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Yağış verilerinin yapay sinir ağları ve dalgacık dönüşümü yöntemleri ile tahmini
Get PDFForecasting the precipitation which is one of the most important meteorological variables is very important for planning and management of the water resources. Accurate precipitation prediction is one of the most difficult tasks in the meteorology because the complex physical processes involved and the variability of the precipitation is highly dependent on small scale processes and local geography. Especially the daily precipitation forecasting is one of the most challenging works and very important for the flood and drought analyses. Artificial Neural Networks (ANN) are a useful tool to identify this relation. ANN approach is extensively used in the water resources literature in recently years. Artificial neural networks which is a black-box model, is used successfully in the modeling of non-stationary and complex variables. Black-box models are divided generally as linear and nonlinear and in particular artificial neural networks method is used in the modeling of nonlinear system behavior. The artificial neural networks have some advantages, such as easily applied, not needing much data. However the accuracy of model predictions is very subjective and highly dependent on user's ability, knowledge and understanding of the model. Especially, the input selecting is one of the most important phases in any ANN modeling study Because of this, wavelet transformation is used for increase of user ability and success of artificial neural networks. The wavelet transform, which can produce a good local representation of the signal in both the time and frequency domains, provides considerable information about the structure of the physical process to be modeled and has positive effects on the ANN modeling ability. Because of these reasons, coupling wavelets with the ANN can provide significant advantages on predicting. This study aims to predict the daily precipitation data of three belong to Turkish meteorological stations by applying the ANN methods and discrete wavelet transform. For this reason, the original time series were decomposed into a certain number of sub-time series using the wavelet transform. Then, the suitable sub time series constituted the inputs of the ANN and the resulting model was applied to forecast the original time series. The sub time series decomposed by discrete wavelet transform from the original time series provide detailed information about the data structure and its periodicity. Behavior of each sub-series is different. For the selection of dominant sub-series, the correlation coefficients between the decomposed wavelet sub-series and the observed precipitation time series are computed. The selection of dominant sub-series becomes effective on the output data improving ANN model's performance. In this study, the wavelet transforms and the ANN has been applied to estimate the daily precipitation. The meteorological data belong to the three station were investigated for this study. These are the daily mean temperature, the daily maximum temperature, the daily minimum temperature, the daily total specific humidity, the daily total evaporation and the daily total precipitation. Each of the meteorological data considered as input for the ANN model was decomposed into the wavelet sub-series by Discrete Wavelet Transform (DWT). Then, ANN configuration is constructed with appropriate wavelet sub series as input and the original precipitation time series as output. So, different wavelet-ANN models were prepared for each station. Precipitation estimation was applied with the two different algorithms of the artificial neural networks. Employment of the Feed Forward Back Propagation (FFBP) in the precipitation estimation is compared with the Radial Basis Function (RBF) performances. The results were also compared with linear regression model. As a result, it was seen that the wavelet-feed forward back propagation method provided the best estimation performance. Results indicate that the wavelet-ANN model estimations were superior to the ones obtained by the multi linear regression model. The wavelet-ANN models have provided a good fit with the observed data, especially for the time series which have zero precipitation in the summer months. It was seen that the ANN-wavelet method provided very successful estimation performance. This study is the first application to the daily precipitation estimations using the wavelet sub-series of the various meteorological variables in the water resources literature. The wavelet-ANN method is especially convenient in variables having non-linear dynamics such as predicting of precipitation data. Keywords: Artificial Neural Networks, wavelet, precipitation.Meteorolojik değişkenlerden birisi olan yağış, su kaynakları açısından çok önemlidir. Yağış, akışı meydana getiren en önemli değişkendir. Kısa süreli aşırı yağışlar önemli taşkınlara neden olmaktadır. Uzun sürelerde yeterli yağışın meydana gelmemesi durumunda kuraklık meydana gelmektedir. Karmaşık bir fiziksel süreç sonucunda meydana gelen yağışın doğru tahmin edilmesi genellikle zordur. Özellikle yersel değişimlerden ve bölgesel özelliklerden oldukça etkilenmesi yağışın tahminini daha zorlaştırmaktadır. Lineer olmayan sistemlerin davranışında başarıyla kullanılabilen bir kara-kutu modeli olan yapay sinir ağları, böylesine karmaşık değişkenlerin tahmininde başarıyla kullanılmaktadır. Yapay sinir ağlarında tahminin başarısı üzerinde kullanıcının etkileri sınırlıdır ve daha çok girdilere bağlıdır. Yapay sinir ağları yönteminin tahmindeki başarısını arttırmak için dalgacık dönüşümü bu çalışmada kullanılmıştır. Dalgacık dönüşümü, verilerin hem zaman hem de frekans ortamında incelenmesine olanak sağlayan bir yöntemdir. Bu çalışmada Yapay Sinir Ağları (YSA) ve dalgacık dönüşümü yöntemleri ile günlük yağış tahmini yapılmıştır. Bu amaçla Türkiye’ye ait 3 istasyonun günlük meteorolojik verileri kullanılmıştır. YSA yönteminin literatürde en çok kullanılan algoritmalarından, İleri Beslemeli Geriye Yayılmalı Yapay Sinir Ağları (İBGYSA) ve Radyal Tabanlı Yapay Sinir Ağları (RTYSA) yöntemleri yağış tahmini amacıyla kullanılmıştır. Farklı girdi kombinasyonları denenerek her istasyon için en uygun model bulunmaya çalışılmıştır. Sonuçlarda ileri beslemeli geriye yayılmalı yapay sinir ağları algoritmasının kullanıldığı yöntem en iyi performansı göstermiştir. Dalgacık dönüşümü-YSA yönteminin tahmin sonuçları çoklu lineer regresyon yönteminin sonuçları ile kıyaslanmış ve performans kriterlerine göre daha iyi olduğu bulunmuştur. Anahtar Kelimeler: Yapay Sinir Ağları, dalgacık dönüşümü, tahmin, yağış
