摘要
为了探讨植物木质部空穴化过程超声发射的特性和产生机理,基于Rayleigh-Plesset方程建立了描述空泡在导管中运动的方程并求解,同时构建超声检测系统并对植物木质部超声发射进行检测与分析。根据方程计算出气泡的平衡半径,当气泡受到扰动,如木质部液压强变化等原因造成半径大于或小于平衡半径时,用四阶龙格-库塔法求解方程,结果显示气泡会以减幅振动的方式回到平衡状态,形成振源发射超声。实测侧柏、元宝枫、刺槐切片在失水过程中的超声发射信号,并对其进行分析。结果表明:实测超声发射信号的频率、振铃数等与植物导管或管胞大小和材质无显著关系,约80%的信号特征与仿真计算结果一致。说明植物导管或管胞中,气泡以减幅振动的形式膨胀和塌缩所产生的超声信号是木质部空穴化过程中产生超声发射信号的原因之一。
This study focused on the characteristics and mechanism of ultrasonic acoustic emissions （UAEs） from the cavitation in xylem sap. A bubble motion equation based on the Rayleigh-Plesset equation was established and solved. The UAEs from xylem were detected by constructing an ultrasonic detection system and then the equilibrium radius was calculated. By solving the equation with a four-order Runge- Kutta method, we found that the radii of the bubbles were greater or less than the equilibrium radius when disturbed by other changes, such as changes of xylem sap pressure; the bubbles would get back to the stable equilibrium by the way of convergent oscillation, which was the source of UAEs. UAEs from slices of Platycladus orientalis, Acer truncatum and Robinia pseudoacacia when losing water were detected and analyzed. The results showed that the frequency and ringing counts of the signals detected had no significant correlation with conduits or tracheids. About 80% of the signals detected were similar to that calculated. The tiny air bubbles in conduits or tracheids emited UAEs when they were expanded and contracted by the way of convergent oscillation.
出处
《北京林业大学学报》
CAS
CSCD
北大核心
2012年第3期36-40,共5页
Journal of Beijing Forestry University
基金
国家自然科学基金项目(30270343)
关键词
空穴化
木质部
超声发射
数值模拟
cavitation
xylem
ultrasonic acoustic emission
numerical simulation
