In this study, we investigated the effect of hull dynamics in shallow water on the hydrodynamic p... more In this study, we investigated the effect of hull dynamics in shallow water on the hydrodynamic performance of rowing shells as well as canoes and kayaks. An approach was developed to generate data in a towing tank using a test rig capable of reproducing realistic speed profiles. The impact of unsteady shallow-water effects on wave-making resistance was examined via experimental measurements on a benchmark hull. The data generated were used to explore the validity of a computational approach developed to predict unsteady shallow-water wave resistance. Comparison of measured and predicted results showed that the computational approach correctly predicted complex unsteady wave-resistance phenomena at low oscillation frequency and speed, but that total resistance was substantially under-predicted at moderate oscillation frequency and speed. It was postulated that this discrepancy arose from unsteady viscous effects. This was investigated via hot-film measurements for a full-scale single scull in unsteady flow in both towing-tank and field-trial conditions. Results suggested a strong link between acceleration and turbulence and demonstrated that the measured real-world viscous-flow behaviour could be successfully reproduced in the tank. Thus a suitable tank-test approach could provide a reliable guide to hull performance characterization in unsteady flow.
This paper covers an extension of the study of Doctors et al. (J Ship Res 52(4):263–273, 2008) on... more This paper covers an extension of the study of Doctors et al. (J Ship Res 52(4):263–273, 2008) on oscillations in wave resistance during the constant-velocity phase of a towing-tank resistance test on a ship model to the case of relatively shallow water. We demonstrate here that the unsteady effects are very prominent and that it is essentially impossible to achieve a steady-state resistance curve in a towing tank of typical proportions for a water-depth-to-model-length ratio of 0.25. This statement is particularly true in the speed region near a depth Froude number of unity. However, on the positive side, we show here that an application of unsteady linearized wave-resistance theory provides an excellent prediction of the measured total resistance, when one accounts for the form factor in the usual manner. Finally, a simple application of the results to the planning and analysis of towing-tank tests is presented.
Although the catamaran configuration has been known for a long time, it is only in the recent pas... more Although the catamaran configuration has been known for a long time, it is only in the recent past that such hull forms have enjoyed unprecedented usage in the high-speed ferry industry. One of the design challenges faced by naval architects is the accurate prediction of the hydrodynamic characteristics of such vessels, primarily in the areas of resistance, propulsion and seakeeping. Even though a considerable amount of research has been carried out in this area, there remains a degree of uncertainty in the prediction of calm-water resistance of catamaran hull forms. In our research, we examine the calm-water wave-resistance characteristics of a chine-hull-form transom-stern slender catamaran, based on computational fluid dynamics (CFD) modelling and thin-ship theory. We include here a validation and comparison of CFD predictions with experimental data. We also include the results of calculations by Hydros, a computer program developed at The University of New South Wales, which gives very accurate predictions of resistance of high-speed marine vessels. The hull forms comprise a conventional catamaran along with longitudinally staggered demihull configurations.
An analysis of the input impedance of a Rectangular Dielectric Resonators Antenna (RDRA) operated... more An analysis of the input impedance of a Rectangular Dielectric Resonators Antenna (RDRA) operated at the dominant mode TE 111 is presented. The effects of the probe length and its position with respect to the resonator on the resonance frequency and the input impedance of the antenna are investigated. The antenna structure is numerically simulated using the High Frequency Structure Simulator (HFSS) software package based on the Finite Element Method (FEM). A few experimental set-ups were examined and resonance frequency and input impedance were measured. The results show good agreement between theory and experiments and also the significance of the distance between the resonator and feed probe in simulation.
In this study, we investigated the effect of hull dynamics in shallow water on the hydrodynamic p... more In this study, we investigated the effect of hull dynamics in shallow water on the hydrodynamic performance of rowing shells as well as canoes and kayaks. An approach was developed to generate data in a towing tank using a test rig capable of reproducing realistic speed profiles. The impact of unsteady shallow-water effects on wave-making resistance was examined via experimental measurements on a benchmark hull. The data generated were used to explore the validity of a computational approach developed to predict unsteady shallow-water wave resistance. Comparison of measured and predicted results showed that the computational approach correctly predicted complex unsteady wave-resistance phenomena at low oscillation frequency and speed, but that total resistance was substantially under-predicted at moderate oscillation frequency and speed. It was postulated that this discrepancy arose from unsteady viscous effects. This was investigated via hot-film measurements for a full-scale single scull in unsteady flow in both towing-tank and field-trial conditions. Results suggested a strong link between acceleration and turbulence and demonstrated that the measured real-world viscous-flow behaviour could be successfully reproduced in the tank. Thus a suitable tank-test approach could provide a reliable guide to hull performance characterization in unsteady flow.
This paper covers an extension of the study of Doctors et al. (J Ship Res 52(4):263–273, 2008) on... more This paper covers an extension of the study of Doctors et al. (J Ship Res 52(4):263–273, 2008) on oscillations in wave resistance during the constant-velocity phase of a towing-tank resistance test on a ship model to the case of relatively shallow water. We demonstrate here that the unsteady effects are very prominent and that it is essentially impossible to achieve a steady-state resistance curve in a towing tank of typical proportions for a water-depth-to-model-length ratio of 0.25. This statement is particularly true in the speed region near a depth Froude number of unity. However, on the positive side, we show here that an application of unsteady linearized wave-resistance theory provides an excellent prediction of the measured total resistance, when one accounts for the form factor in the usual manner. Finally, a simple application of the results to the planning and analysis of towing-tank tests is presented.
Although the catamaran configuration has been known for a long time, it is only in the recent pas... more Although the catamaran configuration has been known for a long time, it is only in the recent past that such hull forms have enjoyed unprecedented usage in the high-speed ferry industry. One of the design challenges faced by naval architects is the accurate prediction of the hydrodynamic characteristics of such vessels, primarily in the areas of resistance, propulsion and seakeeping. Even though a considerable amount of research has been carried out in this area, there remains a degree of uncertainty in the prediction of calm-water resistance of catamaran hull forms. In our research, we examine the calm-water wave-resistance characteristics of a chine-hull-form transom-stern slender catamaran, based on computational fluid dynamics (CFD) modelling and thin-ship theory. We include here a validation and comparison of CFD predictions with experimental data. We also include the results of calculations by Hydros, a computer program developed at The University of New South Wales, which gives very accurate predictions of resistance of high-speed marine vessels. The hull forms comprise a conventional catamaran along with longitudinally staggered demihull configurations.
An analysis of the input impedance of a Rectangular Dielectric Resonators Antenna (RDRA) operated... more An analysis of the input impedance of a Rectangular Dielectric Resonators Antenna (RDRA) operated at the dominant mode TE 111 is presented. The effects of the probe length and its position with respect to the resonator on the resonance frequency and the input impedance of the antenna are investigated. The antenna structure is numerically simulated using the High Frequency Structure Simulator (HFSS) software package based on the Finite Element Method (FEM). A few experimental set-ups were examined and resonance frequency and input impedance were measured. The results show good agreement between theory and experiments and also the significance of the distance between the resonator and feed probe in simulation.
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Papers by Lawrence Doctors