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Coupled shaft-torsional and blade-bending vibrations in rotor-blade systems
Get PDFUçak ve helikopter pervaneleri, kompresörler, turbomakinalar gibi önemli uygulamalara sahip olmaları nedeniyle rotor–pala sistemlerinin dinamiği, özellikle de titreşimleri önemli bir araştırma konusudur. Anılan uygulama alanlarında prototip geliştirme ve test maliyetlerinin yüksek, hizmete alınma sonrasında ortaya çıkan hasarların sonucunun ise genellikle gerçek bir felaket olması nedeniyle bu sistemlerin çalışma koşullarında sahip olacakları titreşim karakteristiklerinin daha tasarım aşamasındayken gerçeğe uygun olarak öngörülebilmesi büyük önem taşır. Bu çalışmada, her kademesinde birden çok özdeş pala taşıyan, tek ve çok kademeli rotor–pala (mil–disk–pala) sistemleri ele alınmış ve mil burulma titreşimleriyle, palaların dönme düzlemi içerisindeki eğilme titreşimlerinin bağlaşıklığına ilişkin bir inceleme gerçekleştirilmiştir. Bu yapılırken, Euler–Bernouilli kirişi olarak göz önüne alınan palaların Galerkin yöntemi ile, burulma elastikliğine sahip milin ise sonlu elemanlar yöntemi ile modellendiği karma bir modelleme yöntemi önerilmiş ve uygulanmıştır. Yöntem, ele alınan sistemin nispeten düşük serbestlik dereceli bir modelle başarılı bir şekilde mo-dellenmesini sağlamış ve modele ilişkin özdeğer problemi analitik olarak geliştirilerek, birbirinden bağımsız, çok düşük boyutlu, “mil burulma–pala eğilme bağlaşık modları” ve “rijid mil modları” adı verilen ve iki farklı mod şekli sınıfına karşılık gelen alt problemlere ayrılmıştır. Bu alt problemlerin incelenmesiyle bağlaşıklığın, ele alınan sistemlerin doğal frekansları ve titreşim biçimleri üzerindeki ciddi etkileri gösterilmiş ve bazı sistem parametrelerinin titreşim davranışı üzerindeki etkileri ortaya konmuştur. Anahtar Kelimeler: Rotor–pala sistemleri, turbomakinalar, bağlaşık titreşimler.Vibrations of rotor-blade systems is an important research topic due to very important applications such as aeroplane and helicopter propellers, compressors, fans, turbo-machines, etc. In those application areas, accurate prediction of vibration characteristics is crucial in the design stage because prototyping and testing costs are exceptionally high and failure is generally disastrous. As the vibratory failures generally occur in the blades, most of the researches are concentrated on the blade vibrations. Bending and torsional vibrations of the shaft are also treated in the literature as other important sources of vibration failure. However, vibrations of different elements are generally considered separately, overlooking thus possible coupling effects, though the few works considering the coupling, pointed to serious interaction between shaft and blade vibrations. The aim of this study is to study the coupling effects between shaft torsional and blade in-plane bending vibrations in single and multi stage rotor-blade systems through an analytical approach. For this purpose, an idealized model, that consists in a torsionally elastic shaft carrying a number of rigid disks, which in turn, carry a number of identical blades modelled as cantilevered, uniform Euler-Bernouilli beams is considered. The equations of this multi body system is derived through a synthetical (elements of the system are considered first), multiframe (the motion of each element is referred to the most appropriate frame) and mixed (each element is modelled by a different method) approach. Thus, the torsionally elastic shaft is modelled by finite element method to obtain a discrete model and the blades are modelled by Galerkin's method to obtain a similar model. The resulting equations of motion are linear in shaft's torsional coordinates, nonlinear in blades' bending coordinates, and include both linear and nonlinear coupling between them. A consistent small vibrations assumption leads to a fully linear model. Then, the resulting linearized equations are brought together into a single hyper-matrix-vector equation whose matrices have repetitive structures owing to the identity of the blades on each stage. The related eigenvalue analysis problem is developed analytically and splitted into two independent sub-problems corresponding to two kinds of possible normal mode motions of the system. These are referred to as coupled shaft torsion-blade bending modes and rigid shaft modes by the authors. The dimensions of the sub-problems are independent of the number of blades on each disk. This corresponds to a considerable model reduction and enables systems with high number of blades to be examined without difficulty. In the coupled shaft torsion-blade bending modes that exist in both single and multi blade systems, all the blades of the same disk have the same mode shape. The dimension of the related sub-problem equals the model degree of freedom of the shaft plus that of one blade per stage. In these modes, eigenvalue loci veering phenomena occur and this makes the coupling to have a strong effect on the vibration characteristics of the system at certain combinations of the design parameters. In the rigid shaft modes that are peculiar to multi-blade systems, the shaft behaves like a rigid body and the blades of all the disks except one are at rest. The blades of the remaining disk have similar mode shapes but their total effect on the disk vanishes. The number of these sub-problems equals the number of stages of the system and the dimension of each sub-problem equals the model degree of freedom of one blade of the related disk. In this study, a single stage rotor-blade system, which consists of a torsionally elastic shaft carrying a bladed rigid disk attached at its right end, is first considered. The variation of the natural frequencies with certain dimensionless system parameters, such as shaft rotation speed, disk radius, is examined. Then, a rotor-blade system with three identical and equally spaced stages is considered and the variation of the natural frequencies with the dimensionless rotation speed is studied. In these studies, un-coupled analysis results are also given along with the coupled ones and it is shown that eigenvalue loci veering phenomena occur between shaft torsion and blade in-plane bending modes. This makes it necessary the coupling to be considered in the eigenanalysis whenever accuracy is required in the calcula-tions. Keywords: Rotor-blade systems, turbomachinery, coupled vibrations
Optimization of coasting points in a mass rail transit system
Get PDFBir raylı taşıma sisteminde enerji tüketimi birçok farklı parametreye bağlıdır. Ancak, bir raylı sistemde tren rotası boyunca hız profilini en uygun hale getirmek, enerji tüketimini azaltmada en etkili yöntemlerden biridir. Makalede trenler için boşta gitme noktalarının optimize edilebilmesi için yeni geliştirilmiş bir yöntem sunulmaktadır. Çalışmada önerilen yaklaşım GA (Genetik Algoritma), YSA (Yapay Sinir Ağları), ve çok hatlı ve çok trenli sistem simulasyon yazılımının birlikte kullanımıyla gerçekleştirilmiş olan gerçekçi sistem modellemesini içermektedir. Simulasyon yazılımı araçların regeneratif frenleme yapabilme ve düşük gerilimdeki performansını da modellemektedir. Simulasyon yazılımı, YSA için eğitim ve test verilerinin oluşturulmasında kullanılmıştır. Bu veriler YSA’ların eğitiminde ve bu eğitilmiş YSA’lar ise değişik boşta gitme konumları için yolculuk süresi ve enerji tüketimini tahmin etmede kullanılmıştır. Optimizasyon kısmında hedef yolculuk süresi, hedef enerji tüketimi ve ağırlık faktörleri içeren bir uygunluk fonksiyonu sunulmuş ve YSA’lar bu uygunluk fonksiyonunu hesaplayan optimizasyon prosedürünün hızını arttırmada kullanılmıştır. Uygunluk fonksiyonunu minimize eden en uygun boşta gitme noktalarının belirlenmesinde GA araştırma yöntemi kullanılmıştır. Gerek GA’nın gerekse kullanılan uygunluk fonksiyonunun değişik parametreleri için optimizasyon çalışmalarının tekrar edilmesi işlemi mevcut literatürde bulunan yöntemlerle çok fazla zaman almaktadır. Çalışmada önerilen yöntemde eğitilmiş olan YSA’ların kullanılması ile parametre değişiklikleri için tekrarlanan optimizasyon çalışmlarında simülatörün kullanılmasına gerek kalmamakta, dolayısı ile yeni parametreler için optimizasyon sonuçları çok