2020 Cilt 25 Sayı 1

Permanent URI for this collectionhttps://hdl.handle.net/11452/12663

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Aerodynamic mechanisms on a ground-mounted solar panel at different wind directions
(Bursa Uludağ Üniversitesi, 2020-03-05) Yemenici, Onur; Mühendislik Fakültesi; Makine Mühendisliği Bölümü; 0000-0003-0011-8343
Aerodynamics mechanisms on a solar panel were studied using Computational Fluid Dynamics methodology at different wind directions. The wind velocity was chosen as 10 m/s that corresponding turbulent flow. The inclination angle of the panel was fixed as 25°, while the wind directions were varied as 180°, 135°, 45°, and 0°. Governing equations were solved by utilizing a finite volume method with a realizable k-ε turbulence model and standard wall functions. The results showed that the recirculation area occurred for the straight wind directions, but it was not observed for the oblique wind directions. The highest pressure coefficients occurred at the leading edges of the solar panel and they reduced to the trailing edge for all wind directions. The maximum drag and uplift coefficient was obtained at the wind direction of 00 and 180 0 , respectively.
Analytical investigation of curvature ductility of reinforced concrete columns
(Bursa Uludağ Üniversitesi, 2020-01-12) Foroughi, Saeid; Yüksel, S. Bahadır
In this study; the effect of axial load, longitudinal reinforcement diameter, transverse reinforcement diameter and transverse reinforcement spacing were investigated on the moment curvature relationships of reinforced concrete columns. Reinforced concrete columns having different geometries were designed considering the regulations of Turkish Building Earthquake Codes (2018). Investigations of the effect of axial load, longitudinal reinforcement diameter, transverse reinforcement diameter and transverse reinforcement spacing on the behavior of the concrete columns are the main purpose of this study. The behavior of the columns was investigated from the moment-curvature relation, by considering the nonlinear behavior of the materials taken into account. The moment-curvature relationships of the reinforced concrete column cross-sections having different axial load levels have been obtained by considering Mander model which considers the lateral confined concrete strength. The examined effects of the parameters on the column behavior were evaluated in terms of curvature ductility and the moment capacity of the cross-section. In the designed column cross-sections, different parameters effecting the moment-curvature relationships were calculated and compared. It is observed that the variation of the axial load, longitudinal reinforcement diameter, transverse reinforcement diameter and transverse reinforcement spacing have an important effect on the moment-curvature behavior of the reinforced concrete columns.
Comparison of prony and adaline methods in interharmonic estimation
(Bursa Uludağ Üniversitesi, 2020-03-30) Yalçın, Nedim Aktan; Vatansever, Fahri; Mühendislik Fakültesi; Elektrik Elektronik Mühendisliği Bölümü; 0000-0002-0049-7841; 0000-0002-3885-8622
Especially in energy and power systems, harmonic estimation has crucial role. Many techniques developed in the subject of harmonic and inter-harmonic estimation. These techniques and methods include mathematical transformation (Fourier, Hartley, Hilbert-Huang, etc.) filters (adaptive, Kalman, etc.) and parametric methods (Prony, ADALINE, MUSIC, etc.) In realized study, performance of ADALINE and Prony methods are investigated in terms of harmonic and inter-harmonic prediction capability. Required data for simulations are produced from P&O MPPT algorithm for photovoltaic systems. Therefore, this model gives opportunity to try compared methods according to different harmonic intensity (closeness of harmonics to each other). At the result of different simulations, it is observed that Prony method is more preferable for low number of data and ADALINE produces more successful results than Prony method if there is high number of data and selection of high neuron size relatively.
A comparison of several methods in tracking short-term trends associated with the precipitation time series
(Bursa Uludağ Üniversitesi, 2020-03-03) Vaheddoost, Babak
Precipitation trends can be linked to large-scale climatic events or cyclic behaviors. However, exploring these patterns in short data records can be problematic. In this study, the monthly precipitation time series recorded across the Bursa district in Turkey were addressed between January 2005 to October 2018. Stations with the minimum data loss and the longest time records in the region were selected for the analysis. Therefore, Osmangazi, Keles, Uludag, Gemlik, Iznik, Karacabey, and Mustafakemalpasa stations were selected. Linear trend (LT), moving average (MA), Mann-Kendall (MK), turn points (TP), Spearman rank-order correlation (SROC), innovative Şen (IS), innovative trend analysis (ITA), changes in distribution (CD), and standardized precipitation index (SPI) methods were used to detect short-term trends in the precipitation time series. Results indicated that the trends, reported by the previous studies could not be reproduced at a monthly scale when using LT, MK, SROC, IS, ITA, and MA. However, the trends observed by the SPI-48 were also tracked down using CD, and SPI methods. It is concluded that the detection of the short-term trends is problematic whilst the outliers deviate results of the analysis. Hence, a combination of CD, ITA, and IS methods is a key in evaluation of the short-term trends within a data run.
