Mechanical Engineering / Makina Mühendisliği

Permanent URI for this collectionhttps://hdl.handle.net/11147/4129

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Now showing 1 - 10 of 28
  • Conference Object
    Determination of Interfacial Heat Transfer Coefficient for a Mixed Convection Heat Transfer in a Vertical Channel Filled With Uniformly Heated Blocks
    (Begell House Inc., 2015) Çelik, Hasan; Mobedi, Moghtada; Manca,O.; Buonomo,B.
    The interfacial convective heat transfer coefficient of a periodic porous medium under mixed convection heat transfer is determined computationally by using volume averaging method. The porous medium consists of square blocks in inline arrangement. The continuity, momentum and energy equations are solved in dimensionless form for a representative elementary volume of porous medium and the velocity and temperature fields for different values of Richardson and Reynolds numbers are obtained. Based on the obtained results, the interfacial convective heat transfer coefficient is calculated by using volume average method. The temperature of the solid phase is considered uniform and different than the inlet temperature. A detailed discussion on the effect of the governing dimensionless parameters (i.e. Reynolds, Richardson numbers, and porosity) on the local and average interfacial Nusselt number is done. It is concluded that the local interfacial convective heat transfer coefficient increases with Reynolds number, however the rate of increase depends on Richardson number and porosity. The study is performed for two values of porosity of 0.51 and 0.94. © 2021, Begell House Inc. All rights reserved.
  • Conference Object
    A Numerical Study on the Determination of the Effects of Pore To Throat Size Ratio on the Thermal Dispersion in Porous Media
    (Begell House, 2014) Özgümüş, Türküler; Mobedi, Moghtada; Özkol, Ünver
    Direct pore-level numerical simulations are widely used to estimate macroscopic properties of fluid flow and heat transfer in porous media. Thermal dispersion is one of the most important macroscopic transport parameters for analyzing convective heat transfer in a porous medium. It should be known in order to predict the macroscopic temperature distribution. In the present study, a microscopic scale analysis is performed for a porous medium with periodic structure. A representative elementary volume is chosen from an infinite medium consists of rectangular rods in inline arrangement. The continuity and momentum equations are solved to obtain flow field and the energy equations for fluid and solid phases are solved to obtain microscopic temperature distributions in two phases. There are velocity and temperature deviations between macroscopic and microscopic local values. Volume averaging method is applied to the computed deviations and thermal dispersion conductivity of porous media is determined. The aim of this study is to analyze the effects of pore to throat size ratio on the longitudinal and transverse thermal dispersion in porous media. The study is performed for representative elementary volumes with different pore to throat size ratios and Reynolds numbers from 1 to 100. The study is performed for high porosity porous media (ε = 0.7 and 0.91). It is shown that the porosity and pore to throat size ratio have more influence on the transverse rather than longitudinal thermal dispersion. © 2014, Begell House Inc. All rights reserved.
  • Article
    Citation - WoS: 8
    Citation - Scopus: 8
    Free Vibration Analysis of Damaged Composite Beams
    (Techno Press, 2015) Cünedioğlu, Yusuf; Beylergil, Bertan
    In this study, free vibration analyses of symmetric laminated cantilever and simply supported damaged composite beams are investigated by using finite element method (FEM). Free vibration responses of damaged beams are examined using Euler Bernoulli beam and classical lamination theories. A computer code is developed by using MATLAB software to determine the natural frequencies of a damaged beam. The local damage zone is assumed to be on the surface lamina of the beam by broken fibers after impact. The damaged zone is modeled as a unidirectional discontinuous lamina with 0 degrees orientations in this study. Fiber volume fraction (v(f)), fiber aspect ratio (L-f/d(f)), damage length (L-D) and its location (lambda/L), fiber orientation and stacking sequence parameters effects on natural frequencies are investigated. These parameters are affected the natural frequency values significantly.
