Research On Mechanism Of Ice Jam Evolution And Simulation Of Velocity And Ice Particle Solid-Liquid Two-Phase Flow Under Ice Cover

Based on an analysis of current research both in China and abroad, the experiment data for the straight channels and curved channels were analyzed. The velocity distributions for the straight and curved channels were simulated. Based on solid-liquid two-phase flow theory, the two-dimensional ice particles trajectory for the vertical profile was simulated. The three-dimensional distribution of deposited rate under ice cover for ice particles in a curved channel was numerically simulated.After evaluating the research findings on ice floes stability at the front edge of the ice cover. the formulas of submergence criteria derived from the experimental data were compared with those currently used in China and abroad. Based on the submergence criteria of field, the formulas with more reasonable results were evaluated. The Incipient motion of non-cohesive sediment under ice cover was analyzed. The findings indicated that an increased ice cover roughness was more favorable to move bed material.Through the experiments on the ice jam accumulation and development in the curved channels, the patterns identified in the experiments were analyzed. When a simulated ice cover was covered in the flume first, the velocity for the initial ice cover front edge to advance towards the downgradient direction increased as the flow Froude number increased. The ice accumulation in the curved channel had two possible open area. These two open area were approximately symmetrical to the apex of curve. When the initial ice cover or jam condition was simulated at the downstream end of bend, the experiment results indicated the ice jam accumulation processes had two sequences: the ice accumulation in a curved channel was developing from upstream to downstream for Fr＜0.035; ice wave was formed during the ice accumulation for 0.035＜Fr＜0.06; the ice accumulation in a curved channel was developing from downstream to upstream for Fr＞0.06. In addition, threshold values existed for the ice accumulation in the curved channel. Within the range of 0.0065～0.0103 for the dimensionless ice discharge Q_i/Q in the experiment, ice jam was formed in the curved channel when Fr≤0.14; partial ice jam was formed in the curved channel when 0.14＜Fr≤0.15; and no ice jam was formed in the curved channel when Fr＞0.16.The experiments revealed that ice jam evolution and the water level change were not synchronous in the curved channel. The change in water level lagged behind the ice jam formation. During the ice jam formation, the water level upstream increased earlier and to a higher level than the water level downstream. Most of ice jam level increase occurred in the initial stage. Single hydraulic factor test indicated that the increase rate for stage with ice jam decreased as the water flow velocity increased. Initial water depth had no notable impact on the increase of ice jam level. An increase in ice discharge increased the ice jam level. To calculate the ice jam level in a curved channel, a method of using ice jam accumulation volume or using the average ice jam thickness was developed. This method could improve the calculation accuracy.It was proved in theory that the assumption of the average velocity for each grid being equal to the average velocity of entire channel under ice jam or cover was erroneous for the shallow channel. However, the numerical analysis revealed a small difference among these average velocities and the maximum of profile with rougher is lager than that of symmetry profile but the location of maximum value of velocity figure changes only in the limited range. Therefore, it was still feasible to assume them to be equal in the engineering applications.The simulation of ice particle movement, based on random trajectory model, indicated that ice particles with large size moved up quickly towards the bottom of the ice jam cover, due to linger buoyancy. The simulated percentages of floating up of ice particles were consistent with those reported by current formulas.