It is also found by comparing with different mean cross sections that there is similar variability for the mean attenuation and scattering cross sections as a function of the different variance , expectation and the wave lengths , but there is much difference for the mean scattering and back scattering cross sections especially when the rotatory axes are oriented randomly in normal distribution in oxy plane or oyz plane and 3d space 还对比各种平均截面可知:对于平均衰减截面、平均散射截面两者随方差、期望及波长有着相似的变化规律;但平均散射截面、平均后向散射截面之间,有着很多的不相同,特别在旋转轴在oxy平面、 oyz平面内和在空间oxyz内随机正态取向时的情形。
By driving expressions and using the method in numerical integration , the results of numerical calculations are analyzed , discussed and contrasted with different conditions , and they showed that there are evident differences in the mean attenuation , scattering , and back scattering cross sections of oblate spheroid particles when the variance is so small that it is near to zero namely it is the same as the rotatory axes are parallel with one direction and when h - polarized and v - polarized incident waves happened . these differences are depended on the relative differences in the average orientation of rotatory axes and the polarized directions of incident wave 通过公式推导和数值积分计算并对结果做了讨论和分析,对比各种情况表明:扁椭球粒子群在方差很小接近为0时,与粒子群旋转轴一致取向的情况相同,入射波水平极化和垂直极化时的平均衰减截面、平均散射截面、平均后向散射截面有明显的不同,这决定于旋转轴平均取向和入射波极化方向的相对差异。
At last , the valid data based fast emd algorithm was proposed . chaper five aimed to the requirement of the emd based time - frequency analysis in the field of rotating machinery signal analysis and fault diagnosis . studied the method of rotatory speed prediction to improve the precision of complete period sampling of vibration signals in rotating machinery , then , discussed the phenomenon of mode fission in noise signal anlysis by emd and provided the filter method to weaken the phenomenon . after then , found a process to analysis the signals using emd - based method in the field of rotating machinery signal analysis and fault diagnosis 第五章针对旋转机械信号进行emd时频分析的要求,提出了提高整周期采样精度的预测算法和适合于单片机计算的近似公式;论述了模态裂解现象,并通过仿真信号和实际信号的研究,提出了使用滤波技术来减弱模态裂解现象的方法;给出了适合于旋转机械振动信号基于emd时频分析的工作步骤;研究了基于emd的旋转机械振动信号自适应滤波技术。