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Cost accounting problem for not-for-profit production based organizations: A model
Get PDFBu çalışmada kâr amaçlı olmayan imalata yönelik işletmelerin maliyet muhasebesi sorunları incelenmiş ve uygulamaya yönelik iyileştirme güdüsü ile Türk Deniz Kuvvetleri Komutanlığı bağlısı Gölcük Tersanesi için “Faaliyet Tabanlı Maliyetleme” sistematiğine dayalı maliyet analiz ve kontrol modeli geliştirilmesi hedeflenmiş; bu hedefe uygun olarak tersane ürün portföyünde yer alan 1400 tonluk 209 sınıfı denizaltının inşa maliyeti hesaplanmıştır. İşletme literatüründe; değişik kaynaklarda, farklı bakış açılarına göre farklı işletme sınıflandırmalarına rastlanmakta olup, bu sınıflandırmaların büyük çoğunlukla hatalı olduğu ve örneğin askeri tersaneler gibi karmaşık üretim ve servis çıktıları üreten ve kar amacı gütmeyen işletmelerin klasik eserlerde doğru konumlandırılmadığı tartışılmıştır. Safha maliyet, sipariş maliyet sistemi gibi geleneksel maliyetleme sistematiklerinin ortak zayıf noktaları üretim genel giderlerinin ürünlerle ilişkilendirilmesinde üretim kapasitesinin yegâne maliyet sürücüsü olduğu varsayımının esas alınmasıdır. Son dönemde üretim hacmi dışında bazı maliyet sürücülerinin de mevcut olduğu gerçeğinden hareketle “Faaliyet Tabanlı Maliyetleme” (Activity Based Costing, ABC, FTM) sistematiğinin kullanımında yoğunluk göze çarpmaktadır. Ancak; FTM’nin genel kabul gören uygulama konsepti işletme bünyesinde kullanılan safha maliyetleme, sipariş maliyetleme gibi mevcut muhasebe sistemlerinin destekleyicisi olarak kullanımını öngörmektedir. İş kollarının sektörel yapısı baz alındığında tersanelerin; sahip oldukları karmaşık süreçlerin doğal neticesi olarak yüksek genel giderlere sahip işletmeler oldukları görülmektedir. Bu itibarla tersaneler FTM için son derece elverişli uygulama potansiyeline sahip kuruluşlardır. Anahtar Kelimeler: Kar amaçlı olmayan işletmeler, Gölcük Tersanesi, faaliyet tabanlı maliyetleme, yönetim ve maliyet muhasebesi, verimlilik.In this study cost accounting problems faced by not-for-profit production based organizations have been analyzed and being motivated for improvement in practice; it was aimed to construct a cost accounting and analyze procedure for the use of Gölcük Naval Shipyard, Turkish Navy, based on "Activity Based Costing" systematical approach and in accordance with the aim the total production cost of a 1400 tons 209 class submarine which is one of the products of the shipyard has been calculated as well. On the theoretical basis; it was discussed that the accounting literature included a variety of enterprise classifications based on different approaches and it was assessed that majority of those were not suitable for use since they did not imply the not-for-profit state enterprise having complex production and service outputs such as military shipyards. It is a fact that the generally accepted management conceptual steps including planning, organizing, execution and control; additionally performance and productivity measurements are not limited to private enterprise and are valid for not-for-profit organizations as well. Unfortunately; being lack of final benchmarking criteria namely profits; and because of some other related issues the major problematic areas on the context of managerial functions and decision making accumulate on productivity issues and performance measurements. So, necessary performance measurement and cost analyzing techniques applicable to the organizational structure should be set forth for the use of managers in such an environment. The most important input factor needed by management authorities during decision making process is the cost figure of the operations. Managers need to have accurate cost analysis data for both planning the company operations and performance evaluation. As for the private enterprise; classification and analyzing the costs resulting from the operations is also vital for not-for-profit organizations. It is generally accepted that cost accounting in not-for-profit organizations is more important than the private enterprise accounting in the scope of national economy as a whole system. The Turkish Armed Forces and its organic subordinate Turkish Navy pays high attention and priority to cost effectiveness in planning and executing the activities while sustaining national defence and security. Gölcük Naval Shipyard is the major supplier of Turkish Navy in the context of ship construction, repair, maintenance and keeping Turkish Navy operational. The common problematic performance and productivity measurement issues are also valid for Gölcük Naval Shipyard which is a not-for-profit production based organization. That?s why she has a great potential for not-for-profit organization accounting research and applications. The common liable characteristic for traditional costing systems such as process costing or job order costing is the assumption that the production capacity is the unique cost driver for allocating the overheads to the products. Nowadays, it has been observed that ?Activity Based Costing? discipline got to be used on a wider scale stemming from the fact that there are some other cost drivers. Considering the typical characteristics of business sectors; shipyards are observed to have high overheads since they possess complex production processes. That?s why activity based costing seems to be a useful technique to be adapted to shipyards. In the application section it is aimed to built a cost analysis and control model based on activity based costing systematical approach for Gölcük Naval Shipyard, one of the not-for-profit production based enterprises and the total production cost of a 1400 tons 209 class submarine which is one of the outputs of the shipyard has been calculated as well. The study includes five steps: a through structural analysis in order to identify major activities creating costs, determining and defining the activity-cost pools, allocation of overheads to relevant cost pools, determining the activity rates and allocation of activity rates to the cost object. The most important outcome is the confirmation of the hypothesis that ABC is the most suitable cost accounting technique for shipyards. ABC puts forth effective solutions for managerial purposes. The final result obtained by the study is that ABC possesses many advantages for not-for-profit organizations as a management concept and has a great potential in order to be adapted to the organizations such as Gölcük Naval Shipyard. Keywords: Not-for-profit organizations, Gölcük Naval Shipyard, activity based costing, managerial accounting, cost accounting, productivity
Service value creation in supplier-buyer interactions
