attached airfoil to the root will result in a significant reduction in the radius of steady turning and will improve the maneuverability. In addition, the airfoil EJ 85, which is similar to the airfoil EPPLER 378 in shape and camber but has a larger thickness of 6.5% chord length, is attached to the root of the original flapping wing. The same experiment and modeling procedure are performed on the airfoil EJ 85 to analyze the difference in performance of the flapping wing with different airfoil thickness.

Splines in aero-engine are often excessively worn, seriously affecting flight safety. Manufacturing errors and parallel offset lead to unequal tooth loads, which is one of the main reasons to reduce the spline wear life. However, spline wear life with multiple errors is sometimes hard to predict due to technical or cost reasons. To obtain a more realistic spline wear life, a spline clearance calculation method considering manufacturing errors and parallel offset is proposed. The tooth contact pressure is developed based on the equivalent model of force carried by each tooth. Then, the relative sliding speed between the tooth and the tooth space is deduced by equating the two contact points on the spline as a crank-slider mechanism. Finally, a numerical model of spline wear is established by using the improved Archard’s wear model. The case results show that the maximum wear depth at torque of 240 N·m is 1.7 times the wear depth at torque of 80 N·m for the spline with a total of 2x105 motion cycles. For a spline with a parallel offset of 30 μm, the maximum wear depth is 66.8 μm, which is 3 times the offset of 5 μm. The wear life results show that the average life of the spline is 0.7 times that of parallel offset when considering multiple errors.

Autonomous navigation in unknown environment is still a hard problem for small Unmanned Aerial Vehicles (UAVs). Recently, some neural network-based methods are proposed to tackle this problem, however, the trained network is opaque, non-intuitive and difficult for people to understand, which limits the real-world application. In this paper, a novel explainable deep neural network-based path planner is proposed for quadrotor to fly autonomously in unknown environment. The navigation problem is modelled as a Markov Decision Process (MDP) and the path planner is trained using Deep Reinforcement Learning (DRL) method in simulation environment. To get better understanding of the trained model, a novel model explanation method is proposed based on the feature attribution. Some easy-to-interpret textual and visual explanations are generated to allow end-users to understand what triggered a particular behaviour. Moreover, some global analyses are provided for experts to evaluate and improve the trained network. Finally, real-world flight tests are conducted to illustrate that our path planner trained in the simulation is robust enough to be applied in the real environment directly.

Birds in nature have many unique devices to help them acquire excellent flight abilities under various complex flight conditions. One of the unique devices is the leading-edge alula, located at the junction of the arm wing and the hand wing of most birds. It often spreads out during takeoff and landing, probably playing a similar role to high-lift devices in fixed-wing aircraft. This paper analyzed and reviewed the results of current research on leading-edge alula, finding some important factors, such as the complex flapping motions, flexibility, and the plane and section shape of the wing, that have been ignored in current research to a certain extent. These would greatly affect the conclusions obtained. Hence, for a deeper understanding of the aerodynamic mechanisms and functions of the alula, some new study predictions for future research are presented. In addition, the feasible models and methods for further research based on these predictions are discussed and proposed. For example, the higher-accuracy LES or hybrid LES/RANS method and the combinations of these methods with wind-tunnel experiments using PIV technology are recommended.

This paper describes the design and development of the Dove, a flapping-wing micro air vehicle (FWMAV), which was developed in Northwestern Polytechnical University. FWMAVs have attracted international attentions since the past two decades. Since some achievements have been obtained, such as the capability of supporting an air vehicle to fly, our research goal was to design an FWMAV that has the ability to accomplish a task. Main investigations were presented in this paper, including the flexible wing design, the flapping mechanism design, and the on-board avionics development. The current Dove has a mass of 220 g, a wingspan of 50 cm, and the ability of operating fully autonomously, flying lasts half an hour, and transmitting live stabilized color video to a ground station over 4 km away.

