Çavdar, Bora; Karaca, Eda; Okumuş, Hatice; Nuroğlu, Fatih Mehmet

Nowadays, the rapid increase in PV plants in power systems has reached a point that may negatively impact power system stability. Battery storage systems have also begun to be integrated into power systems to mitigate the negative effects of non-rotating plants such as PV plants. The expected increase in PV penetration levels and BESS size must be analyzed jointly to address stability issues in power systems. It is evident that existing reviews on the hybrid integration of PV and BESS are limited. This paper aims to contribute to future developments by reviewing the most recent status and potential outcomes of studies related to the impact of PV plants and battery storage system (BESS) units on power system stability. The reviewed studies have been classified to provide valuable insights into the impact of PV plants and BESS units on power system stability. Each classification focuses on the studies in terms of the stability analysis type, the PV/BESS unit combination, the analysis method, the structure of the power system, the PV penetration level, the size of the BESS, whether frequency support is provided, and the use of simulation programs. In the classification of stability, frequency stability and rotor angle (for transients) stability are the most discussed topics. In the review for the units, it was found that studies on the stability of PV power plants were frequently addressed. In addition, studies on BESS and PV-BESS configurations have increased over time. Almost all stability studies focus on time-domain analysis. In addition, modal analysis, which is widely used in small-signal stability studies, is the second most frequently used analysis method in studies. In the studies, the effect of a three-phase short circuit fault on the stability of the system is usually analyzed. Apart from this fault, the implementation of a fault in the load is among the popular cases considered. In the power system classification used, either large or small power systems are usually considered. It is rare for an impact to be considered in both a small and a large power system. Different penetration levels and sizes of PV and BESS units, respectively, are usually analyzed separately in terms of stability. The number of papers investigating the effect of both PV and BESS together on the stability of a power system is quite rare. As a result of the classification on frequency support, it is seen that research on frequency support of PV power plants is handled from similar perspectives, although it has gained popularity recently. When the simulation programs used, which represent the last classification group, are examined, it is observed that DigSilent PowerFactory and MATLAB are generally preferred.

Mola, Erhan; Bayrak, Osman Ünsal; Baş, Fatih İrfan; Bayata, Halim Ferit

In this study, the hybrid usage of Kevlar and steel fiber in concrete pavements was investigated. For this purpose, the concrete was designed using the water/binder ratio (0.40, 0.45, 0.50), silica fume (instead of cement 0, 5, 10%), Kevlar fiber (0 gr/m3, 500 gr/m3, 1000 gr/m3) and steel fiber (0 gr/m3, 500 gr/m3, 1000 gr/m3). Taguchi method was used as the experimental design, and optimum levels of parameters were determined for 28-days compressive strength, flexural strength, and toughness. According to the experiments and observations, the positive effect of Kevlar fiber upon energy absorption capacity (toughness), compressive and flexural strength of concrete was determined. Using only Kevlar fiber increasing up to 5.1% in compressive strength and up to 14.5% in flexural strength were observed. Considering the obtained results, Kevlar was noticed as a possible recycling material to be introduced into the economy by adding concrete.

Erışır, Tülay; Eren, Kemal

Spinors play a fundamental role in geometry and physics. The Clifford algebra is the natural linear algebraic setting where spinors and spin groups are formulated. In this study, spinors, which have many uses in Clifford algebras, have been given with a different representation in E3. Firstly, the directional q -frame has been considered, and this frame is represented with a spinor in spinor space. Later, considering the relations between the directional q -frame and Frenet frame, the relations between spinors corresponding to these frames have been obtained. In this way, a different construction of the spinors by using in Clifford algebras has been shown.

