Makine Mühendisliği Bölümü Yayın Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/263
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Article Citation - WoS: 1Numerical Analysis of Pulsating Circular Impinging Laminar Jet on a Planar Disc(Turkish Soc thermal Sciences Technology, 2017) Kahroba, Mitra; Türkoğlu, Haşmet; Turkoglu, Hasmet; Makine MühendisliğiIn 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.Conference Object Neck Protection in Autonomous Car Crashes(Kauno Technologijos Universitetas, 2020) Yavuz, Samet; Yavuz, S.; Himmetoglu, S.; Makine MühendisliğiAutonomous cars which are expected to be on the market in the upcoming years, present new challenges to restraint system design since unconventional seating plans can put the occupants at more risk. For instance, an occupant sitting on a rear facing seat can experience higher risk of whiplash in a frontal impact considering the fact that statistically frontal impacts do happen at higher severities than rear impacts as seen in the crash test conditions of US NCAP. In this study, an improvement to car seat design is presented in which the seatback is automatically rotated into a more upright position prior to impact in order to increase the energy absorbing potential of the seatback. The study involves computer simulation of a seat-occupant system to demonstrate the benefits of the proposed system. © 2020 Kaunas University of Technology. All rights reserved.Article Citation - WoS: 2Citation - Scopus: 2Analysis of Heat Transfer Enhancement in Tubes With Capsule Dimpled Surfaces and Al2o3-Water Nanofluid(Turkish Soc thermal Sciences Technology, 2022) Ibrahim, Mahmoud Awni A. Haj; Turkoglu, Hasmet; Yapici, Ekin Ozgirgin; Haj Ibrahim, Mahmoud Awni A.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.Conference Object Citation - Scopus: 5Design and Optimization of a Walking Over-Constrained Mechanism(Springer Science and Business Media B.V., 2019) Ceccarelli, M.; Selvi, Ö.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.Conference Object Citation - Scopus: 4Design and Dimensional Optimization of a Novel Walking Mechanism With Firefly Algorithm(Springer Netherlands, 2018) Selvi, Ö.; Yavuz, S.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.Conference Object A Study of the Structural and Mechanical Characterization of Hybrid Nanocomposite Material(Trans Tech Publications Ltd, 2017) Al-Nassar, S.I.; Demiral, M.; Kadhim, H.M.; Mahmoud, A.K.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.Conference Object Citation - WoS: 1Citation - Scopus: 3Redesign and Construction of a Low-Cost Capaman Prototype(Springer international Publishing Ag, 2019) Karaahmet, S. B.; Selvi, O.; Cafolla, D.; Ceccarelli, M.; Arslan, O.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.Conference Object Citation - WoS: 1Citation - Scopus: 1Inverse Kinematics and Dynamics of an Overconstrained Manipulator for Upper Extremity Rehabilitation(Springer international Publishing Ag, 2017) Yilmaz, K.; Selvi, O.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.Article Citation - WoS: 16Citation - Scopus: 22Cavitation in Hydraulic Turbines(Edizioni Ets, 2019) Ayli, EceHydroenergy 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.