TY - JOUR T1 - Effects of Combined Submerged Vanes and Collar on the Scour Reduction around Cylindrical Bridge Piers TT - تأثیر توأم صفحات مستغرق و طوق در کاهش عمق آبشستگی پایه‌های استوانه‌ای شکل پل‌ها JF - JSTNAR JO - JSTNAR VL - 15 IS - 57 UR - http://jstnar.iut.ac.ir/article-1-1857-en.html Y1 - 2011 SP - 23 EP - 33 KW - Bridge pier KW - Collar KW - Scouring KW - Sediment transport KW - Shear stress KW - Submerged vanes. N2 - Submerged vanes are low aspect ratio flow-training structures mounted vertically on the river bed at an angle to the prevailing flow. The aim of application of vane is to generate a secondary circulation in the main flow, designed to modify the near-bed flow pattern and thus redistribute flow and sediment transport within the channel cross section. Collar is a flat sheet with low thickness fixed vertically on the pier at stream bed level or near it. Installation of a collar leads to protect the river bed against the direct impact of downflow produced at the upstream face of the pier and therefore reduces the scour depth. This research is a laboratory study that examines the effectiveness of submerged vanes and combination of submerged vanes and collar as a pier scour protection device. Experiments were conducted in an 8 m long and 0.8 m wide flume and a cylindrical pier used was 6 cm in diameter. Clear-water scour tests with u*/u*c = 0.9 were performed with a collar 3 times wider than the pier diameter at the stream bed level and submerged vanes 1.5 times longer than the pier diameter at the stream bed level (H=0). Different arrays of vanes with different angles to main flow direction were employed. The highest reduction in the depth of scour hole with four vanes and a collar showed 61% reduction in scour depth. M3 ER -