Corrosion behavior of annealed stainless steel mesh in different electrolytes
(Bursa Uludağ Üniversitesi, 2020-04-16) Yavuz, Abdulcabbar; Kaplan, Kaan; Aktas, Sitki
This study aimed to investigate the corrosion behaviour of annealed stainless steel mesh. Thermal oxidation treatments were applied to steel mesh in a muffle furnace at 500 °C, 700 °C and 900 °C. Surface morphology of annealed and non-annealed stainless steel meshes was compared before and after polarization. The roughness of the steel surface was increased after heat-treatment. The corrosion properties of non-annealed and annealed steel were determined using linear sweep voltammetry. The corrosion behaviour of annealed stainless steel was examined utilizing a potentiostat in a 3.5 wt.% NaCl, 1 M H2SO4 and 1 M KOH electrolytes. The corrosion susceptibility of heat-treated stainless steel was more than that of non-heat treated stainless steel in alkaline electrolyte. While pitting corrosion of non-annealed and annealed stainless steel was different, corrosion potential and current of steel mesh without heat treatment were the same as the steel meshes annealed at 500 °C and 700 °C. Corrosion current and corrosion potential of non-annealed steel were the same as 500 °C annealed steel mesh in acidic medium.
Effects of crack initialization angle on crack propagation path of thin rim gears for wind turbines
(Bursa Uludağ Üniversitesi, 2020-03-29) Doğan, Oğuz; Kalay, Onur Can; Karpat, Fatih; Mühendislik Fakültesi; Makine Mühendisliği Bölümü; 0000-0003-4203-8237; 0000-0001-8643-6910; 0000-0001-8474-7328
Nowadays, wind turbines are one of the main subjects of the designers due to the everincreasing interest in renewable energy sources. Due to dynamic loads that effect the gear system, cracks may observe on the gear teeth. These cracks may proceed along either the tooth or the rim. In similar cases, if the crack proceeds along with the tooth, crack classified as benign. If the crack proceeds along with the rim direction, the cracks can be classified as catastrophic cracks. In this study, the effects of crack initialization angle and backup ratio on the crack propagation path are investigated numerically for spur gears. The maximum stress location at the gear root is defined as the crack starting point. The initial cracks are opened with 0° - 45° - and 90° crack initialization angles. Also, five different backup ratios are used for crack propagation analysis. The analyses are performed in ANSYS Workbench, SMART Crack Growth module. The crack propagation paths are evaluated for fifteen analyses. As a result, if the rim thickness is high, the crack initialization angle has no effects on the crack paths. It has an influence on the crack propagation paths for the special rim thickness.
Friction-wear characteristics of plasma nitrided cold work tool steels
(Bursa Uludağ Üniversitesi, 2020-04-21) Yılmaz, Ahmet; Aydın, Hakan; Mühendislik Fakültesi; Makine Mühendisliği Bölümü; 0000-0001-7364-6281
D2, D6 and Calmax cold work tool steels were heat treated in vacuum hardening, made grinding and plasma nitrided in 75% N2 + 25% H2 atmosphere at 450 °C for 12 h at 2 mbar. Characterization of samples has been carried out by means of surface roughness, microstructure, microhardness and wearfriction. Wear-friction characteristics of samples have been investigated using a ball-on-disc tribosystem with a WC-Co ball. Plasma nitriding increased the surface roughness of samples. However, this effect was decreased with higher surface roughness of base metal. Fe4N (γ'), Fe3N (ε) and CrN phases were obtained on the surfaces of samples. Higher surface hardness was obtained in the plasma nitrided D2 and D6 steels. No significant mass loss was observed in the ball on-disc tribosystem. So, the wear of samples was characterized with the worn surfaces using a scanning electron microscope (SEM). Plasma nitriding improved the wear resistance and decreased the friction coefficient of steels. Plasma nitrided D2 steel showed the highest wear resistance, whereas plasma nitrided Calmax steel exhibited the lowest wear resistance. However, plasma nitrided Calmax tool steel had relatively lower friction coefficient than the other plasma nitrided steels. In general, brittle layer fractures have determined the friction coefficient.
