纤维墙元模型在剪力墙结构非线性分析中的应用

钢筋混凝土剪力墙是目前高层与超高层建筑中最主要的抗侧力构件,本文在对已有的微观及宏观计算模型进行比较的基础上,基于纤维模型概念,建立了便于高层剪力墙结构非线性分析应用的纤维墙元模型,即由承受轴力及弯矩的纤维子单元与承受剪切变形的剪切子单元相合成的墙元计算模型;同时,对该模型中剪切子单元高度的取值进行了分析,明确了其物理含义;推导了单元的刚度矩阵,并分别建立了纤维子单元及剪切子单元的骨架曲线及滞回规则。另外,应用该计算单元模型,对一栋40层框架剪力墙结构进行了非线性时程分析,计算结果与相应模型的振动台试验结果进行了对比,比较结果表明两者在结构动力特性,位移响应方面等均吻合较好,验证了该计算单元模型的准确性与有效性,可为推广使用提供参考。     

一种确定均匀动脉壁面切应力的非线性方法

从Ling和Atabek提出的``局部流'理论出发，提出一种利用测量血液黏度、管轴上 的血流速度、压力和管径波形计算均匀动脉管壁切应力的非线性方法. 将这种方法与柳兆荣 等提出的利用测量血液黏度、管轴上的血流速度和平均管径计算切应力的线性方法比较，结 果表明，当管壁脉动幅度较小时，两种方法计算的压力梯度、流速剖面和管壁切应力差别较 小；而当管壁脉动幅度增大时，两种方法计算的压力梯度、流速剖面和管壁切应力差别增大. 对于小幅脉动均匀动脉，用线性方法计算管壁切应力有较高的精度；而对于大变形 均匀动脉，则需要考虑非线性因素对管壁切应力的影响. 由于作为输入量的血液黏度、轴心 血流速度、压力波形和管径波形可在活体上通过无损伤或微损伤的检测方法得到， 所提出的计算切应力的方法为在体或离体研究切应力与动脉重建的关系提供了方法学基础.     

悬索大挠度风振响应的有限体积法分析

基于Lagrange原理,建立了一套新的悬索大挠度动力特性和动力响应分析的有限体积法列式,推导了结点力向量、质量矩阵和单元刚度矩阵的显式表达式。该列式的一个显著特点是直接利用工程应变定义结构变形,其物理意义明确,列式简单,适用于各种垂度和荷载情况的悬索大挠度动力分析。实例动力特性和随机风振响应分析表明,该有限体积列式不仅计算效率高,而且具有良好的计算精度。     

A SIMPLIFIED CALCULATING METHOD OF NONLINEAR FREQUENCY OF CABLE NET UNDER MEAN WIND LOAD

The cable net supported glass curtain wallas the most advanced technique in dot point supported glass curtain wall, is widely used in China. Because of its large deflection and high nonlinearity under wind load, the dynamic performance of the cable net is greatly different from that of the conventional linear structures. The continuous membrane theory is used to construct the nonlinear vibration differential equation of the cable net, and the harmonic balance method is used to solve the analytic formula of the nonlinear frequency. In order to verify the accuracy of the above analytic formula, the results of the formula and the nonlinear FEM time-history method are compared and found to be in good agreement. Furthermore, the nonlinear vibration differential equation and the nonlinear frequency obtained in this paper are the basis for the wind-induced response analysis of a cable net under fluctuating wind load.     

投影栅相移法中的相位波动误差及修正算法研究

分析了因测量系统非线性响应及局部饱和投影栅图像所导致的相位误差及其波动特性。经过实验验证,四步相移算法在抑制系统非线性响应所引起的相位误差方面优于三步相移算法。通过模拟分析得出,在采用传统相移算法对局部饱和条纹图像分析时,相位误差较大,且相位分布具有周期波动特性。为减小因图像局部饱和而产生的相位误差,文中采用了新的算法提取相位。实验分析结果验证了算法的正确性。     

Nonlinear study of the dynamic behavior of a string-beam coupled system under combined excitations

In this paper,the nonlinear dynamic behavior of a string-beam coupled system subjected to external,parametric and tuned excitations is presented.The governing equations of motion are obtained for the nonlinear transverse vibrations of the string-beam coupled system which are described by a set of ordinary differential equations with two degrees of freedom.The case of 1:1 internal resonance between the modes of the beam and string,and the primary and combined resonance for the beam is considered.The method of multiple scales is utilized to analyze the nonlinear responses of the string-beam coupled system and obtain approximate solutions up to and including the second-order approximations.All resonance cases are extracted and investigated.Stability of the system is studied using frequency response equations and the phase-plane method.Numerical solutions are carried out and the results are presented graphically and discussed.The effects of the different parameters on both response and stability of the system are investigated.The reported results are compared to the available published work.     

TWO-SCALE FINITE ELEMENT DISCRETIZATIONS FOR PARTIAL DIFFERENTIAL EQUATIONS

Some two-scale finite element discretizations are introduced for a class of linear partialdifferential equations. Both boundary value and eigenvalue problems are studied. Basedon the two-scale error resolution techniques, several two-scale finite element algorithmsare proposed and analyzed. It is shown that this type of two-scale algorithms not onlysignificantly reduces the number of degrees of freedom but also produces very accurateapproximations.     

基于二倍频预放大的超快光学参量放大研究

利用钛蓝宝石飞秒激光泵浦的大能量超快光学参量放大技术在强场光学和阿秒科学领域研究中具有重要应用。现有技术利用基频激光(波长为800 nm)对其产生的超连续谱种子信号进行预放大,这对超连续谱中的红外成分转化效率提出较高要求,影响了系统的可靠性。本文在实验中利用转化效率较高的超连续谱绿光成分作为种子光,在预放大过程中使用二倍频激光泵浦得到红外闲频光,再进行第二级功率放大,得到1200～2500 nm范围的宽谱可调的近红外飞秒激光脉冲输出,脉冲能量转换效率达到25%。     

VANET中基于区块链的分布式匿名认证方案

身份认证是阻止恶意车辆传播虚假交通信息的第一道防线。然而由于车载自组网（VANET）中网络带宽和计算能力有限,现有方案不能满足对车辆身份的高效认证需求,也无法实现对恶意车辆的快速匿名追溯。鉴于此,提出一种基于区块链的分布式匿名认证方案。该方案利用零知识证明对VANET中车辆进行快速匿名认证,并采用非线性对的聚合签名实现快速批量认证,有效减少认证过程中产生的计算量。另外,区域性可信机构（RTA）可以实现对恶意车辆身份的匿名追溯,并基于区块链对其身份进行快速撤销;还可以基于本地密钥对车辆的短期匿名身份进行及时更新,保证车辆的匿名性和签名的新鲜性。安全分析与仿真实验表明,所提方案能够满足匿名性、不可链接性等多种安全需求,并能有效降低计算与通信开销,比同类方案在性能上至少提升27.28%。     

面向OTFS的时延-多普勒域信道估计方法综述

为了在高移动性场景中提供稳定可靠的通信服务,6G系统可考虑基于时延–多普勒（DD）域的正交时频空间（OTFS）作为其调制方案。OTFS通过将发送符号映射到DD域,再将其二维变换到时间–频率（TF）域,使所有发送符号具备获取时频全分集的潜力,有效提高了双选择性信道下的通信性能。由于DD域等效信道具有很多良好性质,现有OTFS信道估计方法大多在DD域完成。考虑实现思路的差异和算法应用场景的区别,已有面向OTFS的DD域信道估计方法被划分为3类并进行综述。最后总结分析了当前DD域信道估计方法的挑战及潜在解决思路。