Calculation of radiation in gas around a descent space vehicle

The problem of numerical modeling of the effect of radiation processes on gas dynamic parameters around a descent space vehicle in the Earth’s atmosphere is studied. A relatively new approach is suggested of direct modeling of radiation processes oriented to the use of high performance multiprocessor computer systems. The physical model of radiation transfer is described by a diffusion approach with a discretization of radiation and absorption spectra and a set of quasigasdynamic equations. The computations were carried out on both triangular and hybrid locally refined grids. The gas-flow modeling results taking into account radiation processes are represented for bodies of different shapes.     

Flatness-based hypersonic reentry guidance of a lifting-body vehicle

This paper deals with the design of a guidance algorithm for the hypersonic phase of a lifting-body vehicle. The guidance strategy is based on a particular kind of nonlinear dynamic inversion, the so-called flatness approach. The main advantage of this approach is that the longitudinal guidance law is in-flight self-adaptive to any feasible hypersonic trajectory and can be written in analytical form with a small set of design parameters. Therefore, the required on-board computational resources are limited, and a reduced off-line design effort is needed for the change of vehicle parameters. Moreover, the closed-loop longitudinal guidance commands are computed on-board in a coupled way without relying on an explicit deceleration profile. Consequently, the approach leads to an efficient management of the degree of freedom associated with the angle-of-attack. PID controllers are then designed based on the longitudinal flat model in order to circumvent uncertainties and parameters dispersions. The crossrange is controlled by a series of bank reversals determined by an azimuth error deadband. The robustness and performance of the proposed guidance law are assessed by performing Monte Carlo runs with various sets of dispersions.     

一种压差式车用气体流量传感系统的设计

介绍了一种车用压差式气体流量传感系统的结构设计和测量电路,指出了传感器的使用范围。通过实验测出了其特性曲线,并对影响测量误差的因素进行了分析,可满足车用发动机曲轴箱窜气量参数的检测,为发动机不解体故障诊断提供了一种新的测试方法。     

Input-to-state-stability modular command filtered back-stepping attitude control of a generic reentry vehicle

A command filtered back-stepping attitude controller is exploited and analyzed to design a dynamic state-feedback controller for a generic Reentry Vehicle. A novel back-stepping control that obviates the need to compute analytic derivatives in the traditional back-stepping design is presented by combining command filtered back-stepping method, sliding-mode-based integral filters and inputto-state stability (ISS) analysis. The ISS-modular approach provides a simple and effective way for controlling non-linear Reentry Vehicle satisfying the strict-feedback form, simultaneously solving the problem of “explosion of complexity” in traditional back-stepping approach. The stability analysis of the closed-loop system and the convergence of the aerodynamic angles are verified based on the smallgain theorem. Numerical simulations are included to demonstrate the effectiveness of the proposed control scheme.     

基于递归神经网络的再入飞行器最优姿态控制

针对再入飞行器的姿态跟踪问题,基于递归神经网络提出最优跟踪控制.采用反步法和递归神经网络,设计自适应前馈控制,将再入飞行器的最优姿态跟踪问题转化为等价的姿态角误差/角速率误差最优调节问题.采用自适应动态规划技术,解决最优调节问题.引入神经网络估计最优控制中的代价函数,推导最优反馈控制律,同时保证Hamilton–Jac...     

载人登月飞行器高速返回再入制导技术研究

返回再入段是载人登月任务完成后,保证宇航员安全返回地球的关键阶段,其跳跃式再入制导方法的研究是我国载人登月任务需要突破的一项重要关键技术.由于探月返回飞行器速度极高,其弹道特性与神舟飞船一类的近地轨道返回的飞行器有较大差别,也给制导导航与控制(简称GNC,以下同)系统设计带来较大挑战.与无人再入飞行器相比,载人飞行器需要具备防过载超限能力、大范围再入航程适应能力、高精度落点控制能力.为了满足上述要求,本文提出了一套基于全系数自适应校正的预测制导方案.在再入前,通过对基本倾侧角进行校正,提高了规划弹道对再入初始条件散布的适应性;再入后利用外环的预测与全系数自适应校正实现对规划弹道的持续修正,保证规划弹道与飞行器状态的匹配性,内环则采用短周期的弹道跟踪制导;对于横向制导,本文给出和比较了采用实时漏斗制导律、独立预测–校正制导律方案以及横航向独立自校正和耦合自校正方案.     