Avian flight has an outstanding performance than the manmade flapping wing MAVs. Considering that the feather is light and strong, a new type of the flapping wing was designed and made, whose skeleton is carbon fiber rods and covered by goose feathers as the skin. Its aerodynamics is tested by experiments and can be compared with conventional artificial flapping wings made of carbon fiber rods as the skeleton and polyester membrane as the skin. The results showed that the feathered wing could generate more lift than the membrane wing in the same flapping kinematics because the feathered wing can have slots between feathers in an upstroke process, which can mainly reduce the negative lift. At the same time, the power consumption also decreased significantly, due to the decrease in the fluctuating range of the periodic lift curve, which reduced the offset consumption of lift. At the same time, the thrusts generated by the feather wing and the membrane wing are similar with each other, which increases with the increase of flapping frequency. In general, the aerodynamic performances of the feather wing are superior to that of the membrane wings.

This paper analyzes the functional principle and functional hazard analysis for a landing gear cabin door lock mechanism, concluding that the unlocking function of the lock mechanism is the one at most risk. Then the failure probability of the unlocking process of the lock mechanism is calculated, based on the simulation model of the lock mechanism and the response surface method. At last, the failure boundary of the lock mechanism is studied, including: (a) A method for the failure boundary analysis of the lock mechanism is proposed; (b) The failure boundaries respectively with single-parameter and with double-parameter are obtained based on the simulation model; (c) With the lock mechanism's assembly error taken into consideration, the failure boundary of the lock-ring position is verified through the cabin door lock system test, which is quite helpful for the maintenance and management of the aircraft lock mechanism.

A new unsteady three-dimensional aerodynamic performance prediction approach is established to achieve fast and accurate prediction of the unsteady aerodynamics of cycloidal propellers. This model is developed by the coupling of momentum theory, lifting-line method, free wake model, and the Leishman–Beddoes semi-empirical dynamic stall model. The overall calculation process includes two parts. Firstly, to reduce the computational time and improve the computational convergence, the momentum theory is coupled with the Leishman–Beddoes semi-empirical dynamic stall model to predict a uniform inflow velocity through the cycloidal propeller disc, which is set as the initial induced velocity for iterations in the subsequent process. Then, the blade aerodynamic model, which couples the unsteady lifting-line method with the Leishman–Beddoes dynamic stall model, is used to calculate the unsteady aerodynamic response of blades. The wake of cycloidal propeller is represented by a serious of finite-length shed and tra...

The paper presents a qualitative study of the effect of the wing flexibility on the flight stability of flapping wing micro air vehicles in forward flight. The longitudinal dynamic flight stability is compared between rigid wing flapping wing micro air vehicles and flexible-wing flapping wing micro air vehicles. The aerodynamics derivatives are computed respectively using the method of computational fluid dynamics and fluid–structure interaction method, and the techniques of eigenvalue and eigenvector analysis are applied to solve the equations of motion. It is shown that the flexibility can change the stability properties of the flapping micro air vehicles from unstable to stable. Besides, the position of mass center of flapping micro air vehicles is also a key factor to the flight stability, which provides a new insight to design a stable flapping wing micro air vehicle.

Splines have been widely using in aerospace and other fields. Their reliability has important impact on the capability of mechanical equipment. When a slot on the internal spline is combined with different teeth on the external spline due to machining errors,, different tooth clearances are generated. Therefore, when the spline is assembled in different sequences, the loads on the spline teeth will be different, which can affect the bearing capacity of the spline. However, in the actual assembly process of the spline, this effect has not been considered. To overcome the issue as listed above, a method for optimizing spline assembly sequence is proposed. First of all, the calculation method of the tooth clearances depended on the spline assembly sequence is established. Then, a spline load distribution model is proposed, and the spline assembly sequence is optimized by the maximum clearance method. Compared with the traditional random assembly method, the results show that the mean value of the maximum nominal tangential force of the spline is reduced by 25%. The obtained results can be used to guide the high reliability design of the spline.

