小直径超薄壁管纵缝的激光焊接

小直径超薄壁管纵缝焊接的主要问题是烧穿,解决这个问题的关键是严格控制焊接接头的装配质量及焊接工艺。本文介绍了采用激光焊接小直径超薄壁管纵缝的焊接经验,对整个生产过程中的关键问题进行了分析。     

基于神经网络的激光陀螺误差测试与建模

用人工神经网络中的反向误差传播网络(BP网络)来建立温度补偿模型,通过训练后的BP网络对刻度因子误差以及随机漂移进行温度补偿。     

激光辐照充压柱壳温度场和应力场数值模拟

考虑了材料参数随温度的变化,用有限元法计算了充压柱壳在不同预应力载荷、光强分别为均匀分布和高斯分布的激光辐照下的瞬态热力学耦合过程,计算出温度场和应力场。分析了热力学耦合规律,给出了破坏的危险部位。计算得到,应力峰值出现在激光加热的高温区和常温区的交界处;对于光强高斯分布,破坏首先发生在光斑中心附近;而对光强均匀分布,破坏首先会发生在边缘处。     

KrF激光对高速飞片的驱动特性研究

利用诱导空间非相干技术平滑的KrF准分子（248nm）激光驱动带有烧蚀层的平面靶，研究激光空间均匀性对产生完整飞片的影响，结果表明激光不均匀性在2％以下，能够产生完整的高速飞片，且完整飞片能够维持20ns以上不破裂；当激光不均匀性达到5％，激光引入流体力学不稳定性种子应很强，冲击波在靶内输运过程中不稳定性不断发展增强，到靶背时强到足以使飞片解体甚至气化，不能产生完整的飞片。为了获得尽可能高的飞片速度，采用激光与烧蚀层参数不匹配方法，使冲击波对飞片作多次加速。利用功率密度为1012 W/cm2的KrF激光与含50μm Kapton烧蚀层的5μm铝飞片作用，得到速度约10km/s的高速飞片，与模拟结果吻合得很好。     

Mission feasibility analysis on deflecting Earth-crossing objects using a power limited laser ablating spacecraft

This paper analyzes several mission capabilities to deflect Earth-crossing objects (ECOs) using a conceptual future spacecraft with a power limited laser ablating tool. A constrained optimization problem is formulated based on nonlinear programming with a three-dimensional patched conic method. System dynamics are also established, considering the target ECO’s orbit as being continuously perturbed by limited laser power. The required optimal operating duration and operating angle history of the laser ablating tool are computed for various types of ECOs to avoid an Earth impact. The available final warning time is also determined with a given limited laser power. As a result, detailed laser operating behaviors are presented and discussed, which include characteristics of operating duration and angle variation histories in relation to the operation’s start time and target object’s properties. The calculated durations of the optimal laser operation are also compared to those estimated with first-order approximations previous studies. It is discovered that the duration of the laser operation estimated with first-order approximations could result in up to about 50% error if the operation is started at the final warning time. The laser operation should be started as early as possible because an early start requires a short operating duration with a small operating angle variation. The mission feasibility demonstrated in the present study will give various insights into preparing future deflection missions using power limited spacecraft with a laser ablation tool.     

粒子拖尾长度对高频DPIV测量误差的影响

基于连续激光源的高采样频率DPIV系统在进行曝光时可能会产生粒子拖尾现象。明渠湍流试验和数值模拟试验结果显示，粒子拖尾长度的增加会导致平均流速减小和湍流强度增大。分析表明，导致平均流速误差的原因之一是诊断窗口边缘局部粒子图像的缺失，且图像缺失程度会随着粒子拖尾长度增加而增大，从而使平均速度随粒子拖尾长度增加而减小；粒子拖尾的另一个直接后果是增大了粒子图像的有效粒径，从而导致湍流强度增大。通过增大第二个诊断窗口的尺寸，进行相关函数标准化和相关系数补偿等方法，可以消除粒子拖尾长度引起的误差。     

Influence of atmospheric turbulence on planetary transceiver laser ranging

In this paper we investigate the influence of atmospheric turbulence on the performance of the uplink of a planetary transceiver laser ranging system using a single photon detector. We numerically combine the influence of turbulence in the mean intensity profile variations, scintillation, beam-wander induced pointing errors and stochastic time-of-flight variations, using the Hufnagel–Valley turbulence profile to model the ground turbulence behavior. We map the intensity variations due to turbulence to variations in the probability distribution of the arrival time of the 1st photon in a laser pulse, which influences the range measurement error probability distribution. The turbulence models are applied to assess the influence on single-pass range accuracy and precision statistics, as well as the parameter estimation quality of a Phobos Laser Ranging (PLR) mission.     

Lightweight structure of a phase-change thermal controller based on lattice cells manufactured by SLM

Thermal controllers equipped with phase-change materials are widely used for maintaining the moderate temperatures of various electric devices used in spacecraft. Yet, the structures of amounts of thermal controllers add up to such a large value that restricts the employment of scientific devices due to the limit of rocket capacity. A lightweight structure of phase-change thermal controllers has been one of the main focuses of spacecraft design engineering. In this work, we design a lightweight phase-change thermal controller structure based on lattice cells. The structure is manufactured entirely with AlSi10 Mg by direct metal laser melting. The dimensions of the structure are 230 mm × 170 mm × 15 mm, and the mass is 190 g, which is 60% lighter than most traditional structures(500–600 g) with the same dimensions. The 3 D-printed structure can reduce the risk of leakage at soldering manufacture by a welding process. Whether the strength of the designed structure is sufficient is determined through mechanical analysis and experiments. Thermal test results show that the thermal capacity of the lattice-based thermal controller is increased by50% compared to that of traditional controllers with the same volume.     

航空发动机叶片激光冲击处理过程控制研究

分析了在水约束模式下,光路、约束层、吸收层、靶材等主要因素对激光冲击处理过程控制工艺稳定性的影响。通过研究LSP、MIC、GE、RR等公司在航空发动机叶片激光冲击处理稳定性方面的经验,特别是涉及工艺稳定性的约束控制、光路清理、质量控制等技术,结合叶片激光冲击处理的工艺试验,系统地研究了航空发动机叶片激光冲击处理工艺稳定性的关键控制技术。     

沟槽面湍流边界层湍流度分布

应用激光测速(LDV)技术对沟槽面湍流边界层湍流度分布进行了精细的测量,实验结果表明,在湍流边界层区域沟槽面湍流度最大值比光滑面要小,但出现的位置比光滑面要远.此外,紧靠沟槽面,即y++<4内,沟槽面有较大的湍流度,说明沟槽面有使近壁区流动紊动增加的趋势.对于y/δ≥0.06的区域,湍流度可用u′\u=2.3 exp (-0.9y/δ)描述,而在y/δ<0.06内,则有u′/u =36.4y/δ.