hızlı elde edilebilmektedir. Anahtar Kelimeler: Raylı sistem, enerji verimliliği, boşta gitme, yapay sinir ağı, optimizasyon.Energy consumption of a rail transit system depends on many parameters such as train weight, maximum speed, power supply system voltage level, and operation concepts. One of the most effective methods of reducing energy consumption in a rail transit system is optimizing the speed profile of the trains along the route: Trains consume the maximum energy during flat-out mode operation where they speed up to the maximum speed and keep that speed until it reaches to the braking point which is determined by deceleration rate. This type of operation gives the shortest journey time. A small trade-off from this journey time gives high saving in energy consumption. This subject poses an optimization problem which could be very complicated. In this study, a new efficient method will be presented for optimization of the coasting points for trains in a global manner. The new method suggest using Artificial Neural Networks (ANN) together with classical approach of simulator tool and genetic algorithms.Trains run along the line according to a timetable. Timetables define the travelling time for every train from every station to station. Timetables always include some slack time for an unexpected time loss which could be caused by faulty equipment, but mostly by passengers. Slack times and station dwell times are very important for providing a punctual service. Delays disturb the punctual operation as well as reducing energy efficiency by consuming the slack times which can be used in normal operation conditions for energy efficient driving. Simulation software is used for creating training and test data for ANNs. These data are used for training of ANNs. Test data are used to validate the outputs of trained ANNs. The trained ANNs are then used for estimating energy consumption and travel time for new sets of coasting points. Finally, the outputs of ANNs are optimized to find optimal train coasting points. For this purpose, a fitness function with target travel time, energy consumption and weighting factors is proposed. Genetic algorithms were used for this search purposes. An interesting observation is that the use of ANNs increases the speed of optimization, and gives researchers the ability to test different optimization with differing genetic algorithm parameters. Proposed method is used for optimizing coasting points for minimum energy consumption for a given travel time of first 10 km section of Istanbul Aksaray-Airport metro line, where trains operate every 150 seconds. The section covers 9 passenger stations, which means 8 coasting points for each line. It has been demonstrated that an 16 input ANN can be trained with acceptable error margins for such a system .The optimization method finds the near optimum points for different target travel times and weight factors of the fitness function. It was found for the given line configurations that the energy saving potential with coasting schemes for the same amount of time increase is far less in the multi-train case, where trains regenerate and feed each other. In the 3 station case, 4.81% increase in travel time with optimum coasting points compared to the flat-out case creates 30.85% energy saving, whereas in the 5 station case, 4.65% increase in travel time with optimal coasting scheme creates only 18.25% energy saving. Using ANN and GA in combination speeds up optimization, and bigger line segments with more stations can also be optimized with this proposed method. A simple way of application of the proposed method is using a Driver Information System (DIS). Aksaray - Airport LRT system has been recently equipped with such a system. It is planned to find the optimum coasting points for different headways, and enter these values into the DIS as time and location dependent values. The DIS will give a warning to the driver for start of coast at these pre-defined locations. It should be noted, however, that some operational parameters are changing dynamically in real life. The train weights and the station waiting times, for instance, affect the energy consumption and the travel time. Authors are aware of staggering difficulties in finding optimum coasting points online for such operational variants. Nevertheless, the paper reveals the advantages of using ANN, and its possible application to optimization of coasting points for the case of multiple stations and multiple lines, and hopefully paves the road for future research in this direction. Keywords: Mass rail transit, energy efficiency, coasting, artificial neural networks, optimization.
Seismic response of isolated upright cylindrical liquid storage tanks with the Friction Pendulum System
Get PDFLiquid storage tanks are considered as critical elements of infrastructure systems. These structures are mainly used to store fuel, industrial chemicals and water. Failure of fuel or industrial storage tanks following earthquakes may result in substantial environmental and financial damages (Jaiswal et al., 2004), (Koller and Malhotra, 2004). Studies on the seismic response of tanks show that the bottom portion of the contained liquid moves in unison with the tank while the portion near the free surface oscillates with a long period sloshing motion. Dynamic models built on this principle make the assumption that the continuous liquid media can be represented with two components: a short period impulsive component and a long period convective component responsible for the sloshing motion. Impulsive component is predominantly responsible for the hydrodynamic pressures acting on the tank wall and foundation in ground supported liquid storage tanks. Field studies conducted by various researchers to investigate the seismic damage mechanisms of liquid tanks reveal that these structures generally perform poorly during earthquakes due to a lack of a substantial ductility mechanism that can dissipate large amounts of energy and that new methods should be developed to increase their performance. Seismic isolation is an example of these new methods that aim to protect the liquid storage tanks against earthquakes by increasing their energy dissipation capacity and by lengthening their vibration periods to decrease the hydrodynamic pressures generated by the short period impulsive component. Recently, the application of seismic isolation and energy dissipation systems has been extended to critical fuel, chemical and fire-fighting water storage tanks. Although there are only a few seismically isolated liquid storage tanks, the number is steadily increasing. However, information on the observed performance of isolated tanks subjected to strong earthquakes is very limited and currently there are no provisions for these structures in the current tank design codes. Sloshing phenomena and the nonlinear behavior of seismic isolation components which have mechanical characteristics that are subject to change due to aging, environmental and loading conditions etc. complicate the design of both the tank and the seismic isolation system. Therefore, there is a growing need to develop new methods and tools to design and evaluate seismically isolated tanks. This paper begins by outlining the mechanical analogue system to be used for calculating the overturning moment and the base shear in tank wall as well as the free surface displacements for an upright cylindrical tank with rigid walls subjected to a horizontal base excitation. Force-displacement characteristics of the friction pendulum bearings were modeled with the Bouc-Wen hysteresis model. The effect of variation of friction on the response of the upright cylindrical liquid storage tanks has been investigated through a parametric study, which was conducted using a script that utilizes the Matlab state-space solvers. Aforementioned Matlab script also has the capability to generate normalized plots of the results of the parametric analysis in order to facilitate the design of the seismic isolation system and the estimation of the forces and moments to be used in tank design. Parametric approach to selection of seismic isolation system parameters and the calculation of tank design forces