Yazar "Durhasan, Tahir" seçeneğine göre listele
Listeleniyor 1 - 20 / 25
Sayfa Başına Sonuç
Sıralama seçenekleri
Öğe A unified and experimentally validated design framework for long-endurance solar UAVS using model-based multi-objective multidisciplinary optimization(Springer, 2025) Khaneghaei, Mohammad; Asadi, Davood; Ebrahimi, Benyamin; Hazeri, Majid; Farsadi, Touraj; Nabavi Chashmi, Yaser; Durhasan, TahirDesigning long-endurance, solar-powered unmanned aerial vehicles (UAVs) requires careful coordination across aerodynamic, structural, and energy subsystems, particularly when targeting flexible, high-aspect-ratio configurations. This paper presents a mission-driven design and optimization framework for solar-powered long-endurance UAVs, tailored to post-disaster urban surveillance scenarios. A modular, multidisciplinary approach is adopted to account for the coupled effects of structural deformation and solar energy availability, both of which critically affect flight endurance. A key feature of the framework is the simultaneous integration of aeroelastic constraints and a time-dependent solar power and battery model, capturing realistic energy generation and storage behavior over diurnal cycles. This energy model is experimentally validated using a custom-built testbed and incorporated directly into the design loop. The framework is implemented using a Multidisciplinary Design Optimization (MDO) architecture that employs a coupling strategy to effectively manage interdependencies among subsystems. A comprehensive sensitivity analysis using Latin Hypercube Sampling highlights key performance-driving parameters. The final UAV design is fabricated and flight-tested, demonstrating the satisfaction of mission-level requirements derived from a simulated post-earthquake damage assessment in Adana, T & uuml;rkiye. Battery state-of-charge, trajectory, and attitude data collected during flight tests demonstrate that the UAV operates in accordance with design predictions, despite environmental variability. The study highlights how the integration of validated subsystem models within an established optimization process can lead to reliable, application-specific solar UAV designs suitable for real-world deployment.Öğe Aerodynamic coefficient prediction of bio-inspired camber morphing wings with flexible surfaces using an explainable transformer(Elsevier France-Editions Scientifiques Medicales Elsevier, 2026) Mowla, Md Najmul; Durhasan, Tahir; Asadi, Davood; Kesilmi, Zehan; Jafari, Javad RashidBio-inspired morphing wings with flexible surfaces can enhance aerodynamic efficiency at low Reynolds numbers (Re), yet predicting their fluid-structure interaction remains challenging. We present PhysAero-MHANet, a physics-aware, interpretable deep learning framework coupled with controlled wind tunnel experiments for aerodynamic prediction of camber-morphing finite wings. The campaign yielded 911 samples spanning Re is an element of [3 x 10(4), 1 x 10(5)], camber deflections up to 10(degrees), and angles of attack from-18(degrees )to 18(degrees). Experiments showed up to 34% drag reduction at small angles of attack, a stall delay of approximate to 6(degrees), a maximum lift coefficient C-L,C-max approximate to 1.44, and a peak lift-to-drag ratio C-L/C-D approximate to 8.84. The proposed model is a transformer-based multi-task surrogate with physics-informed attention, hierarchical cross-feature fusion, and shapley additive explanations (SHAP) for interpretability. Against 11 machine-learning, deep-learning, and attention baselines, PhysAero-MHANet achieved R-2 approximate to 0.985 and MAPE < 12% across lift (C-L), drag (C-D), and rolling moment (C-M,C-R) predictions. These results provide new insight into morphing-wing aerodynamics and support real-time control, performance optimization, and integration into unmanned aerial vehicles (UAVs) and micro aerial vehicles (MAVs).Öğe An experimental investigation of the flow control of a circular cylinder in near wake with parallel plates at Re=7500(Elsevier Science Inc, 2024) Durhasan, Tahir; Ekinci, Firat; Firat, Erhan; Akilli, HuseyinThe vortex street suppression in the near wake region of the cylinder with parallel plates was investigated using particle image velocimetry (PIV) at Reynolds number of Re = 7500. The rigid plates are designed as flat, parallel with the free-stream direction, and located on both sides of the cylinder. Two different plate lengths (0.5D and 1D based on the cylinder diameter, D) were examined at gap ratios of g/D = 0.1, 0.3, 0.5, 0.7, and 0.9, respectively. Proper Orthogonal Decomposition (POD) analyses were also employed to reveal vortex mechanism in the near wake region. The gap ratio significantly influences the interaction of the vortices. At low gap ratios, the plates directly affect the development of shear layers on both side of the cylinder. The shear layers elongate downstream with a reduction of the vortex shedding frequency. Moreover, Reynolds shear stress, vortex shed-ding instabilities and vortex street are suppressed in the near wake region with the help of using parallel plates. On the other hand, vortex shedding reinforces instabilities at higher gap ratios. Besides, the most effective gap ratio is different for each the plate lengths to suppress instabilities.