空间光学遥感器主镜加工过程中疲劳寿命研究

针对空间光学遥感器主镜镜面加工过程中,磨盘与主镜间磨削动作往复运行引起的主镜柔性支撑结构疲劳寿命问题,通过建立主镜组件的有限元模型,利用MSC.Fatigue软件按应力-寿命(S-N)法对主镜组件进行了疲劳寿命分析,确定了支撑结构的薄弱部位,并对仿真过程进行了误差分析,讨论了影响仿真结果的各个因素.对比热真空试验和动力学试验前后主镜镜面面型数据,验证了支撑结构加工、设计参量的合理性.通过疲劳寿命仿真分析,可以有效预示光学结构在加工过程中的疲劳情况,为空间光学遥感器结构的设计、加工提供理论依据和参考.     

空间光学遥感器主镜加工过程中疲劳寿命研究

针对空间光学遥感器主镜镜面加工过程中,磨盘与主镜间磨削动作往复运行引起的主镜柔性支撑结构疲劳寿命问题,通过建立主镜组件的有限元模型,利用MSC.Fatigue软件按应力-寿命(S-N)法对主镜组件进行了疲劳寿命分析,确定了支撑结构的薄弱部位,并对仿真过程进行了误差分析,讨论了影响仿真结果的各个因素.对比热真空试验和动力学试验前后主镜镜面面型数据,验证了支撑结构加工、设计参量的合理性.通过疲劳寿命仿真分析,可以有效预示光学结构在加工过程中的疲劳情况,为空间光学遥感器结构的设计、加工提供理论依据和参考.     

激光空间合束主镜优化设计与分析

本文对激光空间合束主镜进行优化设计与分析,以抑制强激光空间合束系统主镜热畸变,提高主镜面形精度。首先,对比分析了选择不同材料作为主镜基底的优缺点,从理论上初步确定了主镜材料、镜体厚度、支撑方式和轻量化结构形式;然后,利用有限元方法对空间合束主镜进行了热畸变分析,并结合热畸变结果对镜体结构形式进行拓扑优化设计;最后,对主镜进行重力、环境适应性和基频分析,验证设计的合理性。分析结果表明:6光合束主镜在单束10 kW激光辐照下,随着辐照时间的增加,镜面温升值和P-V值逐渐增大;辐照3 min后初设计主镜表面温度达83.4℃,P-V值为155 nm,受镜体结构影响,辐照区内热畸变值不一致,差值约占镜面P-V值的1/6;为改善热畸变的不一致性,提高镜体强度,对主镜进行拓扑优化设计,优化后主镜轻量化达54.5%,辐照区热畸变一致性好,镜面热畸变量减小了近1/3;不同俯仰姿态下,主镜重力变形值基本相同,不足10 nm;环境温度的改变会引起主镜的镜面畸变和平移,稳态温差值越大,主镜面形P-V值和镜面平移量越大;模态分析显示主镜基频满足系统要求。本文研究结果将对激光空间合束系统的设计提供依据。     

温度对大口径主镜面形变形的影响分析

从理论上论述了温度梯度对主镜面形变形的影响,分析了当光轴位置不同、主镜支撑方式不同时,在轴向温度梯度和径向温度梯度作用下的面形变形。通过计算,得出轴向温度梯度对面形变形的影响要远大于径向温度梯度对面形的影响,而且镜面变形不仅与主镜的线胀系数和其他材料、结构特性参数有关,与温度梯度的大小和方向均有密切的关系。     

大口径平背形主镜背部支撑位置优化计算方法

针对背部支撑方式的平背形反射镜,提出了一种确定主镜最佳背部支撑位置的优化计算方法。利用AN-SYS软件中的APDL语言建立了主镜的参数化模型。利用有限元法,以主反射镜光轴垂直时自重作用下的镜面最大变形量为目标函数,以相同工况下一阶自振频率为约束条件,对背部支撑点位置的相关参数和中心镜厚进行了优化分析,得到了满足镜面面型误差要求的最佳背部支撑位置及中心镜厚。     