Jeodezik ölçüler ile deprem kaynak parametrelerinin belirlenmesi
Get PDFFunctional relations can be established between geodetic observations and earthquake source mechanism under certain assumptions. In this way, it is possible to compute surface displacements with direct modeling using certain fault geometry and slip values. However, computation of fault geometry and slip values which best fit to the surface displacements requires advanced optimization methods together with complicated analytical functions. Although, geological surface observations and seismic focal mechanism solutions provide first-order information about fault geometry and slip vector, they are particularly inadequate for relatively small earthquakes where no surface ruptures are formed and seismic networks are not sufficiently dense. For this type of inversion situations, classical parameter estimation methods such as least-squares and derivative-based optimization methods may fail depending on the a priori values of parameters and produce local estimates of a global optimization problem. Monte-Carlo methods which have been in use for years in other fields of engineering are quite slow for large optimization problems. However, statistical mechanisms behind such methods are particularly useful for investigating complicated problems which intrinsically contain many local minima. In such cases, these heuristic methods provide sufficient convergence when iteration number is kept high. Other methods such as exhaustive searches or grid approximations prove to be inefficient when number of parameters is more than three. This study employs Simulated Annealing for determining fault geometry parameters from a set of surface geodetic observations. In this method, Monte-Carlo runs are controlled by a parameter called critical temperature. When the cost is lower than the previous iteration, new set of parameters are always accepted while the cost is higher than the previous iteration new set of parameters are only accepted if the temperature is sufficiently cool. Critical temperature decreases with according the pre-assumed probability distribution. In terms of inverting geodetic observations for fault parameters, a standard normal distribution was found to be sufficiently efficient. This procedure is analogous to cooling of metals after being exposed to high temperature heat which gives the name of the algorithm. Determination and modeling of seismic displacements can be considered a two-fold phenomenon. One is dispersing such effects from geodetic networks and the other one is quantifying the effects of earthquakes at cm level precision which are inevitable for Turkey and presenting them as input to the other disciplines. Turkish National Horizontal Control Network (TNHCN) has been serving surveying community for more than half a century. However, seismic deformations of 20th century are predicted to have distorted the network up to 10 meters. Considering the relatively less geometrical precision, TNHCN is often regarded as inappropriate for demanding applications. Nevertheless, most cadastral maps and other plans are expressed in TNHCN and TNHCN has to be accurate at a specified level. İzmit Earthquake which occurred on August 17th, 1999 has been an interest of geosciences community for years. While the efforts to quantify the related deformation was mostly focused on the geodynamical aspects of surface deformation. Considering that the region of earthquake is a dense population area involving intensive cadastral applications, deformation of geodetic networks due to earthquakes is an equally important topic. Restoration and re-organization studies which immediately begin after an earthquake need a well-maintained geodetic re-infrastructure which is also subject to displacements of a few meters. In this study, possible methods of inverse modeling using various geodetic observations ranging from Global Positioning System to high-precision spirit leveling were investigated and simulated annealing, which is considered the most appropriate method, was tested for 1999 İzmit Earthquake, using the software tools developed within the study. Comparison of results with other studies shows that vertical components are noisier in terms of dynamical modeling than horizontal components up to an order of ten implying non-earthquake vertical deformation. Results also reveal that computed fault geometry and slip values fit geodetic surface displacements are largely dependent on the optimization method. A new set of fault geometry and slip parameters for İzmit Earthquake are considered to better fit to the data than any other available studies. Keywords: Fault mechanism, displacement, optimization, inverse modeling, geodetic observations.Jeodezik ölçüler ile deprem kaynak mekanizması ilişkisi için belirli varsayımlar altında fonksiyonel ilişkiler kurulabilir. Bu şekilde belirli bir fay geometrisi ve kayma değerleri kullanarak yüzeyde meydana gelen yer değiştirmeleri “direkt modelleme” ile hesaplamak olanaklıdır. Ancak jeodezik ölçüler ile yüzeyde hesaplanan yer değiştirmelere en iyi uyan fay geometrisi ve kayma değerlerinin bulunması için karmaşık analitik ilişkiler yanında gelişmiş optimizasyon yöntemlerine ihtiyaç duyulmaktadır. Fay geometrisi ve kayma vektörünün yüzeyde gerçekleştirilen ölçüler yardımıyla bulunması “ters modelleme” olarak adlandırılmakta olup, söz konusu ilişkiyi sağlayan fonksiyon çok sayıda yerel minimuma sahiptir. Parametrelere ait başlangıç değerlerinin iyi bilinmediği durumlarda ters modelleme ile tümel minimum elde edilememektedir. Jeolojik yüzey gözlemleri ve jeofizik odak mekanizması çözümleri, fay geometrisi ve kayma vektörüne ilişkin belirli doğrulukta başlangıç değerleri sağlamakla birlikte özellikle yüzey kırıklarının gelişmediği ve sismik ağların sık olmadığı göreli olarak küçük depremlerde fay geometrisi ve kayma vektörüne ilişkin yeterli doğrulukta bilgi mevcut olmamaktadır. Bu çalışmada ters modelleme için uygun yöntem araştırması yapılmış, geliştirilen yazılım araçları yardımıyla en uygun olduğu değerlendirilen “benzetimli yaklaşım” yöntemi 17 Ağustos 1999 İzmit Depremi için test edilmiştir. Elde edilen sonuçlar farklı gruplarca yapılan çözümlerle karşılaştırıldığında bulunan fay geometrisi ve kayma değerlerinin jeodezik ölçüler ile bulunan yüzey yer değiştirme değerlerine diğer mevcut çalışmalardan daha iyi uyum sağladığı görülmüştür. Jeodezik yüzey ölçüleri ile yapılan ters çözümlerde özellikle başlangıç değerlerinin iyi bilinmediği durumlarda kullanılan optimizasyon yönteminin daha fazla önem kazandığı değerlendirilmektedir. Anahtar Kelimeler: Fay mekanizması, yer değiştirme, optimizasyon, ters modelleme, jeodezik ölçüler
