To investigate the ice breaking processes of the ice-breaking air cushion platform, a series of model tests in the ice tank of Tianjin University had been carried out based on an actual ice-breaking air cushion platform model. The regularities of ice breaking resistance varying with the hover-height and navigation speed were finally established. And the key mechanism of the high-pressure sub-ice air cavity was found, which formed by the high-pressure air flow from the bottom of the skirt. This study provides necessary basic data for designing and safety operating of ice-breaking air cushion platform.
The basic principle of air cushion platform (ACP) is utilizing the fan to format high pressure air and then guiding them into the bottom of the platform. The dynamic air cushion forms to lift the platform away from the support surface, such as ground, water or ice (Gao XY, et al. 2021; Jiang YY, et al. 2021). The initial exploration of air cushion platform used for ice breaking work began in the winter of 1971-1972. The researchers refitted the air cushion platform ACT-100 into an Arctic drilling platform in the Great Nu Lake (or Great Slav Lake) in Yellowknife, Canada (Zhu SK, 2008; Howard SF, 1976). When moving the ACT-100, the researchers found the platform having the ability to break ice, and about 0.76 m thick ice was breaking. Several ice breaking tests have been carried out in Thunder Bay, Parry Bay, Toronto and Montreal around the Arctic, and the ice breaking ability had been verified (Dickins DF., et al. 2008). From 1975 to 1976, the Canadian Coast Guard used the ACT-100 platform destroyed about 40 cm thick ice in thunder Bay which was pushed by icebreaker Alexander Henry. The CCGS Waban-Aki ACP was also used to verify the ice breaking ability at low speed in the St. Lawrence River of USA (Jones S, 2008). Hinchey and Colbourne (Hinchey M and Colbourne DB, 1995) summarized a lot of ACP ice breaking results, and then the ice breaking mode of air cushion platform is divided into low-speed ice breaking and high-speed ice breaking. In low-speed ice breaking mode, a sub-ice air cavity will generate first, and then the ice body destroyed by the ACP. In high-speed ice breaking mode, the ACP moves on the ice under high-speed, a large amplitude gravity wave generated at the same time, and then damaged the ice. Kozin (Kozin V, Novolodsky I, 1990) a conducted deeply research on the resonant ice breaking mechanism of ACP. In this research, the structure of air cushion platform is simplified as a moving load, ice-water medium is simplified into semi-infinite ice surface and semi-infinite water surface models. The propagation characteristics of bending gravity wave on ice surface and the possibility of ice breaking by resonance method are deduced. Zhestkaya and Kozin (Zhestkaya VD, Kozin VM, 2008) combined the integral transformation method with the finite difference hybrid algorithm to study the deformation process of ice under different loads, and the deflection of ice under single point pulse is calculated. Lu Zaihua et al. (Lu ZH et al., 2014; 2012) studied the ice-breaking process of ACP at high speed on ice surface. LS-DYNA was used to simulate the movement of an ACP on ice surface at critical speed (11 kn) and supercritical speed, and the variation law of ice wave induced stress excited by ACP motion was obtained. Liu Jubin et al. (Liu JB, et al. 2012; 2013] also carried out research on the wave generation problem of ice surface. The Rankine source calculation method for solving ship wave making was used to calculate the wave and ice deformation of ACP sailing on ice at high speed, and the wave-generating resistance was also solved. Based on the viscoelastic thin plate hypothesis and potential flow theory, Li Yuchen et al. (Li YC, et al., 2017) simulated the sailing conditions of ACP at sub-critical speed, critical speed (11 kn) and supercritical speed on ice surface. The wave propagation, stress variation and ice-breaking effect under different conditions are calculated and analyzed. Based on the gravity flow theory, Xue Yanzhuo et al. (Xue YZ, et al., 2018) assumed the air cushion pressure under the ACP as uniformly distributed load and carried out numerical simulation. The relationship between air cushion pressure and maximum ice breaking thickness was obtained, which will provides beneficial reference for the design work of ACP. Based on the elastic thin plate vibration differential equation and similar theory, Zhang Zhihong et al. (Zhang ZH, et al., 2014; Zhang ZH, et al., 2012) established the phase velocity and group velocity calculation formulas for the propagation of vibration waveform when the ACP sails on the ice surface. And obtained the phase velocity and group velocity phases for the propagation of fluctuations in the ice-water system. Following that, polyurethane (PU) thin film material is used to simulate the ice surface by model experimental researching. These tests were carried out to analyze the ice sheet affect by air cushion speed, hover-height, pressure, and water depth.
