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Swelling kinetics of iota carrageenan gels: Fluorescence study
Get PDFFiziksel jeller, sıcaklık ve iyon etkisi gibi faktörlerin değiştirilmesi ile sol ve jel durumları arasında tersinir bir dönüşüm meydana getirirler. Gıda sektöründe katkı maddesi olarak, tıp ve ilaç sektöründe yapay organ uygulamalarında ve ilaç denetim sistemlerinde, tekstil sanayinde boyama ve giyim eşyalarında dayanıklılık arttırıcı olarak kullanılmaktadırlar. Birçok uygulama alanına sahip olan fiziksel jellerin yapısında bulunan başlıca biyopolimerlere örnek olarak hayvansal dokulardan elde edilen jelatin, deniz yosunu ve alglerden elde edilen karagenan ve agarose gösterilebilir. Karagenan, kırmızı deniz yosunundan elde edilen sülfatlı polisakkarittir. İçerdikleri 3.6 anhidro-D-galaktoz miktarı ve ester sülfat gruplarının sayısı ve konumunun farklı olması farklı tipte karagenanlar oluşmasına neden olur. Kappa, iota ve lambda olmak üzere üç temel çeşit karagenan vardır ve hepsi farklı jel özelliklerine sahiptir. Bu çalışmada fiziksel jeller sınıfından iota karagenan jelleri kullanılmıştır. Disk şeklinde hazırlanan iota karagenan jellerin şişme kinetiğine sıcaklık etkisini incelemek için floresans teknik kullanılmıştır. Floresans molekül olarak suda çözünebilen piranin kullanılmıştır. Floresans şiddet, I ve saçılan ışık şiddeti, Isc şişme zamanının fonksiyonu olarak izlenmiştir. Floresans şiddet zamanla artarken saçılan ışık ise zamanla azalmıştır. Su buharı altında şişen jellerde bu sonuçları açıklayabilmek için jellerde şişme kinetiğini tasvir eden Li-Tanaka denklemi kullanılmıştır. Sıcaklığın artması şişme zaman sabitinin azalmasına neden olurken kooperatif difüzyon katsayısı buna bağlı olarak artmıştır. Difüzyon katsayısının sıcaklıkla değişiminden Arrhenius bağıntısı kullanılarak şişme enerjileri bulunmuştur. Anahtar Kelimeler: Şişme, floresans, karagenan.Carrageenans are water soluble polysaccharides extracted from red algae. Their basic structure consists of a repeating unit of 3,6-anhydro-a-D-galactose and b-D-galactose. They are differentiated by the number and the position of ester sulphate groups and the amount of 3,6-anhydro-D-galactose which they contain. They come in three major types designated by means of Greek letters as kappa (k-), iota (i-) and lambda (l-). They are well known for their gel forming properties and are used extensively in food and pharmaceutical industry as gelling or thickening agents. Kappa carrageenan and iota-carrageenan undergo a temperature dependent coil (disordered state) to helix (ordered state) transition in aqueous solution. k-carrageenan usually forms firm, brittle gels and it is sensitive to potassium ions. i-carrageenan usually generates soft, elastic gels and it is sensitive to calcium ions. Iota carrageenan is the most highly sulphated of the helix-forming polysaccharides and is also the most fully characterized in the solid state and in solution (Morris etal., 1980). It is well known that iota carrageenan forms a three dimensional network constituted of polysaccharide chains structured as double helices. This gelation is induced by cooling heated suspensions of the polysaccharide in water under appropriate salt conditions resulting in a coil-helix conformational transition (Morris etal., 1980; Tako etal., 1987). It has been known that in solution, iota carrageenan can reversibly transform from an ordered to a disordered conformation. Naturally at high ionic strength and low temperature iota carrageenan forms an ordered state. On heating, the helices dissolve and the -carrageenan forms a random coil conformation (Rees etal., 1982). Intermolecular double helix formation should result in a doubling in the observed molecular weight of the -carrageenan, which has been observed in many groups (Austen etal., 1985; Morris etal., 1980). However some authors have proposed monomolecular single-helix formations (Norton etal., 1983). The swelling shrinking and drying kinetics of physical gels are important in many technological applications. Especially in pharmaceutical industries, in designing controlled release of drugs and in using cosmetic ingredients, understanding the kinetics of gels is highly desirable. The knowledge of the gel kinetics is an important requirement for producing storable foods in agricultural industry and developing artificial organs in medical applications. Many different experimental techniques have been used to study the kinetics of swelling and shrinking of chemical and physical gels such as neutron scattering (Bastide etal., 1984), quasielastic light-scattering (Peters and Candau, 1988), macroscopic experiments (Zrinyi etal., 1993), in situ interferometric measurements (Wu and Yan, 1987) and photon transmission techniques (Kara and Pekcan ,2000). A different method was employed namely the steady state fluorescence technique, to study the swelling of iota carrageenan gels. The fluorescence technique is efficiently used for analyzing the structural properties of gels. This technique ensures the fluorescence molecules added in a structure to be considerably sensitive to the structural properties of a system and provide information about the medium in which they are located. In this work, we studied the swelling process of i-carrageenan gels at various temperatures by using steady state fluorescence technique. The fluorescence intensity measurements were carried out with Perkin-Elmer LS-50 model spectrometer equipped with a temperature controller. Pyranine was embedded in i-carrageenan and used as a fluorescence probe. i-carrageenan gels were completely dried and then swelled in water vapor. The swelling experiments were performed at 30, 40, 50 and 60oC. At each temperature, the disc-shaped gel samples were placed in the wallof a 1x1x4.5cm3 quartz cell saturated with vapor for the swelling experiments. Scattered light intensities, Isc and fluorescence intensities, I were monitored during the swelling of i-carrageenan gels. The scattered light intensity, Isc decreased, however the fluorescence intensity increased exponentially as swelling time is increased. The increase in I was modeled using Li-Tanaka equation from which selling time constants, tc and cooperative diffusion coefficients, Dc were determined. It was observed that swelling time constants, tc decreased and cooperative diffusion coefficients, Dc increased as the swelling temperature was increased from 30 to 60oC. The swelling energies, DE were obtained by using Arrhenius relation and found to be 63.1kJmol-1. Keywords: Swelling, fluorescence, carrageenan
