Browsing by Author "Fedakar, Halil Ibrahim"

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Comparative analysis of hybrid geothermal-solar systems and solar PV with battery storage: Site suitability, emissions, and economic performance
(ELSEVIER, 2024) Fedakar, Halil Ibrahim; Dinçer, Ali Ersin; Demir, Abdullah; 0000-0002-7561-5363; 0000-0002-4662-894X; 0000-0002-6392-648X; AGÜ, Mühendislik Fakültesi, İnşaat Mühendisliği Bölümü; Fedakar, Halil Ibrahim; Dinçer, Ali Ersin; Demir, Abdullah
Renewable energy integration has become a critical focus in the global effort to reduce carbon emissions and diversify energy sources. In regions with distinct geographic features, such as Türkiye, combining different renewable technologies can offer enhanced energy security. This study investigates the site suitability and economic and environmental performance of hybrid geothermal-solar systems and solar PV systems with battery storage across the provinces of Osmaniye, Hatay, and Kilis, of Türkiye. Using the fuzzy-AHP method, site suitability is evaluated, addressing a key gap in comparing these systems' adaptability to varying geographic conditions. This study is the first to directly compare these two renewable energy technologies in terms of site suitability. The findings reveal significant differences in site suitability, with solar PV systems with battery storage demonstrating broader applicability across the region. The suitable sites (20–100 % suitability) cover 1260.82 km² for solar PV systems with battery storage and only 122.18 km² for hybrid geothermal-solar systems. In terms of environmental impact, hybrid geothermal-solar systems exhibit significantly lower carbon emissions, averaging 44.6 kg CO₂/MWh, compared to 123.8 kg CO₂/MWh for solar PV systems with battery storage. Economically, hybrid geothermal-solar systems also outperform with a lower levelized cost of electricity of $0.091 kWh versus $0.254 kWh for solar PV systems. These results highlight the environmental and economic advantages of hybrid geothermal-solar systems, while also emphasizing their limited scalability to regions with geothermal activity. Conversely, solar PV systems, despite their higher emissions and costs, offer greater flexibility and potential for widespread deployment.
Deformation characteristics of medium-dense sand-clay mixtures under a principal stress rotation
(ELSEVIERRADARWEG 29, 1043 NX AMSTERDAM, NETHERLANDS, 2021) Fedakar, Halil Ibrahim; Cetin, Bora; Rutherford, Cassandra J.; AGÜ, Mühendislik Fakültesi, İnşaat Mühendisliği Bölümü; Fedakar, Halil Ibrahim
A moving wheel load induces a principal stress rotation (PSR) in pavement foundation geomaterials including subgrade/subbase soils. Simulating such a stress condition is not possible with stress path tests conducted with conventional cyclic triaxial (CT) equipment. More complex stress paths such as a heart-shaped stress path are required to determine the deformation characteristics of these under a PSR. A heart-shaped stress path can be simulated on a soil specimen in cyclic hollow cylinder (CHC) tests via user-defined waveforms for its stress components (axial stress, and torsional shear stress). In this study, a series of CT and CHC tests were performed to analyze the impact of a PSR on strain behaviors of medium-dense sand-clay mixtures. The specimens contained 0%, 5%, 10%, and 20% clay by weight and were prepared at an initial relative density of 50%. All specimens were anisotropically consolidated under K-0 approximate to 0.5. It was determined that all CT specimens underestimated the strain performances (both axial strain and shear strain) of the sand-clay mixtures. On the other hand, a heartshaped stress path was simulated successfully in CHC tests and thus, all specimens yielded more accurate strain results. At low clay content (<= 10%), the impact of a PSR on strain performances of the sand-clay mixtures was observed to be less (axial strain (epsilon(z)) < 0.12%, and shear strain (gamma(z theta)) 0.8% after number of load cycles (N) = 5000) due to the low stress ratios (CVSR = 0.15 and eta = 1/3). On the other hand, despite the low stress ratios, a PSR caused a rapid increase in axial strain and shear strain (epsilon(z) = 5%, and gamma(z theta) 0.8%) of the specimen containing 20% clay, which resulted in the failure of the specimen at N = 478. Results of this study clearly indicated that the effect of a PSR should be taken into consideration while evaluating the strain characteristics of the sand-clay mixtures that contain clay particularly at high contents (>= 20%) under traffic loads.
Developing New Empirical Formulae for the Resilient Modulus of Fine-Grained Subgrade Soils Using a Large Long-Term Pavement Performance Dataset and Artificial Neural Network Approach
(SAGE Publications Ltd, 2022) Fedakar, Halil Ibrahim; 0000-0002-7561-5363; AGÜ, Mühendislik Fakültesi, İnşaat Mühendisliği Bölümü; Fedakar, Halil Ibrahim
Artificial neural network (ANN) has been successfully used for developing prediction models for resilient modulus (Mr). However, no reliable Mr formula derived from these models has been proposed in previous studies, although engineers/ researchers need empirical formulae for hand calculation of Mr. Therefore, this study aimed to propose reliable empirical formulae for the Mr of fine-grained soils using ANN. For this purpose, thousands of ANN models were developed using the long-term pavement performance (LTPP) and external datasets. The input parameters were the percentage of soil particles passing through #200 sieve (P200), silt percentage (SP), clay percentage (CP), liquid limit (LL), plasticity index (PI), maximum dry density ([rdry]max), optimum moisture content (wopt), confining pressure (sc), and nominal maximum axial stress (sz). The ANN models were compared with several constitutive models. The results indicate that the constitutive models failed to predict the Mr, and the best Mr predictions were obtained by the ANN-C9 (P200, SP, CP, LL, PI, sc, and sz), ANN-C10 (P200, SP, CP, [rdry]max, wopt, sc, and sz), and ANN-C11 (P200, SP, CP, LL, PI, [rdry]max, wopt, sc, and sz) models. Thus, the structures of these ANN models were formulated and proposed as the new empirical formulae for the Mr of fine-grained soils. Sensitivity analysis was also performed on these ANN models. It was determined that (rdry)max is the most influential parameter in the ANN-C10 model, and LL is the most influential parameter in the ANN-C9 and ANN-C11 models. On the other hand, sc and sz are the least influential parameters.
