Researchers cracked the scientific mystery using a theoretical model
"Here comes another big wave, just be careful not to fall", sings Danny Sanderson to all surfers in the sea. One of the most common and well-known natural phenomena is the formation of sea waves by winds and gusts of air, but it turns out that although the well-known phenomenon has been studied for about 150 years - to this day the perfect mathematical model has not yet been found that would fully describe the process of the mechanism and be verified experimentally. Researchers from Tel Aviv University have developed an innovative and first-of-its-kind theoretical model that sheds light on the mystery. The model was designed to explain the process of creating waves and was tested in a series of complex experiments carried out over a long period of time. The conclusions of the groundbreaking research will assist in the development of tools for climate forecasting and the ability to predict the movement of pollutants on the surface of the water.
A collection of frequencies
Mechanical waves, including water waves, can be described as a collection of frequencies, just as a melody can be broken down into notes and harmonies. The most common models today consider the growth of a single harmonic, the most unstable, and assume that its spatial development is uniform. The new model proposed by the researchers takes into account all the unstable harmonics and the limitations that apply to them, including a breaking limit of very steep harmonics, a gradual decay as a result of the concealment of low harmonics by higher waves and a spatial development time limit. In this way, the new theory makes it possible to describe the physical situation with high reliability, compared to the previous models.
The researchers who led the research are Prof. Lev Shemer and Dr. Mittal Geva from the Water Wave Laboratory in the School of Mechanical Engineering in the Ivy and Alder Fleishman Faculty of Engineering. The research was published in the prestigious journal Physical Review Letters.
"The development of wind waves on the surface of the water is a complex phenomenon. One of the reasons for the lack of an overall theory of the process stems from a lack of detailed experimental results. Wave field and wind measurements in the sea are very limited, mainly due to the inability to control the environmental conditions and the difficulty of conducting experiments in the open sea, even near the coast," explains Dr. Geva. "In the wave laboratory at the School of Mechanical Engineering there is a unique and autonomous experimental system for examining the interaction between water and wind, and this system enables the collection of comprehensive information on the behavior in space and time of the water surface under different wind regimes."
overcome the theoretical difficulty
The problem inherent in the previous theories, which were used by the researchers in this field for about 65 years, stems from the many assumptions on which they were based and their inability to be realized in a quantitative way, which greatly limited the ability of physical prediction. The researchers add that the theoretical difficulty that existed in developing a complete model was due to the fact that complex dynamic shapes and patterns are created in water that react with each other and are characterized by a large degree of randomness in time and three-dimensional space. Also, a multitude of mechanical forces such as gravity, viscosity and surface tension are involved in the problem, and the transitions of energy and momentum between air and water must be taken into account - a non-trivial issue in fluid mechanics.
"In this research, for the first time, we are using exact equations and accepted methods from the field of statistical mechanics in order to analyze the random and non-linear processes that occur during the formation of the waves. In fact, the proposed model is the only one that allows a description in time and space of the wave field starting from the state of a smooth water surface to a final state fixed in time, and most importantly - it is the first model that has been fully verified against experimental results and describes the process not only qualitatively, but also quantitatively," she elaborates Dr. Geva on the new model and its applications.
Predict the movement of pollution in the sea
"The formation of wind waves is the result of a mutual interaction between the ocean and the atmosphere, so the process has a decisive effect on the transfer of mass, momentum and energy at the water surface interface. Based on this, we believe that the proposed description is an important step in improving short-term weather forecasting models and climate change in longer time frames. Also, understanding the interaction will allow an assessment of environmental conditions that affect life in the sea and the ability to predict the movement of pollutants on the surface of the water. With the conclusions from the research it is possible to go one step further in these areas, whose importance is increasing in the age of the climate crisis in which we live. Beyond that, it's always great to solve mysteries in science and we're happy with the results," concludes Dr. Geva.
It should be noted that the water wave laboratory led by Prof. Lev Shemer has also been used for years to verify models from other fields of knowledge in engineering and physics, including a number of recently published new discoveries such as focusing darkness similar to the sourcing of light rays, as well as a new type of waveguide, both of which are the work of Prof. Adi Aryeh from the School of Electrical Engineering.
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