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Buckling of nonlocal bars and initial value method in nanotechnology
Get PDFBu çalışmada, yerel olmayan elastisite çerçevesinde başlangıç değerleri yöntemi kullanılarak bir çubuğun burkulması araştırılmıştır. Bilindiği gibi nanoteknoloji, moleküler boyutta (1-100 nm) fonksiyonel sistemlerin mühendisliğidir. Atom ve moleküller ölçeğinde özel yöntem ve tekniklerle yapıların, materyallerin ve araçların inşâ edilmesini, bu ölçekte ölçme, tahmin etme, izleme ve yapım faaliyetlerinde bulunmayı, benzeri görülmemiş özelliklerde yeni nanoteknolojik aygıtlar üretmeyi hedefler. Nanoteknolojiyi uygulanabilir kılan şey, atomların yapısı ve aralarındaki olağanüstü organizasyon özelliği olduğundan atomların yapısı ve davranış biçimlerinin çok iyi bilinmesi gerekir. Nanoteknolojide ilk uygulamalar karbon nanotüp yapısı kullanılarak gerçekleştirilmiştir. Karbon nanotüpler hem yapısal, hem de mekanik özellikleri bakımından nano ölçekteki malzemelere en güzel örneklerden biri olup, sahip oldukları olağanüstü özelliklerden dolayı bilinen en sert ve en güçlü liflerdir. Ayrıca karbon nanotüpler, moleküler boyutta grafit karbonların içi boş silindirik çubukları olarak düşünülür ve geniş çapta nanoteknolojik uygulamalarda kullanılırlar. Çalışmada başlangıç değerleri yönteminin uygulanabilirliği için gerekli olan taşıma matrisi verilmiştir. Bir çubuğa ait taşıma matrisinin bilinmesinin en önemli avantajlarından biri, çubukların kuvvetler etkisi altındaki davranışlarını sistematik olarak incelemeyi mümkün kılmasıdır. Taşıma matrisi elde edildikten sonra çeşitli türlerde desteklenmiş çubuklar için kritik yükler hesaplanmıştır. Uygulamalarda elde edilen sonuçlar, yerel olmayan etkilerin nanoyapıların mekanik davranışlarını anlamada klasik elastisiteye göre çok daha güçlü olduğunu ve karbon nanotüplerin burkulmasında da yerel olmayan etkilerin önemli olduğunu göstermektedir. Anahtar Kelimeler: Nanoteknoloji, yerel olmayan elastisite, başlangıç değer yöntemi, nanotüpler.Nanotechnology is a field of applied science and technology covering a broad range of topics. The main unifying theme is the control of matter on a scale smaller than 1 micrometer, normally between 1-100 nanometers, as well as the fabrication of devices on this same length scale. Nanotechnology cuts across many disciplines, including colloidal science, chemistry, applied physics, materials science, and even mechanical and electrical engineering. Carbon NanoTube (CNT) is a new form of carbon, configurationally equivalent to two dimensional graphene sheet rolled into a tube. It is grown now by several techniques in the laboratory and is just a few nanometers in diameter and several microns long. They are the stiffest and strongest known fibers and have unique electrical properties. An ideal nanotube can be thought of as a hexagonal network of carbon atoms that has been rolled up to make a seamless cylinder. In classical elasticity theory the stress tensor at a given point depends linearly on the strain tensor of the same point. Thus, local elastic theory contains no information about the long range forces between atoms i.e., there is no internal length scale. On the other hand, the theory of nonlocal continuum mechanics assumes that the stress state at a given reference point is considered to be function of the strain states of all points in the body. Properties of materials at the nanoscale differ fundamentally from those of their bulk counterparts. Carbon nanotubes are one of the structural elements that are used in nanotechnological applications widely. In this study, they are envisioned as hollow cylindrical bars of graphitic carbon at the nanoscale. For these reasons nonlocal theory is more capable to display the mechanical behaviour of materials at the nanoscale. Carbon nanotubes hold substantial promise for the development of nanotechnology. However, thorough understanding of the mechanical behavior of carbon nanotubes is essential. Currently, theoretical treatment of buckling of carbon nanotubes has relied on the use of classical continuum mechanics models, such as the elastic shell model or the Bernoulli-Euler beam bending model. Although classical continuum models are relevant to some extent, and efficient in computation for models at large length scales, the applicability of these classical continuum models at small length scales is questionable. Multiple recent experimental results have shown a significant size-effect in mechanical properties when the dimensions of the specimen or the probed material volume become small. The classical continuum theories lack the capability of representing such effects since they do not include any internal length scale. Consequently, these theories are expected to fail when the specimen size become comparable with the internal length