基于H_∞滤波的主/子惯导组合中挠曲变形补偿算法

针对舰载环境下,主/子惯导组合中主、子惯导间的挠曲变形问题,设计了H?滤波算法。算法将主、子惯导间的挠曲变形作为一种能量有限的量测噪声,通过H?滤波对不确定噪声的鲁棒性来保证滤波精度。在经典的"速度+姿态"匹配方法的基础上,仿真比较了:1)方案一,已知挠曲变形时的标准Kalman滤波算法;2)方案二,未知挠曲变形时的标准Kalman滤波算法;3)方案三,未知挠曲变形时的H?滤波算法。仿真误差曲线直观表明:基于H?滤波算法可以在未知挠曲变形时有效提高组合精度;统计结果表明:滤波方案三得到的姿态与速度的系统误差、随机误差均与理想条件下的方案一相当;相较于方案二,滤波方案三得到的姿态与速度的系统误差至少可减小40%,随机误差至少可减少15%。     

General techniques for constructing variational integrators

The numerical analysis of variational integrators relies on variational error analysis, which relates the order of accuracy of a variational integrator with the order of approximation of the exact discrete Lagrangian by a computable discrete Lagrangian. The exact discrete Lagrangian can either be characterized variationally, or in terms of Jacobi’s solution of the Hamilton-Jacobi equation. These two characterizations lead to the Galerkin and shooting constructions for discrete Lagrangians, which depend on a choice of a numerical quadrature formula, together with either a finite-dimensional function space or a one-step method. We prove that the properties of the quadrature formula, finite-dimensional function space, and underlying one-step method determine the order of accuracy and momentum-conservation properties of the associated variational integrators. We also illustrate these systematic methods for constructing variational integrators with numerical examples.     

Modifying and Reducing Numerical Dissipation in a Two-Dimensional Central-Upwind Scheme

This study presents a modification of the central-upwind Kurganov scheme for approximating the solution of the 2D Euler equation. The prototype, extended from a 1D model, reduces substantially less dissipation than expected. The problem arises from over-restriction of some slope limiters, which keep slopes between interfaces of cells to be Total-Variation-Diminishing. This study reports the defect and presents a re-derived optimal formula. Numerical experiments highlight the significance of this formula, especially in long-time, large-scale simulations.     

Impact of Internal Heat Source on Mixed Convective Transverse Transport of Viscoplastic Material under Viscosity Variation

This communication addresses the impact of heat source/sink along with mixed convection on oblique flow of Casson fluid having variable viscosity. Similarity analysis has been utilized to model governing equations, which are simplified to set of nonlinear differential equations. Computational procedure of shooting algorithm along with 4th order Range-Kutta-Fehlberg scheme is opted to attain the velocity and temperature distributions. Impact of imperative parameters on Casson fluid flow, temperature, significant physical quantities such as skin friction, local heat flux and streamlines are displayed via graphs.     

分辨率优化的混合WENO格式

为提高有限差分格式的分辨率,利用傅里叶分析对WENO格式进行色散及耗散优化,并给出优化的线性权重.用优化后的WENO格式与保单调格式（MP）进行加权混合,得到新的加权混合WENO格式（H-WENO）.通过一维激波管问题、Shu-Osher问题及二维双Mach反射问题及R-T不稳定性问题对格式进行数值测试.结果显示,新格式具有强健的激波捕捉能力和对小尺度波结构的高分辨率,与原WENO格式相比改进明显.     

