Extension of the low diffusion particle method for near-continuum two-phase flow simulations

The low diffusion (LD) particle method, proposed by Burt and Boyd, is modified for the near-continuum two-phase flow simulations. The LD method has the advantages of easily coupling with the direct simulation Monte Carlo (DSMC) method for multi-scale flow simulations and dramatically reducing the numerical diffusion error and statistical scatter of the equilibrium particle methods. Liquidor solid-phase particles are introduced in the LD method. Their velocity and temperature updating are respectively, calculated from the motion equation and the temperature equation according to the local gas properties. Coupling effects from condensed phase to gas phase are modeled as momentum and energy sources, which are respectively, equal to the negative values of the total momentum and energy increase in liquid or solid phase. The modified method is compared with theoretical results for unsteady flows, and good agreements are obtained to indicate the reliability of the one-way gas-to-particle coupling models. Hybrid LD-DSMC algorithm is implemented and performed for nozzle discharging gas-liquid flow to show the prospect of the LD-DSMC scheme for multi-scale two-phase flow simulations.     

FM73M 胶膜及其与PMI 泡沫芯的胶接机理

采用DSC研究了不同升温速率下FM73M胶膜的固化反应特性,根据DSC曲线得到了胶膜的凝胶化温度和固化温度等工艺参数,建立了其固化动力学模型,确定胶膜的固化参数为(125±2)℃/90min.在此基础上,通过SEM研究了胶膜在PMI泡沫芯材内的分布以及界面结合状况(界面润温情况、气孔、缺陷),分析了胶膜与泡沫芯的胶接机理.     

复合材料螺栓连接失效的数值模拟

作为一种重要的连接及承载形式,复合材料螺栓的连接性能直接影响到结构组件的承载可靠性.本文针对复合材料各向异性及渐进损伤特点,建立了包含复合材料螺栓及复合材料板的有限元模型.通过编制U-Mat程序,利用ABAQUS商用软件对复合材科螺栓连接的失效过程进行了数值模拟,得到了连接件的载荷-位移曲线,并对连接件的失效模式进行了分析.     

倾斜射流撞壁实验研究及液膜几何参数建模

倾斜射流撞壁在液体火箭发动机液膜冷却、射流撞壁雾化等领域具有广泛的应用。为了研究倾斜射流撞击壁面后形成的液膜的关键特征，开展单股圆柱射流撞击壁面的实验研究。从实验中研究各射流参数对液膜外形的影响规律，继而开展理论建模，获取液膜外形的关键几何参数表达式。实验研究发现随着射流倾角增大，液膜长度减小而宽度增大，随着射流孔径和射流速度增大液膜长度和宽度均增大这一定性规律。理论分析得到了液膜最大宽度位置与液膜对称面的夹角近似等于射流倾角α，液膜的长宽比近似等于1+cot α。通过进一步分析得到液膜宽度、最大宽度距撞击点的距离、液膜长度这几个液膜关键参数的表达式。建立的液膜几何参数表达式预测结果与实验结果的误差均在20%以内。     

Non-destructive Evaluation of Absolute Stress in Steel Members Using Shear-Wave Spectroscopy

Non-destructive measurement of absolute stress in steel members can provide useful information to optimize the design of steel structures and allow the safety of existing structures to be evaluated.This paper investigates the non-destructive capability of ultrasonic shear-wave spectroscopy in absolute stress evaluation of steel members.The effect of steel-member stress on the shear-wave amplitude spectrum is investigated,and a method of absolute stress measurement is proposed.Specifically,the process for evaluating absolute stress using shear-wave spectroscopy is summarized.Two steel members are employed to investigate the relationship between the stress and the frequency in shear-wave echo amplitude spectrum.The H-beam loaded by the universal testing machine is evaluated by the proposed method and the traditional strain gauge method for verification.The results show that the proposed method is effective and accurate for determining absolute stress in steel members.     