scale(s) of the material. Several modifications of the classical elasticity formulation have been proposed to address this deficiency. They are of nonlocal or gradient type and, as a common feature, include one or several intrinsic length scales. Nonlocal elasticity theory was proposed to account for the scale effect in elasticity by assuming the stress at a reference point to be a function of strain field at every point in the body. When the structure considered falls into the nanometer range, nonlacality parameter has a significant influence on the outcomes of this study. In some cases, the ratio of local and nonlocal buckling loads can be 1.4. The buckling of carbon nanotubes has been studied by molecular mechanics in literature. In this paper the method of initial values is used in the frame of nonlocal elasticity. This method gives the values of the displacements and stress resultants throughout the rod once the initial displacements and initial stress resultants are known. A priority of this method is that the high degree of statical indeterminancy adds no extra hardship to the solution of the problem. It is interesting to note that the size of the matrix (2x2) from which the buckling determinant obtained in the presented method is the half of its classical counterpart. Local modeling of nanomaterials can be inaccurate, inadequate and misleading. Proposed nanotechnology devices are envisioned to have lengths on the order of nanometers(10-7 cm < L < 10-6 cm). It is clear that for the devices of this size nonlocal effects could be significant. The results are used to display that nonlocal effects could be significant in buckling of carbon nanotubes. Keywords: Nanotechnology, nanobar, carbon nanotubes, nonlocal elasticity, initial value problems
An experimental investigation on the cylinder pressure and valve displacement of reciprocating compressors
Get PDFPistonlu kompresörler soğutma, iklimlendirme ve proses endüstrileri başta olmak üzere bir çok farklı alanda havanın veya soğutucu akışkanın basıncını arttırmak amacıyla kullanılmaktadır. Bu kompresörlerde emme ve egzos valf yapraklarının zamana bağlı hareketi nedeniyle oluşan basınç salınımları, hem kompresörün enerji verimliliğini veya soğutma etkinlik katsayısını (SEK), hem de kompresör ses gücü düzeyini önemli ölçüde etkilemektedir. Bu etkileri incelemek amacıyla yapılan çalışmanın burada sunulan ilk kısmında, soğutucu akışkan kompresörlerinde silindir içerisindeki basıncın ve valf yaprağı deplasmanının zamana bağlı değişiminin deneysel olarak incelenmesinden elde edilen bulgular tartışılmıştır. Bu deneysel çalışmalar şu başlıklar altında sıralanabilir: i-) “Kompresör Kalorimetresi” adı verilen bir test sisteminden yararlanılarak, belirli şartlar altında kompresör soğutma kapasitesinin ve giriş gücünün ölçülmesi; ii-)Optik kodlayıcı ve yüksek frekanslı basınç sensörlerinden yararlanılarak, silindir içerisindeki basıncın kompresör krank açısına bağlı olarak ölçülmesi. 50 Hz nominal çalışma frekansında sıkıştırma yapan bir kompresörde, genişleme, emme, sıkıştırma ve egzos safhalarından oluşan bir tam çevrim yaklaşık 20 ms sürmekte ve bu sürenin yarısından daha az bir zamanda, emme valf yaprağı birden fazla kez açılma kapanma hareketi yaparak silindire gaz geçişine izin vermektedir. Bu nedenle, emme valf yaprağı hareketinin kompresör krank açısına bağlı olarak ölçülebilmesi için de bir yöntem geliştirilmiş ve örnek bir model kompresörde uygulanmıştır. Anahtar Kelimeler: Pistonlu kompresör, silindir basıncı, valf yaprağı titreşimi, pulsatif akış.The energy efficiency and the sound power level of hermetic reciprocating compressors used in refrigeration and air conditioning applications are effected by the pressure pulsations caused by the vibrations of valve leaves during the suction and discharge phases. In the first part of this study a compressor calorimeter set-up is used to measure the refrigeration capacity and the input power of a specific compressor model at standard rating conditions. High frequency pressure transducers and an optical encoder are used to measure the cylinder pressure as a function of compressor crank angle. A method to measure the suction valve displacement as a function of crank angle by standard strain gauges is also developed and applied to the compressor model used in the study. The compressor calorimeter set-up used to measure the mass flow rate and input power of compressors at specified operating conditions is indeed a basic refrigeration circuit equipped with different pressure, temperature and power measurement devices. The suction and discharge pressures of the compressor which correspond to the evaporation and condensation temperatures in the refrigeration circuit are measured by pressure transducers. The subcooling after the condenser and the superheating at the end of the evaporator