An assessment of water reserve changes in Salt Lake, Turkey, through multi-temporal LANDSAT imagery and real-time ground surveys
Get PDFBu makale, Tuz Gölü’ndeki suyla kaplı alanlarda meydana gelen zamansal değişimin eş-zamanlı uzaktan algılama verileri ile analiz edilmesini konu almakta olup iki aşamada gerçekleştirilmiştir: (1) Eş-zamanlı yer ve uydu verilerinin birlikte analizi (2) Çok zamanlı LANDSAT uydu verileri ile zamansal değişim analizi. Çalışmanın ilk aşamasında, Tuz Gölü ve yakın çevresinde ayrıntılı bir arazi çalışması yapılmış ve LANDSAT-5 uydusunun 16.05.2005 (saat:1031) tarihindeki üst geçişiyle eş-zamanlı olarak ve yer koordinatları el tipi GPS ile belirlenen noktalarda yersel spektroradyometre ölçmeleri gerçekleştirilmiştir. Uydu görüntülerinin işlenmesi aşamasında geometrik ve radyometrik düzeltme işlemleri gerçekleştirilmiştir. Geometrik düzeltme işlemi ile tüm uydu görüntüleri UTM (Universal Transverse Mercator) projeksiyon sistemine (36. Dilim) referanslandırılmıştır. Bu işlem esnasında karesel ortalama hata (KOH) tüm uydu verileri için ±0,5 pikselin altında bulunmuştur. Daha sonraki aşamada ise uydu verilerini yersel spektroradyometre ölçmeleri ile karşılaştırılabilir hale getirmek amacıyla radyometrik düzeltme işlemi gerçekleştirilmiştir. Bu aşamada, LANDSAT-5 TM uydu verisine ait parlaklık değerleri öncelikle radyans, daha sonra reflentans değerlerine dönüştürülmüştür. Radyometrik düzeltme işlemi sonrasında LANDSAT-5 TM uydu verisinden ve eş-zamanlı yersel spektroradyometre ölçmeleriyle elde edilen yansıma değerlerinin yüksek korelasyona (0.84<R2<0.97) sahip oldukları belirlenmiştir. Daha sonraki aşamada, çok zamanlı LANDSAT-5 uydu verileri ile zamana bağlı değişim analizi gerçekleştirilmiş ve Tuz Gölü’ndeki suyla kaplı alanların 1990-2005 yılları arasında 1/3 oranında azaldığı tespit edilmiştir. Göl çevresinde su kaynaklarının kullanımının kontrol altına alınması ve gölün (en az yılda bir kez olmak üzere) güncel uzaktan algılama verileri ile düzenli olarak izlenmesi önerilmektedir. Anahtar Kelimeler: Tuz Gölü, uzaktan algılama, spektroradyometre, radyometrik düzeltme.This paper focuses mainly on the investigation of water reserve changes in Salt Lake, Turkey, using real-time and multitemporal remote-sensing data. The Salt Lake, which is a specially protected area, is natural resource and the second largest lake in the Central Anatolia in Turkey. The region has been experiencing drought over the last two decades resulting from two main phenomena; (1) uncontrolled use of underground water resources for agricultural purposes, and (2) the lack of precipitation (or natural drought). As a result of this event, very striking coastline changes occurred in the Salt Lake and its vicinity within the last 20-year period. In this study, these changes were analyzed by using multitemporal LANDSAT-5 imagery and real-time ground spectral measurements carried out around Salt Lake, Turkey. The study is performed in two stages: (1) correlation analysis for real-time ground spectral measurements and LANDSAT-5 TM image data and (2) assessment of water reserve changes using multi-temporal LANDSAT imagery. In the first stage of the study, the relationship between ground and satellite spectral data captured on the same day and time was investigated. For this purpose, a real-time field work was done in May, 2005. Taking into account the overpass of LANDSAT-5 TM (16 May 2005, 10:31 local time), spectral measurements were taken on the same day between 9:30 and 12:30 in a total of 20 sample points along the northern coasts of Salt Lake. Sample points were selected along four paralel transects representing four major cover types naturally and regularly located along the coast: lake water, salt, muddy area and bare soil. The distance between samples was approximately 300 m and their locations were recorded with a hand-held global positioning system (GPS) receiver.The measurements were done using an ASD FieldSpec®Pro field-portable spectroradiometer, which consists of a data analyser attached to a laptop computer. In the next stage, LANDSAT scenes (for 1990, 2001 and 2005) covering the study site were geometrically corrected. The images were converted to the UTM coordinate system (Zone 36) using a total of 50 control points both extracted from 1:25000-scale topographic maps and recorded by GPS during the fieldwork. A first order polynomial transformation method was performed to create the output images with 30 m ground resolution. The root-mean-square error of the polynomial transformation is less than half a pixel for all the data set. In the radiometric correction procedure, first, the LANDSAT-5 TM 2005 image and then the 1990 and 2001 historical images were radiometrically corrected to enable comparison with in-situ measurements and with each other. The aim of radiometric correction is to minimize the atmospheric effects and to convert remotely sensed digital numbers (DNs) to ground surface reflectance in order to make the data spectrally comparable. The procedure includes conversions from digital numbers to radiance and from radiance to at-satellite reflectance. After the radiometric correction procedure, the correlation between real-time ground and satellite data was examined. The regression results show that measured surface reflectance and converted at-satellite reflectance are in good agreement with R2 values of about 0.95 in the selected study area. The results show that simultaneous ground and LANDSAT-5 TM data are highly correlated (0.84 R2 0.97). Here, it can be indicated that the use of the real-time data set collected on the same day and time increased the consistency between ground and satellite data. The results also show that sensing using just the spectral band in the near infrared region, such as by LANDSAT TM4, is favourable for distinguishing salt and water in Salt Lake, which has a salt-covered bottom. This plays a key role in determining multi-temporal water reserve changes using satellite sensor data.The results of multi-temporal analysis show that the water reserves in Salt Lake, Turkey, have decreased markedly over two decades. The change of water reserve quantified by using LANDSAT images from 1990 and 2005 is more than 43 ha for a 15-year period. It is suggested that the use of water supplies around Salt Lake should be controlled and that the lake should be monitored regularly by current remote-sensing data (at least annually) for better management of the water resources. Keywords: Salt Lake, remote sensing, field spectroradiometer; radiometric correction.
