Breaking wave

Wave breaking at designated water waves the critical degree of wave transformation, in which the surface tension is overcome at the wave crest, the orbital motion loses its characteristic shape and falls leaking water into the forward slope of the wave contour. Such unstable waves are called breakers.

The generating of the sea waves ( gravity waves ) required energy is transferred from the wind on the water surface over hundreds of kilometers and propagates possibly still thousands of miles away as a wave. The conversion of this energy into heat, however, through the process of wave breaking usually in shallow water zones, often on only a very few meters in the surf zone. Especially with such constraints devastating destruction forces can occur on the coasts. The breaking process of the shaft itself is characterized by the orbital motion of the continuously deformed to the point of breaking wave.

Criteria wave breaking

Both the ratio of the instantaneous orbital velocity w to the wave celerity c and the ratio of the orbital acceleration a to the gravitational acceleration g is of importance. After George Gabriel Stokes periodic waves are unstable when is at anwachsender wave height of the tangent angle at the crest. For deep-water waves John Michell has the associated limiting steepness for H / L = 0.142 determined (H = wave height, L = wavelength) and Rankine (1860 ) the consistency of the orbital velocity w at the crest of the wave celerity c.

For the breaking waves in surf zones apply to the critical angle and comb for the critical orbital velocity w about the same above findings. The maximum limiting steepness H / L in shallow water, however, is also d depends on the water depth, which comes under the theory of individual waves in the ratio of breaker height to the water depth expressed. So are the criteria wave breaking in shallow water:

Breaker forms

For water waves, the fascination assumes that the observer they often present themselves as waves with a imperfect form, and the more so the more they deviate from a regular sinusoidal shape. This is the case, in which there is in the region to a comb consisting of water and air, the two-phase mixture ( foam ), especially for breaking waves. In marine structures and vessels is of particular importance that the hazards of breaking waves force effects in the comb area reach their maximum. Extreme force effects - such as the pressure shock in buildings and the wash of the sea ( slamming ) for ships - are dependent on the current breaker form.

In contrast to those produced by strong winds on the open sea forms of wave breaking (white capping), different breaker types can be defined near the shore, depending on the

• Lake bottom slope ( or artificial slope inclination )

And the

• Wave steepness.

Here it comes as a result of refraction and küstenwärtig decreasing water depth ( shoaling ) to anwachsender wave height H and reduced wavelength L to at the maximum wave steepness max ( S) waves break begins. Using the on Irribarren and Nogales (1949 ) receding surf similarity parameter

There can be three main forms of each other as follows delimit:

This is particularly striking forms. In contrast, in the nature is often observed a continuous transition from one form to another.

In surge breakers first, the surface tension is overcome at relatively symmetric wave crest; bubbles form, the down move along with the wave emerging from the water on the front of the shaft. On a track that corresponds to the multiple wavelength, the wave energy into turbulence and finally is converted into heat. After falling breakers this is the preferred by surfers breaker form.

The fall crusher is characterized in that with increasing steepening also increasing asymmetry occurs until finally the küstenwärtige slope of the shaft is vertical. Only then enters water from out of the comb and moves - the case of the parabola following - over the front slope away into the trough in front of it inside. On the one hand, the incident water gets together with folded- air to the ground, on the other hand it is transported according to the present there orbital velocity direction in a roll back to the wave crest. Both mechanisms cause an intensive mixing of air, so that the energy is at a distance corresponding to a fraction of the wavelength converted. Does the fall of crusher directly to an approximately anhydrous surface pressure shock occurs.

The surfing under the parabolic breaker tongue is called Tube -surfing.

When reflection breaker of the water outlet and the bubbling is minimal and to pursue a real crushing process hardly. Here there is a move operation, the more with a standing wave ( clapotis ) is to be compared.

Yet, this is a transitional form on the border to overthrow crusher, which is referred to as a partial fall breaker. In this, only the lower part of the slope is vertically küstenwärtigen. The point at the first exit water from the shaft, located inshore and a lot deeper than the wave crest.

Related mechanism

The breaking of unsteady waves in the surf zone is the well-known from the stationary channel flow process of change jump comparable: in both transactions occur for energy conversion rates that are orders of magnitude higher than friction on the sole or internal friction between the fluid particles. It is noteworthy that in both natural processes called the considerable energy sales to a relatively short distance can take place.