In order to further improve the efficiency of flapping wings, inspired by bird flight, a new compliant joint structure is proposed, which is easy to manufacture. The joint has the capacity of passive bending, twisting and sweeping under the aerodynamic effect of the flapping wing. A multi-objective optimization program for the compliant joint is developed, which is combined with the measured joint load. The optimized compliant joint has the effect of asymmetric passive deformation in a flapping cycle. The model wings with compliant joints are studied in the windless flapping experiment, wind tunnel experiment and free flight test. The experimental results show that the model wings have a significant advantage of power consumption compared with the original wings, and also have an advantage in the aerodynamic performance at low flight velocity and low angle of attack.

Gaps between feathers can be observed when some birds are flying. They can control the opening and closing of gaps to achieve the goal of good aerodynamic performance. The effects of the wing gaps on aerodynamic performance is investigated by experimental study. Firstly, a kind of flapping wing with one-way holes is designed and tested. The holes are connected by hinge, which is open during the up-stroke process and close during the down-stroke process. One-way holes can increase the lift significantly. However, the hinge connection makes the movement process less continuous. And there’s more resistance because the windward area is increased by hinged holes. Further on, the method was improved by using one-way deforming characteristics of bird feathers. The goose feathers are used as a covering skin of flapping wing, which can have continuous opening and closing gaps, making the flapping process more smoothly and getting smooth aerodynamic characteristics. The results show that the one-way holes/gaps flapping wing can effectively increase the lift and reduce the power consumption. The using of natural feathers as flapping wing covering skin is a conducive way to improve the aerodynamic performance.

FWMAVs (Flapping Wing Micro Air Vehicles) turn to be a flexible multibody system when the inertia and flexibility of flapping wing are considered. The flight dynamic stability considering the oscillation of body in forward flight are still an open question. In this study, based on a method coupled CFD (Computational fluid dynamics), CSD (Computational structural dynamics) and equations of longitudinal motion for FWMAVs, the periodic derivatives of forces and moment during whole flapping course can be computed. The dynamic stability is analysed by Floquet method specially for the cyclic-motion equilibrium. Results show that the FWMAV in forward flight is stable and character of eigenvalue is similar to that of fixed-wing vehicles. However, the effect of pitch rate damping is different from its role played for the fixed wing vehicle. As the pitch rate damping increases, the system turns to be unstable. These results can inform designs of FWMAV from the perspective of dynamic stability.

A slat is one of the most importance high-lift devices on an aircraft, whose performance influences the safety of an aircraft directly, and its failure may lead to serious consequence. This study focuses on the failure mechanism analysis and reliability assessment of the slat. Firstly, based on the work principle, FTA (failure tree analysis) and FMEA (failure modes and effect analysis) are used to analyze the potential failure modes and mechanism of failure modes. Secondly, simulation model is established using LMS Virtual.Lab and it is validated based on test data and mathematic model. Finally, the reliability and failure cases are assessed based on the results of dynamic simulation. The reliability analysis results show that transmission shaft fracture and motion seizure are the main failure modes. Failure assessment shows that the safety margin decreases to a very low value if transmission shaft fracture occurs, while a roller seized can lead to slat motion seizure.

This work proposes a hierarchical nonlinear control scheme for quadrotor to track 3D trajectory subject to payload variation and fast time-varying wind gust disturbance. In terms of dynamics model, the 6 DOF dynamics model with parametric and nonparametric uncertainties is built up. Wind gust and propeller momentum drag model are implemented to quantify the wind impact (force and moment disturbances) on quadrotor. In terms of control design, adaptive robust controller is developed for dynamic subsystem to deal with moment disturbance and estimate the system parameters. Global sliding mode controller is implemented for kinematic subsystem to generate adequate desired attitude angles for tracking the planned 3D trajectory. Simulations and experiments under various conditions are carried out for verification, and the results indicate the effectiveness, adaptiveness and robustness of the control strategy.