再入系统的热流分析

针对再入过程中返回舱体存在严重的气动热问题,提出一种新型再入系统.通过建立减速系统的阻力估算模型和求解动力学方程,分析再入过程的速度特性和驻点热流密度,计算结果与文献算例数据吻合,验证飞行器再入过程的热流特性.采用Euler数值计算与边界层内工程算法相结合的方法计算充气阻力罩表面热流密度,结果表明热流密度在驻点附近较大,远离驻点后迅速减小.     

空间再入飞行体多传感观测融合仿真研究

空间飞行器再入飞行的可靠观测无疑是一个值得关注和探讨的问题。弹道导弹是一种典型的空间再入飞行器,其沿着预定弹道飞行,速度快,且可发生机动。对于弹道导弹的运动可以用较为简单和基本的运动模型的交互来近似,也可以用地面雷达和光学传感器来观测。将近似运动模型和观测值代入专门针对非线性估计问题的无味卡尔曼滤波(UKF)框架中,再利用数据融合算法,可以实现弹道导弹的航迹估计。文中首先描述了弹道导弹的运动模型,继而给出了不同传感器的量测方程和运动体的基本运动模型,然后阐述了交互多模型(IMM)、UKF及多传感数据融合算法,最后在仿真系统中实现航迹并得出结论。     

A comparison of several nonlinear filters for reentry vehicle tracking

This paper compares the performance of several non-linear filters for the real-time estimation of the trajectory of a reentry vehicle from its radar observations. In particular, it examines the effect of using two different coordinate systems on the relative accuracy of an extended Kalman filter. Other filters considered are iterative-sequential filters, single-stage iteration filters, and second-order filters. It is shown that a range-direction-cosine extended Kalman filter that uses the measurement coordinate system has less bias and less rms error than a Cartesian extended Kalman filter that uses the Cartesian coordinate system. This is due to the fact that the observations are linear in the range-direction-cosine coordinate system, but nonlinear in the Cartesian coordinate system. It is further shown that the performance of the Cartesian iterative-sequential filter that successively relinearizes the observations around their latest estimates and that of a range-direction-cosine extended Kalman filter are equivalent to first order. The use of a single-stage iteration to reduce the dynamic nonlinearity improves the accuracy of all the filters, but the improvement is very small, indicating that the dynamic nonlinearity is less significant than the measurement nonlinearity in reentry vehicle tracking under the assumed data rates and measurement accuracies. The comparison amongst the nonlinear filters is carried out using ten sets of observations on two typical trajectories. The performance of the filters is judged by their capability to eliminate the initial bias in the position and velocity estimates.     

有机气体分子结构与势能参数的关联和测算

物质的性质是由其结构决定的。对于有机气体分子来说,研究其具体构象,探究其分子结构与势能参数之间的关联性十分重要。本文在构建合理分子模型的基础上,运用遗传程序设计算法对130种有机气体分子的势能参数进行了8个结构参数模拟计算,得到了精算值σ_cal,并与文献提供的势能参数值σ_exp进行比较,结果表明其平均相对误差0.75%,说明该算法是比较可靠的。在缺少有机气体物性参数时,可采用该算法来获取,以节省实验费用和时间。     

Neural network based adaptive fuzzy PID-type sliding mode attitude control for a reentry vehicle

This work investigates the attitude control of reentry vehicle under modeling inaccuracies and external disturbances. A robust adaptive fuzzy PID-type sliding mode control (AFPID-SMC) is designed with the utilization of radial basis function (RBF) neural network. In order to improve the transient performance and ensure small steady state tracking error, the gain parameters of PID-type sliding mode manifold are adjusted online by using adaptive fuzzy logic system (FLS). Additionally, the designed new adaptive law can ensure that the closed-loop system is asymptotically stable. Meanwhile, the problem of the actuator saturation, caused by integral term of sliding mode manifold, is avoided even under large initial tracking error. Furthermore, to eliminate the need of a priori knowledge of the disturbance upper bound, RBF neural network observer is used to estimate the disturbance information. The stability of the closed-loop system is proved via Lyapunov direct approach. Finally, the numerical simulations verify that the proposed controller is better than conventional PID-type SMC in terms of improving the transient performance and robustness.

