Novel attitude determination method by integration of electronic level meter,INS, and low-cost turntable for level attitude evaluation and calibration of INS

Attitude references are greatly needed for the evaluation and calibration of Inertial Navigation Systems (INSs), which are widely used in gravimeter, marine, and aeronautical navigation. High-accuracy turntable, INS, and Global Navigation Satellite System have been utilized to verify the performance of relatively low-accuracy INS. The accuracy requirement of the attitude reference continuously increases with the rapid improvement of inertial sensors and navigation algorithms. However, the cost of attitude determination system increases rapidly with the increase of attitude accuracy requirement. To solve this limitation, the integration of level meter, INS, and low-cost turntable is proposed to provide level attitude, such as roll and pitch. The turntable is utilized to rotate the INS. An integration model of the level meter and INS is built to estimate the level attitude and reduce the cost of the turntable. The proposed method successfully avoids the dependence on high-accuracy turntables. An observability degree analysis is conducted to improve the level attitude accuracy further. The simulation and turntable test results indicate that the proposed method can provide high-accuracy level attitude without high-accuracy INS or turntable and is applicable to error calibration and attitude evaluation of INS.     

A novel temperature-compensation method based on correlation analysis for multi-FOG INS

Aimed at improving the bias stability of Fiber-Optic Gyroscope (FOG)-based inertial navigation systems in environments of various ambient temperatures, a novel temperature-compensation method based on a correlation analysis of the same batch of FOGs is proposed. The empirical mode decomposition method was employed to filter the high-frequency noises of the FOGs. Then, the correlation information of the multiple FOGs was used to analyze the feasibility of the method. Eventually, the same residual error of the FOGs was compensated via the simple piecewise linear models. The experimental results indicate that excellent compensation effects for both high- and low-accuracy FOGs are achieved using the proposed method. Specifically, the accuracies of high-accuracy FOGs are improved by approximately 33.9%, 20%, and 31.2%, while those of low-accuracy FOGs are improved by approximately 39.1%, 20.8%, and 26.1%. The method exhibits the merits of simplicity, validity, and stability, and thus is expected to be widely used in engineering applications.     

Orbit determination of BeiDou navigation satellite system maneuvered satellites based on instantaneous velocity pulses parameters

The BeiDou navigation satellite system (BDS) comprises geostationary earth orbit (GEO) satellites as well as inclined geosynchronous orbit (IGSO) and medium earth orbit (MEO) satellites. Owing to their special orbital characteristics, GEO satellites require frequent orbital maneuvers to ensure that they operate in a specific orbital window. The availability of the entire system is affected during the maneuver period because service cannot be provided before the ephemeris is restored. In this study, based on the conventional dynamic orbit determination method for navigation satellites, multiple sets of instantaneous velocity pulses parameters which belong to one of pseudo-stochastic parameters were used to simulate the orbital maneuver process in the orbital maneuver arc and establish the observed and predicted orbits of the maneuvered and non-maneuvered satellites of BeiDou regional navigation satellite system (BDS-2) and BeiDou global navigation satellite system (BDS-3). Finally, the single point positioning (SPP) technology was used to verify the accuracy of the observed and predicted orbits. The orbit determination accuracy of maneuvered satellites can be greatly improved by using the orbit determination method proposed in this paper. The overlapping orbit determination accuracy of maneuvered GEO satellites of BDS-2 and BDS-3 can improve 2–3 orders of magnitude. Among them, the radial orbit determination accuracy of each maneuvered satellite is basically better than 1 m. simultaneously, the combined orbit determination of the maneuvered and non-maneuvered satellites does not have a great impact on the orbit determination accuracy of the non-maneuvered satellites. Compared with the multi GNSS products (indicated by GBM) from the German Research Centre for Geosciences (GFZ), the impact of adding the maneuvered satellites on the orbit determination accuracy of BDS-2 satellites is less than 9 %. Furthermore, the orbital recovery time and the service availability period are significantly improved. When the node of the predicted orbit is traversed approximately 3 h after the maneuver, the accuracy of the predicted orbit of the maneuvered satellite can reach that of the observed orbit. The SPP results for the BDS reached a normal level when the node of the predicted orbit was 2 h after the maneuver.     

扰动线运动对惯性系粗对准影响分析及优化方法

针对扰动线运动对惯性系粗对准精度影响较大的问题,通过分析惯性体坐标系下重力加速度积分矢量的物理含义,给出了受扰动线运动影响的惯性系粗对准的误差分析。并在此基础上提出了基于位移积分矢量构造定姿矢量矩阵的抗扰动粗对准算法,利用对速度积分矢量进一步积分得到的3个时间点的位移积分矢量构建姿态解算矩阵,抑制扰动线运动对粗对准精度的影响。仿真结果表明,该算法可有效减小扰动线运动影响下的对准结果振动幅值,能够快速收敛到满足精对准使用的精度范围,从而提高武器装备环境适应性。     

