Makine Mühendisliği Bölümü Yayın Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/263

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Citation - Scopus: 0
A Study of the Structural and Mechanical Characterization of Hybrid Nanocomposite Material
(Trans Tech Publications Ltd, 2017) Mahmoud, A.K.; Demiral, Murat; Al-Nassar, S.I.; Demiral, M.; Kadhim, H.M.; Makine Mühendisliği
This work is devoted on the synthesized new hybrid nanocomposite materials by using mechanical stirring method through a combination of different types of material; epoxy based matrix and nanofiller (TiO2 nanoparticles) as a reinforcement material. In additional this paper studies the effect of TiO2 nanoparticles with percentage 2-8 wt% added to epoxy based matrix on the mechanical properties (tensile properties and hardness property). The results showed that the tensile strength of nanocomposite material increased gradually by increasing the weight percentage of TiO2 nanoparticles from 2 wt % to 8 wt % TiO2, while the best tensile strength was at 8 wt % TiO2. The maximum value of tensile strength was 270% higher than the neat epoxy matrix. The hardness increase gradually with increasing percentage of TiO2 nanoparticles from 2wt% TiO2 up to 8wt% TiO2, the maximum value of hardness was at 8wt % TiO2, so the hardness of nanocomposite is around 86% higher than the neat epoxy matrix. © 2017 Trans Tech Publications, Switzerland.
Citation - WoS: 1
Citation - Scopus: 1
Analysıs Of Heat Transfer Enhancement In Tubes Wıth Capsule Dımpled Surfaces And Al2o3-Water Nanofluıd
(Turkish Soc thermal Sciences Technology, 2022) Yapici, Ekin Ozgirgin; Türkoğlu, Haşmet; Ibrahim, Mahmoud Awni A. Haj; Turkoglu, Hasmet; 31329; Makine Mühendisliği
This study aims to numerically investigate and evaluate the enhancement of heat transfer by new capsule dimples on tube surfaces for flow of water and Al2O3-water nanofluid with different concentrations, under uniform surface heat flux. The originality of this work lies in combining two passive heat transfer enhancement methods such as geometrical improvements and nanofluids together. Capsule dimples with different depths were considered. Al2O3- water nanofluid was modeled as a single-phase flow based on the mixture properties. The effects of dimple depth and nanoparticle concentrations on Nusselt number, friction factor and performance evaluation criteria (PEC) were studied. Numerical computations were performed using ANSYS Fluent commercial software for 2000-14000 Reynolds number range. It was found that when laminar, transient and fully developed turbulent flow cases are considered, increase in the dimple depth increases the Nusselt number and friction factor for both pure water and Al2O3-water nanofluids cases. Also, the friction factor increases as dimple depth increases. Results show that increase in PEC is more pronounced in the laminar region than in the transition region, it starts to decrease for turbulent flows. For nanofluid, PEC values are considerably higher than pure water cases. The variation of PEC for capsule dimpled tubes are dependent on flow regimes and dimple depths. Increasing the nano particle volume concentration and dimple depth in laminar flows increase the PEC significantly.
Citation - WoS: 4
Citation - Scopus: 4
ANN and ANFIS Performance Prediction models for Francis type Turbines
(Turkish Soc thermal Sciences Technology, 2020) Ayli, Ece; Ulucak, Oguzhan; 265836
Turbines can be operated under partial loading conditions due to the seasonal precipitation fluctuations and due to the needed electrical demand over time. According to this partial working need, designers generate hill chart diagrams to observe the system behavior under different flow rates and head values. In order to generate a hill chart, several numerical or experimental studies have been performed at different guide vane openings and head values which are very time consuming and expensive. In this study, the efficiency prediction of Francis turbines has been performed with ANN and ANFIS methods under different operating conditions and compared with simulation results. The obtained results indicate that it is possible to obtain a hill chart using ANFIS method instead of a costly experimental or numerical tests. ANN and ANFIS parameters which effect the output, have been optimized with trying 100 different cases. 75% of the numerical data set is used for training and 25 % is used for validation as testing data. To asses and compare the performance of multiple ANN and ANFIS models several statistical indicators have been used. Insight to the performance evaluation, it is seen that ANFIS can predict the efficiency distribution with higher accuracy than the ANN model. The developed ANFIS model predicts the efficiency with 1.41% mean average percentage error and 0.999 R-2 value. To the best of the author's knowledge, this is the first study in the literature that ANN and ANFIS are used in order to predict the efficiency distribution of the turbines at different loading conditions.