In this paper, the concept of ply drop sequence (PDS) is introduced for designing of composite laminate structures with multiple regions. The PDS describes the order of ply-drops from the thickest guide laminate to a series of thinner ones, and further ensures laminate continuity across the entire structure. Comparing with deleting a contiguous innermost/outermost plies in the classical guide-based blending, using PDS is more flexibly of dropping plies between adjacent regions. A fully blended design is represented by a stacking sequence of the guide, a PDS and a thickness distribution over the whole regions of the structure. A genetic algorithm (GA) with special operators and codification is adopted for the PDS-based blending optimization, which guarantees the design is completely blended within the GA iterations. The proposed method is applied to an 18-panel horseshoe benchmark problem to demonstrate its flexibility and potentiality.

The aerodynamics of a cycloidal propeller operating in hovering flight is systematically studied using numerical method. By solving the time-dependent incompressible Navier–Stokes equations and using a dynamic mesh technique, the complex unsteady flow field around the cycloidal propeller and the time-varying aerodynamic forces are investigated. The wake flow deflection can be observed in the flow field of the cycloidal propeller, which results in a deflection of the thrust. Strong downwash around cycloidal propeller and unsteady interference between blades are induced by the rotation and pitch motion of the blade. The instantaneous vertical, horizontal and resultant thrusts fluctuate cyclically with the azimuths in a pattern similar to sinusoid, and although the direction of instantaneous resultant thrust varies in a comparatively large region during rotating, the direction of averaged resultant thrust produced in each revolution is almost constant at different rotation speeds. This is beneficial to the flight stability and maneuverability of a cyclogyro. When one blade moves upward, the aerodynamic forces of the blade are much higher than that produced when moving downward. With the increase of the blade number, the unsteady interference between blades and the wakes of other blades tend to be stronger, producing great effects on aerodynamic forces of the blades as well as the aerodynamic performance of cycloidal propeller.

A hybrid aerial vehicle (HAV), featured combination of a quadrotor system and a fixed-wing system, is one of the most promising configurations having both a vertical take-off and landing (VTOL) capability and high cruise performance. In this paper, a HAV has been designed and prototyped to analyze the performance of the HAV. The specifications of the HAV are summarized. The aerodynamic coefficients of the HAV derived from CFD data and the influence of axial flow on the maximum thrust of quad propellers that is calculated using QPROP are demonstrated, respectively. The wind resistant capability of the HAV is analyzed from two aspects according to different wind direction. The factors which have important influence on the wind resistant capability of the HAV are analyzed and the solutions to improve the wind resistant capability of the HAV are presented.

Rare earth permanent magnet brushless direct current motor is the energy conversion device between power system and propeller of high-altitude airship. Its performance has a profound effect on the overall performance of the high-altitude airship. Limited by the output torque of the permanent magnet brushless direct current motor, propeller on the ground cannot reach the rated angular speed when propeller works at high altitude, so it is difficult to carry on rotation test on the ground. In addition, performances of the permanent magnet brushless direct current motor system such as control accuracy, reliability and efficiency cannot be tested. The functional level of the motor load simulator is proposed considering the dynamic properties of the propeller and the basic functions of the propulsion system. Different loading actuators are evaluated and the conceptual design of the load simulator is accomplished. Inertia is realized by relatively small flywheel and inertia electrical emulation method. Torque is simulated by servo motor that can work at braking state and thrust is exerted on the motor by hydraulic servo valve control system. Finally, depending on the proposed scheme and design parameters, co-simulation model of the load simulator is established utilizing software MATLAB/Simulink and AMESim. After comparing co-simulation results with real propeller properties, the feasibility of the conceptual design of permanent magnet brushless direct current motor load simulator is proved, and what is more, the effectiveness of control strategies and the rationality of parameters settings for co-simulation are testified.

