Theoretical and Experimental Studies on the Resistance of SWATH Ships

Chun, Ho Hwan (1988) Theoretical and Experimental Studies on the Resistance of SWATH Ships. PhD thesis, University of Glasgow.

Abstract

Even though there are currently only 11 SWATH vessels at sea worldwide, there is increasing interest in SWATH ships due to their markedly superior seakeeping performance compared to monohulls. Today this growing interest is reflected by the reports on SWATH design which fill technical press. This thesis is concerned with some hydrodynamic aspects of SWATH ships, mainly resistance performance in calm water and in waves and by implication, some motion aspects as well. The main objectives of the work presented in this thesis are 1) to develop an analytical tool which can give an improved prediction of SWATH ship resistance, 2) to compare the computational values of resistance with experimental results in order to verify the applicability of the tool and 3) on the basis of the computational and experimental analysis, to provide recommendations for the design of high performance SWATH ships with special reference to making feasible practical developments such as rectangular (with rounded comers) hulled SWATH ships. Instead of the line source distribution commonly used for the submerged body of a SWATH ship, a plane source distribution is introduced in order to calculate wave-making resistance. This method is applicable to bodies with non-circular cross section. For this purpose, linearised wave theory and the linear superposition principle are effectively used due to the slenderness of the components of the SWATH ship. In addition, flat ship theory is applied to calculate the wave-making resistance of controllable fins which are essential to conventional SWATH ships in the light of pitch stability requirements. Considering the total resistance of a SWATH ship in components of wave making, frictional, appendage and additional drag form effect, eddy, viscous pressure, wave-breaking and spray), two computer programs were written to predict the resistance of SWATH ships with and without fins. One deals with SWATH ships defined by mathematical formulae and the other is designed for SWATH ships defined in offset forms. The ITTC57 frictional line is used to calculate the frictional resistance based on the Reynolds Number for the individual lengths of the components of a SWATH ship. Based on the difference between the calculated wave-making and measured residuary resistances, two curves of form resistance coefficient accounting for the aforementioned additional drag are derived: one is intended for circular hulled SWATH ships and the other is applicable to non-circular hulled SWATH ships. These coefficients are compared with other published form effect correlations. Treating the resistance of controllable fins in profile, induced, hull-fin interference, tip and wave -making components, the drag of controllable fins is calculated. For this purpose, empirical formulae for foil sections and streamlined bodies are used for each component calculation. The experimental results of 9 SWATH models (three G. U models, two Polish models, one Chinese model and three NSRDC models) giving a total of 46 individual configurations are compared with the computational results. Also, the present predictions are compared with other published computational results. In order to validate the developed theory, a large number of experiments with three SWATH models including a total of 24 configuration changes were conducted to measure the total calm water resistance at the Hydrodynamics Laboratory of Glasgow University. Two of the models are tandem strut configurations, one having circular cross section bodies, and the other having bodies of rectangular cross section with rounded comers. The third model is a single strut configuration with hulls of circular cross section. Mean sinkage and trim were measured to help improve the understanding of the speed-resistance characteristics of the SWATH models. This experimental data provides not only the validation of the theory developed but also empirical form correction factors. (Abstract shortened by ProQuest.).

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Naval engineering
• Date of Award: 1988
• Depositing User: Enlighten Team
• Unique ID: glathesis:1988-77642
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 14 Jan 2020 11:53
• Last Modified: 14 Jan 2020 11:53
• URI: https://theses.gla.ac.uk/id/eprint/77642