声发射波形包含煤岩体失稳破坏的微观细致结构特征,为了得到煤岩体在不同加载阶段更多的煤岩失稳细观结构特征,本文采用HHT方法对不同加载阶段的声发射波形特征进行分析.研究结果表明,HHT可以将目标波形分解成多个IMF分量,能量主要集中在c1~c4 IMF分量,其中c1分量频率最高,能量也最大,随着加载进行低频IMF分量所占的能量比例呈现增加的趋势.Hilbert边际谱在初始压密阶段集中在0~40 kHz的低频部分,塑性变形阶段在0~25 kHz和200~350 kHz的范围内有明显的能量集聚特征,而在失稳破坏时集中在0~25 kHz,并在20 kHz时达到最大.各个阶段均有一个较为明显的瞬时能量峰值,在初始压密和压密结束阶段波形的瞬时能量峰值较高,但由于波形有效持续时间较短,携带的总体能量较小,破坏时瞬时能量高值持续时间较长,波形的总能量达到最大.Hilbert三维能量谱在真实能量为0的区域,其能量谱一般为0,并且分布是断续而非连续的,跟前述几个动态范围的特点是一致的,但更为明显地表明了失稳破坏临界阶段的能量低频集聚.该研究反映了煤岩失稳破坏演化过程的地球物理信号的响应规律,为监测煤岩动力灾害提供依据.
Acoustic Emission (AE) waveforms contain information on microscopic structural features that can be related with damage of coal rock masses. In this paper, the Hilbert-Huang transform (HHT) method is used to obtain detailed structural characteristics of coal rock masses associated with damage, at different loading stages, from the analyses of the characteristics of AE waveforms. The results show that the HHT method can be used to decompose the target waveform into multiple intrinsic mode function (IMF) components, with the energy mainly concentrated in the c1?c4 IMF components, where the c1 component has the highest frequency and the largest amount of energy. As the loading continues, the proportion of energy occupied by the low-frequency IMF component shows an increasing trend. In the initial compaction stage, the Hilbert marginal spectrum is mainly concentrated in the low frequency range of 0?40 kHz. The plastic deformation stage is associated to energy accumulation in the frequency range of 0?25 kHz and 200?350 kHz, while the instability damage stage is mainly concentrated in the frequency range of 0?25 kHz. At 20 kHz, the instability damage reaches its maximum value. There is a relatively clear instantaneous energy peak at each stage, albeit being more distinct at the beginning and at the end of the compaction phase. Since the effective duration of the waveform is short, its resulting energy is small, and so there is a relatively high value from the instantaneous energy peak. The waveform lasts a relatively long time after the peak that coincides with failure, which is the period where the waveform reaches its maximum energy level. The Hilbert three-dimensional energy spectrum is generally zero in the region where the real energy is zero. In addition, its energy spectrum is intermittent rather than continuous. It is therefore consistent with the characteristics of the several dynamic ranges mentioned above, and it indicates more clearly the low-frequency energy concentration in the critical stage of instability failure. This study well reflects the response law of geophysical signals in the process of coal rock instability and failure, providing a basis for monitoring coal rock dynamic disasters.