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Akpinar A.,Gumushane University | Komurcu M.T.,Karadeniz Technical University
Applied Energy | Year: 2013

In this study, the existence and variability of wave energy resource potential of the Black Sea based on 15-year hindcast data is described in detail. The hindcasts of wave parameters were carried out by using the third generation wave prediction model (Simulated WAves Nearshore - SWAN), which is one of the most popular numerical wave models and has been widely used for estimating ocean waves. The model was forced with the ECMWF ERA Interim wind fields and applied with a spatial resolution of about 0.0167°. ×. 0.0167° and a model time step of 6. h to resolve efficiently offshore and nearshore wave conditions. The results were presented in the form of charts of the spatial distribution of significant wave height and wave power, on a monthly, seasonal and annual basis. Annual energy was calculated in the study region with the hindcast data set covering 15. years (1995-2009). The areas with the highest wave energy resource were determined and the south west coasts of the Black Sea are suggested as the best site for the installation of a wave farm. It was determined the western parts of the Black Sea (especially the south-west) are exposed to energetic waves more than the eastern parts. © 2012 Elsevier Ltd.

Cavdar A.,Gumushane University
Composites Part B: Engineering | Year: 2012

The flexural strength and ductility properties of cementitious composites (mortar) under high temperature may be significantly improved by incorporating different types of fibers. In this study, four different types of fibers are added to cement mortars with the aim to investigate their mechanical contributions to mortars under high temperature, comparatively. Polypropylene (PP), carbon (CF), glass (GF) and polyvinyl alcohol (PVA) fibers are chosen for research. These fibers are added into mortars in five different ratios (0.0%, 0.5%, 1.0%, 1.50% and 2.0%) by volume. The mortars are subjected to the following temperatures: 21°C (normal conditions), 100°C (oven dry), 450°C and 650°C. The mechanical properties investigated are flexural strength, deflection and compressive strength of the cement mortars. In addition, thin sections of mortars are investigated to obtain changes in mortar because of high temperature. It is concluded that all fiber types contribute to the flexural strengths of mortars under high temperature. However, this contribution decreases with an increase in temperature. The samples with PVA show the best flexural performance (75-150%) under high temperature. CF which does not melt under high temperature also gives high flexural strength (11-85%). The compressive strengths of the mortars reduce under high temperature or with fiber addition. The highest increase in flexural strength and the lowest decrease in compressive strength is at 0.5-1.5% for CF if all temperature conditions are taken into consideration. The optimum fiber addition ratios of the samples containing PP and GF are 0.5% by volume. And for PVA, it is between 0.5% and 1.5% by volume. © 2011 Elsevier Ltd. All rights reserved.

In this study, mechanical properties of double-strap joints with aluminum or composite patches of different orientation angles at their overlap area were investigated under tensile loading. For this purpose, AA2024-T3 aluminum was used as adherend, while patches were either AA2024-T3 aluminum or 16-ply laminate of carbon/epoxy composite with five different orientation angles ([0]16, [90]16, [0/90]8, [45/-45]8, [0/45/-45/90]4). A two-part paste adhesive (DP 460) was used to bond adherend and patches. Six different types of joint samples were subjected to tensile loading. The effect of patch material on failure load and stress distribution was examined experimentally and numerically. As a result, it was concluded that the data obtained from 3-D finite element analysis were coherent with experimental results and additional to that fiber orientation angles of the patches markedly affected the failure load of joints, failure mode and stress distributions appeared in adhesive and composite. © 2013 Elsevier Ltd.

Polymeric fibers are cheap and popular materials used in the concrete industry, and they may improve the mechanical properties of cementitious composites under high temperature. In this study, three different types of polymeric fibers - Copolymer Polypropylene/polyethylene (CPP), Homopolymer Polypropylene (HPP), and Aramid (AR) - are added to cement mortars with the aim to investigate their mechanical contributions to mortars under high temperature, comparatively. These fibers are added into mortars in five different ratios (0.0%, 0.3%, 0.6%, 0.9% and 1.2%) by volume. The mortars are subjected to following temperatures: 21 °C (normal conditions), 100 °C (oven dry), 450 °C, 650 °C and 850 °C. It is concluded that polymeric fibers used in this study contribute to the flexural strength of mortars under normal dry conditions (100 °C). This effect continues clearly up to 450 °C and polymeric fibers show effects on flexural strength especially at 450 °C. Each fiber shows the best performance different addition ratio when flexural and compressive strength are taken into consideration at the same time under high temperature. The highest increase in flexural strength and the lowest decrease in compressive strength are at 0.3-0.9% fiber addition ratio for HPP, at 0.3-0.6% fiber addition ratio for CPP and at 0.9% fiber addition ratio for AR for every temperature. © 2012 Elsevier Ltd. All rights reserved.