Öğe Analysis of attack angle effect on flow characteristics around torpedo-like geometry placed near the free-surface via CFD(2021) Kılavuz, Alpaslan; Ozgoren, Muammer; Durhasan, Tahir; Sahın, Besir; Kavurmacıoglu, Levent Ali; Akıllı, Huseyin; Sarıgıguzel, FuadIn this study, the flow characteristics of torpedo-like geometry placed near the free-surface at various angles of attack were investigated numerically. The study was carried out at the Reynolds number of Re=4x104 between immersion ratios of 0.75?h/D?3.5 and angles of attack ?=0°,4°, 8°, and 12°. Large Eddy Simulation (LES) turbulence model was used along with the Volume of Fluid (VOF) multiphase model to investigate the effects of free-surface. Wake region had an asymmetrical structure near the free-surface as a result of the interaction. A jet-like flow region was observed between the geometry and the free-surface at lower immersion ratios due to the restriction of the flow area. This flow region had a downward movement towards the lowerpressure wake region. The drag coefficient, CD, values were increased with the decrease of immersion ratio. At angles of attack ?=8° and 12°, the flow separation occurring near the nose caused an additional restriction in the flow area and directed the jet-like flow toward free-surface. Variation of Froude numbers (Fr) depending on the immersion ratio is examined, and it is found that Fr number and corresponding drag coefficient have higher values for the lower immersion ratio. The free-surface effect was found negligible at h/D?2.5 for all cases.Öğe Dye visualization over double delta wing with various kink angles(Springer, 2019) Durhasan, Tahir; Karasu, IlyasIn this study, the aim is to exhibit vortical behaviors of flow on double delta wings having 70 degrees strake sweep angle and kink angles of 150 degrees, 160 degrees and 165 degrees using dye visualization technique in a water channel. Experiments were performed at Reynolds numbers based on the chord length Re=10,000 and 25,000 for angle of attack in the range 5 degrees to 35 degrees. The visualizations were performed for both end-view and cross-flow planes. The results revealed that the kink angle has a significant role on the interaction of vortices and the strake vortex breakdown locations. The interaction between the strake vortex and the wing vortex is dominant on the flow behaviors at alpha <= 10 degrees. The flow behavior is affected by the kink angle. Two interaction mechanisms which are spiral and enveloping are observed. The spiral interaction alternates to enveloping interaction with increasing Reynolds number. Moreover, the trajectory of the strake vortex core moves outboard with increasing Reynolds number at alpha=10 degrees. For alpha >= 15 degrees, Reynolds number is less effective on the strake vortex breakdown location and also the vortex breakdown locations move the apex gradually with increasing angle of attack. Wake-alike flow structure takes place after occurrence of the vortex breakdown since vortex core splits into disorganized small-scale vortices. On the other hand, development of the wing vortex is more complex than the strake vortex since it collapses near the vicinity of the junction.Öğe Experimental study on passive flow control of circular cylinder via perforated splitter plate(Techno-Press, 2021) Sahin, Serdar; Durhasan, Tahir; Pinar, Engin; Akilli, HuseyinPresent experimental investigation aims to reduce the shedding of vortex in the near wake region of a circular cylinder using a perforated splitter plate. Perforated plates were placed in the wake region of the cylinder and aligned with the streamwise direction. The length of the plates was equal to the diameter of the cylinder. Different plate porosities and locations were examined and obtained results were compared to the baseline cylinder. Flow measurements downstream of the cylinder were performed in a water channel by employing a particle image velocimetry technique (PIV) at a Reynolds number of Re=5×103. It is observed that the effect of the porosity on the flow characteristics of the cylinder depends on the location of the plate. The strength of shear layers and flow fluctuations in the near wake region of the cylinder are considerably diminished by the perforated splitter plate. It is found that the porosity of ?