The existing difference between Tsunamis (seaquakes), large waves generated when an earthquake with epicentre occurs in the bottom of the sea; the Meteorological tide, a super-elevation of the average sea level associated with low pressures; and the Astronomical tide, owing to the gravitational attraction of the stars on the oceanic mass, which originates periodic rises and falls of the sea level, are object of study in the book Fundamentos del movimiento oscilatorio (Oscillatory movement fundamentals), a work of the professors of the University of Granada Barquerizo Azofra, Losada Rodríguez and López Rodríguez, which has just been published by the University of Granada Publishing Service.
The waves observed in any water body in contact with the atmosphere are due to forces that act on the fluid trying to deform it and are compensated for the force of gravity and the superficial tensions that try to restore the balance. The form of these waves and their energetic content depend on the magnitude of the force that originated them.
Maritime engineering
This book studies oscillatory movements, hydrodynamic fundamentals, the linear wave theory, the cinematic and dynamic characteristics of oscillatory movement, fluids and average amounts associated with oscillatory movement and wave transformation processes.
According to the authors of the text: “the study of this type of oscillations is very important as any element inside a mass of water or close to it can be subjected to its action. In the case of maritime engineering, they study, among other aspects, the effect of the different types of sea waves on beaches, building works for littoral protection, ports or off-shore structures, as they will determine their design and maintenance”.
The authors of Fundamentos del movimiento oscilatorio (Oscillatory movement fundamentals) say that swell is the fundamental agent to consider in the design of any maritime construction work.
Wind is the generator mechanism of swell: waves originate in the open sea when the velocity of wind goes beyond certain critical level. From this moment, waves of small length and period and different directions start to form, fundamentally characterized by their asymmetry, giving a chaotic appearance to the open surface of the sea.
According to the authors of this book, “under the continuous action of wind, waves grow in height, length and period reaching maximum levels depending on the velocity of the wind, the length of the area over which it blows out or «Fetch», how long it has been blowing and water’s depth. In this case it is called fully developed sea, in other case it is known as partially developed sea”.
When swell has left the generation area, the components of different periods are segregated due to their dispersive nature. Long-period waves travel faster and are characterized by a higher symmetry and look more ordered. They look quite similar to sinusoidal waves. This surge is known as bottom sea or swell.
According to the authors of the text “when they propagate to more reduced depths, a moment comes when swell starts to feel the bottom: the waves are cambered, the height of the crests increases, the sinus wave decreases and the horizontal axe starts to lose symmetry. This phenomenon, called shoaling, is more marked in that the wave propagates to less deep waters”.
Reference
Professor Asunción Barquerizo Azofra. Dpt. Civil Engineering. Phone numbers: 958 24 8315. 958 248954
E-mail: abaqueri@ugr.es.
Professor Miguel Ángel Losada Rodríguez. Dpt. Civil Engineering. Tlfs. 958 24 8316. 958 246136. E-mail: mlosada@ugr.es
