Browsing by Author "Gokmener, Serkan"

Now showing 1 - 5 of 5

Citation - WoS: 3
Citation - Scopus: 2
Critical Submergence for Single and Multiple Horizontal Intake Structures
(Springer Heidelberg, 2023) Gogus, Mustafa; Gokmener, Serkan; 6062; 01. Çankaya Üniversitesi
In this study, a series of experiments were carried out to investigate the variation of the critical submergence of air-entraining vortices with the related flow and geometric parameters at single and multiple horizontal intake structures. Three identical intake pipes were tested at a wide range of discharges with varying sidewall clearances under symmetrical and asymmetrical approach flow conditions. Experimental results indicated that increasing the number of intake structures in operation results in a more complicated flow pattern in front of the intake structures due to the mutual effects of the intakes on each other. Therefore, critical submergence values are higher for multiple intake structures than those of single water intake structures for a given Froude number. Dimensionless empirical equations were derived for each single, double and triple unit operation to calculate the critical submergence as a function of relevant flow and geometric parameters, and they were compared with the related equations available in the literature. These equations can be used to determine sufficient submergence to avoid air-entraining vortices at single and multiple horizontal intakes within the ranges of dimensionless parameters tested in this study.
Citation - WoS: 2
Citation - Scopus: 2
Effects of Collars in Reducing Local Scour Depth Around Bridge Abutments Under Unsteady Flow Conditions
(Springer int Publ Ag, 2025) Gokmener, Serkan; Gogus, Mustafa; Altan-Sakarya, A. Burcu; 01. Çankaya Üniversitesi
In this experimental study, semi-circular end collars around semi-circular end abutments and rectangular collars around rectangular abutments were tested in order to investigate the efficiencies of the collars in reducing the local scour depth under unsteady-state clear-water approach flow conditions. Experiments were conducted in a rectangular sediment channel having a sediment pool filled with uniform sand as the bed material. Three different abutment lengths having constant widths were tested under three distinct successive flow intensities that were applied continuously for a duration of 2 h during each experiment. Varying sizes of collars were located at different elevations relative to the bed level. The effect of abutment length, collar width, collar elevation, flow intensity and temporal variation on local scour reduction performances of collars were tested. According to the experimental results, it can be stated that the application of collars around the semi-circular end and rectangular bridge abutments decreases the local scour depth by up to 72% and 51%, respectively. In addition, semi-circular end collars around semi-circular end abutments gave better results in reducing the scour depths than rectangular collars around rectangular abutments. Best collar performances were generally achieved for the largest collar width located around the bed level for semi-circular end abutments and below the bed level for rectangular abutments.
Citation - WoS: 1
Citation - Scopus: 3
Effects of Collars on Local Scour Around Semi-Circular End Bridge Abutments
(Emerald Group Publishing Ltd, 2023) Gogus, Mustafa; Daskin, Sueyla; Gokmener, Serkan; 01. Çankaya Üniversitesi
The occurrence of scour around bridge elements due to the transportation of bed material during flood events can cause serious structural damage and loss of life. Increased uncertainties in precipitation and runoff predictions due to climate change make this phenomenon more complex and dangerous. Bridge scour countermeasures should thus be more focused on decreasing scour formation around bridge elements. In this study, abutment scour under clear-water conditions with constant flow intensity was conducted and collars were tested as scour countermeasures around semi-circular end bridge abutments. The experimental study was performed in a rectangular channel with an almost uniform cohesionless bed material for 3 h with and without collars. Collars of various lengths located at different elevations around the abutments were tested to investigate the effect of collars on scour development. The results of the study showed that the scour depth decreased with increasing collar width and when the collar was placed below the bed level for a given abutment length. The results were compared with those of similar earlier studies to show the effect of abutment shape, size of the bed sediment and test durations on the development of scour depth around abutments.
Effects of Floating Rafts as Anti-Vortex Devices at Horizontal Intakes
(International Association for Hydro-Environment Engineering and Research, 2023) Gogus, Mustafa; Gokmener, Serkan; 6062; 01. Çankaya Üniversitesi
Air- entraining vortices created by swirling flows on intakes cause serious problems such as; increasing loss of hydraulic load and discharge at water intake structures, loss of efficiency, operational problems, cavitation and vibration problems in hydraulic machines. Hence the position of the intake should be justified for the most critical scenario as the reservoir is at dead or at minimum storage level to avoid the occurrence of air-entraining vortices. Although intakes are designed by considering the formation of air-entraining vortices, they cannot be prevented due to approach flow conditions and submergence. Therefore, some structural changes should be considered in order to avoid the occurrence of air-entraining vortices. One of these methods is using anti-vortex devices to prevent the formation of air-entraining vortices. In this experimental study, floating rafts at different sizes were tested as anti-vortex devices to prevent the formation of air-entraining vortices at single and multiplehorizontal intake structures under symmetrical and asymmetrical approach flow conditions. Three identical pipes of diameter Di=0.265 m were tested at a wide range of discharge with varying sidewall clearances. Experiments were conducted for three different combinations of the intake structures: single, double and triple water intakes were operated, respectively. Different side wall distances in the approach channels of the intake structures were specified previously to create symmetrical and asymmetrical flow conditions. The side walls were located according to these distances before each experiment. For single and double water intake structures, Wraft=10 cm and triple water intake structures, Wraft=20 cm raft width were found to be successful for vortex prevention. Moreover, Wrafts/Di values that gave successful results are 0.38 for single and double intake structures and 0.75 for triple intake structures. © 2023 IAHR – International Association for Hydro-Environment Engineering and Research
Citation - WoS: 3
Citation - Scopus: 3
Local Scour Evolution Around Semi-Circular End Bridge Abutment in Quasi-Unsteady Condition
(Ice Publishing, 2022) Gokmener, Serkan; Gogus, Mustafa; 6062; 01. Çankaya Üniversitesi
In this experimental study, the temporal development of local scour is studied around semi-circular end bridge abutments under quasi-unsteady clear-water flow conditions in a rectangular sediment channel. A step-wise hydrograph of 6 h duration is used in the experiments. Six different abutment lengths having constant width, with uniform sand as bed material, were tested for three different successive flows - each applied continuously for 2 h. Bathymetry of the bed level was measured around the abutment every 15 min with the help of a measurement device to observe temporal development of the local scour around the semi-circular end abutment. Effects of the abutment length, flow intensity and time on the scour depths around semi-circular end bridge abutments, along with those at the front, upstream and downstream faces of the abutment, are also investigated and discussed. It is shown that the maximum scour depth always occurs at the front noses of the abutments compared with those at the upstream and downstream noses. A dimensionless empirical formula is derived to predict the scour depth at the front nose of the abutment as a function of related parameters. The results reveal that flow intensity is the most critical parameter in scour development.