are measured by thermocouples where these temperatures are 32.2°C at the standard ASHRAE test conditions. The temperature at the inlet of the compressor is also 32.2°C and by specifying these values the vapor compression cycle is fully determined. The refrigeration capacity of the compressor is determined via two different methods and the relative difference between the results should be lower than 3 % for a stable test. The first method is to measure the electric power utilized by the heater which is placed in a well insulated shell with the evaporator where the second method relies on the measurement of the mass flow rate of the compressor. The input power of the compressor is directly measured and the coefficient of performance (COP) for the compressor can be calculated from the refrigeration capacity and input power. The refrigeration capacity and input power of the specific compressor model under consideration are found to be 189.01 W and 127.06 W with standard deviations of 0.38 and 0.26 % respectively. In addition to the calorimeter set-up a specific test system is used to measure the instantaneous cylinder pressure as a function of compressor crank angle. An optical encoder which gives 360 signals per revolution is placed at the top of the crank shaft of the compressor and a specific pressure transducer is placed in the valve plate where it can detect the cylinder pressure. Another pressure transducer is also placed in the suction plenum of the compressor in order to see the pulsation effects caused by the suction valve movement. The nominal running frequency of the compressor under consideration is 50 Hz which corresponds to a 20 ms cycle time where the complete cycle consists of four processes: expansion of the gas in the dead volume, suction of fresh to the cylinder from the plenum, compression of the gas in the cylinder and finally the discharge to the discharge plenum. Since the complete cycle takes only 20 ms, the suction phase where the suction valve opens and closes several times per one cycle takes 8 to 9 ms. Therefore a strain-gage was used to investigate the suction valve leaf vibration behavior as a function of the compressor crank angle. Both the cylinder pressure and valve displacement measurements were carried out at approximately 18 kHz. The results of the tests conducted for the cylinder pressure can be used to identify the losses caused by the suction and discharge port and valve leaves and it can be concluded that the experimental indicator diagram of reciprocating compressors is an important tool for research activities to develop high efficiency compressors. The results of this study showed that the pressure drop losses associated with the suction and discharge port and valve leaves consist 5.1 % of the net piston work done on the refrigerant gas for the compressor model under consideration. Though the test carried out both with the cylinder pressure transducer and the strain-gage shows that the 60 mm thick strain-gage has an effect on the pressure pulsations, and hence the force exerted on the valve leaf, the general vibration characteristics of the valve leaf can be observed with such a method. Keywords: Reciprocating compressor, cylinder pressure, valve leaf vibration, pulsating flow
A hybrid expert system approach for evaluation systems
Get PDFSistemlerin, sentetik ortamların, insanların performansının değerlendirilmesi genellikle karmaşık olup çok zaman gerektirmektedir. Mevcut değerlendirme sistemleri belli bir alana yönelik olarak geliştirilmişlerdir ve sistemin değerlendirme sonuçlarına nasıl ulaştığını açıklamazlar. Elde edilen yeni değerlendirme bilgilerinin, değerlendirme sisteminde güncellenmesi kolay değildir. Değerlendirme süreci, uzmanlık gerektirmektedir. Fakat uzmanlar az sayıda olup, bilgilerinin bilgisayar ortamına aktarılarak daha fazla istifade edilmeleri gerekir. Bu çalışmada, değerlendirme sürecini kolaylaştıran, hızlandıran ve farklı alanlarda kullanılabilen “Genel Değerlendirme Modeli” ve “Zeki Değerlendirme Sistemi” (ZeDeS) geliştirildi. Bu kapsamda, farklı alanlardaki uzmanlardan elde edilen sezgisel bilgilerin ve farklı kaynaklardan elde edilen bilgilerin bilgisayarla değerlendirme amaçlı kullanılabilmeleri için bir yöntem geliştirildi. Bu yöntemde, değerlendirme bilgileri, değerlendirme amaçlarının, değerlendirme kurallarının, ölçümlerinin, metotlarının ve parametrelerinin referans modeli olarak ifade edildi. Melez uzman sistem ve bulanık mantıktan meydana gelen “Zeki Değerlendirme Sistemi”, öğrencileri, eğitmenleri, işe başvuranları, bilgisayar tarafından meydana getirilmiş kuvvetler gibi sentetik kuvvetleri değerlendirdiği gibi gerçek sistemleri de değerlendirebilmekte olup “Genel Değerlendirme Modeli”ne ve değerlendirme ihtiyaçlarına göre geliştirildi. Değerlendirme bazı açılardan belirsizlik içerdiğinden, değerlendirmede