Different schemes of a propulsion system have a distinguished influence on the overall performance of high altitude airship. There is an optimum power, called optimum power unit, to achieve the lowest propulsion system and energy system weight for a high altitude airship. The paper represents an optimization model of the optimum power unit for a high altitude airship. Firstly, the optimal Latin hypercube design method is applied to obtain the sample points of the distributed low power propulsion system. Secondly, the surrogate model, which is used to establish the optimization model, is obtained by responding surface method based on these sample points. The computational model of the energy system is obtained by the airship’s location and the working time. Finally, the multi-island genetic algorithm is used to find the optimum power unit for a typical high altitude airship. Furthermore, the optimization work under different typical power levels and diameters is carried out to verify the effectiveness of the optimum power unit design method. It has been found that the identical result validates the effectiveness of the optimum power unit design method.

In this paper, the characteristics of the kinetic reliability of space four-links mechanism are analyzed and the relationship between the kinetic accuracy and wear clearances in joints is explored, using Advanced First Order and Second Moment (AFOSM) method and Monte-Carlo Simulation (MCS). The Archard wear model is applied to analyze the increasing wear clearances in joints; and the function between the joint clearance and the equivalent length of links is built; then the kinetic accuracy of the space four-links mechanism with the increase of wear clearances is analyzed. Finally a demonstrative application is given, illustrating the reliability degradation of kinetic accuracy with the increase of wear clearances, and AFOSM has much higher computational efficiency compared with MCS. Besides, the influence of the contact forces in joints to the kinetic accuracy of space four-links mechanism is analyzed, with instructive results for the design of space four-links mechanism in engineering applications.

Pilot real time decision has a significant influence on the aircraft battlefield survivability. The ability of datalink is transmitting and sharing information which will provide support to pilot to make real time decision. In this paper, an algorithm is proposed to build a pilot real time decision model considering the performance of datalink. Firstly, an active deception jamming model is built which is used between the aircraft and the radar guided missile. Secondly, a Link16 model is built by OPENT and the throughput of two different slot assignment schemes is obtained by the simulation. Thirdly, a pilot real time decision model is built based on the influence diagram. The example shows that: the throughput will increase as the repetition rate increases which will lead that the pilot has a low level mental pressure and will obtain an optimal decision and the aircraft also has a high battlefield survivability.

Phase-to-phase short-circuit faults in a permanent-magnet synchronous machines are quite dangerous because of the extremely high short-circuit transient current after fault. This paper presents a fault detection and identification diagnosis approach for asymmetrical faults in permanent-magnet synchronous machines, considering both inter-turn and phase-to-phase short-circuit faults, and employing both current- and voltage-based residual along with the cumulative-sum algorithm. The sum of positive- and negative-sequence current- and voltage-phase angles is used to identify the faulty phase(s); the two fault types are distinguished by defining different detection thresholds for the residuals. Simulations of phase-to-phase short-circuit with different short-circuit resistance have been carried to obtain the values of faulty phase indicators. Both the simulation results and the proposed diagnosis have been verified by practical experiments on a 2-kW test bench.

The flexibility of flapping-wing strongly affects the aerodynamic performance of Flapping-wing Micro Air Vehicle (FMAV), and the deformations in span-wise and chord-wise directions are coupled together in flight. In this study, the flexible deformation is formulated in span-wise and chord-wise separately in order to analyze its effects on aerodynamic behavior. The preconditioned Navier-Stokes equations based on chimera grid are used in the computational fluid dynamics method to study the aerodynamic effects caused by flexible deformation, and the simulation results are compared with experimental test to illustrate the capability of above method. Based on our results, it is clearly showed that the span-wise flexible deformation should be limited in a small range to achieve higher aerodynamic performance and the chord-wise deformation could enhance the aerodynamic performance. The results also suggest that FMAV designers should design the flapping-wing with high stiffness leading edge to limit the span-wise deformation, and more flexible chord ribs to keep chord-wise deformation in suitable range. FMAV, flexible flapping-wing, Navier-Stokes equations, chimera grid, span-wise deformation, chord-wise deformation

An optimization method for the design of large composite structures is presented. This optimization method can make the stacking sequence and thickness optimize simultaneously. First, on the basis of region division, a lengthcontrol indicator is added to decide the covered regions of each ply. Second, the master–slave parallel genetic algorithm is adopted to make it a high-efficiency algorithm. Finally, the method proposed is used to optimize a composite wing box to demonstrate its high efficiency. The acceleration effect of the parallel genetic algorithm is also analyzed.

