Mekatronik Mühendisliği Bölümü Yayın Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/255

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A Comparison of Iterative Fourier Transform Algorithms for Image Quality Estimation
(Optical Soc Japan, 2018) Alsaka, Dina Yaqoob; Arpali, Caglar; Arpali, Serap Altay; 20809
A comparison was established between two iterative Fourier transform algorithms (IFTAs), such as the original Gerchberg-Saxton (GS) and the mixed-region amplitude freedom (MRAF) algorithms, for the hologram reconstruction of different target images through the full reference image quality estimation (IQE) and pixel homogeneity in the Fourier plane presented theoretically and experimentally. The comparison was applied depending upon both algorithms based on a computer-generated hologram (CGH) implemented utilizing a reflective phase-modulated liquid-crystal spatial light modulator (LC-SLM) to obtain the digital kinoform holograms of the desired intensity distributions. These digital holograms were applied to reconstruct the intensity patterns for 852 nm, which represents a laser beam source. The theoretical and experimental results of the reconstructed patterns obtained using the MRAF algorithm were found to be smoother and better than the patterns obtained using the GS algorithm. Unmodulated light beam (dc term) is removed from the reconstructed patterns attributed to digital kinoform holograms of MRAF algorithm as an alternative to the theoretical and experimental results without using any additional optic equipment at the light path. Moreover, this paper discussed the full reference objective quality estimations, such as mean square error (MSE), peak signal-to-noise ratio (PSNR), structural content (SC), normalized absolute error (NAE), normalized cross correlation (NK), and homogeneity of pixels, through the contrast (Cont) and inverse difference moment (IDM) for numerical and experimental results. According to the two desired intensity distributions processed theoretically and experimentally, the results of MRAF algorithm were found to be in the highly accurate recovered phase, the quality of image was enhanced, and the dc term was decreased. Image quality estimation of full reference objective relay on the feedback algorithms experimental attestation has not been implemented yet.
A new systematic and exible method for developing hierarchical decision-making models
(Tubitak Scientific & Technological Research Council Turkey, 2015) Beldek, Ulas; Leblebicioglu, Mehmet Kemal; 59950
The common practice in multilevel decision-making (DM) systems is to achieve the final decision by going through a finite number of DM levels. In this study, a new multilevel DM model is proposed. This model is called the hierarchical DM (HDM) model and it is supposed to provide a flexible way of interaction and information flow between the consecutive levels that allows policy changes in DM procedures if necessary. In the model, in the early levels, there are primary agents that perform DM tasks. As the levels increase, the information associated with these agents is combined through suitable processes and agents with higher complexity are formed to carry out the DM tasks more elegantly. The HDM model is applied to the case study 'Fault degree classification in a 4-tank water circulation system'. For this case study, the processes that connect the lower levels to the higher levels are agent development processes where a special decision fusion technique is its integral part. This decision fusion technique combines the previous level's decisions and their performance indicator suitably to contribute to the improvement of new agents in higher levels. Additionally, the proposed agent development process provides flexibility both in the training and validation phases, and less computational effort is required in the training phase compared to a single-agent development simulation carried out for the same DM task under similar circumstances. Hence, the HDM model puts forward an enhanced performance compared to a single agent with a more sophisticated structure. Finally, model validation and efficiency in the presence of noise are also simulated. The adaptability of the agent development process due to the flexible structure of the model also accounts for improved performance, as seen in the results.
Classification of low probability of intercept radar waveforms using gabor wavelets
(Gazi Univ, Fac Engineering Architecture, 2021) Ergezer, Halit; Ergezer, Halit; 29339
Low Probability of Intercept (LPI Radar) is a class of radar with specific technical characteristics that make it very difficult to intercept with electronic support systems and radar warning receivers. Because of their properties as low power, variable frequency, wide bandwidth, LPI radar waveforms are difficult to intercept by ESM systems. In recent years, studies on the classification of waveforms used by these types of radar have been accelerated. In this study, Time-Frequency Images (TFI) has been obtained from the LPI radars waveforms by using Choi-Williams Distribution method. From these images, feature vectors have been generated using Gabor Wavelet transform. In contrast to many methods in the literature, waveform classification has been performed by directly comparing the feature vectors obtained without using any machine learning method. With the method we propose, classification accuracies were obtained at intervals of 2 dB between -20 dB and 10 dB and performed at reasonable classification accuracy rates up to -8 dB SNR value. Better results than the best reported in the literature were obtained for some signal types. The results obtained for all waveform types are given in comparison with the results of the existing methods in the literature.
