جستجوی مقالات مرتبط با کلیدواژه "drag coefficient" در نشریات گروه "آب و خاک"

In this study, experimental research was conducted to determine the effect of  arrangement and canopy density and other common non-dimensional hydraulic parameters on drag coefficient of rigid vegatations, during long waves. The beach and vegetation model was fitted at a knife edge flume.  A dynamic loads were measured by Load Cell device (Type Single base with a capacity of 50 kg) and 3D velocities were measured by Acoustic Doppler Velocimeter  equipment.  The experiments were performed in two triangular and rectangular layouts, which include densities of 12 to 273( stem/m 2). The results showed that the vegatations Drag  coefficient was indirectly related to the flow velocity. As the flow velocity of rigid vegatations decreases, the Drag coefficient increases. It was also found that rigid vegatations have a significant  influence on energy absorption and energy dissipation. On average, with an increase of 15%, the area occupied by the coverage is increased by 12% to the values of the Drag coefficient. In the most dense case, 273 stems per unit area with increasing relative wave height, due to the fact that the wave is involved in colliding with the beach and breaking the wave with more coverage, the traction force is increased and 18% is added to the Drag coefficient. In the most dense case, with a decrease of 8% in the Reynolds value, the Drag coefficient increased by 33%, and in the lowest density, the increase in the Drag coefficient increased to 44%.

In order to investigate the flow formation on dunes, the experimental data from a flume 12 meters long, located in Hydraulic Lab at Technical University of Graz (Austria), were collected. In this study, dunes (particle sizes of 13 and 6 mm) in a 2-D plan were developed with the wavelength of 1 meter, the lee angle of 8 degree, and the crest heights of 4 and 6 cm; these were uniformly installed across the width of flume. The analysis of the experimental flow velocity profiles measured by ADV and PIV technology and the numerical profiles modeled by SSIMM showed that in the same hydraulic conditions, there was no significant relation between drag coefficients of particles on dunes and flow discharge variation, while the water depth reduction caused a sudden increase in the drag coefficient up to 66%. Also, reducing particle size of the dune increased the drag coefficient and there was a significant relation between particle size (diameter) and dune formation, so that in smooth crested conditions, as compared with the sharp crested dune, the drag coefficient was increased up to 32%.

Wave attack is the main source of irreparable damages to the sea coast line. The coastal protection techniques are now improved from structural protection to biological ones. This includes plantation of trees and development of vegetation canopy (called green belt) along the shorelines and protection of coastal structures against the waves created by tsunami. For this¡ the application of green belt has been studied and effect of vegetation density and wave height on wave force is evaluated for waves in broken condition. Experiments were conducted in a flume with 8.3m length¡ 0.8m width¡ and 0.55m height. Experimental variables include four bed slopes¡ four vegetation densities¡ and 110 wave heights. The results show that absorption of wave force increase with increase of wave height and density of vegetation. At the highest vegetation density the wave force effect was reduced by about 75% compared to the case without vegetation.