was explained through a case study. The liquid tank used in the case study has a radius of 42 m and is filled with LNG up to 36 m. Friction pendulum bearings used in this study had curvatures of 1m, 1.55 m and 2.23 m. The range of coefficient of friction at the slider interface used in the analysis varied between 0.03 and 0.08. Although, the use of a single convective mode is usually sufficient for most design applications, five convective modes were used in this study to capture the interaction between the long period sloshing component and the isolation system. Damping provided by the liquid storage tanks is usually very limited. Even though a single acceleration record (Scaled Erzincan 1992 EW (0.6g)) was used in this example, this approach can easily be adapted to handle multiple earthquake acceleration records. Tank design forces were decreased in the order of 50% with a slight increase in the freeboard height. In general, seismic isolation of liquid storage tanks with friction pendulum bearings was found to be an effective method for decreasing hydrodynamic effects in liquid storage tanks. Keywords: Seismic isolation, Friction Pendulum System, liquid storage tanks.Sıvı depoları; başlıca yakıt, endüstriyel kimyasallar, kullanma ve yangın söndürme suyu depolamakta kullanılan önemli mühendislik yapılarıdır. Sıvı depolarını depremin zarar verici etkilerinden korumayı hedefleyen yeni tekniklerden biri de sismik yalıtımdır. Sismik yalıtım sistemleri yardımıyla sıvı depolarının sönüm kapasitelerinin arttırılması ve periyot uzaması etkisiyle depo içerisinde dabesel bileşenden kaynaklanan hidrodinamik etkilerin azaltılması amaçlanmaktadır. Ancak, sistem bileşenlerinin doğrusal olmayan davranışı, mekanik özelliklerinin çevre koşulları, yaşlanma, yükleme koşulları vb. nedeniyle zaman içerisinde değişimi ve depo içerisindeki çalkalanma hareketi, depo ve sismik yalıtım sisteminin tasarımını zorlaştırmaktadır. Bu çalışmada sürtünmeli sarkaç sistemine mesnetlenen düşey silindirik sıvı depolarının yalıtım sistemi parametrelerinin seçimi ve boyutlandırmada kullanılacak kuvvetlerinin hesaplanması için bir yöntem önerilmiştir. Bu kapsamda, deponun hizmet süresince sismik yalıtım sistemi elemanlarının mekanik özelliklerinde oluşabilecek değişim ve bunun depo tasarımına yansıyacak özellikleri parametrik olarak değerlendirilmektedir. Sürtünmeli sarkaç mesnetleri Bouc-Wen modeli ile modellenmiştir. Düşey silindirik sıvı depolarında hidrodinamik etkilerin hesaplanmasında Veletsos tarafından geliştirilen model kullanılmıştır. Sismik yalıtım sistemi bileşenlerinin mekanik özelliklerinin, zaman içerisinde çevresel etkiler nedeniyle değişiminin, depo tasarım parametreleri üzerindeki etkilerini değerlendirmek amacıyla MATLAB üzerinde çalışan bir yazılım geliştirilmiştir. Söz konusu yazılım tarafından üretilen grafikler kullanılarak tasarımda izlenen yöntem, bir örnek üzerinde açıklanmıştır. Sürtünmeli sarkaç sisteminin depo tasarım kuvvetlerini önemli ölçüde azalttığı, çalkalanma yüksekliğinde ise bir miktar artışa neden olduğu görülmüştür. Anahtar Kelimeler: Sismik yalıtım, sürtünmeli sarkaç sistemi, sıvı depoları
Basin edge effect on dynamic response of soil layers: 1D and 2D behaviour
Get PDFSurface geology and the geotechnical properties of near surface soil layers have important effects on the earthquake ground motion. Site effects can be defined as the variation in the characteristics of incoming wavefield such as amplitude, frequency content and duration because of the geotechnical, dynamic and geometrical properties of soil layers and surface topography. The main source of site effects is the specific impedance contrast between near surface and deep soil layers. The calculation methods which were developed for the dynamic analysis of soil layers are defined as one, two and three dimensional. In one dimensional approach the soil medium is assumed as horizontally layered for simplicity and the analyses are based on the principal of body waves travelling up and down in the near surface layers. However, in fact sedimentary deposits form mediums which can only be defined by 2 or 3 dimensional methods. This kind of deposits with lateral geological discontinuities show trap behaviour. This trap affects the surface waves which develop during earthquakes and reverberate back and forth on the interface of sediment deposit and bedrock. As a result, the amplitude of surface ground motions may show variation dependent on the site where it occurs, also the frequency content of this surface motion will differ from site to site at the edge of deep deposits. In this paper, two dimensional basin edge models with four different slope values (H/D=10, 5, 2, 1) were constituted to investigate the effects of basin edge on the variation of surface motion under earthquake excitations with different frequency content. Duzce basin shear wave velocity profile, which had been obtained from the analyses of microtremor array and single point measurements, was used to form the two dimensional geometry of soil layers and bedrock in the basin edge models. One (1D) and two dimensional (2D) dynamic analyses were performed for six different bedrock acceleration records by using these basin edge models. The results which would be obtained from the 1D and 2D analyses were aimed to reflect the seismotectonical structure of the faults in Turkey. Therefore four bedrock acceleration time histories were selected among the Turkey earthquakes. In order to eliminate the "box effects" which can occur during the two dimensional dynamic finite element analyses because of the model geometry and boundary conditions; viscous dashpots, which are calculated proportional to the shear and pressure waves of the relevant layers, were put at the vertical and horizontal layers. Modified equivalent linear method and equivalent linear methods were used in the 1D and 2D analyses respectively. After performing 1D and 2D dynamic analyses on the models, the calculated results were compared. The variations of the soil amplifications and acceleration spectrum intensity (ASI) values with the distance from the valley edges were investigated. To understand the difference between 1D and 2D dynamic behaviours, the 2D/1D spectral acceleration ratios which are known as "aggravation factors", were calculated for different period values. Remarkable increase in soil amplification, ASI and aggravation factors was observed between the rock outcropping site and X/D=3 point at basin edges. The highest aggravation factor values were obtained at 0.2 sec-0.5 sec interval for all valley models, also especially for models with H/D= 2 and 1 these values reached to peak. Regardless of the periods considered, the aggravation factors generally converged to 1 after the points X/D=5, 4, 2, 1.5 for the basin models with H/D=10, 5, 2 and 1 respectively. The 2D effects were mostly becoming negligible after these points. After this, the acceleration time histories and absolute acceleration spectrums which had been evaluated for the different points on edge surface were considered statistically and the relation between the results of 1D and 2D dynamic analyses was investigated by calculating aggravation factors for different period values. After evaluating the aggravation factors for different periods statistically, an aggravation factor relation was defined for the basin edge models with different edge slope values. It was revealed that by using the 2D/1D aggravation factor relation, the limiting effect of the second dimension at basin edges can be reflected to the spectral accelerations evaluated from the results of one dimensional dynamic analysis, as a function of the distance from rock outcrop site and seismic bedrock depth. Also the X/D values, which the aggravation factors can be neglected after, were determined. Keywords: 1D and 2D dynamic analysis, aggravation factor, ASI, basin edge effect.Deprem sırasında oluşan yer hareketinin genliğinde, frekans içeriğinde ve süresinde incelenen bölgeye bağlı meydana gelen değişimlere “yerel etkiler” denir. Yerel etkiler; başlıca, yüzeydeki zemin tabakalarıyla daha altta yer alan anakaya arasındaki özgül direnç farklılığından kaynaklanmakla birlikte, ova/vadi gibi derin oluşumlar ile