贴体曲线坐标系中恢复函数的一种构造方法及应用

本文在结构网格下，从三点迎风紧致逼近出发提出了一种适合于有限体积离散的恢复函数生成办法，在光滑区它具有三阶精度，并且在捕捉激波时有较高的激波分辨率。典型的几个内流算例表明：用该方法得到的恢复函数去计算数值能量时能得到与实验数据较接近的数值解。     

Adaptive mesh refinement computation of acoustic radiation from an engine intake

A block-structured adaptive mesh refinement (AMR) method was applied to the computational problem of acoustic radiation from an aeroengine intake. The aim is to improve the computational and storage efficiency in aeroengine noise prediction through reduction of computational cells. A parallel implementation of the adaptive mesh refinement algorithm was achieved using message passing interface. It combined a range of 2nd- and 4th-order spatial stencils, a 4th-order low-dissipation and low-dispersion Runge–Kutta scheme for time integration and several different interpolation methods. Both the parallel AMR algorithms and numerical issues were introduced briefly in this work. To solve the problem of acoustic radiation from an aeroengine intake, the code was extended to support body-fitted grid structures. The problem of acoustic radiation was solved with linearised Euler equations. The AMR results were compared with the previous results computed on a uniformly fine mesh to demonstrate the accuracy and the efficiency of the current AMR strategy. As the computational load of the whole adaptively refined mesh has to be balanced between nodes on-line, the parallel performance of the existing code deteriorates along with the increase of processors due to the expensive inter-nodes memory communication costs. The potential solution was suggested in the end.     

High-order implicit discontinuous Galerkin schemes for unsteady compressible Navier–Stokes equations

Efficient solution techniques for high-order temporal and spatial discontinuous Galerkin(DG) discretizations of the unsteady Navier–Stokes equations are developed. A fourth-order implicit Runge–Kutta(IRK) scheme is applied for the time integration and a multigrid preconditioned GMRES solver is extended to solve the nonlinear system arising from each IRK stage. Several modifications to the implicit solver have been considered to achieve the efficiency enhancement and meantime to reduce the memory requirement. A variety of time-accurate viscous flow simulations are performed to assess the resulting high-order implicit DG methods. The designed order of accuracy for temporal discretization scheme is validate and the present implicit solver shows the superior performance by allowing quite large time step to be used in solving time-implicit systems. Numerical results are in good agreement with the published data and demonstrate the potential advantages of the high-order scheme in gaining both the high accuracy and the high efficiency.     

基于非结构动态网格的翼型积冰过程数值模拟

讨论了积冰气象条件下翼型积冰过程的非结构动态网格数值模拟方法。外部无黏绕流流场采用基于非结构网格的分布式并行计算技术,空间离散采用VanLeer迎风有限体积格式,时间推进为5步显式龙格 库塔方法。采用四阶龙格 库塔方法求解过冷水滴运动轨迹方程,使用了一种合理、简单的物面水积冰量计算方法,提高了计算效率。使用非结构动态网格技术对积冰后的翼型网格进行快速调整。在对NACA0012翼型积冰形状进行校核验证后,对某型飞机在积冰气象条件下飞行时翼型积冰过程进行了数值模拟,得到了与参考文献结果相符的冰形特性。     

浸入式贴体网格边界方法

提出一种基于重叠网格的浸入式边界方法,用以模拟复杂的三维黏性跨声速流动。该方法采用一套固定的笛卡儿正交网格,用以主流的求解;采用一套可以移动的贴体等距面网格,用以拟合或者离散物面的作用力,通过空间插值,实现两套网格重叠部分的信息传递。分析了浸入式贴体网格边界方法的优势,介绍了贡献单元的寻找策略和物理通量的插值方法。流场求解采用Spalart-Allmaras带湍流模型的Navier-Stokes方程组,其中对流项采用流通矢量分裂和5阶WENO(weighted essentially non-oscillatory)-Z格式离散,黏性项采用6阶中心差分格式离散,时间项采用龙格库塔显式格式离散。数值验证算例表明:该方法具备高于4阶的空间求解精度,并适用于刚体动网格非定常流场模拟,且无需更新网格形状。等距面贴体网格生成过程简单,避免了繁琐的人工调节过程,与笛卡儿网格结合,可提供足够的壁面附近网格密度,同时有效减少了网格总量需求。     