genel çıkarım için bulanık mantıkla uzman sistemler beraber kullanıldı. ZeDeS, Hava Savunma Sistemi, öğretici performansı, pilot performansı değerlendirmesi ve eleman seçimi gibi çeşitli alanlarda ilk defa olarak kullanıldı. Makalede bir Hava Savunma Sistemi değerlendirmesinin ZeDeS kullanılarak nasıl yapıldığı ayrıntılı şekilde verilmiştir. Anahtar Kelimeler: Zeki Değerlendirme Sistemi, yapay zekâ, melez uzman sistem, bulanık mantık.Evaluation of systems, synthetic environments and human performance are generally complicated and time-consuming tasks. Evaluation is needed nearly for all engineering tasks and the obstacles related with evaluation are increased proportional with complexity. Existing evaluation systems are domain dependent and do not provide explanation on how the system reaches the evaluation results. Expertise is needed for the evaluation process. Elicited new evaluation information cannot be updated to the system easily. Forming an evaluation definition is a complicated and time-consuming task. Finding out and formulating the required knowledge from the domain for which the evaluation is to be performed, is generally difficult due to lack of structured approach. It is not only important to formulate the knowledge, but finding out the right source of knowledge is also essential. Structured knowledge architecture is especially important in order to utilize evaluation knowledge automatically, especially in distributed environments. In this study, Common Evaluation Model (CEM) and INtelligent Evaluation System (INES), which simplify, speed up the evaluation process and decrease the evaluation cost, were developed. The study indicates that it is possible to put knowledge related to evaluation into a structured format. In this scope, a methodology was developed to handle the heuristic knowledge of experts from different domains and information from different sources for evaluation purposes. In this method, evaluation knowledge was represented as a reference model of evaluation objectives, production rules, measures, methods and parameters. Evaluation Objectives indicate what is going to be evaluated. Evaluation rules are criteria used to assess the collected parameters or calculated evaluation measures. Evaluation parameters are variables needed for applying rules or calculating the result of methods. The results of methods are defined as measures in order to simplify the evaluation rules and provide reusability. Evaluation methods are the algorithms for analyzing the collected parameters or / and calculating measures used in the rules. CEM shows the relation between evaluation objectives, rules, measures, methods and parameters. Using Reference Model of Evaluation Knowledge and CEM decreases the number of evaluation rules that are necessary to perform an evaluation to the related application. CEM also simplifies the representation of evaluation knowledge. INES is a hybrid expert-fuzzy system and was developed based on CEM and evaluation needs. Before development of INES, AI techniques including expert systems, fuzzy logic, neural networks, genetic algorithms, intelligent agents and conventional programming were investigated and compared with respect to achieving high level requirements of Evaluation Systems. INES?s Knowledge Base (KB) and KB Editor were developed for forming, editing and updating evaluation knowledge. INES?s Inference Engine was developed for executing the evaluation definition, which includes evaluation objectives, production rules, measures, methods and parameters. Backward chaining technique was used for INES?s inferencing. Some benefits of INES, which are mostly AI related, are speeding up the evaluation process, decreasing the evaluation cost, explaining the reason of evaluation results, modelling the uncertainty on an overall evaluation, providing reasoning on linguistic variables, providing a flexible structure, allow updating evaluation knowledge base without changing the source code, reducing the complexity associated with the evaluation and providing an objective and a reliable evaluation. INES was successful and was tested in the following conditions: Knowledge of experts from the related domain and knowledge (or information) from the related sources for evaluation purposes are existed. Identifying evaluation criteria from the expert knowledge and information from different sources is possible. INES was implemented for the first time in various areas from different domains such as evaluation of Air Defence System, instructor performance, personnel selection, and pilot performance. Evaluation of an Air Defence System using INES is given in the paper. As the evaluation includes uncertainty in some aspects, Fuzzy Logic was used for reasoning. But it was realized that Fuzzy Logic could be used to perform overall performance or assessment instead of the evaluation itself for complex tasks. In other words, fuzzy logic can be more beneficial and more easily used for overall evaluation of main objective instead of all aspects of evaluation. A lot of parameters for evaluation are required and writing a lot of rules for these parameters in fuzzy logic is not an efficient way. As more rules are needed for complex systems, it becomes increasingly difficult to relate these rules to the system. Therefore, fuzzy system was used at an abstract level of evaluation. Keywords: Intelligent Evaluation System, artificial intelligence, hybrid expert-fuzzy system
