Active Control of Free Paraboloidal Membrane Shells Using Photostrictive Actuators

The paraboloidal membrane shell with free boundary condition is actively controlled using photostrictive actuators which can provide contactless actuation under the illumination of ultraviolet light. The governing equations of the paraboloidal shell laminated with paired photostrictive actuators are established based on membrane approximation. The modal control actions of meridional/circumferential actuators are respectively formulated and evaluated by case studies. Constant light intensity related to the velocity of the shell is adopted, and then the governing equations are written in a closed-loop form which can be solved with Newmark-β method. Considering the multi-field coupling behavior of photostrictive actuators, time histories of transverse displacement and control light intensity are simulated and evaluated. The results show that photostrictive actuators can effectively control the vibration of the paraboloidal membrane shell, and the photostrictive actuators oriented along circumferential direction can give better control effect than photostrictive actuators placed along the meridional direction.

Theories and Analyses Thick Hyperbolic Paraboloidal Composite Shells

This paper presents the stress resultants of hyperbolic paraboloidal shells using higher order shear deformation theory recently developed by Zannon [1]-[3]. The equilibrium equations of motion use Hamilton’s minimum energy principle for a simply supported cross-ply structure by Zannon (TSDTZ) [2] [3]. The results are calculated for orthotropic, two-ply unsymmetrical [90/0] shells. The extensional, bending and coupling stiffness parameters are calculated using MATLAB algorithm for laminated composite hyperbolic paraboloidal shells. A comparison of the present study with other researchers in the literature is given, and is in good agreement.

Bioconvection Mangnetohydrodynamic Tangent Hyperbolic Nanofluid Flow with Quartic Chemical Reaction Past a Paraboloid Surface

In this numerical study,the effect of quartic autocatalysis type of chemical reaction,buoyancy force and thermal radiation phenomenon and magnetic effect on tangent hyperbolic nanofluid past an upper horizontal surface of a paraboloid has been studied.By considering the Buongiorno model approach,a diffusion of unequal coefficients in the presence of gyrotactic microorganism is discussed.Implementation of microorganism’s idea is used to stabilize the nanoparticles through bioconvection.The modeled PDEs of the problems are converted into nonlinear ODEs with the assistant of the similarity transformations.To tackle nonlinear ODEs,MATLAB package bvp4c is used.In addition,a hallmark of the Matlab code with the reported results in the literature is achieved by benchmarking.The variations in motion,concentration,temperature,and motile density due to sundry parameters have been analyzed in-depth via graphs.Our analysis shows that the density profile of motile of microorganism is hiked with an increment in the bioconvection Rayleigh number but decreases for higher thermal Grashof number.

A Yield Mapping Procedure Based on Robust Fitting Paraboloid Cones on Moving Elliptical Neighborhoods and the Determination of Their Size Using a Robust Variogram

The yield map is generated by fitting the yield surface shape of yield monitor data mainly using paraboloid cones on floating neighborhoods. Each yield map value is determined by the fit of such a cone on an elliptical neighborhood that is wider across the harvest tracks than it is along them. The coefficients of regression for modeling the paraboloid cones and the scale parameter are estimated using robust weighted M-estimators where the weights decrease quadratically from 1 in the middle to zero at the border of the selected neighborhood. The robust way of estimating the model parameters supersedes a procedure for detecting outliers. For a given neighborhood shape, this yield mapping method is implemented by the Fortran program paraboloidmapping.exe, which can be downloaded from the web. The size of the selected neighborhood is considered appropriate if the variance of the yield map values equals the variance of the true yields, which is the difference between the variance of the raw yield data and the error variance of the yield monitor. It is estimated using a robust variogram on data that have not had the trend removed.

Surface registration algorithm for rapid detection of surface thermal deformation of paraboloid antennas

In order to obtain and master the surface thermal deformation of paraboloid antennas,a fast iterative closest point( FICP) algorithm based on design coordinate guidance is proposed,which can satisfy the demands of rapid detection for surface thermal deformation. Firstly,the basic principle of the ICP algorithm for registration of a free surface is given,and the shortcomings of the ICP algorithm in the registration of surface are analysed,such as its complex computation,long calculation time,low efficiency,and relatively strict initial registration position. Then an improved FICP algorithm based on design coordinate guidance is proposed. Finally,the FICP algorithm is applied to the fast registration test for the surface thermal deformation of a paraboloid antenna. Results indicate that the approach offers better performance with regard to fast surface registration and the algorithm is more simple,efficient,and easily realized in practical engineering application.

