Nonplanar post-buckling analysis of simply supported pipes conveying fluid with an axially sliding downstream end

In this study,the nonplanar post-buckling behavior of a simply supported fluid-conveying pipe with an axially sliding downstream end is investigated within the framework of a three-dimensional(3 D)theoretical model.The complete nonlinear governing equations are discretized via Galerkin’s method and then numerically solved by the use of a fourth-order Runge-Kutta integration algorithm.Different initial conditions are chosen for calculations to show the nonplanar buckling characteristics of the pipe in two perpendicular lateral directions.A detailed parametric analysis is performed in order to study the influence of several key system parameters such as the mass ratio,the flow velocity,and the gravity parameter on the post-buckling behavior of the pipe.Typical results are presented in the form of bifurcation diagrams when the flow velocity is selected as the variable parameter.It is found that the pipe will stay at its original straight equilibrium position until the critical flow velocity is reached.Just beyond the critical flow velocity,the pipe would lose stability by static divergence via a pitchfork bifurcation,and two possible nonzero equilibrium positions are generated.It is shown that the buckling and post-buckling behaviors of the pipe cannot be influenced by the mass ratio parameter.Unlike a pipe with two immovable ends,however,the pinned-pinned pipe with an axially sliding downstream end shows some different features regarding post-buckling behaviors.The most important feature is that the buckling amplitude of the pipe with an axially sliding downstream end would increase first and then decrease with the increase in the flow velocity.In addition,the buckled shapes of the pipe varying with the flow velocity are displayed in order to further show the new post-buckling features of the pipe with an axially sliding downstream end.

Nonplanar Shock Excitations in a Four Component Degenerate Quantum Plasma:the Effects of Various Charge States of Heavy Ions

A theoretical study on the nonlinear propagation of nonplanar （cylindrical and spherical） electrostatic modified ion-acoustic （mIA） shock structures has been carried out in an unmagnetized, collisionless four component degenerate plasma system （containing degenerate electron fluids, inertial positively as well as negatively charged light ions, and positively charged static heavy ions）. This investigation is valid for both non-relativistic and ultra-relativistic limits. The modified Burgers （mB） equation has been derived by employing the reductive perturbation method, and used to numerically analyze the basic features of shock structures. It has been found that the effects of degenerate pressure and number density of electron and inertial positively as well as negatively charged light ion fluids, and various charging state of positively charged static heavy ions significantly modify the basic features of mIA shock structures. The implications of our results to dense plasmas in astrophysical compact objects （e.g., non-rotating white dwarfs, neutron stars, etc.） are briefly discussed.

Time-Dependent Nonplanar Dust-Ion-Acoustic Gardner Double Layers

A theoretical investigation has been made on the nonplanar (cylindrical and spherical) dust-ion-acoustic (DIA) double layers (DLs) in a dusty plasma system, containing inertial ions, Boltzmann electrons, and negatively charged stationary dust. In this investigation, in order to analyze the time dependent nonplanar DIA DLs, we have used the modified Gardner equation, which has been obtained by employing the reductive perturbation method. It has been found that the behaviors of DIA DLs have been significantly modified by the time period and the nonplanar geometry. The nonplanar DIA DLs has been found to be similar with planar DIA DLs only at large time scale and the cylindrical DIA DLs have been found to be smaller than the spherical DLs, but larger than the planar DLs.

Trajectory tracking control of characteristic model for nonplanar hex-rotor UAV

The nonplanar hex-rotor unmanned aerial vehicle(UAV)has much higher driving property,greater payload capacity and damage tolerance than quad-rotor UAV.It is difficult to design a highperformance controller of easy engineering implementation for strongly coupled nonlinear hex-rotorUAV system.In response to this practical problem,an adaptive trajectory tracking control based oncharacteristic model for nonplanar hex-rotor is studied.Firstly,the dynamic model for the hex-rotorUAV is devised.Secondly,according to dynamic characteristics,environmental characteristics andcontrol performance requirements,the characteristic model of the hex-rotor UAV is constructed.Then,based on the characteristic model,a golden section adaptive controller is designed to realizetrajectory tracking.Furthermore,the stability analysis of the closed loop hex-rotor system is given.Finally,the validity of the proposed trajectory tracking control method adopted in the nonplanar hex-rotor UAV is demonstrated via numerical simulations and hex-rotor prototype experiments.

