Sürdürülebilir Kalkınma Amaçları
Yayınlar
- MakaleYalnız künye2026Stationarity or nonlinear nonstationarity? Assessing standard duration extreme rainfall under Türkiye’s complex topography and climate variability
Şahin, Nagehan; Şan, Murat; Kankal, Murat
The impact of climate change on extreme rainfall regimes requires a reassessment of the design processes of traditional hydrological structures. For this purpose, conducting an in-depth analysis of the nonstationary nature of extreme rainfall in regions with complex topography and climate is of great importance. This study examines the stationary and nonstationary states of standard duration (5 min–24 h) annual maximum rainfall data across Türkiye. For this purpose, the intensity-duration-frequency relationship was analyzed using data at 100 homogeneous stations during 1980–2020. The analyses were performed using the generalized extreme value (GEV) distribution with eight linear and non linear location and scale parameters, based on stationary and nonstationary models. Time was included as a covariate in nonstationary models. The corrected akaike information criterion and likelihood ratio test were used to select the appropriate GEV distribution. Findings indicate that stationarity is generally dominant, but nonstationarity is relatively higher in a nonlinear manner in cold climates and complex topography. The effect of location and scale parameters was found to be individual in the short duration and combined in the long duration. It was observed that nonstationarity was relatively higher in complex topography than in flatter regions up to 8 h. Still, the diversity of nonlinear models decreased over the long duration. In conclusion, this study emphasizes the need to consider nonstationary approaches in designing hydrological structures, especially in climate change.
- MakaleYalnız künye2023Hydrodynamic performance evaluation of screening on the physical unit operations in wastewater treatment based on experimentally validated CFD computations
Şahin, Nagehan; Şibil, Rahim
This paper introduces an evaluation of the hydrodynamic performance of the flow in the screens used on the physical unit operations in a selected full-scale wastewater treatment plant (WWTP) based on Computational Fluid Dynamics (CFD) simulations. The numerical study was carried out with the ANSYS Fluent, CFD software by using the three-dimensional (3 D), steady, incompressible flow based on the Reynolds-Average Navier-Stokes equations with three different turbulence modeling. The hydrodynamic behavior of the screening facility, combined with head pond-upstream channel-bar screens was evaluated under different conditions of the mass flow rate and velocity fields. Also, the numerical study was validated against the experimental study, which implemented in-situ measurements by Acoustic Doppler Velocimeter (ADV), and consistent results were obtained between the numerical and experimental study. Interestingly, while the Realizable (real) k-ε turbulence model with the relative error of 9.31% gave the best predicting results in the head pond, the renormalization group (RNG) k-ɛ turbulence model with the relative error of 9.05% gave the best predicting results in the upstream channel and through bar screens. As a result of the experimental measurements and CFD analyses carried out in the full-scale WWTP, the function of the screening facility was found to be incomplete. Moreover, a hydraulically improved new geometry was presented to operate the existing WWTP efficiently.