Cooperative adaptive cruise control for vehicle following during lane changes
(Elsevier, 2017) Schmidt, Klaus W.
This paper addresses the longitudinal vehicle behavior before and during lane changes. Hereby, it is desired that the lane-changing vehicle simultaneously follows its predecessors on the lanes before and after the lane change. Specifically, the lane changing vehicle should keep a safe distance to the rearmost predecessor vehicle, while maintaining a small inter vehicle spacing and supporting driving comfort. To this end, the paper develops an extension of cooperative adaptive cruise control (CACC). Instead of following a single vehicle as in the classical realization of CACC, it is proposed to follow a virtual vehicle that is evaluated based on distance measurements and communicated state information from the predecessor vehicles. A simulation study demonstrates the practicability of the proposed method. (C) 2017, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.
Development of air-to-ground engagement analysis model of fighter aircrafts
(Gazi Univ, Fac Engineering Architecture, 2022) Erdogan, Sinem; Ergezer, Halit; Bektas, Almila; Ergezer, Halit; 293396
In operational analysis studies; it is possible to model and simulate at an engineering level, engagement level, task level and campaign forces level. In this study, modelling and simulation studies are performed in engagement-level allowing the analysis of air-to-ground engagement effectiveness of fighter aircraft according to the operational environment. The operating environment of the combat aircraft, which provides survivability analysis based on low visibility and electronic mixing capabilities, is created. The search radar and tracking radar models for ground-to-air threats have been designed in accordance with the engagement level. The dynamic model of the fighter aircraft and the ground-to-air missile have been modelled using pseudo 5 degree-of-freedom. Modelling has been carried out to allow the use of changes in the Radar Crosssectional Area (RCS), which is one of the most important factors affecting the survivability of the aircraft, with respect to azimuth and elevation angles. The Radio Frequency (RF) jamming capability of the fighter aircraft has also been modelled in accordance with the engagement level. The results of the generic scenarios for the analysis of the effect of these models' parameters on the survivability of fighter aircraft have been presented.
Effect of use of cu-cr p/m electrodes on machining performance of electric discharge machining
(Gazi Univ, Fac Engineering Architecture, 2015) Gulcan, Orhan; Çoğun, Can; Uslan, Ibrahim; Usta, Yusuf; Cogun, Can; 3113; 118190; 3837
In this study, the effect of use of Cu-Cr powder metal (P/M) electrodes on EDM performance outputs, namely material removal rate (MRR), electrode wear rate (EWR), mean and maximum roughness of machined surface (R-a and R-z) and workpiece surface recast layer thickness, was investigated experimentally. The Cu-Cr P/M electrodes produced at different mixing ratios, compacting pressures and sintering temperatures were used to machine SAE 1040 steel. The analyses performed have shown that the electrode material is deposited on to the work surface as a layer and the powder mixing ratio, the compaction pressure and sintering temperature affect the EDM performance outputs.
ELECTROCHEMICAL SMALL DIAMETER DEEP HOLE DRILLING OF POWDER METAL STEEL
(Univ Zagreb Fac Mechanical Engineering & Naval Architecture, 2020) Ozerkan, Haci Bekir; Çoğun, Can; Cogun, Can; 3837
In this study, a new hybrid electrochemical drilling (ECD) method is proposed. The method makes use of a tubular tool capable of rotating and an electrolyte flushing through the inner hole at the same time. The designed and manufactured small size ECD machine's most important features are the regulation of the tool feed rate via current feedback control and the use of a rotating tubular tool with internal electrolyte flushing. The powder metal (PM) FLN2 4405 steel was drilled by using a brass tubular tool with various combinations of machining parameters such as machining voltage, electrolyte concentration and flushing pressure, and tool rotation speed. The machining performance outputs, namely, material removal rate (MRR), average radial overcut (RADOC), conicity (CO) and hole geometries were calculated and compared in different machining conditions. The results have shown that the aforementioned variables had a direct impact on the machining performance outputs in ECD. In all experiments, MRR increased with an in increase in machining voltage, tool rotational speed, electrolyte concentration and flushing pressure. RADOC values decreased with the rotational speed of the tool. The present study shows that deep holes with precise geometries and dimensions can be drilled successfully by employing the proposed hybrid ECD method. The method is economical and environmentally friendly since it requires low machining current values (0.1 to 0.7A) and a small amount of non-hazardous halide salt solutions instead of acidic solutions throughout the drilling process.
