Aeroelastic and Non-linear Structural Dynamic Interactions of Slender Structures

随着更细长、更冒险的结构（如斜拉桥）的建造，它们越来越容易受到大振幅振动的影响，特别是由于空气动力载荷的影响。风引起的桥面、电缆、塔、灯柱和架空电缆的振动确实很常见。这可能导致不可接受的大运动，直接的结构破坏，或结构部件的危险的长期疲劳损伤。风与结构之间以及结构的不同组件（如电缆和桥面）之间的复杂相互作用可能导致振动问题，因此为了正确理解其行为，需要考虑空气动力学和结构效应。虽然一些结构的风荷载机制已经被很好地理解了，但其他的还没有，而且许多振动的例子，特别是电缆的振动，也没有得到很好的解释。最近的研究开发了一种分析“飞驰”振动的通用方法。这是由于建筑物开始移动时风力的变化造成的，这实际上倾向于增加运动。对于典型的桥梁电缆（或其他类似大小的结构），在中等强风中，电缆周围的气流会发生特殊的变化，称为阻力危机。这改变了缆索上的力，导致了一种特殊的飞奔型振动，这种新的分析方法第一次能够预测到这种振动。将这些计算结果与斜圆柱体风洞试验结果进行比较，证实了基本方法的有效性，但需要考虑额外的影响，如风湍流、结构的扭转运动以及更准确地描述结构运动时气动力的变化。研究人员建议，利用进一步的风洞数据，开发包括这些影响的方法，以最终创建一个统一的框架，用于任何实际结构的风荷载分析，以及其他气动机制抖振（由于风湍流）和颤振。同时，结构构件振动之间的相互作用会造成严重的影响。例如，通过“参数激励”机制，桥面非常小的振动可以引起支撑它的电缆的非常大的振动。更令人惊讶的是，在其他情况下，局部缆索振动会导致整个结构的振动。另一项拨款下的研究已经在考虑非常简化的结构的这些影响，但建议将分析扩展到现实的完整结构。此外，通常将电缆绑在一起是为了防止单个电缆的振动，但它们可以作为一个网络一起振动。因此，该项目旨在分析完整的电缆网络，以了解如何限制它们的振动。最后，建议将上述两个主要领域结合起来，在细长结构的分析中包括气动和结构动力相互作用。例如，由于相互作用，风荷载作用在相对较小的元件上，如电缆，可以对大型结构的整体动力响应产生惊人的大影响。目前这一点一般被忽视，但联合的办法将解决这个问题。此外，在某些情况下，只有对现象的综合看法才能解释实际中在全尺寸结构上观察到的行为。风荷载和结构行为的整体观点应该提供工具，以帮助避免未来细长结构振动的不良和潜在危险影响。根据分析，这可以通过改变元件的形状来改变风荷载，或者引入阻尼器来吸收足够的振动能量来实现。

As more slender and more adventurous structures, such as cable-stayed bridges, are constructed, they become increasingly susceptible to large amplitude vibrations, particularly due to aerodynamic loading. Wind-induced vibrations of bridge decks, cables, towers, lamp columns and overhead electricity cables are indeed very common. This can lead to unacceptably large movements, direct structural failure, or dangerous long-term fatigue damage of structural components. Complex interactions between the wind and the structure and also between different components of the structure (e.g. cables and bridge deck) can lead to vibration problems, so for proper understanding of the behaviour, both aerodynamic and structural effects need to be considered.Whilst some of the mechanisms of wind loading of structures are reasonably well understood, others are not, and many instances of vibrations, particularly of cables, are not well explained. Recent work has developed a generalised method for analysing 'galloping' vibrations. These are caused by changes in wind forces on a structure when it starts to move, which actually tend to increase the motion. For typical bridge cables (or other similar size structures) in moderately strong winds, a particular change in the wind flow around the cable occurs, known as the drag crisis. This changes the forces on the cable and causes a special case of galloping-type vibrations, which the new method of analysis is able to predict, for the first time. Comparisons of these calculations with wind tunnel test results on inclined cylinders have confirmed that the basic method does work, but there is a need to consider additional effects, such as wind turbulence, torsional motion of the structure and more accurate account of the changes in the aerodynamic forces as the structure moves. It is proposed to develop the approach to include these effects, using further wind tunnel data, to eventually create a unified framework for wind loading analysis of any real structure for galloping, together with the other aerodynamic mechanisms buffeting (due to wind turbulence) and flutter.Meanwhile, interactions between vibrations of structural components can cause serious effects. For example, very small vibrations of a bridge deck can cause very large vibrations of the cables supporting it, through the mechanism of 'parametric excitation'. Even more surprisingly, in other instances, localised cable vibrations can lead to vibrations of the whole structure. Research under another grant is already considering these effects for very simplified structures, but it is proposed to extend the analysis to realistic full structures. Also, often cables are tied together to try to prevent vibrations of individual cables, but they can then all vibrate together as a network. This project therefore aims to analyse full cable networks, to understand how their vibrations can be limited.Finally, it is proposed to bring together the above two main areas, to include both aerodynamic and structural dynamic interactions in the analysis of slender structures. For example, because of the interactions, the wind loads on relatively small elements, such as cables, can have surprisingly large effects on the overall dynamic response of large structures. At present this is generally ignored, but the joint approach will address this issue. Also, in some instances, only a combined view of the phenomena may be able to explain the behaviour observed on full-scale structures in practice. The holistic view of the wind loading and structural behaviour should provide tools to help avoid undesirable and potentially dangerous effects of vibrations of slender structures in the future. Based on the analysis, this could be achieved by modifying the shape of the elements to change the wind loads, or introducing dampers to absorb enough vibration energy.