图像法求液滴表面张力和接触角

空间流体实验具有无人操作的特殊性,需要对监控图像进行实时处理,得到目标参数.本文研究了利用照相机捕捉到的液滴灰度图像,分析求取液滴的表面张力、接触角、体积等物理参数的方法.针对液滴的灰度图像,利用边界提取、域值分割等图像处理方法,得到液滴的基本轮廓.建立基于液面像素点坐标的拉普拉斯方程,运用牛顿一拉夫逊法、龙格-库塔法、坐标轮换法等多种数值方法,对液滴的边界进行拟合,寻求最优的轮廓拟合点.根据最优的拟合点,确定液滴的物理参数.提出了利用牛顿法与一维寻优相结合的算法进行轮廓拟合的方法,并与文献[1]提出的算法进行了比较,证明了该方法具有收敛速度较快,拟合精度较高的特点.该方法是实现空间蒸发液滴热毛细对流和接触角测量实验的一项关键技术,同时也可以运用到非接触测量的实验场合. 

Determine the Surface Tension and Contact Angle of Drop by Image Processing Method

The liquid experiment in space needs intelligence to deal with the surveillance image right away to obtain the goal parameters.A method is investigated to analyze the physical feature of a drop,such as surface tension,contact angle and volume through fitting contour of the drop picture. From the grey picture,generally contour of a drop is obtained by edge detection and segmentation algorithms.Constructed the Laplace equation of the drop,made contour approach process through comparing and using Newton-Raphson method,Runge-Kutta method and coordinate optimizing method.With the help of contour approach,physical feature of the drop is obtained.A new algorithm which nests Newton-Raphson method with One-dimensional optimization is presented. Compared with the original algorithm raised by Ref.[1],the new one reached convergence quickly with high accuracy.It is a key technique of the space experimental system for liquid experiment. The method is especially applicable for unmanned environment as well as non-contact measurement in the experiments.