Transmittance Measurement of the Nonplanar Optical Based on Focal-Plane-Array Camera

Aiming to solve the problem that it is difficult to accurately measure UV cut-off transmittance of xenon quartz glass by using present spectrophotometer in China SG III project. Through the analysis, we believe that its reason was that the xenon quartz glass was nonplanar so the outgoing beam geometry from under-test was different from that from standard sample. A method of transmittance measurement based on focal-plane-array camera was proposed in this article. The effects of camera uniformity and spot sampling on transmittance measurement were analyzed theoretically. This method, which can reduce the effect of beam geometry on transmittance measurement and eliminate the cutting error occurring during light transmission by monitoring the completeness of incident beam in real-time, is verified from experiments. The random standard uncertainty of this method here is 0.035% or less. It is particularly useful in the transmittance measurement of nonplanar optical.

Robust boundary-induced bulk propagations in elastic waveguides with nonplanar surfaces

Trivial elastic waveguides induced by line defects and nontrivial elastic waveguides protected by topological edge states have been extensively examined in planar waveguide systems.Despite these investigations,little is known about topologically protected bulk states and their resulting robust transmission properties,especially in nonplanar elastic waveguides with folded,curved,and twisted surfaces.Elastic Dirac waveguides with robust boundary-induced bulk states are presented.These states arise from the truncated boundaries of bulks with linear Dirac conical dispersions,differing from topologically protected edge states ensured by the bulk-edge correspondence.Experimental proof is provided,in which boundary-induced bulk states show robustly high-throughput transmissions along the waveguides,even with folded,curved,and twisted surfaces.These results not only open up new avenues for examining novel topological phenomena about bulk but also offer new platforms for developing topological devices with nonplanar surfaces.

非平面全驱动多旋翼无人机的鲁棒预测控制

针对非平面全驱动多旋翼无人机飞行时易受外部风场与未建模动态影响等问题,设计了鲁棒性较好的预测控制系统。采用牛顿-欧拉法构建了无人机六自由度非线性运动模型;设计了线性扩张状态观测器,将同时受匹配与非匹配干扰影响的无人机系统转化为仅受匹配干扰影响的等效系统,用以估计系统的状态变量;针对等效系统设计预测控制器以降低系统输出振荡和输入激增,设计干扰补偿器以提升闭环系统抗干扰的鲁棒性。仿真实验表明:与常规的非线性动态逆控制方法相比,该算法下的闭环系统具有更强的抗干扰能力与更高的轨迹跟踪精度。

Nonplanar Electrostatic Solitary Waves in a Relativistic Degenerate Dense Plasma

By employing the reductive perturbation technique, the propagation of cylindrical and spherical ion acoustic solitary waves is studied in an unmagnetized dense relativistic plasma, consisting of relativistically degenerate electrons and cold fluid ions. A modified Korteweg-de-Vries equation is derived and its numerical solutions have been analyzed to identify the basic features of electrostatic solitary structures that may form in such a degenerate Fermi plasma. Different degrees of relativistic electron degeneracy are discussed and compared. It is found that increasing number density leads to decrease the aznplitude the width of the ion acoustic solitary wave in both the cylindrical and spherical geometries. The relevance of the work to the compact astrophysical objects, particularly white dwarfs is pointed out.

图的哈密顿路骨架上的BB-染色

为了有效解决网络信息传输系统中的频道分配问题,在设计网络线路时,只对该网络线路中更重要的子结构(称为骨架)给出更多的限制,而对其他的部分作较少的限制,这类问题可抽象为图的BB-染色模型,它是经典染色理论的重要变体.利用圈平方图和广义Petersen图描述两类特殊的网络信息传输系统,采用哈密顿路径作为图的骨架,对圈平方图和广义Petersen图的λ-BB-染色展开研究,得到了BBC_(λ)(G,P)=λ+2.

