为了验证三角形和四边形准则的二值逻辑反投影(Binary Logic Back Projection,BLBP)算法在超声层析成像重建过程中的可行性,以超声层析成像的重建区域中同时含有圆柱形和椭圆柱形障碍物为例,利用COMSOL对成像区域内存在障碍物的声场进行仿真,得到声场声压分布。然后,通过提取和处理所获取的声压分布,获得信号矩阵。最后,将信号矩阵代入二值逻辑反投影算法进行图像重建。仿真结果表明:当入射波的波长λ远小于障碍物的尺寸时,声衍射的现象并不明显。重建结果表明:两种准则在几何近似理论下可行,且四边形准则的效果优于三角形准则。
搭建蒸汽测试实验系统,结合经典ECAH(Epstein-Carhart-Allegra-Hawley)理论模型,提出三频率超声波声衰减颗粒测量方法,采用中心频率为22,40和200 k Hz的超声波开展蒸汽液滴粒径和含量(体积分数)的超声法测量实验,在相同工况下基于光散射法的原理,同时开展多波长消光法和激光散射法对比测试研究。实验结果表明:超声衰减法测得蒸汽液滴粒径和含量与消光法和激光散射法的测量值接近,超声衰减法有望用于气液两相流中蒸汽液滴粒径以及含量(湿度)参数的在线监测。
For the study of predicting ultrasonic attenuation of elastic, spherical mixing par- ticles in the liquid-solid two-phase system, the Monte Carlo method （MCM） is introduced, serving as a probability and statistics technique to evaluate the inside ultrasonic events during the ultrasound propagation. On the basis of ultrasonic scattering and aborption, the continuous ultrasonic waves are represented as discrete and independent phonons. By recording the scat- tering events, tracing the trajectory of a moving phonon and calculating the number of phonons that finally reach the receiving transducer, the ultrasonic attenuation coefficient is obtained to be a frequence-dependent spectrum. Numerical investigations have been carried out to predict and compare the ultrasonic attenuation for a solid-liquid two-phase system with a single type particle. After verifing its feasibility, such a method is then appalied into mixing particle sys- tern, where the mixing iron particles and glass beads with various ratios are set as examples for the purpose of predicting ultrasonic attenuation for the monodisperse and polydisperse mixing particle systems. The results of MCM, the ECAH model, the Lloyd ~z Berry （LB） model and the Waterman model match well when the particle volume concentration is lower than 10%, corresponding to iron particles and glass beads respectively. In the case of two-phase system with mixing particles, it is shown that as the particle volume concentration increases to 10%, the variation of the ultrasonic attenuation coefficient with mixing ratio yields a nonlinear tendency. The physical properties of particles can also influence ultrasonic attenuation significantly.
LI YunsiSU MingxuYANG HuinanFAN FengxianCAI Xiaoshu