Get PDFTedarik Zinciri Yönetimi (TZY), imalat, yöneylem, müşteri yönetimi ve dağıtım gibi değişik disiplinlerin ilgisini çekmiştir. Küresel tedarik, zaman ve kalite temelli rekabet, teknolojik gelişmeler ve çevresel belirsizlik unsurları sonucunda, TZY akademik araştırmalar için güncel bir başlık haline gelmiştir. Artan küresel rekabet, tedarik zinciri halkalarının birbirleri ile daha yakın koordinasyon sağlamasını ve kendilerini diğer halkaların konumlarını dikkate alarak daha iyi hizalamalarını gerektirmektedir. Bu sebeple, tedarikçi-alıcı çiftlerinin yakından incelenmesi hayati önem taşımaktadır. Fiyat bir ürünün en önemli özelliği haline dönüştükçe karlılık düşmekte, rekabet avantajı azalmaktadır, buna ek olarak bilişim teknolojilerinin tedarikçi-alıcı çiftlerinin daha yakın koordinasyonuna imkan tanımayan araçları geliştikçe, tedarikçiler ürünlerini sundukları hizmetler ile desteklemektedirler. Öyle ki, hizmet kalitesi, ürün kalitesinden daha önemli bir sipariş kazandıran olarak anılmaktadır. Ancak, hizmetler yolu ile farklılaştırma yakalanması zor bir kavramdır. Ürünlere eşlik ederek melez ürün oluşumuna katkıda bulunan hizmetler, tedarikçilerin rekabetçiliklerini daha da geliştirebilecekleri unsurlar arasında yer almaktadır. Ancak, alıcıların hizmetlere dair öznel beklentilerinin gelişimleri ve değişkenlikleri sebebi ile tedarikçiler sunumunda bulunacakları hizmet seviyesi gereklerini öngörmekte zorlanmaktadırlar. Bu çalışmanın hedeflediği amaçlar çeşitlidir. Hizmetlerin Tedarik Zinciri Yönetimi (TZY) içerisindeki önemini ortaya koyarak, tedarikçi-alıcı etkileşimlerinde katma değer yaratabilme kabiliyetlerini ortaya koymak bu amaçlardan ilkidir. Ayrıca, tedarikçilerin alıcılarının hizmet seviyesi gereklerini belirleyebilmeleri için Snell Kanunu’ndan yararlanılarak, tedarikçilere ışık tutacak bir model geliştirmek de amaçlanmaktadır. Anahtar Kelimeler: Tedarik zinciri yönetimi, tedarikçi-alıcı etkileşimi, hizmetler, değer yaratımı.Supply chain management has attracted attention from various multi-disciplinary fields, which include manufacturing, operations management, customer management and transportation. Global sourcing, time and quality based competition, improvements in technology, and environmental uncertainties have placed supply chain management as a timely topic for academic research. Defect-free, fast and reliable delivery has almost become the necessities to be in the market, rather than competitive advantage. Ever stiff competition in the global arena calls for closer coordination and better alignment between supply chain participants. Therefore, a closer examination of supplier and buyer interactions is vital. As price becomes the most important feature of a product and reduces profitability and competitive advantage, and as information technology tools that help in a closer coordination with buyer and supplier emerge, suppliers get engaged in providing services around their products. Moreover, service quality is referred as a more important order winner than the product quality. Yet differentiation via services dimension is not an easy concept to grasp. Firms often perform services according to the norms they have established over years of experience. Though, the breadth of experience commonly varies from one firm to another. Therefore, norms adopted for services vary, too. A norm considered for a specific service in one company might not exist at another company, or even if exist could be underestimated. When placed in the context of complex supply chains, this presents a supplier with often buyers that have different services' norms. A certain aspect of a supplier's service might be deemed superior at one buyer, while normal or even inferior at another buyer. Therefore, provision of services in supply chain management presents a promising research area. There is a need to understand if supplier's provision of services is capable of generating superior or inferior perceived buyer value. For a firm to gain and retain value additive beneficial relationships with its buyers, its offer should often involve some social values (something that will make buyer's life a better one) either by clearly identifying the needs of its buyers or by outperforming what other suppliers already do. Suppliers demand more information on sophisticated norms and specifications of their buyers to formulate their services. This research attempts to shed the light on the issues discussed, and also uncover the possible causes of superior perceived buyer value creation upon supplier's provision of services in supply chain. An exploratory research model has been developed by the aid of an analogy from Snell's Law of the physics as services creation of value has an instantaneous nature like that of the passage of a beam of light from one medium to another one. Two propositions had stemmed from the exploratory research. Firstly, lower operational medium on supply side is likely to cause inferiority in perceived buyer value for an encounter. Secondly, higher operational medium on supply side is likely to cause superiority in perceived buyer value for an encounter. A panel of experts had been devised to confirm usefulness and meaningfulness of the developed model. The research process for the panel of experts was a qualitative technique based on an interpretive orientation. Participants included 9 provincial individuals. In all, there were 19 interviews, involving 9 individuals. In four instances more than one person participated in an interview. Thirteen of the interviews were face-to-face, and three were conducted by telephone. Interviewees confirmed the model by the practices they are involved within the industry, as well as with the exemplifying issues they have presented. No changes were requested for the developed exploratory model. The main contribution of this research endeavor to academia is the developed exploratory model, which explains creation of superior perceived buyer value via provision of services in a supplier-buyer interaction. Therefore, reference disciplines, including supply chain management and services have received contribution. High levels of services are often costly for suppliers to adopt for the entire buyer base due to two major reasons: the unnecessary high costs incurred for buyers who were not necessarily expecting such high services for value creation, and the dramatically raised expectations which will set the base for all forthcoming services of the supplier that'll force the supplier to perform an ever higher levels of services. Developed model facilitates detection of possible opportunities to improve service levels through which a supplier can create superior perceived buyer value. Keywords: Supply chain management, supplier-buyer interaction, services, value creation
Blending mechanism based set-point regulator
