高超声速再入飞行器的特征建模及自适应递推滑模控制

针对高超声速再入飞行器非线性程度高、参数不确定性大、快时变等特点，提出一种基于神经网络特征模型的自适应滑模姿态控制方案。首先，采用现有特征建模方法，将对象模型中的非线性、时变不确定性压缩至特征参量中；进一步，结合模糊神经网络，将快时变特征显式地表征在特征模型中，使得待估计的特征参量具有时不变特性，从而易于其自适应律的设计。然后，在该神经网络特征模型的框架下，设计递推形式的自适应滑模控制律，以进一步提高飞行控制系统的鲁棒性。最后，通过仿真校验了所提出控制方法的正确性和有效性。     

Rapid ionospheric variations at high latitudes: Focusing on Greenland

The Helheim glacier, located in southeast Greenland, has more than ten campaign-type Global Positioning System (GPS) sites; data processing led to the observation of a very rapid change in the ionospheric delay. To identify the cause of these sporadic disturbances, we analyzed the slant total electron content (STEC), single-differenced STEC (SD-STEC) and scintillation proxy index called the delta phase rate (DPR). From this analysis, the abrupt change of those ionospheric indicators was attributed to the line-of-sight direction to the satellite and the temporal sequence of the event was found to be highly correlated with the geometry of the GPS sites. In addition, the disturbance based on the result of SD-STEC occurred mostly during the night, from 17 UTC through 7 UTC, and across a band spanning the east-west direction. Based on the DPR indices obtained from GPS stations distributed across all of Greenland, Iceland, and northeastern Canada, the rapid ionospheric variation was found to be correlated with the time of the day and the geomagnetic latitude of the station. The disturbance was larger at the relatively low geomagnetic latitudes at night but was more significant at higher latitudes in the daytime. These rapid ionospheric variations tended to appear in band shapes parallel to the geomagnetic field. These results allow us to attribute such disturbance observed at the Helheim glacier to aurora-related phenomena.     

Ionospheric precursors of earthquakes recorded by VLF receiver at Tashkent IHY station

Tashkent International Heliophysical Year (IHY) station is a member of Atmospheric Weather Electromagnetic System for Observation, Modeling and Education (AWESOME) network being operated globally to study the ionosphere and the magnetosphere with the help of electromagnetic waves in Very Low Frequency (VLF) band. Regular monitoring of the D- and F-layers of ionosphere over Central Asia territory is being performed on the permanent basis starting year 2008. We have studied VLF amplitude anomalies related to the EQs occurred in 2008–2009 years with magnitude more than 5 on the path way from the VLF transmitters to the Tashkent station assuming that propagation of VLF ground-based transmitters signals can be perturbed by EQ preparation detectable from the ground-based measurements in the VLF bands. For analyzing narrowband data we have used the nighttime fluctuation (NF) method paying attention to the data obtained during the local nighttime (20:00 LT–04:00 LT) in Tashkent where the VLF receiver is operating. The mean nighttime amplitude (or trend) and nighttime fluctuation are found to increase significantly before the EQ occurred on the path way from the transmitters to the receiver. The obtained results have revealed an agreement with VLF amplitude anomalies observed in Tashkent VLF station during the strong EQs occurred on the path way from the transmitters to the receiver. Some results are presented to show the probing potentiality of VLF waves to predict short term EQs with high magnitude.     

SNR periodical variation of Chang'E-3 spacecraft orbiting the Moon

Chang'E-3 spacecraft was orbiting the Moon from December 6–14, 2013, and very long baseline interferometry(VLBI) observations were performed to improve the accuracy of its orbit determination. In the process of recording VLBI raw data, 2 bits quantization was implemented.Interesting phenomenon was that signal-to-noise ratio(SNR) of each VLBI station experienced periodical change and had large variation on amplitude while in the Moon's orbit, whereas SNR kept in a stable level after Chang'E-3 landed on the Moon. Influence of varying elevation angle on SNR was analyzed and compensation of 2 bits quantization harmonics to SNR calculation was investigated. Most importantly, telescope system noise temperature increase caused by the Moon was computed along the time of Chang'E-3 orbiting the Moon, and well matched SNR changing trend in terms of correlation coefficients.     

