This paper describes progress on the development of methods for modelling the non-linear response to waves of harbour and offshore structures, ships and submarines. Progress has been made over a long period, and in a number of different and apparently unconnected research studies. Three examples from these studies are described here, along with a summary and references that show how the studies combine into a long term organised research programme. The current position is that fairly simple techniques are being developed, and are being successfully applied to very difficult problems. These include the long period motion of large ships moored to exposed jetties, the motion of deep water moored FPSOs (Floating production, storage and offloading vessels), and the long period response of submarines under way at periscope depth. The work described here has already enabled significant improvements to be made in the modelling and design of harbours, jetties and mooring systems. In particular, it has enabled accurate predictions of the long period motion of container ships, oil and gas carriers subjected to wave action when moored. The motion of container ships can seriously impede loading and unloading operations, and the motion of oil and gas tankers has potentially serious operational, environmental, and safety implications. The work has also enabled the development of a hybrid modelling technique in which physical and numerical models are used concurrently to study the behaviour of deep-water offshore systems. Hybrid models enable deep-water systems to be modelled in shallow water test facilities, and also enable a number of great simplifications in model set-up and operation. A prototype hybrid model of an FPSO on tensioned fibre moorings has provided some new insights into the physics that controls the non-linear response of such systems. The hybrid modelling work has recently been extended to include vessels that are under way through the waves that excite their motion. This new method has been used for specifying and simulating the heave motion of a submarine at periscope depth under waves. The results re expected to lead quickly to new methods of specifying and evaluating submarine autopilot designs. In the longer term, it will provide modelling and analysis tools that complement new design and analytical tools developed, leading to improved safety and better performance for future offshore systems.
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