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Öğe A CFD Study On the Hydrodynamic Characteristics of the Antifouling Paints(Galenos Publ House, 2019) Karabulut, Utku Cem; Ozdemir, Yavuz Hakan; Barlas, BarisThis paper presents a computational fluid dynamics (CFD) approach which can be used to investigate the hydrodynamic performances of various antifouling paints. Steady Reynolds - Averaged - Navier - Stokes (RANS) equations were solved for the flows around a flat plate at Reynolds number of 2,8x10(6) and 5,5x10(6). The surface roughness effects were modelled as downward shift of the velocity profile at the log - law region of the boundary layer. Granville's similarity law was used to extrapolate the results for a full scale ship. Results are in good agreement with the previous experimental and numerical studies.Öğe FREE SURFACE FLOW SIMULATION AROUND AN APPENDED SHIP HULL(Univ Zagreb Fac Mechanical Engineering & Naval Architecture, 2018) Ozdemir, Yavuz Hakan; Barlas, BarisThis study brings forward the results of previously published work of free surface flow simulation around a fast ship model. Experimental measurements and numerical simulations of a fast bare-hull ship model form are now extended to the same ship form with appendices for a wide range of Froude numbers. The governing equations are discretized by means of an unstructured finite volume mesh. The standard k-epsilon turbulence model and Volume of Fluid Method to capture the two phase media are used. The total resistance, due to wave and wake fields of the ship model with appendages and the resistance of the appendages alone are calculated numerically, and compared with the experiments. The experiments and computations were performed for 11 different Froude numbers between 0.103 and 0.322. For Froude numbers up to 0.25, numerical simulations found to be quite in agreement with the experiments. It has been found that appendages increase the total drag mainly by increasing the pressure resistance, and the effect of the appendages becomes more important as the flow speed gets higher.Öğe Investigation of a cross-flow turbine under natural conditions(Springer India, 2022) Kaya, Alaattin Metin; Ozdemir, Yavuz Hakan; Yigit, Kadri SuleymanIn this study, the computational and experimental examination of the hydraulic cross-flow turbine (CFT) is presented. The experimental studies are conducted at the turbine laboratory of Gebze Technical University. The commercial Computational Fluid Dynamics (CFD) software, Star CCM+, is employed to calculate three-dimensional, incompressible, steady Reynolds-Averaged Navier-Stokes (RANS) equations for the flow inside the CFT. In the numerical model, the rotational motion of the blades is modeled by means of the moving reference frame approach. The correlation between the turbulent viscosity and the velocities is acquired using the standard k-e turbulence model. The computational results are obtained in terms of the torque, power, and efficiency of the turbine. The outcome of this research reveals that the CFD software used in this study can reliably be used to predict experiments since the numerical model can accurately estimate the experimental values of the torque, power, and efficiency of the CFT.Öğe Numerical Investigation of the Effect of Surface Roughness on the Viscous Resistance Components of Surface Ships(Springernature, 2022) Karabulut, Utku Cem; Ozdemir, Yavuz Hakan; Barlas, BarisRecently, computational fluid dynamics (CFD) approaches have been effectively used by researchers to calculate the resistance characteristics of ships that have rough outer surfaces. These approaches are mainly based on modifying wall functions using experimentally pre-determined roughness functions. Although several recent studies have shown that CFD can be an effective tool to calculate resistance components of ships for different roughness conditions, most of these studies were performed using the same ship geometry (KRISO Container Ship). Thus, the effect of ship geometry on the resistance characteristics of rough hull surfaces is worth investigating. In this study, viscous resistance components of four different ships are calculated for different roughness conditions. First, flat plate simulations are performed using a previous experimental study for comparison purposes. Then, the viscous resistance components of three-dimensional hulls are calculated. All simulations are performed using two different turbulence models to investigate the effect of the turbulence model on the results. An examination of the distributions of the local skin friction coefficients of the DTMB 5415 and Series 60 showed that the plumpness of the bow form has a significant effect on the increase in frictional resistance with increasing roughness. Another significant finding of the study is that viscous pressure resistance is directly affected by the surface roughness. For all geometries, viscous pressure resistances showed a significant increase for highly rough surfaces.