增材制造数字化模型平面与非平面切片及路径规划研究进展

增材制造技术基于“离散-堆积”原理,通过对三维数字化模型进行数据预处理、切片与路径规划,并生成增材系统可识别的执行代码,驱动增材设备实现零件的快速制造,近年来,该技术在航空航天、汽车、船舶、医疗、建筑等行业得到了广泛应用。切片与路径规划是增材制造三维数字化模型数据处理的核心步骤,决定着制造过程的工艺变量、零件形状精度和性能。首先综述了目前增材制造中基于CAD模型、点云模型、STL模型、体素模型等多种数字化模型切片方法研究进展,并从各模型生成精度、切片算法原理、算法效率等方面展开了评述;其次,对平面与非平面的等厚度、变厚度、变方向及分区组合等多种切片算法,以及平面单区域、多区域、局部特征及非平面等多种路径规划算法进行了综述,初步分析和梳理了切片及路径规划算法的设计要点;最后,总结了目前增材制造数字化模型平面与非平面切片及路径规划的研究现状,并对其发展趋势进行了展望。

非平面2自由度上肢康复外骨骼设计与分析

为了满足患者对康复训练以及生活辅助的需求,针对当前低自由度上肢康复外骨骼康复训练空间有限的问题,设计了一种非平面2自由度上肢康复外骨骼。参照人体上肢结构和肘部运动特点,建立了上肢康复外骨骼的三维模型。采用D-H法建立其参数模型,此外,采用蒙特卡罗法分析了上肢康复外骨骼的可达工作空间,并利用MATLAB对其运动进行轨迹规划,验证了其整个运动过程的稳定性,上肢康复外骨骼能够以2自由度实现连续的四分之一球面训练空间。

三维数值流形法在裂纹扩展中的应用研究

运用三维数值流形法(3D NMM)进行三维裂纹扩展分析,并采用C++语言编写了相应的程序。充分利用三维数值流形法模拟裂纹扩展的优势,只需要更新裂纹尖端线附近的边界环路和流形单元,不需要使用阶跃函数。根据三维数值流形法计算得到的应力结果,应用非局部求迹方法分析每个裂纹尖端的破坏状态,如果发生破坏则沿垂直于其最大主应力方向扩展。针对裂纹扩展后的不同状况,采用四边形或三角形推进法。裂纹扩展后为了使变形后的面保持平面,必须对新生成的面进行三角化分割。对诸如单边裂纹、平行钱币型裂纹和倾斜钱币型裂纹扩展问题进行数值模拟。计算结果表明,采用三维数值流形法进行裂纹扩展模拟是可行的,文中方法对裂纹尖端线非闭合和闭合的情形均适用,且文中方法对于裂纹尖端线位于单元内部的非平面裂纹扩展也是有效的。

超声速反舰导弹末端非平面机动研究

基于过载控制技术,对超声速反舰导弹的末端非平面机动进行了研究,包括摆式机动和螺旋机动。对于每种机动方式,提出了控制信号的计算方法,并举例进行了仿真研究。仿真结果表明,采用过载控制设计的反舰导弹可以实现各种末端非平面机动,在提高反舰导弹的突防能力方面具有很大的潜力。

基于最小二乘估计的多站交会方法

在多台电视经纬仪组成的测量网络中,为了提高目标的捕获、跟踪能力,减少交会模型切换带来的引导数据的波动,提出一种基于最小二乘估计的多站交会方法。该方法根据电视经纬仪实时跟踪被测目标时的几何关系,利用电视经纬仪的站点位置和实时获得的目标测角信息,对于每台电视经纬仪都构造两个垂直相交于其测量方向线的平面,再用最小二乘原理估计被测目标的空间坐标。在两台电视经纬仪实时交会时,异面交会法是该方法的特例,于是证明该方法是有效的。仿真试验结果表明,与异面交会法相比,此方法产生的引导数据平滑、无波动,二者的定位误差均小于0.18m,能满足电视经纬仪多站交会定位的要求。

应用非线性规划求解异面最优轨道转移问题

研究了一种应用非线性规化求解有限推力作用下异面最优轨道转移问题的方法。采用改进春分点根素形式的高斯行星方程,从庞德里亚金极小值原理出发,将有限推力作用下异面最优轨道转移问题转化为两点边值问题;在考虑边界条件、横截条件及开关函数的前提下,将两点边值问题转化为针对协状态初值等的参数优化问题;最后应用非线性规划方法求解形成的参数优化问题。本方法特点是能得到开关函数从而得到最优发动机开关机逻辑。文章最后通过一个仿真计算,演示了完整的求解过程,验证了方法的有效性。

