圆柱体结构涡激振动是典型的流固耦合问题，其响应规律大多是在远离壁面和升速流动条件下获得的。而在许多工程应用中，圆柱体通常位于固体边界附近。近壁面圆柱体的涡激振动涉及沿结构表面和底部壁面发展的多个边界层之间的复杂相互作用，可呈现与远离壁面圆柱体不同的响应特征；此外，自然环境流动通常不断地经历升速和降速过程。本文围绕圆柱体涡激振动的近壁面效应问题，主要采用物理模型实验，辅以理论分析的方法，系统研究了近壁面圆柱体的绕流流场特性、涡激振动的临界触发速度和幅频响应特性，以及升降流速作用下涡激振动的迟滞效应。
基于量纲分析方法和相似理论，推导了单向流作用下近壁面圆柱体涡激振动的相似准则，获得了柱体涡激振动的主要无量纲控制参量。在横向涡激振动触发过程的物理模拟中，流固耦合系统阻尼是控制近壁面圆柱体振动响应的关键参量之一。为此，研制了一套具有低结构阻尼参数的圆柱体涡激振动模拟装置，其结构阻尼远小于流体阻尼。
采用“自下向上”激光扫射的粒子图像测速系统（PIV），测量并分析了近壁面圆柱体绕流流场特性。对于远离壁面柱体，在亚临界雷诺数范围内，流动具有相似性，无量纲回流区长度、无量纲旋流强度和雷诺应力幅值等受雷诺数影响较小。对于固定的近壁面柱体，当间隙比e/D ≥ 0.40，壁面对旋流强度的影响可忽略，但间隙流对流动结构（尾流向上偏移）和斯特劳哈尔数的影响较大。当e/D < 0.40时，规则的涡脱落（卡门涡街）受到壁面的抑制作用，同时回流区长度急剧增大，相应的雷诺应力幅值和无量纲旋流强度显著减小。但对尾流脉动的频谱分析表明，此时尾流脉动本质上仍具有周期性，进而可以触发低质量-阻尼组合参数圆柱体涡激振动。对于浸没在近壁面剪切层内的柱体，以柱体中心高度位置来流速度定义的斯特劳哈尔数随着间隙比的减小逐渐增加并最终趋于一个恒定值，最大值较远离壁面圆柱体的斯特劳哈尔数约大25%。在非常小间隙比（e/D ≤ 0.10）条件下，观测到了尾流脉动频谱的多峰特性。
为获得近壁面圆柱体涡激振动的临界触发速度和幅频响应特性，开展了系列大型水槽模型实验，分别采用激光位移传感器（LDT）和声学多普勒流速仪（ADV）以及PIV同步测量圆柱体涡激振动位移时程和远场来流速度变化以及绕流流场特性。近壁面圆柱体的涡激振动触发过程可以分为四个典型的阶段，包括：阶段-①：完全静止；阶段-②：间歇振动；阶段-③：急剧阶跃；阶段-④：涡激振动的上部激励阶段。阶段-②和阶段-③也称为涡激振动的初始激励阶段，但是当e/D ≤ 0.20时，间歇振动阶段消失。在急剧阶跃阶段，振动幅值阶跃的峰值随着间隙比的减小而减小，同时，振动频率阶跃的峰值与其呈负相关关系。和近壁面固定柱体绕流的涡脱落强度被削弱或抑制不同，弹性支撑的圆柱体涡激振动的临界触发速度呈现随间隙比的减小而减小的变化趋势，建立了考虑近壁面效应的圆柱体涡激振动临界触发约减速度公式。
研究发现了自然环境流动，升降流速作用下圆柱体涡激振动的迟滞效应：振动在初始激励阶段和上部激励阶段之间过渡时，升速和降速条件下柱体振动幅值和频率响应曲线并不重合，而是取决于接近过渡状态的方向，即从较低的约减速度升速或从较高的约减速度降速。流动降速条件下涡激振动停振所对应的下临界约减速度明显小于升速时涡激振动触发所对应的上临界约减速度，采用上临界与下临界约减速度的差值定量表征涡激振动迟滞程度，研究发现该值随着间隙比的减小呈线性增大趋势。柱体涡激振动的临界触发速度是评价工程结构稳定性的关键参量，为此，以海底悬跨管道为工程案例，研究了迟滞效应对海底管道允许悬跨长度的影响。采用下临界约减速度估算的允许悬跨长度显著小于常用的上临界约减速度估算的值，提出了一个无量纲参数用以定量描述涡激振动迟滞效应对允许悬跨长度的影响。

Vortex-induced vibration (VIV) of a circular cylindrical structure is a typical fluid-solid coupling problem. Previous investigations on VIV responses were mainly made under increasing-velocity flow and wall-free conditions. Nevertheless, in many engineering applications, the circular cylinder is installed in proximity of a solid boundary. VIV of a near-wall circular cylinder involves complex interactions between the boundary layers developed along the cylinder surface and the bottom wall, so that the VIV responses of a near-wall cylinder hold different characteristics from that of a wall-free cylinder. Moreover, the natural flow always features with alternately increasing or decreasing velocities. In this dissertation, the wall-proximity effects on VIV of a circular cylinder are mainly focused on. The characteristics of flow field around a near-wall cylinder, the critical reduced velocity for the triggering of transverse VIV and the amplitude frequency response characteristics, the hysteresis effect of VIV under the action of increasing-velocity and decreasing-velocity flows have been physically modeled and analyzed theoretically.

