جستجوی مقالات مرتبط با کلیدواژه « پروفیل بستر » در نشریات گروه « آب و خاک »

One of the complicated phenomena in sediment hydraulic engineering is scouring around bridge pier. Regard to three-dimensional and complicated flow pattern around piers, measuring some hydraulics parameters during the tests such as flow pattern, variation of bed profile and shear stress are difficult, in this situation application of numerical models in order to extract results and more detailed study is useful. Aim of this research is numerical modeling of flow pattern, variation of bed profile and scour depth and shear stress around rectangular pier using Flow 3D and applying the results to protect piers against scouring. Results showed, for aligned pier with flow, shape of scour hole and flow pattern were symmetrical, the side in contact with flow is high-pressure and the other side is low-pressure. As increase of pier angle, shear stress in front of the pier increased so that for pier with 10° angle with flow direction, shear stress was 0.55 N/m2. Also fluctuations of bed profile and water surface increased. Application of submerged vanes, changed scour pattern and moved sediment in front of pier which scouring was reduced. Increase of height and angle of submerged vanes improved their protective role. Base on the results of numerical model, after 30 minutes, scour depth in front of pier in aligned pier with flow and angle of submerged vanes 30°, in same level with bed, 1.25 cm and 2.5 cm on the bed, was 3.1 cm, 0.035 cm and +0.005 cm (on the bed), respectively. As increase of pier angle, performance of submerged vanes to control scouring in front of pier and in side of high-pressure wall decreased, but in side of low-pressure wall scouring compared with alone pier was less.

The scour around the bridge piers is one of the main causes of bridge failure and the extraction of aggregates may aggravate this phenomenon. The present study comprehensively investigated the scour around the groups of bridge piers in the presence of aggregate extraction pits, using different discharges. The bridge piers roughened by gravel had been compared with the simple bridge piers; so, the results showed that the roughening caused the reduction of the scour depth. Scour depth change rate led to an increase in the equilibrium time. The results also showed that the reduction of the scour depth at the downstream groups of piers was more than that in the upstream. For the lowest discharge, the aggregate extraction pits had a considerable effect on the scour depth difference for the groups of piers in the downstream and upstream. On the other hand, the effects were decreased when the rate of discharge was increased. The experimental results obtained by the rough surface models showed that as the discharge was increased, the local scour was increased too; at the same time, the bed profile was posed at the low level. Generally, the scour depth of the groups of piers in the downstream of the extraction pit was more than that in the upstream. The results of the current research, therefore, demonstrated that the surface of the bridge pier roughened by gravel reduced the scour depth.