A hybrid airship denotes one kind of aircraft that combines the use of aerodynamic and buoyant lift. It is supposed to achieve the best combination of the high-speed characteristics of the airplane and the heavy-lifting capacity of the airship. In this work, an improved flight performance analysis method for a hybrid airship is proposed, aiming to provide a set of new formulas that are more suitable for a hybrid airship. The new formulas for analyzing the steady and accelerated performances of a hybrid airship are derived in a systematic way. The main advantage of the new formulas is that the relationship between the flight performances of a hybrid airship and airplane is indicated in a clearer and simpler expression. Base on the derivation, the theoretical comparisons are performed to show the advantage and disadvantage of the hybrid airship. An example of estimating flight performance of a model hybrid airship is presented to preliminarily demonstrate and evaluate the developed method, which shows a reasonable result.

Aircraft survivability assessment is one of the most important steps of the aircraft survivability project. Many models were developed to assess one-on-one engagement aircraft survivability; however, most of them belong in the simulation category. Based on the theory of stochastic duel, this paper constructs an analytic model for engagement-level aircraft survivability assessment. The analytic model explicitly represents the encounter process between the aircraft and the weapon system, such as target detection, acquisition and firing, and reloading and firing. The general solution of aircraft survival probability is obtained in quadrature form and the explicit expression is derived from a particular detection-time distribution and a firing-time distribution. According to this model, not only can the aircraft survival probability be calculated, but the survivability contour maps can also be easily plotted with the mean time of detection, the single-shot kill probability, and other parameters. The numerical examples and analysis of the results show that the model is reasonable and effective.

A method is proposed for calculating the vulnerability of aircraft to spray fragments of a missile. The input data of aircraft or components for vulnerability assessment is organized by the finite element models. First, the `shot line scanning method' is used to calculate the single-hit vulnerability of aircraft by a fragment of missile. Utilizing Markov-Chain method, the vulnerability of aircraft is obtained at the threat of multiple hits by spray fragments. An example that shows the distributions of probability of kill at the typical missile detonation locations around the aircraft has been provided. In this example, the interaction regions of aircraft with fragments of missile are analyzed and the correctness and feasibility of the proposed method are demonstrated. Application shows that (1) the proposed method is generic and easy to be programmed; (2) to provide a realistic and effective aircraft vulnerability assessment, the method has taken into consideration the factors such as missile velocity, missile detonation location, missile charge ratio, fragment shape, air drag, aircraft altitude, and aircraft velocity; (3) the vulnerability assessment of aircraft to fragments of missile is useful for aircraft survivability enhancement design, missile effectiveness assessment, and optimizing missile fuse design.

In order to analyze the reliability of the new lock mechanism which is an important part of aircraft cabin door system, this paper studies the reliability and sensitivity for the lock mechanism based on surrogate models and variance methods respectively. Function hazard analysis (FHA) and failure mode effects analysis (FMEA) of lock mechanism is studied firstly. Then, based on dynamics simulation model, performance function and various random variables, the widely used surrogate models of lock mechanism is established and verified. Based on the most accurate metamodel which has been established, the unlocking reliability which is the most hazardous function is calculated. Finally, the variance-based sensitivity method is used for sensitivity analysis of influence factors, the result shows that the tension of lock-hook from lock-ring is the largest influence factor on the unlocking reliability, which could contribute to the analysis and further improvement of lock mechanism.Copyright © 2015 by ASME

This paper presents a numerical method to simulate the dynamic interaction between the structural deformation and the aerodynamic characteristics of flexible flapping wing for micro air vehicle (MAV). A fluid-structure coupling solver is developed based on the Navier-Stokes equations and the structural dynamic equations. In addition, the interface data exchange method based on the radial basis function and the moving mesh generation method based on the infinite interpolation are applied, which play an important role in the coupling research. The preceding method is validated by comparison with the wind tunnel experimental results. For the research scope of this article (R=5×104), the flexible deformation impacts of flapping wing on aerodynamic performance are presented. The simulation results proved that the structural deformation has a significant effect on the aerodynamic forces, especially on the thrust, and the structural deformation is determined by aerodynamic and inertial forces together, b...

