Vibrant Body: Water memory will make fish robots and aquadrons more maneuverable

Russian scientists have developed a model that takes into account the "memory" of fluid — the effect of previous flows created by body movement on its movement. The new approach will make it possible to create silent fish robots capable of maneuvering like living organisms. Such drones will be in demand for underwater exploration, bottom exploration or studying marine fauna without affecting it. The development will also help design vehicles for landing on other planets. However, under certain conditions, the accuracy of the model may decrease, experts noted.

How to create silent underwater robots

Researchers from Kazan Federal University have developed a mathematical model that takes into account the "memory" factor of fluid when moving a body in this environment. We are talking about the effects when the previous flows created by the fins or other propellers continue to influence subsequent actions, the experts explained.

According to the developers, the model can become the basis for creating underwater robotic fish of a new generation, which, compared with modern screw vehicles, will move silently and more maneuverably.

— Oscillatory movements in liquids and gases surround us everywhere. These are sea waves that run up against bridge supports, and gusts of wind that rock high-rise buildings. These processes are also the basis for the swimming and flight of living organisms, from microscopic bacteria to whales and birds. The calculation of such movements is important both in engineering practice and in fundamental science," Artem Nuriev, a leading researcher at the Laboratory for Intelligent Biomimetic and Natural Systems at the Lobachevsky Institute of Mathematics and Mechanics at KFU, told Izvestia.

According to him, previously this problem was solved according to the principle "each shape has its own model": for cylindrical bodies there was one solution algorithm, for elliptical bodies — another, for winged bodies — a third, and so on. In each case, the formula was derived anew. The proposed theory, on the contrary, offers a universal way to calculate any configurations.

— One of the advantages of the method is taking into account the "memory" of the liquid. This effect means that the current stores information about the history of fluid movement, when, roughly speaking, it does not have time to "forget" what happened in previous cycles of fluctuations, the specialist explained.

Among the main areas of application of the new theory is the creation of machines that repeat the principles of movement and structure of living organisms. For example, underwater drones, which, like fish, are able to move due to the vibrations of their fins, the scientist noted. An accurate assessment of the forces that affect the propellers will allow us to calculate the optimal shape of the fins and their operating modes. This will make it possible, for example, to create more maneuverable vehicles that move underwater without making noise. They are in demand when exploring the seabed and studying animals in their natural environment, as well as for the purposes of covert surveillance underwater.

How the model will help guide ships through the ice

— The model is universal in the sense that it can describe bodies in any viscous media. Only their physical parameters change. Therefore, in addition to liquids, it is applicable to both the air on Earth and the atmosphere of Venus. For example, for designing maneuvering descent vehicles," emphasized Artyom Nuriev.

Another area of application is microfluidics, the specialist said. These are systems where small amounts of liquids move through miniature channels, which allows chemical reactions and biological analyses to be carried out with minimal consumption of reagents. Precise control of such flows will make it possible to carry out reactions with individual cells or microparticles.

— The question covers a wide field of research. With any complex movement — acceleration, vibration or maneuvering — there is a specific response of a viscous medium, including the so—called "memory" of a liquid, which needs to be accurately predicted," Andrey Sebin, associate professor of the Department of Shipbuilding and Aviation Engineering at the Institute of Transport Systems of the R. E. Alekseev Nizhny Novgorod State Technical University, told Izvestia.

According to him, NSTU specialists also have experience in solving similar tasks, but they consider these tasks at the macro level — in relation to large-tonnage vessels and marine complexes. For example, they simulate the movement of ships in solid ice. In particular, when an icebreaker moves through hummocks, huge variable loads act on it, and in order to predict the behavior of the vessel, inertia, water resistance, impacts on ice, and other factors must be correctly assessed.

— Previously, the "memory" factor of the liquid was taken into account only to a limited extent, due to its nature. This effect depends on the previous history of the movement. The liquid seems to "remember" how the body fluctuated in the past, and this information affects the force that acts on it at the current moment. Mathematically, this is described by an integral, which is a difficult task to deduce. The solution found makes it possible to reduce the number of expensive field tests for each new part at the design stage, because now you can substitute the data into the formula and get the result," said Almaz Sayfutdinov, Professor of the Department of General Physics at Kazan National Research Technical University named after A.N. Tupolev — KAI.

However, the proposed method does not yet take into account a number of points, the expert noted. For example, it does not fully describe the separation of the flow on sharp edges and does not take into account the creation of thrust for directional movement. In addition, at low frequencies or large oscillation amplitudes, the accuracy of the model may decrease. These issues require its further development.