Yazar "Baysal, Selman" seçeneğine göre listele

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    Öğe
    Numerical Investigation of Transitional Oscillatory Boundary Layers: Turbulence Quantities
    (Mdpi, 2025) Baysal, Selman; Kirca, V. S. Ozgur
    This study investigates the organized flow structures and turbulence quantities in a transitional oscillatory boundary-layer flow over a smooth bed using a DNS model set up by the open-source framework Nektar++ (v5.2.0). The present model was validated against the results of a previous study involving a bypass transition mechanism in the intermittently turbulent regime. To trigger the initial perturbations, a roughness element was placed on the bed and removed at the very moment a two-dimensional vortex tube, caused by an inflectional-point shear-layer instability, was observed on it. Then, the turbulent spots where the flow experienced intense fluctuations in an otherwise laminar boundary layer were identified from the bed shear-stress distribution on the bed, which served as a reliable indicator of turbulence. These flow features emerged as the first sign of the initiation of turbulence. Several measurement points were selected to follow the bed shear-stress variations and to observe the spatial and temporal development of turbulent spots at a low-wave Reynolds number, Re=1.8x105. Along with these observations, phase-resolved turbulence quantities were also investigated over successive half-cycles for the first time in the literature to understand how turbulence develops and spreads over the flow domain. The results show that the turbulence generated in the near-bed region becomes stronger in the deceleration stage due to the adverse pressure gradient and diffuses away from the bed during the subsequent phases of the developing oscillatory boundary-layer flow. The findings related to the turbulence quantities also indicate that the turbulence gradually evolves and spreads into the fluid domain in successive half-cycles.
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    Öğe
    Prescreening of Sedimentation Potential in Harbor Approach Channels: A Parametric Model
    (Asce-Amer Soc Civil Engineers, 2025) Baysal, Selman; Kırca, V. Ş. Özgür
    In this study, a parametric model was developed to prescreen the sedimentation potential and maintenance dredging frequency for harbor approach channels under the action of combined current and nonbreaking waves. The model is fast, easy to implement, and well-suited for preliminary assessment for a given set of ship, metocean, and sediment characteristics. To resolve the velocity profile, a refined wave-altered current profile was implemented in the model in favor of a simple power-law current profile, which improved the model performance substantially. The model was first validated against the results reported in an experimental study, and then verified against field measurements of the Damietta Harbor approach channel. Finally, a parametric study was conducted to investigate the influences of (1) median grain size of seabed sediment, (2) wave severity, and (3) depth-averaged current velocity on the sedimentation in approach channels. The results showed that the dredging frequency of approach channels is mainly governed by the wave characteristics, i.e., wave severity, in the case of combined waves and current. It was further shown that representing the wave-altered current profile in simplified models is particularly important. Otherwise, the model would yield unrealistically high dredging frequencies when the current velocity approaches zero, even under severe waves.
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    Öğe
    Seyhan Havzası’nda düşük akımların analizi
    (2025) Baysal, Selman; Yılmaz, Selahattin Utku; Kaçar, Furkan Sencer; Onoz, Bihrat
    Bu çalışmada Seyhan Havzası’nda yer alan istasyonlarda düşük akım analizi gerçekleştirilmiştir. Bu doğrultuda kısa, orta ve uzun vadeli kuraklık tespiti için d = 1, 7, 10 ve 15 günlük yıllık ortalama minimum debi değerleri kullanılarak düşük akım frekans analizi yapılmıştır. İki parametreli Log-Normal (LN2), Gamma (G2), Weibull (W2), Üstel (E2), Gumbel (GEV-I), Lojistik (L2) dağılımları ile üç parametreli GEV (GEV-III), Log-Normal (LN3), Pearson Tip III (P3), Log-Pearson Tip III (LP3) ve Genel Lojistik (GL3) dağılımları kullanılarak farklı dönüş aralıklarına sahip düşük akım tahminleri gerçekleştirilmiştir. Kolmogorov-Smirnov (K-S) uygunluk testi ile farklı istatistiksel dağılımların mevcut zaman serilerine uygunluğu tespit edilmiştir. Elde edilen düşük akımlardaki eğimin (trend) belirlenmesi için Mann-Kendall (MK), Trend-Free Pre-Whitening (TFPW) ve yenilikçi trend analizi (ITA) testleri uygulanmıştır. Çalışmada altı farklı istasyon ölçümleri kullanılarak elde edilen bulgular, Seyhan Havzası’nda en iyi tahminlerin LN2, P3, GEV-III ve LN3 dağılımları ile elde edildiğini göstermiştir. Seçilen anlamlılık düzeyinde üç istasyonda azalan trend bulunmuş olup, anlamlı bir trend tespit edilemeyen diğer istasyonlarda ITA testleri ile azalan bir eğilim belirlenmiştir. Elde edilen bulgular doğrultusunda, bu istasyonlarda özellikle son 10-15 yıllık süreçte ölçülen debilerin önemli miktarda azaldığı ve dolayısıyla küresel iklim değişikliği de göz önüne alındığında kuraklık riskinin olabileceği sonucuna ulaşılmıştır.