A study on hydrodynamics of the air cushion of a high-speed PACSCAT

Abstract

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.

Nonlinear air dynamics of a surface effect ship in small-amplitude waves

“…The distinctive nonlinear features of the air pressure and the motion response should result from the small displacement proportion of the air cushion (only 33% of the SES displacement), which reduces the influence of the fluctuating air pressure on the SES motions. Thereby, in our previous works [8][9][10][11] , only the linear models were applied to predict the seakeeping motions. Once the displacement of the air cushion contributes to a larger proportion, e.g., 80%, the motions of the SES show significant nonlinear effects, which requires more appropriate models for analysis.…”

“…For simplicity, the framework of air dynamic model and its linear components similar to Guo et al . [8] are given in Appendix A , and here we only present the nonlinear air leakage model that is different from the one in Guo et al [9][10][11] .…”

“…To enhance the computational efficiency, Guo et al . [8][9][10] employed a linear 2.5D method to calculate the hydrodynamic parameters in connection with demihulls of an SES running in small-amplitude waves and obtained satisfactory results. The 2.5D method is highly efficient due to the dimensionality reduction on the control equation and body conditions from 3D to 2D [ 5 , 9 , 10 , 17 ], while only the free surface condition remains 3D.…”

“…According to the experimental results from authors' SES model in small-amplitude waves [8] , the heave and pitch responses are almost linearly proportional to wave amplitudes while the fluctuating cushion air pressure, midship accelerations have significant nonlinear effects. It also suggests that the nonlinear effects of the SES should not be neglected and the existing linear models [8][9][10][11] are not appropriate for the nonlinear performance prediction. To this end, the source of nonlinearity for the SES will be examined and a novel efficient seakeeping motion prediction model will be developed to take into account the nonnegligible nonlinear effects of the seakeeping performance in this paper.…”

A Study on the Motion of Partial Air Cushion Support Catamaran in Regular Head Waves

“…In 2010, Harbin Engineering University (HEU) begun the research of PACSCAT based on the sidewall hovercraft technology and improved its resistance and sea-keeping performance by a series of hull form optimizations and model tests. Guo et al utilized a numerical method to investigate the seakeeping performance of PACSCT, which combines the 2.5D theory for solving hydrodynamics problem with simplified wave-equation for solving aerodynamic of pressurized air [9]; their method was further improved to evaluate the waves due to pulsating pressure of air cushion [10]; the related studies were also performed for SES (surface effect ship) [11] and T-craft [12]. In order to verify the implementation effect of the developed technology, HEU designed and built a 12 m long aluminous test craft (Figure 3), based on which the experiment could be implemented in real scale and reliable trial data could be recorded-their work laid a good foundation for further investigation.…”