Theoretical Analysis On Relative Hidden Degrees Of Sediment Particles And Its Application

Researching on incipient motion of sediment is of great significance to theconstitution of the system of basic theory associated sediment movement. Within twoand a half centuries, a series of problems with respect to incipient motion aboutcohesionless uniform sediment, cohesionless non-uniform sediment, cohesionaluniform sediment and cohesional non-uniform sediment were explored gradually.Owing to the different research methods to the incipient motion of sediment, thecognitions on the incipient mechanism, incipient condition, incipient index andincipient characteristic concerning sediment particles can not be integrated. Theexperiment showed that, with the wide grading non-uniform sediment speaking,"large grain"was much easier to start than the same size uniform sediment, the"smallgrain"was much harder to start, and the incipient condition of"medium grain"correspond to the same size uniform sediment. The hidden and exposed effect amongthe sediment particles were cognized gradually,and a series of problems of absolutelyhidden degree(exposed degree), relative hidden degree(exposed degree) andexposed(hidden) coefficient were turned into hotspot and difficulty gradually.There are two different schools to study the hidden degree of sediment particles:absolute hidden degree and relative hidden degree. Due to the constraints ofexperimental conditions, the research progress on sediment particles were not smoothgoing. The relative hidden degree of sediment particles established by Han Qi-weiwas applied to the research on incipient motion and examined appropriately by someexperiments. Basing on the research concept of Han Qi-wei, the relative hiddendegree and its applications was studied emphatically. This paper includes three parts,as follows:(1) Research on relative hidden degree with respect to different dimensions:Basing on the concept of 2-D relative hidden degree of sediment particlesestablished by Han Qi-wei, the concept of 3-D relative hidden degree was proposed,the veryformula of uniform and non-uniform sediment was deduced in the statistical sense,the regularity of distribution of relative hidden degree was discussed, and theconcepts of"large grain","small grain"and"medium grain"associated with broadlygraded non-uniform sediment were proposed.(2) Research on incipient motion of cohesionless sediment on the basis ofrelative hidden degree:When using the rolling circle model to study the incipient problem of sediment onthe bottom slope and bank slope, the effective formulas of incipient velocity near thebed were deduced, a series of concepts, such as'Completely Hidden','ExtremeJump','Pseudo Completely Hidden'and'Critical Exposure'were proposed, thestarting characteristic of non-uniform sediment was proved, the reason for the ShieldsFillet Curve was proposed, and the numerical relations between the hidden degree andincipient motion conditions were established.(3) Experimental study basing on physical test based on the relative hiddendegree of sediment particles:The doubt about the most basic understanding in the sediment filed, which is"submarine rest angle is equal to internal friction angle associated with sedimentparticles", was put forward. That submarine rest angle is less than internal frictionangle of sediment particles was discovered via the experiment.