Fixed job scheduling: a literature survey and a solution proposition through meta heuristic methods
Get PDFFixed Job Scheduling (FJS) is defined as the arrangement of the works, which have fixed ready times and deadlines in a shift with particular number of machines. In fixed job scheduling problems, the objective is to select a set of jobs for processing so as to maximize the total weight. This problem is known to be NP-hard. The Fixed job scheduling problem has two variants based on objective functions (Eliiyi, Azizoğlu, 2006). The first variant is the Operational Fixed Job Scheduling (OFS), where each job j has a weight wj that represents its value or relative importance, and the concern is maximizing the total weight of the processed jobs with a given number of processors. The second variant is the tactical fixed job scheduling problem, which considers the minimization of the total cost or the number of the machines needed to process all jobs (Eliiyi, Azizoğlu, 2006). FJS has been studied extensively in recent years. Arkin and Silvenberg (1987) analyzed the jobs scheduling problems with fixed start and end times. They proposed an algorithm which maximizes the value of jobs completed by k identical machines. They also showed that the problem is NP-Complete. Kolen and Kron (1992) investigated FJS problem which appears in the aircraft maintenance process at an airport. They show that the polynomially solvable cases of these problems can be solved by a combination of linear programming and network flow algorithms. Dondeti and Emmons (1992) study fixed job scheduling problem that involves two types of processors but three types of jobs. They present a polynomial algorithm for finding the minimal cost combination of the two types of processors required to complete all jobs. Fischetti et al. (1992) introduce several polynomial-time approximation algorithms for fixed job schedule problems. Some of the algorithms they present make use of a simple procedure for assigning to processors, in a greedy way. A later study by Kolen and Kroon (1994) addresses the fixed job schedule problem which appears in the aircraft maintenance process at an airport. They present an analysis of the problem of finding the minimum total number of engineers required for carrying out all jobs. In their study the engineers are addressed as machines. Another study of Kroon et al. (1995) is exact and approximation algorithms for the operational fixed interval scheduling problem. They discuss the occurrence of the fixed interval scheduling problems in practice and develop exact and approximation algorithms for solving OFS problem. Bouzina and Emmons (1996) present a polynomial solution to several interval scheduling problems. The objective of their algorithm is maximizes the number of processed jobs. A later study of Kroon et al.(1997) is exact and approximation algorithms for the tactical fixed interval scheduling problem. They present exact and approximation algorithms for solving the tactical fixed interval scheduling problem. In the first study on interval scheduling problems to solve by a Meta heuristic method has been proposed by Santos and Zhong (2001). They developed a Genetic algorithm (GA) and reinforcement learning for the tactical fixed interval scheduling problem.. A graph based heuristic is described to solve the operational fixed job scheduling problem by Garcia et al. (2005). They compared their solution with other heuristic from literature. Eliiyi and Azizoğlu (2006) propose a branch and bound algorithm for solving operational fixed job scheduling problem. Despite its practical importance and broad range of usage area from the maintenance process of planes at the airports to the car repair /rental services, there are very few studies in literature on the subject of fixed job scheduling problem. In this study, a literature survey on fixed job scheduling problems has been done for the last twenty years and also two meta heuristic methods such as Genetic algorithm(GA) and Simulated annealing(SA) are proposed for solving the operational fixed job shop scheduling problems. To show the performance of Genetic algorithm and simulated annealing, an example is presented in the study. A random test problem for the operational fixed job scheduling on identical parallel machine is solved with Bouzina and Emmons (1996) algorithm, and proposed GA and SA algorithms. The computational results indicate that the proposed metaheuristic methods are effective for operational fixed job scheduling problems. Keywords: Fixed job scheduling, Genetic algorithm, Simulated annealing. Sabit iş çizelgeleme; sabit bir başlangıç ve bitiş zamanında, tamamlanması gereken işlerin ve belirli sayıda makinelerin bulunduğu bir vardiyada, işlerin çizelgelenmesi olarak tanımlanmaktadır. Sabit iş çizelgeleme, amaç fonksiyonuna göre iki temel alt problemden oluşmaktadır. Bunlar; sabit