Science in China Series E: Technological Sciences

The aerodynamics, dynamic responses and aeroelasticity of tiltrotor aircraft in the tilting of rotor i.e. in conversion flight are extraordinarily complicated. The traditional quasi-steady assumption model can not reflect the unsteady aerodynamic problems in the tilting of rotor. The CFD method based on the vortex theory can get better results, but it consumes a lot of computing resources. In this paper, a wake bending dynamic inflow model of tilting rotor was established firstly based on the Peters-He dynamic inflow model used in helicopter. Then combining with the ONERA unsteady aerodynamic model, a wake bending unsteady dynamic inflow model of tilting rotor in conversion flight of tiltrotor aircraft was established. The wake bending unsteady dynamic inflow model of tilting rotor was verified by using the experimental data of an isolated rotor model in large angle pitching up maneuver and was used to calculate the dynamic responses of tilting rotor in conversion flight of a tiltrotor aircraft model. The calculated results were analyzed to be physically reasonable.

The effects of compressive stress parallel and perpendicular to the polar axis of PZT ceramics on the nonlinear electromechanical behavior of the materials has been experimentally studied. A domain-switching model that divides each 180° switching to two successive 90° switching is proposed to explain these effects. In the case of stress parallel to the polar axis, domain switching in the ceramics is approximately axisymmetric and can be simulated by an analytical model. While in the case of stress perpendicular to the polar axis, domain switching is three-dimensional and cannot be simplified. The simulated results that match the experiments well show the validity of the proposed domain-switching model.

An accurate estimation of the sensor systematic error is significant for improving the performance of target tracking system. The existing methods usually append the bias states directly to the variable states to form augmented state vectors and utilize the conventional Kalman estimator to achieve state vectors estimate. So doing is expensive in computation, and much work is devoted to decoupling variable states and systematic error. But the decentralied estimation of systematic errors and reduction of the amount of computation as well as decentralied track fusion are far from being realized. This paper addresses distributed track fusion problem in multi-sensor tracking system in the presence of sensor bias. By this method, variable states and systematic error is decoupled. Decentralized systematic error estimation and track fusion are achieved. Simulation results verify that this method can get accurate estimation of systematic error and state vector.

Time-domain approaches are presented for analysis of the dynamic response of aeroservoelastic systems to atmospheric gust excitations. The continuous and discrete gust inputs are defined in the time domain. The time-domain approach to continuous gust response uses a state-space formulation that requires the frequency-dependent aerodynamic coefficients to be approximated with the rational function of a Laplace variable. A hybrid method which combines the Fourier transform and time-domain approaches is used to calculate discrete gust response. The purpose of this approach is to obtain a time-domain state-space model without using rational function approximation of the gust columns. Three control schemes are designed for gust alleviation on an elastic aircraft, and three control surfaces are used: aileron, elevator and spoiler. The signals from the rate of pitch angle gyroscope or angle of attack sensor are sent to the elevator while the signals from accelerometers at the wing tip and center of gravity of the aircraft are sent to the aileron and spoiler, respectively. All the control laws are based on classical control theory. The results show that acceleration at the center of gravity of the aircraft and bending-moment at the wing-root section are mainly excited by rigid modes of the aircraft and the accelerations at the wing-tip are mainly excited by elastic modes of the aircraft. All the three control schemes can be used to alleviate the wing-root moments and the accelerations. The gust response can be alleviated using control scheme 3, in which the spoiler is used as a control surface, but the effects are not as good as those of control schemes 1 and 2.

By using comparison operations, three basic operations, AND, OR and NOT, in Boolean algebra are re-defined. Based on the characteristic that the voltage signals are easy to implement comparison operation, various logic functions realized by connecting emitters of the bipolar transistor are analyzed. Furthermore, a novel multiple-β transistor and the linear AND-OR gate, whichis composed of the transistor, are investigated. Super high-speed characteristic and multiple-cascade capability of the linear AND-OR gate are verified by PSPICE simulation. Based on the analysis of high-speed switch, which is compatible with the linear AND-OR gate, a high-speed inverter is proposed, which is composed of multiple-β transistors. The corresponding flip-flop design is also given. Finally, the criterion for using linear AND-OR gate to design high-speed switching circuits are presented. Some combinational and sequential circuits are designed as the practical examples. Discussion indicates that the switching circuits based on multiple-β transistor can be applied in high-speed design field.

