nan Binns

Experimental investigation into wave-induced design loads on a large moored catamaran

A new concept uses a large catamaran, Gas Cat, as a floating natural gas processing, storage and offloading facility. The concept design of the vessel is based on two retrofitted very large crude carriers allowing for the processing and storage of 1 million bbls of condensate and approximately 240,000 m3 of liquid natural gas. Key to the development of this concept is the accurate estimation of the wave-induced cross-demi-hull loads experienced by the catamaran in a variety of operational scenarios. Model experiments were conducted in the model test basin of the Australian Maritime College using a 1:78 scale model of two full-form hulls, converted into a catamaran configuration, to measure the wave-induced forces and moments. Tests were conducted in head, beam and oblique seas for two hull spacings and a range of wave heights. The experimental results show that for the range of wave conditions tested, good linearity of the forces and moments can be expected with respect to wave height. This allows the results to be used to determine expected loads for a range of wave conditions. Changes in demi-hull separation were found to have little influence on the measured cross-demi-hull loads. Forces and moments were the least for the head sea condition; therefore, in order to minimise the wave-induced loads on the vessel, it is recommended that it be allowed to weathervane with the prevailing swell direction. The forces and moments which may be expected in Timor Sea 10,000-year return storm conditions have been estimated based on the model results. These provide valuable data for the preliminary design of an appropriate structural configuration for the vessel.

Power profile for segment rigid sail

ABSTRACT Rigid sails have the potential to lower fuel consumption on powered ships by using the wind as a supplementary source of propulsive power. The amount of propulsive power that can be provided by each sail is dependent on a number of variables, which include the sail type, sail area and number of sails deployed. Since each type and size of rigid sail has its own performance characteristics, it is difficult to estimate the propulsive power that could be provided by a particular rigid sail and to make comparisons between different rigid sails. To overcome this problem, a rigid sail power profile is proposed. This power profile will outline key performance characteristics and allow comparisons to be made between different types of rigid sails.

Tracking the vortex core from a surface-piercing flat plate by particle image velocimetry and numerical simulation

The wake flow around the tip of a surface piercing flat plate at an angle of incidence was studied using two-dimensional particle image velocimetry as part of benchmarking the particle image velocimetry technique on the moving carriage in the Australian Maritime College towing tank. Particle image velocimetry results were found to be in close agreement with those of the benchmarking work presented by the Hydro Testing Alliance, and a method of tracking the tip-vortex core near a free surface throughout numerical simulation has been demonstrated. Issues affecting signal to noise ratio, such as specula reflections from the free surface and model geometry were overcome through the use of fluorescing particles and a high-pass optical filter. Numerical simulations using the ANSYS CFX Solver with the volume of fluid method were validated against the experimental results, and a methodology was developed for tracking the location of the wandering vortex core experimentally and through simulation. The ability of the scale-adaptive simulation shear stress transport turbulence model and the shear stress transport model to simulate three-dimensional flow with high streamline curvature was compared. The scale-adaptive simulation shear stress transport turbulence model was found to provide a computationally less resource-intensive method of simulating a complex flow topology with large eddies, providing an insight into a possible cause of tip-vortex aperiodic wandering motion. At high angles of attack, vortex shedding from the leading edge separation of the test geometry is identified as a possible cause of the wandering phenomena. In this study, the vortex centre and point of extreme core velocity were found not to be co-located. The point of extreme stream wise velocity within the vortex core was found to be located within half the vortex radius of the vortex centre.

The effect of geometry on the surface waves generated by vertical surface–piercing cylinders with a horizontal velocity

Bluff bodies advancing through a free surface at high Froude numbers create intricate flow patterns worth further investigation. An example of such flows includes a submarine operating near the free surface which generally will have one or more masts piercing the free surface. These have the potential to produce large wakes at the surface. This article describes the numerical analysis used to investigate possible design modifications to reduce the wake profile of a singular cylindrical mast piercing the free surface. The large eddy simulation model carried out in OpenFOAM computational fluid dynamics software was validated against experimental data obtained by the authors using tow tank experiments. The modifications included the use of a double mast system based on the cylindrical mast and truncated NACA0012 sections. All configurations were performed with a mast cross-sectional area corresponding to a typical submarine snorkel across speeds ranging from two to eight knots. The plume size and mast drag were recorded, and the results show that a 30% reduction in wake profile can be obtained using a double mast system at speeds around eight knots, while at the lower speeds the benefit is not as significant.