geliş ve teslim zamanına sahip işlerin, özdeş paralel makinelerde işlem görmek üzere, her işin wj ile ağırlıklandırılması sonucunda, toplam kâr maksimizasyonu amaçlı olan, Operasyonel sabit iş çizelgeleme ve sabit geliş ve teslim zamanlı işlerin ck sabit maliyetli paralel özdeş makineler üzerinde çizelgelenmesi ile maliyet minimizasyonu amaçlı olan, taktiksel sabit iş çizelgeleme problemleridir (Eliiyi, Azizoğlu, 2006). Havalimanında uçak bakım sürecinden, araç tamir/kiralama sistemlerine kadar geniş kullanım alanı bulunan sabit iş çizelgeleme probleminin, pratik önemine rağmen, literatürde çok az çalışma yapıldığı bilinmektedir. Bu araştırmada, sabit iş çizelgeleme problemi üzerine son yirmi yılda literatürde yapılan çalışmalar incelenmiştir. Ayrıca meta sezgisel yöntemlerde olan, Genetik Algoritma (GA) ile Tavlama Benzetiminin (TB) Operasyonel sabit iş çizelgeleme problemlerinin çözümünde kullanımı üzerine öneride bulunulmuştur. Bouzina ve Emmons (1996) tarafından geliştirilen algoritma (klasik yöntem) ile meta sezgisel yöntemlerden olan Genetik algoritmalar ve Tavlama benzetiminin, Operasyonel sabit iş çizelgeleme problemleri üzerindeki çözüm performansı, bir örnek üzerinde karşılaştırılmıştır. Araştırmada, meta sezgisel yöntemlerin daha iyi sonuçlar verebileceği belirlenmiştir. Anahtar Kelimeler: Sabit iş çizelgeleme, genetik algoritma, tavlama benzetimi. 
Development of anisotropy coefficient (r-value) for the cold rolled if steels
Get PDFOtomotiv endüstrisinde iç ve dış panellerin üretiminde kullanılan, çok az miktarlarda karbon ve azot içermeleri nedeniyle pres altında şekillendirmeye uygun çeliklerdir. Arayer atomsuz çeliklerde, şekillendirilebilme özelliğini olumsuz yönde etkileyen arayer atomlarının (C ve N), çelik üretim prosesi esnasında bileşimden kontrollü bir biçimde uzaklaştırılması Titanyum (Ti) ve/veya Niobyum (Nb) atomlarının C ve N atomları ile reaksiyona girerek çökelti fazları oluşturması ile olmaktadır. Sıcak haddeleme prosesinde slab fırınında belli sıcaklığa kadar ısıtılarak çökeltilerin çözeltiye alınması sağlanır. Bu işlem nihai sıcak band dokusunu ve tane büyüklüğünü belirleyici ilk prosestir. İkmal ve sarılma sıcaklıkları da arayer atomsuz çelik üretiminde önemli olan proses parametrelerdir. Her iki proses parametresi de çökelti ve tane büyüklüğünü önemli ölçüde etkileyerek çeliğin nihai mekanik özellikleri üzerinde büyük oranda etkili olmaktadır. Şekillendirilebilme özelliğinin önemli bir göstergesi olan r değerinin arttırılmasında en önemli parametre soğuk ezme oranıdır. Artan tavlama sıcaklığı tane büyüklüğünün artmasında etkili olmaktadır. Çelikhane prosesinden itibaren sıcak haddeleme ve soğuk haddeleme prosesleri arayer atomsuz çeliğin mekanik özellikleri üzerinde etkili olmaktadır. Endüstriyel ölçekte gerçekleştirilen bu çalışmada, çelik kimyasal bileşiminde bulunan Ti ve Nb elementleri ile soğuk haddeleme ve sürekli tavlama parametrelerinin optimizasyonu sonucunda mekanik özelliklerde oluşan değişimler irdelenmiştir. Yapılan çalışmaların sonucunda Ti+Nb elementleri içeren kompozisyonlarda, yüksek ezme oranları (%80) ve tavlama sıcaklıklarında (870°C) yüksek r değerleri elde edilmiştir. Otomotiv sektörünün önemli oranda kullandığı arayer atomsuz çeliklerin mekanik özelliklerinde iyileştirmeler sağlanarak endüstrinin kullanımına sunulmuştur.Anahtar Kelimeler: IF Çelikleri, soğuk haddeleme parametreleri, r değeri, mekanik özellikler.Interstitial free steels (if steels) are very suitable material for automotive industry and they are used for inner and outer body panel applications due to their high formability properties. They have extremely high formability characteristics under forming presses. Interstitials damages formability characteristics of steel. Elimination of interstitials (C and N) is achieved through careful control of the steelmaking process by the addition of titanium and/or niobium to react with carbon and nitrogen to form precipitates. In the hot rolling process, firstly, slabs are heated upto some temperature and those precipitates are taken into solid solution. This process affects grain size and texture of hot rolled product. The other important process parameters in hot rolling are; finishing temperature and coiling temperature. Both parameters mainly affect grain size and size of the precipitates in hot rolled coil.and thus mechanical properties are affected. The most important parameter for formability is r value. And it is mainly affected by cold deformation.ratio. Also increasing annealing temperature increases grain size and results in higher formability. All the process parameters through steelmaking to the cold rolling process affects mechanical properties of interstitial free steels and thus affects r value of interstitial free steel. In this study, mechanical properties related with steel chemical composition by optimizing Titanium (Ti) and Niobium (Nb) contents and continuous cold rolling and annealing parameters were investigated in industrial scale. As a result, the highest r values were obtained at 80 % cold deformation ratio and annealing at 870 C for steel with Ti+Nb alloying addition. In this study, experiments were done in industrial scale. Firstly, interstitial free steels containing titanium and titanium+niobium were produced at steel shop. And then slabs produced at continuous casting machines were hot rolled After hot rolling process, those coils were sent to cold mill for cold rolling and annealing process. Also some coils were sent to galvanising line after cold deformation. Each process are controlled by high level process computers in Erdemir plants. Therefore process parameters for trial coils are taken from this computer results. Chemical analysis of heats were done at steel