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.

Effect of Porosity on the Wind Loads on a Hyperbolic Paraboloid Canopy Roof

A discussion is made of the wind force coefficients for designing the main wind force resisting systems of H.P. （Hyperbolic-Paraboid）-shaped porous canopy roofs on the basis of a wind tunnel experiment. Roof models with a number of small circular holes were made of nylon resin using laser lithography. The porosity was changed from 0 （solid） to 0.4. Besides the porosity, the geometric parameters of the models were the rise to span ratio and slope of the roof. The overall aerodynamic forces and moments acting on a model were measured by a six-component force balance in a turbulent boundary layer. The results indicate that the porosity significantly reduces the wind loads. The design wind force coefficients for porous canopy roofs can be provided by those for solid roofs with the same configuration multiplied by a reduction factor. The proposed wind force coefficients are verified by a comparison of the load effect predicted by the proposed wind force coefficients with the maximum load effect obtained from dynamic analyses using the time history of wind force and moment coefficients. The axial forces induced in the columns supporting the roof are regarded as the load effect for discussing the design wind loads.

Wind Loading on a Hyperbolic Paraboloid Free Roof

Wind loading on an H.P. （hyperbolic paraboloid） free roof has been investigated on the basis of a wind tunnel experiment. The roof models of 1 mm thickness were made of nylon resin using laser lithography. The parameters under consideration are the rise to span ratio and slope of the roof. The overall aerodynamic forces and moments were measured by a six-component force balance in a turbulent boundary layer. Based on a combination of the lift and moment coefficients, the design wind force coefficients, CNW^＊ and CNL^＊, on the windward and leeward halves of the roof are proposed. Focus is on the column axial forces induced by wind loading as the load effect for discussing the design wind loads, assuming that the roof is rigid and supported by four comer columns. Indeed, two pairs of CNW^＊ and CNL^＊, generating the maximum tension and compression in the columns, are provided for each of the two or three wind directions parallel to the roof＇s diagonal lines. The proposed values of the wind force coefficients are compared with the specified values in the Australia/New-Zealand Standard for a limited range of rise to span ratio.

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.

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.

Numerical and Experimental Investigation of an Elliptical Paraboloid Shell Model

For practical engineering purpose, a new flat shell element baptized （ACM_Q4SBE1） is presented in this paper. The formulated element can be used for the analysis of thin shell structures; no matter how the geometrical shape might be. Tests on standard problems have been examined. Since, the analysis of thin shell structures has generally been purely carried out on a theoretical basis; it is of importance to present some experimental results of an elliptical paraboloid under uniformly distributed load pressure. The results obtained from both numerical and experimental work are presented.

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.

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.

双曲抛物面在建筑造型设计中的文化表达

双曲抛物面具有良好的结构受力性能与优美的曲面形态,是建筑设计中常用的造型曲面。随着社会、经济、文化的发展,以及数字技术的进步,建筑设计中对双曲抛物面的运用得到空前发展。文章以双曲抛物面在建筑设计中运用的大量案例,探讨双曲抛物面在体育文化承载、地域文化融合、城市历史文化传承与科技文化展现上充满张力和动感艺术特性的文化表达。

双曲抛物面形态和传统近似牙槽嵴形态3D打印钛网的力学性能研究

目的探究双曲抛物面空间结构对个性化钛网的力学性能影响。方法使用3-Matic 15软件为牙槽嵴吸收患者的下颌骨三维模型进行虚拟骨增量,分别增量为双曲抛物面结构和近似牙槽嵴结构,并制作孔隙为圆形、三角形、四边形和六边形,厚度为0.2 mm、0.3 mm、0.4 mm的个性化钛网,构建有限元分析模型,施加力和约束,分析各组钛网的应力和位移。结果同一厚度下,不同孔隙结构的双曲抛物面钛网应力和位移均明显低于近似牙槽嵴形态的钛网;随厚度减小,各组钛网的应力和位移显著增加。结论双曲抛物面这一空间结构可以均匀的分散应力,减少个性化钛网的应力集中,减少钛网受力后的位移,使钛网兼具了良好的力学性能和较薄的厚度,降低了对软组织的刺激,减少钛网暴露的可能。

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。

不同施肥方法对马来沉香和土沉香苗期根系生长的影响

以珍贵树种马来沉香、土沉香1年生播种苗木为材料进行试验,研究指数施肥、平均施肥对2种沉香苗期根系生长动态及对N的响应特征。结果表明,经氮素处理的马来沉香、土沉香的根系生物量、根系长度、根系表面积、根系平均直径、根体积等指标均显著高于对照处理(P<0.05)。经指数施肥处理的苗木根系生长及各形态指标均高于平均施肥处理。同一时期在相同施肥处理方式下,马来沉香苗根系生长及根系形态指标值均高于土沉香。洛伦兹模型对不同施肥方法处理下马来沉香、土沉香苗木生长指标与根系生物量进行拟合,具有较高的R2(0.95—0.99)和较低的RSMD(0.538—2.352);抛物面模型对不同施肥方法处理下马来沉香、土沉香苗木生长指标与比根长进行拟合,具有较高的R2(0.92—0.99)和较低的RSMD(3.218—6.692)。

采动裂隙椭抛带动态演化及煤与甲烷共采

为研究采动覆岩裂隙演化及其中瓦斯的运移规律,通过物理相似模拟及数值模拟发现,煤层开采后采动覆岩裂隙形态可用椭抛带来表征。基于岩层控制关键层理论,建立了考虑采高及第一亚关键层与煤层顶板间距的采动裂隙椭抛带动态演化数学模型。运用环境流体力学,传质学,渗流力学,采动岩体力学等理论,得到采动煤体应力与卸压瓦斯渗流,纵向破断裂隙区瓦斯升浮,以及横向离层裂隙区瓦斯扩散等方程,构建出椭抛带中卸压瓦斯渗流-升浮-扩散综合控制模型。分析了椭抛带卸压瓦斯抽采机理,提出相应的煤与甲烷共采技术。通过山西天池煤矿抽采卸压瓦斯的现场实践,说明采动裂隙椭抛带是卸压瓦斯的储运区,将瓦斯抽采系统布置其中,可取得良好效果。

一种大型反射面天线面板测试与调整方法及其应用

针对大型抛物面天线反射面分块面板的特点,基于最佳吻合的概念,从机电耦合学科交叉的角度,研究了反射面分块面板的调整问题,推导出了靶标点与调整量之间的影响关系矩阵,给出了数值方法,研制了准实用软件.将程序软件应用于某实际天线中,收到了满意的结果.

用FDTD和物理光学混合法分析毫米波抛物面天线

抛物面天线通常的分析方法是几何光学法和物理光学法 ,对于电大尺寸的抛物面天线这两种方法都可以得到较好的结果 ,对于电小尺寸馈源的抛物面天线 ,馈源方向图不仅取决于辐射器本身的辐射特性 ,其馈电结构对馈源方向图也有较大的影响 ,在此情况下 ,用上述方法得到的结果与实验结果之间有较大的误差 .利用FDTD可以把整个馈电结构纳入计算域中 ,得到辐射器完整的近区场 ,由等效原理可求出抛物面上电流分布 ,从而用物理光学方法计算抛物面天线远区场 .本文用这种混合方法分析计算了毫米波波导裂缝作为辐射器的抛物面天线 ,计算结果和测试结果相当吻合 ,证明了方法的有效性 .