Browsing by Author "Aksoy, Aysegul Ozgenc"

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Citation - WoS: 1
Effects of Flow Unsteadiness on the Transport of Bimodal Bed Material
(Turkish Chamber Civil Engineers, 2023-11-01) Bombar, Gokcen; Aksoy, Aysegul Ozgenc; Guney, Mehmet Sukru
The grain size distribution of the bed load was experimentally investigated under unsteady flow conditions with bimodal mixture of sand and gravel in a laboratory flume. Five various triangular hydrographs were generated. A clockwise behavior for the total bed load versus shear velocity was observed meaning that the bed load during rising limb was higher than that of falling limb. It was found that the percent finer at the plateau of bimodal sediment size distribution curve had higher values during the initial and final phases compared to those obtained during the peak time. At all plateaus, the percent finer values related to the hydrograph peak discharge were in the same order of magnitude with that of the bed material. The sand content of the transported bed material initially decreased, then maintained a constant value during a certain time interval and finally returned to its original value. The sand percent of the bed load decreased in the falling limb showing a counterclockwise loop and within the limits of the experimental campaign, the duration of the hydrograph did not affect the results considerably. Greater peak flow rate of the hydrograph resulted in greater hysteresis. The bimodality index was calculated for all transported sediment samples and it was revealed that its initial and final values were less than that of the bed material but it was approximately the same elsewhere. The 5% finer sediment amount was nearly equal during rising and falling limbs. It was revealed that D50 value of the bed load decreased in the rising limb showing a clockwise loop. The hysteresis was not considerably changed according to the hydrograph characteristics. The clockwise type hysteresis was also observed for the size group of D95. The lag increased as the peak flow rate increased. A strong relation was found between the dimensionless total bed load Wt* and the total work index Wk as well as Wk and the ratio WR/WF. The correlations between the dimensionless total bed load and the unsteadiness parameters P, and Pmod were very weak, whereas a quite high value of determination coefficient was obtained with the unsteadiness parameter Pgt, implying an appreciable interdependence.
Citation - WoS: 6
Citation - Scopus: 5
Experimental and Numerical Investigation of the Flood Waves Due To Partial Dam Break
(Springer Int Publ Ag, 2022-07-20) Aksoy, Aysegul Ozgenc; Dogan, Mustafa; Guven, Semire Oguzhan; Tanir, Gorkem; Guney, Mehmet Sukru; Özgenç Aksoy, Ayşegül; Oğuzhan Güven, Semire
The potential destruction of dams is a serious danger for the settlements. Dam break events cause serious loss of life and property in the region, regardless of the reason. The time required to give warn the people of the region is very short since floods develop suddenly during dam breaks. For this reason, the investigation of the flood wave propagation that will occur at the time of possible collapse is important for the emergency action plans to be prepared. In this study, the dam break experiments were carried out in the distorted physical model of the Urkmez Dam and at its downstream part also involving the vegetation. The horizontal and vertical scales are 1/150 and 1/30, respectively. The water depths and local velocities were measured by means of elaborated devices, and the propagation of the flood wave was recorded by high-precision cameras. In addition, numerical analysis was achieved by using the FLOW-3D program. According to the results, it is concluded that as the water level decreases, the time to reach the measurement points of the flood increases and the spatial distribution is delayed. The computed values obtained from the numerical model simulated by using the dam reservoir are in better agreement with those obtained from experiments than those calculated by using the outlet hydrograph.
Citation - WoS: 17
Citation - Scopus: 17
Experimental Investigation of the Equilibrium Scour Depth Below Submerged Pipes Both in Live-Bed and Clear-Water Regimes Under the Wave Effect
(Elsevier Sci Ltd, 2018-11) Dogan, Mustafa; Aksoy, Aysegul Ozgenc; Arisoy, Yalcin; Guney, Mehmet Sukru; Abdi, Vahid
Pipelines are the key structures to carry fluids such as oil, petroleum, gas and water; any inadequate design induces bottom stability problems causing unintended consequences. In the present study, the equilibrium scour depth below submerged pipes due to regular waves was investigated experimentally. During the experiments various pipe diameters, bed material grain sizes and wave characteristics were used. The novelty of the study is that the experiments were performed both in live-bed and clear-water regime conditions. The analysis of the experimental data showed that the equilibrium scour was correlated with Shields parameter as well as Keulegan-Carpenter number, especially for live-bed scour condition. However, in the case of clear-water scour, the Keulegan-Carpenter number was found as a unique non-dimensional parameter that dominates the scour phenomenon. New empirical relations were also proposed for clear-water and live-bed scour separately.