涡轮支板与导向器一体化气动设计方法研究

针对大涵道比发动机低压涡轮设计要求,开展了大、小叶片组合叶栅形式的低压涡轮支板与导向器一体化设计方法研究。以常规参数化方法为基础,建立了大、小叶片设计参数关联关系,提出1种参数化程度高和参数关联性强的大、小叶片组合叶栅参数化叶型设计方法,并用于低压涡轮支板与导向器一体化气动方案设计。结果表明:涡轮支板与导向器一体化气动方案的总压恢复系数为0.981,叶片表面载荷分布合理,流场质量良好,叶栅出口流场参数分布均匀且周期性好。涡轮支板与导向器一体化叶型参数化设计方法具有良好的工程应用价值。     

航空发动机燃烧室参数化建模

实体建模和网格生成在CFD中占重要地位。针对航空发动机燃烧室开发了专用的CFD前处理软件,主要包括参数化的燃烧室3维建模程序,提供从构建模型到生成网格的有效途径,可快速完成燃烧室CFD的前处理工作,从而有效提高燃烧室的设计效率,缩短研制周期。此外,还利用UG2次开发语言UG／OpenGRIP编制了数据转换程序,实现了本参数化设计软件和其他CAD软件（UG）的数据共享。     

基于乘幂伸缩因子的参数曲线自由变形

为了改进参数曲线自由变形方法,构造了一种新的基于乘幂函数的伸缩因子,它不仅具有已有伸缩因子的特性,还具有区域峰值性,并且变形操作对Bézier曲线和NURBS曲线具有封闭性.在将伸缩因子作用于待变形曲线方程时,通过交互改变控制参数来控制曲线的形状,从而得到变形效果.实验结果表明,该方法计算简单、易于控制,可以得到丰富的变形效果,适用于几何造型、计算机动画等领域.     

基于三维参数化模型构建的飞机重量重心快速估算方法

 针对飞机总体设计阶段重量重心(c.g.)估算的专业要求、设计方案反复调整的特点,提出了基于三维参数化建模的重量重心快速估算方法,从而实现后续的快速参数化调整。基于该方法的分析流程,通过分析飞机外形建模和结构、系统重量建模的工作对象和专业逻辑,对各个重量组成及其建模过程进行了参数化描述和流程定义,用于指导完成整个设计分析系统的开发实现。最后,通过算例演示了基于三维参数化建模进行重量重心快速估算的步骤。     

Using a pressure controlled vortex design method to control secondary flow losses in a turbine stage

A turbine design method based on pressure controlled vortex design （PCVD） is presented to design a small-size turbine stage. Contrary to the conventional controlled vortex design （CVD） method, the main objective of PCVD is to control the axial velocity and radial pressure in the sta- tor rotor gap. Through controlling axial velocity, the PCVD establishes a direct tie to meridional stream surface. Thus stream surface variation is induced, resulting in a large secondary flow vortex covering the full blade passage in the respective stator and rotor. This secondary flow vortex could be dedicated to control the secondary flow mitigation and migration. Through radial pressure, the PCVD is also associated with the macroscopic driving force of fluid motion. So the better benefit of CVD can be achieved. The core concept behind PCVD is to mainly control the spanwise pressure gradient by altering profile loading at various spanwise locations. Therefore not only the local pro- file lift is affected, but also the resulting throat widths, stage reaction degree, and massflow rate are altered or redistributed respectively. With the PCVD method, the global stage efficiency is increased successfully while the mass flow rate keeps constant. Additionally there is no endwall shape optimization, stacking optimization, or pitch/chord variations, concentrating solely on varying blade profile deflections and stagger.