Unsteady effects during resistance tests on a ship model in a towing tank

It is known that there are oscillations in the wave resistance during the constantvelocity phase of a towing-tank resistance test on a ship model. In this work, the unsteady thin-ship resistance theory has been applied to this case. The results have been compared with experiment data obtained using a towing carriage the velocity history of which can be programmed. It is demonstrated here that generally excellent correlation exists between the theory and the experiments. In particular, one can predict the influence of Froude number, rate of acceleration, and type of smoothing of the acceleration on the characteristics of the oscillations. These characteristics include the amplitude, rate of decay, frequency, and phasing of the oscillations in the curve of wave resistance versus time

A Theoretical Study of the Optimal Dynaplane Vessel

A dynaplane is a planing vessel in which the wetted surface at the operational speed possesses a downward curvature, thereby replicating the camber associated with high efficiency lifting airfoils. In addition, the aspect ratio is chosen to be large in order to further improve the lifting efficiency. It is the higher planing efficiency together with the relatively small wetted surface that leads to the low resistance of the dynaplane. Typical resistance-to-weight ratios as low as 0.1 have been achieved in the past.We demonstrate here that a simple analysis can be based on modeling the hydrodynamic influence of the planing surface by means of the corresponding pressure distribution. Remarkably, the precise form of the pressure distribution is unimportant. The efficiency is greatly enhanced by choosing large aspect ratios of the order of 10 - a result analogous to the aerodynamic lifting problem. The investigation here shows that resistance-to-weight ratios as low as 0.025 are possible; hence, even higher levels of performance are ideally possible

Wave generation of a compartmented surface-effect ship

A series of carefully controlled experiments on the wave-generation characteristics of a model of a compartmented surface-effect ship has been conducted in a towing tank. Configurations of the model included cases encompassing one subcushion and two subcushions, as well as differing values of the pressures in the subcushions. It was shown that a reduced wave generation in the appropriate Froude number range could be achieved in this manner. Furthermore, a previously developed theory for the wave generation of marine vessels was verified for the model for a Froude number greater than 0.40

The Waves Generated by a Trimaran

The question of the wave generation by river vessels is one that has been studied at length by many researchers, particularly since the advent of the RiverCat, a catamaran designed specifically for operation on the Parramatta River, which leads into Sydney Harbour. There was good correlation between the measured height of the generated waves and the theoretical predictions of the wave resistance, as was shown by Doctors, Renilson, Parker, and Hornsby (1991). In the current work, we compare the wave system generated by a model trimaran with the theoretical predictions of a classic inviscid approach, called HYDROS, which has now been enhanced to include surface tension as well as viscosity, both of which are now understood to be important for small models at low speeds. As a consequence, experimental and theoretical results presented demonstrate the effectiveness of the stagger (longitudinal position) of the sidehulls of the trimaran, along with depth and Fn combinations, on its wavegenerating characteristics

The Waves Generated by a Trimaran

The question of the wave generation by river vessels is one that has been studied at length by many researchers, particularly since the advent of the RiverCat, a catamaran designed specifically for operation on the Parramatta River, which leads into Sydney Harbour. There was good correlation between the measured height of the generated waves and the theoretical predictions of the wave resistance, as was shown by Doctors, Renilson, Parker, and Hornsby (1991). In the current work, we compare the wave system generated by a model trimaran with the theoretical predictions of a classic inviscid approach, called HYDROS, which has now been enhanced to include surface tension as well as viscosity, both of which are now understood to be important for small models at low speeds. As a consequence, experimental and theoretical results presented demonstrate the effectiveness of the stagger (longitudinal position) of the sidehulls of the trimaran, along with depth and Fn combinations, on its wavegenerating characteristics

2020年7月-9月アイテム別ダウンロード回数

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