bunların kenarlarında yanal jeolojik süreksizlikler tarafından meydana getirilen etkileri de kapsar. Yanal süreksizliklere sahip bu tür ortamlarda zemin tabakalarının yatay yönde sınırlı genişliğe sahip olması, vadi kenarlarında dalga hareketi dönüşümlerine sebep olmakta ve kuvvetli yer hareketinin süresi uzayabilmektedir. Bu tip durumlarda, yüzeydeki hareketin genliği ova/vadi üzerinde elde edildiği bölgeye göre değişim gösterecek ve frekans muhtevası aynı bölgede bir boyutlu analizle hesaplanana göre farklılaşabilecektir. Bu çalışmada, iki boyutlu kayma dalgası hızı profili geniş açıklıklı eş zamanlı mikrotremor ağ ve tekil mikrotremor ölçümleriyle belirlenmiş olan Düzce Ovası modelinde, kenardaki anakaya eğiminin değişmesi halinde farklı frekans içeriğine sahip deprem hareketleri karşısında yüzey hareketinin nasıl etkileneceği anlaşılmaya çalışılmıştır. Bu amaçla, modellerde farklı noktalar için bir (1D) ve iki boyutlu (2D) dinamik analizler yapılmış, ova kenarındaki zemin büyütmelerinin ve şiddet parametrelerinin geometriye bağlı değişimi incelenmiş, ova kenarındaki kısımlar için 2D/1D spektral ivme oranları (şiddet faktörleri) hesaplanmıştır. Farklı periyotlar için hesaplanan bu değerlerin istatistiksel açıdan değerlendirilmesiyle, farklı anakaya eğimine sahip modeller için ova kenarındaki anakaya mostrasından olan uzaklığa ve sismik anakaya derinliğine bağlı şiddet faktörü ilişkisi tanımlanmış ve bir boyutlu dinamik analizin yaklaşık geçerlilik sınırları belirlenmiştir. Anahtar Kelimeler: 1D ve 2D dinamik analiz, kenar etkisi, şiddet faktörü, yerel etkiler, zemin büyütmesi
Synthesis, production and characterization of soda-lime photosensitive glasses
Get PDFIşığa duyarlı camlar, özel bir bileşime sahip olup mor ötesi (UV-ultraviolet) ışın yardımıyla çeşitli renklerin elde edildiği camlardır. Işığa duyarlı cam, cam harmanının hazırlanması, elde edilen camın geleneksel yöntemlerle şekillendirilmesinin ardından içeriğinde bulunan elementlerin UV ışınının aktinik özellik göstererek camın mikroyapısında değişikliklere neden olmasıyla elde edilmektedir. Cam içeriğinde bulunan kolloid metal olan gümüşün, cam içerisindeki boyut ve dizilimine bağlı olarak, camın saydam ya da opak olması sağlanabilmektedir. Bu çalışmada daha önce patenti alınan ana cam kompozisyonu olarak sodyum silikat yerine, soda-kireç camı seçilmiş ve camın ticari olarak üretilme olanağı incelenmiştir. Ayrıca, ışığaduyarlı camların kompozisyonunda ana camı renklendirmeyecek miktarda Ho2O3 eklenmesinin etkileri irdelenmiştir. Mevcut ticari kompozsiyonuna gümüş, alkali oksit, florür ve klorür, bromür ve iyodür grubundan en azından birini içeren ve Ce2O3 kullanımıyla 2000 W gücünde UV ışın kaynağı kullanılarak bu ışının aktinik radyasyon etkisi gösterdiği camın üretilmesi ve farklı oranlarda holmiyum oksit eklenmesiyle cam üzerindeki ve fotokimyasal süreç sonrası spektrometrik etkisi incelenmiştir. Ho2O3 eklenmesi ile cama fotokimyasal proses uygulaması ardından numunelerde beklendiği gibi, görünür bölgede fazla değişim olmamasına karşın yapıda değişim olduğu belirlenmiştir. Bu çalışmada, cam kompozisyonunun sodyum silikat matrisinden soda-kireç-silis cam matrisine modifiye edilmesi ve fotokimyasal proses aşaması için geliştirilen UV lamba sisteminin kullanımı ile Ho2O3 içeren camlara ışığa duyarlılık özelliği verilmiştir. Anahtar Kelimeler: Işığa duyarlı cam, renklendirme, optik karakterizasyon.For centuries, as an attractive feature in glass design, colour is one of the most important factors in glass production. Coloured glasses have always taken a special place in the assortment of every glass producer and for their production different methods have been developed Photosensitive glasses, which have special compositons, can be produced in a variety of colours with the help of UV (ultraviolet) radiation After preparing the glass batch, the melting and glassification are carried out by applying conventional methods. In a second step, with the help of special materials in the recipe, the actinic radiation applied changes the microstructure of the glass. The resulting glass becomes photosensitive. Depending on the size, shape and orientation of colloidal metal particles, such as silver, the transparency of glass can be controlled and even opaque materials can be obtained. Photosensitive glasses have sodium silicate base glass composition, are known in various colors in opal or transparent form for many years ever since they were patented in 1977. These have been produced by applying conventional methods. They contain alkali halide silver (AgX), alkali oxide, fluorine, and at least one of the following substances: chlorine, bromine or iodine. Later on they are exposed to high energy or actinic radiations followed by a unique heat treatment. However, because of the instability within the end product and having a slow reaction rate, this product has never been commercially feasible, its applications have always been limited. At the beginning of the experiments, the glass batches to produce photosensitive glass were prepared by adding glass forming oxides, silver, alkali oxides, cerium oxide, antimony oxide, tin oxide, fluoride, chloride, bromide and iodide. These batches were then melted following the conventional method of glass production. The glass samples were exposed to UV (ultraviolet) radiation at room temperature. This was followed by a first heat treatment and a second UV exposure. Finally, a second heat treatment was applied after which samples were left in the furnace to cool down to room temperature. This photochemical process was carried out in a specially designed temperature-controlled box that was equipped with a UV lamp. Depending on the UVexposure time and the heat treatment temperature, a variety of colours can be produced with this photochemical process. The present study shows the effects of addition of Ho2O3, for the first time in literature. Optical characterization has been also performed before and after UV exposure. In this study, a soda lime silica glass composition was chosen instead of sodium silicate in order to produce a commercially more feasible glass. The photosensitive glasses were designed by adding the following substances: silver as sensitizer and colorant, Sb2O3 as thermal sensitizer, SnO as redox and refining agent, CeO2 as optical sensitizer, and compounds of alkali halides with Na and Ag ions to form a crystalline structure. Photosensitive glasses have been produced in laboratories for over 30 years but at very high costs and without having been able to achieve the necessary stability. The aims of this study can therefore be described as; the modification of base glass in soda lime silica glass matrix, the optical characterization of the final product, the development of a new system for the photochemical process to be used in mass production, evaluating the effect of Ho2O3, on glass in visible range. Beside these, gaining knowledge on nature of photosensitivity before and after photochemical process studied. Despite its low absorption in the UV region, the effect of Ho2O3, on the properties of photosensitive glasses was also studied. The amount of holmium oxide was chosen so as to keep base glass colourless and was determined experimentally. The effects of changing the amount of holmium oxide on the photosensitivity of glass composition were also determined. Furthermore, the relationship between the photochemical process and the time and temperature of the heat treatments were examined for all compositions that were used in this study. By modifying chemical composition and using inhouse UV lamp system, photosensivity can be reached in soda lime silica glass matrix.The results showed that modification of soda-lime-silica composition with doping minor amount of holmium oxide cause small change in resultant color. However, result of solar degredation can be minimized by the help of applied photochemical process. It is expected that with increasing amount of Ho2O3 above 0.06 % level this effect is predominant. Keywords: Photosensitive glass, colored glass, optical characterization
Investigation of the climate change effects on wheat yield: Kırklareli Case