shop chemical laboratories and they were produced according to instructions given by metallurgical department. Mechanical test samples were taken after continuous annealing line and continuous galvanising line processes. Mechanical properties including yield strength, tensile strength, and elongation at fracture strain hardening exponent and anisotropy coefficient were determined by mechanical tensile tests. Tensile specimens were cut along rolling direction, transverse direction and 45° to the rolling direction. Samples were taken from the middle section of each coil. Tests were done on Zwick Z-100 testing machine. All tests were made at a strain ratio of 2 % Lo/min. The tensile test samples were processed according to DIN EN 10002-1 type 2 standards.The effect of process parameters on mechanical properties were investigated according to these results. Optical microscopy was used for the microstructural examinations and grain size measurements of the samples. Microstructural examinations were conducted on the cross sections perpendicular to the rolling direction. Microstructures of materials including ferrite grain size, carbide type and distributions were investigated with a leco 500 optical microscope. Also scanning electron microscopy was used for the determination of the microstructure and carbide distribution of the samples. The scanning electron microscope was a jeol 5600 jsm type machine. As a result of microstructure analysis effect of process parameters on microstructures analysed. In this study, texture analysis was conducted with a rigaku d-max ultima x-ray diffractometer with a pole figure attachment. Test samples were prepared from annealed samples, punched to a 4mm diameter and then metallographically prepared. The next step was data collection from an x-ray diffractometer. The xrd measurements of samples were carried out in the range of 20-90 2teta degrees with 0.02 steps. Then pole figure measurements were done with different alfa and beta angles in 110, 111 and 200 diffraction lines. As a result of that study, the best composition of interstitial free steel containing titanium and niobium were determined by optimization of titanium and niobium content. Also the best process parameters at the cold mill determined through analysis of results taken from mechancal tests and microstructure analysis in which the highest r value obtained. And interstitial free steel produced after that study put into use for the automotive market as a new quality of steel.Keywords: Interstitial free steel, cold mill process parameters, r-value, mechanical properties
Effects of material properties on anelastic behavior
Get PDFMetallerin anelastik davranışı, metroloji biliminin özellikle kütle, basınç ve boyutsal alanlarında, yerçekimiyle ilgili deneylerde, yüksek hassasiyet gerektiren cihaz ve sensör elemanlarının tasarımıyla ilgili bir malzeme özelliğidir. Sensöre uygulanan yükün genliği ve onun uygulanma sıklığı cihazın ölçüm belirsizliğini etkiler. Metallerin anelastiklik özelliği, malzemenin iç sürtünmesinin kaynağı olarak değerlendirilmiş ve sönümlemenin, uygulanan yükün hızıyla orantılı olarak değiştiği modellenmiştir. Bazı mekanik modeller, metallerde uygulanan yükün izi olarak sönümlemeyi tanımlamak amacıyla kullanılmıştır. Gecikmiş cevabın ve sönümlemenin tanımlanmasında elastiklik modülü, frekans alanında karmaşık bir sayı olarak ele alınabilmektedir. Bu sayının gerçel ve sanal kısımları kuvvet ile ortaya çıkan şekil değişimleri arasındaki fazı ve faz kaymasını göstermektedir. Bu değerlerin oranı malzemenin modül kaybını vermektedir. Bu çalışmada anelastiklik ölçümü için, esnek elemanı bakır berilyum (Cu-Be) malzemeden imal edilmiş yeni bir ters sarkaç tasarlanmış ve performansının temel sınırları belirlenmiştir. Yeni sarkacın esnek elemanı dikey pozisyonda basma değil çekme gerilmesine maruz kalmaktadır. Bir çok esnek eleman çekme gerilmesi altında çalışmakta olup, basma gerilmesi uygulamalarında performansları kötüdür. Esnek elemanın çekme gerilmesine maruz kalabilmesi için, bağlandığı sarkaç koluyla yeni bir şekilde monte edilmiştir. Sarkacın kalite faktörü, üstel bir fonksiyon olarak azalan salınımların CCD (Charge-Coupled Device: Işığa duyarlı hassas bir cihaz) kamera ile, 2 s ile 30 s arasındaki periyotlarda tespit edilmesiyle elde edilen veriler kullanılarak hesaplanmıştır. Farklı içyapı özellikleri için modül kayıpları tespit edilip gerilmeye göre bu kayıpların miktarı araştırılmıştır.Anahtar Kelimeler: Anelastiklik, iç sürtünme, ters sarkaç, esnek eleman, bakır berilyum alaşımı.A new inverted pendulum with a copper-beryllium (Cu-Be) flexure element is designed and its performance is determined by detecting the respective angular changes of the pendulum using a ccd camera within an oscillation period range of 2 s and 30 s. A new arrangement was made by clamping of the flexure element and pendulum rod to avoid subjecting them to compression stress due to the weight of the overall pendulum mass on the flexure. This new form of inverted pendulum employs a flexure specially clamped to the pendulum rod to provide tension deformation under the weight of mass and could be used for dynamic testing of highly sensitive flexure elements. The quality factors of the pendulum were determined with respect to flexure elements by measuring free oscillations decaying exponentially. The results showed that the new inverted pendulum with a different connection between the flexure element and pendulum rod can be used to measure the anelasticity of materials and to test elements under bending deformation in a dynamic way. Many experimental apparatuses have been designed and used to investigate the anelastic behavior of materials. These are divided into three main types, in