面向服务的防汛GIS支撑平台设计与实现

将GIS技术和面向服务的集成技术引入到了防汛信息系统建设的实际应用中,系统定义了防汛GIS支撑平台,制定了平台实现的技术路线,阐述了平台的设计思想,论述了平台的构建过程．其中,创建了汛情Web数据服务及其空间数据服务,在此基础上,建了一个面向web数据服务的开放式的防汛平台,实现了应用功能与汛情信息数据的分离,统一了汛情发布功能的展现方式,提高了平台的复用性、可维护性和可扩展性,为三维WebGIS技术在防汛减灾中的应用及建立类似系统提供了良好的设计思路和有益参考．     

一种简单的局部离散速度统一气体动理论格式

统一气体动理论格式UGKS(Unified Gas-Kinetic Scheme)是一种适用于从连续流到自由分子流的全流域计算格式。在该格式中一般使用统一的离散速度空间。而在高速流动中,不同节点的分布函数往往差异很大。为了保证计算的精度,离散速度空间必须满足所有节点的需要,占用了大量的内存。采用局部的均匀离散速度空间,离散速度的范围随节点状态的变化而变化,从而降低了内存的需要,并通过引入背景网格避免了不同节点离散速度的插值。最后,通过两个一维算例对该方法进行了测试。测试结果显示,采用局部离散速度空间能够得到可靠的结果,并且在模拟高速流动时计算效率明显提高。     

水槽涡的变化规律数值模拟

建立了不可压缩Navier-Stokes方程的Crank-Nicolson有限差分方法,数值模拟水槽晃动中流场及其涡流的数值变化规律。将数值解与解析解和前人的数值解进行比较,数值验证了不可压缩Naver-Stokes方程有限差分方法的有效性。通过数值模拟得到水槽在不同程度的倾斜激励晃动下流场及涡流的数值变换规律,当倾斜激励晃动的频率接近或远离共振频率时,水槽涡场的变化逐步由双涡变成单涡,再到不规则的涡场。当倾斜激励晃动的频率靠近共振频率ω_p=0.95ω_1附近时,水槽流场上部形成一个小涡,然后小涡扩大成整个水槽中的大涡,大涡下沉分裂成两个单涡,最后在底部消失;当倾斜激励晃动的频率在ω_p=0.75ω_1附近时,水槽底部形成一个小涡,然后扩大成大的单涡,最后在自由面消失;当倾斜激励晃动的频率在ω_p=0.55ω_1附近时,水槽底部出现小涡,然后扩大成大的单涡,大涡在自由面消失,继而出现不规则的大涡和不规则的小涡。     

基于动态本构模型的整流罩铰链系统自冲击分析

整流罩铰链系统结构分析是大型整流罩分离分析的重要环节,也是国内新一代运载火箭研制过程中的关键技术之一。基于30CrMnSiA和ZTC4-1的力学性能试验研究,得到材料的动态本构模型,并建立整流罩及动态本构模型下的铰链系统有限元模型。通过非线性显式动力学分析方法,对铰链系统自冲击过程进行仿真,得到冲击作用下铰链系统的应力和应变情况,并通过内力分析得到自冲击过程中铰链系统的主要内力形式。最后,通过比较铰链系统动态本构与准静态本构下的自冲击响应,验证并说明了动态本构模型对铰链系统自冲击仿真的影响。计算结果表明,自冲击作用会使铰链系统发生塑性变形,且动态本构模型有利于反映真实结果,为新一代运载火箭的研制提供一定的参考价值。     

Two-color laser wavelength effect on intense terahertz generation in air

Near-IR femtosecond lasers have been proposed to produce high-field terahertz radiation in the air via the laser-plasma interaction, but the physical mechanism still needs to be further explored. In this work, we theoretically investigate the effect of the two-color laser wavelength on the terahertz generation in the air based on a transient photocurrent model.We show that the long wavelength laser excitation can greatly enhance the terahertz amplitude for a given total laser intensity. Furthermore, we utilize a local current model to illustrate the enhancement mechanism. Our analysis shows that the terahertz amplitude is determined by the superposition of contributions from individual ionization events, and for the long wavelength laser excitation, the electron production concentrates in a few ionization events and acquires the larger drift velocities, which results in the stronger terahertz radiation generation. These results will be very helpful for understanding the terahertz generation process and optimizing the terahertz output.