A Dynamic River Ice Model Based On Coupled Discrete Element Method And Hydrodynamics And Its Applications

The river ice flood is significant for water conservancy projects in cold regions.It has a great impact on the utilization of river water resources and is critical to river flood control,navigation,hydropower,water supply and the environment.In recent years,river ice theories have been established based on field observation,laboratory experiments and numerical simulation,which can explain the physical mechanism of most river ice processes.However,there are still some unsolved issues,such as the determination of initial ice jam position,the development of suspended ice dam,ice cover breakup process,the interaction between ice and structure,ice-water-sediment simulation,etc.Since measurements of the parameters by in-situ observation and laboratory experiments are hardly sufficient in river ice research,it is of great value to develop an appropriate numerical model to simulate the river ice process.Ice is a brittle material and has obvious discrete characteristics in distribution and morphology,which is difficult to be described by traditional methods.Therefore,a new river ice model,that can describe the dynamic process of river ice transport,accumulation,fracture,jamming,as well as can be applied in real river engineering,needs to be established.In this thesis,the study focuses on the development of the river ice dynamic model and its application in the simulation of river ice transport,ice jam formation and evolution,ice cover breakup,ice stoppage,and other processes.The proposed model is verified and shows great value in river ice research.The main contents of this thesis are as follows:(1)The dynamic model of river ice based on the coupled discrete element method and hydrodynamic is established.Considering the driving forces of wind,flow,gravity,internal force and boundary resistance,the motion equation is solved by the discrete element method.The hydrodynamics are modeled by the two-dimensional shallow water equation.The information transmission of ice and water flow is carried out by linear interpolation and averaging.(2)The bond-fracture model under arbitrary contact pattern of dilated polyhedron elements is developed.The virtual bond surface and bond points are set up at the initial contact point of two adjacent elements,and the force and moment between the bonded elements can be transferred.The damage process is characterized by the hybrid fracture criterion and fracture energy is calculated according to Benzeggagh-Kenane theory.The model has been successfully applied to simulate the punch-through process of ice rubble,and the difference in mechanical properties between consolidated and unconsolidated ice rubble is analyzed.(3)The dynamic process of ice cover fracture and transverse crack propagation caused by waves is simulated and analyzed.The ice cover is modeled by bonded dilated polyhedral elements,and the triangular-shaped wave is constructed by adjusting the hydraulic boundary conditions in the modelling.The main mechanisms of ice cover deformation and fracture as a wave passing by are illustrated.The influence of varying wave characteristics such as wave height,wavelength,wave slope,and the influence of ice properties such as ice thickness and ice flexure strength on the process of cracks propagation are investigated.(4)The process of ice jam formation is simulated by the proposed river ice dynamic model.The ice transport,accumulation and mechanical thickening are described in the results.The accuracy and applicability of the model in simulating ice jam are verified by comparing with Dyna RICE.Furthermore,the formation and evolution of ice jam under the influence of ice cover are simulated and the results show that the stability of ice jam at the leading edge of the ice cover can be influenced by ice discharge,bank resistance,ice cover strength and hydraulic condition.The compression of the ice jam can lead to the destruction of the leading edge of the ice cover and the force induced by the ice jam on the ice cover fluctuates while the ice jam pushing downstream.The breaking blocks from the ice cover will be incorporated into the jam rubble and cause more serious backwater.(5)The river ice dynamic model is applied to simulate the ice dynamic process in natural rivers.Based on the increasingly improved monitoring technology,a framework of a numerical model is proposed aiming at reflecting the ice condition comprehensively.Ice transport in the Shisifenzi reach of the Yellow River in Inner Mongolia is simulated,and the influence of border ice,flow velocity,the density of ice supply on river ice stoppage is analyzed.In addition,the ice dynamic process under influence of bridge pier is investigated.