=0.3 is the most effective control element for gap ratio of G/D=0.5. On the other hand, proper gap ratio is determined as G/D=2 for porosity of ?=0.7. It is concluded in the present study that the perforated splitter plate could be used as alternative passive flow control technique in order to reduce vortex shedding of the cylinder. Copyright © 2021 Techno-Press, Ltd.Öğe Flow Characteristics over Double Delta Wings at Low Reynolds Numbers(Asce-Amer Soc Civil Engineers, 2020) Karasu, Ilyas; Durhasan, TahirWithin the scope of this study, a quantitative investigation was carried out employing the particle image velocimetry (PIV) technique to determine vortical flow characteristics of 70 degrees/40 degrees, 70 degrees/50 degrees, and 70 degrees/55 degrees double delta wings (DDWs). Experiments were performed in four chordwise sections (x/c=0.5, 0.6, 0.8, and 1) at two Reynolds numbers (R=1x104 and 2.5x104) and different angles of attack (alpha=5 degrees, 10 degrees, 15 degrees, and 25 degrees). It was observed that the secondary vortex is dominant on flow characteristics of double delta wings at low Reynolds numbers. The strengths of vortices increase with increases of both the wing sweep angle and Reynolds number. Furthermore, the location of wing vortex breakdown moves farther downstream as the wing sweep angle increased. Depending on the angle of attack, Reynolds number, and the wing sweep angle, either dual (strake and wing) or triple (strake, wing, and secondary) leading-edge vortices were observed. At a Reynolds number value R=1x104 and angles of attack in the range of alpha <= 15 degrees, the interactions of the vortices influence the flow structure significantly. Dominant frequencies of the vortices are detected near the shear layer formed between the strake vortex and secondary vortex, generally. Moreover, the spectral analyses indicated that bursting of the vortices causes complicated flow patterns over double delta wings, including small-scale vortices. It was found that the transverse Reynolds normal stress concentrates at chordwise sections where secondary vortices are dominant, whereas the locations of peak magnitude of vertical Reynolds normal stress coincide with the strake vortex cores.Öğe FLOW CONTROL OF A CIRCULAR CYLINDER BY PERMEABLE SPLITTER PLATE WITH DIFFERENT POROSITIES AND ANGLE VALUES(Turkish Soc Thermal Sciences Technology, 2024) Sahin, Serdar; Durhasan, Tahir; Pinar, Engin; Akilli, HuseyinFlow control of bluff bodies has been studied extensively to eliminate adverse effects of wake flow such as vibration and acoustic noise or resonance. The circular cylinder has been studied as the bluff body since it is basic geometry and has been used in engineering applications such as heat exchanger tubes, power transmission lines, chimney stacks, bridges, radio telescopes, power lines, offshore drilling rigs etc. In this study, a permeable splitter plate was located at various downstream locations to control the wake flow of the cylinder. All experiments were carried out in a large-scale closed-loop water channel in the Fluid Mechanics Laboratory at Cukurova University. PIV was used to measure the instantaneous velocity vector field in the wake region of the cylinder at Reynolds number Re=5000, which is based on the cylinder diameter, D. Four different splitter plate angle values (0 =0 degrees; 15 degrees; 30 degrees; 45 degrees), three different porosity values (epsilon=0.30; 0.50; 0.70) were investigated. The porosity (epsilon) of the separator plates is defined as the ratio of the total hole area to the plate surface area. All lengths are nondimensionalized by dividing by the cylinder diameter and shown with the * index. The splitter plate length kept to constant during the experiment as ls*=1. The distance between the leading edge of the splitter plate and the cylinder (lg*) is variable due to the rotation of the separator plate at certain angles in the flow direction. To overcome this, the distance between the splitter plate rotation axis and the cylinder was taken as a parameter and shown with the **. The gap between splitter plate midpoint and cylinder (lg**) kept to constant during the experiments as lg**=1.5. When the plates are rotated, the cross-section parallel to the flow decreases, which increases the interaction between the boundary layers. Since the permeable separator plates prevent the interaction of the boundary layers formed in the flow around the cylinder, the effect of the permeable separator plates increases in the downstream regions where the interaction of the boundary layers increases. Thus, the fluctuations are reduced, and a more stabilized trail flow occurs downstream of the cylinder. It was observed that the vortex formation was delayed with the increase of the separator plate angle. In this study, the effect of the separator plate angle and the effect of the plate permeability were clearly observed.