高层建筑风荷载反演研究

本文研究了结构参数未知条件下的高层建筑风荷载反演问题,通过将平均风速的实测特性作为识别计算中的辅助条件,文中提出了一类荷载归一化统计平均方法,结合工程实例,进行了高层建筑风荷载反演分析,结果表明,本文建议方法可以在幅值、时程等方面均给出良好的风荷载反演结果,同时识别得到的结构参数具有良好的精度。从而为高层建筑风荷载研究提供了一条可行途径。     

未知输入条件下的结构物理参数识别研究

研究在输入信息未知条件下识别结构物理参数的问题,根据建筑结构风荷载的作用特点,提出一类时域识别算法,用于高层建筑结构的结构物理参数识别     

基于无迹卡尔曼滤波的高层建筑风荷载反演

基于无迹卡尔曼滤波提出了一种高层建筑风荷载的反演算法，该方法利用有限测量楼层的风致响应数据，实时识别结构的未知风荷载和风致响应。通过典型高层建筑的风洞试验进行风荷载反演实例分析，验证了该方法的准确性和适用性，评估了模态参数误差、测量噪声水平对风荷载反演的影响。研究结果表明，文中提出的算法对模态参数误差不敏感，在一定噪声水平下反演的结果基本能够满足实际工程需要，该算法为实时评估高层建筑的风荷载和风致响应提供了有效的工具。     

桥梁结构移动平稳随机荷载识别新方法

移动的平稳随机荷载对简支梁的作用,相当于固定的调制函数已知的非平稳随机荷载对简支梁结构的作用.本文以此为基础,研究了移动平稳随机荷载的识别问题.首先基于虚拟激励法的思想,利用特征值分解及奇异值分解技术,由虚拟位移响应反演虚拟广义坐标,有效地避免了矩阵求逆,得到高精度的广义坐标谱;同时利用Wiener-Khintchine关系及Duhamel积分,由广义坐标谱值反演得到平稳随机激励谱密度.仿真算例表明,只要适当地选取参振振型及测点位置,本文方法可以有效地识别桥梁结构的移动平稳随机荷载.     

基于小波分析与子结构法的未知风荷载作用下高层剪切结构参数识别方法研究

对于未知风荷载作用下高层剪切结构,通过子结构理论将其余部分对子结构的效应作为外荷载施加给子结构,并建立风荷载作用下的动力方程。应用函数的小波多尺度逼近方法将产生低频响应的风荷载表示为尺度函数的线性组合,根据动力方程构造结构参数和低频小波系数的识别方程。用最小二乘法识别结构参数和低频小波系数,由识别的参数和结构响应计算未知激励。分析结果表明,该方法对结构参数的识别误差在2%以内,有一定的抗噪性。     

基于荷载形函数的大跨桥梁结构移动荷载识别

大跨桥梁结构中的移动荷载识别是结构健康监测的重要组成部分之一,其作为动力学中的反问题,存在唯一性及稳定性等病态问题。本文首先推导出移动荷载作用下结构响应的卷积形式的离散公式,然后利用有限元理论中的形函数拟合移动荷载,推导出基于荷载形函数的移动荷载识别表达式。将移动荷载的识别转化为荷载形函数拟合系数的识别,降低了需要识别的未知量,减小了逆运算的计算量,消除或减弱逆问题病态性,并提高了计算效率。利用某大跨刚构-连续预应力混凝土桥梁修正后的有限元模型进行数值仿真,考虑路面粗糙度,由模态叠加法计算移动荷载作用下的响应;然后采用荷载形函数方法识别移动荷载,证明该方法在5%以下的噪声时能快速并精确识别复杂桥梁结构的移动荷载。     

杆系结构多荷载识别的三角级数分析法

本文提供了一种识别杆系结构受到多荷载的作用的三角级数识别方法.将集中荷载展成三角级数且借助结构力学中的位移法建立了单根基本梁(梁单元)的位移方程,利用位移测量值反演所受到的集中荷载大小和位置.算例表明本文所用级数收敛性较好,可获得稳定的收敛值.     