Öğe Numerical Study on the Hydrodynamic Performance of Antifouling Paints(Springernature, 2020) Karabulut, Utku Cem; Ozdemir, Yavuz Hakan; Barlas, BarisThis study presents a simple numerical method that can be used to evaluate the hydrodynamic performances of antifouling paints. Steady Reynolds-averaged Navier-Stokes equations were solved through a finite volume technique, whereas roughness was modeled with experimentally determined roughness functions. First, the methodology was validated with previous experimental studies with a flat plate. Second, flow around the Kriso Container Ship was examined. Lastly, full-scale results were predicted using Granville's similarity law. Results indicated that roughness has a similar effect on the viscous pressure resistance and frictional resistance around a Reynolds number of 10(7). Moreover, the increase in frictional resistance due to roughness was calculated to be approximately 3%-5% at the ship scale depending on the paint.Öğe Occupational Diseases and Shipyards in Turkey(Karabük Üniversitesi, 2020) Barlas, Barış; Şenol, Serhat; Ozdemir, Yavuz HakanIn this study, the current level of occupational health and safety awareness for occupational diseases in Turkey is investigated as a compilation article. The diagnosis of occupational diseases has great importance in terms of treatment methods and progressive outcomes. Making risk analysis for occupational diseases within the framework of legal obligations will be a guiding role in reviewing the deficiencies in this field throughout the world and in Turkey. The importance and necessity of periodic health examinations can be better understood with the establishment of awareness for responsibility and prevention of occupational diseases. Scores of casualties in Turkish shipyards are due to occupational accidents and diseases. Due to inadequate awareness and imprudent approaches based on a lack of foresight in occupational diseases, there can be undesirable resultsÖğe Parameter estimation using the extended Kalman filter applied to the roll decay experiment(Taylor & Francis Ltd, 2025) Ozdemir, Yavuz HakanIn this study, an inverse technique using the augmented extended Kalman filter (EKF) is discussed. Parameter estimation in damped roll motion was conducted by Ozdemir [2023]. Estimation of ship roll damping and natural frequency using an extended Kalman filter applied to URANS output. Sadhana. 48(3):168; 2024. Nonlinear roll damping coefficients and natural frequency estimation via augmented extended Kalman filtering for floating body. Ships Offsh Struct. 19(12):2076-2087] using the EKF. In these studies, roll decay response measurements obtained from CFD simulations and mathematically simulated pseudo experimental data were used to estimate the unknown time dependent damping coefficient and natural frequency of a floating body. In the present study, the EKF method is employed to actual model experiment results. The suggested method is applied to the model test results of the well-known benchmark DTMB 5415 hull form, as obtained from the literature.Öğe Türbülans Modeli Seçiminin Zemin Etkisindeki 3B Bir Kanatın Sayısal Modellemesine Olan Etkisi(Osman SAĞDIÇ, 2022) Ozdemir, Yavuz Hakan; Çoşgun, TanerBu çalışma, farklı RANS türbülans modellerinin Zemin etkisinde çalışan 3B simetrik bir kare kanatın sayısal modellemesindeki etkisini incelemektedir. Katı bir Zemin yakınında hareket etme, ya da bilinen ismiyle yer etkisi, bir kanatın aerodinamik karakteristiğini öenmli oranda etkiler. Bu makalede amaç, farklı eddy viskozitesi türbülans modellerinin yer etkisi esnasındaki aerodinamik davranışı modelleme yönünden performansının araştırılmasıdır. Üç farklı türbülans modeli, realizable , SST and Spalart-Allmaras modelleri incelemeye dahil edilmiştir. Türbülans modellerinin etkinlikleri farklı hücum açıları ve kanat yükseklikleri için deneysel verilerle karşılaştırmalı olarak test edilmiştir. Sonuçlar göstermektedir ki, türbülans modellerinin yer etkisi aerodinamiği hesaplamaları konusundaki başarısı irtifa ve hücum açısı ile doğrudan ilişkilidir. Türbülans modeli seçimi kanat yere çok yakın hareket edşyorken ve hücum açısı düşük ya da negatifken önemli hale gelmektedir. Elde edilen sonuçların birbirlerinden farklılığı temel olarak kanat alt yüzeyindeki basınç dağılımından kaynaklanmaktadır. Yüksek hücum açıları ve irtifalarda farklı türbülans modelleri ile elde edilen tahminler arası fark ihmal edilebilir düzeyde kalmaktadır