Get PDFBitki-Toprak-Atmosfer arasındaki karmaşık süreç, bu süreci yöneten meteorolojik faktörlerin etkisi altında gerçekleşmektedir. Söz konusu etkinin olası sonuçlarının öngörülebilmesi, bitki gelişimi ve verimi açısından da önemlidir. Bu sebepten, tarım ve orman meteorolojisi alanındaki araştırmalar, son yıllarda özellikle iklim değişikliği üzerine yoğunlaşmaktadır. Dünyadaki uygulamaların izlenerek, karşılaşılan sorunların ve çözüm seçeneklerinin araştırılması, tarımın önem taşıdığı Türkiye için de gereklidir. Trakya, yüksek tarım potansiyeli ve sanayi bölgelerine yakınlığı nedeniyle fenoloji ile kuraklık bakımından araştırılması gerekli bir bölgedir. Bu çalışmada, buğdayın olası iklim değişiminden etkilenme durumu, Trakya Bölgesi’nde kışlık buğday tarımının yapıldığı illerden Kırklareli’nde açıklamalı bir bitki-iklim simulasyon modeli (CERES-Wheat) kullanılarak incelenmiştir. Model 1975-2005 arası ortalama gelişme dönemleri için buğday dane verimini %3.1’lik bağıl hata ile tahmin etmiştir. Bunun ardından model girdi altyapısı, sırasıyla hassasiyet analizleri ve iklim değişimi senaryoları için düzenlenerek simulasyon sonuçları analiz edilmiştir. Yağışın %40 azalması durumunda verim %38.4 düşmektedir. Buğday, sıcaklık artışlarına da olumsuz verim tepkileri vermektedir. Karbondioksit (CO2) konsantrasyonundaki artışların verimi artırıcı etkisi dikkat çekmektedir. CO2x2 uygulamasının verimi %10.5 artıracağı öngörülmüştür. Birden fazla meteorolojik parametrenin birlikte değiştiği simulasyonların verime etkisi de fazlalaşmaktadır. 2071-2100 arası dönemin senaryo sonuçları, ortalama buğday veriminin Kırklareli’nde %9 oranında artış göstereceğine işaret etmiştir. Bu artış, ekstrem sıcak gelişme dönemi (2099-2100) için ortadan kalkmaktadır. Ekstrem kurak gelişme döneminin (2085-2086) verim değeri ise 1975-2005 ortalamasının %65’ini karşılayabilmektedir. Buğday genelde CO2 artışlarına en olumlu verim tepkilerini vermiş, tersi durum ise yağış azalışı için belirlenmiştir. Anahtar Kelimeler: İklim değişimi, bitki-iklim modeli, hassasiyet analizi, kışlık buğday, Trakya.The Thrace Region is located in The European part of the northwestern Turkey, which is responsible for a considerable portion of rice, sunflower and winter wheat productions of Turkey. Winter wheat (Triticum Aestivum L.) production rate in Thrace is generally higher than that in the rest of Turkey. However, there is not enough qualified study on the effects of drought and possible climate change on the region’s agriculture. The dynamics and complex structure of the plant growth are under the influence of many factors which are out of human control. Meteorological parameters are the dominant ones among these factors. Hence, reliable research studies are to be conducted from the agricultural meteorological viewpoint. Using crop growth simulation models, possible effects of the variations in plant, soil and atmosphere on wheat development and yield can be estimated. In this study, the CERES-Wheat crop growth simulation model have been used for wheat during the years between 1975 and 2005 to take a first step for filling the gaps in the desired drought related research in the Kırklareli City, in which the winter wheat production is popular. At first, the average growing season have been determined by considering long term phenological data (3 November-22 July). Afterwards, the associated soil-and crop parameters have been supplied into the model database as well as the calculated daily average meteorological data (daily totals for precipitation). Average wheat grain yield was calculated as 2827 kg/ha by the model with an relative error of 3.1%. Model sensitivities to temperature, precipitation, global radiation and CO2 have been done by considering single and combined variations. The (Rg30%; CO2x4) combined application gave the highest yield increase response as 67.1%, where the opposite output was a 63.1% decrease for the (T+5;P-40%) application. Another step was the investigation of the development and yield reactions of the crop to the IPCC A2 scenarios from 2071 to 2100. To achieve this, model database used daily output from the RegCm3 Regional Climate Model by considering the associated field coordinates. The model showed a 9% increase in winter wheat grain yields during the mentioned time interval. It has been determined that the winter wheat yield was sensitive especially to variations in T and CO2.This study represents a part of the PhD named “Determination of the Agrometeorological Properties of the Thrace Region”, in which additional cities (Edirne and Tekirdağ) have been investigated from the point of wheat production.30% yield increase has been simulated for Edirne, while a 13% decrease was expected for Tekirdağ during the averaged 2071-2100 growing period. Rice production has been also estimated for Edirne with a decrease of 53%. RegCm3 data were also arranged and adapted into CERES meteorology files to enable model runs for the hottest and driest growing seasons for the 2071-2100 interval. Moreover; three drought indices, namely the percentage of normal, z score and standardized precipitation indices have been calculated and interpreted for seasonal field crops (wheat, rice and sunflower) and forests (pine, oak and beech) during the years between 1975 and 2005 to take a first step for filling the gaps in the desired drought related research in the region. In general, dry periods were determined with low severities and continuities. Growing Degree Day (GDD) and vernalization calculations for field crops have been also applied. Among the average growing seasons in Kırklareli, the winter wheat collected 2893 GDD’s for 0°C base temperature. Same parameter was calculated as 2719 and 2639 for Tekirdağ and Edirne, successively. It has been calculated that the wheat needs 70 and more vernalization days to complete it’s average growth. Variations in the Normalized Difference Vegetation Index (NDVI) on the agricultural and forest areas were also estimated using the satellite data. Furthermore, correlations of the drought indices with the GDD’s and NDVI’s were investigated. Highest average NDVI values were calculated for the flowering periods of wheat (NDVI=0.45) and rice (NDVI=0.50), consequently. June showed the highest mean NDVI’s for pine (NDVI=0.4), oak and beech (NDVI=0.65) when the forest areas were considered. Some growing periods showed nearly linear correlations between SPI and NDVI, while this was not the case when the whole growing periods were considered. On the other hand, high nonlinear relationships between NDVI and BDG were estimated for both field crops and trees. Keywords: Climate change, crop growth simulation model, sensitivity analysis, Winter wheat, Thrace
Dynamic analysis of overhead crane beams under moving loads
Get PDFBu çalışmada, üzerinde hareketli yükler bulunan köprülü kren kirişlerinin dinamik davranışını belirlemek amacıyla bir Berneuolli-Euler esnek kiriş sistemi incelenmiştir. Bilgisayar analizi SAP 2000 programında modelleme yapılarak gerçekleştirilmiştir. Dinamik analizlerde Newmark doğrudan zaman integrasyonu metodu ve oransal sönümleme tercih edilmiştir. Yükün hareket hızının ve kiriş kütlesine olan oranının farklı değerleri için kirişin dinamik davranışı diyagramlarda verilmiştir. Kren kirişlerinin dinamik davranışı, üzerindeki hareket eden yükün hareket hızına ve kütlesine bağlı olarak değişmektedir. Hareket eden yük, kiriş sisteminin tabii titreşim frekansını değiştirmekte ve yük kiriş üzerinde ilerlerken kiriş sistemi farklı titreşim yapmaktadır. Yükün hızı arttıkça maksimum yer değiştirmenin oluştuğu yer, kiriş orta noktasından ileriye gitmektedir. Bazı hız değerleri için maksimum nokta orta noktanın gerisinde de olabilmektedir. Kirişin hareketi dinamik olduğundan bazı durumlarda, yük statik olarak maksimum yer değiştirme oluşturacak orta noktada iken, kirişin hareketinin zıt yönde olabilmesiyle orta noktada maksimum yer değiştirme oluşmamaktadır. Kren kirişlerinin tasarımında verilen kiriş uzunluğuna göre kiriş orta noktasının yer değiştirme miktarının tasarım açısından yeterli olamadığı gösterilmiştir. Maksimum noktanın kiriş üzerinde sabit bir yerde oluşmamasından dolayı kiriş üzerinde hafif konstrüksiyon veya diğer nedenlerle oluşturulan kesit süreksizlikleri yüksek hızlarda çalışması