Aeroelastic and Non-linear Structural Dynamic Interactions of Slender Structures

随着更细长和更冒险的结构，如斜拉桥的建造，它们变得越来越容易受到大振幅振动的影响，特别是由于空气动力学载荷。桥面、电缆、桥塔、灯柱、架空电缆等的风振，其实是很常见的。这可能导致不可接受的大位移、直接结构故障或结构部件的危险的长期疲劳损坏。风与结构之间以及结构不同部件之间的复杂相互作用（例如缆索和桥面）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。虽然结构的风荷载的某些机制已得到合理的理解，但其他机制则不清楚，许多振动情况，特别是缆索，并没有得到很好的解释。最近的工作已经开发了一种通用的方法来分析“驰振”振动。这些是由结构开始移动时风力的变化引起的，这实际上往往会增加运动。对于典型的桥梁缆索（或其他类似尺寸的结构），在中等强风中，缆索周围的风流会发生特定的变化，称为阻力危机。这改变了电缆上的力，并导致了一种特殊的驰振型振动，这种新的分析方法首次能够预测。将这些计算结果与倾斜圆柱体的风洞试验结果进行比较，证实了基本方法确实有效，但需要考虑附加效应，例如风湍流、结构的扭转运动以及更精确地计算结构移动时气动力的变化。建议发展包括这些影响的方法，使用进一步的风洞数据，最终创建一个统一的框架，用于任何真实的结构的驰振风荷载分析，以及其他空气动力学机制抖振（由于风湍流）和颤振。同时，结构部件之间的振动相互作用可能会导致严重的影响。例如，桥面的非常小的振动可以通过“参数激励”机制引起支撑桥面的缆索的非常大的振动。甚至更令人惊讶的是，在其他情况下，局部电缆振动可能导致整个结构的振动。在另一项资助下的研究已经考虑了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，通常电缆绑在一起，试图防止个别电缆的振动，但它们可以作为一个网络一起振动。因此，本项目旨在分析完整的索网，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空气动力学和结构动力学相互作用。例如，由于相互作用，相对较小的元件（如电缆）上的风荷载可能对大型结构的整体动态响应产生惊人的影响。目前，这一点普遍被忽视，但联合办法将解决这一问题。此外，在某些情况下，只有对这些现象的综合看法才能解释实际上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。分析表明，可以通过改变单元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。

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.