弯曲河流拟序扰动的边界效应及其非线性动力理论研究
发布时间：2019-06-02 21:29
【摘要】：弯曲河流作为一个非线性系统,压力梯度和边界引起的离心力可看作外在驱动。系统的非线性特征使得河流不仅呈现驱动力对应的特征,还会呈现河流自身的固有特征,以及由二者相互作用产生的新特征,比如共振现象、分岔混沌等。拟序扰动对边界特征的响应是弯曲河流的固有特征。河道水流内部存在一种大尺度的拟序结构,这种水流结构是塑造河流平面形态的主要动力,形态的起伏会影响水流内部的拟序结构,拟序结构又进一步塑造河流形态。因此,本文认为使拟序扰动最稳定的平面形态即为河流的稳定平面形态。通过计算分析,我们发现当边界波数为0.39-0.41时拟序扰动最稳定,其对应的平面形态与Leopold and Wolman,Yalin、Julien等人的统计结果很相近。边界直接导致的水动力和地形特征的力学实质是河流系统的受迫振动。本文采用摄动方法,得到了弯曲河流全域动平衡下的弱非线性摄动解,各物理量均可由三个基本函数族组合而成,及纵向分布基本函数族ri(s)、横向分布基本函数族gj(n)、垂向分布基本函数族fk(ξ)。根据纵向分布基本函数族的不同特征,可将摄动解分为线性同步部分、线性相位差部分和非线性耗散部分。前两部分为色散项(rDp)仅使得河段物理量重分布,并不改变河段的整体特征量;非线性耗散部分(rDs),是河流平面形态阻力(弯曲阻力和伸缩阻力)产生的内在机理,使得河段产生附加坡降和阻力。因此,河道的平面形状弯曲、伸缩也是一种阻力。岸线摆动对强弯水流呈现明显的时空特征影响很大,弯顶断面分别在靠近凹岸上部和凸岸下部形成两个大的环流,二者分别由Naot,Rodi(1982)的凹岸上环流和凸岸下环流经弯曲作用发展而来。相邻两弯环流对强弱的相互转换,使得曲率为零的过渡断面附近流场急剧变化,流体微团发生急剧的旋转、变形。槽壁摆动引起瞬时水流不仅空间分布不均,在长时间尺度上也呈现波动变化。近水面处主要受水面波动的影响,高于1 Hz的高频部分即进入Kolmogorov-5/3衰减区,而近底处水流紊动主要受条带结构的影响,需要在更高的频段才能进入Kolmogorov区域。
[Abstract]:As a nonlinear system, the centrifugal force caused by pressure gradient and boundary can be regarded as external drive. The nonlinear characteristics of the system make the river not only present the characteristics of the driving force, but also the inherent characteristics of the river itself, as well as the new characteristics caused by the interaction between the two, such as resonance phenomenon, bifurcation chaos and so on. The response of quasi-ordered disturbance to boundary characteristics is an inherent feature of curved rivers. There is a large scale quasi-order structure in the river flow, which is the main driving force to shape the plane shape of the river. The fluctuation of the shape will affect the quasi-order structure inside the flow, and the quasi-order structure will further shape the river shape. Therefore, this paper holds that the plane form that makes the quasi-order disturbance the most stable is the stable plane form of the river. Through calculation and analysis, we find that the quasi-ordered disturbance is the most stable when the boundary wavenumber is 0.39-0.41, and the corresponding plane shape is very close to the statistical results of Leopold and Wolman,Yalin,Julien et al. The mechanical essence of hydrodynamic and topographic characteristics caused directly by boundary is the forced vibration of river system. In this paper, the perturbation method is used to obtain the weak nonlinear perturbation solution under the global dynamic equilibrium of curved rivers. Each physical quantity can be composed of three basic function families, and the longitudinal distribution basic function family ri (s),. Transverse distribution basic function family gj (n), vertical distribution basic function family fk (Zeta). According to the different characteristics of the basic function family of longitudinal distribution, the perturbation solution can be divided into linear synchronization part, linear phase difference part and nonlinear dissipation part. The first two parts are dispersion term (rDp), which only redistributes the physical quantity of the reach and does not change the overall characteristic quantity of the reach. The nonlinear dissipative part (rDs), is the internal mechanism of the plane form resistance (bending resistance and telescopic resistance) of the river, which makes the river reach produce additional slope drop and resistance. Therefore, the plane shape of the river is curved and telescopic is also a kind of resistance. The swinging of the shoreline has a great influence on the spatial and temporal characteristics of the strong curved flow. The curved top section forms two large circulation systems near the upper part of the concave bank and the lower part of the convex bank, respectively, which are caused by Naot,. The concave and subbank circulation of Rodi (1982) developed through bending. The transformation of the strength and strength of the adjacent two curved circulation makes the flow field near the transition section with zero curvature change sharply, and the fluid micromass rotates and deforms sharply. The instantaneous flow caused by the swing of the trough wall not only has uneven spatial distribution, but also fluctuates on a long time scale. The high frequency part above 1 Hz is mainly affected by the fluctuation of the water surface, while the turbulence near the bottom is mainly affected by the strip structure, so it is necessary to enter the Kolmogorov region in a higher frequency band.
