Mechanical Engineering / Makina Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4129
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Conference Object Citation - Scopus: 2Adaptive Actuator Failure Compensation for Concurrently Actuated Manipulators(Elsevier, 2003) Keçeci, Emin Faruk; Tang, Xidong; Tao, GangThis paper presents an adaptive actuator failure compensation method, which compensates for uncertainties due to unknown actuator failures and system dynamics, for a class of redundant manipulators where some joints concurrently actuated. Physical realization of concurrently actuated manipulators and their advantageous of use have been understood before, but adaptive failure compensation is still an open issue. In this research, failure formulation, controller structure and adaptive update rules for handling uncertainties from both the system dynamics and the failures are studied. The system stability is shown by a modified Lyapunov. Simulation results show the effectiveness of the proposed adaptive failure compensation control design.Conference Object Adaptive Actuator Failure Compensation for Cooperating Multiple Manipulator Systems(Elsevier, 2003) Keçeci, Emin Faruk; Tang, Xidong; Tao, GangThis paper presents adaptive actuator failure compensation for a cooperating multiple manipulator system with uncertain actuator failures in the task space. Advantages of designing control schemes in task spaces are emphasized, applications of task space control in robotics are discussed and a short review on control algorithms for cooperating multiple manipulator systems is given. Dynamic equations of motion of the multiple manipulator system in the task space are derived, and the adaptive actuator failure compensation problem is formulated. A compensation controller structure is proposed, for which adaptive parameter update laws are developed. The adaptive control scheme is able to compensate for the uncertainties arising from both the system parameters and the actuator failures. Based on Lyapunov stability analysis, the closed-loop signal boundedness and the convergence of the tracking error to zero are ensured. © 2003 International Federation of Automatic Control.Conference Object Citation - Scopus: 2Importance of Load Based Automatic Control in Geothermal Energy Systems(Elsevier, 2003) Şener, Adil Caner; Toksoy, Macit; Aksoy, NiyaziGeothermal energy production is not possible without use of electricity, since electricity is needed to pump geothermal fluid from underground to consumption point. The biggest portion of the operating cost in geothermal district heating systems comes from pumping energy consumption. In ibis study Balcova-Narhdere geothermal district heating system has been analysed and the optimum control strategies minimising the energy consumption in the system discussed. Then decisive factors in the efficient control and operation of geothermal healing systems have been studied. Finally fundamental automation requirements for efficient operation of geothermal district heating systems has been introduced. Copyright © 2003 IFAC.Article Citation - WoS: 120Citation - Scopus: 136Numerical Study on Latent Thermal Energy Storage Systems With Aluminum Foam in Local Thermal Equilibrium(Elsevier, 2019) Buonomo, Bernardo; Çelik, Hasan; Ercole, Davide; Manca, Oronzio; Mobedi, MoghtadaThe paper analyzes the behavior of a Latent Heat Thermal Energy Storage system (LHTES) with a Phase Change Material (PCM), with and without aluminum foam. A numerical investigation in a two-dimensional domain is accomplished to investigate on the system thermal evolution. The enthalpy-porosity method is used to describe the PCM melting. The open-celled aluminum foam is described as a porous medium by means of the Darcy-Forchheimer law. A hollow cylinder represents the considered thermal energy storage and it consists of the enclosure between two concentric shell tubes. The external surface of the internal tube is at assigned temperature with a value greater than the melting PCM temperature, while the other surfaces are adiabatic. Local thermal equilibrium (LTE) is numerically adopted for modelling the heat transfer between the PCM and the solid matrix in aluminum foam. In the case with metal foam, simulations for different porosities are performed. A comparison in term of liquid fraction, average temperature of the system, temperature fields, stream function and a performance parameter are made between the clean case and porous assisted case for the different porosities. A scale analysis is developed for evaluating the time and the melting zone in different regimes (i.e. conduction, mixed conduction-convective and convective) during the melting processes of the PCM in porous media. Numerical simulation shows that aluminum foam increases overall heat transfer by a magnitude of two, with respect to the clean case.Article Citation - WoS: 33Citation - Scopus: 42Thermodynamic Assessment of Downhole Heat Exchangers for Geothermal Power Generation(Elsevier, 2019) Yıldırım, Nurdan; Parmanto, Slamet; Akkurt, Gülden GökçenDownhole heat exchanger is a device to extract heat from geothermal fluid. While it is widely used for heating purposes, its use for power generation has not been reported. The aim of this study is to examine the feasibility of power generation from a 2500 m deep existing geothermal well with high temperature gradient and insufficient flowrate by using a downhole heat exchanger. For this purpose, a thermodynamic and an economic evaluation model are developed by the use of Engineering Equation Solver software. Additionally, the parametric studies have been carried out to identify the effects of insulation, geothermal well conditions, geometry of downhole heat exchanger, mass flowrate and type of working fluids on the performance of downhole heat exchanger system. Consequently, work output of the best alternative is computed as 2511 kW(e) with 64 kg/s mass flowrate of R-134a for 2500 m-deep downhole heat exchanger having inner pipe diameter of 0.127 m. Electricity generation cost and simple payback time are calculated as 46 $/MWh and 2.25 years, respectively. The obtained results showed that the downhole heat exchanger system can be a feasible alternative for wells with very