一种改进的流场计算加速收敛方法

探讨了二维非结构网格无粘流场计算的加速方法。在对残差平均和多重网格这两种主要加速方法进行分析后,提出了一种改进的兼具多重网格思想的残差平均方法。经对绕NACA0012翼型无粘流动计算的验证,收效明显。在几乎不增加计算量的情况下,比原有的残差平均方法可减少迭代步25%～30%.该思想可推广用于三维、有粘流动计算和结构化网格中。     

惯导/北斗/里程计一体化紧组合导航方法研究

当前,主要通过采用惯导/卫星导航组合或者惯导/里程计组合的方式来实现 车辆的定位定向;卫星信号良好时,惯导系统与卫星导航组合实现车辆定位定向,当卫 星导航信号不好甚至没有信号无法正常工作时,惯导系统与里程计组合实现车辆定位定 向。提出一种惯导/卫星导航/里程计三者的一体化组合方案,针对惯导、北斗、里程计 这三项测量设备构成的组合系统建立了统一的误差状态模型、组合量测模型以及反馈修 正模型,并通过卡尔曼滤波器来实现三者的一体化紧组合,这种惯导/北斗/里程计一体 化的紧组合方式,能更好地实现三者信号之间的充分交流与融合。将这种一体化紧组合 方法与传统的惯导/北斗组合、惯导/里程计组合方法进行了仿真比较,结果表明：惯导/ 北斗/里程计一体化的紧组合方法能更加快速、准确得到传感器误差（ 包含惯组误差、 北斗误差、里程计误差）的在线估计,更能有效提高各传感器的测量精度。     

二维平行剪切层声波产生和辐射的数值模拟

 在二维线化Euler 方程的基础上解决了第3 届计算气动声学专题讨论会的第5 类标准问题: 二维平行剪切层声波的产生和辐射。频散相关保持有限差分格式用于空间离散, 低频散低耗散的龙格库塔法用于时间积分。重点使用了远场无反射边界条件。计算结果与NASA GLENN 研究中心的解析解符合得很好。     

Optimum Integration of Aircraft Navigation Systems

A current problem in aircraft navigation is determining how to effect alow cost navigation system consistent with required mission operationswhich will render a high degree of accuracy and reliability. One wayto achieve this is through optimum integration of equipment,subsystems, and computer mechanizations. Consistent with this approach,the overall objectives of this paper are to show the advantages of anoptimally integrated aircraft navigation system, and to illustrate howto effect a low cost navigation system with high accuracy performance.An integrated aircraft navigation system employing a Kalman optimumestimation filter is configured and analyzed in detail. The results ofthe analysis clearly indicate how to achieve high accuracy performanceusing low cost subsystems; namely, via optimum systems integration.     

水下单信标导航航路规划和最优航路接近方法

相比于传统的长基线和超短基线等导航方式，水下单信标导航具有布放简单的优点，但其导航精度有待进一步提高。为此，提出了单信标导航的航路规划方案，通过泰勒级数展开推导了水平位置精度因子的表达式，并分析了导航点和声信标的相对几何位置关系对导航精度的影响，最终提出了航路规划方案。在此基础上，还提出了自主水下航行器(autonomous underwater vehicle，AUV)从其他位置接近最优航路的方法，包括两部分：一是建立以时延为观测量的滤波模型，利用滤波算法实时获取AUV的位置估计值；二是基于可观测度分析结果对最优航路接近过程的轨迹进行了设计。二者的结合使得AUV高效率且高精度地逼近最优航路。仿真证明了采用所提出的航路规划方案和最优航路接近方法可以提高导航精度，航路规划方案使得AUV位置估计的均方根误差近似为2 m。     