High-K volcanics were produced in two different Late Cretaceous cycles during the infilling of back-arc basins of the eastern Pontides. The first cycle, represented by shoshonitic trachyandesites and associated pyroclastics, containing high K2O (2.74-4.81 wt-%) and NaK2O (3.60-5.51 wt-%), overlies a mid-Cretaceous ophiolitic-olistostromal melange formed during the rifting stage of a back-arc basin (Neotethys). 40Ar39Ar dating of biotite from trachyandesite at the base of the first cyle indicates that shoshonitic volcanism in the far south of the eastern Pontides started in the early Campanian. Volcanic rocks of this cycle are overlain by upper Campanian-Maastrichtian rudist-bearing reefal limestones. The second cycle of high-K volcanism is represented by analcime-bearing volcanic rocks erupted in a Neotethyan lagoonal environment. These volcanic rocks, intercalated with continental detritus, are characterized by high a2O (3.22-7.16 wt-%), now concentrated in secondary analcime crystals. Their K2O contents also range between 0.83 and 6.05 (wt-%). All of these units are disconformably overlain by Eocene turbidites with a basal conglomerate. Volcanic rocks belonging to both cycles show various enrichment degrees in LILE, HFSE, LREE, and HREE with respect to primitive mantle and chondrite [(La/Lu) cn=11.10-25.89]. Negative Nb, Ta, Zr, Hf, and Ti anomalies are typical of these subduction-related arc magmas. Geochemical similarities between the two volcanic cycles suggest that trachyandesites and analcime-bearing volcanics were derived from similar enriched mantle sources, and that they formed in the same geotectonic setting of a back-arc basin environment of the eastern Pontide magmatic arc during the Late Cretaceous. In addition, Nd-Sr and Pb isotope ratios of the investigated volcanic units indicate that their mantle melt sources were similar. The new geological, geochemical and isotopic data suggest that southward subduction of the Palaeotethyan oceanic crust can be separated into two main stages for the late Mesozoic Pontide orogenic belt. Early southward subduction ended by slab break-off during the mid-Cretaceous, resulting in upwelling and injection of asthenospheric mantle that caused the opening of the eastern Pontide back-arc basin (Neotethys). Resumption of southward subduction began with intense TH-CA bimodal volcanism in the northern front of the arc during the Turonian-Coniacian. The intensity of this Late Cretaceous magmatism in the north decreased towards the south, and a transition to monogenic calcalkaline-alkaline (CA-A) Campanian andesitic volcanism developed in the southern zone. Yet farther south, andesitic igneous activity graded into the Campanian-Maastrichtian shoshonitic and ultrapotassic volcanism in the Bayburt-Maden, Tokat, Amasya, and Gümüshaciköy areas. This zoning of the Late Cretaceous arc magmatism (TH-CA, CA-A and shoshonitic-ultrapotassic, from north to south) also supports the concept of southward subduction during late Mesozoic evolution of the eastern Mediterranean region.

Sezer I.,Gumushane University
Energy Education Science and Technology Part A: Energy Science and Research | Year: 2011

In this study, the use of dimethyl ether (DME) and diethyl ether (DEE) in diesel engines as alternative fuels investigated. A commercial suction (naturally-aspirated) direct injection (SDI) automobile diesel engine was chosen for investigation. Thermodynamic and performance analysis has been performed via a thermodynamic diesel engine cycle model. Thermodynamic and performance parameters computed and compared for diesel, DME and DEE fuels at two different situations. Results showed that DME and DEE presented the lower cylinder temperature and pressure, so a lower engine performance than diesel fuel for equal injection conditions. Brake power decreases about 32.1% and 19.4% at 4200 rpm while brake specific fuel consumption increases about 47.1% and 24.7% at 2200 rpm for DME and DEE, respectively. However, engine performance of DME and DEE extensively improves for the equal equivalence ratio condition, although more amount of fuel injection about 64 percent for DME and 32 percent for DEE is essential. The increments obtained by DME and DEE are about 13.6% and 6% in brake power at 4200 rpm compared to diesel. Brake specific fuel consumption is still higher about 43.5% for DME and 23.6% for DEE than diesel. Brake thermal efficiency of DME and DEE is generally better than diesel fuel. © Sila Science.