Inertial aided BDS triple-frequency integer ambiguity rounding method

The integer ambiguity resolution (AR) of carrier phase is significant for Global Navigation Satellite System (GNSS) precise positioning. However, in kinematic case, single-epoch AR methods based on alone GNSS are usually not reliable due to the instable pseudorange accuracy. Moreover, the computation of classical AR method Least Squares Ambiguity Decorrelation Adjustment (LAMBDA) is large. Thus, the inertial measurement unit (IMU) is introduced, a new inertial-aided AR method that directly rounds the float ambiguity of BeiDou triple-frequency combined observations, which is characterized by long wavelength, low carrier-phase noise and ionospheric delay, is proposed. The mathematical model of the new method is derived first. Then the impacts of the carrier-phase noise, ionospheric delay and inertial navigation system (INS) position error on the AR success ratio of combined observation are analyzed through probabilistic approach. Based on above investigation, the combinations (0, ?1, 1), (1, 4, ?5) and (4, ?2, ?3) are selected to resolve the original ambiguity. A vehicular integrated navigation test is performed to demonstrate the proposed method. The results show that the average AR success ratios of the three selected combinations, whose float ambiguity errors are 0.041, 0.146, 0.279 cycle respectively, are above 97.25% without regard to low-elevation C05. With respect to positioning accuracy based on our AR method when compared with IE software, the east, north, up error RMS of position are 0.042, 0.024, 0.069 m, respectively. In terms of the AR recover after the BeiDou signals outage, as long as 62 s BeiDou signal complete outage, all the ambiguities of all satellites could be re-fixed immediately. Besides, during the 90 s signals partial outage, the AR is not influenced by the position error, since the float ambiguity errors are all below half-cycle. The research of this contribution demonstrates the effectiveness of the proposed new method, which indicates it is applicable to kinematic positioning, even in BDS degraded and denied environments.     

风云二号卫星地面控制系统自适应同步控制方法

针对风云二号07星测控实施过程中部分姿章联控参数未能正常执行的系统间时序控制不同步问题,研究提出一种地面控制系统自适应同步控制方法,分析卫星历史数据得到有效接收时间区间,取所有有效接收时间区间的交集得到最终有效接收时间区间。经验证,方法可有效解决系统间时序不同步的问题,精度高,控制效果好。     

Hierarchical scheduling for real-time agile satellite task scheduling in a dynamic environment

The imaging processes of optical satellites can be easily affected by unexpected environmental changes, such as changes in cloud coverage. Given the difficulty to predict environmental uncertainties, traditional offline scheduling methods need a follow-up re-scheduling process that responds to real-time environmental information. This repetitive scheduling processes make the offline fine scheduling process a waste of computational resources. Additionally, the offline scheduling method is quite complex owing to its lack of a hierarchy mechanism. To solve these problems, we propose a hierarchical scheduling method for the real-time scheduling problem. This method divides the scheduling process into three steps: pre-assignment, rough scheduling, and fine scheduling. A hierarchical scheduling algorithm based on ant colony algorithm is proposed. Tests with 36 scenarios show that the calculation time is efficiently reduced with this new mechanism. With this consideration of the dynamic environment, the re-scheduling process becomes unnecessary, meaning the wasting of computational resources is avoided and the solution profit is improved.     

变化风场对舰载飞机着舰安全性影响

建立了复杂环境下舰载机进舰着舰的数学仿真模型,并通过大量的仿真计算,研究了舰尾流和侧风风场对舰载机进舰着舰安全性的影响,给出了一定进舰条件下舰载机所能抗御的最大侧风强度.研究结果表明,舰载机在进舰过程中必须通过驾驶员操纵抑制舰尾流扰动,否则将引起较大的着舰偏差,影响着舰安全;对于一定的进舰初始条件,舰载机只能抗御一定强度的侧风,超出允许侧风强度时舰载机将不能成功着舰.