     

Hybrid state estimation and model-set design of invariable-structure semi-ballistic reentry vehicle

Multiple-model approach is one of the main streams for hybrid estimation.The difficulty of this approach to estimate the hybrid state of the semi-ballistic reentry vehicle (SBRV) is model-set design.This paper proposes a quasi-Monte Carlo model set that can ensure the estimator near-optimal in the sense of minimum mean square error (MMSE).The SBRV has a high nonlinearity and its mode is spanned by multiple parameters with known bounds.The design methods and characteristics of the quasi-Monte Carlo model set...     

Thermal stress analysis of reentry vehicle nosetips at angle of attack

The ASAAS (Asymmetric Stress Analysis of Axisymmetric Solids) computer program is applied to the prediction of thermal stresses in a reentry vehicle nosetip subjected to asymmetric temperature distributions and angle-of-attack loadings during reentry. This three-dimensional stress analysis computer program has the unique capability of properly accounting for the circumferential variation of temperature dependent material properties. It is based on a meridional finite element discretization of an axisymmetric solid combined with a Fourier series representation of circumferentially dependent variables. In contrast with similar methods where material properties cannot be expressed as a function of temperature, this method requires that the large system of equations be solved simultaneously. This is handled efficiently in ASAAS by several newly developed approaches to stiffness matrix generation and simultaneous equation solution.

The nosetip analyzed is fabricated from an orthotropic, temperature dependent graphite material that is susceptible to thermal shock. Analyses are performed at several points in a trajectory and the effects of both aerodynamic heating and pressure loading are considered. The complete states of temperature, stress, strain and displacement throughout the graphite material are obtained as a product of ASAAS. Results are presented in the form of meridional contour plots at selected circumferential stations.

The usefulness of ASAAS in performing angle-of-attack analysis of nosetips is evaluated by comparison to an axisymmetric analysis based on single ray heating. In addition, the convergence of solutions with increasing numbers of harmonics is demonstrated and computer run times are discussed.     

不变结构半弹道式再入飞行器的混合状态估计与模型集设计

多模型方法是混合估计的主流方法之一,以该方法估计不变结构半弹道式再入飞行器(SBRV)混合状态的难点在于设计有效的模型集.文中提出了一种伪Monte Carlo模型集可以使SBRV混合状态估计器在最小均方差(MMSE)意义下接近于最优.SBRV的再入估计具有高度的非线性,同时其模式由多个边界已知的参数张成.给出了这种伪Monte Carlo模型集的设计方法,并分析了其性能特征.该模型集相比于Monte Carlo方法生成的模型集有更高的精度,理论分析和仿真结果表明了新设计模型集的有效性与合理性.     

Control variable parameterisation with penalty approach for hypersonic vehicle reentry optimisation

An efficient trajectory optimisation approach combining the classical control variable parameterisation (CVP) with a novel smooth technology and two penalty strategies is developed to solve the trajectory optimal control problems. Since it is difficult to deal with path constraints in CVP method, the novel smooth technology is firstly employed to transform the complex constraints into one smooth constraint. Then, two penalty strategies are proposed to tackle the converted path and terminal constraints to decrease the computational complexity and improve the constraints satisfaction. Finally, a nonlinear programming problem, which approximates the original trajectory optimisation problem, is obtained. Error analysis shows that the proposed method has good convergence property. A general hypersonic cruise vehicle trajectory optimisation example is employed to test the performance of the proposed method. Numerical results show that the path and terminal conditions are well satisfied and better trajectory profiles are obtained, showing the effectiveness of the proposed method.     

