In this paper, we study the problem of wave slamming on the cross structures of both fast ferry type catamarans and ocean going racing sailing catamarans. The emphasis is given to the prediction of the statistical distributions of slamming occurrence and slamming pressure magnitudes in a random seaway. A partly non-linear high-speed strip theory sea-keeping program is used to calculate the vessel motions and the relative motions between any part of the hull and the sea surface, including slamming impact velocity. Impact velocities are classified in 5 groups, and slamming pressures calculated for each group. To calculate vessel motions of heeled sailing catamarans a strip method for an asymmetric multi-hull is developed; the theory and initial results are presented. An investigation into the effect of sail forces on motions and slamming occurrence is also performed. The sail forces are found to be an important factor in predicting motions of sailing catamarans. The procedure proposed in this paper gives the necessary information to estimate the maximum slamming pressures the vessel is likely to encounter and equally importantly the expected frequency of lighter slams, which is useful for fatigue calculations.
The objective of the work is to assess the feasibility of a tension leg platform (TLP) dry tree unit (DTU) with tenderassisted drilling (TAD) for the harsh metocean conditions offshore North West Australia, characterized by the occurrence of tropical cyclones and persistent swells. Making use of the drilling tender vessel's accommodation, power generation, mud pumping, cleaning and storage facilities etc. can reduce the production platform topsides weight by up to 3,000 tonnes. Such weight and associated cost savings could become enablers for some of the deepwater gas field developments offshore Western Australia.A TLP configuration is evaluated as the DTU in a water depth of 500 m. The TLP is sized for a specific payload for gas production. A typical 6-column semisubmersible is configured as the drilling tender vessel (DTV), for which a preliminary TAD mooring system is defined. Hydrodynamic models for the combined DTU/DTV systems are developed and used to perform extreme response and operability analyses.The coupled TLP/DTV TAD system is analyzed in 1, 10 and 100-year return period environments. It is shown that the DTU and DTV vessel can be safely moored together by hawsers without collision in up to 10-year return cyclonic storm events. This means that the mooring system operability of up to 99.97% is achievable.In environmental conditions harsher than 10-year return cyclonic storms, the DTV will be disconnected from the DTU and a full 8-point mooring pattern will be required to moor the DTV to survive up to 100-year return period cyclones.
The idea of using float-over installations for minimal facilities platforms was shown to offer significant advantages, especially when coupled with a substructure installed by a jack-up rig. Recently, float-over installations of minimal facilities have been conducted by the cantilevered method by ICON Engineering Pty Ltd (ICON). The operation involves the platform topsides being loaded and transported to site on a barge, skidded over the barge bow, and lowered onto the jacket. The paper presents results of a research project undertaken by the Australian Maritime College (AMC) in conjunction with ICON, with the objective to investigate motions of a barge and loads exerted on the jacket when the two are docked together for a smooth load transfer operation. The model of an installation barge has been tested in the AMC wave basin and response amplitude operators of the barge motions have been determined for both the free floating and docked conditions. A range of wave periods and heights has been investigated. Model test results have been used to verify numerical predictions used in the design, and to get insight into uncertainties, which may otherwise be difficult to assess using standard software.
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