  • Article
    Citation - Scopus: 1
    Sizing of Autonomous Wind/Solar Hybrid Energy Conversion Systems for Urla, Turkey
    (ACTA Press, 2009) Özerdem, Barış; Ekren, Orhan
    In this paper, an optimum sizing procedure of autonomous hybrid (wind + solar) energy system is presented which can be used to satisfy the requirements of given load distribution. The main purpose of this study is to find out an appropriate wind-photovoltaic hybrid energy system to satisfy electricity consumption of GSM (Global System for Mobile communication) base station at Izmir Institute of Technology Campus Area, Urla, Izmir, Turkey. To do this, monthly average daily solar radiation and wind speed data are collected. The monthly average wind speeds are measured at 10 m height during 3 years period on Izmir Institute of Technology Campus Area. The monthly average wind speed values are obtained between 5.7 and 7.7 m/s, on the other hand, the monthly average daily value of solar radiations on horizontal surfaces are ranged from 1.4 to 6.9kWh/m2 at Izmir Institute of Technology Campus Area. The hybrid system considered in the present analysis consists of one 5kW nominal power wind energy conversion systems (WECS), 21.82 m2 of photovoltaic (PV) panels (18 mono crystal PV panels each having 75 W power output) together with a battery storage system.
  • Conference Object
    Problem of Cracked Infinite Hollow Cylinder With Two Rigid Inclusions
    (Civil-Comp Press, 2000) Artem, Hatice Seçil; Geçit, Mehmet Ruşen
    This paper is concerned with the fracture of an axisymmetric hollow cylindrical bar containing rigid inclusions. The cylinder is under the action of uniformly distributed axial tension applied at infinity. The hollow cylinder contains a ring-shaped crack at the symmetry plane whose surfaces are free of tractions and two ring-shaped rigid inclusions with negligible thickness symmetrically located on both sides of the crack. Geometry and the loading is symmetric about z-axis. Along the rigid inclusions displacements are constant and continuous whereas stresses have jumps. The inner and the outer surfaces of the cylinder are free of tractions It is assumed that the material of the cylinder is linearly elastic and isotropic. The mixed boundary conditions of the problem lead the analysis to a system of three singular integral equations for crack surface displacement derivative and normal and shear stress jumps on rigid inclusions. These integral equations are solved numerically and the stress intensity factors at the edges of the crack and at the edges of the inclusions are calculated. Results are presented in graphical form.
  • Conference Object
    Kinematic and Dynamic Analysis of a New Type of Spatial 6-Dof Parallel Structure Manipulator
    (China Machine Press, 2004) Alizade, Rasim; Bayram, Çağdaş
    This paper addresses the dynamics and kinematics of a 6xUPS type parallel structure manipulator that consists of six branches and a platform. The problem of forward and inverse displacement analysis is considered on the base of solution of the forward displacement problem for each UPS branch as a serial manipulator. Basic dynamics equations have also been considered. The values of reduced moments and forces have been determined that provides the required input forces and moments. Thus, we deal with inverse dynamics problems. Dynamic model of this type of spatial manipulator is described by a system of six non-linear differential equations of second order with applying Lagrange-Euler methods.
  • Conference Object
    Cash Flow Forecasting by Using Time Series Methods in Geothermal District Heating Systems: Balcova - Narlidere Case
    (National Technical University of Athens, 2006) Erdoğmuş, Abdullah Berkan; Özerdem, Barış
    Cash flow forecasting is one of the difficult and important tasks in an economic evaluation of a geothermal investment. Geothermal district heating systems are characterized by a high capital cost. In addition, relatively low operation and maintenance costs occur throughout their life. The aim of this research is to estimate the potential cash flows for Balcova - Narlidere Geothermal District Heating System by using historical data accumulated over a period of time and several forecasting methods: moving average, exponential smoothing, adjusted exponential smoothing and curve fitting functions. Mean absolute percentage deviation (MAPD) which is the most common approach to select the appropriate method to a particular time series is used in the selection of the most suitable model. Alternative methods are compared with each other regarding to their MAPD values. It is found that the models represented by exponential curve fitting functions have smaller MAPD values and give better results in cash flow forecasting of investment investigated.
