Energy-efficient control of nanosatellites during distributed region formation flying

In this paper, we present an energy-efficient method for distributed region formation flying of nanosatellites. The proposed framework consists of two concurrent sub-schemes that include estimation and formation. In the estimation sub-scheme, unlike the existing methods on satellite formation flying, that assume the availability of the reference orbital elements to all followers, here, a distributed estimator is developed so that the follower nanosatellites estimate the position of the leader in its orbital slot. In the formation sub-scheme, we consider a region formation strategy which is an efficient method in dealing with the formation of a large number of nanosatellites. We propose an optimal region following formation method based on the receding horizon control (RHC) using the estimated reference orbital elements. Subsequently, an algorithm is presented to solve the proposed energy-efficient formation flying method. Finally, the simulation result is presented that illustrates the purposed method improves the power consumption for each nanosatellite with respect to the existing non-optimal region formation flying controllers.     

发动机初级工况对冷却夹套隔片损伤影响分析

针对可重复使用液体火箭发动机推力室冷却夹套隔片的损伤问题,为确保发动机的工作寿命,对建立了冷却夹套隔片的夹芯梁结构模型、粘塑性模型和细化损伤模型,发动机起动过程中初级工况给冷却夹套隔片损伤发展的影响进行了仿真计算。结果表明:初级工况过高,压力等性能参数振荡明显,振幅也较大,但引起的冷却夹套隔片损伤较小;初级工况选择过低,引起的冷却夹套隔片损伤较大,且压力等性能参数振荡也比较明显,但振幅较小。通过对比分析给出了用于发动机起动的合适初级工况,采用此工况使发动机起动过程中引起的损伤较小,而且压力等性能参数的振荡也较小。     

应用控制系统设计工具箱PIMCSD求解卫星编队重构问题

利用线性时变系统终端约束最优控制方法,为椭圆轨道卫星编队的队形重构控制问题设计了均衡耗能最优控制器.由于描述椭圆轨道卫星编队相对运动的Lawden方程是时变方程,给卫星编队重构的最优控制器设计带来一定的困难.利用基于精细积分算法的控制系统设计工具箱-PIMCSD进行系统设计,求解卫星编队重构所需的时变最优反馈控制律和前馈控制律,最后给出了由三颗卫星组成的编队队形重构控制仿真计算结果.     

基于精细积分理论与算法体系的时变最优控制方案工程应用

以航天器的编队飞行控制为工程背景,利用PIMCSD工具箱设计了航天器远/近程逼近的时变控制方案,并在飞行控制仿真平台上通过了验证.仿真结果表明,相对于传统的定常控制器方案,新的时变控制器方案可以在更短的控制时间内,以更少的燃料消耗,达到更高的终端控制精度,从而验证了控制方案的可行性、有效性和先进性.同时,提出的时变控制器简化实现方案不仅可以保持良好的性能指标,也便于工程设计和实现.这些工作为航天器编队控制系统的工程设计提供了有益的参考.     

浅谈《计算机组装与维修》课程的实践环节

使用模拟软件解决实际教学中的实训难题。     

毁伤概率评估的加权蒙特卡洛方法

由于经典蒙特卡洛方法的仿真效率不高,文中利用概率论和数理统计的基本原理,可以推导得到加权蒙特卡洛方法.加权蒙特卡罗方法不但能有效的缩小了样本方差,还能提高目标事件出现概率,相当于提高了样本的抽样效率,从而提高了仿真效率.与此同时,文中分别利用经典蒙特卡洛和加权蒙特卡洛这两种方法对典型目标进行了仿真计算,仿真计算最终证明了加权蒙特卡洛方法的仿真效率明显优于经典蒙特卡洛方法,能使仿真工作量成数量级的衰减.     

Thermodynamic assessment of RuO4 oxide

RuO₄ oxide appears much less stable than RuO₂(s) in the Ru–O binary system with a melting point close to room temperature and a certain propensity to vaporize or decompose at low temperatures. Ab initio simulations in the framework of density functional theory (DFT) on RuO₄(s) are performed to analyze the cubic and monoclinic structures and to evaluate the heat capacities at low temperatures. Then, a critical evaluation of thermodynamic data from calorimetry and vapor pressure determinations - was carried out coupled with ab-initio calculations to propose new thermodynamic data: the entropy.S° (RuO_4, s, cubic, 298K) = 132.7 J·K⁻¹mol⁻¹ and formation enthalpy.Δ_fH° (RuO₄, s, cubic, 298K) = −252.4 ± 5.5 kJ mol⁻¹.     

Structural damage identification via time domain response and Markov Chain Monte Carlo method

The present work addresses the problem of structural damage identification built on the statistical inversion approach. Here, the damage state of the structure is continuously described by a cohesion parameter, which is spatially discretized by the finite element method. The inverse problem of damage identification is then posed as the determination of the posterior probability densities of the nodal cohesion parameters. The Markov Chain Monte Carlo method, implemented with the Metropolis–Hastings algorithm, is considered in order to approximate the posterior probabilities by drawing samples from the desired joint posterior probability density function. With this approach, prior information on the sought parameters can be used and the uncertainty concerning the known values of the material properties can be quantified in the estimation of the cohesion parameters. The assessment of the proposed approach has been performed by means of numerical simulations on a simply supported Euler–Bernoulli beam. The damage identification and assessment are performed considering time domain response data. Different damage scenarios and noise levels were addressed, demonstrating the feasibility of the proposed approach.     

Structural damage diagnosis using incomplete static responses and LS-SVM

This paper presents novel approach to structural damage detection and estimation using incomplete static responses of a damaged structure and least squares support vector machine (LS-SVM). The presented method is based on the reduced stiffness matrix to formulate incomplete static responses as input parameters to the LS-SVM. The presented method is applied to a plane steel bridge, a four-span continuous beam and four-storey plane frame containing several damages. Also, the effect of the discrepancy in stiffness between the finite element model and the actual tested system has been investigated. The results show that the presented method is sensitive to the location and severity of the structural damage in spite of the incomplete noisy data and modelling errors.