düşünülen krenlerde risk oluşturmaktadır. Ağır şartlarda hızlı çalışacak krenlerin hizmet ömrünün belirlenmesi için tasarım aşamasında kren kiriş sisteminin dinamik davranışının hassas olarak belirlenmesi zorunludur. Kaldırılacak yükün miktarı ve arabanın hızı, taşıyıcı kiriş sisteminin dinamik özellikleri dikkate alınarak yapılacak hesapların daha doğru olacağı gösterilmiştir. Anahtar Kelimeler: Köprülü kren kirişleri, hareketli yük, dinamik davranış.In this study dynamic behavior of Overhead Crane beams is investigated. A Bernoulli-Euler thin beam under moving (carriage) load is studied. Computerized analysis was carried out in SAP 2000. Moving load or loads are applied to the system by lanes which can be determined on the geometry of beam structure. For frame finite elements this lane is placed on the axis of the beam and goes parallel to throughout whole length of the beam. For shell, area and solid elements lane or lanes can be determined on the upper plates of the beam structure. The computer program allows obtaining time history analysis for very short time interval. In the dynamic analyses linear transient direct integration method called Newmark method was used. Structures under moving loads have been studied for more than a hundred years. Early studies were made by some scientist who studied on dynamic behavior of railway bridges and motorway bridges. The need of high speed transportation, aviation and sky studies and high speed precision machining studies increases the importance of the subject. Beside deflections due to self weight of the beam and the static effect of moving load on it, it is obvious that dynamic deflections occur due to interaction of moving load and the beam vibration. The total deflection may be much higher than static deflection. Analysis carried out the mass ratios (mass of the load/mass of the beam m/M) 0.2, 0.5, 0.8 and for load velocities of 0.01, 0.5, 1.25, 2.5, 4, 5 and 6.25 m/s. Dynamic response of the beam was obtained depending on the mass ratio of the load to the mass of the beam and the velocity of the load. Dynamic response of crane beams depends on velocity and mass of moving load. Since the position of the moving mass on the crane beam changes, it causes changes in the natural frequency of the system. While the load moving, depending on the position of the mass of load the vibration of the system varies. Generally, if the velocity of the load increases, the position of the maximum response on the beam occurs far from the midpoint. At very high speeds the maximum deflection of the beam occurs close to the end of the beam. For some values of the velocity the maximum response may occur before the middle of the beam. Dynamic response of very slow carriage velocity of 0.01m/s is, with an error in a thousand, very near to static deflection of the beam when the carriage is at the middle of the beam. At very slow speeds maximum deflection of the beam occurs near the middle of the beam because the system reduces to a quasi-static solution. For same mass ratio when the velocity of the load increases, the deflection of the beam goes higher. The dynamic behavior of the beam is more affected from the velocity of load than mass ratio of the system. Since the maximum point is not at a definite point throughout the beam length, every section on the whole length of the beam may be under high stress. For light construction or other needs in the design of the crane beams there can be desired section discontinuities. But, if an overhead crane will run at high speeds, the section discontinuities of the beams may cause risk of destruction. It is very important to determine dynamic behavior of beam system of overhead cranes which is desired to use at heavy condition. Generally, today to avoid uncontrollable vibration, overhead cranes work at very low speeds and the design of these cranes is made due to FEM (Federation Europenne de la Manutention) and DIN (Deutsches Institut für Normung) standards. To eliminate dynamic effects some magnification constants are used. Usage of above mentioned standards in designing of high speed crane beams will be insufficient. Global competition and serial service needs will direct manufacturers to build high speed cranes and it is necessary to define dynamic effects of high speed motion of carriage on the crane beams. This work aims to study dynamic behavior of overhead crane beams under moving loads and to give engineers some idea in the design of crane beams. It is showed that carrying analysis in terms of only the midpoint deflection or midpoint stresses in engineering calculations of the beam systems is insufficient. Taking into account the mass and velocity of the moving load and dynamic properties of carrying system in dynamic analysis brings out more accurate results. Keywords: Overhead crane beams, moving loads, dynamic response
An inverse problem related to an arbitrarily shaped impedance cylinder buried in a dielectric cylinder
Get PDFTers saçılma teorisinde yanına yaklaşılamayan cisimlerin fiziksel özelliklerinin belirlenmesi önemli bir araştırma konusu olarak bilinmektedir. Bu çalışmada, iki boyutta keyfi bir şekle sahip dielektrik silindir içerisine gömülü keyfi şekilli bir cismin üzerinde tanımlanan inhomojen empedans fonksiyonunun saçılan elektromagnetik alan verisinden yararlanılarak bulunması için sınır integral denklemlerin çözümüne dayanan bir metod önerilmiştir. İntegral denklemler bir potansiyel yaklaşımı altında türetilmiştir. Bu bağlamda saçılan ve toplam alanlar, içerisinde kaynak (yoğunluk) ve Hankel fonksiyonları içeren integral gösterilimler şeklinde tek-katman potansiyelleri ve bunların kombinasyonları kullanılarak ifade edilmiştir. Fiziksel olarak tek-katman potansiyelleri üzerinde monopollerin bulunduğu bir katmana karşı gelmekle beraber homojen Helmholtz dalga denklemini ve Sommerfeld radyasyon koşulunu sağlar. Problemin çözümünde dielektrik silindirin içerisindeki ve dışarısındaki aynı türden magnetik özellik gösteren basit ortamlara ait dalga sayılarının, silindirlerin şekillerinin ve yakın/uzak saçılan alan verisinin bilindiği varsayılmıştır. Empedans fonksiyonunun bulunabilmesi için her bir bölgedeki elektromagnetik alanların hesabına yönelik yeni bir algoritma sunulmuştur. Saçılan alandan saçıcıların üzerinde tanımlı yoğunluk fonksiyonlarının kararlı ve yaklaşık çözümlerini elde edebilmek amacıyla kötü-kurulmuş integral denklemler Tikhonov anlamında değerlendirilmiştir. Yoğunluk fonksiyonlarının bulunması, dielektrik silindir içerisindeki toplam alanı hesaplanabilir kılmış ve uygun sıçrama koşulları altında empedans fonksiyonu empedans sınır koşulundan en küçük kareler yöntemi ile elde edilmiştir. Önerilen metodun uygulanabilirliği ve etkinliği nümerik deneylerle test edilmiş ve başarılı sonuçlar elde edilmiştir. Anahtar Kelimeler: Ters saçılma, empedans sınır koşulu, sınır integral denklemleri. Main research areas of inverse scattering theory is the reconstructions of geometrical (location and shape) and / or physical (dielectric permittivity, conductivity, impedance etc.) properties of inaccessible obstacles from the knowledge of the scattered waves (electromagnetic, acoustic, elastic etc.) at large distance. Radar / sonar applications, medical tomography, geophysical exploration and non-destructive testing lead to this type of problems. Motivated by the applications researchers proposed different types of solution methods for the mentioned problems especially after the II.World War. Impedance boundary condition is used to simplify scattering problems involving complex structures. Such that in electromagnetics, imperfectly conducting scatterers, perfectly conducting objects with a penetrable or absorbing boundary layer can be modeled by an impedance boundary condition. In this context, one can study with a simpler model for complex typed structures. The aim of the direct scattering problem for an impedance cylinder is to obtain scattered near- or far-field data for given shape of the cylinder, the impedance function and the wave number of the background medium in the case of an electromagnetic wave illumination. However in the inverse problem case one recovers the impedance function defined on the cylinder from the knowledge