Get PDFBu çalışmada, Harmanlama Mekanizması (HM) içeren iki serbestlik dereceli (2-SD) bir kontrol yapısı sunulmuştur. Bu yeni yapıyla, bir Serbestlik Dereceli (1-SD) ve 2-SD kontrol yapıları kaynaştırılmıştır. Harmanlama Mekanizmalı Referans Ayarlayıcı (HAM-RA) olarak adlandırılan bu yeni yapıda birinci mertebeden ölü zamanlı bir filtre çıkışı ile saf referans işareti uygun bir şekilde harmanlanır ve yeni referans işareti oluşturulur. Böylelikle sistemin geçici hal davranışı şekillendirilirken kontrol yapısından dolayı ise yük bozucularını bastırma ve referans değer takibi hedefleri birbirinden ayrılmış olur. Endüstride karşılaşılan süreçlerin oldukça büyük bir bölümü Birinci Mertebeden Ölü Zamanlı (BMÖZ) sistem olarak modellenebilmektedir. Bu sebeple çalışmada ele alınan sistemler öncelikle BMÖZ olarak modellenmiştir. İçsel Model Kontrole dayalı (İMK) PID kontrolörü yük bozucularını bastırmak amacıyla geribesleme kontrolörü olarak tasarlanmıştır. Böylelikle tasarımcı PID kontrolörünün üç parametresini belirlemek yerine İMK filtre sabitini belirleyerek kontrolör parametrelerini bulabilmektedir. Kontrolör PI tipinde seçildiğinde HM’da yer alan harmanlama dinamiği bir sabite dönüşür. Bu harmanlama sabiti modelde belirlenen ölü zamana, İMK filtre sabitine ve HAM-RA yapısındaki önfiltenin zaman sabitine bağlıdır. Öte yandan kapalı çevrim kontrolörü PID tipinde seçildiğinde harmanlama dinamiği birinci mertebeden bir filtre olarak elde edilir. Bu filtrenin zaman sabiti model ölü zamanının yarısıdır. Önerilen HAM-RA yapısının getirilerini göstermek amacıyla iki adet benzetim örneği ele alınmıştır. Elde edilen sonuçlar, önerilen yeni yapının geçici halde 1-SD ve 2-SD yapılara olan üstünlüğünü ortaya koymaktadır. Anahtar Kelimeler: Referans ayarlayıcı, harmanlama mekanizması, süreç kontrol, içsel model kontrol, PID kontrolörleri, referans değer takibi.Automatic control strategies force physical systems to behave in prescribed ways using the error value that is the difference between the system output and the desired reference input. This idea gives rise to feedback control systems. Since the only signal processor is the feedback controller, this classical control structure is also known as a one degree of freedom (1-DOF) control structure. In recent times, there has been considerable interest in more general control structures. In the two degree of freedom (2-DOF) case, the reference input is processed by the filter F(s), and the classical error is processed by the primary controller C(s). The pre-filter F(s) is used as the second DOF to weight the set-point change in a desirable manner. In literature, there are many applications that use 2-DOF control structure which is sometimes called as model following control. Since PID controllers assure satisfactory results for a large range of processes and due to the simplicity of their structures, they still often represent the best solution from a cost/benefit ratio point of view. Therefore, the controller C(s) used in 2-DOF control structure is mostly a PID controller. Therefore, through this study, PI and PID controllers are used to design the proposed new structure. Internal Model Control (IMC) based PID is preferred for the feedback controller which is designed for a fast disturbance rejection performance. The processes are modeled as first order plus dead time (FOPDT) systems. Therefore the static gain (K), the time constant (T), and the time delay (L) of the model are obtained using well-known area method. The parameters of the PID controller depend on the process model parameters and in addition on IMC filter time constant. İs the only tuning parameter to be selected by the designer to achieve an appropriate compromise between the performance and the robustness issues in control system design. A smaller provides a faster closed loop response, but causes the manipulated control variable to become more vigorous, while a larger provides a slower but smoother response and a mild control effort. In this paper, a new 2-DOF control structure is proposed in which the advantages of 1-DOF and 2-DOF control structures are both exploited. In this new structure, the filtered output of the reference and the pure reference signals are blended so that the overall performance of the system is ameliorated with respect to load disturbance rejection and set-point following. This new structure proposed in this study is named as a set-point regulator with blending mechanism (HAM-RA, SPR-BM). When the blending dynamics is set to be equal to zero then the proposed structure turns out to be a 2-DOF control structure; when the same dynamics is taken as unity, the proposed structure becomes 1-DOF control structure. The blending dynamics is determined with the aim of producing a system output that exactly matches to the filtered reference signal. The prefilter of the SPR-BM defines the desired behavior of the system and in order not to have an oscillatory behavior it is designed as FOPDT filter. When the feedback controller type is chosen to be a PI, the resulting blending mechanism becomes a pure gain. This blending constant is a function of system time delay (L), prefilter time constant and IMC filter time constant. On the other hand, when the feedback controller is chosen to be a PID type, the blending mechanism then becomes a first order filter. The time constant of the obtained blending filter is half of the system time delay (L). Moreover, the static gain of the filter is again defined using the system time delay (L), prefilter time constant and IMC filter time constant. In order to show the effectiveness of the proposed set-point regulator over classical 1-DOF and 2-DOF control structures, two simulation examples are given. A first order plus dead time (FOPDT) system is chosen for the first example. As a second example, a high order system with large dead time is used and the system is modeled as FOPDT. The aim of the second example is to show the effectiveness of the proposed structure even when there is a modeling error. In order to have a fair comparison of different control structures five different performance criteria are used for simulation studies. The results obtained from the simulation show that the set-point regulator with blending mechanism (SPR-BM) ameliorate the overall performance of the system with respect to load disturbance rejection and set-point following. Also it shapes the reference signal during the transient response; therefore it exhibits the best system output. Keywords: Reference regulator, blending mechanism, process control, internal model control, PID controllers, set-point following
Improving the performance of blocking supervisors
Get PDFSon otuz yıl içerisinde bilgisayar, haberleşme ve elektronik teknolojisindeki hızlı gelişimin bir sonucu olarak yeni bir tür dinamik sistem ortaya çıkmıştır. Öyle ki bu tür dinamik sistemler incelendiğinde, büyük bir bölümünün çoğu zaman tamamının ayrık, zamandan bağımsız değişkenlerle kontrol edildiği görülmektedir. Üretim sistemleri, bilgisayar sistemleri, haberleşme sistemleri, hava trafik sistemleri gibi birçok sistem bu tür sistem sınıfına girmektedir. Bu tür sistemlerin davranışı genellikle eş zamansız olarak oluşan ayrık olaylara bağlı olarak değişir. Bu özellikleri nedeniyle bu sistemler Ayrık Olay Sistemleri olarak adlandırılmaktadır. Ayrık olay sistemi çok fazla olası kilitlenme içerdiğinde denetimsel gözetleyici olarak en az kısıtlamalı kilitlenmesiz çözümü seçmek tutucu bir çözüm oluşturabilir. O zaman toplam performansı arttırmak için kilitlenmesiz olma koşulunu esnetmek kaçınılmaz bir olgudur. Diğer bir taraftan tam başarımlı çözümü denetimsel gözetleyici olarak seçmek bazı olası kilitlenmelerden dolayı ciddi sistem arızalarına sebebiyet verebilir. O zaman bu iki sonucu bağlayan bir denetimsel gözetleyiciye ihtiyaç vardır. Bu yüzden bu çalışmada optimizasyon yaklaşımını kullanarak kilitlenme ve başarım arasındaki denge araştırılmıştır. İlk olarak kilitlenme ve başarılara karşılık gelen kelimelerin nümerik değerlerine dayanan yeni bir performans ederi ortaya çıkartılmıştır. Önerilen formülasyon klasik optimizasyon yaklaşımını barındıran temel değiş tokuş özelliğine