基于广义卡尔曼滤波的桥梁结构物理参数识别

基于广义卡尔曼滤波提出了随机荷载作用下桥梁结构物理参数的识别方法。首先,以荷载为观测对象,推导出基于有限元模型的桥梁结构系统的观测方程,以结构待识别的物理参数为状态向量,建立系统状态方程;然后,对该状态方程和观测方程构成的非线性参数系统应用广义卡尔曼滤波,从而识别出结构的物理参数。对一座简支梁桥和一座三跨连续梁桥在不同工况下的物理参数识别进行了数值仿真,结果表明本文方法能够准确地识别桥梁结构全部刚度参数、质量参数和阻尼参数,且具有很强的抗噪性能,从而验证了本文方法的有效性和鲁棒性,可应用于识别大型桥梁结构的物理参数。     

非线性杆单元荷载矩阵积分算子直接集成算法

在文献[1]的基础上，将积分算子直接集成单元刚度矩阵的方法扩展应用于非线性杆单元的荷载矩阵集成．该方法将分布荷载产生的内力函数分解为由未知参数表示的线形项，和与分布荷载特性相关的已知函数项的组合，计算积分算子，由积分算子的线形组合得到分布荷戟产生的杆件内力函数，从而得到荷载矩阵．该方法没有采用任何假定，具有广泛的普适性，能用于求解任意刚度分布杆件上作用任意分布荷载或集中荷载的单元荷载矩阵．对于刚度非连续、荷载分布非连续的情况，该方法避免了高斯数值积分的误差，具有更高的计算精度。     

上海中心大厦脉动风荷载模拟研究

风荷载是超高层建筑设计的主要荷载之一,对超高层建筑进行风振时程分析能更准确和直观地了解结构风振响应的特性.为了进行风振响应时程分析,必须较为准确地模拟作用在结构上的脉动风荷载.首先,本文采用基于自回归(AR)模型的线性滤波法对上海中心大厦场地的脉动风速时程进行了数值模拟,通过检验模拟脉动风速的功率谱和相干函数平方根与目标值的吻合程度,验证了基于AR模型模拟超高层建筑脉动风速时程的可行性.然后,本文考虑了上海中心大厦外形向上扭转收缩的特点,由模拟的脉动风速时程计算生成作用在结构上的脉动风荷载.     

Computing the structural buckling limit load by using dynamic relaxation method

The numerical structural analysis schemes are extensively developed by progress of modern computer processing power. One of these approximate approaches is called "dynamic relaxation (DR) method." This technique explicitly solves the simultaneous system of equations. For analyzing the static structures, the DR strategy transfers the governing equations to the dynamic space. By adding the fictitious damping and mass to the static equilibrium equations, the corresponding artificial dynamic system is achieved. The static equilibrium path is required in order to investigate the structural stability behavior. This path shows the relationship between the loads and the displacements. In this way, the critical points and buckling loads of the non-linear structures can be obtained. The corresponding load to the first limit point is known as buckling limit load. For estimating the buckling load, the variable load factor is used in the DR process. A new procedure for finding the load factor is presented by imposing the work increment of the external forces to zero. The proposed formula only requires the fictitious parameters of the DR scheme. To prove the efficiency and robustness of the suggested algorithm, various geometric non-linear analyses are performed. The obtained results demonstrate that the new method can successfully estimate the buckling limit load of structures.     

区间参数结构平稳随机载荷识别方法

针对贫信息下不确定性结构的随机载荷识别问题,使用基于Taylor展开的区间分析方法,提出了一种不确定性结构随机载荷识别的非概率区间方法。该识别方法在频域中进行,识别时使用区间变量描述工程结构中的不确定性参数。基于测点的响应谱密度函数,首先对不确定性参数的名义值点进行随机载荷识别,其次计算载荷关于不确定性参数的灵敏度,最后基于区间扩张理论获得识别载荷谱的上下界值。算例结果表明,使用区间方法得到的不确定性结构的载荷谱识别区间界值都能完全包含载荷真值,此方法能够在结构设计时给出更为可靠的载荷工况。     

