M. Sami Aköz

Experimental and theoretical analyses of two-dimensional flows upstream of broad-crested weirs

Using the particle image velocimetry (PIV) technique, the laboratory experiments are conducted to measure the velocity fields of two-dimensional turbulent free surface flows upstream of rectangular and triangular broad-crested weirs. The experimental flow cases are analyzed theoretically by a computational fluid dynamics (CFD) modeling in which the finite element method is used to solve the governing equations. In the CFD simulation, the volume of fluid (VOF) method is used to compute the free surfaces of the flows. Using the standard k–e and standard k–ω turbulence models, the numerical results for the velocity fields and flow profiles are compared with the experimental results for validation purposes. The computed results using k–ω turbulence model on compressed mesh systems are found in good agreement with measured data. The flow cases are also analyzed theoretically using the potential flow (PF) approach, and the numerical results for the velocity fields are compared with measurements.

The Effect of Cross-Shore Sediment Transport on Bar Parameters: an Experimental Study

The cross-shore sediment transport in a coastal region causes the important changes in beach morphological properties. The accurate estimation of the cross-shore sediment transport is important for the designing of the marine structures such as seawalls, jetties, breakwaters etc, and the preventing coastal erosion and accretion due to on-off shore sediment transportation. In this study, the experiments on cross- shore sediment transport carried out in a laboratory wave channel for initial beach slopes of 1/8, 1/10 and 1/15. Using the regular waves with different deep-water wave steepness generated by a pedal-type wave generator, the geometrical characteristics of beach profiles under storm conditions and the parameters affecting on-off shore sediment transport are investigated for the beach materials having medium diameters of =0.25, 0.32, 0.45, 0.62 and 0.80 mm. The experimental results obtained from this study compared with previous experimental work and found to be of the same magnitude as the experimental measurements and followed the expected basic trend.

Eşik Mansabındaki Kritik Üstü Açık Kanal Akımının Deneysel ve Sayısal Analizi

Acik kanalda esik sonrasi olusan kritik ustu acik kanal akiminin hiz alani, laboratuvar ortaminda Lazer Doppler Anemometresi (LDA) ile olculmus ve deney ile ayni kosullardaki akim icin temel denklemler, sonlu hacimler yontemine dayali ANSYS-Fluent paket programi ile uc boyutlu olarak cozulmustur. Sayisal hesaplamalarda, Reynolds Ortalamali Navier Stokes (RANS) denklemlerine dayali Realizable k-e turbulans kapatma modeli ve Large Eddy Simulasyon (LES) modeli kullanilmis, su yuzu profili Akiskan Hacimleri Yontemi ile hesaplanmistir. Sayisal modellerden elde edilen akim hizlari ve su yuzu profilleri deneysel olcumlerle karsilastirilmistir. Farkli iki modelin deneysel olarak dogrulanmasi amaciyla yapilan karsilastirmalarda, Realizable k- turbulans kapatma modelinin, hiz alaninin hesaplanmasinda ve su yuzunun belirlenmesinde LES modeline gore daha basarili oldugu gorulmustur.

Determination of Nearshore Sandbar Crest Depth Using Neural Network Approach

For the coastal structure designs, nearshore sandbars are crucial since they are affected highly from various parameters like beach slope, the height and period of the wave and the properties of the material forming the bed. In this study, it was investigated the sediment movements in nearshore by using various bar crest depths and a physical model. Erosion profile output is used for determination of the bar crest depths. Linear and non-linear regression methods are used for obtaining the non-dimensional equations with the experimental data. These equations are then compared with the ones found in the literature. Transportation of on-off shore sediments is affected by bar crest depth which has been examined with the materials forming the beach by using various diameter of the medium as d50=0.25, 0.32, 0.45, 0.62 and 0.80 mm. In order to estimate nearshore sandbar crest depth, we have developed an approach by using neural network (ANN). For proposing the efficiency of the study, ANN and multi-nonlinear regression models are compared with each other.

Experimental and Numerical Modeling of Flow over a Spillway

In this study, the experimental data for two different flow rates collected earlier from a laboratory spillway model were used for the validation of the numerical results obtained for the same conditions. The governing equations of flow interacting with the spillway model were solved with finite volume method based on ANSYS-Fluent software package. In order to obtain grid independent numerical solutions, three different concentrations of grids (coarse, medium and fine) were designed and the suitability of the fine grid was tested with Grid Convergence Index (GCI) method. Six turbulence closure models namely; Standard k- (SKE), Renormalization-Group k- (RNG), Realizable k- (RKE), Modified k- (MKW), Shear Stress Transport (SST) and Reynolds Stress Model (RSM) were used for the numerical solution of the velocity field. For the calculation of water surface profile Volume of Fluid Method (VOF) was used. The free surface profiles and velocity field obtained from the numerical simulations were compared with measured values, and the success of the chosen turbulence closure models were discussed.