Boundary Effect Of Coherent Perturbation And Nonlinear Dynamics Theory Of Meandering River

River is a nonlinear system with gradient and centeifugal external forces. It has its own inherent patterns, as well as characters drived by external forces, and always take on some typical nonlinear characteristics, such as resonance, bifurcation and chaos.Response of coherent disturbance to wall bounder parameters is one of inherent patterns of meandering river. Large-scale flow structure is the main cause of plane form. Fluctuation of wall bounder change coherent disturbances in meandering river, and flow structure combinded with coherent disturbances make further efforts on shaping river plane form. A nearly constant bounder wavenumber was found as 0.39-0.41. When it came to this meander wavenumber, all scales of coherent disturbances were most stable. The corresponding meander length-width ratio was well fit to statistical results from Leopold and Wolman, Yalin and Julien.Secondary flow and meandering river topography are results of forced vibration of the river system in essence. Perturbation method was used to abtain a weak nonlinear equation solution at bedload global equilibrium. The solution could be based on three families of fuctions, and devided three parts by longitudinal distribution function family: synchronous part, asynchronous part and nonlinear dissipation part. The first two parts were dispersion parts that redistributed unsolved physical quantity, while the last one was dissipation part that caused additional surface slope and energy loss. Therefore, river meandering and width-varation are two kinds of resistance just like well-known grain resistance and dune resistance.In addition, a sin-generated curve shape bend flume was produced to study the strong nonlinear characters of meandering flow structure. Naot and Rodi showed us four circulations of secondary flow structures in straight open channel, caused near flume corners. A couple of section circulations at the top of bend were improved from Naot’s circulations, and the center of circulation current near convex bank was lower than one near concave bank, effected by flume bending. All of physical quantities, such as velocity, turbulence intensity, vorticity and strain, varied along the flow path from one bendtop to the next neighbor bendtop. The energy density distribution varied at different temporal scales, as well as at spatial scales. The enegy density near water surface obeyed Kolmogrov law at higer frequent region more than 1 Hz, domonited by water surface fluctuation, while that near bottom would go to Kolmogrov region at smaller frequency, affected by much smaller streak structure.