sahiptir. Aynı zamanda istenilen işaretli dili olabildiğince üreten optimal kilitlenebilir çözümü araştıran yeni bir algoritma önerilmiştir. Anahtar Kelimeler: Ayrık olay sistemleri, kilitlenme, düzenli diller, performans değerlendirme.We can not model discrete event systems by employing ordinary differential equations, this being their most important difference from time-varying dynamic systems. Rather discrete event systems evolve in time in the form of events occurring at possibly irregular time intervals. Therefore, we often model them as regular languages represented by deterministic finite state automata. In addition, in order to examine the behavior of the system, we modify the behavior by a control action. Ramadge and Wonham's supervisory control theory is a powerful tool to build variety of modifications in the model through a supervisor. However, the supervisor can not usually mark all the desired behaviors of the system, which are built according to nonblocking and controllability constraints. Thus blocking becomes a crucial task in discrete event systems. Industrial examples give support to this observation too. We observe that supervisory control problems with blocking are generally more widespread than those without blocking, and blocking supervisors are preferred to nonblocking ones in several applications. Among these applications, database concurrency control, the protocols coupled with deadlock detection schemes are most popular since deadlock prevention and avoidance are impractical. When we examine a discrete event system within the corresponding admissible language, too many blockings may be realized. We then usually select minimally restrictive nonblocking solution as the supervisor, even though it is inadequate due to its restrictive behavior. Since it prevents all uncontrollable events that lead to blocking minimal restrictive nonblocking solution can provide a conservative result. As a result, the supervisor can generate only a small part of admissible marked language. As such this strategy may constrain the behavior of the system considerably. On the other hand, the completely satisfying solution generates all the admissible marked strings, but its price adds too many blockings to the supervised language. Therefore, neither of these two results can be acceptable in many discrete event system problems. Here the success of the supervisor is related to the generated admissible marked language. Then it will be of interest to relax the nonblocking requirement and consider the synthesis of blocking supervisors. What motivates us to consider blocking solutions is that by allowing a certain amount of blocking, we can increase the part of admissible marked language that can be achieved under control. At this point the following question needs to be answered. "How many blockings do arise?" This work aims to find a formal answer to this question. In the literature blocking supervisors were first studied by Chen and Lafortune. If possible, the proposed solution may improve the performance either by reducing the supervised language's blocking without affecting its achievement or by increasing the supervised language's achievement without affecting its blocking. But, the literature did not concern with improving the performance by reducing the blockings and achievements at the same time. Furthermore, the generated strings on the system have different meanings in practice. For example, some strings, which symbolize critic tasks, have high importance compared to other strings. Thus the differences between the strings have to be taken into consideration to select the best supervisor. In this work, we propose a new approach to overcome these drawbacks. Firstly, we suggest a new metric space and introduce a new performance measure including blocking. The performance of blocking supervisors hold on two concepts: blocking and failure. The defined performance measure captures the fundamental concept, as it is given over sum of blocking measure and non-satisfying measure. Afterwards we propose a new method to select an optimal blocking but also maximally permissive supervisor from the acceptable solution set. The proposed algorithm removes some strings in a sequence from the initial language in order to optimize the performance. As it is usually required to generate as many as possible admissible marked strings, the complete satisfying solution is selected as the initial language. Also it is proved that the final solution obtained will be the maximally permissive and the optimal blocking supervisor. Also, the method is explained over a database management system. Keywords: Discrete event systems, blocking, regular languages, performance evaluation
Radyal ve çembersel çatlaklı halka plakta serbest titreşimler
Get PDFIn this study, free vibrations of annular plates with radial and circumferential cracks are investigated by means of finite element method. The cracks occurring in the plate are non-propagating and open. The crack in the element was modeled by an additional flexibility matrix, the terms of which were calculated using fracture mechanics. For vibration analysis of annular plate by using finite element method, an isoparametric sector type element with radial through and circumferential crack of four nodes and three degrees of freedom at each node is considered. In the event of the selection of small half sector angle, taking into account the closeness of the geometries of the sector and trapezoidal type element, the flexibility matrices of the sector type element with radial and circumferential crack are derived by means of the flexibility matrix of the trapezoidal type element. The natural frequencies of annular plates are examined for different length, number of cracks and locations of cracks. The theoretical results are also obtained with different boundary conditions. The obtained results of improved elements are compared with the theoretical and experimental results in the literature. The results are in good agreement with the results in the literature. It is observed that the changes of the length, location and number of cracks have various effects on the natural frequencies of the plate. Keywords: Radial crack, circumferential crack, free vibration, sector type element, annular plate. Bu çalışmada radyal ve çembersel çatlaklı halka plakların serbest titreşimleri sonlu elemanlar yöntemiyle incelenmiştir. Açık ve ilerlemeyen yapıda kabul edilen çatlak, terimleri kırılma mekaniği yardımıyla hesaplanabilen bir ek esneklik matrisi ile modellenmiştir. Küçük yarı sektör açısı seçilmesi durumunda, sektör ve yamuk elemanın geometrik yakınlığından dolayı, radyal ve çembersel çatlaklı sektör elemanın esneklik matrisleri yamuk plak elemanın formülasyonları kullanılarak elde edilmiştir. Çatlaklı halka plağın doğal frekansları farklı sınır şartları, çatlak boyu ve sayısı kullanılarak elde edilmiştir. Geliştirilen elemanla elde edilen sonuçlar literatürdeki teorik ve deneysel çalışmalarla karşılaştırılmış ve uygun sonuçlar elde edilmiştir. Çatlak boyu, yeri ve sayısının halka plağın doğal frekanslarına değişik etkileri olduğu gözlenmiştir. Anahtar Kelimeler: Radyal çatlak, çembersel çatlak, serbest titreşim, sektör eleman, halka plak. 
