超高层建筑气动参数识别的分段线性化-最小二乘法

柔性超高层建筑在强风作用下会产生气动反馈效应,在结构振动分析中通常通过附加的非线性/线性气动阻尼和气动刚度来考虑其影响。因此,提出了一种用于此类非线性系统识别的谐波分段线性化-最小二乘回归方法。该方法不但可以识别灰箱系统,即已知典型非线性振动系统方程,仅需识别其系统参数,还可以识别黑箱系统,即非线性振动系统的方程和参数均未知。该方法首先把非线性振动系统视为分段的线性振动系统并识别出时变的阻尼比,然后根据最小二乘回归分析获得阻尼比与时间或振幅的关系表达式,最终建立其非线性振动方程。最后,以492m的上海环球金融中心为研究对象进行了气动弹性模型振动测量风洞试验,首先采用随机减量法对横风向振动位移响应进行处理获得其自由振动响应,然后应用谐波分段线性化-最小二乘法识别其横风向非线性/线性气动阻尼比和气动刚度,并讨论了其平均气动阻尼比(线性)、气动刚度、非线性气动参数随风速的变化情况。研究结果表明:该方法对识别柔性超高层建筑在强风作用下的此类非线性振动黑箱系统是可行的。

凹叶厚朴二元立木材积方程的研究

通过实测239株凹叶厚朴样木的胸径、树高和材积,采用遗传算法,三次设计法,改进单纯形法拟合材积方程并与对数线性化最小二乘法进行比较.结果表明:采用遗传算法、三次设计法和改进单纯形法建立二元材积方程优于对数线性化最小二乘法;对数线性化最小二乘法的适用性检验统计量F不能服从F分布,说明不能用对数线性化最小二乘法拟合凹叶厚朴的材积方程;同时用模外25株凹叶厚朴样木进行检验,遗传算法、三次设计法和改进单纯形法建立的二元材积方程的理论材积与实测材积相吻合.采用遗传算法建立的立木材积方程编制了凹叶厚朴的胸径、树高二元材积表.

一种非线性振动系统参数辨识方法

文献 [1]提出了一种对非线性系统线性化的最小二乘法理想线性化方法 ,此方法当动态参数在较大范围变化时 ,仍能较准确地逼近原系统。本文利用理想线性化的结论来对非线性系统进行参数辨识。先假设原系统非线性模型是由某些已知的非线性函数构成 ,并找到一个系统较为逼近的线性模型 ,再利用理想线性化的结论推导出线性模型系数和非线性模型系数之间的关系 ,反推出系统的非线性模型。数值仿真结果表明 ,此非线性模型比最初线性模型更加逼近原系统。

三分量磁通门梯度仪校准算法研究

针对三轴磁通门传感器非正交、灵敏度不一致、零偏以及构成梯度仪的两个磁通门传感器位置不一致引起的测量误差问题,建立了误差模型;基于地磁矢量模值短时不变原理,采用线性化最小二乘算法进行一个磁通门传感器参数的辨识;基于校准后三分量差值F范数最小原理,采用多元线性回归的方法进行另一个磁通门传感器参数以及两个磁通门传感器相对位置关系参数的辨识。实验结果表明,该方法能够将两个磁通门中最大总场误差从1 194.4 n T降低到30.0 n T,将三分量梯度仪最大输出误差从529.1 n T降低到13.4 n T,有效地改善了梯度仪性能。

凹叶厚朴地径材积方程的研究

通过实测 97株凹叶厚朴样木的地径和材积值 ,采用遗传算法、三次设计法、改进单纯形法拟合地径材积方程并与对数线性化最小二乘法进行比较。结果表明 :遗传算法、三次设计法和改进单纯形法拟合地径材积效果优于对数线性化最小二乘法 ,且 4种方法均能通过适用性检验。进一步建立了地径、胸径及树高之间的相互关系 。

Application of nonlinear partial least square in catalyst modeling

The neural network partial least square (NNPLS) method was used to establish a robust reaction model for a multi-component catalyst of methane oxidative coupling. The details, including the learning algorithm, the number of hidden units of the inner network, activation function, initialization of the network weights and the principal components, are discussed. The results show that the structural organizations of inner neural network are 1-10-5-1, 1-8-4-1, 1-8-5-1, 1-7-4-1, 1-8-4-1, 1-8-6-1, respectively. The Levenberg-Marquardt method was used in the learning algorithm, and the central sigmoidal function is the activation function. Calculation results show that four principal components are convenient in the use of the multi-component catalyst modeling of methane oxidative coupling. Therefore a robust reaction model expressed by NNPLS succeeds in correlating the relations between elements in catalyst and catalytic reaction results. Compared with the direct network modeling, NNPLS model can be adjusted by experimental data and the calculation of the model is simpler and faster than that of the direct network model.

Phase Equilibrium of Isobutanol in Supercritical CO2

Vapor-liquid phase equilibrium data including composition,densities,molar volume and equilibrium constant of isobutanol in supercritical carbon dioxide from 313.2K to 353.2K were measured in a variable-volume visual cell.The properties of critical point were obtained by extrapolation.The results showed that critical temperature,critical pressure and critical compressibility factor of CO2-isobutanol system decreased with the increase of critical CO2 content.The phase equilibrium model was established by Peng-Robinson equation of state and van der Waals-2 mixing regulation,and model parameters were determined by optimization calculation of nonlinear least square method.The correlation between calculated values and the experimental data showed good agreement.

On minimum cavitation number of the ventilated supercavity in water tunnel

A numerical method consisted of the cavitation number correction and the model coefficient correction algorithms is presented to simulate the supercavity in water tunnel considering blockage and gravity effects based on the Logvinovich model.A model of the minimum cavitation number is also proposed based on the dimensional analysis theory,and the minimum cavitation number is formulated based on the model and numerical results using the nonlinear least square method(NLLS).The formula is verified by experiment to some extent.