Citation - WoS: 14
Citation - Scopus: 20
Cavitation in Hydraulic Turbines
(Edizioni Ets, 2019) Ayli, Ece; 265836
Hydroenergy is one of the richest and most useful renewable energy sources in the world. Hydropower is a vital source as it is the clean energy source, sustainable and last but not least it is also cost-effective. One of the most important parameters that affect the performance of the hydraulic machines is the cavitation phenomenon, which is defined as the formation of the vapor bubbles in the liquid through any hydraulic turbine. In this paper, hydraulic machines, cavitation, types of cavitation are briefly described. After theoretical studies, analytical and numerical researches about cavitation in hydraulic machinery are discussed extensively. With those studies which are summarized in this paper covers a lot of ground about cavitation on the other hand further studies are needed about cavitation in hydro turbines. Numerical methods provide sufficient predictions for cavitation. However, numerical results should be verified by experimental measurements and detection methods to decide what intensity and which shape of cavitation is hazardous and vital, where the local pressure is lower than the vapor pressure and at which static pressure cavities start to grow and collapse.
Citation - Scopus: 4
Design and Dimensional Optimization of A Novel Walking Mechanism With Firefly Algorithm
(Springer Netherlands, 2018) Selvi, Özgün; Selvi, Ö.; Yavuz, S.; Yavuz, Samet; 237938; Makine Mühendisliği
In this paper, a walking mechanism named Atlas is proposed which is a Watt-I type 6 link mechanism. First, the geometry is proposed and then kinematic analysis is done that will be used for the synthesis problem. Furthermore, constraints and an objective function are obtained from kinematic analysis. Then, these constraints are implemented to the Firefly Algorithm and dimensional parameters are obtained for a desired step profile. Finally, these dimensional parameters are tested. © Springer International Publishing AG 2018.
Citation - Scopus: 5
Design and Optimization of A Walking Over-Constrained Mechanism
(Springer Science and Business Media B.V., 2019) Selvi, Ö.; Yavuz, Samet; Ceccarelli, M.; 46949; Makine Mühendisliği
In this paper, a walking overconstrained mechanism with one DoF is presented. Firstly, its dimensional parameters and geometry are shown and a step profile which is wanted to be followed by end point of the walking mechanism is proposed. Kinematic equations of the walking mechanism are extracted to use them later as constraints for Firefly Algorithm. Algorithm is run in get the optimized dimensional parameters to provide the desired step profile. Results are presented. © 2019, Springer Nature Switzerland AG.
Citation - WoS: 0
Citation - Scopus: 0
Experimental Study and Theoretical Investigation of High Temperature Proton Exchange Membrane Fuel Cell Micro-Cogeneration Application
(Turkish Soc thermal Sciences Technology, 2018) Devrim, Yilser; Ozgirgin Yapici, Ekin; 31329
In this study, a house hold micro-cogeneration system is designed using high temperature proton exchange membrane (HTPEM) fuel cell. HTPEM type fuel cells gain the highest interest lately, due to their advantages in terms of increasing efficiency and power quality, reducing harmful emissions and flexibility of operation with respect to the other fuels. The micro-cogeneration system involves producing both electrical energy and hot water and/or vapor together in an economical way, utilizing single fuel (HTPEM fuel cells) for household applications. During the operation of the fuel cell, for high efficiency and stable power production, the access heat of the stack should be removed constantly and the temperature of the stack should be held stable. Heat recovered from the designed innovative cooling system is used for acquiring energy for heating water. This way, thermal efficiency is almost doubled compared to simple cycle. In the scope of this study, 225 W HTPEM fuel cell stack is designed and tested at 160 degrees C operation temperature with hydrogen gas and air. During operation, for homogenous distribution of temperature among the cells, for a short start up period leading to a fast required steady state temperature and for constantly removing the access heat produced in the cell, the cell stack is cooled by using a cooling fluid (Heat Transfer Oil 32- Petrol Ofisi). Selection of insulation material type and thickness for the cell stack is done using natural convection and radiation loss calculations. For the most efficient operating conditions, micro-cogeneration system water inlet and exit temperatures, water and cooling fluid flow rates, convenient pipe diameter and pump power calculations are done to finalize the design. With the cogeneration system designed during the studies, by recovering the access heat of the insulated HTPEM cell stack, district water with initial temperature of 15-20 degrees C is heated around 50 degrees C. Data gathered during studies indicate that fuel cell micro-cogeneration application is highly viable.