Investigation of the opportunities for railway based combined freight transport in Turkey
Get PDFBu çalışmada, bir ağ modeli geliştirilerek Türkiye’de demiryolu ağırlıklı kombine yük taşımacılığı olanaklarının araştırılması amaçlanmıştır. Geliştirilen model, çeşitli mal gruplarından oluşan yüklerin karayolu ile demiryolunu içeren bir ağ üzerinde taşınmasının benzetimini gerçekleştirmektedir. Yolcu trafiğinin de aynı ağı kullandığı göz önünde tutularak yolcu taşımaları da modelde dikkate alınmaktadır. Modelde yük ve yolcu taşımacılığı için talep, bir matrisler kümesi ile tanımlanmaktadır. Bu yüzden iller arasında gerçekleştirilen yük ve yolcu taşımalarına ait matrisler elde edilmiş ve çoklu regresyon analizi kullanılarak yük ve yolcu taşımalarının ileriye dönük tahmininde kullanılabilecek çekim modeli tarzında denklemler geliştirilmiştir. Karayollarında gerçekleştirilen iller arası yük ve yolcu taşımalarına ait matrislerin belirlenmesi için eksenler bazında verilen araç sayılarından O-D matrisleri oluşturabilen ve Bell tarafından geliştirilen modelden yararlanılmıştır. Demiryolu yük ve yolcu matrislerinin belirlenmesi için TCDD tarafından sağlanan yük taşımalarına ilişkin veriler ile ekspres ve bölgesel yolcu trenleri cetvelleri kullanılmıştır. Karayolu, otoyolu, bağlantı yolları, demiryolu, transfer ve merkez bağlantılarından oluşan bütünleşik ulaştırma ağı ile sadece merkez, karayolu, otoyolu ve bağlantı yollarından oluşan karayolu ağları ve yine sadece merkez ve demiryolu bağlantılarından oluşan demiryolu ağı üzerine yük grupları ve yolcular için elde edilen O-D matrislerinin atamaları gerçekleştirilmiştir. Bu atamalardan sonra hangi demiryolu bağlantılarında sıkışıklık oluşacağı belirlenmiştir. Elde edilen sonuçlara göre Türkiye’de kombine yük taşımacılığının yaygınlaşması için neler yapılması gerektiği tartışılmıştır. Anahtar Kelimeler: Ağ analizi, matris tahmini, çekim modelleri, kombine taşımacılık.If some special cases are excluded, highway transportation is the only mode used to provide the door-to-door movement of goods. Although highway transportation is used commonly, it is not suitable for freight to be carried over long distances because of its cost and environmental impacts. For this reason, more than one mode must be used to carry goods economically and safely. This kind of transportation is called multimodal transport, or intermodal transport, or combined transport and has also been increasing in Turkey. However, in addition to the shortcomings in railway infrastructure, the deficiencies in operating the existing system prevents railways from playing an important role in combined transport. In this study, the requisities that must be brought in to improve the opportunities of combined transport in Turkey have been investigated by developing a network model. The model developed carries out simulating the freight flows consisting of various commercial goods on a multimodal network representing highway and railway modes. The existence of more than one mode between two adjacent regions is represented with parallel links. In order to model transfer of freight between transportation modes, transfer links have been formed. In addition, passenger transportation is taken into account, considering that it also uses the same network. However, it is assumed that travellers determine in advance which transportation mode they will use and that there are no transfers between these transportation modes. Different cost functions are defined for passenger and freight transport. These cost functions depend on the volume of goods and the amount of passenger traffic on the link. Similarly, a cost function is associated with each transfer link. The demand for each product and passenger traffic is specified by a set of O-D matrices. The mode choice for each product and passenger traffic is also indicated by defining for each of these O-D matrices. The demand matrices for passenger transportation are determined separately for highway and railway modes. Highway passenger traffic is also divided into two groups as automobile and bus passenger. The Bell Model that estimates matrices from traffic counts was used to determine the intercity highway passenger and freight transportation matrices. For highway freight transportation, the initial matrices were formed by modelling the observed matrices obtained from roadside interviews with respect to some socioeconomic parameters, using multiple regression analysis. After these freight matrices were used as the initial matrices in Bell?s model, the other set of matrices that are consistent with the average annual daily truck traffic on 250 highway sections were determined. The matrices obtained for each freight type by using the Bell Model were also analysed statistically. The model developed by Bell was utilized to determine intercity automobile and bus travel matrices. In this case, the principles of Gravity Model were also used to form the initial matrices. After the intercity automobile and bus travel matrices were determined by using Bell?s method, statistical analyses were performed for the O-D information obtained from these matrices. In order to determine the railway freight and passenger matrices, the freigt transport database provided by TCDD and the charts of express and regional passenger trains were used. The multimodal as well as the highway and railway networks were coded, considering all link attributes such as distance, speed, time, and price. The O-D matrices obtained for all freight and passenger types were then assigned onto the related networks, taking into account the unit time values of all freight types and passengers. As a result of these assignments, the freight and passenger volumes carried on links as well as numbers of vehicles and trains were found. For each link, the numbers of vehicles and trains on the links that result from assigning the freight and passenger matrices onto the related networks were added up, and the total numbers of vehicles and trains on links were found. In conclusion, it is seen that the highway, freeway and connection links are not congested, and that some of the railway links carry freight volumes beyond their capacities. Finally, the requisites that must be brought in to improve the possibilities of combined transport in Turkey were discussed, based on the results obtained from this study. Keywords: Network analysis, matrix estimation, gravity models, combined transport
Modeling of circulating fluidized bed combustors