Erdoğdu, Şakir; Nayir, Safa; Kandil, Ufuk; Kurbetci, Şirin; Nas, Memduh

Determination of the compressive strength of concrete in existing reinforced concrete structures is important, particularly in some cases. Destructive and non-destructive test methods are used to determine the compressive strength in such structures. Amongst these, coring is the most widely used method as a destructive method in determining the compressive strength in existing reinforced concrete structures. However, even though numerous studies have been carried out on the variation of the determined compressive strength depending on the coring direction, the discussions continue. In this study, concrete blocks containing fly ash (FA) and silica fume (SF) and aggregates of different maximum sizes were produced. In the mixtures, cement was replaced by fly ash at ratios of 20%, 40%, and 60% and silica fume at ratios of 5%, 10%, and 15%, respectively. Two aggregates with the maximum aggregate sizes of 16 mm and 31.5 mm were used in the production of the concrete blocks. The concrete blocks were kept in a laboratory by covering them with burlaps moistened intermittently for 28 days and then cores of 10 cm diameter were taken and cut to have 20 cm height then capped and tested to determine compressive strength. Core drilling was carried out parallel and perpendicular to the casting direction and then the compressive strengths were determined. Cubes of 15 cm were also prepared and tested to determine the compressive strength level of concrete and to make comparisons accordingly. The compressive strength of mineral-added core samples taken parallel to the casting direction is higher than those of taken perpendicular to the casting direction, in all mixtures. The ANOVA test applied on the results obtained, it was found that the maximum aggregate size (Dmax) and the core drilling direction with respect to casting direction is statistically significant in terms of the compressive strength of concrete produced using fly ash and silica fume at certain substitution ratios.

Keleş Güner, Eda; Özer, Abdulkadir

In this study, silica xerogels were synthesized by the sol gel method using TEOS (tetraethyl orthosilicate), ethanol, water and sulfuric acid as acidic catalyst and ammonia as basic catalyst. The structural characterizations of the synthesized acid-catalyzed silica xerogels (ACXs) and base-catalyzed silica xerogels (BCXs) were investigated by thermal gravimetric analysis (TGA), scanning electron microscopy (SEM) and N2 adsorption and desorption techniques. It was seen from TGA analyzes that the thermal decomposition process of silica xerogels consists of two steps. The SEM images show that the solid skeletal phase of ACXs has a globular morphology with primary particles that are joined together to form agglomerates. In contrast, SEM images of the BCXs indicate a hierarchical morphology with the clusters of these agglomerates organized into larger spherical particles. The pore size distributions (PSD) of ACXs and BCXs samples show a main peak in the micropore and micro-mesopore regions, respectively.

Akoğuz, Harun; Çelik, Semet; Bariş, Özlem

Several soil improvement techniques are successfully implemented today. Studies are increasingly becoming popular on microbially induced calcite precipitation (MICP) as an environment-friendly and sustainable method that is an alternative to other soil improvement techniques. Our study examined the effects of different sources of calcium on an improvement that was carried out on a sand soil with a 35% relative density by using the MICP method. The results were analyzed by using unconfined compression, permeability, calcite formation percentage, pH, SEM (scanning electron microscopy) and XRD (x-ray diffraction) experiments. As a result of the unconfined compression test, the strength values were obtained as 2406 kPa in the specimens where calcium chloride was used as a calcium source, 2435 kPa in the specimens where calcium nitrate was used and 64 kPa in the specimens where calcium acetate was used. The permeability experiment revealed a decrease in permeability of 80.8% for calcium chloride, 23% for calcium nitrate and 90.4% for calcium acetate. According to the results of the SEM analyses, the structures that formed in all specimens bound the grains to each other and coated the surfaces of the grains. In the XRD analyses, calcite formation was observed in the specimens where calcium chloride and calcium nitrate were used as the source, while, in contrast, vaterite formations were also observed in the specimens where calcium acetate was used as the source. It was determined that different sources of calcium had different effects on improvement of sand soils by microbially induced calcite precipitation (MICP).

Terzi̇Oğlu, Zeynep Özge; Kankal, Murat; Yüksek, Ömer; Nemlı, Murat Özer; Akçay, Fatma

Hydrological and meteorological studies indicate that hydrological processes and water resources are significantly affected by the climate change, particularly with increasing greenhouse gases and temperature. In this study, the trend analyses of the biggest precipitation intensity values in Trabzon, the most populous province of the Eastern Black Sea Basin in Turkey, have been carried out by using Mann-Kendall and Şen's Innovative Trend methods. In line with this purpose; the precipitation intensity data of standard time series from 5 minutes to 24 hours for two meteorological stations in Trabzon (Trabzon and Akçaabat) were used. Before carrying out trend analyses, the Run (Swed Eisenhart) Homogeneity Test was applied to all data and non-homogeneous data were not analysed. Before applying the Mann-Kendall Method, the internal dependency of the data was examined. When the analysis results are reviewed; in Trabzon Meteorology Station an increasing trend for intensities of all-time series has been detected, whereas in the Akçaabat Meteorology Station, a general result of the trend could not be obtained as most the data related to different time series were not homogeneous data.