Hovercraft stability problem solved by UNN scientists
Lobachevsky University researchers have developed a mathematical model for the stability of air cushion vehicles (ACVs) also known as hovercraft. This type of craft is supported by a continuously generated cushion of air blown under the vessel’s bottom, due to which it rises above the water surface and therefore has less resistance to movement (hydrodynamic drag) compared to traditional displacement ships and can therefore reach higher speeds. A team of UNN scientists comprising Vasily Shabarov, Fedor Peplin and Pavel Kalyasov from the Department of Theoretical, Computer and Experimental Mechanics of the UNN Institute for Information Technologies, Mechanics and Mathematics, and Vitaly Shaposhnikov from the RAS Institute of Applied Physics examined in their paper a relatively new type of hovercraft with inflated side seals (also known as flexible skegs).
"These vessels combine the advantages of other types of hovercraft, such as amphibious abilities, seaworthiness, yaw direction stability, as well as operational safety. Until recently, the displacement of such ACVs was relatively small (up to 2-3 tonnes). However, there has been a growing interest in much bigger hovercrafts with inflated side seals. At present, various organisations are developing, testing and building vessels with a displacement of 20 to 200 tonnes," the scientists said.
One of the challenges that stand in the way of introducing on a large scale this much-needed type of transport is the problem of ensuring the stability of the “air cushion - flexible skeg” system. Oscillations of inflated side seal elements are virtually non-existent on small displacement vessels, but become an increasingly dangerous phenomenon as the weight of the hovercraft increases. The frequencies and amplitudes of these oscillations are such that they are hard for the crew and passengers to bear, and they can cause damage to the vessel's structures and result in an accident. It is clear from operational experience that any further increase in the displacement of such hovercrafts is impossible without solving the problem of preventing oscillations of the flexible side seal elements. The mathematical model developed by UNN researchers is based on a combination of analytical methods and computational fluid mechanics (CFD) approaches.
The model makes it possible to reveal the main regularities of flexible seal oscillations and to outline feasible ways for increasing the vehicle’s stability by eliminating such oscillations. Thus, it was shown that when a large vehicle is designed as a scaled copy of the small one, then the large vehicle exhibits less stable behavior compared to the small one. This phenomenon, called the scale effect in fluid mechanics, has been demonstrated both numerically and analytically. The authors have also demonstrated how, by varying vessel design parameters, it is possible to achieve stable operation of the hovercraft lift system. The advantages of the mathematical model include the simplicity of its implementation and physical transparency, which allows its use at the earliest design stages.
The authors hope that the findings of their study will contribute to expanding the field of application of hovercraft with flexible inflated seal. This type of hovercraft can solve many transport tasks in Russia and other countries in the most rational way. Besides, the methods elaborated by the research team can be applied in the development of other types of high-speed water transport (hydrofoils, air-cavity craft, ram-wing surface-effect vehicles).
The scientists' results have been published in the prestigious journal Applied Ocean Research (Q1) and can be accessed here.