Get PDFSirkülasyonlu akışkan yataklı yakıcıların dizaynı; kömürün yüksek bir verimle yakılması ve baca gazı emisyonlarının kabul edilebilir seviyelerde tutulması için oldukça önemlidir. Bununla beraber, sirkülasyonlu akışkan yataklı yakıcıların optimum tasarım ve işletme parametrelerinin tespitinde, gerçek boyuttaki yakıcılarla çalışmanın gerek zaman ve ekonomiklik, gerekse uygulama açısından pratik olmayacağı açıktır. Bu nedenle, geliştirilen bir model ile sirkülasyonlu akışkan yataklı kömür yakıcılarında etkin olan tasarım ve işletme parametrelerinin tespiti ve sistemin optimum çalışmasını sağlayacak gerekli parametrelerin belirlenmesi mümkün olacaktır. Bu amaçla, bu çalışmada kömür yakan sirkülasyonlu akışkan yataklı yakıcılar için dinamik iki boyutlu bir model geliştirilmiştir. Model sonuçları Gazi Üniversitesi Isıl Güç Labaratuvarı’ndaki 50 kW’lık pilot sirkülasyonlu akışkan yatak yakıcı ve 18 Mart Çan Termik Santrali’nde bulunan 160 MW’lık bir sirkülasyonlu akışkan yatak yakıcının test sonuçları ile karşılaştırılmıştır. Model sonuçlarının küçük ve büyük ölçekli yatak test sonuçları ile göstermiş olduğu uyum modelin geçerliliğini kanıtlamıştır. Modelde ayrıca sirkülasyonlu akışkan yataklı yakıcılar için yakıcı verimi tanımlanarak, küçük ve büyük ölçekli yataklar için hava fazlalık katsayısının yakıcı verimi üzerindeki etkileri; farklı yatak basınç değerleri için incelenmiştir. Genel olarak hava fazlalık katsayısının pilot ve endüstriyel ölçekli yatakta verimi olumsuz etkilediği görülmekle beraber hava fazlalık katsayısı sabit tutulurken artan basıncın yatak içerisindeki yanmayı iyileştirdiği ve pilot ölçekli yatakta yakıcı verimi üzerinde belirgin bir değişime sebep olmazken endüstriyel ölçekli yatakta basıncın etkisinin daha fazla olduğu görülmüştür. Anahtar Kelimeler: Sirkülasyonlu akışkan yatak, temiz enerji teknolojileri, yakıcı verimi.Fluidized bed combustion allows clean and efficient combustion of coal. A well-designed circulating fluidized bed combustor can burn coal with high efficiency and within acceptable levels of gaseous emission. It is also important to determine the effects of operational parameters in circulating fluidized bed combustors via a simulation study instead of expensive and time consuming experimental studies. A very good appreciation of the combustion process is needed for a reliable performance prediction through modeling. The main goal of the modeling of circulating fluidized bed combustors is to constitute a system that maximizes combustion efficiency, and minimizes operating and investment costs and air pollutant emissions. From this point of view, in the present study a dynamic two dimensional model for a circulating fluidized bed combustor integrates and simultaneously predicts the hydrodynamics, heat transfer and combustion aspects, which can be employed to simulate under a wide range of operating conditions, has been developed. In the model, the circulating fluidized bed riser is divided in two regions: bottom zone as a fast bubbling fluidized bed and upper zone as a core-annulus solids flow structure. In the model, pressure drop due to solids acceleration is considered. Char particles are divided into n size groups in the model burn and undergo attrition. In the model, volatiles are released at a rate proportional to the solid mixing rate. Volatile nitrogen and sulphur increases as a function of bed temperature. Heat transfer model is based on cluster renewal process. In the model, return cycle of solids has been considered. Inputs for the model are combustor dimensions and construction specifications (insulation thickness and materials, etc.), primary and secondary air flow rates; coal feed rate and particle size distribution, coal properties, calcium to sulfur ratio, limestone particle size distribution, inlet air pressure and temperature, ambient temperature and the superficial velocity. Simulation model calculates the axial and radial distribution of voidage, velocity, particle size, pressure drop, gas emissions and temperature at each time interval for gas and solid phases. Developed model?s hydrodynamic structure is given and validated with cold beds test results obtained from various CFB test rigs of different size in the literature in previous studies (Eskin and Güngör, 2005a-b). The model should be flexible enough in order to be used in different applications of circulating fluidized beds. The computer code should be modular to allow users to update component modules easily as new findings become available. The set of differential equations governing mass, momentum and energy are solved using the Gauss-Seidel iteration and combined Relaxation Newton-Raphson methods. Time step is 10-11 seconds using in the model. The calculation domain is divided into grid nodes, in the radial and the axial directions respectively. With the cylindrical system of coordinates, a symmetry boundary condition is assumed at the column axis. At the walls, a partial slip condition is assumed for the solid and the gas phases. The simulation results are compared with test results obtained from 50 kW Gazi University Heat Power Laboratory pilot scale unit of 12.5 cm internal diameter. In this comparison, oxygen molar ratio and carbon monoxide emissions along the bed axis and oxygen, carbon dioxide mole ratios and sulphur dioxide emissions response are obtained for the pilot circulating fluidized bed unit using the same input variables in the tests as the simulation program input. The simulation results are in good agreement with experimental ones. Simulation results are also compared with the data obtained during the commissioning period from 160 MW Çan Power Plant circulating fluidized bed unit of 8.55 m internal diameter and 37 m in height. Simulation and test results at the riser exit were compared at different coal feed rates and the results are in good agreement with large-scale circulating fluidized bed unit data. In this study, combustor efficiency has been defined and combustor efficiency for pilot scale and industrial scale has been investigated. It is generally observed that air to fuel ratio has a negative effect on combustor efficiency in both pilot and industrial scale circulating fluidized bed combustors. As pressure increases for constant air to fuel ratio, combustion in the bed becomes more effective, causing little distinctive change on pilot scale bed combustor efficiency, whereas an explicit change is observed in industrial scale bed due to pressure effect. Keywords: Circulating fluidized bed, clean energy technologies, combustor efficiency
Evaluation of pile integrity testing by signal matching method and determination of pile quality
Get PDFBu çalışmada, bir toplu konut inşaatında kazıklı temel olarak inşaa edilen temellere, tahribatsız kazık süreklilik deneyleri uygulanmış ve Hollandalı Profound firması tarafından geliştirilen “TNOWAVE: SITWAVE” programı ile kazık sürekliliği ve imalat kalitesi incelenmiştir. Süreklilik deneyleri yapıldıktan sonra kontrol amacı ile sinyal eşleme “signal matching” programı kullanarak, daha emin sonuçlara ulaşmak mümkündür. Analizde test sinyalleri ile referans sinyalleri eşleştirilir ve arazideki yaklaşık kazık şekline ulaşılır. Böylece arazideki kazık üzerindeki kusurları net bir biçimde görebilmek mümkün olabilmektedir. Esenyurt’ta bir toplu konut inşaatındaki, 191 kazık üzerinde yapılan tahribatsız düşük deformasyonlu süreklilik deneylerinden elde edilen sinyaller, sinyal eşleme programı yardımı ile analiz edilmiş ve “hız-zaman” grafikleri çizilmiştir. Analiz ile kazığın kesiti hakkında büyük bir yaklaşıklık ile bahsedilen kusurları saptamak mümkün olmuştur. Kazık kesitindeki genişlem, kazık performansını olumsuz yönde etkileyecek bir faktör değildir. Ayrıca bu etki kazığın çevre sürtünmesi ile taşınan yükü arttıran bir etken olduğu için, kazık kesitindeki genişlemeler fazla dikkate alınmamaktadır. Buna karşın kazık kesitindeki daralmalar, kazık performansını olumsuz yönde etkileyebileceği için, mevcut kazığın yerine yeni bir kazık yapılması veya ilave kazık imalatı gibi sonuçlar ortaya çıkabilmektedir. Bu çalışmada süreklilik deneyi yapılmış kazıkların sinyal eşleme yardımı ile tekrar kontrol edilmesi, kazıkların güvenilirliğinin teknik olarak irdelenmesi, gerekirse kusurlu kazıklarda düzeltme önerilebilmesi ve böylece