Sevket Cokgor

Hydrodynamic forces on partly buried tandem, twin pipelines in current

Abstract This study extends the investigations of the forces on a cylinder, laid on, or partly buried in the bed with a parallel twin dummy cylinder nearby and without it, and were determined by measuring the pressure distribution on the cylinder in the case of a steady current. The pressure distribution around the cylinder was measured by using pressure transducers. The forces on the cylinder were calculated by the integration of the measured pressures on the surface of the cylinder. Force coefficients were obtained for the ranges of Re=0.8×104–1.5×104 for the burial depth to diameter ratio=0:0.7. The distance between axis of the measurement and dummy cylinders to diameter ratio (x/D) was 2, 1.5 and 1. The dummy cylinder was replaced downstream and upstream of the measurement cylinder.

Laboratory experiments of sediment transport from bare soil with a rill

Abstract Mathematical models developed for quantification of sediment transport in hydrological watersheds require data collected through field or laboratory experiments, but these are still very rare in the literature. This study aims to collect such data at the laboratory scale. To this end, a rainfall simulator equipped with nozzles to spray rainfall was constructed, together with an erosion flume that can be given longitudinal and lateral slopes. Eighty experiments were performed, considering microtopographical features by pre-forming a rill on the soil surface before the start of each experiment. Medium and fine sands were used as soil, and four rainfall intensities (45, 65, 85 and 105 mm h-1) were applied in the experiments. Rainfall characteristics such as uniformity, granulometry, drop velocity and kinetic energy were evaluated; flow and sediment discharge data were collected and analysed. The analysis shows that the sediment transport rate is directly proportional to rainfall intensity and slope. In contrast, the volumetric sediment concentration stays constant and does not change with rainfall intensity unless the slope changes. These conclusions are restricted to the conditions of experiments performed under rainfall intensities between and 105 mm h-1 for medium and fine sands in a 136-cm-wide, 650-cm-long and 17-cm-deep erosion flume with longitudinal and lateral slopes varying between 5 and 20%. Editor Z.W. Kundzewicz; Associate editor G. Mahé Citation Aksoy, H., Unal, N.E., Cokgor, S., Gedikli, A., Yoon, J., Koca, K., Inci, S.B., Eris, E., and Pak, G., 2013. Laboratory experiments of sediment transport from bare soil with a rill. Hydrological Sciences Journal, 58 (7), 1505–1518.

Hydrodynamic forces on a partly buried cylinder exposed to combined waves and current

The present study extends the investigations of the hydrodynamic forces on a cylinder, laid on, or partly buried in the bed. They were determined by measuring the pressure distribution on the cylinder surface in the case of steady current, waves and coexisting flow. The pressure distribution around the cylinder was measured by using pressure transducers, which were replaced in the cylinder. Force coefficients were obtained for the ranges of Re=0.8×104–1.5×104, for steady current, low KC numbers (KC<5) for wave alone case and, for current-to-wave velocity ratio=0, 3, 6 and infinity (current) for coexisting flow. The forces were also determined for the various burial-depth-to-diameter ratios between 0 and 0.7 values of the cylinder.

Performance of Submerged Breakwaters as Environmental Friendly Coastal Structures

An experimental study on the improvement for the problem of wave transmission in slightly submerged breakwaters is carried out in the present paper. The breakwater shape, effect of the porosity, water depth regarding the breakwater crest height and, dynamic stable deformed breakwater were examined as parameters. During the experiments, porosity was varied between 0.57–0.34, breakwater crest height to water depth ratio changed from 1 to 0.83. The similarity between a longshore bar and a dynamic stable submerged breakwater was also studied in one set of the experiments. Results indicated that a dynamic stable breakwater similar to a longshore bar resulted in better energy dissipation and the best transmission coefficient values determined between 0.3–0.1 in the mentioned condition.

Boulder-flow interaction associated with self-aeration process

In this experimental study, the boulder-flow interaction associated with the self-aeration process was investigated in a 0.50m wide flume. Experiments were performed with three different boulder arrangements and four different relative boulder submergences using Reynolds numbers from 5×103to 5 × 104. A boulder-flow interaction can trigger air–water mass transfer by generating turbulence, a hydraulic jump and plunging jet flow. When the boulders are submerged by the water, the maximum local aeration efficiency tends to decrease rapidly as does the flow resistance. Furthermore, the maximum local aeration efficiency is positively related to the blockage ratio of the boulder(s). The blockage ratio appears to represent the head loss, suggesting a possible interrelation between the aeration efficiency and the energy dissipation

Forces on partly buried, tandem twin cylinders in waves at low Keulegan-Carpenter numbers

Abstract This study deals with the forces on the circular cylinder, laid on, or partly buried in the bed with a parallel twin dummy cylinder nearby and without it. They were determined by measuring the pressure distribution on the cylinder in the case of wave at low KC numbers. The forces on the cylinder were calculated by the integration of the measured pressures determined by pressure transducers on the surface of the cylinder. Force coefficients were obtained for the low KC numbers (KC