Akpinar A.,Gumushane University
Renewable Energy | Year: 2013

In this article, an attempt is made to better understand the contribution of hydropower in meeting electric energy needs of Turkey. Thus, a comparison between Turkey and other countries, which have some similarities with Turkey or which are more developed nations compared to Turkey, for evaluating from different aspects the contribution of hydropower in meeting electric energy needs is performed. The producers of electricity and hydroelectricity in the world, and the electric sectors of all the selected countries are firstly examined. Thereafter, Turkey's water resources and its potential, hydropower potential, and current status of hydropower in Turkey are investigated in detail. A detailed discussion regarding economic and energy indicators, hydroelectricity versus thermal electricity, the contributions of hydroelectricity to the total and renewable electricity generation, and the usage status of hydro potential of each selected nation is also made. Finally, it is found that hydropower is the second largest contributor in meeting Turkey's electric energy needs after thermal, mainly natural gas. It is also estimated that the contribution of hydropower will continue because a vast amount of its economically feasible hydro potential (about 64%) is undeveloped. Besides, it is determined that the contribution of hydropower in the total electricity generation in Turkey is greater than that of China and India, but it is lower than that of Norway, Brazil, and Canada. © 2012 Elsevier Ltd.

This study aims to determine and evaluate wind energy potentiality along coastal locations at the North Eastern of Turkey. For this purpose, the present study has statistically analysed wind power potentials and wind characteristics from six meteorological stations (Sinop, Samsun, Ordu, Giresun, Trabzon, and Hopa) along the North Eastern (NE) geo-political coastal region of Turkey using the hourly or 3-hourly wind speed data measured at 10 m height during 9 years. The diurnal, monthly, and seasonal mean wind speed and wind power density at all the stations are assessed to have remarkable variations. The annual and seasonal frequency distributions and dominant wind directions of the all locations are determined. It is observed that the monthly mean wind speed in this region ranges from 1.53 m/s to 4.06 m/s. The maximum annual mean wind power density was found to be 59.96 W/m2 at Sinop while the maximum annual mean wind energy density was obtained to be 525.25 kWh/m2/year at the same station. It is further shown that Sinop, Hopa, and Trabzon have the higher wind power potential than other locations and their potential are close to each other. © 2012 Elsevier Ltd.

Cavdar A.,Gumushane University
Composites Part B: Engineering | Year: 2014

Fibers are used for improving some properties of conventional concrete (which is a brittle material) such as tensile strength, abrasion resistance, absorption and crack control. This study investigates the usability of fibers against the harmful effects of freeze-thaw cycles on cement mortars. For this objective, five different types of fibers, i.e., Polypropylene (PP), Carbon (CF), Aramid (AR), Glass (GF) and Poly vinyl alcohol (PVA) in four different ratios (0.0%, 0.4%, 0.8% and 1.2%) were added to cement mortars along with an amount of air agent. These samples were then subjected to five different freeze-thaw cycles (0, 25, 50, 75 and 100). Thus, mechanical behaviors were investigated under freeze-thaw effects. The most important results of the study are summarized; the fibers increase flexural strength and deflection ability of the samples while decreasing compressive strength, dynamic modulus of elasticity and specific mass. The highest flexural strength was obtained with a 1.2% addition of CF fiber for the samples in normal conditions. The mechanical properties of the samples subjected to repetitive freeze-thaw cycles were also investigated; the best flexural strength was provided with 1.2% CF addition, while the highest dynamic modulus of elasticity was obtained with a 1.2% PP addition. © 2013 Elsevier Ltd. All rights reserved.

A three-dimensional backfill-structure-soil/foundation interaction phenomenon is simulated using the finite element method in order to analyze the dynamic behavior of cantilever retaining wall subjected to different ground motions. Effects of both earthquake frequency content and soil-structure interaction are evaluated by using five different seismic motions and six different soil types. The study mainly consists of three parts. In the first part, following a brief review of the problem, the finite element model with viscous boundary is proposed under fixed-base condition. In the second part, analytical formulations are presented by using modal analysis technique to provide the finite element model verification, and reasonable agreement is found between numerical and analytical results. Finally, the method is extended to further investigate parametrically the effects of not only earthquake frequency content but also soil/foundation interaction, and nonlinear time history analyzes are carried out. By means of changing the soil properties, some comparisons are made on lateral displacements and stress responses under different ground motions. It is concluded that the dynamic response of the cantilever wall is highly sensitive to frequency characteristics of the earthquake record and soil-structure interaction. © 2012 Elsevier Ltd.

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