利用HHT方法对非平稳风力的时频分析

Time-frequency analysis of a non-stationary wind pressure with HHT method

非平稳信号的分析方法是信号分析领域中的一个重要问题。以风洞试验获得的非平稳风压信号和升力系数信号为研究对象,采用HHT方法对信号进行时频分析。HHT(Hilbert-Huang transform)方法可以获得有意义的瞬时频率,从而给出频率随时间变化的精确表达;信号最终被表示为时频平面上的能量分布,成为Hilbert谱;该方法适用于分析生活中普遍存在的大量频率随时间变化的非线性、非平稳信号,可将复杂的信号直接分离成从高频到低频的若干阶固有模态函数。分析结果虽然没有表现出明显的频谱分布特性,但与以往HHT分析结果提取的固有模态函数不同,如果对该试验获得的非平稳信号提取的固有模态是低频部分的残余信号,忽略其他高频信号,则风压时程和升力系数时程的残余信号曲线就可以分别回归为一个线性函数和一个正弦函数。这也说明,该非平稳信号的主成分仍然是由平稳信号组成的,可以用分析平稳信号的方法进行时程分析。

The analysis method of non-stationary signals is a major issue in signal analysis field.Taking signals of non-stationary wind pressure and lift coefficient obtained from wind tunnel tests as research objects,time frequency analysis of signals was presented with HHT method.Based on HHT method,the meaningful instantaneous frequency,and the exact expression of frequency changing with time were obtained,the signal was finally expressed as the energy distribution in the time frequency plane,i.e.,a Hilbert spectrum.This method could be used to analyze a large amount of nonlinear and non-stationary signals whose frequencies changed with time,and to decompose complex signals into a number of intrinsic mode functions with higher to lower frequencies.The analysis results did not show significant characteristics of spectral distribution,however,they were different from the previous intrinsic mode functions extracted with HHT.If intrinsic mode function extracted from a non-stationary signal in the test was a residual signal with lower frequencies and the other parts with higher frequencies were neglected,the residual signal curves of the time histories of the wind pressure and the lift coefficient could be regressed a linear function and a sine function,respectively.It was shown that the main components of this non-stationary signal are mostly stationary ones,and their time histories can be analyzed with the method of stationary signal analysis.