非线性随机系统的概率密度追踪控制

针对目前非线性随机系统控制方法的设计复杂、计算成本高以及缺乏稳定性或收敛性证明等缺点,提出了一种全新的基于等效非线性系统法求近似稳态解的思想设计的非线性随机系统的反馈控制,使受控系统输出的稳态概率密度函数逼近事先给定的目标概率密度函数.利用Lyapunov函数法证明了受控系统的收敛性.数学仿真结果证明了这种方法的可行性和正确性.

考虑几何非线性的海底悬跨管道疲劳可靠性分析方法

疲劳可靠性是海底悬跨管道安全性分析的一个重要组成部分。考虑海底悬跨管道的几何非线性特征,建立了悬跨管道疲劳可靠性分析方法。该方法结合模态分析,首先把系统隐式的非线性项转化为由模态坐标高次组合表示的显式非线性项,在此基础上引入虚拟激励法,建立结构在随机流力作用下的等效线性化系统,从而确定结构非线性随机响应,在此基础上进一步分析悬跨管道的疲劳可靠性。通过对某一海底管道的分析结果,表明该方法具有较好的计算精度和较快的计算速度。同时分析了不同悬跨长度对计算结果的影响,分析结果表明在管道悬跨长度较小时忽略几何非线性因素对结果影响很小,当悬跨长度较大时,忽略结构几何非线性的影响将会产生显著误差。

多自由度柔性结构非线性随机振动响应分析方法

随机等效线性化方法是多自由度结构非线性随机振动分析的有效方法,然而柔性结构隐式的系统方程限制了该方法的应用。本文首先提出了把多自由度柔性结构隐式系统方程显式化的等效非线性系统建立方法,该方法结合模态分析,将系统几何非线性作用等效为模态坐标的高次多项式组合,把多自由度物理系统转化为容易求解的模态系统;在此基础上运用随机等效线性化技术建立柔性结构非线性随机振动响应分析方法。该方法通过引入虚拟激励原理,大幅提高了计算效率,使对多自由柔性结构的非线性随机振动响应分析成为可能。通过算例分析,本文分析结果和精确解与数值模拟解的比较结果表明,本文方法具有较好的计算精度和较高的计算效率,能够应用于实际柔性工程结构的随机振动响应分析。

随机部分可积拟哈密顿系统的概率密度追踪控制

目前非线性随机系统的控制方法存在设计复杂,计算成本高,以及缺乏稳定性或收敛性证明等缺点,针对这些问题,本文在作者前期研究的基础上发展了一种全新的针对部分可积的非线性随机系统的反馈控制,使得受控系统输出的稳态概率密度逼近事先给定的目标概率密度,并利用Lyapunov函数法证明受控系统的收敛性.数学仿真结果证明了这种方法的可行性和正确性.

考虑几何非线性海底悬跨管道随机振动分析方法

考虑海底悬跨管道的几何非线性特征,建立了悬跨管道非线性随机振动响应分析方法。该方法结合模态分析,首先把系统隐式的非线性项转化为由模态坐标高次组合表示的显式非线性项,在此基础上引入虚拟激励法,建立结构在随机流力作用下的等效线性化系统,从而确定结构非线性随机响应。通过对某一海底管道的分析结果,表明该方法能够有效的考虑几何非线性的影响且具有很高的计算效率。同时分析了悬跨长度、管道外径和残余应力因素对计算结果的敏感性。结果表明:当悬跨长度达到较大跨度后,忽略结构几何非线性的影响,将会导致较大的误差;在较大的跨距、较浅的水深、较小的外径、初始压应力这些因素下,管道响应幅值较大。因此在这些因素存在时,要引起高度的关注。

竖向参激作用下刚性滑动体系响应的稳态概率分布

运用等效非线性系统法推导了库伦摩擦刚性滑移结构在竖向高斯白噪声地面作用下响应的稳态合概率密 度函数的解析解。结果表明，竖向阻尼参激对水平稳态振动的影响不大。

Super-harmonic resonance of gear transmission system under stick-slip vibration in high-speed train

This work deals with super-harmonic responses and the stabilities of a gear transmission system of a high-speed train under the stick-slip oscillation of the wheel-set.The dynamic model of the system is developed with consideration on the factors including the time-varying system stiffness,the transmission error,the tooth backlash and the self-excited excitation of the wheel-set.The frequency-response equation of the system at super-harmonic resonance is obtained by the multiple scales method,and the stabilities of the system are analyzed using the perturbation theory.Complex nonlinear behaviors of the system including multi-valued solutions,jump phenomenon,hardening stiffness are found.The effects of the equivalent damping and the loads of the system under the stick-slip oscillation are analyzed.It shows that the change of the load can obviously influence the resonance frequency of the system and have little effect on the steady-state response amplitude of the system.The damping of the system has a negative effect,opposite to the load.The synthetic damping of the system composed of meshing damping and equivalent damping may be less than zero when the wheel-set has a large slippage,and the system loses its stability owing to the Hopf bifurcation.Analytical results are validated by numerical simulations.

Calculations of the bounds on limit cycle oscillations in nonlinear aeroelastic systems based on equivalent linearization

The nonlinear aeroelastic system of an airfoil with an external store was investigated,with emphasis on the bounds of limit cycle oscillations(LCOs).Based on the equivalent linearization,an approach was proposed to calculate the bounds on LCOs over the full flight envelope.The bounds are determined directly without solving LCOs one by one as the flow speed varies.The presented approach can provide us with the maximal LCO amplitudes and the lower threshold for flow speed beyond which LCOs may arise.Numerical examples show that the obtained bounds are in nice agreement with numerical simulation results.The speed threshold can be predicted to a relative error less than 0.1%,and the maximal LCO amplitude to about 3%.The influences of the system parameters on the speed threshold for speed were investigated efficiently by the proposed approach.