Based on dimensional analysis method and similarity theory, the similarity criterion of VIV of a near-wall cylinder under current is established, and the main dimensionless control parameters are obtained. In the physical modeling of the triggering process of transverse VIV, the damping of the fluid-solid coupling system is one of the key parameters controlling the vibration responses of the near-wall cylinder. Therefore, a VIV simulation device with low structural-damping parameters is developed, the structural damping is far less than the fluid damping.

The characteristics of the flow field around a near-wall cylinder are studied systematically with a specially designed Particle Image Velocimetry (PIV) system with bottom-up laser scanning. Under wall-free conditions, the Reynolds number has little effect on the dimensionless recirculation length, swirling strength and Reynolds stress amplitude in the subcritical Reynolds number range. For a fixed near-wall cylinder, when the gap-to-diameter ratio e/D ≥ 0.40, the wall-proximity effect on swirling strength is weak, but the gap flow will have a significant effect on the flow structure (upward shift) and the Strouhal number. Whe e/D < 0.40, the regular Kármán-like vortex-shedding could be suppressed by the bottom wall, at the same time, the dimensionless recirculation length, the corresponding Reynolds stress amplitude and dimensionless swirling strength decrease significantly. However, the present power spectra analyses on the velocity fluctuations in the lee-wake indicate that the characteristic frequency can still be well identified, which could further trigger the vibrations of a low mass-damping cylinder. For a circular cylinder immersed in the near-wall shear layer, the Strouhal number defined by the incoming flow velocity at the center height of the cylinder increases gradually with the decrease of the gap-to-diameter ratio, and finally tends to a constant value. The maximum value is approximately 25 percent larger than that of the wall-free cylinder. Under the condition of very small gap-to-diameter ratio (e/D ≤ 0.10), multi-peaks of the vortex-shedding frequency were observed.

To obtain the critical reduced velocity for the triggering of transverse VIV of a near-wall cylinder and the amplitude-frequency response characteristics, synchronous measurements were made for the time-variation of vibration displacement, far-filed flow velocity and the corresponding flow fields around the cylinder with Laser Displacement Transduser (LDT), Acoustic Doppler Velocimetry (ADV) and PIV, respectively. Four typical stages can be identified in the process of the vibration being triggered, including: stage-①: the fully-stationary; stage-②: the intermittent-vibrating; stage-③: the sharp-jump; and stage-④: the upper excitation branch of VIV. Stage-② and stage-③ are also called the initial excitation branch of VIV, but for e/D ≤ 0.20, the intermittent-vibrating stage disappeared. During the sharp-jump stage, the peak jump-amplitude decrease dramatically as the cylinder approaching the bottom, which has negative correlation with the vibration frequency. Unlike the vortex shedding strength around a fixed near-wall cylinder is weakened or suppressed, the critical reduced velocity for the triggering of transverse VIV of an elastically-mounted circular cylinder shows a decreasing trend with the decrease of gap-to-diameter ratio. The formula of critical reduced velocity for the triggering of transverse VIV of a circular cylinder considering wall-proximity effects is finally established.

The hysteresis effect of VIV under the action of alternately increasing-velocity and decreasing-velocity of natural flows is found, during the transition between the initial and upper excitation branches, the curves of vibration amplitude and frequency responses obtained by increasing-velocity and decreasing-velocity are not coincident with each other but dependent on the direction of approaching the transition regime, i.e., from a lower or a higher reduced velocity. The lower-critical reduced velocity for the cease of VIV under decreasing-velocity flows is significantly smaller than the upper-critical value for the onset of VIV under increasing-velocity flows, and the deviation of the upper-critical reduced velocity from the lower-critical one is used for quantitative characterization of the hysteresis, which increases approximately linearly with the decrease of e/D. The critical reduced velocity for the triggering of VIV is crucial for evaluating the stability of engineering structures. Therefore, a case study is then performed to examine such VIV hysteresis effects on the allowable span lengths of submarine pipelines by the theoretical analyses. The lower-critical span lengths are much smaller than those estimated with the commonly-used upper-critical reduced velocity. A dimensionless parameter is proposed and derived for characterizing the VIV hysteresis effects on the allowable span lengths.