of scattered field, shape of cylinder and wave number of the host medium. In this study, we considered an inverse scattering problem for arbitrarily shaped cylindrical objects that have inhomogeneous impedance boundaries and are buried in arbitrarily shaped cylindrical dielectrics. This consideration is realistic, since the problem will have many possible practical applications. For example, in the non-destructive testing of a coating on a wire; the coating is characterized by an inhomogeneous lossy cylinder layer and the conducting wire is modeled by an inhomogeneous surface impedance, or in biomedical applications; the bone of the arm can be modeled in terms of an impedance boundary condition while the muscular structure over it, can be considered as an inhomogeneous lossy cylindrical layer. For the sake of brevity we assume cylinders are infinitely long and illuminated by a TM polarized electromagnetic wave whose electric field vector is always parallel to -axis. Due to the symmetry and homogeneity along the -axis the total electric field vector will be polarized both inside and outside of the cylinder parallel to the -axis. Then the problem is reduced to a scalar one in terms of total fields that have to satisfy homogeneous Helmholtz equation. In order to determine inhomogeneous impedance function we have to reconstruct the field occuring in the interior domain of the dielectric cylinder. Therefore since layer potentials are the solutions of homogeneous Helmholtz equation and they satisfy Sommerfeld radiation condition we use a potential approach to represent fields in every domain via single-layer potentials. Then the far-field expression can be obtained from the asymptotic representation of the scattered field. We note that one can use these representations under proper assumptions for the wave numbers. Roughly speaking, layer potentials are the integrals defined over the boundary of the scatterers which contain Hankel and density (source) functions. In our problem we define two density functions on the boundary of the exterior cylinder and one density function on the buried obstacle. Afterwards, one of the densities on the exterior cylinder can be reconstructed from the solution of an ill-posed far-field equation with measured far field pattern as a data via Tikhonov regularization. The rest two unknown densities are found from the integral equation system obtained by using dielectric (transmission)conditions which ensure the continuity of the fields and their normal derivatives across the boundary of the exterior cylinder. However the compactness of the operators in the system expresses its ill-posedness. Therefore to obtain a stable solution of the system for the densities we apply Tikhonov regularization. Now one can read off the values of the impedance function by substituting interior total field values to the standard impedance boundary condition using jump relations. However, the reconstruction of the impedance function will be sensitive to errors. In order to obtain stable reconstructions we express the unknown impedance function in terms of basis functions and apply least squares approximation. Furthermore, we test the applicability and the effectiveness of our inversion method with noisy data and obtain satisfactory numerical results as illustrated in the last section of the paper. Keywords: Inverse scattering, impedance boundary condition, boundary integral equations
A videogrammetric system design
Get PDFThe testing and monitoring of structures and structural components under different loading conditions are a standard engineering application. Geometrical measurements are performed for the examination of the behavior of test objects and for the verification of theories or mechanical models. This is often realized by static, quasi-static, or dynamic short and long time load experiments on test objects. In these tests, it is demanded to determine parameters and effects such as the changes in shape, load and strain which are commonly measured by LVDTs, extensometers and strain gauges. These devices provide on-line results with a high geometric precision and reliability. A general disadvantage of these techniques, however, is their point wise and only one-dimensional measurement capability. The techniques are generally not suited for tasks requiring a large number of measurement points distributed over an object surface or for complete surface measurements. In these cases, techniques of digital photo-grammetry depict a valuable option for the design of powerful and flexible measurement tools. However, while the measurement of the absolute coordinates and the movement of signalized targets on an object can be solved by commercial software packages, non standard monitoring tasks or applications with real time or near real time requirements will often necessitate the development of customized software tools. In this study, a videogrammetric system is developed to measure the coordinates of signalized targets on structural components during both dynamic and static load tests. After the system calibration, the entire process from acquisition multi image sets to computation of 3D object coordinates are solved by the system at almost real time. The system consists of two basic components: hardware and software. The software which was developed by using Borland C++ builder programming language presents many functions such as acquiring images, locating targets and calculating their centroids, converting target centroids to spatial coordinate in object space, and computing displacement. The hardware component of the system comprises of 3 Basler A302fc video cameras, PCI IEEE-1394 interface card, connecting cables and calibration object. The entire measurement process is realized as a two-stage process which are a preliminary offline phase and online photogrammetric triangulation process. Offline photogrammetric processing stage includes system calibration which is defined as the calibration and orientation parameters of all the components involved in the acquisition system and a zero measurement. Camera calibration refers to the determination of the parameters describing the internal geometry of the individual imaging devices and other parameters modeling the systematic errors caused by the optical system and other sources. Camera orientation includes the determination of the parameters of exterior orientation to define the camera station and camera axis in the 3D space. After orientation procedure, it is required that the cameras ought to stable during the entire measurement process. For zero measurement, images of the test object on which the signalized targets are placed are acquired firstly. Then, the image coordinates of all targets are measured with sub-pixel accuracy automatically via intensity weighted centroiding. Afterward, matching process is implemented to establishment of correspondences in the multi-images. Finally the 3D coordinates of the matched points are computed by forward ray intersection using the results of the calibration process. The main aim of on-line data processing was the determination of the displacement values at each measurement epoch associated with the current loading. Online photogrammetric processing stage is composed of three steps as follows: the simultaneously acquisition of multi-image sets of the structural element at defined time intervals or after load applications; the measurement of the image coordinates of targets which are labeled in the zero measurement and computation of the 3D coordinates of the points whose image coordinates are measured. The system was used for unconfined compression tests in order to demonstrate the functionality of it and measurement results obtained from two different systems obtained were compared. This study has been shown that the developed system was successfully employed to determine the displacement measurements in structural components during loading tests. The achieved average theoretical precision is about 16 microns in the X and Z directions and about 62 microns in the Y direction. The RMS value of image co-ordinate residuals which are important quality indicators was determined between 0.02 and 0.05 pixel. Keywords: Videogrammetric