【学位授予单位】：天津大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TV147
本文编号：2491436
[Abstract]:As a nonlinear system, the centrifugal force caused by pressure gradient and boundary can be regarded as external drive. The nonlinear characteristics of the system make the river not only present the characteristics of the driving force, but also the inherent characteristics of the river itself, as well as the new characteristics caused by the interaction between the two, such as resonance phenomenon, bifurcation chaos and so on. The response of quasi-ordered disturbance to boundary characteristics is an inherent feature of curved rivers. There is a large scale quasi-order structure in the river flow, which is the main driving force to shape the plane shape of the river. The fluctuation of the shape will affect the quasi-order structure inside the flow, and the quasi-order structure will further shape the river shape. Therefore, this paper holds that the plane form that makes the quasi-order disturbance the most stable is the stable plane form of the river. Through calculation and analysis, we find that the quasi-ordered disturbance is the most stable when the boundary wavenumber is 0.39-0.41, and the corresponding plane shape is very close to the statistical results of Leopold and Wolman,Yalin,Julien et al. The mechanical essence of hydrodynamic and topographic characteristics caused directly by boundary is the forced vibration of river system. In this paper, the perturbation method is used to obtain the weak nonlinear perturbation solution under the global dynamic equilibrium of curved rivers. Each physical quantity can be composed of three basic function families, and the longitudinal distribution basic function family ri (s),. Transverse distribution basic function family gj (n), vertical distribution basic function family fk (Zeta). According to the different characteristics of the basic function family of longitudinal distribution, the perturbation solution can be divided into linear synchronization part, linear phase difference part and nonlinear dissipation part. The first two parts are dispersion term (rDp), which only redistributes the physical quantity of the reach and does not change the overall characteristic quantity of the reach. The nonlinear dissipative part (rDs), is the internal mechanism of the plane form resistance (bending resistance and telescopic resistance) of the river, which makes the river reach produce additional slope drop and resistance. Therefore, the plane shape of the river is curved and telescopic is also a kind of resistance. The swinging of the shoreline has a great influence on the spatial and temporal characteristics of the strong curved flow. The curved top section forms two large circulation systems near the upper part of the concave bank and the lower part of the convex bank, respectively, which are caused by Naot,. The concave and subbank circulation of Rodi (1982) developed through bending. The transformation of the strength and strength of the adjacent two curved circulation makes the flow field near the transition section with zero curvature change sharply, and the fluid micromass rotates and deforms sharply. The instantaneous flow caused by the swing of the trough wall not only has uneven spatial distribution, but also fluctuates on a long time scale. The high frequency part above 1 Hz is mainly affected by the fluctuation of the water surface, while the turbulence near the bottom is mainly affected by the strip structure, so it is necessary to enter the Kolmogorov region in a higher frequency band.
【学位授予单位】：天津大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TV147
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