terms of the frequency of use: subresonance, resonance and supraresonance methods. The resonance method is particularly useful for the dynamic testing of the flexure in a pendulum. There are many types of pendulum apparatus and various clamping orientations are used for the measurement of anelasticity. The most frequently used type of pendulum to determine anelastic phenomena in materials is the torsion pendulum consisting basically of a mass as an inertia member suspended from a wire specimen that is subjected to a twisting deformation. The standard pendulum is used with various modifications. The simple pendulum is known as the basic arrangement of the standard pendulum, the specimen is under tension stress and subjected to bending stress but low frequencies cannot be easily generated because frequencies depend on the length of pendulum rod. The frequency changes in inverse proportion to the square root of the rod length so that periods of more than a few seconds require a very long pendulum rod, which is not useful for experimental purposes. An inverted pendulum is another version of the standard pendulum known as the "swinging type". It consists of a rod on the top of which a suspension mass placed. The rod is supported by a spring attached to its bottom in order to hold the pendulum rod vertically. The spring comes under compression stress and is subjected to a twisting deformation due to the suspended mass. The oscillation of the pendulum rod depends mainly on torque acting on the spring element and can easily vary over a wide band. Some researchers have used various types of combined and torsional pendulum apparatuses to determine the anelasticity of copper-beryllium flexures, for the purpose of designing a highly sensitive mass comparator. Different types of flexures were used as pivot elements. Some measurements were carried out by using an inverted pendulum with an instant steel flexure element which was under compression and subjected to bending deformation, and it has been shown that the inverted pendulum was a valuable tool for the study of internal friction, that it could be used to probe anelasticity within a wide band of frequencies, and that it allowed direct tests of the features of anelastic behavior that were hard to perform in other ways. An inverted pendulum is a valuable instrument for precision measurement, gravitational physics, and also for measuring the anelasticity of , which is one of the mechanical properties connected to designing highly accurate measurement devices and sensors used in the mass, force, pressure and dimensional fields of metrology. The frequency of an inverted pendulum can easily be changed over a wide band by either adding mass on top of the pendulum or by changing the centre of gravity of the suspended mass. This enables dynamic testing of metals, especially anelasticity in the flexure elements of the pendulum. This study covers the attempts of searching the relationships between microstructural material properties of flexure elements and their respective anelastic behavior by using an inverted pendulum.Keywords: Anelasticity, internal friction, inverted pendulum, flexure element, copper beryllium alloy
Kompozit plakların dinamik nonlineer davranışı
Get PDFEmploying Galerkin technique, analyses on the dynamic nonlinear behavior of composite plates are performed in the course of this study. First order shear deformation theory and von Karman type nonlinearity are utilized and the governing differential equations are solved by choosing suitable polynomials as trial functions to approximate the plate displacement functions. The trial functions satisfy the geometric boundary conditions, whereas natural boundary conditions are not satisfied. In this case, simultaneous approximation is made to the solutions of differential equations and to the boundary conditions. The choice of trial functions is crucial to approximate the two dimensional displacement field. Dynamic large deflection analysis of composite plates is investigated using the Galerkin and the Newton-Raphson methods with Newmark direct time integration scheme. In order to demonstrate the applicability of the present method, linear transient analysis of an isotropic plate is considered at first. Geometrically nonlinear transient analysis of a cross-ply laminate is accomplished as a case study. The solutions are compared to that of Chebyshev series and finite elements. A very close agreement has been observed with these approximating methods. The method is found to determine closely the displacements with a few number of terms. In the solution process, analytical computation has been done wherever it is possible, and analytical-numerical type approach has been made for all problems. Keywords: Galerkin method, plates, large deflection, time integration.Bu çalışma kapsamında Galerkin yöntemi kullanılarak kompozit plakların dinamik nonlineer davranışları üzerine analizler gerçekleştirildi. Birinci dereceden kayma şekil değiştirmesi teorisi ve von Karman tipi nonlineerlik kullanıldı ve olayı yöneten diferansiyel denklemler, plak yer değiştirme fonksiyonlarına yaklaşım için uygun polinomların seçilmesi ile çözüldü. Galerkin ve Newton-Raphson yöntemleri Newmark doğrudan zaman integrasyonu yöntemiyle beraber kullanılarak kompozit plakların dinamik büyük çökme analizleri araştırıldı. Elde edilen çözümler Chebyshev serileri ve sonlu elemanlar yöntemlerinin çözümleri ile karşılaştırıldı. Bu yaklaşım yöntemlerinin sonuçları ile uyum içinde kalındığı gözlendi. Çözüm aşamasında işlemler mümkün olduğunca analitik olarak yapıldı ve bütün problemlerde analitik-sayısal tip yaklaşım uygulandı. Anahtar Kelimeler: Galerkin yöntemi, plaklar, büyük çökme, zaman integrasyonu. 