再入机动飞行器的模糊自适应H2/H∞ 控制

针对再入机动飞行器(MRV)动态的非线性和不确定性,将模糊自适应理论与鲁棒H2/H∞控制理论相结合,提出一种MRV的模糊自适应H2/H∞控制方法。该方法利用模糊逻辑系统逼近导弹模型的非线性函数,补偿其建模的不确定性;并且基于H2/H∞混合优化控制与非零和博弈理论,设计了鲁棒H2/H∞控制器补偿模糊系统的逼近误差和外界干扰,进而改善控制性能,使得性能指标在达到最优化的同时满足H2/H∞性能指标。通过仿真分析,验证了所提出控制方法的有效性。     

基于光滑二阶滑模的可重复使用运载器有限时间再入姿态控制

针对可重复使用运载器(reusable launch vehicle,RLV)的六自由度再入模型,考虑模型不确定和外界干扰对再入姿态控制的影响,提出了一种非线性鲁棒控制策略.首先,根据多时间尺度特性将RLV的再入姿态模型分为姿态角子系统和姿态角速率子系统.其次,对每个子系统分别设计光滑二阶滑模控制器和滑模干扰观测器实现子系统的有限时间稳定.利用干扰观测器可以实现对不确定和外界干扰的精确估计,从而对控制器进行有效的补偿.进而,基于Lyapunov理论证明了整个系统的有限时间稳定.最后,通过仿真验证了提出的控制策略具有良好的控制性能和鲁棒性.     

Compressible laminar flow around a wall-mounted cubic obstacle

The fully-compressible, viscous and non-stationary Navier-Stokes equations are solved for the subsonic flow over a block placed on the floor of a channel. The Reynolds number is varied from 50 to 250. The Mach number is varied between 0.1 and 0.6. In all cases studied the flow field proves to be steady. Several distinct flow features are identified: a horseshoe vortex system, inward bending flow at the side walls of the obstacle, a horizontal vortex at the downstream upper-half of the obstacle and a downstream wake containing two counter-rotating vortices. The shape and size of these flow features are mainly dominated by the Reynolds number. For higher Reynolds numbers, both the horseshoe vortex and the wake region extend over a significantly larger area. The correlation of the position of the separation and attachment point with the Reynolds number has been calculated. Increasing the Mach number (at a fixed Reynolds number of 150) shows its influence in the reduced size, due to compression, of both the wake region and the horseshoe vortex.     

Transient state analysis of separated flow around a sphere

Transient state solutions of the Navier-Stokes equations were obtained for incompressible flow around a sphere accelerating from zero initial velocity to its terminal free falling velocity. By assuming rotational symmetry about the axis in the direction of motion, the Navier-Stokes equations and the continuity equation were simplified in terms of vorticity and stream function. The instantaneous acceleration of the falling sphere was calculated by considering the difference between the gravitational force and the drag force in a transient state. A set of implicit finite difference equations was developed. In order to obtain accurate information around the body, an exponential transformation along the radial direction was used to provide finer meshes in the vicinity of the surface of the sphere. The vorticity equation was solved by an alternating direction implicit (ADI) method while the stream function equation was solved by a successive over-relaxation (SOR) method. Simultaneous solutions were obtained. Transient state solutions were compared with steady state solutions for Reynolds numbers up to 300. Separations first occurred at a Reynolds number 20 for steady state flows and at Reynolds numbers 22·46 and 28·24 for transient state flows with terminal Reynolds numbers of 100 and 300, respectively. Separation angles, sizes of separation regions, and drag coefficents were calculated for both steady and unsteady states. Good agreement was obtained with existing experimental data in the steady state.     

基于改进分段Gauss伪谱法的带推力高超声速 飞行器再入轨迹规划

再入轨迹规划是高超声速飞行器领域的热点问题,已吸引了众多国内外专家的关注. Gauss伪谱法以及分段Gauss伪谱法是解决含有多约束轨迹规划问题的一类有效工具.然而,发动机多次点火熄火导致推力不连续以及点火时刻控制输入的连续性要求是带推力高超声速飞行器再入轨迹优化面临的新挑战.本文将问题简化为多脉冲再入轨迹规划问题,基于改进分段Gauss伪谱法生成满足多条件约束的最优再入轨迹.通过设置分段Gauss伪谱法连续性条件,确保飞行器状态与控制输入在分段点处连续衔接.通过无动力自由再入与带推力再入算例对改进分段Gauss伪谱法进行说明,仿真结果也表明,改进分段Gauss伪谱法可有效求解带推力高超声速飞行器再入轨迹规划.