温度和支撑方式对1.2 m SiC主镜面形的影响分析

为了研究温度和支撑方式对大口径SiC主镜用于地基望远镜的影响,基于1.2 m SiC主镜建立了有限元模型,分析了主镜在被动支撑和自由膨胀时,恒定温度场,轴向温度梯度,径向温度梯度和内外温差等对主镜面形的影响.结果表明,存在温度梯度时,支撑方式影响不明显,无论是被动支撑还是自由膨胀,镜面面形均很大.在达到热平衡后,即稳态温度场下,支撑方式的影响明显,只有在主镜自由膨胀时,温度对主镜面形的影响比较小,镜面的RMS<0.02 nm/℃.因此如果主镜采用柔性支撑或浮动支撑方式,大口径SiC主镜可以应用在地基望远镜中.     

经纬仪主镜在支撑系统下的面形变化

为研究在重力作用下主镜支撑系统对经纬仪主镜处于不同工作角度时面形误差的影响,以600 mm口径主镜为研究对象,利用Abaqus软件分别建立了600 mm主镜在加工状态下和工作状态下的有限元支撑模型,并进行了重力变形分析,然后借助4D干涉仪对在不同支撑系统下的主镜进行相关的面形检测。实验结果表明,在吊带支撑系统和主镜室支撑系统下,主镜的自身面形误差RMS为16.18 nm和16.90 nm。利用有限元分析了理想状态的主镜在不同仰角工况下的面形误差,结合主镜自身的面形误差,计算得到了主镜面形误差在光轴由水平变化到竖直的过程中逐渐变大,其RMS最大为19.58 nm,表明该主镜室支撑系统具有良好支撑效果,可满足工程要求,同时也验证了主镜室支撑系统有限元理论模型的准确性。     

φ1.8m轻质镜能动磨盘技术抛光的柔性限位支撑设计仿真与优化分析

大口径轻质反射镜采用柔性支撑结构可以降低外界力载荷、惯性载荷及热载荷的负作用,从而保证光学系统的成像质量。为消除加工、检测与系统装调过程的定位误差,研究了应用于计算机控制能动磨盘加工(CCAL)技术抛光的柔性限位支撑模型。利用有限元分析软件(Ansys),分析φ1.8m轻质镜采用柔性限位支撑时,CCAL技术抛光引起轻质镜的最大倾斜量、最大主应力以及主镜面变化范围,对支撑盘的口径及位置进行了优化设计,模拟仿真18点弹簧在不同压缩量下的镜面变形。仿真分析结果表明,柔性限位支撑的结构刚度、轻质镜底板倾斜量满足能动磨盘加工条件,最大主应力强度远小于主镜的许用应力,主镜面变形符合加工要求。     

8m能动薄主镜侧支撑设计

薄主镜支撑系统分为轴向和侧向支撑两部分,侧向支撑承担主镜垂直于光轴方向的重力分量。介绍了pushpull-shear侧支撑及能动校正原理,并针对一块8 m口径薄主镜进行了侧支撑设计。设计了5种备选侧支撑方案,并考虑到主镜对面形的能动校正能力,借助有限元计算对它们进行了分析和比较,选出了一种最佳方案作为8 m薄主镜的侧支撑方案。该侧支撑方案共有64个侧支撑点,每个侧支撑点仅施加沿主镜切向的支撑力。当主镜竖直放置时,主镜能动校正后的镜面均方根值为19.2 nm,校正力范围为-318.9~301.4 N。相比传统push-pull-shear侧支撑方式,该侧支撑方案结构简单,易于实现,同时支撑效果良好。     

一种光学仪器镜面面形的处理方法

光学镜面表面变形包含刚体位移和表面畸变,其中表面畸变是影响成像质量的主要因素,因此需去除刚体位移,分析表面畸变。通过坐标变换生成一个新的理论镜面,用该镜面拟合变形镜面,用拟合镜面与变形镜面轴向差值计算出表面畸变的RMS值及PV值。实例计算表明该算法拟合精度较高,适用于抛物面、球面镜在支撑和装夹下的镜面面形精度分析。     