kazık imalat kalitesinin daha iyi belirlenebilmesi hedeflenmiştir. Sonuç olarak, 15 m boyunda 0,50 m çapında imal edilen 191 tane kazık üzerinde herbir kazık için kazık boyu üç eşit kısıma ayrılarak, (0-5)m, (5-10)m ve (10-15)m olacak şekilde, kazık alt, orta ve üst kısmını göz önüne alacak şekilde üç ayrı değerlendirme yapılmış ve bu noktalar arasında kazık kesitinde meydana gelen genişleme ve daralmalar ele alınıp, incelenmiş ve kazık kalitesi değerlendirilmiştir. Anahtar Kelimeler: Süreklilik deneyi, sinyal eşleme, gerilme dalga teorisi. Use of pile integrity tests are common in the engineering applications in order to find the discontinuities of the piles. The aim of the pile integrity tests is to confirm the integrity of the pile and determine major faults in the pile. The integrity tests are based on the method ASTM D-5882. The integrity of individual vertical or inclined piles are analyzed by measuring and analyzing the velocity response of the pile induced by a hand held hammer with plastic tip applied axially to the pile normally at the pile head. The top of the pile is hit with a plastic hammer and the reflected waves are recorded by a suitable computerized equipment. From the resulting signal, or reflectogram, one can determine both length and continuity of the pile. SIT (Sonic Integrity Testing) provides quick and inexpensive results compared to core drilling, inspection by excavation and load tests which are time-consuming and costly. Hundreds of piles can be tested in a single day by using SIT equipment. However the sonic integrity testing should not be used to estimate bearing capacity. To obtain the best results from the analysis, the pile head should be clean, accessible and free from water. SIT is not generally suitable for prefabricated piles and piles with permanent casings. In the future, because of the increasing need in the civil engineering developments, the use of deep foundations will increase. For the analysis and check of the piles to be cast in these projects, the pile integrity testing is the most economical solution. The stress wave theory is used for the interpretation of the pile integrity tests. A. L. Smith produced the first general solution for the practical application of stress wave theory to piles. The method became practical by the adaptation of the analysis to the newly developed digital computers. Smith's model is still the basis for modern wave equation analysis. In SITWAVE we use TNO soil model is used for the analysis. In both of them soil is reflect by springs and dashpot systems. The springs shows the elasticity of pile which will model by the characteristic of pile material and the dashpot systems refers to the damping of the soil. The aim of this study is to determine the quality of piles that were driven in Esenyurt Mass Housing Project. The piles were analyzed using Profound's "TNOWAVE" software package which utilizes stress wave equation systems. SITWAVE is one of these programs which simulates the sonic integrity testing and performs automatic signal matching. Using the signal matching method, the piles previously tested by the pile integrity test were analyzed. In this research, totally 191 cast-in-situ piles 15m long and 50cm in diameter were tested. The reference signals were matched with the test signals by using SITWAVE software. The reference signals are the signals taken from the site and the test signals are created by the software in terms of the pile and soil data. The deviations from the reference signals show that the locations where enlargement and decrement in the cross-section occured. At the end of the analysis, the graphics given by the software include velocity and radius as function of time and length. The piles were considered in three equal lengths, (0-5)m, (5-10)m and (10-15)m to find out the piles which had discontinuities. For the evaluation of the piles the piles which are determined to have enlargement more than %3 in diameter are considered as enlargement type and the piles which have decrement more than %3 in diameter as decrement type. The piles which have decrement in diameter more than %10 are considered as problematic because it can affect the structural performance of the piles. Enlargement in cross-section is not considered as a factor which will effect pile performance negatively because it will increase the pile load which will carried by the skin friction but decrement in cross-section should have negative effect on pile performance. Consequently, it should be considered as a problematic situation, if there is a decreament in cross-section which will cause a decrease in bearing capacity of piles. Keywords: Pile integrity test, signal matching, stress wave theory
Backcalculation of mechanical properties of flexible pavements using neural networks
Get PDFEsnek üstyapıların performans değerlendirmesi için, genel olarak tahribatsız deney metotları tercih edilmektedir. Tahribatsız deney metotları içerisinde en çok tercih edilen, Düşen Ağırlık Deflektometresi (FWD) yöntemidir. Bu yöntem ile, yol üzerindeki çok sayıda yerde, uygulanan yük sebebi ile meydana gelen zamana bağlı defleksiyon değerleri kaydedilir. Uygulamada, FWD deneyi ile elde edilen defleksiyon değerleri ve geri-hesaplama programları kullanılarak, üstyapı tabakalarına ait mekanik özellikler hesaplanır. Fakat, bu programlar, parametre tanımlama algoritmaları kullanmakta ve bu da zaman kaybına neden olmaktadır. Bu çalışmada, FWD testinden elde edilen defleksiyonları kullanarak, esnek üstyapı tabakalarındaki mekanik özellikleri yapay sinir ağları ile geri-hesaplayan bir model geliştirilmiştir. Sonuçlar, modelin hassasiyetinin son derece yüksek olduğunu ve gerçek-zamanlı geri-hesaplama yapılabilmeye olanak sağladığını göstermiştir.Anahtar Kelimeler: Düşen Ağırlık Deflektometresi, geri-hesaplama, yapay sinir ağları Performance evaluation of flexible pavements is usually performed using nondestructive testing methods. Basic advantage of nondestructive testing methods is that it's possible to obtain pavement performance data by these methods without resulting any damage to the pavement system. Of all nondestructive testing methods, Falling Weight Deflectometer (FWD) is the most popular technique. Falling Weight Deflectometer, measures time-domain deflections from numerous road sections emerging by the applied impulse load. The common way for the evaluation of FWD results is to backcalculate the mechanical properties with the help of backcalculation software. However, these software utilize parameter identification routines, which are quite time consuming and computationally expensive. Under the way of this, in this study, a neural network model was developed to backcalculate mechanical properties of flexible pavement layers in order to shorten the processing time. For the development of optimal neural network model, the effects of network's architecture and learning parameters were comprehensively examined. The results indicated that, both network's architecture and learning parameters significantly affect the neural network's performance. Consequently, the accuracy of developed neural network model is successful and the model enables real-time backcalculation opportunity that is crucial for highway engineers working on pavement evaluation studies and developing pavement maintenance strategies.Keywords:Falling Weight Deflectometer, backcalculation, neural networks.