A dynamic node model for point queue modelling
Get PDFBu çalışmada; karayolu ağlarında akım yayılımını modelleyen ve bir dinamik ağ yükleme sürecinde tümleşik olarak kullanılabilen analitik bir dinamik düğüm noktası modeli yardımıyla, bağ girişlerinde meydana gelen nokta kuyruklanmanın modellemesi yapılmıştır. Önerilen dinamik düğüm noktası modelinin; bağ çıkış formülasyonu temelli bir karma-boyut bağ modeli bileşeni ve akım korunumu, kapasite, akım dağılımı ve negatif olmama kısıtlarını içeren bir düğüm noktası kuralları bileşeni vardır. Oluşturulan dinamik düğüm noktası formülasyonu, belirlenen kısıtlar altında benzetim yoluyla çözülmüştür. Nokta kuyruk varsayımı ile oluşturulan bağ modeli bileşeni; aşırı-doygun trafik akım durumunu değerlendiren bir yapıdadır. Zaman boyutunda yapılan ayrıklaştırma, aşırı-doygun duruma ilişkin konulan kapasite kısıtı ve düzgün ivmelenen taşıt hareketi varsayımı ile oluşturulan bağ modeli bileşeni, gerçekçi trafik akım dinamiklerinin temsiline olanak sağlamıştır. Bağ modeli ile belirlenen akımlar, düğüm noktası bileşenine girdi olmaktadır. Akımların düğüm noktası bileşeninde, önceden tanımlı dağılım oranları ve ayrılan bağ özellikleri ile işlenmesi ile ayrılan bağ giriş akımları hesaplanır. Modellenen nokta kuyrukların; i) kapasitenin aşıldığı herhangi durumda ve ii) modeli çözmek için zaman düzeyinde yapılan ayrıklaştırmaya bağlı olarak, bir önceki hesaplama anından arta kalan akım hacmi varolduğu durumda belirdiği varsayılmıştır. Nokta kuyruk modellemesi için önerilen yeni dinamik düğüm noktası modeli, karma-boyut yaklaşımı temeli üzerinde yapılandırılmış tek düğüm noktası modelidir. Yeni modelin aşırı-doygunlukta gerçekçi sonuçlar verdiği görülmüştür. Anahtar Kelimeler: Ulaştırma ağı, trafik akımı, düğüm noktası modeli, benzetim.Point-queuing and physical queuing are the two main assumptions that have been made in problems of Dynamic Network Loading (DNL) in order to model link and network performances. The queue spillback can only be captured by physical-queue approach, which is more realistic. Accordingly, the recent trend on traffic flow modeling for Dynamic Traffic Assignment (DTA) is to propose models with physical-queue assumption. However capturing the effects of physical-queuing in DNL modelling brings difficulties in obtaining an optimal solution of a DTA problem. As an alternative, the point-queue assumption handles vehicles as points without physical lengths. The storage capacity of each link can be ignored. The queue spillback on a link can be simulated by assuming the existence of a buffer area in the initial node of the link, for the temporary storage of vehicles exceeding the maximum density. Therefore, all links can contain unconstrained number of vehicles and capacity constraint on a link can be applied without numerical and computational difficulties. Moreover, the outflow rate of a link is only affected by its own flow considering that the downstream links will always have sufficient storage capacities. In the literature, point-queue assumption has been made in a varying structure of flow models adopting both exit-flow function approach, and in travel time function approach to perform DNL. In this paper, a mesoscopic dynamic node model for network loading is proposed, based on discrete packets, to model the point-queue process on a highway node with multiple merging and diverging links. The model is run using theoretical input data to simulate point-queuing in over-saturation condition. The presented dynamic node model has two components; a mesoscopic link model set with an exit link function formulation, and an algorithm written with a set of node rules considering the constraints of conservation, capacity, flow splitting rates and non-negativities. First, the time-varying flows that enter to multiple merging links (inflows) simultaneously are input to the mesoscopic link model. The link model component is developed by both considering the over-saturation phenomenon and improving the computational efficiency on a previously proposed link model. This model, is set out with link exit function formulation, discretisation on time dimension, defining capacity constraint rules for over-saturated states and uniformly accelerated speed assumption, which allows a realistic representation of outflow dynamics. Model has an iterative structure, which enables convergence to any target performance criteria with the coded algorithm. The flows that exit from these merging links (outflows) are computed regarding the link and flow characteristics. Then outflows of the merging links are input to a node as inflows. These conflicting flows are processed within the node component with predefined splitting rates and characteristics of the diverging links, and then the nodal exiting flows are computed. The main difference of the proposed dynamic node model in comparison to other models is that it respects capacity constraints regarding to splitting rules and consequently holds first-in-first-out rule. For the link model component of integrated model structure has been set out with the point-queuing assumption, the point-queues and the delays calculated in the presence of these vertical queues are considered instead of the physical queues and the delays occurring as a result of over-saturation. The node model problem is formulated as to maximize the total flow passing through the node subject to the constraints of conservation, capacity, flow splitting rates and non-negativities. The optimization problem is solved by simulation within the modelling horizon. Simulation process of the proposed model lasted as the inflows to merging links are wholly discharged from the entire node structure. The integrated model structure provided more realistic results in representing outflow dynamics. It is seen that the outflows of the link model component existed respecting to capacity constraints and the diagrams of these outflows seemed alike the sinusoidal inflow curves under the set node configuration. Despite the flows requiring to enter the diverging links are above over-saturation rates, the capacity restraint is respected. The results show that the model appears realistic in the representation of point-queuing process and diverging link flow dynamics, and is quite easy to calculate. The future extension of this study will be on the application of the proposed model to a general network. Keywords: Traffic networks, traffic flow, node model, simulation
Artımsal yapay sinir ağları kullanılarak ultrasonik görüntülerin bölütlenmesi
Get PDFComputer aided segmentation systems are being used in order to help physicians in diagnosis. Mainly, two operations must be implemented for computer aided segmentation; 1) feature extraction, 2) segmentation. Feature extraction is the process in order to determine the different tissue characteristics of the image. However, segmentation is performed for extraction of different (discriminating) tissues found in the image. In this study, two novel incremental artificial neural networks, incremental self-organizing map (ISOM) and incremental self-organizing map trained by genetic algorithms (GISOM), are proposed for the segmentation of tissues in ultrasound (US) images. The elements of the feature vectors are formed by using the discrete cosine transform (DCT). The performances of the ISOM and the GISOM network are investigated for segmentation of the phantom cyst image. Feature vectors are formed by applying 2D-DCT and then taking only the coefficients (windows of 4x4 pixels) that represent low frequencies. Thus, the vector size is decreased and also the effect of noise in the image becomes minimum. There are two critical parameters that must be taken into account in extraction of features from US images when DCT is used. First one is the size of the window and the other one is the number of coefficients that will be used in feature vector after transform. Selection of big window size increases the frequency resolution but decreases the time resolution. On the other hand, selection of small window size increases the time