Experimental Study On Sediment Transport Of Coral Sand By Current

Vigorously exploiting marine resources is of great strategic significance to raising the level of the national economy,protecting maritime rights and interests,and safeguarding national sovereignty.Rich coral reef resources are distributed in coastal islands,Hainan Island,Taiwan Island and mainland coasts of South China.Coral reef ecosystem is an important offshore ecosystem,and coral sand is of great significance to the formation of natural sand islands and the maintenance of ecological environment.However,sea level rise caused by global warming in recent years has led to increased shore erosion and coral sand loss.In view of this problem,further research is needed on the kinematic properties of coral sand.At present,coral sand research is mostly focused on engineering properties,and there are fewer studies on motion characteristics.The study of the motion properties of coral sand is not only of academic value,but also of engineering application value.Based on the above research background,this paper conducts experimental studies on the motion of non-uniform coral sand by steady and unsteady flow through laboratory tank experiments,and obtains the following main conclusions:(1)According to the sediment incipience of coral sand,based on the unidirectional steady flow action,the incipient velocity of coral sand by different water depths is measured.Compared with the classic sediment incipience formula,the classic incipience formula was modified to make it suitable for coral sand.Due to the high porosity,poor roundness and irregular shape of coral sand,the incipient velocity is smaller than that of quartz sand.(2)Aiming at the sediment transport of coral sand by steady flow,based on the laboratory tank,the coral sand transport rate experiment by steady flow is carried out,and the coral sand transport rate by different depths and velocities of water is measured.Based on the theory of sediment motion,the effects of water depth and velocity on the sand transport rate of coral sand were analyzed.The sediment transport rate of coral sand is greatly affected by water depth,and the larger the water depth,the more stable the transportation law.Compared with the classic sediment sand transport rate formula,the results show that the coral sand transport rate is smaller,the classic uniform sand sand transport rate formula is not applicable to the experimental coral sand,and some non-uniform sand transport rate formula can better calculate the coral sand transport rate of this experiment.The sediment transport rate formula of non-uniform coral sand bedload by steady flow is derived.(3)Based on the unsteady flow process method.the coral sand transport experiment by unsteady flow is carried out to measure the sand transport rate of coral sand by different water depths,base velocities.peak velocities and current acceleration.A formula for characterizing the unsteady intensity of current was constructed,and the effects of current intensity and unsteady intensity change of current on the sand transport rate of coral sand were analyzed.The unsteady intensity of current and the intensity of thrust mass exercise showed a positive correlation.and the intensity of thrust mass movement increased with the increase of unsteady intensity of current:the unsteady intensity of current showed an exponential relationship with the intensity of pushing mass movement,and the growth rate of thrust mass exercise intensity gradually decreased with the increase of unsteady intensity of current.The sediment transport rate formula of non-uniform coral sand bedload by unsteady flow is derived.(4)In view of the change of coral sand push mass gradation by steady flow,the relationship between coral sand push mass gradation and water depth and velocity is studied,and compared with the existing quartz sand push mass grading formula,the results show that the quartz sand push mass gradation formula is not applicable to the calculation of coral sand push mass gradation in this experiment.