low geothermal flowrate to generate power. (C) 2019 Elsevier Ltd. All rights reserved.Book Part Citation - WoS: 3Citation - Scopus: 4Design and Optimization of Fiber Composites(Elsevier, 2017) Aydın, Levent; Artem, Hatice SeçilIn engineering, design, and optimization processes are very important issues to establish sustainable engineering systems. Compared to isotropic materials, it is necessary to deal with more complicated mathematical models that address the material anisotropy for fiber-reinforced composites. Due to the unique characteristics of fiber-reinforced composite materials such as different directional properties, interlaminar stresses, less notch sensitivity, and having positive and negative coefficients of thermal expansion, they require more material constants for characterization of the hygrothermomechanical responses. Therefore, the design process of composites for the effort required or the benefit desired has to be systematic, which includes innovative approaches to synthesize alternative solutions. In this regard, the main goal of all such attempt is relevant to reach minimizing the effort required or to maximize the desired benefit.Book Part Citation - WoS: 4Citation - Scopus: 4Mechanics of Fiber Composites(Elsevier, 2017) Aydın, Levent; Artem, Hatice Seçil; Öterkuş, Erkan; Gündoğdu, Ömer; Akbulut, HamitThe objective of this chapter is to emphasize the context in which the mechanics of fiber composites is examined. Constitutive equations describing the stress-strain relations, micromechanics and acromechanics approaches for mechanical analysis are reviewed. Since interfacial mechanics of composites is of primary importance in discussing the material behavior, this concept is also presented with its constitutive and governing equations. Finally, at the end of the chapter, strength failure theories for orthotropic materials and dynamic behavior of composites are discussed.Article Citation - WoS: 15Citation - Scopus: 11The Relation Between Thermal Comfort and Human-Body Exergy Consumption in a Temperate Climate Zone(Elsevier, 2019) Turhan, Cihan; Gökçen Akkurt, GüldenHuman body exergy balance calculation method gives minimum human body exergy consumption rates at thermal neutrality (TSV = 0) providing more information on human thermal responses than other methods. The literature is lacking the verification of this method in various climatic zones. The aim of this study is to investigate the relationship between thermal comfort and human body exergy consumption in a temperate climate zone. A small office building in Izmir Institute of Technology campus, Izmir/Turkey, was chosen as a case building and equipped with measurement devices. The occupant was subjected to a survey via a mobile application to obtain his Thermal Sensation Votes. Objective data were collected via sensors and used for predicting occupant thermal comfort and for exergy balance calculations. Under given conditions, the results show that Thermal Sensation Votes are generally zero at a T-i range of 21-23 degrees C and, are mostly lower than Predicted Mean Votes in summer while the opposite is observed in winter. Predicted Mean Votes at minimum Human Body Exergy Consumption rates were on slightly warm side while Thermal Sensation Votes are zero. It means that for given case, the HBexC rate calculation gave a better prediction of the environmental parameters for the best thermal comfort. (C) 2019 Elsevier B.V. All rights reserved.Article Citation - WoS: 12Citation - Scopus: 12Geometrical Analysis of a Continuously Variable Transmission System Designed for Human-Robot Interfaces(Elsevier, 2019) Mobedi, Emir; Dede, Mehmet İsmet CanNew robotic systems are placed out of their constrained workspaces in order to work alongside humans. Consequently, these applications call for robots monitoring and regulating physical human-robot interaction. These robots’ mechanical compliance should be varied when they are in physical contact with the human or their changing environments. This compliance variation can be achieved in a variety of ways. However, one common idea is the variation of joint stiffness mechanically, electromechanically or by control. The solution presented in this paper is an electromechanical way of varying the joint stiffness. Among the electromechanical methods for varying the joint stiffness, continuously variable transmission (CVT) systems can be used in human-robot interfaces if a set of design criteria are met. These criteria include backdrivability, independent output position and stiffness variation, shock absorbing and low mass/inertia. In this paper, a novel two-cone CVT design with a double spherical transmission element is introduced by taking into account the abovementioned criteria. Additionally, design parameters are identified via carrying out a geometrical analysis of this new CVT system.Article Citation - WoS: 3Citation - Scopus: 4Function Generation With Two Loop Mechanisms Using Decomposition and Correction Method(Elsevier, 2017) Kiper, Gökhan; Dede, Mehmet İsmet Can; Maaroof, Omar W.; Özkahya, MerveMethod of decomposition has been successfully applied to function generation with multi-loop mechanisms. For a two-loop mechanism, a function y = f(x) can be decomposed into two as w = g(x) and y = h(w) = h(g(x)) = f(x). This study makes use of the method of decomposition for two-loop mechanisms, where the errors from each loop are forced to match each other. In the first loop, which includes the input of the mechanism, the decomposed function (g) is generated and the resulting structural error is determined. Then, for the second loop, the desired output of the function (f) is considered as an input and the structural error of the decomposed function (g) is determined. By matching the obtained structural errors, the final error in the output of the mechanism is reduced. Three different correction methods are proposed. The first method has three precision points per loop, while the second method has four. In the third method, the extrema of the errors from both loops are matched. The methods are applied to a Watt II type planar six-bar linkage for demonstration. Several numerical examples are worked out and the results are compared with the results in the literature.