Experimental Investigation on Wire Electric Discharge Machining of Biodegradable AZ91 Mg Alloy
(Springer, 2021) Çoğun, Can; Urtekin, Levent; Ozerkan, Haci Bekir; Esen, Ziya; Cogun, Can; Genc, Asim; Esen, Ziya; Bozkurt, Fatih; 3837; 52373
The AZ91 magnesium alloy, used commonly as a biodegradable material in biomedical applications, is generally formed by conventional casting method (CCM) and high-pressure die casting method (HPDCM). The AZ91 alloys exhibit poor machinability with conventional chip removal methods since they degrade at elevated temperatures. In this study, the wire electric discharge machining (WEDM) was presented as a candidate process to machine the AZ91 alloy since no cutting stresses and plastic deformations were applied by the cutting tool to the part causing elevated temperatures. In this context, the WEDM machinability of the AZ91 alloy samples produced by cold chamber HPDCM and CCM at different process parameters, was experimentally investigated. The machining performance outputs (the machining current (I), the machining rate (MR), the average surface roughness (R-a), and surface topography) were found for the varying process parameters [pulse time (t(s)), pulse-off time (t(off)), dielectric flushing pressure (P-d), and wire speed (V-w)]. The present study revealed that the I and the MR were significantly dependent on the density, the porosity, and the micro structure of the samples, and the HPDCM samples gave the higher MR and the smoother surface than that of the CCM.
Fault-tolerant control of discrete-event systems with lower-bound specifications
(Elsevier, 2015) Moor, Thomas; Schmidt, Klaus Werner
Fault-tolerant control addresses the control of dynamical systems such that they remain functional after the occurrence of a fault. To allow the controller to compensate for a fault, the system must exhibit certain redundancies. Alternatively, one may relax performance requirements for the closed loop behaviour after the occurrence of a fault. To achieve fault tolerance for a hierarchical control architecture, a combination of both options appears to be advisable: on each individual level of the hierarchy, the controller may compensate the fault as far as possible, and then pass on responsibility to the next upper level. This approach, when further elaborated for discrete-event systems represented by formal languages, turns out to impose a hard lower-bound inclusion specification on the closed-loop behaviour. The present paper discusses the corresponding synthesis problem and presents a solution. (C) 2015, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.
Influence of the material properties on the elastic-plastic deformation in a heat generating composite solid cylinder
(Gazi Univ, Fac Engineering Architecture, 2013) Ozturk, Ali; Gülgeç, Müfit; Gulgec, Mufit; 30494; 4168
Based on Tresca's yield criterion and its associated flow rule, the elastic-plastic deformation of a centrally heated composite cylinder with fixed ends is investigated by considering the influence of geometric parameters as well as material properties such as yield strength, modulus of elasticity, Poisson's ratio, coefficient of thermal conduction and thermal expansion. In the study, stress, strain and displacement distributions in the composite cylinder made of elastic-perfectly plastic material are derived. Stress distribution and evolution of plastic regions in the composite are presented for different levels of heat generation in the core.
Modeling distributed real-time systems in TIOA and UPPAAL
(Assoc Computing Machinery, 2016) Kartal, Yusuf Bora; Schmidt, Ece Guran; Schmidt, Klaus Werner; 17337
The mission- and life-critical properties of distributed real-time systems require concurrent modeling, analysis, and formal verification in the design stage. The timed input/output automata (TIOA) framework and the UPPAAL software package are two widely used modeling and verification tools for this purpose. To this end, we develop the algorithm TUConvert for converting distributed TIOA models to UPPAAL behavioral models and formally prove its correctness. We demonstrate the applicability of our algorithm by the formal verification of a distributed real-time industrial communication protocol that is modeled by TIOA.