Identification material properties by modal calibration method based on ambient vibration tests
(Bursa Uludağ Üniversitesi, 2020-02-25) Yanık, Yusuf; Türker, Temel; Yıldırım, Ömer; Dede, Tayfun
Nowadays, different structural members can be used in structures. The mechanical properties of the materials are variable. For this reason, it is very important to identify the material properties correctly. The main parameter used to define the material properties is the elasticity modulus. In this study, the elasticity modulus of structural members was determined by Model Calibration Method using dynamic characteristics obtained from Ambient Vibration Test data. The application of the proposed method was presented on a steel structure member. First of all, experimental natural frequencies were obtained by conducting Environmental Vibration Test on the selected model. A measurement system consisting of accelerometers for experimental measurements and an electronic circuit used as signal collection unit are designed. The data obtained from this measurement system were transferred to the computer environment and analyzed in the Matlab program. Using the SAP2000 package program, the theoretical natural frequencies were found by Finite Element Method. The difference between the experimental and theoretical results was reduced to the lowest as a result of repeated analysis by modifying the elasticity modulus in the Finite Element model created in SAP2000 program via software generated in Matlab. The calibrated finite element model and the elasticity modulus of the steel structural member are determined by the process.
An implementation that diagnosis anisocoria disease using image processing techniques
(Bursa Uludağ Üniversitesi, 2020-03-02) Ćorović, Nerma; Arslan, Emel
Human pupil abnormalities can be an indicator of many diseases. Anisocoria is a common condition that has been estimated at 20% of the average population. It is specified by inequality in the size of the pupils of the eyes. This paper proposes an anisocoria determining algorithm from a digital image by using the MATLAB computing environment that involves the usage of MATLAB Computer Vision and Image Processing Toolbox. The image used in this work as input data is an image that has been fetched from Siblings Image Database. An input image where anisocoria is present has been downloaded from the Internet. The paper gives an idea of understanding how pupil detection and measurement can be used in medical and psychology diagnostics by using a simple algorithm.
Investigation of concrete filled composite plate shear walls using finite element methods
(Bursa Uludağ Üniversitesi, 2020-01-09) Polat, Erkan
Concrete filled composite plate shear wall is an innovative structural lateral force resisting system that is being investigated experimentally and numerically. It consists of pre-fabricated steel web plates that are spaced parallel to each other by having regularly spaced cross-connecting tie bars (rods) which is then filled with concrete. This paper make use of previously developed numerical models and extends the study to investigate different aspects of wall behavior. In this study, two of the previously tested wall models were used to investigate percentage of steel plate yielding at certain wall elevations per certain drift levels, steel plate von-Mises stress contours, the distribution of cracks in concrete, relative contribution of steel plates and concrete to total wall base shear and axial stress distribution of steel plate and concrete. The study assumes fixed-based walls and describes the development of finite element models using LS-Dyna.
Investigation of the effect of fusible interlining on stiffness and drapability of woollen fabrics
(Bursa Uludağ Üniversitesi, 2020-03-10) Gürarda, Ayça; Mühendislik Fakültesi; Tekstil Mühendisliği Bölümü; 0000-0002-7317-8163
Woollen fabric most popular tailored clothing material because of the fabric excellent and natural properties. In woollen garments, upper back, sleeve holes, collars, lapels, patch and welt pockets, and sleeve cuffs are the areas to apply interlining for more rigid appearance. Interlining is a layer fabric sticked on the fabrics of the garment to give form and to improve stiffness of garment. In this study, the effect of fusible interlining on stiffness and drapability of woollen woven fabrics with different structural properties were investigated. For this purpose, eight woollen woven fabric samples having different structural properties were obtained. Same kind of fusible interlining applied all of these fabric samples. Therefore, woollen fabric samples without fusible interlining and with fusible interlining were obtained. The results showed that the fabric weigth, cover factor and weave structure of woollen woven fabrics effect fabric stiffness and drapability. All woollen fabrics with fusible interlining had significantly higher stiffness and drape coefficient values than woollen fabrics without fusible interlining.
A modified firefly algorithm-based feature selection method and artificial immune system for intrusion detection
(Bursa Uludağ Üniversitesi, 2020-03-27) Günay, Melike; Orman, Zeynep
Intrusion detection systems generally produce high dimensional data in network-based computer systems. It is required to analyze this data effectively and create a successful model by selecting the important features to save only the meaningful data and protect the system against suspicious behaviors and attacks that can occur in a system. Firefly Algorithm (FFA) is one of the most promising meta-heuristic methods which can be used to select important features from big data. In this paper, a modified Firefly Algorithm-based feature selection method is proposed. The traditional Firefly Algorithm is improved by using the K-Nearest Neighborhood (K-NN) classifier and an additional feature selection step. The proposed method is tested on 4 different datasets of various types of attacks. Three different sub-feature sets are obtained for each dataset and the classification performances are compared. Artificial Immune System (AIS) method is also implemented to generate artificial data for the datasets that have an insufficient number of data. This study shows that the proposed Firefly Algorithm performs successfully to decrease the dimension of data by selecting the features according to the obtained accuracy rates of the K-NN method. Memory usage is dramatically decreased over 50% by reducing the dimension with the proposed FFA. The obtained results indicate that this method both saves time and memory usage.