A simulation-based decision support tool for economical materials management system in the construction industry
Get PDFBir yüklenici inşaat firması, projenin en başında, bolluk miktarı (büyük, orta veya küçük), planlama yaklaşımı (iyimser, nötr veya kötümser) ve parti hacmine (büyük veya küçük) bağlı olarak değişen 18 değişik malzeme yönetim alternatifinden birini seçebilir. Bu araştırmada, yüklenici inşaat firmalarına, en düşük toplam envanter maliyetini oluşturacak olan bolluk miktarını, planlama yaklaşımını ve parti hacmini tavsiye edecek simulasyon tabanlı karar destek modeli geliştirilmiş ve bu model yardımı ile tamamlanmış olan üç ticaret merkezi projesinden elde edilen veriler kullanılarak sözkonusu malzeme yönetim sistem alternatifleri için toplam envanter maliyeti hesaplanmıştır. İncelenen projelerde, geliştirilen modelin uygulanması, yüklenici inşaat firmalarına %4.2-7.3’lük bir maliyet kazancı sağlamıştır. Anahtar Kelimeler: Malzeme yönetimi, tam zamanında yönetim, simulasyon modeli. Materials constitute a large proportion of the total cost of construction. Proper management of the material flow may play a significant role in enhancing the effectiveness of a contractor. The generally acknowledged rules of materials management are small orders, frequent deliveries, and reduced inventory. A contractor should be familiar with the impacts of lot size (large or small) and buffer size (large, medium or small) as governed by contractor's scheduling practice (optimistic, neutral or pessimistic) in handling uncertainty and variability on the economics of the each material management alternative at the beginning of the project in order to make a decision on the most economical alternative that will be used throughout the project. The main objective of this study is to provide contractors with an objective and dynamic tool, namely a discrete event simulation model, to assist them in selecting the most economical materials management system by recommending buffer sizes, a scheduling practice, and lot sizes given the special conditions of the project at the beginning of the project. After the simulation-based decision support tool was completed, it was time to plug the actual data obtained from the completed three trade center projects into the simulation model and run the model. The case studies revealed that using the simulation-based decision support tool provided the contractor with a cost saving of 4.2-7.3% in the studied projects. Keywords: Materials management, just-in-time management, simulation modeling.
Hydrogeochemistry of the region between Çorlu-Çerkezköy of Ergene basin
Get PDFErgene Havzası, Çerkezköy ve Çorlu kesiminde sanayi kuruluşları ve nüfusun fazlalaşması ile artan su gereksinimi ve proses sularının Ergene ve Çorlu Derelerine bırakılması ana akifer olan Ergene Formasyonu için kirlenme riski oluşturmuştur. Ergene Formasyonundan su alan 9 adet gözlem kuyusundan örnekleme yapılarak, iyon ve ağır metal analizleri yapılmıştır. Bölgedeki yeraltısuları Schoeller’in içilebilirlik diyagramına göre, 1. 2. ve 3. kalite sular sınıfındadır. ABD Tuzluluk diyagramına göre C2-S1 ve C3-S1 grubunda bulunan sular, Wilcox diyagramına göre çok iyi-iyi ve iyi-kullanılabilir sular grubuna girer. Yeraltısularında ağır metal kirliliği olduğu akiferin dinamik rezervinin azaldığı yağışa rağmen bu azalmanın sürdüğü tespit edilmiştir.Anahtar Kelimeler: Hidrojeokimya, hidrojeolojik, Ergene Havzası, yeraltısuyu, kirlilik. Irrigational lands and industrial zones cover most of the area between Çorlu and Çerkezköy. Groundwater is the only major source of water for agricultural, industrial and domestic purposes. The main aquifer in the study area is the Ergene Formation. Çorlu creek, which is contaminated by the process waters of factories, flows on Ergene Formation and has become a contamination source for the groundwater. Main ion and heavy metal investigations are carried out from 9 sampling wells selected on the basis of well inventory survey to reveal the hydrogeochemistry and contamination status of the aquifer in the study area. Also three surface water samples are being analyzed from Çorlu and Ergene creeks. Results of the analysis are plotted on diagrams and interpreted. All waters are classified as first, second and third quality water according to Schoeller's drinking diagram. However, they are in the groups of C2-S1 and C3-S1 on US Salinity Lab. Diagram. According to Wilcox diagram all groundwaters are in the groups of very good to good and good to permissible but surface waters from Ergene creek is classified as suspicious non permissible, and Çorlu creek is classified as non permissible. High heavy metal concentrations are also being observed in the groundwater as an indicator of the contamination of the aquifer. The static water levels also fall down although precipitation has increased in recent years. Keywords: Hydrogeochemistry, hydrogeology, Ergene Basin, groundwater, contamination.