Fuzzy logic approach for damage assessment of seismic damaged buildings
Get PDFDeprem hasarı gören binaların hasar düzeyinin tespiti konusu, özellikle sıkça depreme maruz kalan ülkelerde her zaman çözüm bekleyen önemli bir sorun olmuştur. Bu özelliğiyle konu bilim dünyasının hep gündeminde kalmış ve pek çok çalışmaya esas oluşturmuştur. Binalarda oluşacak hasarın tespitindeki belirsizlik, karmaşıklık ve insana ait olan yargılardaki bulanıklık bu konuda ön plana çıkan zorluklardandır. Bu çalışmada, deprem sonrası hasar görmüş yapıda deprem hasarının tespitinde kullanılan katlar arası kalıcı yer değiştirme ve karakteristik beton basınç dayanımının hasar tespitine etkisi daha gerçekçi olan bulanık mantık yaklaşımı ile ele alınmıştır. Sonuçlar irdelendiğinde klasik mantığın keskin ve tavizsiz sınırlarına kıyasla, bulanık mantığın insan düşünüş ve yargısına daha uygun sonuçlar verdiği gözlenmiştir. Anahtar Kelimeler: Deprem hasarlı binalar, hasar tespiti, bulanık mantık.Especially in countries which are frequently exposed to earthquake, damage assessment of seismic damaged buildings has been always an important problem. Therefore, this subject has not lost its actuality in earthquake engineering. Various studies have been carried out to find a procedure for damage assessment having wide application spectrum. Studies about damage assessment methods have been fairly developed as computer technology improves in recent years. Vagueness, complexity and fuzziness in human judgements lead into several difficulties related to damage assessment of seismic damaged buildings. In this study, state of art of damage assessment of seismic damaged buildings has been studied by using fuzzy logic. In the study, the effect to damage assessment of permanent interstory displacements and characteristic concrete compression strength which have substantial effects on the extent of seismic damage of buildings, have been taken into consideration by using the fuzzy logic approach. When the results are scrutinized, it has been observed that the fuzzy logic compared with the conventional logic having crisp and nonconcession boundary has given more convenient results to human thinking and judgement and fuzzy logic solution has softened and it has clearly gained flexibility as to sharp passing of conventional solution. Furthermore, it is observed that this situation gives more reliable results. Keywords: Seismic damaged buildings, damage assessment, fuzzy logic
Elimination of transducer mass loading effects from frequency response functions
Get PDFFrekans Tepki Fonksiyonlarının (FTF) kalitesinin parazit ve sistematik hatalar gibi faktörlerle olumsuz yönde etkilendiği bilinmektedir. FTF’larını kullanan çeşitli analizlerin doğruluğu ve güvenilirliği de ölçülmüş verilerin kalitesine bağlıdır. Bu çalışma ölçülmüş FTF’larındaki en önemli sistematik hatalardan biri olan transdüser kütle etkisini kaldırmayı amaçlamaktadır. Bu çalışmada ölçülmüş FTF’larındaki transdüser kütle etkisinin kaldırılması için Sherman-Morrison eşitliğine dayalı olarak geliştirilen yeni bir yöntem sunulmaktadır. Burada sunulan formülasyon genel amaçlıdır ve hem sabit hem de hareketli transdüser durumlarına uygulanabilmektedir. Transdüserin gezdirildiği test durumunda yardımcı bir kütle kullanımından yararlanılmaktadır. Bununla beraber, yapının transfer FTF’nun ölçümünde yardımcı kütle kullanımına gerek duyulmaması yeni yöntemin üstün özelliklerinden biridir. Bu sayede transfer FTF’nda ilave etkiler oluşturulmamaktadır. Yöntemin uygulanabilirliği sayısal simülasyonlarla ve deneysel veriler kullanılarak incelenmiştir.Anahtar Kelimeler: Frekans Tepki Fonksiyonu (FTF), transdüser kütle etkisi, Sherman-Morrison eşitliği.It is well known that the quality of measured Frequency Response Functions (FRFs) is adversely affected by many factors, most significant sources being noise and systematic errors. It is also known that the accuracy and the reliability of various analyses using the measured FRFs depend strongly on the quality of measured data. This paper aims to remove one of the major systematic errors in measured FRFs, namely the mass loading effects of transducers. This paper presents a new method based on the Sherman-Morrison identity for the elimination of mass loading effects of transducers from measured FRFs. The formulation presented here is general in the sense that it can be applied for both fixed and moving transducer cases. In the case of moving transducer type of tests, the use of dummy mass is utilized. However, one of the distinct features of the new method is that it avoids the need for the measurement of cross-FRFs of a structure with a dummy mass attached to the structure, hence avoiding further contamination of cross-FRFs. The applicability of the method is also assessed using experimental as well as simulated data. Keywords: Frequency Response Functions (FRFs), transducer mass effect, Sherman-Morrison identity
Binder removal and characterization of zirconia ceramics prepared by hot molding