systems, displacement measurements, image matching, calibration.Bu çalışmada, yapı elemanlarının dinamik yük deneylerinde yer değiştirmelerin izlenmesinde kullanılmak üzere videogrametrik bir sistem tasarımı yapılmıştır. Sistem, yazılım ve donanım olmak üzere iki bileşenden oluşmaktadır. Borland C++ builder programlama dili kullanılarak geliştirilen yazılımda, video kameralardan görüntü alma, hedef görüntülerin resim koordinatlarını piksel altı doğrulukta ölçme, görüntü eşleme ve ek parametrelerle demet dengelemesi gibi birçok fonksiyon sunulmuştur. Sistemin donanım bileşeni ise, üç adet Basler A302fc video kamera, PCI IEEE 1394 arabirim kartı, bağlantı kabloları ve kalibrasyon cismini içermektedir. Sistemin ölçme prensibi kısaca, kamera parametre ve konum bilgilerinin belirlendiği sistem kalibrasyonu ve sonra tanımlanan zaman aralıklarında ya da yükleme sonrası, sabit kamera konumlarından yapı elemanı üzerindeki ilgili noktaların üç boyutlu koordinatlarının uzaysal ileriden kestirme dengelemesiyle hesaplanması ilkesine dayanır. Görüntülerin elde edilmesinden yapı elemanı üzerindeki işaretli noktaların 3 boyutlu koordinatlarının hesaplanmasına kadar bütün işlem adımları gerçek zamana yakın biçimde sistem içerisinde çözülebilmektedir. Test edilmesi amacıyla sistem, zemin numunelerinin serbest basınç deneylerinde kullanılmış ve ölçme sonuçları, deney aletinden okunan ölçme değerleriyle karşılaştırılmıştır. Geliştirilen sistemle gerçekleştirilen fotogrametrik değerlendirmelerde, her bir deney için resim koordinat düzeltmelerinin karesel ortalama hata değerleri, 0.02 pikselle 0.05 piksel aralığında elde edilmiştir. Cisim koordinatlarının ortalama prezisyonu ise X ve Z doğrultularında 16 μm, Y doğrultusunda, 62 μm olarak hesaplanmıştır. Anahtar Kelimeler: Videogrametrik sistem, yer değiştirme ölçmeleri, görüntü eşleme, kalibrasyon
Evaluation of CO2 reduction strategies on pas-senger cars
Get PDFBu çalışmada önerilen hedef programlama modeli, binek otomobil üreticilerine yeni araç geliştirme veya mevcut araçlarının performanslarını iyileştirmeye yönelik stratejilerini oluştururken yol gösterecek niteliktedir. Modelin çalıştırılması neticesinde karar vericilere hedeflerine ulaşabilmeleri için araç portföylerinin hangi yakıt tipi, hangi motor tipi ve hangi egzoz tipi dağılımına sahip olmaları gerektiğinin yanı sıra ortaya koymuş oldukları stratejilerine yönelik de bir değerlendirme sunulmaktadır. Önerilen model, binek otomobillerde CO2 emisyon miktarını azaltma sorununa ait birbiri ile çelişen tüm hedefleri ve kısıtları dikkate almaktadır. Modelde yer alan hedeflerin ağırlıkları ise bir çok kriterli karar verme yöntemi olan analitik ağ süreci (ANP – Analytical Network Process) yönteminin uygulanması neticesinde elde edilmiştir. ANP yönteminin kullanılması ile birlikte hedef programlamanın en zor adımlarından biri olan hedeflerin önceliklendirilmesi veya ağırlıklandırılması aşaması sistematik bir yaklaşım ile oluşturulmuştur. Diğer taraftan, hedef programlamanın kullanılması ile bütçe, toplam yakıt kullanım miktarı, toplam araç sayısı gibi kısıtlar da göz önünde bulundurularak ANP yönteminin önemli dezavantajlarından bir tanesi ortadan kaldırılmıştır. ANP ve hedef programlamanın birarada kullanılmasının en önemli nedeni de bu şekilde birbirlerinin zayıf taraflarını ortadan kaldırabiliyor olmalarıdır. Oluşturulan model için sonrasında duyarlılık analizi yapılarak farklı durumlarda sonuçların nasıl değiştiği de incelenmiştir. Önerilen model diğer araç ve hatta diğer sektörler için de söz konusu araç tiplerine veya sektörlere ait dinamikler göz önünde bulundurularak ve bu dinamiklere göre revize edilerek kullanılabilir. Anahtar Kelimeler: Çok kriterli karar verme, hedef programlama, ANP, CO2 emisyon salınım miktarının azaltılması.Climate change problem is being more and more important in the last decades and is one of the most important problems that humankind is facing. Climate change is the result of the global warming which is caused by the absorption of the sunlight by the greenhouse gases rather than deflection of it from the atmosphere. Intergovernmental Panel on Climate Change (IPCC), one of the leading organizations created by 2500 scientist from 150 different countries, makes research on climate change and states precisely that global warming depends to the greenhouse gases which results with human acts. Houghton et al. (1992) indicates that there is an increase of global warming with approximately 98% confidence level. On the other hand, it was stated with a confidence level greater than 90% that global warming is due to the greenhouse gases (Parry et al, 2007). Greenhouse gases are carbon dioxide (CO2) with very high amounts in atmosphere, nitrous oxide, nitrogen oxide, methane, water vapor, ozone, and chlorofluorocarbons. Therefore, it comes out during the Climate Change Conferences and within the publications that the effective targets for reduction of CO2 emissions have to be set-up immediately as from the developed countries. The climate change problem was examined via a detailed literature survey during this study. According to this survey, it has to be highlighted that the main reason of the climate change is due to the greenhouse gas effects and the energy sources which cause the production of the above mentioned greenhouse gases. The conflicting goals and constrains defined in accordance with survey results are making this problem more complex. That's why the scope of this study was limited with a specific application as defined in the following phrases. In the light of the literature survey results on CO2 emission reduction, it comes out that each sector has its own dynamics to reduce CO2 emissions. Therefore, the application area of this study is limited with a special sector to ensure more effective, sensitive, and robust proposals to solve this real problem. The scope of this study was identified as CO2 emission reduction on transportation sector. When the transportation sector was reviewed in detail, the results show that different vehicle types release different amount of CO2 emission and the biggest portion with 81% in transportation sector is road transportation. The details of the 81% show that 63% of the transportation is made for passenger transportation and 37% for commercial transportation. Therefore, it was decided to apply the decision model to CO2 emission reduction on passenger cars. This study proposes a new ANP based goal programming model which guides the passenger car producers while they are building-up their CO2 emission reduction related strategies. ANP is very helpful through its strength to deal with relationships and feedbacks among the criteria. The feedbacks and the relationships necessitate a very difficult evaluation of the decision makers. Therefore, a group decision making process based on ANP can be used for such decision problems to ensure the success of the study (Wey and Wu, 2007). On the other hand, the strength of the goal programming results from its ability to combine the conflicting goals and the constraints in a mathematical model to ensure an optimized result (Lee and Kim, 2001; Wey and Wu, 2007). The success of the combination of these two methods comes out from the elimination of other's weaknesses. The difficult step for a goal programming model is to define the importances and/or the priorities by decision makers at the beginning. This disadvantage was eliminated via including ANP method as a beginning step of the goal programming method. The main disadvantage of the ANP is that ANP does not take into account the resources limits and other constraints. The application of goal programming together with ANP solves this problem (Karsak et al., 2002). In our study, the results of the ANP are used as the importances of the goals in proposed model and the results of this model presents the optimized solutions in order to propose which strategies are to be taken into account, which motor types, exhaust types and fuel types are to be used for the new developed passenger cars or for the performance improvements of the existing cars. Keywords: Multi criteria decision making, goal programming, ANP, reduction of CO2 emission
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