Long-range aerosol transport from Europe to Turkey
Get PDFŞehirleşmenin yaygın olduğu Türkiye’nin kuzey ve batı kısımlarında genellikle yüksek hava kirliliği olayları ile karşı karşıya kalınmaktadır. Bununla birlikte, bu kirliliğin büyük bir kısmından sorumlu olduğu düşünülen Avrupa ülkeleri için, şu ana kadar, uzun mesafeli taşınımlar açısından kapsamlı bir araştırma yapılmadığı görülmüştür. Bu çalışmada amaç, Istanbul hava kirliliğine, Avrupa kökenli uzun mesafeli aerosol taşınımlarının hem niteliksel hem de niceliksel olarak katkısını araştırıp, tüm yönleriyle açıkça ortaya koymaktır. Bu çalışmanın sonucunda, söz konusu katkının zaman zaman şehrin kirliliğinin yarısından sorumlu olduğu açıkça ortaya konulmuştur. Anahtar Kelimeler: Hava Kirliliği, Uzun mesafeli taşınım, Emisyon modeli, PM10.Northern and western parts of Turkey frequently experience air pollution episodes. Transport of air pollutants from Europe to these regions has not been studied sufficiently. This study aims to identify and analyze the contribution of long range aerosol transport to air pollution in the city of Istanbul. Istanbul is the largest urban settlement in northwestern Turkey, with more than 12 million inhabitants in the metropolitan area. Whenever the prevailing wind direction is westerly or northwesterly, such as the case of the episode studied here, a significant fraction of the pollutants emitted from Europe are transported to and deposited in Turkey. The response of Istanbul PM10 can be as much as 26% according to the sensitivity analyses results, when anthropogenic emissions throughout Europe are changed by 50%. This result suggests that trans-boundary sources may be responsible for as much as half of the poor air quality of Istanbul. This paper presents the methodology developed in this study as well as the results obtained. An emission processing module was developed to prepare the emission inputs required by an advanced air quality modeling system. The long-range aerosol transport simulated by this modeling system was further supported by trajectory analysis. Backward trajectories and long-range transport modeling indicated similar source/receptor relationships between Europe and Turkey.Keywords: Air pollution, transboundary aerosol transport , emission modeling, PM0
Ant colony optimization parameter tuning for flow shop scheduling problem
Get PDFBu çalışma kapsamında, NP-zor tipi problem olarak bilinen permütasyon akış tipi çizelgeleme probleminin Karınca Kolonileri Eniyileme (KKE, Ant Colony Optimization-ACO) ile çözümünde kaliteli sonuçlar elde et-mek üzere parametre eniyileme gerçekleştirilmiştir. Ele alınan çizelgeleme problemi, tüm makinelerde aynı sıraya sahip işlerin çizelgelenmesinden oluşur. KKE, birleşik eniyileme (combinatorial optimization) prob-lemleri için son zamanlarda kullanılan umut verici metasezgisel bir yaklaşımdır. Burada öncelikle örnek test problemleri üzerinde denemeler yapılmış ve test edilecek uygun parametre değerleri tespit edilmiştir. Daha sonra en uygun parametreleri tespit etmek üzere iki seviyeli bir deneysel tasarım uygulanmıştır. Yapılan de-neysel çalışmalar sonucunda algoritmanın performansının dikkate değer şekilde arttığı gözlenmiştir.Anahtar Kelimeler: Karınca kolonileri eniyileme, akış tipi, metasezgisel, parametre eniyileme.In this study, parameter tuning is performed to improve the solution of Ant Colony Optimization (ACO) of permutation flow shop scheduling problem, which is known as NP-hard type. The permutation flow shop scheduling problem consists of scheduling jobs with the same order of entry at all machinery. The job can be processed at most on one machine; meanwhile one machine can process at most one job. Ant colony optimi-zation is one of the most recent and promising metaheuristics for combinatorial optimization problems. Similar to other heuristics based on biological systems (such as genetic algorithms, evolutionary strategies, artificial neural network, artificial immune systems) ant algorithms have been inspired by the behavior of real ant colonies. In the ant colony optimization metaheuristic, a colony of artificial ants cooperate in finding good solutions to optimization problems. Here, in order to determine the tendency for the value of ACO parameters, first sample experiments are designed and accordingly appropriate values are determined. Later, experiments are extended to fine-tune of the parameters. A two-level experimental design is used for fine-tuning of parameters. During this study, a total of 3350 runs is carried on 30 test problems with 5, 10 and 20 machines and 20 jobs for makespan objectives. As a result of these experimental studies, a noticeable performance increase was observed.Keywords: Ant colony optimization, flow shop, metaheuristic, parameter tuning
Experimental investigation of charge distribution and dynamic modeling of refrigeration
Get PDFBu çalışmada R600a ile yapılan deneylerle sistem çalışma şartlarını daha iyi anlaşılmasını sağlamak amacıyla sistem elemanlarındaki şarj dağılımı ve çeşitli parametrik değişimlerin bu dağılıma etkileri incelenmiştir. Bu amaçla iki farklı deney düzeneği kurulmuştur; ilk deney düzeneği yük hücreleri ile ısı değiştiricilerin sürekli tartılması prensibine dayanmaktadır. İkinci düzenek ise soğuma sistemi elemanlarında şarjın çevrimin belli bir anında vanalar yardımıyla birbirinden ayrılarak büyük bir tanka genişletilmesi ile aşırı kızmış şartlara geçmesi ve sıcaklık, basınç değerleri yardımıyla yoğunluğunun hesap edilmesi prensibine dayanmaktadır. Bu deney düzenekleri ile sürekli çalışma ve çevrimsel çalışma durumlarındaki şarj dağılımları yanı sıra toplam şarj miktarı, değişken kapasiteli kompresör kullanımı ve çevrim süresi değişimlerinin soğutma sistemi elemanlarında biriken şarj miktarı tespit edilmiştir. Farklı toplam şarj