Analysis of integrated corner mirrors by using a wide-angle beam propagation method

An integrated corner mirror is analyzed by using a two-dimensional (2D) wide-angle beam propagation method (WA-BPM) combining with an effective index method (EIM). Both the reflection efficiency and the phase variation due to a total internal reflection (TIR) for the TE and TM modes are calculated. A non-perfect fabrication (such as a tilted or displaced mirror) introduces an additional reflection loss and some errors of the phase variation. The additional reflection loss due to a tilted mirror increases rapidly as the tilted angle increases and becomes more sensitive to the tilted angle when the confinement of the waveguide becomes weaker. It is shown that the displacement of a mirror influences the phase variation greatly and the difference of the phase variation between the TE and TM modes is not sensitive to the displacement of the mirror.     

高斯反射镜及其倾斜对平凹腔激光场分布的影响

 从菲涅尔-基尔霍夫衍射积分公式出发，运用边界元法数值计算了平凹腔平面镜均匀反射率时倾斜和未倾斜情况下基模的场强分布、相位分布和本征值，同时与高斯反射率平面镜在腔镜倾斜时的情况做了比较。研究表明，腔镜倾斜使激光场模式分布沿发生倾斜的方向向镜边缘偏移，而且在腔镜倾斜较严重时模式分布发生畸变，不再是对称的高斯分布，基模本征值随倾斜角增大而变小，光束远场分布变差。同等条件下，高斯反射率平凹腔腔镜倾斜对谐振腔引起的模畸变小于均匀反射率平凹腔，且基模光场及本征值随镜倾斜的变化关系稍不同于均匀反射率平凹腔。     

空间遥感器高体份SiC/Al复合材料反射镜组件设计

为消除反射镜与支撑结构材料线胀系数差异产生的热变形对反射镜面形精度、系统成像质量的影响, 采用高体份SiC/Al复合材料作为新型反射镜组件的材料。首先, 通过合理的结构设计及有限元分析比较, 确定了Ф600 mm口径反射镜结构参数, 然后, 对反射镜组件进行了静力学和动力学分析, 在1 g重力载荷作用下, 反射镜X、Y、Z方向去除刚体位移后的镜面变形RMS值分别为12.6, 12.7, 12.6 nm, 达到了λ/50(λ=632.8 nm)。最后, 为了验证高体份SiC/Al复合材料反射镜组件的结构性能及检验结构在振动条件下的抗干扰能力, 对反射镜组件进行了力学试验, 反射镜组件的一阶谐振频率为556.6 Hz。力学试验前后, 反射镜镜面面形误差RMS分别为0.021λ、0.025λ, 没有明显变化。实验结果表明:高体份SiC/Al复合材料反射镜达到了与SiC材料反射镜相同的设计指标要求, 能够满足空间应用。     

Ф210mm超薄超轻SiC反射镜多目标集成优化设计

为了提高轻小型碳化硅反射镜的面形精度并减轻其加工成本,针对某空间相机的Φ210mm SiC反射镜进行超轻量化设计.采用背部三点支撑并优化支撑点的位置,通过拓扑优化,得到反射镜背部需保留和可去除材料的分布情况.结合背部开放式、三角形孔的轻量化方案,确定反射镜轻量化结构的初始模型.应用多目标集成优化方法,建立以反射镜重量和X向自重工况面形为目标,Z向自重工况面形值为约束的优化模型,对该反射镜进行了优化设计.优化后反射镜的X向自重工况下RMS值仅为0.18nm,Z向自重工况下RMS值为2.38nm,重量仅为0.568kg,面密度达到16.9kg/m~2,X、Y、Z三向基频都在500Hz以上.本文设计的反射镜结构有良好的力学性能,本文优化设计方法是合理有效性.     