Get PDFSeramik tozlarının çeşitli şekillendirilme yöntemleri vardır. Bu yöntemler soğuk veya sıcak, yaş veya kuru olmak üzeri çeşitli şekillerde sınıflandırılabilir. Bu çalışmada, mühendislik seramiklerinin şekillendirilmesinde diğer şekillendirme yöntemlerine nazaran daha düşük maliyetli ve daha kolay bir üretim prosesine sahip yeni bir şekillendirme yöntemi denenmiştir. Bu yöntem iki farklı şekillendirme yönteminin birleştirilmesi esasına dayanır. Yaş döküm yöntemi ile enjeksiyon kalıplama yönteminin birleşimi şeklindedir. Polimer katkılı sıcak akışkan seramik toz karışımı bir kalıp içine basınç uygulamadan dökülerek şekillendirilir. Zirkonya (ZrO2), magnezya (MgO) ve kalsiya (CaO) tozlarından farklı bileşimlerde mekanik alaşımlama tekniği ile karışımlar hazırlanmıştır. Bağlayıcı sistemi, parafin (%95 ağ.) ve oleik asit (%5 ağ.) olan, hacimce %60 bağlayıcı ve %40 seramik tozu içeren karışımlardan basınçsız sıcak şekillendirme yöntemiyle numuneler hazırlanmıştır. Hazırlanan numunelerden bağlayıcı giderme çalışmalarında iki kademeli bir işlem kullanılmıştır. Bağlayıcı giderme çalışmalarının ilk aşamasına ait şartlar, 120°C’de 5 saat olarak belirlenmiştir. Ağırlıkça yaklaşık %33 bağlayıcı giderilen söz konusu şartlar, çalışılan tüm numunelere uygulanmıştır. İkinci aşamada ise, geri kalan bağlayıcı, atmosfer şartlarında bağlayıcı giderme fırınında 600°C’nin al-tında tamamen giderilmiştir. Bu işlem tamamlandıktan sonra numuneler, 1600°C’de 3 saat sinterlenmiş ve oda sıcaklığına soğutulmuştur. Sinterlenmiş bazı numuneler 1450°C’de 4 saat yaşlandırmaya bırakılmıştır. Sinterlenmiş numunelerin XRD ve SEM kullanılarak faz analizi ve mikroyapısal karakterizasyonu yapılmıştır. Anahtar Kelimeler: Stabilize zirconia, basınçsız sıcak şekillendirme, bağlayıcı giderme, sinterleme, karakterizasyon.Oxide ceramics include alumina, zirconia, silica, aluminum silicate, magnesia and other metal oxide based materials. Oxide ceramics have high melting points, low wear resistance, and a wide range of electrical properties. Oxide ceramics are used in a variety of applications. Examples include chemical and materials processing, electrical and high voltage power applications, Radio Frequency (RF) and microwave applications, and foundry and metal processing. "Zirconia-Ceramic steel" The title of the first scientific paper to highlight the possibilities offered by the "transformation toughening" mechanism which occurs in certain zirconia ceramics. Since the publication of this seminal work in 1975, considerable research, development, and marketing efforts have been expanded on this single material which offer the traditional ceramic benefits of hardness, wear resistance and corrosion resistance, without the characteristic ceramic property of absolute brittleness. Zirconia, ZrO2 exists as a monoclinic crystal at room temperature inverting to tetragonal phase above approximately 1200°C. The addition of large amounts of a stabilizer such as magnesium oxide will induce a cubic crystal structure during firing that does not revert to the monoclinic phase upon cooling. The addition of generally less than 10% by weight of stabilizers yields high-density ceramic bodies known as transformation toughened zirconia. Two fundamentally different microstructures exist depending upon the added stabilizer. The addition of MgO yields a relatively coarse grained (50-100 micron) microstructure known as Mg-PSZ. The grains are predominantly cubic morphology with a fine precipitate of tetragonal phase dispersed within the grain. Yttria, Y2O3, additions yield an extremely fine grained (less than 1 micron) microstructure known as Y-PSZ or TZP or tetragonal zirconia polycrystal. The individual grains are completely tetragonal. In present study, Calcia and Magnesia stabilized fine Zirconia powders in various ratios were studied. Powder mixtures (Ca(OH)2, Mg(OH)2 and ZrO2) were prepared in acetone and milled as wet with YSZ (yitria stabilized zirconia) balls of 10 mm Ø for 3 h. Particle size of Calcia, Magnesia and Zirconia powders were submicrometer. The pressureless hot molding technique has been selected for forming of the partial stabilized zirconia with MgO and CaO. Binder system for pressureless hot molding was a mixture of paraffin wax as primary binder and oleic acid as surfactant. Paraffin wax/oleic acid ratio was maintained at a value close to 95/5 as weight. Typical feedstock contained 40 vol. % ceramic powders, and 60 vol. % binder phases. A two-step process was used for debinding of green samples. In wicking step by capillary action, samples embedded in same ZrO2 powder in a copper box were put in an furnace in the 120, 150 and 180°C temperatures for 1, 3, 5 and 10 hours. The variation of sample weight with temperature and time was measured to calculate the debinding ratio. In the second step of debinding process, partially debinded samples were heated to 600°C at a slow heating rate. After completing this process, green ceramics were fired at 1600 °C for 3 hours in an electric-heated furnace and then cooled quickly. Some of the fired ceramics were aged in the same furnace for 4 hours at 1450 °C. After annealing, the some specimens were sectioned, ground, polished to 1 mm surface-finish and finally thermally etched in air for 30 min. at a temperature 1420 °C. The density and porosity of sintered samples were measured by Archimedes principle. The microstructural characterization of the sintered samples was carried out using scanning electron microscopy. The morphological parameters of the various phases were characterized by using a semiautomatic image analyzer, EDS and the formed phases were analyzed by X-ray powder diffractometer using Co K? radiation. Ca-ZrO2 and Mg-ZrO2 ceramics have been prepared by solid state reaction synthesis. The beneficial effects on the binder removal, microstructural characterization and phase structure of zirconia ceramics prepared by pressureless hot molding have been analyzed. t- ZrO2 and c- ZrO2 phase value increased with the addition of Calcia (CaO) and fired temperature and time. The addition of Calcia (CaO) to Zirconia (ZrO2) matrix the highest the value of t- ZrO2 and c- ZrO2. Keywords: Stabilized zirconia, pressureless hot molding, debinding, sintering, characterization
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