miktarı ile yapılan deneysel çalışmalar eleman bazında incelendiğinde en önemli değişimin buharlaştırıcı şarj miktarlarında olduğu görülmektedir. Bu sonuçlardan sistemin çalışması için yeterli belli bir şarj değerinin üstünden yapılan değişikliklerin direk olarak buharlaştırıcı doluluk oranı üstünde etkili olduğu diğer elemanların belirli bir denge içinde çalışmaya devam ettikleri görülmektedir. Isı değiştirici hesaplamalarından seçilen boşluk oranı korelasyonu kararlı halde soğutma sistemi performansını hesaplandığı bir soğutma sistemi modelinde sistem elemanlarındaki şarj miktarının hesaplanması için kullanılmıştır. Deney sisteminden telli borulu ısı değiştiricili bir derin dondurucu için ölçülen değerler kararlı hal modeli sonuçları ile karşılaştırılmıştır. Karşılaştırmada vana deney düzeneği için olan ölçümlerin model sonuçları ile uyumlu olduğu, yük hücresi deney düzeneği ile buharlaştırıcıda şarj miktarını daha yüksek ölçüldüğü görülmektedir. Anahtar Kelimeler: Buhar sıkıştırmalı soğutma çevrimi, R600a, buharlaştırıcı, yoğuşturucu.Vapor compression refrigeration cycle is widely used in industrial and residential refrigeration systems. The system performance is seriously affected by refrigerant selection and amount used as well as choice of cycle components like compressor, evaporator, and condenser. One major milestone for the refrigeration industry is discovery of CFC's at 1930's. CFC's make excellent choice for vapor compression refrigeration with their high molecular weight and non-flammability properties. At 1987 the use of CFC's are limited because of their effects on Ozone layer by Montreal Protocol. In 1990 R134a is launched as a HFC class refrigerant, but the HFC's still have a high global warming potential value beside their suitable ozone depletion potential values. The following years HC's and specially R600a are became popular for small refrigeration systems, because only negative property of R600a is flammability is not a big concern in small amounts. In this study, for better understanding of vapor compression refrigeration system working conditions, the charge distribution at the system components and effects of different parameters to this distribution is investigated with R600a refrigerant. The charge distribution measurement methods expect complicated and expensive ones depend on weighting methods. The separate and weight method usually needs more time and workforce. Two experimental setups are prepared for this purpose; first one is extended version of balance system in literature with replacing balance with load cells that have a higher precision. This system gives rapid results for the measurement but needs a data reduction process for frost formation and waves formed by hanging system. Second setup is based on principle of expanding the refrigerant, closed in components by quick closing valves at a specified moment of the cycle. The refrigerant amount can be easily calculated from pressure and temperature values for the expanded gas that have superheated condition. A computer program developed in the study controls the pressure stabilization, reaching steady conditions, closing of valves at the desired data point and expanding of component charges to the tank one by one. The measurement of one data point takes nearly 8-10 hours, and measurement of an on-off cycle with lots of data points take more than a week. But the data obtained are more precise than the other system and includes results about dryer and compressor gas volume. The refrigerant distribution is measured under steady state and cyclic working conditions, and effect of parameters like total charge value, use of variable capacity compressor and different cycle times with these setups. The experiments for different total charge values show that the maximum change is in evaporator. The value of 35 g for 75 grams total charge decreases to 24 g for 57 g total charge. The other measured charge from components like dryer, compressor volume, and calculated charge dissolved in compressor oil is not affected by total charge change. The results show that for total charge values over the necessary amount of refrigerant changes the charge load for evaporator and the other components are not affected much. The refrigerant regime in heat exchangers that holds the most of the refrigerant and shows the effect of dynamic working conditions is mostly two-phase conditions. The most important parameter for two-phase charge calculations is void fraction value and assumptions for void fraction correlation. The distributed charge amount is calculated for experimental working conditions and literature void fraction correlations. It is obvious that the selection of void fraction correlation have a major effect on charge amount calculation. The Premoli void fraction correlation based on mass flux value gives best validation with the experimental results. The void fraction correlation chosen from heat exchanger calculations is used for charge predictions in a steady state model that calculates the system performance values. The model can calculate the charge amount for different heat exchanger types. The calculated charge distribution for a freezer with wire and tube heat exchangers is compared with charge measurements from two setups. The model result gives good agreement with the valve experiment setup; the evaporator charge is seemed to over measured by load cell setup. Refrigerant system charge distribution for different conditions is calculated and modeling approach for charge assumptions at design period is developed in this study. The correct assumption about refrigerant charge will obtain a shorter design time and less prototyping work. Keywords: Vapor compression refrigeration cycle, R600a, evaporator, condenser
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