基于光线追迹的单频激光多重回馈效应研究

提出一种基于非准直平凹回馈腔的单频激光多重回馈光线追迹模型,采用该模型阐明了单频激光多重回馈效应的产生机理,分析了多重回馈高分辨率条纹的特性,明确了影响多重回馈条纹形状的主要因素,包括回馈镜的倾角、曲率半径、反射率以及回馈外腔长等,获得了回馈镜在不同倾角时的有效回馈阶次及其耦合系数。光线追迹分析与实验结果表明:当回馈镜倾斜角为1.7时,多重回馈效应会产生调制幅度均匀、没有大包络的高分辨率回馈条纹,每个条纹的分辨率可达/50。     

Molecular Dynamic Simulation of High Speed Deformation Effect on Microstructure Change in Thermal Heated Metals

In the present paper computer simulation of high-speed deformation (shock wave propagation) by molecular dynamic method is performed in thin copper sample, having the form of rectangular parallelepiped (10 a ‐ 10 a ‐ 20 a , where a is the lattice constant) with 8000 atoms. On the surfaces Z 0 =0 and Z max =20 a the mirror boundary conditions with rigid walls and the periodic boundary conditions along X and Y directions corresponding to short sides of deformed crystal are used, which allows to investigate the reflection of shock wave from the surfaces in Z direction. The changes of microstructure have been investigated up to 12 ps. The numerical calculations of microstructure changes have been performed here taking into account the effect of thermal heating of crystal lattice before shock wave front. The numerical results show that comparing with the propagation of shock waves under room temperature in thermal heated structure additional displaced atoms (vacancies and interstitials) are produced. The obtained results show that the production of point defects during high-speed deformation is determined by the thermal softening of microstructure and generation rate of point defects very strong increases with an increasing of high speed deformation rate. The peculiarities of microstructure changes in deformed copper are analyzed here at the different initial temperatures and various high-speed deformations (average ion velocities behind shock wave).     

Scattering of electromagnetic radiation by surfaces with a fractal relief

The scattering indicatrix of electromagnetic waves for different types of rough surfaces and angles of incidence is calculated using the Kirchhoff scalar theory. The rough surfaces are modelled by a two dimensional Weierstrass function. The scattering index for a rough surface with a fractal relief is found to have a complicated structure with intensity bursts in directions quite far from the direction of mirror reflection.     

Scattering of a narrow wave beam by a randomly rough locally diffuse surface subject to pulse illumination

We consider the scattering of a narrow pulse wave beam by a randomly rough surface with a complex local scattering indicatrix. Analytical expressions are found for the mean received power for a normal distribution of heights and slopes of the surface in two cases: where the direction to the receiver is close to the direction of mirror reflection and where the direction to the receiver is very different from the direction of mirror reflection. It is shown that in these two cases the echo pulse is very different in shape and is controlled by the parameters of the source and receiver, the sounding scheme, and the variance of heights of a rough surface. The received power is strongly dependent on the width of the local scattering indicatrix, and the form of this dependence is determined by the angles of illumination and reception. The analytical expressions for the mean received power are in good agreement with the results of numerical calculations. Institute for Radioelectronics and Laser Engineering of the N. é. Bauman State Technical University of Moscow, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol.42, No.4, pp. 333–339, April 1999.     

Design of a tilted two-mirror system

Formulae have been derived for eliminating main aberrations on the center of field of the tilted two-mirror system (TTS). The spherical aberration may be eliminated by considering the TTS as a co-axial system. The coma on the center of field will be reduced by conserving certain relationships between the tilting angles of the primary mirror and the secondary. In order to cancel the astigmatism on the center of field, one of the two mirrors must have bi-curvature at the vertex of the mirror. Ray tracing shows that the TTS solved by the given equations produces quite good image quality within a small field of view. In order to increase the useful field of view, the bi-curvature mirror with the shape 0L an inverse ellipsoid must have high order terms in its surface equation.