Clapotis

For water waves is understood (from the French for, rippling ') a standing wave under Clapotis that produced by reflection of a progressive monochromatic wave on a vertical wall ( pier, seawall ).

Here, a wave impinging on the wall of the wavelength L, and the height H ( the vertical distance between the wave trough and wave crest ) is a mirror image reflected wave. The superposition of incoming and reflected wave results in the Clapotis with a wave height 2H. If the distance from the wall with the coordinate x denotes, are antinodes of height 2H at the points x = 0 (wall), x = L / 2, x = 2L / 2, etc.

In between vibration nodes are at x = L / 4, x = 3L / 4, x = 5L / 4, etc., where in a perfect Clapotis there is no water surface elevation. The oscillatory motions of the water particles in the wave field below the water surface ( second picture) are curvilinear, with a horizontal tangent at the nodal points and vertically at the antinodes.

The perfect reflection provides an ideal case dar. In nature, the boundary conditions for stable waves are given at most approximately in building close, because losses occur on the reflecting surfaces. As a result, it leads to the formation of a ( broken ) torn Clapotis, an ( imperfect ) partial Clapotis, or a combination of both.

In Beck formations with low reflection losses, the excitation of natural oscillations can be proven, see Beck vibration. Resonant peak at a supercritical wave steepness S = H / L leads to torn Clapotis, in which the water at the antinodes vertical shoots up. On a vertical wall the appearance of a torn Clapotis is often accompanied by water hammer effects.

Partial Clapotis on a river bank

By involving friction washing action on the building (about at an embankment, right), in particular through the process of wave breaking, is part of the wave energy is absorbed, the amount of the reflected wave is smaller than that of the incoming wave, it forms a partial Clapotis. If monochromatic waves (with and ) provided, as opposed to perfect the Clapotis Wasserteilchenbewegung can be approximated by elliptical orbits in the wave field of the partial Clapotis. Such are indicated in the antinodes by a greater vertical major axis and the shaft node with a larger horizontal main axis. The superimposition of the reflected wave with the oncoming equal frequency resulting in a partially progressive wave, the amount varies between a maximum value and a minimum value. and arise at a distance of L / 4 In the event that the envelope of the wave crests and the wave troughs are known, the reflection coefficient may be determined from these extreme values ​​: