Mechanical Engineering / Makina Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4129
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Article Power transmission entropy(Inderscience Enterprises Ltd., 2008) Özdemir, SerhanMechanical transmissions have been characterised traditionally by their transmission efficiencies. This is given by the ratio of the output to the input of the transmitted power. Unfortunately, the power transmission phenomenon is slightly more complex than that. As any designer would agree, each of these transmission localities is a source of uncertainty. Once formulated, this statement of uncertainty would reflect the designer's trust in the transmission. By virtue of the proposed approach, power transmission is no longer a deterministic entity but becomes a probabilistic one. This paper discusses the overlooked uncertainty inherent in every transmission.Article Local Sparse Coding Control of Cvpsts(Inderscience Enterprises, 2005) Özdemir, SerhanThis paper discusses simulations of a control scheme based on locally sparse coded networks (CMACs) for a novel previously proposed continuously variable transmission (CVT), a hybrid continuously variable power split transmission (CVPST) (Osdemir and Schueller, 2002). Automotive transmissions match the speed and the torque of the power source to the speed and torque requirements of the load. Properly designed CVTs have shown potential to improve efficiency and performance. The main advantage of CMACs is fast computation because of their simple operational principles. Simulation results have shown that memory contents either reach a stable limit cycle or an attractor based on the selection of network parameters and the training method. Both online and offline training are possible.Article Citation - WoS: 2Citation - Scopus: 2Trait-based heterogeneous populations plus (TbHP+) genetic algorithm(Elsevier Ltd., 2009) Tayfur, Gökmen; Sevil, Hakkı Erhan; Gezgin, Erkin; Özdemir, SerhanThis study developed a variant of genetic algorithm (GA) model called the trait-based heterogeneous populations plus (TbHP+). The developed TbHP+ model employs a memory concept in the form of immunity and instinct to provide the populations with a more efficient guidance. Also, it has an ability to vary the number of individuals during the search process, thus allowing an automatic determination of the size of the population based on the individual qualities such as character fitness and credit for immunity. The algorithm was tested against the classical GA model in convergence and minimum error performance. For this purpose, 5 different mathematical functions from the literature were employed. The selected functions have different topological characteristics, ranging from simple convex curves with 2 variables to complex trigonometric ones having several hilly shapes with more than 2 variables. The developed model and the classical GA model were applied to finding the global minima of the functions. The comparison of the results revealed that the developed TbHP+ model outperformed the classical GA in faster convergence and minimum errors, which may be explained by the adaptive nature of the new paradigm.Book Part Citation - Scopus: 6Swarm and Entropic Modeling for Landmine Detection Robots(Springer Verlag, 2008) Bayram, Çağdaş; Sevil, Hakkı Erhan; Özdemir, SerhanEven at the dawn of the 21st century, landmines still pose a global threat. Buried just inches below the surface, combatants and noncombatants alike are all at risk of stepping on a mine. Their very nature is such that these furtive weapons do not discriminate, making it an urgent task to tackle the problem. According to the U.S.State Department [1], based on an estimate reported just a few years ago, there are well over 100 million anti-personnel mines around the world. The existence of these passive weapons causes a disruption in the development of already impoverished regions, as well as maiming or killing countless innocent passers-by. Since the ratification of the anti-personnel mine total ban treaty in 1997, their detection, removal, and elimination have become a top priority. Nevertheless, at the current rate, given the manpower and the man-hours that could be dedicated to the removal of these sleeping arms, it would take centuries. The concerns regarding the speed of removal and safety of the disposers eventually bring us to the discussion of the proposed method. Nature already provided good solutions to manage groups of less able beings: fish schools, ant swarms, animal packs, bird flocks, and so on.With the growing desire of humans to create intelligent systems, these biosystems are being thoroughly inspected [3-10] and implemented [11-14] in various studies. In this study a robotic agent is referred to as a drone, the group of robotic agents is referred to as a swarm, and the agent with mapping abilities is referred to as the alpha drone.Article Citation - WoS: 8Citation - Scopus: 8Measures of Uncertainty in Power Split Systems(Elsevier Ltd., 2007) Özdemir, SerhanThis paper discusses the overlooked uncertainty inherent in every transmission. The uncertainty aspect has been often, for the sake of clarity, ignored. Instead, mechanical transmissions have been characterized traditionally by their transmission efficacies. It is known that transmission localities are sources of power loss, depending on many factors, hence sources of uncertainty. Thus each transmission of power should not only be designated by a constant of efficiency but also by an expression of uncertainty, reflecting the probability of transmission. Furthermore, Shannon's and Renyi's expressions of entropy have been used to quantify this so-called transmission uncertainty. The entropy of a transmitting unit is given in these two forms and then compared. Practical formulations for flow optimization are given.Article Citation - WoS: 11Citation - Scopus: 13Wind Speed Time Series Chacacterization Hy Hilbert Transform(John Wiley and Sons Inc., 2006) Alpay, Selda; Bilir, Levent; Özdemir, Serhan; Özerdem, BarışPredictions of wind energy potential in a given region are based on on-location observations. The time series of these observations would later be analysed and modelled either by a probability density function (pdf) such as a Weibull curve to represent the data or recently by soft computing techniques, such as neural networks (NNs). In this paper, discrete Hilbert transform has been applied to characterize the wind sample data measured on Izmir Institute of Technology campus area which is located in Urla, Izmir, Turkey, in March 2001 and 2002. By applying discrete Hilbert transform filter, the instantaneous amplitude, phase and frequency are found, and characterization of wind speed is acomplished. Authors have also tried to estimate the hourly wind data using daily sequence by Hilbert transform technique. Results are varying.Conference Object Citation - WoS: 4Citation - Scopus: 4A distributed behavioral model for landmine detection robots(International Association of Engineers, 2007) Bayram, Çağdaş; Sevil, Hakkı Erhan; Özdemir, SerhanThis paper presents a distributed navigation, detection and swarming model for a group of minimalist identical robotic agents. Decision making process of agents is weight based in contrast to widely used precedence based rules. The group is indirectly controlled by an alpha agent that has more sophisticated systems. Computer simulations of the proposed behavioral model generated promising results.Conference Object Citation - Scopus: 2Characterization of Swarm Behavior Through Pair-Wise Interactions by Tsallis Entropy(CSREA Press, 2005) Can, Fatih Cemal; Bayram, Çağdaş; Toksoy, Ahmet Kaan; Avşar, Hakan; Özdemir, SerhanThis paper tries to look at the interactions of a swarm of two at an elementary level. The change in the swarm entropy during the interactions is investigated. The characterization of swarm behavior has been subsumed in four modes, i.e. normal-free, normal-swarm, feeding and obstacle modes. Based on these modes, an entropy based algorithm is constructed to observe pair-wise interactions for each mode. For these modes, individuals of swarm are taken into account as self-driven interacting particles in the mathematical model. Statistical entropy definitions are used to control individual's behavior in feeding and obstacle modes. Individuals lose interactions enabling swarm behavior in feeding mode because of the priority of feeding for individuals as in nature. On the other hand, when swarm confronts an obstacle, individuals interact as much as they can. However they may lose interaction, depending on the size of the obstacle and position of the individuals. For feeding and obstacle modes, it is observed that Tsallis Entropy fits in the simulation better than other entropy definitions such as Shannon and Renyi.Conference Object Citation - Scopus: 1The Effects of Bias, Population Migration and Credit Assignment in Optimizing Trait-Based Heterogeneous Populations(CSREA Press, 2005) Gezgin, Erkin; Sevil, Hakkı Erhan; Özdemir, SerhanPopulation based search algorithms are becoming the mainstay in nonlinear problems with discontinuous search domains. The generic name of genetic algorithms (GAs) basicly applies to all population based methods. GAs have spawned many versions to suit new applications. Some of these alterations have reached such points that the algorithms may no longer be called GAs. One similar study may be found in [1], in which a perturbation based search algorithm was proposed, called Responsive Perturbation Algorithm (RPA). In a later work [2], instead of a population of homogenous individuals, as is the case for generic GAs, a population of heterogeneous individuals has been set to compete. Replacing the set of winner parents, the fittest individual is made the parent to yield offspring. The current work is now called, with the supplements, trait-based heterogeneous populations plus (TbHP+). Credit assignment and bias concepts in the form of immunity and instinct has been added to provide the populations with a more efficient guidance. Simulations were made through an RBF neural network training, as it was carried out in earlier works, mentioned above, for comparison. Results were prsented at the end as network testing errors which showed further improvement with TbHP+.Article Citation - WoS: 6Citation - Scopus: 6Intelligence Modeling of the Transient Asperity Temperatures in Meshing Spur Gears(Elsevier Ltd., 2005) Atan, Ebubekir; Özdemir, SerhanTemperature rise in the contact zone of meshing gears is a serious problem in gear design. The temperature rise on lubricated surfaces may result in the significant decrease on the material strength and lubricant viscosity which reduces the film thickness, causing solid to solid contact. The equations and the evaluations of the rise in temperature were given in [Proc. VDI Berichte 2 (1665) (2002) 615-626] and reiterated in this paper briefly. The data from [Proc. VDI Berichte 2 (1665) (2002) 615-626] are used to establish an artificial intelligence model where a multi layer feedforward neural network has been employed. The model accepts surface roughness, gear ratio, horsepower and the number of teeth as input variables, and outputs calculated pinion surface asperity temperatures. The aim of the present work is to provide a straightforward and simple way to compute the asperity temperature rise for a given set of variables, R-square value for the computed temperature values proves the method satisfactory.