激光选区熔化成型316L不锈钢工艺参数研究

针对激光选区熔化成型316L不锈钢工艺参数选择问题,采用单因素条件变量分析法,在激光选区熔化过程中,分析了激光功率、扫描速度对316L不锈钢成型零件表面粗糙度、致密度、硬度和尺寸偏差的影响规律。结果表明：当激光功率降低或者扫描速度提高时,内部能量密度减小,粉末熔化量减少,试样表面球化效应增强,孔隙缺陷增多,试样致密度减小、硬度降低;当激光功率提高或者扫描速度降低时,内部能量密度增大,粉末被过度烧蚀,产生较大的尺寸偏差,所形成熔道易塌陷,导致层间结合较差,试样性能降低。当激光功率为300 W、扫描速度为1000 mm/s时,能量密度适中,形成了较好的冶金结合,抗拉强度可达753 MPa,上表面硬度HRB能达到97.22。该项研究为316L不锈钢激光选区熔化工艺参数的合理选择提供了参考。     

Quantification of parametric uncertainty in γ-Reθ model for typical flat plate and airfoil transitional flows

Owing to the lack of physical knowledge of boundary layer transition, the γ-Re_θ transition model introduces closure parameters, which increase the uncertainty of transition prediction. The objective of this work is to quantify the uncertainties of closure parameters in the quantities of interests and identify the key parameters. The six closure parameters in the uncertainty intervals are used as input variables, and the uncertainties of the output results are propagated by a stochastic expansion based on the point-collocation nonintrusive polynomial chaos method. The relative contribution of each parameter to uncertainty is evaluated by the Sobol index. The computational cases include natural and bypass transitional flows on zero-pressure-gradient flat plates, and subsonic and transonic flows around airfoils. For most cases, c_e2, c_a2, and c_a1 dominate the uncertainty, and the influence of σ_θt is also significant when the history effects of flow are evident. The contribution of parameters in airfoils is more complex than that in flat plates. The transonic airfoil case shows that flow separation dramatically changes the distribution of Sobol indices, which poses a challenge to the accurate prediction of transition. Generally, c_e2 and c_a2 are the key parameters of the γ-Re_θ model.     

真实气体效应对等离子体鞘套及电磁参数的影响

针对高速飞行器高超声速飞行环境，建立了热化学非平衡流动数值模拟技术，并对计算方法的可靠性进行了验证，接着开展了真实气体效应对飞行器等离子体鞘套及其电磁参数的影响规律分析。结果表明:飞行器物面中心线等离子体密度峰值与飞行试验符合良好；对于碰撞频率，沿滞止流线，双温模型以及Park反应模型对等离子体碰撞频率的影响趋势是一致的；对于相对介电常数，除激波附近，流场其他区域的实部接近1，激波附近小于1，虚部沿滞止流线逐渐升高；双温模型以及Park反应模型对相对介电常数实部和虚部的影响趋势是一致的。      

高体积分数SiCp/Al激光诱导氧化辅助铣削研究

为了解决高体积分数的SiC_p/Al复合材料在常规切削加工中存在切削力大、刀具磨损快、表面完整性差等问题。本文针对高体积分数SiC_p/Al材料开展激光诱导氧化辅助铣削技术研究，通过激光辐照铣削区域形成易于去除的疏松氧化层提高切削性能，同时开展氧化层调控策略及激光诱导氧化辅助下的铣削参数优化工艺研究，研究不同激光能量密度、辅助气体对氧化层质量的影响及铣削参数优化。结果表明随激光能量密度的增大热影响区宽度和烧蚀沟槽深度随之增加，在氧气辅助下易形成疏松且易于去除氧化层。选取较高的激光能量密度可获得较好的氧化效果，而使用PCD金刚石铣刀，主轴转速为10 000 r/min，在每齿进给量为7.5 μm /s可获得最佳表面质量。     

中心支板参数对RBCC发动机性能影响研究

针对某宽域加速飞行任务下RBCC发动机中心支板主要几何参数设计问题，采用全流道一体化数值模拟方法，在Ma 0.4-6速域内研究支板阻塞比、顶角及长宽比等参数对发动机引射、亚/超燃模态的性能影响规律。结果表明，随着阻塞比增大，各模态下空气流动受压缩作用增强，燃烧反应更加充分，发动机总推力有0.13%-5%的提升；随着顶角增大，除Ma 2.5工况由流道截面构型变化引起激波形成外，增强的支板前缘激波使得燃烧反应位置较为集中，燃料喷注贯穿主流深度提高，较为充分的燃烧释热使得发动机总推力有2.2%-5.7%的提升；随着长宽比减小，在Ma 0.4-4条件下，增大的流道面积有利于煤油横向扩展，较好的氧燃掺混使得发动机总推力有2%-4.8%的提升，而在Ma 6条件下，支板前缘激波的减速增压作用逐渐减弱，发动机总推力可降低5.2%-7.1%。所得结论可为RBCC发动机中心支板设计参数选择提供依据。     

结构参数对石英纤维针刺毡防隔热和力学性能的影响

为开发具有良好防隔热和力学性能的高性能石英纤维毡,基于传热数学方程,预测了石英纤维毡的厚度对其隔热性能的影响规律;为提高纤维毡的力学性能,探究了在纤维毡中添加不同层数的石英纤维布对其力学性能的影响规律;此外还探讨了针刺密度对石英纤维毡隔热性能和力学性能的影响。结果表明：石英纤维毡传热模型与实验吻合度可达94.8%;石英纤维毡厚度提升2 mm,其隔热性能提高20 ℃左右;添加石英纤维布可以显著提高纤维毡断裂强力和撕破强力;针刺密度可以提升纤维毡力学性能,但针刺密度过大会破坏纤维毡结构,使其力学性能下降。