Deployment dynamics for flexible deployable primary mirror of space telescope with paraboloidal and laminated structure by using absolute node coordinate method

A nonlinear dynamic modeling method for primary mirror of Flower-like Deployable Space Telescope(F-DST)undergoing large deployment motion is proposed in this paper.To ensure pointing accuracy and attitude stability of the paraboloidal primary mirror,the mirror is discretized into equal thickness shell elements by considering shell curvature.And the material nonlinear constitutive relation of flexible mirror is acquired using Absolute Nodal Coordinate Formulation(ANCF).Furthermore,the primary mirror of F-DST can be regarded as a clustered multi-body system,and its dynamic equations of elastic deformation and deployment motion are established by virtual work principle.Finally,the deployment motion of primary mirror by different driving conditions are simulated,the results show that the vibrations of mirrors that driven by elastic hinge device are more than that driven by servo motor.In addition,single sub-mirror deployment process will perturb the pointing accuracy of primary mirror,and the multiple sub-mirrors simultaneously deploying will seriously affect all the sub-mirrors surface accuracy because of the coupling effect.Thus,there are theoretical value and practical significance for the controlling surface accuracy and attitude accuracy of space telescope.

C频段的“推扫式”卫星扫描天线

该设计结合科研实际需求,研制了工作在C频段的“推扫式”卫星扫描天线。首先,从“推扫式”卫星扫描天线的原理出发,对所需要的环焦反射面进行了优化建模,提出一种新型扇形反射面圆角化的方案,并针对密集馈源阵进行分析。通过计算得到了馈源的位置坐标,在仿真软件GRASP中构造反射面天线的整体模型。为了使密集馈源阵的主波束满足设计指标,设计了遗传算法优化合成后的波束来实现对主波束的优化,通过改变馈源阵的幅相值以达到天线方向图的设计要求,利用仿真优化得到了C频段中心波束达到设计指标所需要的馈源阵规模。最后,对整体模型进行了加工组装。使用近场测量的方法在微波暗室中对天线进行测试,测试结果表明天线波束宽度为0.6°时,主波束效率为98.17%,大于98%,满足设计要求。

静电成形薄膜反射面天线的裁剪设计

该文通过裁剪和拼接平面薄膜片来对静电成形薄膜反射面天线的表面进行设计制作。由于抛物面型薄膜反射面是一个不可展开表面,通常由许多平面薄膜片制作而成,将不可避免地降低反射面表面的精度。因此,需要详细地分析裁剪和拼接过程对反射面表面精度的影响,从而获得设计需要的表面精度。该文基于旋转抛物面的无矩理论建立了工作状态的反射面模型,采用常应变三角形单元离散反射面,建立了反射面的展平和拼接有限元模型。将同口径反射面沿经线划分若干组不同数量子曲面,通过子曲面进行展平和拼接数值仿真分析,对薄膜反射面进行裁剪设计。最后,制作了0.55 m口径的薄膜反射器,并进行了摄影测量实验。验证了该方法的有效性,并讨论了制造误差的影响。

基于数据驱动的FAST主动反射面调节优化模型

针对500 m口径球面射电望远镜(five-hundred-meter aperture spherical radio telescope,FAST)的主动反射面调节问题,利用旋转抛物面在三维空间中的定义建立了一个对任意天体角度均适用的工作抛物面方程,该方法不同于以往的坐标旋转的方法。利用反射面板重心点作为反射点,将反射接收比定义为能把光线反射到馈源舱被其接收的面板数量与300 m口径工作抛物面下总面板数量的比值。结合主索节点径向伸缩距离、边界平稳过度和邻接距离变化幅度三个约束条件,以接收比最大化作为目标函数,建立了一个工作抛物面优化模型,并利用节点数据和模拟退火算法对其进行求解,得到了工作理想抛物面。选用两组天体角度进行实例分析,结果显示调节后的接收比增大12.82%,并给出了工作主索节点的部分径向调节方案。本研究为FAST对于任意天体角度的变形提供了一种新的建模方法,也对馈源舱反射接收比提出了一种新的计算方式。

