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Abstract:A novel time-domain Green's function is developed for dealing with two-dimensional interaction between water waves and floating bodies with considering viscous dissipation effects based on the "fairly perfect fluid" model. In the Green's function, the temporal (lower order viscosity coefficient term) and spatial (higher order viscosity coefficient term) viscous dissipation effects are fully considered. As compared to the methods based on the existing time-domain Green's functions that could not account for the spatial viscous dissipation, the method based on the new time-domain Green's function can give much better numerical results and overcome instability problems related to the existing Green's function, according to the numerical tests and comparison with CFD modeling data for a few cases related to floating bodies with a flare angle.

When a surface effect ship (SES) sails in waves, the unsteady velocity potential of water can be decomposed into incident potential, sidehull radiation potential, sidehull diffraction potential and radiation potential due to fluctuating air pressure. The potentials related to sidehulls satisfy Neumann boundary conditions (BC) and have been successfully addressed using the 2.5D method. In contrast, the potential related to fluctuating air pressure satisfies mixed BC consisting of homogeneous Neumann BC on the wetted surface of sidehulls and nonhomogeneous Dirichlet BC on the interface between air and water, which has never been studied using the efficient 2.5D method. In this paper, the 2.5D method is firstly proposed to solve the mixed boundary value problem (BVP), which can deal with the coupling between the fluctuating air pressure and sidehulls. By using the 2.5D method, the radiation wave and other relative hydrodynamic parameters of a SES due to the fluctuating air pressure are evaluated. The numerical results on motion response and the fluctuated air pressure of the SES show acceptable agreement with the experimental ones.

When operated under large water immersion, surface piercing propellers are prone to be in heavy load conditions. To improve the hydrodynamic performance of the surface piercing propellers, engineers usually artificially ventilate the blades by equipping a vent pipe in front of the propeller disc. In this paper, the influence of artificial ventilation on the hydrodynamic performance of surface piercing propellers under full immersion conditions was investigated using the Computational Fluid Dynamics (CFD) method. The numerical results suggest that the effect of artificial ventilation on the pressure distribution on the blades decreases along the radial direction. And at low advancing speed, the thrust, torque as well as the efficiency of the propeller are smaller than those without ventilation. However, with the increase of the advancing speed, the efficiency of the propeller rapidly increases and can be greater than the without-ventilation case. The numerical results demonstrates the effectiveness of the artificial ventilation approach for improving the hydrodynamic performance of the surface piercing propellers for high speed planning crafts.

This paper presents an approximate but efficient method for modeling the hydrodynamics and seakeeping performance of partial air cushion supported catamaran (PACSCAT) with planing demihulls. This method takes into account of the effects of the waves on the air-water interface under the air cushion induced by the pulsating pressure in the cushion and by the demihulls, which are ignored by existing approximate methods. Specifically, the new developments are made in two aspects.One is that the governing equations of the heave and pitch motions of the PACSCAT are derived to include the effects of the waves under the air cushion due to the pulsating pressure and the demihulls.Another one is that an approximate method is developed for evaluating the waves due to the pulsating pressure. Better agreement between the experimental data and the numerical results for pressure is achieved.