Long-span bridges have low structural damping and low and closely-spaced frequencies. Hence, under low-speed wind conditions, they can experience large-amplitude vortex-induced vibrations which jeopardize the bridge serviceability and long-term structural safety. This project proposes a girder-rotation-based concept for multimode vibration mitigation of long-span bridges, along with a practical realization using damped outriggers – an outrigger is installed on the bridge girder near a bridge pylon or a pier to transform girder rotations during bridge vertical vibrations to horizontal displacements of the outrigger at its end. Horizontal dampers along the longitudinal axis of the bridge are installed between the outrigger end and the pylon/pier to dissipate vibration energy. As compared to existing bridge vibration control methods that are based on girder vertical displacements, one damped outrigger can improve multimode damping and the horizontal dampers can absorb and suppress the girder longitudinal deformation induced by thermal effects. The damped outriggers can reduce both wind-induced vibrations and seismic responses of the bridge and thus the traditional dampers between the bridge girder and pylons/piers are no longer necessary. The project will focus on long-span suspension bridges. Both simplified analytical models and refined finite element models will be used to examine the effects of structural and damped outrigger parameters, boundary constraints and coupled vertical-longitudinal girder vibrations on the damping performance, wind-induced vibrations and seismic responses of a suspension bridge with damped outriggers. By this means, the vibration mitigation mechanism of the proposed system will be understood. Subsequently, approximate explicit design formulas and universal optimization procedures will be developed for the design optimization of long-span bridges with damped outriggers. Ultimately, a systematic design principle to achieve high-damping for long-span bridges will be formulated. At last, a model of a suspension bridge with damped outriggers will be established and tested to validate the proposed vibration mitigation system for long-span bridges and the corresponding design optimization theory. The outcome of the project could provide a stable and implementable solution for vibration control of vortex-induced vibrations of long-span bridges, and hence the proposed study is of both scientific and practical significance.
水下悬浮隧道(又称阿基米德桥)受跨度和水深的限制少，在海峡连接工程中有很大应用前景。其借助浮力悬浮于水中，一般采用缆索进行锚固实现稳定。索锚固的悬浮隧道在波流作用下的动力分析，需考虑多种非线性和动力耦合效应，包括索动力特性的非线性、索与隧道动力耦合及波流耦合效应。现有研究通过对上述效应的简化，建立了对悬浮隧道动力特性的一定认识。为推进悬浮隧道的实际应用，本项目对悬浮隧道中的非线性和动力耦合效应开展精细化研究：首先，研究能考虑锚索大垂度效应的建模及模型降阶方法，刻画锚索的非线性动力特性，通过模型实验进行对比研究；然后，研究面向大尺度、精细化分析的索与隧道静动力效应耦合的建模方法；最后，研究非线性波流耦合作用下悬浮隧道的结构响应机制。本项目将加深现有对波流作用下悬浮隧道及锚索非线性动力行为的认识；建立的模型和分析方法可直接用于未来的工程分析和设计，具有重要的科学价值和应用前景。
The Submerged Floating Tunnel (SFT, also known as the Archimedes bridge) is suitable for long-span crossing in deep water and hence is promising for strait crossings. The tunnel (or bridge) is floating in the water owing to the buoyancy effect and it often needs to be anchored to the seabed by mooring cables for its stability. Dynamic analysis of the SFT with mooring cables under waves and currents has to address several nonlinearities and interactions, including nonlinear cable dynamics, the coupled cable-tunnel-tube response, and the wave-current interaction. Existing studies have established some basic understanding of the SFT behaviors with simplification in dealing with those issues. To turn SFT into a reality in strait crossings, this project is therefore aimed to carry out dynamic analysis of the SFT and its cables with refined treatments of those difficulties. First, this project will study the nonlinear models of mooring cables able to consider large sag effects, develop model reduction techniques for mooring cables, and characterize nonlinear mooring cable dynamics, with comparison to cable model experiments; secondly, this project will develop a framework for coupling the cable-tunnel tube motions, on the basis of sub-structuring; lastly, the effects of nonlinear wave-current interactions on SFT responses will be examined. The outcome of this project will advance our understanding of the dynamic behaviors of mooring cables in SFTs and the joint effects of wave-current loads on SFT structural responses. The established mooring models and coupling schemes can be used for design and analysis in future engineering practice. In a word, this project is of both scientific and practical values.
Floating wind and wave are two promising sources for renewable energy. For harnessing these energies, the safety, reliability and survivability of moored floating structures are critical for supporting the energy conversion systems. This requires advanced modelling techniques and thorough understanding of the moored structures in varied ocean conditions. These issues are among the pressing challenges impeding the commercialisation of renewable energy concepts. This project aims at developing a comprehensive and stable numerical method for nonlinear mooring cable dynamics, understanding the cable nonlinear behaviors, and eventually coupling the cable model into state-of-the-art platform models for appreciating the influence of the cable dynamics on platform responses. The proposed study aligns the United Nation’s Agenda 2030 for sustainable development, in particular contributing towards the target for ensuring universal access to affordable, reliable and modern energy services. The outcome of the project will be important for sustainably using the ocean resources. For achieving the research goal, the research will start with the state-of-the-art formulation of mooring cable dynamics and develop numerical techniques to improve the numerical stability of the present solving method; the research will afterwards take advantage of advanced nonlinear analysis techniques including harmonic balance method and numerical continuation for characterizing the mooring nonlinear behaviors and identifying critical conditions for further coupling studies; subsequently, the developed cable model will be coupled with reduced-order and high-fidelity platform models for appreciating the influence of cable nonlinearity on structural vibration control design and extreme platform responses respectively.
斜拉索是斜拉桥的关键受力构件，其自身阻尼很小因而易在环境激励下发生振动，危及斜拉桥的安全。在索近锚固点安装减振器是最有效的减振方法。为了研究实际索减振器的非线性行为并利用其在拉索减振中的优势，本项目拟研究斜拉索-非线性减振系统的动力特性及参数优化方法，将关注该系统的重要动力特性–稳态响应。首先，拟引入近来在机械等领域快速发展、能高效求解强非线性系统的谐波平衡法，研究该方法在分析索减振系统这一多自由度结构中的适用性；进而，研究基于系统稳态动力特性评价其减振性能的合理方法；最终，建立基于谐波平衡法的拉索-非线性减振系统的动力分析及参数优化框架。拟利用该方法，具体分析非线性粘滞阻尼器、摩擦阻尼器及限位装置安装于索近锚固点时对索前几阶振动的最优控制效果及相应装置参数，探讨非线性减振机理。本课题的成果将直接应用于拉索减振装置的优化设计，为索减振方案的开发提供理论基础，具有明确的工程和理论价值。