An efficient explicit framework for determining the lowest structural buckling load using Dynamic Relaxation method

This paper develops an e?cient explicit algorithm for calculating buckling load of structures. Here, the modified Dynamic Relaxation method is utilized so that the first structural buckling load is achieved. The proposed algorithm does not require solving any eigenvalue problem and runs by full vector and iterative operations. Moreover, the suggested procedure is general so that it could be utilized for both symmetric and unsymmetric structures without any additional calculations. For numerical verification, some columns and portal frames are analyzed and the calculated buckling loads are compared with the exact solution and other available approaches. Results show that the proposed algorithm has suitable accuracy and e?ciency that is useful for determining the lowest buckling load of each structure. Moreover, the effect of initial imperfection and time step size on the suggested framework is studies numerically.     

Post-buckling of cantilever columns having variable cross-section under a combined load

Post-buckling of a cantilever column is examined under a combined load consisting of a tip-concentrated load and a distributed axial load, through dynamic formulation. The formulation of the problem is based on the moment–curvature relationship. The two-point boundary value problem described by the governing equations is dependent on the frequency parameter and the two load parameters. The buckling loads are those loads at which the eigencurve, namely, the load versus frequency curve of the column meets the load axis. A simple and reliable iterative procedure to convert the two-point boundary value problem into an initial value problem is followed and solved the non-linear differential equations utilizing a fourth-order Runge–Kutta integration scheme. To demonstrate the potentiality of the adopted numerical scheme, linear vibration frequencies of truncated, tapered cantilever wedges and cones are determined and compared with the published analytical and test results. Buckling and post-buckling loads of a simply supported stepped column are obtained and compared with the published test results. The loads and deflections of non-uniform cantilever columns are obtained for various slopes at the tip. The interaction of load parameters for a free–free truncated conical column has also been examined. The numerical results indicate that the path represented by the two load parameters turns out to be nearly a straight line.     

无轴承旋翼柔性梁载荷特性研究

应用Hamilton原理建立了双路传力的无轴承旋翼运动方程。采用均匀入流模型,基于直升机飞行平衡条件,建立了无轴承旋翼柔性梁载荷的计算模型,并通过算例验证了模型的精度。利用该模型,研究了全机重心位置、机身气动阻力以及平尾安装角对柔性梁载荷特性的影响,给出了各因素对柔性梁载荷的影响趋势,得出了降低柔性梁载荷的方法。数值结果表明:2cm左右重心位置的变化能够引起9%~11%的柔性梁载荷变化量,15%气动阻力的增加会导致约9%的柔性梁载荷的增大;2°平尾安装角的变化引起约10%柔性梁载荷的变化量,3°平尾安装角的变化引起约26%柔性梁载荷的变化。     

Deformation of thin straight pipes under concentrated forces or prescribed edge displacements

The purpose of this paper is to present an efficient analytic method for obtaining the deformation of thin straight pipes, subjected to prescribed edge displacements or concentrated loads.The approach uses the mixed formulation where unknown functions are combined with trigonometric terms. A variational procedure is used to obtain the system of ordinary differential equations. For the applied load a Fourier approach is used to represent the load as an analytical function. For the prescribed displacement, three solutions for the ovalization are evaluated and a method based on energy contribution of each term is used to obtain their superposition.In contrast to finite element method the proposed method is efficient and can be applied to other boundary condition problems leading to continuous displacement and stress fields with a low number of unknowns. Comparisons with experimental and finite element procedures show good agreement that enhances the merits of the analytical solutions proposed.The value of this method is based on solving the differential equations rather than using commercial codes. So far, the solution of prescribed edge displacements has been limited to one term. This paper discusses how to add further terms using the mixed formulation, thus, presenting a novel procedure.     

反求压电薄板智能结构荷载的有限元逆逼近方法

基于压电薄板智能结构提出一种有限元逆逼近反求结构荷载参量的方法，逼近目标函数以压电电荷响应为参量，迭代初值采用单位荷载预逼近方法；数值算例表明了该方法的有效性，可用于解决压电智能结构的荷载识别问题。