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Articles by M.S. Bejestan
Total Records ( 3 ) for M.S. Bejestan
  A. Masjedi , M.S. Bejestan and A. Esfandi
  In this study, the use of collars for reducing the effects of local scour at a bridge pier is presented together with the time aspect of the scour development. The adoption of a collar is based on the concept that its existence will sufficiently inhibit and/or deflect the local scour mechanisms so as to reduce the local scour immediately adjacent to the pier. The overall objective of the research is to study the temporal development of the scour for a pier fitted with a collar and a pier without a collar. The study was conducted using in a 180 degree laboratory flume bend with a relative radius of R/B = 4.67 operated under clear-water conditions. The median size and geometric standard deviation of bed material were equal to d50 = 2 mm and sg = 1.7, respectively. Tests were conducted using one pier with 60 mm diameter in positions of 60 degree under one flow conditions. In this study, the time development of the local scour around the abutment fitted with and without collar plates was studied. The effects of various sizes of collars fitted at different elevations on the temporal development of scour depth at the abutment were also studied. The time development of the scour hole around the model pier with and without a collar installed was compared with similar studies on bridge piers. The results of the model study indicated that the maximum depth of scour is highly dependent on the experimental duration. It was observed that, as the size of a collar plate increases, the scour decreases. The minimum depth of scour occurs for the collar at diameter of 3D placed at elevation of -0.1 D from the bed surface.
  A. Masjedi , M.S. Bejestan and H. Kazemi
  Local scouring around the bridge pier occurs because of flow separation and developing several vortexes around the bridge pier. Such scour hole can cause failure of the bridge especially during the river floods. Because of this several researches, have been conducted during the past three decades in straight flumes. For the case when the bridge piers located in river bend, little information is available. In this study, a series of experimental tests have been conducted in a 180 degree laboratory flume bend with a relative curvature of bend of 4.67. One oblong model pier of width 60 mm and length 180 mm was used for the study in seven different positions of 0, 30, 60, 90, 120, 150 and 180 degree under three different flow conditions were tested. Natural sand with uniform graining of d50 = 2 mm and uniformity factor of 1.7 were used as bed materials. The results of the model study indicated that the maximum depth of scour is highly dependent on the experimental duration. The depth of the scour hole increases as with increasing duration of flow. The extent of scour observed at the pier also increases as the duration of the tests increases. The results of this study showed that, while oblong pier is placed in the bend, the maximum scouring depth is occurs in position of 60 degrees. Also, it was observed that in all positions, increasing the Froude number increases the scouring depth. Measuring depth of scouring based on experimental observation, an empirical relation is developed with high regression coefficient 94%.
  A. Masjedi , M.S. Bejestan and P. Rahnavard
  In this study, investigation on the time development of local scour on around a T-shape spur dike in a 180 degree flume bend are presented. The T-shape spur dikes have been used extensively for erosion control in the external wall of river bends. Experimental investigation on scoring and determination of depth of scoring are among the most important issues in T-shape spur dike designation. The study was conducted using in a 180 degree laboratory flume bend. Experiments were conducted for different locations of T-shape spur dikes at the bend with various Froude number. In this study, the time development of the local scour around the T-shape spur dike plates was studied. The time development of the scour hole around the model T-shape spur dike installed was compared with similar studies on spur dikes. The amount of scour at the upstream of T-shape spur dike is much more as compare to that at the downstream of T-shape spur dike. The results of the model study indicated that the maximum depth of scour is highly dependent on the experimental duration. It was observed that, as Froude number increases, the scour increase. All Froude numbers, at location of 60° results maximum increase in scour depth. Measuring depth of scouring based on experimental observation, an empirical relation is developed with high regression coefficient 92%.
 
 
 
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