  • Conference Object
    Underground Gasification in Western Black Sea Area and Thermodynamic Analysis
    (2006) Atagündüz, Gürbüz
    As known, western Black Sea carboniferous coal fields consist of two main fields: Zonguldak and Amasra. Previous research works have shown that Zonguldak area is not suitable for underground coal gasification. The joint studies done since 1994 by the Department of Geology and the Solar Energy Institute of Aegean University and, the Mineral Research and Exploration Institute of Ministry of Energy and Natural Sources have shown that the Amasra coal field is suitable with certain restrictions for the underground coal gasification. In the present work, the suitability of the Amasra - coal field for underground coal gasification will be discussed and the "Controlled Retraction of the Injection Point; CRIP"- Method which was successfully used and tested in the American field experiments will be described briefly. A brief thermodynamic analysis of the gasification process will be given which should help, as a tool, to the theoretical prediction of the underground coal gasification.
  • Conference Object
    Energy Losses From Outdoor Located Air Handling Unit and Connection Duct
    (Universita degli Studi di Padova, 2007) Erdoğmuş, Abdullah Berkan; Mobedi, Moghtada; Özerdem, Barış
    In the present study, energy losses due to heat transmission and air leakage from outdoor located air handling unit and connection duct are investigated based on EN 1886 and NEN-EN 1507 standard. The EN 1886 standard classifies air handling unit according to heat transmission and air leakage, while NEN-EN 1507 standard specify air leakages of rectangular ducts. In this study, air leakage and heat transmission fluxes for three cities in different regions of Turkey are determined and the economical value of energy losses for a building located in the city of Izmir and services 24 hours is calculated. The ambient air temperatures are taken from Turkish State Meteorological Service. The daily average values are considered for ambient temperature. The energy losses are determined for the variable and constant supply temperatures. Tables and charts are provided to show the variation of energy losses due to transmission and air leakage for the whole year. The total amounts of heat transmission and air leakage energy losses for different classes of air handling unit and connection duct are compared and discussed.
  • Conference Object
    Tıbbi Uygulamalar için Özgün Yapılı Haptik Cihaz Tasarımı
    (Institute of Electrical and Electronics Engineers Inc., 2009) Selvi, Özgün; Bilgincan, Tunç; Kant, Yalkın; Dede, Mehmet İsmet Can
    Robotik sistemler hassasiyet gerektiren işlerde gün geçtilçe günlük hayatımızın bir parçası olmaya başladı. Bu işler genellikle herhangi bir operatör tarafından yapılamayacak kadar hassasiyet gerektiren işler olduğundan dolayı robotik teknolojiye ihtiyaç vardır. Bir robotik alanı olan Haptik teknolojisi, operatör ile çevrenin etkileşimini kuvvet geri beslemesi ile sağlayarak uygulamanın hassasiyet seviyesini arttırmaktadır. Bugünkü haliyle haptik teknoloji tıbbi operasyonlarda yardımcı sistem olarak ve birçok uzaktan kumandalı operasyonlarında (teleoperasyon) kullanılmaktadır. Aynı zamanda haptik teknoloji askeri ve tıbbi eğitim amaçlı sanal gerçeklik programlarında kullanılmaktadır. Bu çalışmanın amacı sistemin hassasiyetini arttırabilecek yapısal olarak yeni bir haptik cihaz tasarlamaktır. Bu kapsamda, önceden gerçekleştirilmiş robot tasarımları araştırıldı ve kavramsal tasarımlar gelistirildi. Sonuç olarak seçilen tasarım sanal ortam da oluşturuldu ve simülasyonu yapıldı, ve ilk prototipi imal edildi