An epoch state filter for use with analytical orbit models of low earth satellites

Kalman filters provide a well established means for satellite orbit determination. In combination with space based sensors like GPS, DORIS or PRARE, accurate estimates of the spacecraft position and velocity can be obtained in real-time on-board the space vehicle. Traditionally, numerical methods of varying complexity are applied for propagating the state vector between measurements and updates of the state vector are referred to the epoch of the latest sensor output. In the present study a different approach is followed, which offers increased on-board autonomy and is particularly promising for small satellites with moderate accuracy requirements. An analytical orbit model is used to describe the spacecraft trajectory and mean elements at epoch are estimated instead of the instantaneous, osculating state vector. This adds the capability of performing on-board orbit prediction over time scales of up to one week, which is required, for instance, for the autonomous forecast of eclipse times or station contacts. Making use of the SGP4 orbit model that is compatible with NORAD twoline elements, an epoch state Kalman filter has been implemented and tested with GPS flight data of GPS/MET (MicroLab-1) and MOMSNAV (MIR). It is demonstrated that the proposed method provides an accuracy compatible with that of the analytical model and is robust enough to handle large data gaps in case of limited on-board resources for GPS operations. By adjusting the ballistic coefficient along with the mean elements, a considerable improvement of mid-term orbit predictions is achieved over methods that are restricted to the estimation of the state vector alone.     

基于五阶容积-二阶平滑变结构滤波算法的捷联惯导系统初始对准技术

为了改进捷联惯导系统大方位失准角初始对准情况下的方位失准角对准精度和稳定性问题,提出了一种组合对准方法。该方法将Kalman滤波对准模型与罗经对准模型相结合构建了一种组合对准机制,并在此模型基础上提出了基于非线性滤波和鲁棒滤波的五阶容积-二阶平滑变结构滤波算法,将五阶容积-二阶平滑变结构滤波算法与组合对准机制相结合,从而实现大方位失准角的初始对准。仿真结果表明,五阶容积-二阶平滑变结构滤波对准方法得到的方位失准角对准精度明显优于常见的几种对准方法,且其对准结果的重现性更高。因此,提出的五阶容积-二阶平滑变结构滤波算法能够很好地适用于大方位失准角的初始对准。     

空间平台机动变轨自主导航研究

针对空间平台在高轨道机动变轨过程中自主导航的需求,采用了基于Kalman滤波器的捷联惯导与星敏感器的组合导航方案。结合Kalman滤波中协方差更新的误差分配分析方法,分析了影响空间平台状态估计误差的主要因素。采用适用于高轨道的球谐重力模型,运用STK工具包设计了变轨机动轨迹,将该轨迹应用于组合导航方案的仿真验证。仿真结果表明,量测噪声是影响空间平台姿态精度的主要因素,加速度计零偏对变轨过程速度精度有决定性影响,改善两者的精度可以实现空间平台机动变轨的高精度自主导航。     

一种用于仿生导航无人机航姿求解的混合滤波方法

针对现有组合导航系统易被干扰欺骗以及姿态求解精度不足的问题，设计了惯性测量单元(IMU)与偏振光传感器组成的航姿参考系统(AHRS)。同时，考虑到传统的姿态求解方法精度不高，提出了一种用于仿生导航无人机航姿求解的混合滤波方法。将Mahony滤波后的姿态值作为系统观测量，再结合扩展卡尔曼滤波(EKF)实现传感器数据的深层融合，以获得高精度的姿态角信息。实验结果表明：在静态环境下采用混合滤波方法求解的姿态值能有效滤除偏振光传感器和加速度计内部噪声干扰，其稳定性明显优于两种方法各自求解时的情况；在动态实验中该方法能有效抑制单独采用Mahony滤波时存在的超调问题，表现出更高的动态解算精度，从而为偏振光组合导航系统提供了更精确的姿态估计信息。     