Öğe Flow control of diamond-shaped cylinders with slots at Re=150(AIP Publishing, 2025) Durhasan, Tahir; Onel, Huseyin C.; Ekinci, Firat; Aksoy, Muhammed MuratThis study presents a comprehensive numerical investigation of passive flow control around diamond cylinders with horizontal and vertical slots at a Reynolds number (Re) of 150. Using a numerical framework, it is systematically analyzed the effects of slot orientation (horizontal and vertical) and width ratio (s/D ranging from 0.05 to 0.30) on the wake dynamics. Results demonstrate that the slot orientation fundamentally determines the flow control mechanism. Horizontal slots progressively extend the vortex formation length and weaken vortex shedding intensity, ultimately achieving complete suppression of periodic shedding at s/D = 0.30, reducing drag by 37%, and eliminating fluctuating forces. In contrast, vertical slots maintain the fundamental wake structure while attenuating vortex strength, achieving a superior 50% drag reduction at s/D = 0.30 without suppressing periodicity. Pressure distribution analysis reveals that horizontal slots primarily modify base pressure through direct wake interaction, while vertical slots enhance pressure recovery without significantly altering separation characteristics. Proper orthogonal decomposition results confirm that the distinct physical mechanisms of horizontal slots redistribution of the energy between coherent modes before stabilizing the wake, while vertical slots preserve the modal structure while systematically reducing fluctuation energy. Time-averaged streamline topology reveals formation of additional focal structures in horizontal configurations, contrasting with persistent sub-wake patterns in vertical arrangements. These findings elucidate the underlying physics of passive flow control and provide crucial design guidelines for engineering applications requiring either maximum drag reduction (vertical slots) or elimination of flow fluctuations (horizontal slots) in diamond-shaped cylinders at low Reynolds numbers.Öğe Flow topology downstream of the hollow square cylinder with slots(Pergamon-Elsevier Science Ltd, 2020) Durhasan, TahirFlow patterns downstream of the hollow square cylinder with slots are experimentally investigated to show effect of the slot ratio on the wake flow characteristics and turbulence statistics at Reynolds number of Re = 6000 using the particle image velocimetry (PIV) technique. Proper orthogonal decomposition (POD) analyses indicate that the self-issuing jet dramatically changes the mechanism of vortex shedding interaction. Penetration of the self-issuing jet into the wake region leads to increasing of the vortex formation length for low slot ratios. On the other hand, the self-issuing jet penetrates further downstream due to increasing momentum coefficient of the jet and splits the wake region in half for high slot ratios. Strouhal number increases with the increasing slot ratio and it attains approximately the twofold of the solid cylinder case, since the self-issuing jet accelerates the vortex shedding process. However, turbulence statistics are significantly reduced for all slot ratios. Distributions of the spectral density in the wake region of the cylinder indicate that the vortex shedding instability could be reduced considerably by the slotted cylinder. Drag coefficient, which is estimated from PIV data, reduces up to 42% in comparison with the solid cylinder model.Öğe Forecasting near-surface air temperature via SARIMA and LSTM: A regional time-series study(Pergamon-Elsevier Science Ltd, 2025) Aksoy, Muhammed M.; Mowla, Najmul; Bilgili, Mehmet; Pinar, Engin; Durhasan, Tahir; Asadi, DavoodAccurate modeling of near-surface air temperature (AT) trends is critical for assessing global and regional climate risks, particularly in light of the intensifying warming signals observed across the northern hemisphere and the tropics. This study proposes a robust and computationally efficient framework for forecasting near-surface AT across the global, the northern hemisphere, the southern hemisphere, and the tropics using two complementary time-series modeling techniques: seasonal autoregressive integrated moving average (SARIMA) and long short-term memory (LSTM) networks. The models are trained to capture both structured seasonal patterns and nonlinear temporal dynamics by leveraging the ERA5 reanalysis dataset (1970-2024) and incorporating preprocessing steps such as detrending and Z-score normalization. SARIMA consistently outperformed