The National Transport University Bulletin

Abstract

In recent years, there is a trend to use permeable structures in the coastal defense structures development. These hydrotechnical structures have the advantage of which is to improve the ecology of the protected water area, saving construction materials. Garbage does not accumulate in running water and free migration is ensured for sea creatures. The permeable coastal protection structures can be closely spaced circular piles, permeable walls consisting of horizontal or vertical slits located at a certain depth. Their effectiveness criteria are the transmission, reflection and energy dissipation coefficients of both regular and solitary waves. The permeable coastal defense structures design requires the calculation and experimental study of wave and waterhammer hydrodynamic loads on the elements of these structures. Experimental research is conducted in laboratory and nature conditions using modern high-precision equipment and data processing and analysis tools, including probability theory statistical methods and mathematical statistics. This paper presents the main results of permeable breakwater hydrodynamic modeling. Experimental studies were carried out in a hydrodynamic wave channel under laboratory conditions. The wave channel had a length of about 60 m, a width and a depth of 1 m. The channel was equipped with a wave generator, a measuring section with visualization and control means and measuring equipment, and a section for wave energy quencher. The measuring area was located at about 50 m from the wave generator and had glass walls for conducting visual studies. The bottom of the measuring area was filled with sifted sand (the average diameter of the sand grains was 0.35 mm) in a layer of about 0.2 m. The model of the permeable breakwater in the form of a vertical wall was located on this sand base. The permeable breakwater was a system of prismatic structures with a width of 60 mm, which were separated by slits with a width of 12 mm. Prismatic structures were immersed in sandy soil to a depth of 200 mm and protruded above the water surface to a height of about 200 mm. The permeable breakwater model was in the wave channel perpendicular to the direction of wave propagation. The physical modeling results of the surface waves with permeable breakwaters interacting showed that the permeable breakwater is a sufficiently effective coastal protection structure which reduces the wave load on the coastal zone and hydrotechnical structures. It is recorded that for the studied modes of wave motion, the permeable wave reduces the wave height by up to 30%, depending on the parameters of the waves. At the same time, a permeable breakwater is more effective for short storm waves. It was also established that during the location of the permeable breakwater on the erosive soil, the largest erosions were observed near the breakwater slits, and the sandy soil alluviation took place in front and behind the prismatic structures of the permeable breakwater. As the depth of the water area and the period of wave motion decreased, soil erosion and siltation increased. The analysis of the data showed that in front of the permeable breakwater model, the spectral components of the wave pressure are higher than behind the breakwater, especially in the high frequency area. It has been established that the construction of a breakwater in the coastal zone along the path of wave movement is an effective way to reduce the catastrophic consequences of the destructive effect of waves on the shore. A characteristic feature of the deformation process are energy losses and a decrease in the amplitude of the wave passing through the permeable breakwater. To determine the real regime of the separated residual wave in the given cases, it is necessary to study the subtle features of the waves with obstacles interacting, including calculations of the parameters of up running and reflected waves in the behind breakwater space, considering phase shifts and wave interference

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