resolution whereas decreasing the frequency resolution. In such case, a paradox of satisfying time or the frequency resolution arises. Selection of window size depends on the structural characteristics of tissue like coarseness and repetition. Window size must be enlarged as tissue becomes coarser. However, if the window size is chosen very large, since the probability of occurrence of different tissues in the same window will be higher, identification of the tissue becomes more difficult. Furthermore, using large windows causes heavier computational costs so training times are getting longer. When the window size is very small, tissue characteristics are lost. Therefore, the selected window must have a size that is capable of identifying the tissue sufficiently. The ISOM is an incremental unsupervised neural network. The topology of the ISOM is not necessarily to be predefined. The topology and the number of nodes of the ISOM are automatically determined during the training. Only a threshold value (ED) needs to be estimated before the training of the network. The threshold value controls the number of classes (tissues) in the US images. Low threshold value reveals the details (different tissues) in the segmented image. ISOM network searches for the optimum nodes to discriminate between tissues in the feature space. A compression-based method that is developed for this purpose is firstly proposed in the study. Both segmentation and compression processes can be accomplished in parallel after the training of the network is completed, nodes are determined and labeled. The weights and labels of all the nodes generated by the network are used to form the codewords stored in the codebook. Codewords stored in the codebook are coded by using Huffman coding and sent to the receiver. The mean square error (MSE) value of the compressed image obtained by this method changes depending on the ED value. MSE values decreases when ED value is set to a low value, and increases for high ED values. It is observed that ISOM network produces high-performance segmentations for low values of MSE. In order to find the nodes that best represent complex tissue distribution in US images and to decrease the number of nodes, incremental self-organizing neural network trained by genetic algorithms (GISOM) is firstly proposed in this study. The weights of only the first layer nodes are searched by genetic algorithms. Nodes are determined during the training depending on need, and the optimum nodes are searched. Each node in the pool represents a unique different tissue. Fitness value calculation, reproduction, crossover and mutation operations are performed in each generation. The string that gives the best fitness value after 20 generations is assigned as the new node of the network. The fitness function used in the training of the network enables the new candidate node to represent the most number of vectors in the training set by minimizing the error of vectors represented by candidate node.The GISOM network gave the best performances with less number of nodes compared to the other network. Keywords: Image segmentation, ultrasound, incremental neural networks, genetic algorithms.Bu çalışmada, yapay US görüntüsü iki yeni artımsal yapay sinir ağı (ArÖz ve GArÖz) kullanılarak bölütlenmiştir. Öznitelik vektör elemanları, iki boyutlu ayrık kosinüs dönüşümü (2B-AKD) uygulanarak sadece alçak frekansları temsil eden katsayıların alınması (4x4 benek büyüklüğündeki pencereler) sonucunda oluşturulmuştur. Böylece hem öznitelik vektör boyutu azalmış hem de görüntüde var olan gürültülerin etkisi azaltılmıştır. Artımsal öz-düzenlemeli (ArÖz) ağın düğüm sayısı, eğitim sırasında ihtiyaca göre otomatik olarak belirlenmektedir. Ağın eğitiminden önce belirlenen eşikdeğeri (ED) düğüm sayısını kontrol etmektedir. Ağın en iyi düğümlerini belirlemek için sıkıştırma temelli bir yöntem geliştirilmiştir. Ağın eğitimi tamamlandıktan ve düğümler belirlenip etiketlendikten sonra, hem bölütleme işlemi hem de sıkıştırma işlemi paralel olarak gerçekleştirilmektedir. Ağ tarafından üretilen tüm düğümlerin ağırlıkları ve etiketleri kod sözcüğünü oluşturmak için kullanılmaktadır. Genetik algoritmalar ile eğitilen artımsal öz-düzenlemeli (GArÖz) ağ, US görüntülerindeki karmaşık doku dağılımını en iyi temsil edecek düğümleri bulmakta ve düğüm sayısını azaltmaktadır. Genetik havuzun derinliği 20 dizi olarak seçilmiş ve eğitim kümesinden rasgele alınan vektörler ile genetik havuz oluşturulmuştur. Ağın eğitiminde kullanılan uyumluluk fonksiyonu, aday düğüm ile temsil edilen vektörlerin hatasını en aza indirgeyerek yeni aday düğümün eğitim kümesinden en fazla vektörü temsil etmesine olanak sağlamaktadır. Her iki ağın yapay kist görüntüsünü bölütleme başarımları karşılaştırmalı olarak incelenmiştir. GArÖz ağının daha az düğüm kullanarak daha yüksek başarımlar verdiği gözlenmiştir. Anahtar Kelimeler: Görüntü bölütleme, ultrason, artımsal yapay sinir ağı, genetik algoritmalar
Use of simulated and real acceleration records for microzonation
Get PDFMikrobölgelemenin bir tanımı; olası deprem özellikleri ile mevcut zemin özellikleri arasındaki karşılıklı etkileşimi göz önüne alarak, zemin yüzeyinde seçilen deprem özelliklerini ve bunlarla ilişkili yapı tasarım parametrelerinin değişimini belirlemek olarak verilebilir. Bu çalışmada, mikrobölgeleme amaçlı zemin davranış analizlerinde yapay ve ölçeklenmiş gerçek kayıtlar kullanılarak farklı deprem ve yapı tasarımı parametrelerinin zemin yüzeyindeki değişimi incelenmiştir. Çalışmanın ilk aşamasında, gerçek deprem kayıtları kullanılarak en büyük ivme ölçekleme yöntemi ve RASCAL yapay kayıt programı yardımıyla iki farklı şekilde ivme zaman kayıtları üretilmiştir. Balıkesir tasarım depremi için üretilen bu kayıtlar, 105 zemin profilinin davranış analizlerinde kullanılmış ve yüzeydeki yer hareketi parametrelerinin frekans dağılımları hesaplanmıştır. En büyük yatay ivme, Arias şiddeti ve spektral ivme olarak seçilen parametrelere ait frekans dağılımlarında, kullanılan gerçek kayıtların önemli bir faktör olduğu görülmüştür. Sonuçlar özellikle en büyük ivme ölçekleme yöntemi için kullanılan gerçek kayıtlara dayalı olarak frekans dağılımlarının önemli oranda değişebileceğini göstermiştir. Diğer taraftan bu etki tasarım parametresine göre de farklılık gösterebilmektedir. Çalışmanın ikinci aşamasında RASCAL programı ile üretilen kayıtların kullanıldığı davranış analizleri için, NEHRP kriterlerinin sağlandığı bir optimizasyon yaklaşımına dayalı olarak spektral ivmeler belirlenmiş ve bu ivmeler aynı tehlike seviyesi için NEHRP yaklaşık yöntemine göre bulunan spektral ivmelerle karşılaştırılmıştır. Sonuçlar tasarım depremi ve zemin özellikleri arasındaki karşılıklı etkileşime dayalı farklılıkların D grubu zeminler için daha yüksek olduğunu ve bu etkileşimde yüzeydeki yer hareketi özelliklerinin zemin davranış analizleri ile bulunmasının önemli olduğunu göstermektedir. Anahtar Kelimeler: Mikrobölgeleme, yapay deprem kayıtları, ölçekleme, en büyük ivme, Arias şiddeti, spektral ivme.Soil layers under earthquake excitations can strongly influence earthquake characteristics on the ground surface. These effects may be evaluated with respect to structural design parameters based on microzonation studies. In a microzonation study, the variation of selected ground motion parameters on the ground surface are determined by taking into account the interaction between ground motion and local soil conditions. In this study, the interaction between earthquake and soil characteristics were evaluated based on simulated and real acceleration records used for site response analyses with respect to different parameters. In the first stage, simulated acceleration records were generated by RASCAL frequency domain procedure (Silva and Lee, 1987) and real acceleration records were scaled with respect to the estimated peak ground acceleration. RASCAL (Response Spectra and Acceleration Scaling) is a semi-empirical procedure, which evolved from random vibration theory-based techniques, with the additional utilization of the observed Fourier phase spectrum