LSTM across most domains, particularly in the global region, achieving lower RMSE (0.0967 degrees C) and higher correlation (R = 0.9975), reflecting its superior capacity for linear and seasonal signal extraction. Quantitatively, SARIMA demonstrates 5%-10% lower RMSE and slightly higher correlation than LSTM across all domains, underscoring the statistical significance of its performance advantage. Projected near-surface AT anomalies by 2050 reveal a marked warming trend, with the SARIMA model estimating a global anomaly of +1.078 degrees C and a northern hemisphere anomaly of +1.474 degrees C, closely aligning with IPCC-reported trajectories and exceeding CMIP5 RCP4.5 projections. The findings underscore SARIMA's reliability for short-to mid-term near-surface AT forecasting and LSTM's potential for future hybrid modeling schemes. This work fills a critical methodological gap by integrating statistical rigor with scalable deep learning, offering enhanced fidelity for regional climate adaptation planning.Öğe Future forecast of global mean surface temperature using machine learning and conventional time series methods(Springer Wien, 2025) Durhasan, Tahir; Pinar, Engin; Uluocak, Ihsan; Bilgili, MehmetOne of the most important indicators of climate change and, consequently, global warming is the rise in the average surface temperature of the entire world. As observed in this light, forecasting the global mean surface temperature is an essential issue that must be addressed to develop adaptation measures for climate change. Many models have been developed to forecast the temperature of the air; however, these models often concentrate on local areas or use a restricted amount of station data. In this study, seasonal autoregressive integrated moving average (SARIMA), long-short-term memory (LSTM), and gated recurrent unit (GRU) models are used to predict global mean surface temperature (GMST) data. The data sets used in the study are GISTEMP and HardCRUT datasets and consist of land surface air temperature and water surface temperature. An evaluation of the performance of the models is carried out using various error measures to guarantee a high level of prediction accuracy. All models' results indicate that the yearly GMST value increase relative to 1961-1990 will be between 0.94 oC and 1.45 oC in 2050. In addition, the yearly GMST value, measured as approximately 14.8-15.00 oC in 2022, will be between 15.15 oC and 15.43 oC in 2050, according to the obtained models.Öğe Global monthly sea surface temperature forecasting using the SARIMA, LSTM, and GRU models(Springer Heidelberg, 2025) Bilgili, Mehmet; Pinar, Engin; Durhasan, TahirGlobal warming has become one of the world's most pressing problems in recent years, accompanied by rising sea surface temperature (SST). The SST time series data are an essential component in balancing the energy at the planet's surface. It is of the utmost importance to forecast future SSTs to assist us in better comprehending the climate dynamics and identifying catastrophic circumstances in advance based on historical observations received from earth observation systems. In this sense, monitoring and forecasting SST has become vital for better understanding future climate trends. In this regard, this study proposes a gated recurrent units (GRUs) model, a long short-term memory (LSTM) neural network technique, and a seasonal auto-regressive integrated moving average (SARIMA) statistical model to predict global monthly SST data. According to the findings from the testing procedure, the MAPE values were 0.1377% for the SARIMA model, 0.1374% for the LSTM model, and 0.1390% for the GRU model. All models were found to have MAE, RMSE, and R values within the ranges of 0.0250-0.0253 oC, 0.032-0.0323 oC, and 0.9772-0.9775, respectively. The results of the proposed SARIMA, LSTM, and GRU models showed that they could accurately and satisfactorily predict the global monthly SST time series.Öğe Hydropower-Assisted Alkaline Electrolysis with NiCo-Modified Electrodes Produced by Additive Manufacturing for Enhanced Hydrogen Evolution Reaction(Springer Heidelberg, 2025) Ekinci, Firat; Durhasan, Tahir; Mert, Mehmet Erman; Dogru Mert, Basak; Esenboga, BurakIn this study, micro hydropower assisted alkaline electrolysis system was investigated to meet small-scale energy needs in rural areas. One of the noteworthy aspects of the study is the modification of metal electrodes produced by additive manufacturing with high HER activity metals such as Ni and Co. Additive manufacturing offers benefits in terms of creating complex geometries, reducing material waste, and enabling rapid prototyping. The NiCo modification created through the galvanostatic method provides advantages in enhancing the