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.
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.