of a real ground motion recording. Input target spectra used in this simulation procedure are uniform hazard spectra developed using two attenuation relationships based on different data sets for predetermined probabilistic earthquake hazard (M=7.5 with epicenter of R=40km corresponding to exceedance probability of 10% in 50 years) (Ansal, 2001). Input acceleration time histories were selected from the earthquake records in Turkey with magnitude range, M≥5 and distance, 27km<R<71km. Taking into account regional source characteristics for Balıkesir, stress drop was taken as Δσ=100 bar. For the whole-path attenuation, frequency-dependent Q model of Q(f)=300 f 0.5 was adopted. As for the near surface attenuation, the kappa values was taken as κ=0.035. With RASCAL program, six simulated time histories were generated based on six different real earthquake records. In the scaling option, previously recorded real acceleration records were scaled with respect to the peak ground acceleration estimated based on the earthquake design parameters (M=7.5, R=40 km). The peak ground acceleration on the rock outcrop was calculated as 0.26g, corresponding to the exceedance probability of 10% in 50 years. Previously recorded real acceleration records were selected with respect to ratio factor determined for scaling procedure. With scaling option, six acceleration time histories were calculated based on different earthquake records. Characteristics of both sets of acceleration records were calculated and compared. It was observed that the range of some parameters such as maximum velocity and velocity spectrum intensity were smaller for the records calculated by RASCAL procedure. Using two groups of acceleration records, site response analyses were conducted by SHAKE91 (Idriss and Sun, 1992) based on 1D equivalent linear method for 105 soil profiles selected previously. Response variability on the ground surface was evaluated in terms of histograms of peak acceleration, Arias intensity and spectral acceleration at 0.2s. In the case of peak and spectral accelerations at 0.2s, the analyses using real scaled records yielded very different statistical distributions for each record. However, the results of the analyses using input records generated by RASCAL gave very similar statistical distributions for all the records in this set. In the case of Arias intensity, both sets of records were found to be more effective yielding different statistical distributions on the ground surface for each input record. In the second stage of this study, the average acceleration response spectra for each soil profile were calculated according to the analyses conducted with records simulated by RASCAL. Utilizing an optimization approach that provide all the requirements of the NEHRP design spectrum, spectral accelerations for short and long periods were determined for average response spectra. These spectral accelerations were compared with spectral accelerations obtained from the NEHRP formulation corresponding to the same earthquake hazard level. The results indicate that the variability based on the interaction between earthquake and soil characteristics was relatively large for D group soils and that the frequency content of ground motions have significant effect on site response. Keywords: Microzonation, simulated acceleration records, scaling, peak ground acceleration, Arias intensity, spectral accelerations. 
Building an expert system for supervising and management of underground rock structures
Get PDFYeraltı kaya yapısı yerkabuğu içinde herhangi bir boşluğun açılmasından sonra bu boşluğu çevreleyen ana kayadan oluşan, mühendislik açısından yeterli ve güvenli taşıyıcı sistemlerdir. Kayanın açım sırasında karşılaşılan niteliklerinin saptanması ve değişimlerinin sürekli olarak izlenmesi yeraltı kaya yapısının denetim çalışmalarını, önlem alınmasını gerektiren durumlarda izlenmesi gereken yöntem ve işlemlerin belirlenmesi ise yönlendirme çalışmalarını oluşturmaktadır. Denetim çalışmaları kapsamında ayrıntılı mühendislik jeolojisi ve geoteknik araştırmalar yapılmaktadır. Yapım sırasında sağlanan çok sayıda veri birbirleri ile ilişkilendirilerek incelenmek zorundadır. Uzmanlık ve titiz çalışma gerektiren denetim çalışmaları yapılmadığında ise tünelde deplasmanlarla karşılaşılabilmekte, göçükler olabilmektedir. Uzman sistemler en genel anlamıyla insanın düşünme yöntemini ve mantığını taklit eden bilgisayar programlarıdır. Yeraltı kaya yapılarının denetimi ve yönlendirilmesi çalışmaları sırasında kullanılacak bir uzman sistem yüzlerce verinin arşivlenmesini sağlayacak, verileri birbirleri ile ilişkilendirecek ve deplasmanları her ölçüm noktası için sürekli olarak izleyecektir. Yazılım uzman sistemlerinin yapısı gereği bir problem olması durumunda problemin nedenlerini ortaya koyacak ve mühendise çözümü rapor edecektir. Çalışmanın amacı; yeraltı kaya yapılarının denetimi ve yönlendirilmesinde uzman sistemlerin uygulanabilirliğinin incelenmesi, örnek bir uzman sistem için algoritmanın kurulması ve bir uzman sistemin hazırlanmasıdır. Uzman Sistem ile Tünel Analizi (USTA) adı verilen yazılım Karadeniz Sahil Yolu Projesi kapsamında inşa edilen Nefise Akçelik tünelinde ve Sarayköy tünelinde uygulanmış ve uzman sistemin denetim ve yönlendirme çalışmalarındaki başarısı ile sağlayacağı faydalar tartışılmıştır. Anahtar Kelimeler: Uzman sistem, yeraltı kaya yapısı, tünel, geoteknik, mühendislik jeolojisi. Underground rock structure is the surrounding rock, which is safe and sufficient for engineering, of an underground opening. Defining the rock mass properties and observing the changes continuously is the supervising works and describing the methodology and process when needed is the management of underground rock structures constructions. In modern tunneling approaches, works which are done to define the rock mass properties, can be summarized as following: definition of geological conditions of tunnel face after excavation stages, definition of rock mass quality and definition of rock support system according to obtained data. The changes of rock properties are observed by geotechnical measurements. If needed, horizontal drillings are applied to determine the rock behavior along the tunnel. The data are evaluated and compared to the design foresights. This information is used to give a decision if displacements occur in the tunnel and underground constructions. Supervising and control works are performed by experienced engineers. If the steps described above are not applied fastidiously, deformation or even subsidence problems may occur during construction. To prevent this kind of problems, benefiting from computer technology could supply both economical and effective solution. Expert systems can be defined as computer programs, which imitate the thinking methodology and logic of human being. Because of being prepared for a specific subject, they are defined as experts. Using these programs in underground rock structure management works would facilitate the supervision and guidance. The expert system would be able to save hundreds of data, would evaluate them, and before a displacement problem occurs, it would warn the engineer, find out the reason of the problem and recommend a solution. Expert systems are having a high capacity to save different kind of projects at the same time. This would allow working on different construction sides simultaneously. The aim of the work is building an expert system for the supervising and management works of underground rock structures. The applicability of expert systems to tunnel management works are discussed by applying a prototype expert system to Nefise Akçelik Tunnel and Sarayköy tunnel, which constructed according to Black Sea Highway Project. An expert system, called USTA (Uzman Sistem ile Tünel Analizi or Universal Systems for Tunnel Analysis as well) is build by using Visual Basic 6.0. The program uses 7 Access files as knowledge base and data bank. It is possible to save 65 different tunnel projects, having a length of 1000 meters. For each excavation step, the user can save 6 photos, which are converted and saved to the data bank to avoid deletion from the disc. USTA uses Ms Excel and Ms Word for reporting and graphs. This makes it easier to share or save the information. What?s more; the program has a sample project library, which can be improved by adding new projects by users. This makes it possible to get solutions or ideas from similar projects. It is important to note that USTA is the first prototype expert system, which is prepared for underground rock structures managements. There are many expert systems around the world, but they are commonly used during design phases. USTA is applied to two tunnel projects, constructed in Black Sea Region in Turkey. Both tunnels encountered to huge displacement problems, up to 12 ? 