electrochemical activity and stability of the electrodes, particularly regarding HER activity. The electrochemical activity of the hydrogen evolution reaction (HER) in 1 M KOH was investigated using linear sweep voltammetry, cyclic voltammetry and bulk electrolysis. Surface characterization was achieved through scanning electron microscopy, energy-dispersive X-ray analysis and X-Ray diffraction analysis. The water wettability characteristics of electrode surfaces were examined using contact angle measurements. The 3Dm NiCo electrode demonstrated higher catalytic performance, with a contact angle of 61 degrees compared to 92 degrees for 3Db, indicating improved wettability. XRD investigation revealed NiCo crystalline phases. At 3 V, compared to the unmodified 3Db electrode, the 3Dm NiCo electrode demonstrated a similar to 64% increase in hydrogen production (46.8 mL vs. 28.5 mL), confirming its enhanced HER performance. Long-term catalyst stability was determined over 180,000 s.Öğe Kavisli Delikli Plaka ile Girdap Kaynaklı Türbülanslı Akışın Kontrolü(2020) Özkan, Göktürk Memduh; Durhasan, Tahir; Fidancı, Pınar EnginBu çalışmada, dairesel bir silindir art izinde oluşan girdap kaynaklı türbülanslı akışın, farklı ve kısmi geçirgenlik oranlarına sahip kavisli delikli plaka (kontrol elemanı) ile kontrolü incelenmiştir. Ele alınan parametre aralıklarında PIV ile hız ölçümleri yapılmış, akış alanında Reynolds kayma gerilmeleri hesaplanmış ve kontrol durumu ile yalın silindir durumunun kontur dağılımları nicel olarak karşılaştırılmıştır. Elde edilen sonuçlara göre, ele alınan Reynolds sayılarının akış kontrolüne benzer oranda etki ettiği anlaşılmıştır. Bununla birlikte, incelenen tüm geçirgenlik oranları ve yay açıları için silindir art izinde oluşan kayma gerilmelerinin azaldığı görülmüştür. 120o? ? ?180o yay açılarında ve ?=0,5 ve ? =0,6 geçirgenlik oranlarında, yalın silindire kıyasla maksimum Reynolds kayma gerilmelerinin %96’ya kadar düştüğü ve silindir art izindeki daimi olmayan akışın tamamen kontrol edildiği ortaya çıkarılmıştır.Öğe Long-term projections of global, northern hemisphere, and arctic sea ice concentration using statistical and deep learning approaches(Pergamon-Elsevier Science Ltd, 2025) Bilgili, Mehmet; Pinar, Engin; Mowla, Md. Najmul; Durhasan, Tahir; Aksoy, Muhammed M.The accelerating decline in sea ice concentration (SIC) poses significant challenges for global climate regulation, maritime navigation, and arctic ecosystem stability. This study develops and evaluates two advanced time-series forecasting models, seasonal autoregressive integrated moving average (SARIMA) and long short-term memory (LSTM) networks, to project SIC trends through 2050 across three spatial domains: the globe, the northern hemisphere, and the arctic. Utilizing the ERA5 reanalysis dataset (1970-2024) from the European center for medium-range weather forecasts (ECMWF), the models capture seasonal cycles and complex temporal dependencies to enable robust long-term projections. Comparative analysis demonstrates that SARIMA effectively models periodic fluctuations, while LSTM excels at learning nonlinear dependencies inherent in SIC dynamics. Performance metrics, including mean absolute percentage error (MAPE), root mean square error (RMSE), and correlation coefficient (R), confirm the high accuracy of both models, with SARIMA showing superior capability in representing structured seasonal patterns. Projections indicate a persistent decline in SIC, with arctic concentrations decreasing from 55.60% in 2023 to approximately 46.84% by 2050, underscoring the pronounced effects of arctic amplification. These results provide valuable insights for climate modeling, arctic policy formulation, and the development of adaptive navigation strategies in a rapidly changing polar environment.Öğe Multimodal deep learning for estimating mean precipitable water vapor(Wiley, 2026) Mowla, Md. Najmul; Aksoy, Muhammed M.; Pinar, Engin; Bilgili, Mehmet; Durhasan, TahirPrecipitable water vapor (PWV) is a crucial atmospheric variable that influences weather systems, climate variability, and hydrological processes. Accurate PWV estimation is essential for improving numerical weather prediction, climate modeling, and remote-sensing applications. However, existing methods often rely on extensive meteorological inputs or computationally intensive architectures, limiting their applicability in data-sparse regions. This study introduces a novel hybrid framework, EMMA-NN-BiGRU-XGBoost, designed to forecast monthly mean PWV across Turkey using only four physically meaningful inputs: latitude, longitude, altitude, and seasonal indicators. The framework integrates an enhanced multimodal attention (EMMA) mechanism that disentangles spatial, altitudinal, and