Prioritizing a new set of environmental management system activities with fuzzy TOPSIS method
(Bursa Uludağ Üniversitesi, 2020-03-06) Polat, Ulviye; Gürtuna, Filiz
Environmental Management System (EMS) studies conducted today are activities where enterprises plan, implement, control and monitor measures related to their activities that can impact the environment, and systematically and sustainably carry out activities aimed at preserving the environment. Given the limited resources of enterprises such as workforce, money, time, machinery and equipment, it is important for enterprises to prioritize their activities so that EMS’s work effectively. In this study, a list of environmental activities was primarily established with the aim of determining the EMS activities to be undertaken by enterprises or evaluating existing environmental activities. An approach for determining prioritized activities was developed from the created activity list according to the evaluation criteria appropriate to the operating conditions of enterprises.
Seismic performance assessment of prefabricated industrial buildings with semi-rigid connections
(Bursa Uludağ Üniversitesi, 2020-03-28) Alemdar, Zeynep Fırat
In this study, the performances of 120 precast factory buildings consisting of five different types in an industrial area in Istanbul, Turkey are examined before and after the applications of retrofit methods through nonlinear time history analyses. The factory buildings were constructed and became operational before the 1999 Kocaeli earthquake. Following the earthquake, they were operationally safe, however, after the evaluation according to the 1998 Turkish Earthquake Code (TEC), most of the connections were found to be inadequate. The buildings were retrofitted by using bolted steel plates in the connection regions and diagonal steel braces in 2005. A detailed finite element model of the connection was developed before and after the retrofit methods and the behavior of the region was implemented in the three-dimensional models of the structures. The buildings were analyzed according to the Turkish Earthquake Code 2007. The number of damaged beams by the TEC-2007 was higher than the rate of damaged beams per the FEMA-356. In three-dimensional performance analysis of buildings, the importance of examination of connection regions and implementing the results to the full building model were emphasized. The performance of the building were increased by reducing the distance between the plane frames in the longitudinal direction and the beam length in the transverse direction.
Statistical analysis on the effect of the solidification rate and quenching mediums on mechanical properties in ETİAL 221 alloy
(Bursa Uludağ Üniversitesi, 2020-01-13) Uludağ, Muhammet; Gemi, Lokman; Dıspınar, Derya
In this study, the effects of different mold types and quenching mediums with different internal stresses on the mechanical properties of ETIAL 221 alloy supplied as a primer were investigated, and analyzed statistically. Firstly, the alloy was poured into the permanent mold (PM) then poured into sand mold with grain size 40/45 and 60/65 AFS. The specimens were subjected to three different T6 heat treatment quenching mediums that are water at room temperature (WRT), oil (OL) and boiling water (BW). The influences of differences in solidification rate due to cooling rates and differences in internal stress due to quenching mediums on mechanical properties were investigated. Additionally, the change in porosity was calculated according to Archimedes principle and obtained results were related to the mechanical properties. The results showed that permanent mold and boiling water quenching medium presented the best mechanical properties for the current study.
Wireless sensor deployment on 3-D surface of moon to maximize coverage by using a hybrid memetic algorithm
(Bursa Uludağ Üniversitesi, 2020-03-06) Ozkan, Omer
The moon has always been a goal for humanity in history to reach and discover. Since the 1950s, many missions have been carried out in order to achieve this goal. Wireless sensor networks can be a good tool for discovering some of the features of the moon and acquiring very important information for the missions to the moon and beyond to be performed soon. The deployed seismic, monitoring, light, temperature, pressure, etc. types of sensors on the surface of the Moon can collect vital data for the missions. Therefore, in this paper, the wireless sensor deployment problem on the surface of the Moon is studied to maximize coverage. Since the deployment of sensors on 3-D terrain is an NP-hard problem, a hybrid memetic algorithm is developed to solve. The real 3-D digital elevation model of the surface of the Moon for two different terrains near the South Pole is used to test the performance of the proposed algorithm with 64 scenarios and the results are compared with local search and simulated annealing algorithms. According to the results, the proposed hybrid memetic algorithm has better coverage values than the others in acceptable CPU times.

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