沙粒蠕移运动速度测量及其统计分析

Statistical study on the velocity of aeolian creeping sands using high-speed digital photography

对大气边界层风洞中沙粒蠕移运动进行了高速光学测量并获取了数字图像序列。经过非负图像减法、自动阈值法及双向粒子追踪算法的依次运算,提取了足量的有效蠕移运动轨迹。从轨迹信息中获取了蠕移速度并进行统计分析,结果表明了以起动方式划分的两种蠕移运动的比重特性及其随摩阻风速的变化规律:流体起动蠕移代表整个蠕移运动的稳定变化部分,而碰撞起动蠕移代表动态变化部分;随着摩阻风速增大,前者比重减小,后者比重增大;在摩阻风速超过临界值之后,蠕移运动的主导形式从流体起动转化为碰撞起动。

High-speed digital photography was adopted to record sand creep motion in atmospheric boundary layer wind tunnel.Non-negative subtraction algorithm,dynamical threshold algorithm and bidirectional particle tracking algorithm were applied successively to abstract adequate and valid creep trajectories from image sequence.Then,velocity magnitude and lift-off velocity of creep sands were statistically analyzed.The results indicated that creep motion initiated by flow and that initiated by collision respectively stood for steadily and dynamically varying parts of whole creep motion;as friction velocity increases,proportions of two parts would go in opposite way and the dominance would eventually turn to latter part once the friction velocity exceeds critical value.