Two precise calculation methods (Markov chain or tree diagram) are commonly used for assessing aircraft vulnerability to multiple hits by nonexplosive penetrators. Because the dimension of Markov transition matrix or the number of tree branches increases exponentially along with the increasing number of redundant components, when the total number of redundant components reaches a certain amount, the "combinatorial explosion" is unavoidable. This paper, using the Monte Carlo technique, proposes a method for solving the combinatorial explosion problem. This method simulates all of the existing states of aircraft to Model of Filling Boxes with Balls; by randomly and uniformly sampling the threat hit locations, the aircraft cumulated probability of kill can be attained. Two provided examples show the correctness and feasibility of the proposed method. Analysis shows that the developed method with high accuracy apparently costs a short amount of time compared with the precise methods, when the total number of the redundant components is relatively large. Moreover, the CPU run time increases almost linearly along with the increasing number of redundant components, and the combinatorial explosion is avoided, and so this method is more applicable to engineering computation.

At present, the precise calculation methods, namely, Markov chain or tree diagram, for aircraft survivability or vulnerability to multiple hits by nonexplosive penetrators cannot deal with the situation where the components overlap in an arbitrary manner. This paper, based on probability theory and the analysis of the kill states of aircraft and components, proposes a method for decomposing the vulnerable area in the components' overlapping region. After vulnerable-area decomposition, the overlapping region becomes several individual "broadly vulnerable components" with different kill properties, and then the multiple-hit vulnerability computation of aircraft with multiple redundant sets and arbitrary overlapping among components can be proceeded utilizing Markov chain or tree diagram method. The examples provide the computation and analysis of the cumulated kill probability of aircraft exposed to the threat of multiple hits and demonstrate the general applicability and feasibility of the proposed vulnerable-area decomposition method in the components' overlapping region.

A numerical study with dynamic mesh technique has been conducted on a cyclorotor operating at Reynolds numbers about 20,000~90,000. The varying total thrust of cyclorotor , the force on blade during revolution and the aerodynamic characteristics of the unsteady flow field around cyclorotor and blade airfoil are investigated in detail. The instantaneous thrust, which are cyclically fluctuating with azimuth as an approximated sinusoidal curve, is found to have close relationship with the corresponding azimuth-varying resultant pitch angle of all blades; the average direction of thrust during revolution is found to remain almost constant as rotating speed change, which is very important for a cyclogiro's stability control; the curves of varying normal force and tangent force coefficients of a blade airfoil with pitch angle are clearly shown to be hysteresis loops both in oneand four-bladed cyclorotor, which indicate the strong unsteady aerodynamics of cyclorotor. The flow field around the blade airfoil of one-bladed cyclorotor and four-bladed cyclorotor are given to show the complex flow field with unsteady interactions between the blades and the wakes of other blades.

Clearances exist in all joints in multi-body system, but traditional dynamic analysis method often treats joints as ideal or perfect, ignoring joint clearance, which leads to a large error in the results. Joint clearance can cause structure vibration, bring some peaks to dynamic response, which is bad to the reliability of the system. And clearance also led to joint wear, it makes the clearance get larger with the increasing of working time. In a word, joint clearance will degenerate the performance of the multi-body system or even cause system failure. In this paper, a slider-crank mechanism is used for example, apply multi-body dynamics software to establish the mechanism simulation model, the joint with clearance was replaced by a contact unit, after calculate the contact force and the relative sliding velocity of the contact unit, applying Archard's Wear model to calculate wear depth of each segment in bushing circumference, and then update the geometry profile of bushing in the multi-body model. Through repeating the above process, the joint wear prediction and the dynamic response of the multi-body system after predetermined cycles can be obtained.