HHT在长江三峡水库入库量时频分析中的应用

APPLICATIONS OF HHT TO TIME-FREQUENCY ANALYSIS OF INFLOW IN THE THREE GORGES RESERVOIR

三峡库区入库量作为随时间变化的序列具有非线性和非平稳性特征,所涵盖的频率信息不仅能够体现长江流域年变化尺度以上的周期特点,而且在每年汛期与枯水期的频率变化也有所不同。主要利用HHT方法对三峡库区入库量信号进行分析处理,首先利用EMD方法对信号进行分解,分析结果能够清晰分辨出由高到低不同频率范围的固有模态函数分量;对固有模态函数分量做Hilbert变换得到时频特征表明:在20d至1a的周期范围内,频率幅值变化不大,但自2003年蓄水开始,频率存在略有增大的趋势,并且洪水期与枯水期频率变化分界不明显;年周期是20a库区信号中稳定的周期性变化信息,而残差信号代表了入库量的整体趋势,反应了整个库区水量自1998年起的减小趋势。

As a time-varying signal,the inflow of the Three Gorges Reservoir is nonlinear and non-stationary,which contains the frequency information that not only can reflect the cycle characteristics of above the annual variation scale in the Yangtze River basin,but also is different in every flood season and dry season.In this paper,the HHT method was used to process and analyze the inflow data in the Three Gorges Reservoir area.By using the EMD method,the signal was decomposed and the analysis results could clearly distinguish the intrinsic mode function components,the frequency of which was different and range from high value to low value.Though Hilbert transfer for the intrinsic mode function components,the time-frequency characteristics showed that the frequency amplitude had a little change in the twenty days to one year cycle range.But the frequency depicted the slight increasing tendency since the impoundment in 2003,and the delimitation of frequency variation was not obvious between the flood and the dry season.Furthermore,annual cycle of periodic change information was stable,and the residual signal represented the inflow of the overall trend,which reflected the trend of decrease in the whole reservoir area since 1998.