基于小波相干的波流相关性分析

本文基于交叉谱和小波相干对不同水深时的波流相关性进行分析。首先对实验室波流信号进行凝聚谱估计,结果显示,在谱峰附近,波流呈现统计意义上的显著相关性,不同水深时的相关性强弱有所区别,中层水深的波流相关性最强。其次采用小波相干估计波流相关性,结果显示,在频率约为0.67~2.70 Hz时波流相关性较强,位于中层水深时,波流呈现强相关性的时间段最长,在浅层和深层水深时,波流呈现强相关性的时间段较短。

波流信号交叉谱估计方法比较

本文利用风浪实验数据,采用Welch、MTM、MVDR等方法估计了波面位移和铅直流速的凝聚谱,以期得到适合于波流信号的交叉谱估计方法。数据分析结果表明,三种方法给出的凝聚谱估计在以谱峰频率为中心的较宽频段上基本一致,均高于临界值,表明波流信号在主导波频段上存在显著的相关性;在高频段,MVDR方法估计存在一个类似单谱的指数衰减趋势,而另外两种方法的估计值持续高于临界值。数值模拟结果亦表明MVDR方法有更强的相关信号识别能力和频率分辨能力,且不易出现伪峰,因而估计结果更加可靠。

Research on the Correlation of the Fluctuating Density Gradient of the Compressible Flows

This work is to study a role of the fluctuating density gradient in the compressible flows tbr the computational fluid dynamics （CFD）. A new anisotropy tensor with the fluctuating density gradient is introduced, and is used for an invariant modeling technique to model the turbulent density gradient correlation equation derived from the continuity equation. The modeling equation is decomposed into three groups proportional to the mean velocity, proportional to the mean strain rate, and proportional to the mean density. The characteristics of the correlation in a wake are extracted from the results by the two dimensional direct simulation, and shows the strong correlation with the vortices in the wake near the body. Thus, it can be concluded that the correlation of the density gradient is a significant parameter to describe the quick generation of the turbulent property in the compressible flows.