窄线宽低噪声可调谐非平面环形激光器

针对空间相干光通信和探测等应用,对非平面环形激光器的线宽、噪声和调谐特性进行了系统的实验研究。单频输出功率达到752 mW,光光效率42%,斜率效率54%。采用延时自外差拍频法测试了激光线宽,其随泵浦功率的增加而增大,输出功率小于200 mW时,线宽小于1 kHz,在最高输出功率下线宽为2.3 kHz。激光强度噪声主要由弛豫振荡引起,相对强度噪声(RIN)随着泵浦功率的提高而降低。在1.78W泵浦功率下,RIN达到-93 dB/Hz。采用温度和压电两种方式进行了激光调谐。温度调谐范围达到62 GHz。压电调谐范围达到130 MHz,响应带宽100 kHz。

非平面型受阻胺共混芴类电致蓝光材料

低能绿光发射带是导致蓝光材料稳定性差的重要原因。为了更有效地抑制聚芴类绿光带的产生,设计共混非平面的抗氧化受阻胺(TMP-BPFT)来提高该类材料的光谱稳定性的方案,该方法可以同时抑制聚集与阻断芴酮生成过程。绿光指数(I(绿光中心波长)/I(第一发射峰))定量衡量了掺杂TMP-BPFT与三聚芴(TDHF)绿光发射带的关系。退火实验表明,在退火144h后,掺杂TMP-BPFT的TDHF与未掺杂的TDHF的绿光指数分别为0.5和4.5,这说明非平面的抗氧化受阻胺具有良好的光谱稳定作用。该研究工作表明具有隔离发色团和抗氧化作用的非平面型受阻胺衍生物是一类有效的电致蓝光材料的稳定剂。

震源动力学破裂过程数值模拟研究

首先阐述了震源动力学过程研究的重要意义,在此基础上,研究了复杂的断层几何形态及介质模型对动力学破裂过程的影响,并对常用的有限元方法、离散元方法、有限差分方法和边界积分方程方法等进行了相应介绍.讨论了这些数值模拟方法各自的优缺点,建议在方法的选择上应视具体问题及计算的精度而定.最后对动力学数值模拟的关键部分,滑动摩擦准则进行了论述.常用的滑动摩擦准则有滑动弱化准则、速率弱化准则和速率-状态依赖摩擦准则.在单纯考虑某个地震的动力学破裂传播过程时,滑动弱化准则较为常用,其中滑动弱化距离的选取至关重要.但若考虑整个地震循环,速率-状态依赖摩擦准则更为合适.

非平面腔四频差动激光陀螺的温度补偿(英文)

为了减小温度对非平面腔四频差动激光陀螺的影响,对不同变温条件下的补偿模型进行了研究。首先进行了静态温度实验,补偿后零偏的标准差为0.01(°)/h。然后进行了1℃/min高低温循环、1℃/min-5℃/min随机变温和急剧升降温三种条件下的动态变温实验,分别建立了三个温度补偿模型A、B、C。前两种变温条件下的零漂能够得到较好的补偿,但急剧升降温时尽管陀螺体实际温度变化不大,补偿效果却最差。在上述三个补偿模型中,温度变化率所起作用从A-C越来越大,表明变温速度越快,陀螺体温度不平衡越大,增大了补偿难度。因此,为了增强补偿效果,除了减小陀螺本体的温度敏感性外,还要尽量减小变温过程中陀螺体上的温度梯度。

用微分求积法分析轴向移动粘弹性梁的非平面非线性振动

用微分求积法分析了轴向移动粘弹性梁非平面非线性振动的动力学行为.轴向移动粘弹性梁非平面非线性振动的数学模型是一非常复杂的非线性偏微分方程组.首先用微分求积法对其控制方程组进行空间离散,得到非线性常微分方程组,然后求解常微分方程组得到数值结果.在数值结果的基础上结合非线性动力学理论,利用分叉图、时间历程图、相图对其非线性动力学特性进行了分析.