Hydraulic performance and wave loadings of perforated/slotted coastal structures: A review

The present paper outlines the numerical calculation of wave interactions with a thin vertical slotted barrier extending from the water surface to some distance above the seabed, and describes laboratory tests undertaken to assess the numerical model. The numerical model is based on an eigenfunction expansion method and utilizes a boundary condition at the barrier surface that accounts for energy dissipation within the barrier. Numerical results compare well with previous predictions for the limiting cases of an impermeable barrier and a permeable barrier extending down to the seabed. Comparisons with experimental measurements of the transmission, reflection, and energy dissipation coefficients for a partially submerged slotted barrier show good agreement provided certain empirical coefficients of the model are suitably chosen, and indicate that the numerical method is able to account adequately for the energy dissipation by the barrier. The effects of porosity, relative wave length, wave steepness, and irregular waves are discussed and the choice of suitable parameters needed to model the permeability of the breakwater is described.

Wave Interactions with Vertical Slotted Barrier

Nonlinear components of wakes from large high-speed ships at times carry a substantial part of the wake energy and behave completely differently compared to the classical Kelvin wave system. This overview makes an attempt to summarize the descriptions of nonlinear parts of a ship’s wake. For completeness, also the basic properties of the Kelvin wake are sketched. The central topic is the generation of solitons by ship motion both in channels and in unbounded sea areas. The discussion is mostly limited to disturbances on the surface of nonstratified water. The optional nonlinear components of the ship wake such as the very narrow V-like wake components, packets of monochromatic waves, ship-generated depression areas, and supercritical bores are also discussed. Specific features of solitonic ship waves and their interactions have numerous applications in naval and coastal engineering, and in adjacent areas of applied mechanics. An overview of the practical use of certain properties of phase shifts, and particularly high wave humps occurring during Mach reflection and nonlinear interaction of solitons in decreasing the wave resistance at supercritical speeds and in the freak wave theory, is also presented. The final part of the paper describes the results of studies of far-field properties of nonlinear wakes and possible consequences of the increase of local hydrodynamic activity. There are 263 references cited in this review article.

Nonlinear Components of Ship Wake Waves

The diffraction of a steady Stokes wave train by a thin wedge with vertical walls is studied when the incident wave is directed along the wedge axis (grazing incidence). Parabolic approximation applied recently by Mei & Tuck (1980) to linear diffraction is extended to this nonlinear case. Significant effects of nonlinearity are found numerically, in particular the sharp forward bending of wave crests near the wedge. The computed features are found to corroborate the existing experiments only qualitatively; the controlling factors in the latter being not completely understood. An analytical model of stationary shock is proposed to approximate the numerical results of Mach stems.

Forward diffraction of Stokes waves by a thin wedge

Extreme wave generation using self correcting method — Revisited

https://icce-ojs-tamu.tdl.org/icce/index.php/icce/article/download/3434/3114

Investigations on Irregular Waves in Hydraulic Models

This paper deals with the wave transmission through a vertical slotted wall. In an experimental study the transmission coefficient has been investigated as a function of the shape of the wall elements (rectangular shape and H-beam shape), of the ratio of solid wall to total wall length (wall-element ratio) and of the wave approach direction. The test results for a wave direction perpendicular to the wall are compared with previous investigations and theoretical derivations. For an oblique wave approach the test results are described by a semi-empirical formula. This formula, combined with a theoretical solution for perpendicular wave approach is used to describe the transmission coefficient for any angle of wave approach.

https://icce-ojs-tamu.tdl.org/icce/index.php/icce/article/download/3006/2671

Wave transmission through vertical slotted walls

As under oblique wave approach water waves are reflected by a vertical wall, a wave branching effect (stem) develops normal to the reflecting wall. The waves progressing along the wall will steep up. The wave heights increase up to more than twice the incident wave height. The £jtudy has pointed out that this effect, which is usually called MACH-REFLECTION, is not to be taken as an analogy to gas dynamics, but should be interpreted as a diffraction problem.

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Mach-reflection as a diffraction problem

Diffraction calculations for breakwaters are often based on SOMMERFELDs solution, which is mathematically exact for thin full-reflecting walls. For breakwaters with low reflecting frontsides, and if guidewalls are used, commonly a modified solution is applied, reducing the second term of the solution- formula proportional to the degree of reflection. It could be shown that this approach is not sufficient in the region just behind the breakwater, especially for small angles of wave attack. Regarding the exact solution for wedges it was possible to determine a special weighing factor for the second term of the SOMMERFELD solution, dependent on the degree of reflection and the wave direction, which leads to a better agreement between model tests and theoretical results.

https://icce-ojs-tamu.tdl.org/icce/index.php/icce/article/download/3298/2966

Influence of breakwater-reflection on diffraction

/pdf/mach-reflexion-als-diffraktionsproblem-niyhjztam9.pdf

Soren Kohlhase

Papers

Investigations on Irregular Waves in Hydraulic Models

Wave transmission through vertical slotted walls

Mach-reflection as a diffraction problem

Influence of breakwater-reflection on diffraction

Mach-Reflexion als Diffraktionsproblem