The controllability prefix for supervisory control under partial observation with an application to fault-tolerant control
(Elsevier, 2017) Moor, Thomas; Schmidt, Klaus Werner
The controllability prefix is known as a useful concept for the discussion and solution of synthesis problems in supervisory control of cp-languages, i.e., formal languages of infinite-length words. There, the controllability prefix is defined as the set of all finite-length prefixes that can be controlled to satisfy prescribed liveness and safety properties. In this paper, we discuss a variation of the controllability prefix to address supervisory control under partial observation for regular *-languages, i.e., formal languages of finite-length words. We derive algebraic properties that are useful for a quantitative analysis on how an upper-bound language-inclusion specification affects achievable lower-bound specifications. Our study is motivated by the synthesis of fault-tolerant supervisory controllers, where the possible occurrence of a fault may restrict the achievable pre-fault behaviour so severe, that a relaxation of the upper-bound specification becomes a practical option. As our study shows, such a relaxation can be systematically constructed in terms of the controllability prefix. (C) 2017, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.
The effect of powder mixed and heated dielectric on drilling performance of electric discharge machining (EDM)
(Gazi Univ, Fac Engineering Architecture, 2016) Erdem, Oguz; Çoğun, Can; Cogun, Can; Urtekin, Levent; Ozerkan, H. Bekir; Uslan, Ibrahim; 3837
In this study, heated silicon oil with added carbon and starch powders was used as dielectric liquid, instead of common hydro-carbon based dielectrics, to obtain better hole surface quality with rotating brass tube electrode in electric discharge machining (EDM). The electro-rheometer tests were conducted to find out the suitable temperature and powder concentration values of the electro-rheological (ER) dielectric under the electric field. Higher workpiece material removal rates (MRR) was obtained in carbon powder added dielectrics than the starch powder added ones for rotating and non-rotating electrodes. The optical microscope observations of the machined hole surfaces indicated that the carbon powder added dielectrics reduced the diameter and depth of the discharge craters, thereby resulting in uniformly distributed and round top peaked surface topography. The starch powder addition to the carbon mixed dielectric further improved the surface quality for both rotating and non-rotating electrodes cases at 30 degrees C and 75 degrees C dielectric temperatures.
Two Majority Voting Classifiers Applied to Heart Disease Prediction
(Mdpi, 2023) Karadeniz, Talha; Maraş, Hadi Hakan; Karadeniz, Talha; Maras, Hadi Hakan; Tokdemir, Gül; Tokdemir, Gul; Ergezer, Halit; Ergezer, Halit; 34410; 293396
Two novel methods for heart disease prediction, which use the kurtosis of the features and the Maxwell-Boltzmann distribution, are presented. A Majority Voting approach is applied, and two base classifiers are derived through statistical weight calculation. First, exploitation of attribute kurtosis and attribute Kolmogorov-Smirnov test (KS test) result is done by plugging the base categorizer into a Bagging Classifier. Second, fitting Maxwell random variables to the components and summating KS statistics are used for weight assignment. We have compared state-of-the-art methods to the proposed classifiers and reported the results. According to the findings, our Gaussian distribution and kurtosis-based Majority Voting Bagging Classifier (GKMVB) and Maxwell Distribution-based Majority Voting Bagging Classifier (MKMVB) outperform SVM, ANN, and Naive Bayes algorithms. In this context, which also indicates, especially when we consider that the KS test and kurtosis hack is intuitive, that the proposed routine is promising. Following the state-of-the-art, the experiments were conducted on two well-known datasets of Heart Disease Prediction, namely Statlog, and Spectf. A comparison of Optimized Precision is made to prove the effectiveness of the methods: the newly proposed methods attained 85.6 and 81.0 for Statlog and Spectf, respectively (while the state of the heart attained 83.5 and 71.6, respectively). We claim that the Majority Voting family of classifiers is still open to new developments through appropriate weight assignment. This claim is obvious, especially when its simple structure is fused with the Ensemble Methods' generalization ability and success.

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