The macroscopic physical meaning of entropy is analyzed based on the exergy (availability) of a combined system (a closed system and its environment), which is the maximum amount of useful work obtainable from the system and the environment as the system is brought into equilibrium with the environment. The process the system experiences can be divided in two sequent sub-processes, the process at constant volume, which represents the heat interaction of the system with the environment, and the adiabatic process, which represents the work interaction of the system with the environment. It is shown that the macroscopic physical meaning of entropy is a measure of the unavailable energy of a closed system for doing useful work through heat interaction. This statement is more precise than those reported in prior literature. The unavailability function of a closed system can be defined as T 0 S and p 0 V in volume constant process and adiabatic process, respectively. Their changes, that is, Δ(T 0 S) and Δ(p 0 V) represent the unusable parts of the internal energy of a closed system for doing useful work in corresponding processes. Finally, the relation between Clausius entropy and Boltzmann entropy is discussed based on the comparison of their expressions for absolute entropy.

According to the trajectory characteristics of ballistic missile, a reduced parameter model is constructed based on difference between telemetry trajectory and trajectory tracking data. By virtue of Bayesian theory and data fusion technique, a new test evaluation method is put forth, which can make full use of the trajectory tracking data, shooting range test data and relevant information. Since the impact point can be derived from trajectory difference and its kinetic characteristics, evaluation of the impact point is a special case of this method. The accurate evaluation and the accuracy of evaluation results can be provided by the new method.

The aeroelastic responses of a high-aspect-ratio wing are investigated based on nonlinear experimental aerodynamic forces. The influences of nonlinear experimental aerodynamic forces and dynamic pressures on the wing loads are studied in the longitudinal and lateral maneuver states. The flight loads of the wing fixed at the root are calculated at different angles of attack. The aileron efficiency with respect to the dynamic pressures and aileron deflections are also studied. The results indicate that the flight loads of the wings vary nonlinearly with the angle of attack and dynamic pressure. Due to the high-lift aerofoil, elastic components are a large portion of the wing loads, especially for small angles of attack and high dynamic pressure conditions. The aileron efficiency is significantly affected by aileron deflections, dynamic pressures and angles of attack when the nonlinear experimental aerodynamic forces are used for calculation. In states with high dynamic pressures and large aileron deflections, aileron reversal can occur. The aileron deflection and angle of attack have a nonlinear effect on the aileron efficiency. An efficient method for analyzing the flight loads and structural design of high-aspect-ratio wings is derived in this study, and the analysis can provide insight into the distribution of flight loads for high-aspect-ratio wings.

A study of leeward vortex structure over chined fuselage and the effects of micro tip perturbation on its vortex flow have been carried out in wind tunnel experiments at Reynolds numbers from 1.26×105 to 5.04×105 with PIV and pressure measurement techniques. Firstly, the experiment results have proved that micro tip perturbation has no effects on the vortex flow and its aerodynamic characteristics over chined fuselage at high angle of attack, in which there are not any non-deterministic flow behaviors. Secondly, the evolution of leeward vortex structure over chined fuselage along the axis of model can be divided into four flow regimes: linear conical developed regime, decay regime of leeward vortex intensity, asymmetric leeward vortex break down regime and completely break down regime. And a correlation between leeward vortex structure and sectional aerodynamic force was also revealed in the present paper. Thirdly, the experiment results show the behavior of leeward vortex core trajectories and zonal characteristics of leeward vortex structure with angles of attack. Finally, the experiment results of Reynolds number effect on the leeward vortex flow have further confirmed research conclusions from previous studies: the flows over chined fuselage at high angles of attack are insensitive to variation of Reynolds number, and there is a little effect on the secondary boundary layer separation and the suction peak induced by leeward vortex.