亚、超音喷管中声传播的数值模拟

采用计算气动声学方法研究了管道近音速区的声传播和声波与激波的相互作用问题。空间离散采用高阶DRP格式,时间离散采用低耗散低频散的龙格库塔方法,边界条件采用Giles的特征变量一维非定常无反射边界条件。计算结果和解析解的精确吻合表明,计算中应用的这种高阶的DRP格式有很高的分辨率和很好的稳定性,适合声传播的计算。      

叶轮机械三维粘性动静叶干涉的数值模拟

本文发展了 1套模拟叶轮机械三维粘性动静叶干涉的数值方法。在成熟的空间离散方法基础上 ,提出了 1种高效的双时间步隐式时间推进方法 ,并构造了一种保证守恒的动静叶交界面处的数值通量计算方法。本文对某三维亚音速涡轮的动静叶干涉进行了数值模拟 ,结果与实验符合较好。     

高超声速滚转阻尼导数数值模拟

采用非定常Ｎａｖｉｅｒ－Ｓｔｏｋｅｓ方程描述物体简谐振动流场,并在Ｅｔｋｉｎ理论下给出绕定轴转动时滚转阻尼导数的计算公式,定常流场的计算采用空间二阶精度的交替方向隐式分解的ＮＮＤ格式,非定常流场的计算采用时、空二阶精度的Ｒｕｎｇｅ－Ｋｕｔｔａ多步格式,采用代数和方法生成物体静、动网格。最后给出高超声速下钝体外形滚转阻尼导数的计算结果,以及滚转力矩系数随瞬时振幅的变化曲线。     

高斯-厄米特滤波器在捷联惯导系统初始对准中的应用

 为提高静基座初始对准精度,缩短对准时间,采用了基于大方位失准角的对准模型,引入了高斯-厄米特滤波器(GHF)。针对GHF中均值和协方差阵的多元非线性高斯积分求解问题,利用初始对准误差方程的非线性是由大方位失准角导致的特点,通过状态的线性变换,求其线性状态解析解,将高维积分转化成一元数值积分,在不损失精度的前提下,解决了GHF在对准应用的"维数灾难"问题。将此算法用于实际系统,对比于扩展卡尔曼滤波器(EKF)、无迹卡尔曼滤波器(UKF),结果表明在大方位失准角条件下,GHF方法偏航角的对准精度提高了16%,对准时间缩短了75％。     

A dimension reduced INS/VNS integrated navigation method for planetary rovers

Inertial navigation system/visual navigation system (INS/VNS) integrated navigation is a commonly used autonomous navigation method for planetary rovers. Since visual measurements are related to the previous and current state vectors (position and attitude) of planetary rovers, the performance of the Kalman filter (KF) will be challenged by the time-correlation problem. A state augmentation method, which augments the previous state value to the state vector, is commonly used when dealing with this problem. However, the augmenting of state dimensions will result in an increase in computation load. In this paper, a state dimension reduced INS/VNS integrated nav-igation method based on coordinates of feature points is presented that utilizes the information obtained through INS/VNS integrated navigation at a previous moment to overcome the time rel-evance problem and reduce the dimensions of the state vector. Equations of extended Kalman filter (EKF) are used to demonstrate the equivalence of calculated results between the proposed method and traditional state augmented methods. Results of simulation and experimentation indicate that this method has less computational load but similar accuracy when compared with traditional methods.     

Joint probabilistic data association for autonomous navigation

A new autonomous navigation scheme based on the joint probabilistic data association (JPDA) approach that processes landmark detections in the field of view (FOV) of an on-board sensor is developed. These detections-some true, some false-are associated to a set of stored landmarks and used to update the state of the vehicle. The results obtained from Monte Carlo simulations prove the ability of this navigation filter to perform in very high false alarm environments. In the different environmental conditions tested in the simulations, the performance of the JPDA navigation filter (JPDANF) is very close to that of the filter based on perfect data association. The very efficient cluster decomposition algorithm presented for the purpose of the navigation problem can also be used in many multitarget tracking applications