Effect of principal stress rotation on deformation behavior of dense sand-clay mixtures
(TAYLOR & FRANCIS LTD2-4 PARK SQUARE, MILTON PARK, ABINGDON OR14 4RN, OXON, ENGLAND, 2021) Fedakar, Halil Ibrahim; Rutherford, Cassandra J.; Cetin, Bora; AGÜ, Mühendislik Fakültesi, İnşaat Mühendisliği Bölümü; Fedakar, Halil Ibrahim
This paper investigated the deformation behaviour of K-consolidated sand-clay mixtures through cyclic triaxial (CT) and hollow cylinder (CHC) tests. The sand-clay mixtures contained 0%, 5%, 10% and 20% clay by weight and were prepared at a relative density of 75%. Clay inclusion caused an increase in the permanent axial strain of mixtures (0.075% to 5% in CT and 0.186% to 5% in CHC), while a relatively insignificant increase in permanent axial strain was observed in the CT specimens containing 5% and 10% clay (0.075% to 1.299%). However, all CHC specimens with clay failed (epsilon(z) >= 5%). It was also observed that shear strain development of sand is significantly influenced by clay inclusion (0.096-2.241%) in CHC tests. Test results clearly show that the effect of a principal stress rotation should be taken into account to better estimate the deformation behaviour of sand-clay mixtures under repetitive traffic loads.
Modeling of suspended sediment concentration carried in natural streams using fuzzy genetic approach
(SPRINGER LINK, 2014) Kisi, Ozgur; Fedakar, Halil Ibrahim; 0000-0002-7561-5363; AGÜ, Mühendislik Fakültesi, İnşaat Mühendisliği Bölümü; Fedakar, Halil Ibrahim
This chapter proposes fuzzy genetic approach so as to predict suspended sediment concentration (SSC) carried in natural rivers for a given stream cross section. Fuzzy genetic models are improved by combining two methods, fuzzy logic and genetic algorithms. The accuracy of fuzzy genetic models was compared with those of the adaptive network-based fuzzy inference system, multilayer perceptrons, and sediment rating curve models. The daily streamflow and suspended sediment data belonging to two stations, Muddy Creek near Vaughn (Station No: 06088300) and Muddy Creek at Vaughn (Station No: 06088500), operated by the US Geological Survey were used as case studies. The root mean square errors and determination coefficient statistics were used for evaluating the accuracy of the models. The comparison results revealed that the fuzzy genetic approach performed better than the other models in the estimation of the SSC.
Poliüretan ile Güçlendirilmiş Balastın Hareket Eden Tekerlek Yükü Altındaki Deformasyon Davranışının Nümerik Olarak İncelenmesi
(Çukurova Üniversitesi, 2022) Fedakar, Halil Ibrahim; 0000-0002-7561-5363; AGÜ, Mühendislik Fakültesi, İnşaat Mühendisliği Bölümü; Fedakar, Halil Ibrahim
Hareket eden tekerlek yükünden dolayı balastlı demiryolu hatlarında meydana gelen düşey deformasyonlar özellikle yüksek tren hızlarında ve zayıf taban zemini koşullarında hat düzensizliklerine sebep olmaktadır. Bu durum ise hat güvenliğini ve inşaat sonrası maliyeti olumsuz etkilemektedir. Bu çalışmada farklı miktarlarda poliüretan ile güçlendirilmiş balast tabakasının (70 kg/m3, 140 kg/m3 ve 210 kg/m3), zayıf taban zemini koşulunda ve farklı tren hızlarındaki (100 km/h, 200 km/h ve 300 km/h) düşey deformasyon davranışları sayısal olarak incelenmiştir. Bu kapsamda geliştirilen iki boyutlu nümerik modellerde statik ve hareket eden tekerlek yükleri uygulanmıştır. Analiz sonuçlarına göre poliüretan kullanımı, zayıf zemine oturan balastlı demiryolu hattında meydana gelen düşey deformasyonu önemli oranda iyileştirmektedir (>%87). Öte yandan düşük hızlarda düşük poliüretan miktarları kullanılabilirken, balast agregaları arasında oluşan daha güçlü poliüretan yapıdan dolayı artan tren hızlarında yüksek poliüretan miktarları tercih edilmelidir. Ayrıca poliüretan ile güçlendirilmiş veya güçlendirilmemiş bir demiryolu hattının analizinde statik tekerlek yükünün yerine hareket eden tekerlek yükü kullanılmalıdır.