Citation - WoS: 1
Citation - Scopus: 1
Inverse kinematics and dynamics of an overconstrained manipulator for upper extremity rehabilitation
(Springer international Publishing Ag, 2017) Selvi, O.; Selvi, Özgün; Yilmaz, K.; 46949; Makine Mühendisliği
In this paper, an overconstrained manipulator is selected for the purpose of rehabilitation of the upper extremity. The geometry of the selected manipulator fits the exact motion of the upper extremity and acts as an exoskeleton. Inverse kinematics calculations are shown for describing the motion of actuators for a desired arm motion. Lagrange Formulation is used for the inverse dynamic model of the system. Due to the geometry of the manipulator, kinematic and dynamic calculations are applied to the two spherical subspaces of the manipulator using imaginary joints.
Citation - WoS: 0
Citation - Scopus: 0
Kinematic Analyses of Metallic Plate Perforation by Penetrators with Various Nose Geometries
(defence Scientific information Documentation Centre, 2022) Akyurek, T.; Akyürek, Turgut; Makine Mühendisliği
This study analyses kinematics of a metallic plate perforation by a penetrator with truncated ogive nose geometry to find solutions also to blunt, conical, ogive, and hemi-spherical nosed penetrators. Plugging, ductile hole enlargement, dishing, and petal forming failure modes are used in the analyses. Acceleration throughout perforation is calculated by using the related failure mode, analytical model, and the target-penetrator interaction geometry. Depending on the failure model; back lip and front lip formation during ductile hole enlargement, plug formation during plugging, and deflection of target plate during dishing is also analysed. Analyses are based on projectile???s equation of motion, momentum and energy equations, and projectile-target plate interactions. The analyses results for selected cases, with the impact velocity range 215-863 m/s, are compared with the test data. The residual velocity estimation for a strike velocity is close to the related test data with an error of 0.3-2.2 %, except for conical nosed penetrators at impact velocities approaching the ballistic limit velocity.
Citation - WoS: 0
Numerical analysis of pulsating circular impinging laminar jet on a planar disc
(Turkish Soc thermal Sciences Technology, 2017) Kahroba, Mitra; Türkoğlu, Haşmet; Turkoglu, Hasmet; 12941; Makine Mühendisliği
In this study, the flow and heat transfer characteristics of pulsating circular air jets impinging on a flat surface were numerically analyzed. The jet velocity pulsated in time. The objective of the work is to investigate the influence of the jet Reynolds number, pulsation amplitude and pulsation frequency on the rate of heat transfer from the target hot surface. For the analysis, a computer program, based on the control volume method and SIMPLE algorithm, was developed. Laminar flow with the time averaged jet Reynolds numbers between 300 and 700 were analyzed. The pulsation amplitude is ranged between 0.0V(0) (steady jet) and 0.8V(0) (m/s) (V-0 is period averaged jet velocity), and the frequency is ranged between 1 and 6 Hz. The nozzle-to-plate distance was kept constant at H/d=3. From the simulation results, it was observed that at any instant of the pulsation period, the local Nusselt number is maximum at the stagnation point, and it decreases along the plate. This decrease in the local Nusselt number is not monatomic as in the steady jet cases. It has local maximum and minimum values (fluctuations) due to the moving recirculating flow regions along the bottom plate. At low frequencies, the time (period) averaged stagnation point Nusselt numbers are lower than the corresponding steady jet Nusselt numbers. However, with the increasing frequency, the stagnation point Nusselt number increases and become higher than the steady jet Nusselt number.
Citation - WoS: 1
Citation - Scopus: 3
Redesign and Construction of a Low-Cost CaPaMan Prototype
(Springer international Publishing Ag, 2019) Arslan, O.; Arslan, Ozan; Karaahmet, S. B.; Selvi, O.; Cafolla, D.; Ceccarelli, M.; 46949; Makine Mühendisliği
In this paper a redesign solution for CaPaMan structure is presented to build a scaled low-cost prototype with market components and 3D printed parts. A CAD design is worked out to define 3D printing manufacturing for link parts and to adjust the mechanical design and its assembly after performance evaluation ensuring characteristic features of CaPaMan operation. A small-size prototype is built and tested with satisfactory functioning.

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