This paper reviews the dynamics of infragravity (long-period) waves over reef systems and the consequences of these waves for operations in ports located behind reefs with particular attention to Western Australia. Swells which originate in the Southern Ocean generate long (infragravity) waves, which propagate to the coast. On the reef edge, the swell waves are largely dissipated, transferring energy to turbulence and heat but also in that process generating long wave energy. The remaining swell waves are dominated by the infragravity waves and propagate towards the mainland and into port basins where they cause moored ship motions with consequences for the operational downtime of the port's operations. When contemplating solutions to mitigate the impact of the long wave problems, these may be addressed from two sides: from the load side (waves) and the strength side (mooring). The former will be discussed in this paper.

Operators who want to im- or export bulk (coal, iron ore, scrap, etc.) by means of offshore bulk transshipment often want to determine the operability of their bulk transshipment configuration in an early stage to assess if offshore floating bulk transshipment is a feasible option for im- or export of the commodity. The downtime of such offshore (un)loading operations may be unacceptably large. The operational windows may become limited. This implies insufficient im- or export volumes, which may result in large and expensive storage capacity onshore. In this paper a methodology is proposed to assess the operability of offshore floating bulk transshipment. Offshore bulk transshipment is a multi-phase operation. For offshore operations consisting of multiple phases, persistency of the environmental conditions has to be considered. Persistency analysis allows for multiple operational phases, individual phase duration and shift of sea states during the operation. The proposed methodology shows that using persistency data of the waves (wind and current are not considered yet), the downtime of an offshore floating bulk transshipment operation can be estimated more accurately. Compared to persistency analysis, scatter analysis (using wave scatter diagrams) resulted in an optimistic estimate of the downtime. Persistency analysis is better in demonstrating the influence due to each consecutive step on the total operability. This methodology could be further extended to other multi-phase offshore operations.

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In the field of port design there is a need for a reliable but time-efficient method to assess the behavior of moored ships in order to determine if further detailed analysis of the behavior is required. The response of moored ships induced by gusting wind and/or waves is dynamic. Excessive motion response may cause interruption of the (un)loading operation. High line tension may cause lines to snap, introducing dangerous situations. A (detailed) Dynamic Mooring Analysis (DMA), however, is often a time-consuming and expensive exercise, especially when responses in many different environmental conditions need to be assessed. Royal HaskoningDHV has developed a time-efficient computational tool in-house to assess the wave (sea or swell) induced dynamic response of ships moored to exposed berths. The mooring line characteristics are linearized and the equations of motion are solved in the frequency domain with both the 1st and 2nd wave forces taken into account. This tool has been termed Less=Moor. The accuracy and reliability of the computational tool has been illustrated by comparing motions and mooring line forces to results obtained with software that solves the nonlinear equations of motion in the time domain (aNySIM). The calculated response of a Floating Storage and Regasification Unit (FSRU) moored to dolphins located offshore has been presented. The results show a good comparison. The computational tool can therefore be used to indicate whether the wave induced response of ships moored at exposed berths proves to be critical. The next step is to make this tool suitable to assess the dynamic response of moored ships with large wind areas, e.g. container ships, cruise vessels, RoRo or car carriers, to gusting wind. In addition, assessment of ship responses in a complicated wave field (e.g. with reflected infra-gravity waves) also requires more research effort.