黏性非均匀沙的起动概率

基于概率论与力学结合的方法，探讨了黏性非均匀沙的起动问题．将促使颗粒运动的外力矩大于颗粒保持静止的外力矩视为泥沙起动的临界力学条件，通过作用力臂的统计处理以反映颗粒在床面排列的随机性，并基于瞬时底流速的概率分布和试验资料建立起适合黏性非均匀沙的起动概率公式．其中作用力包括推移力、上举力、水下重力和黏性力，而黏性力表达式则根据因次分析和交叉石英丝试验得到，涉及到泥沙非均匀性、干密度和水压力等影响因子．摩阻流速的计算值与试验值的比较表明，起动概率和相应临界摩阻流速公式合理地刻画了非均匀沙起动的随机力学特性，考虑因素较为全面，对无黏性和黏性的非均匀沙均适用，可供潮汐河口非均匀沙冲刷预测时使用．

Incipient probability of cohesive nonuniform sediment

Incipient motion of nonuniform sediment in estuaries was studied using probability theory with mechanics approach.Incipient motion of sediment occurs when moments of force that let particles move are larger than those that keep particles static.The formula for incipient probability of nonuniform sediment containing cohesive particles was established after the arms of force were statistically treated and the probability distribution of instantaneous bottom velocity was assumed.Forces acting on a particle include drag force,lift force,gravity and cohesive force.The expression for cohesive force was(derived) from both dimension analysis and cross-quartz-thread experiment,in which several factors,such as nonuniformity,dry density of sediments and water pressure,were taken into account.Comparison of(calculated) friction velocity with the measured friction velocity indicated that the incipient probability and friction velocity(formulas) can describe the stochastic-mechanistic properties of incipient motion of nonuniform sediment.The formulas dealing with many factors were applicable to noncohesive and cohesive nonuniform sediments,and can be used to predict scouring in tidal estuaries.