离轴抛物面超精密加工轨迹时间序列控制方法

离轴抛物面超精密加工轨迹容易出现不可控轴与可控轴位置势函数不一致现象,影响加工次序,导致加工效果不理想。针对该问题,提出了离轴抛物面超精密加工轨迹时间序列控制方法。分析离轴抛物面超精密加工过程,计算点与点之间的旋转角度。以机床零点为基准,将笛卡尔坐标系中零件外形表达式转化到柱坐标系中,使工件方程的坐标系完成转换。将加工轨迹点时间间隔映射成0~1的数值,设定各个处理时间内时间权重,使得各个加工时间点间交互作用。检测基于轨迹点分布聚簇性的加工轨迹,分析加工轨迹聚集特性,消除各种轨迹之间的时间间距对轨迹的影响。采用PMAC的时基控制方式,保证不可控轴与可控轴位置势函数一致。以移动点更新速率为主要计算参量,将实时输入频率作为时基控制的输入频率,以非控制轴为输出频率,由此实现加工轨迹时间序列的时基控制。通过试验验证结果可知,该方法能够获取以(-150,300,0)为加工轨迹中心的完整超精密加工轨迹,且不会出现投影畸变现象,有效控制加工轨迹时间序列。

某单层椭圆抛物面网壳结构荷载试验

网壳结构杆件和节点几何尺寸的偏差以及曲面的偏离对网壳的内力、整体稳定性影响较大。而在既有网壳结构安全鉴定过程中发现质量偏差时,承载力计算应考虑这些偏差情况,但标准并未给出具体方法,文章以某单层椭圆抛物面网壳结构荷载试验为背景,通过荷载试验检验某单层椭圆抛物面网壳结构存在质量偏差的同时,增加额外吊挂荷载情况下结构的承载能力,并为提高结构承载力复核模型的准确性提供依据。

风荷作用下的抛物面天线用螺栓强度分析

为保证实现风载作用下的∅1.3m抛物面天线的功能以及可靠性,对该类型天线上选用的螺栓进行受力计算和强度校核,得出该天线所用螺栓能够满足强度要求。为了验证计算结果的正确性,又对该天线选用的螺栓进行了实验验证,试验结果与计算结果吻合好。该校核计算及验证方法可为同类型天线整体结构设计和螺栓强度校核提供参考。

山坡锚固式超大跨径空间缆索人行悬索桥探讨

为了降低峡谷景区超大跨径人行悬索桥的造价,提出一种山坡锚固式空间交叉网缆索体系的人行悬索桥。在峡谷景区两侧岩石山坡体之上,分散锚固马鞍抛物面空间交叉网缆索体系,取消桥塔结构,降低造价。相比左右两根互相分离的平行缆索体系,马鞍抛物面空间交叉网缆索体系可以产生水平向的分力,解决了人行悬索桥的大幅度侧向摆动问题,提高了峡谷景区人行悬索桥的抗风稳定性。结合某500 m级峡谷景区超大跨径人行悬索桥工程,开展动力模态分析,以便验证山坡锚固式空间缆索体系人行悬索桥的优越性。

某网壳结构分析与设计

某地上连体结构位于四个地块交汇处,采用单层双曲抛物面网壳+预应力拉索杂交的结构形式,网壳下方有栈桥与其形成一体。介绍了该网壳的概况、结构传力体系、设计标准和荷载,以及网壳的承载力、变形,结果表明杆件承载力和变形满足规范要求;介绍了网壳的整体稳定分析,包含几何非线性稳定和几何双非线性稳定分析,结果表明网壳的稳定承载力满足规范要求。此外,还介绍了该工程复杂相贯节点的有限元分析,该项目风洞试验及风荷载取值方法。

基于外置光阑针孔相机的高精度偏折测量技术

设计了一种外置光阑的针孔相机镜头,可免去传统方法复杂的相机标定过程,采用影像仪和三坐标测量机实现测量系统各元件空间位置的几何标定,并依靠相移算法实现屏幕与相机像素的精准匹配。实验结果表明,本文提出的偏折测量结果与干涉仪测试结果偏差优于20 nm RMS,可满足光学镜面加工研磨阶段到抛光阶段的过渡测量需求,为光学加工车间提供了可靠、经济、高效的面型评估,具有广泛的应用前景。

圆锥面与抛物面组合的类牛顿环干涉图样研究

在普通(典型)牛顿环的基础上,讨论由直线旋转形成的圆锥面与二次曲线旋转形成的抛物面或平凸(平凹)透镜组合的类牛顿环的干涉图样.通过理论分析得出类牛顿环的光程差和光强公式,利用Mathematica仿真模拟出干涉图样,并讨论直线系数和二次函数系数大小对干涉图样的影响.研究类牛顿环干涉,有利于拓展对牛顿环干涉的理解,为类牛顿环实验提供新的方法.

双曲抛物面的直纹性质及其应用

双曲抛物面是一类重要的直纹二次曲面,其同族直母线异面,且平行于某共同的平面.该命题的逆命题为:在一定条件下,平行于同一平面、且两两异面的一族直线所形成的几何图形是双曲抛物面.