seasonal influences, improving interpretability and physical consistency. Bidirectional gated recurrent units (BiGRU) capture temporal dependencies, and XGBoost models nonlinear feature interactions within a weighted stacking ensemble. Hyperparameters are optimized via particle swarm optimization and Bayesian optimization, with particle swarm optimization demonstrating superior tuning efficiency. Extensive benchmarking against traditional machine-learning models, using grid search and random search with fivefold cross-validation, as well as deep-learning baselines, demonstrates significant improvements in predictive accuracy, achieving an root-mean-square error of and an of 0.92, representing a 15%-20% reduction in error compared with state-of-the-art methods. The model also exhibits robustness across diverse climatic zones in Turkey. Shapley additive explanations further elucidate feature importance, aligning model outputs with climatological principles. Beyond methodological advances, this work provides a scalable, interpretable, and data-efficient baseline for PWV forecasting, thereby facilitating enhanced climate diagnostics, hydrological risk assessments, and early warning systems, particularly in regions with limited meteorological observations.Öğe Numerical Investigation of Flow Structure around NACA 0018 with slot(2023) Asan, Omer Fethi; Guler, Emre; Aksoy, Muhammed Murat; Pınar, Engin; Durhasan, TahirWe numerically investigated NACA 0018 airfoil with slot at various angles of attack. The computational fluid dynamics (CFD) results were compared with the base airfoil to show the effectiveness of the airfoil. Reynolds number was kept constant as Re=3x105 to thoroughly understand how different locations of slot would provide passive flow control from aerodynamic perspective. We have used three different slot locations to reveal the effectiveness of the slot compared to the base airfoil for higher angles of attack. Our results show that the slotted design would yield to increase the lift and to delay the stall angle of base airfoil.Öğe Passive Flow Control around NACA 0018 Airfoil Using Riblet at Low Reynolds Number(2021) Güler, Emre; Durhasan, Tahir; Karasu, İlyas; Akbıyık, HürremIn this study, aerodynamic capabilities of NACA 0018 airfoil is numerically investigatedby installing riblet on the suction side of airfoil. Numerical results were obtained by ANSYS Fluentusing k-kl-kw transition model at Reynolds number of Re=100 000. Three different riblet airfoilconfiguration was performed at six different angles of attack (?=8°, 10°, 13°, 15°, 17° and 19°) andthese results compared with the clean model. For M1 model the riblet was located at chord wise sectionof x/c=0.3 while it installed at x/c=0.7 for M2 model. For M3 model two riblets were used and theywere located at both x/c=0.3 and x/c=0.7. Obtained numerical result show that the use of ribletremarkably affects the flow characteristics of airfoil. At ?=8° the CL/CD value of M1 model is increasedby 4.5% when compared to clean model. It is indicated that angle of attack at ?=10o , lift coefficient isincreased for all models with compared to clean model. Stall angle is delayed from ?=13° to ?=15° atM1 and M3 with compared to clean model and lift coefficient is increased about 37% because of therestriction of the laminar separation bubble and trailing edge separation.Öğe POD Analysis of Flow around Torpedo-Like Geometry with a Hemispherical Nose(2023) Kenan, Ömer; Yanıktepe, Bülent; Sekeroglu, Ertugrul; Ozgoren, Muammer; Akbudak, Ezgi; Durhasan, Tahir; Kılavuz, AlpaslanThere has been an increased interest in underwater vehicles for a wide range of applications over the past decade. In the current study, flow characteristics around a common, torpedo-like geometry with a Myring profile were investigated at a length-based Reynolds number of Re=20000 using the Particle Image Velocimetry (PIV). As a result of PIV and Proper Orthogonal Decomposition (POD) analyzes in this study; instantaneous streamline topology ?, instantaneous vorticity ?L?U_? contours, instantaneous streamwise velocity component u?U_? graphs, cross-streamwise velocity component v?U_? graphs, instantaneous vorticity ?L?U_? graphs, perpendicular to the flow direction, instantaneous vortex graphs and time-averaged TKE graphs were evaluated and compared. At the same time, as a result of PIV analysis, time-average streamline topology <?> and Time-averaged vorticity <?L?U_? > contours values are given. When the flow characteristics were compared by using the obtained POD method of the PIV results, it was determined that although the POD data were generally quite similar to the PIV results, the POD analysis results had a more uniform flow structure and vortex turbulence was lessened.