14 cm. Support and improvement works have been done by EMAY Int. Eng. Cons. and Trd. Co. Ltd. with cooperation of IT., Engineering Geology division to reduce the displacements. The obtained excavation and geotechnical measurement data were saved to USTA to find out its effectiveness. As a result; USTA was able to warn the user at the right moment when displacement started to occur. The program calculated the displacement velocity and acceleration. The reasoning of the displacements, reported by USTA were very similar to the displacement cautions, defined during design phases. The program recommended in-situ geomechanical parameters for re-calculation phases of support systems. The in-situ geomechanical parameters were very close to the parameters calculated by FEM back-analysis. Keywords: Expert system, underground rock structure, tunnel, geotechnics, engineering geology
The general aspect of anomalous coating behaviour of iron group alloys
Get PDFDemir grubu metal (Fe, Ni ve Co) alaşımlarının sahip oldukları manyetik ve termofiziksel özelliklerden dolayı elektrokaplanmış demir grubu metal alaşımlarının endüstride önemli kullanım alanları mevcuttur. Söz konusu alaşımların endüstriyel öneme sahip olmaları yanısıra anormal kaplama olarak tanımlanan olayın, demir grubu alaşımların elektrokaplamasında görülmesi de bu sistem üzerinde yoğunlaşan çalışmaların bir başka nedenidir. Demir grubu elementleri olan Ni, Fe ve Co arasında termodinamik olarak en soy olanı Ni, en az soy olanı ise Fe elementidir. Bu üç metal arasında ikili ya da üçlü olarak gerçekleşecek alaşım kaplama reaksiyonları kinetik olarak karşılaştırıldığında Ni’in hem Co hem de Fe’e göre öncelikli olarak kaplanması beklenebilir. Ancak anormal kaplama davranışı gereği Ni kaplama, Co ve/veya Fe kaplama tarafından yasaklanmaktadır ki benzer durum Co ile Fe arasında da mevcuttur. Normal alaşım kaplamaya göre ilginç olan bu kaplama davranışı sonucunda endüstriyel anlamda istenilen manyetik özelliklere sahip ikili ve üçlü demir grubu alaşımlar üretilebilmektedir. Anormal kaplama olarak ifade edilen bu sıradışı kaplama olayının mekanizmasına açıklık getirebilmek adına günümüze kadar süregelen çalışmalar yapılmıştır. Yapılan çalışmalarda araştırmacıların hemfikir olduğu nokta termodinamik olarak soy olan metalin kaplanmasının daha az soy olan metal tarafından engellendiğidir. Bu çalışmada alaşım kaplama yöntemlerinden biri olan elektrokaplama yöntemi kısaca tanıtılmıştır. Bunu takiben literatürde yeralan ikili ve üçlü demir grubu alaşımların elektrokaplamasına özgü anormal kaplama davranışını açıklamaya yönelik çalışmalar özetlenmiştir. Anahtar Kelimeler: Elektrokaplama, anormal kaplama, manyetik alaşımlar, ince film.Electrodeposition, also known as electroplating, refers to the process where a thin film of metal is deposited onto a conductive substrate under an applied current. The electrodeposition of alloys on a substrate requires the simultaneous deposition of two or more metals. Electrodeposition is both a cost-effective and simple method to produce thin film materials (such as NiFe, CoNi, CoFe and NiCoFe). Nickel, cobalt and iron, ( iron-group metals), and their alloys are important engineering materials in many applications because of their unique magnetic, corrosion and wear-resistance, thermophysical and electrocatalytic properties. For example, NiFe and NiCoFe alloys are strong candidates for application in high density magnetic recording heads due to their high saturation flux density and low coercivity. These functional materials are usually prepared by electroplating because this technique is often much cheaper and simpler than other methods. In addition, advantages of electrodeposition include low deposition temperature and the simplicity of the required apparatus. The magnetic properties of these materials are seriously affected by their composition and structure thus, reliable control of these properties for the iron-group alloys is important for their wide applications. The standard equilibrium potentials of Ni, Co, and Fe are 0.25, 0.27, and 0.44 V vs. the normal hydrogen electrode (NHE), respectively. Therefore from a thermodynamic consideration Ni is the most noble of the three metals. On the basis of these values, in normal codeposition, nickel is expected to electroplate preferentially to cobalt and cobalt preferentially to iron. When these metals are plated individually, the kinetics of the electrodeposition of individual metals follows the trend expected from the standard equilibrium potential. However, when Fe is present in the same solution with either Ni, Co or both ions, there is often potential range where the rate of Fe deposition exceeds the rate of Ni and Co deposition occurs. The called anomalous codeposition of iron group metals is characterized by the less noble metal deposition preferentially to the nobler one. In other words, the reduction of nickel is inhibited while the deposition of iron and/or cobalt are enhanced when compared with their individual deposition rates. The study on the anomalous deposition of the iron-group alloys can be traced back to 1927. The mechanism of anomalous codeposition of iron group metals has been studied by many researchers and several hypotheses have been presented in the literature. Although many models have been proposed in the literature, the exact mechanism of the anomalous codeposition process is still not well understood. Anomalous codeposition is a term first introduced by Brenner for binary alloy system, such as NiCo, NiFe and ZnNi. Among these, the NiFe system is most studied. One of the earlier explanations of anomalous codeposition in NiFe binary system was put forth by Dahms and Croll. Their model based upon the inhibition of nickel reduction due to the formation of the hydroxide of the less noble metal, Fe(OH)2. The hydroxide is considered stable because of the high pH calculated at the electrode surface. Andricacos and coworkers were the first to systematically examine the role of hydrodynamics in the deposition process of NiFe binary alloy. In their study, iron came under mass transport limitations at high enough currents. The nickel deposition inhibition was seen to increase with increasing rotation rate. Recent studies of NiFe have utilized this theory; both Hesssami and Tobias and Grande and Talbot have focused on the discharging of the monohydroxyl ion on the electrode surface. The most widely accepted explanation for the anomalous codepostion is that precipitation of ferrous hydroxides on the cathode, caused by an increase in the pH due to hydrogen evolution, inhibits Ni and/or Co reductions. The anomalous codeposition of iron group metal is still not completely understood. Therefore, it would be of academic interest to conduct research of the anomalous codeposition of the iron group metal in order to obtain understanding of the factors that control the anomaly of Fe and Co deposition in the codeposition process. This could allow researcher to control the rates of deposition of the individual metal component in the NiCoFe alloys. As a result, it would lead to better control of the physical, mechanical and magnetic properties of electrodeposited iron group alloys. Keywords: Electroplating, anomalous coating, magnetic alloys, thin film
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