The application of wavelet technique to sensorless control of brushless DC (BLDC) motor
Get PDFBu çalışmada fırçasız doğru akım motorunun (FDAM) dalgacık teorisi yardımıyla algılayıcısız olarak kontrolü ve elektrikli otomobile uygulanması amaçlanmıştır. Bu doğrultuda geliştirilen bir kalkış algoritması yöntemiyle, motorun, endüklenen gerilim bilgisinin algılanabileceği belirli bir hıza kadar açık çevrim olarak hızlanması sağlanıp, bu hızdan sonra geribesleme olarak elde edilen beslenmeyen faz endüklenen geriliminden ve faz akımlarından yararlanılarak kapalı çevrim olarak dalgacık dönüşümü yardımıyla fırçasız doğru akım motorunun algılayıcısız kontrolü gerçekleştirilmiştir. Komutasyon anlarının algılayıcısız olarak elde edilmesi sırasında, geliştirilen PID ve Bulanık kontrolör algoritmaları yardımıyla motor hız ve faz akımları gerçek zamanlı olarak denetlenmiştir. Anahtar Kelimeler: Fırçasız DA motoru, bulanık, PID, algılayıcısız, dalgacık, sonlu elemanlar yöntemi (SEY).This paper deals with developing a novel sensorless drive technique for BLDC motors by using wavelet theory. Study adopts two methods of position prediction. The first method involves self phase inductance variation of which finite element analysis is employed. The second method is based upon the induced voltage and zero crossing point estimation. Starting problem is solved by using position inductance function for the first method and by providing a look-up table for each direction of rotation for the second method. The MATLAB/Simulink model of the motor is established and the simulation performances are obtained. A PID and a fuzzy control algorithms are developed, current and speed controlled performance predictions are obtained. Then as an experimental study, BLDC motor?s PWM pulses are produced by DS1005 processor and DS2201 board of dSPACE DSP kit. The time domain currents and induced-voltage waveforms are recorded. The Daubechies wavelet analyses of the experimental and simulation waveforms are obtained with an extra emphasis on commutation intervals. So an algorithm is developed to predict the commutation instants without any position sensor. This procedure is applied experimentally and it is successfully demonstrated that the proposed method described above could be useful for sensorless control of BLDC motors. It is also shown that, results of the simulation model and its wavelet analysis are in a very good agreement with those of experiments. Keywords: Brushless DC motor, fuzzy, PID, sensorless, wavelet, finite element method (FEM)
Avrupa hava kirleticilerinin Doğu Akdeniz bölgesine taşınımının modellenmesi
Get PDFMeasurements of some air pollution species in a rural station located near Antalya (36.47N, 30.34E) on the eastern Mediterranean coasts revealed high concentrations during the years 1992 2000. Since the area is free of any source of pollution, it is believed that such high concentrations of various pollution species are transported from other regions, such as Eastern or southeastern Europe. Long range transport of European air pollution to the Eastern Mediterranean region has been investigated during the episodic period 26 29 August 1998. Meso-scale Meteorological Model, MM5 was applied to forecast the hourly general circulation conditions and hourly 3 and 2 dimensional meteorological variables. Air mass backward trajectory simulations were also predicted by MM5/RIP and HYSPLIT models. Consequently, three main sectors of air mass trajectory originated from Europe were found. MM5 model outputs were used in the three-dimensional Eulerian photochemical model CAMx to simulate the concentration deposition and the long range transport of the air pollution species PSO42- and SO2. CAMx air quality model simulations have revealed a great agreement with the air mass trajectory simulations produced by HYSPLIT and RIP/MM5 models and have demonstrated that sulfate transport from central and southeastern Europe to the eastern Mediterranean has two distinguished paths. The modeling system which is used for the first time in Turkey exhibited a high performance. Keywords: Long range air pollution transport, backward trajectory, MM5, CAMx, HYSPLIT.Avrupa hava kirleticilerinin Doğu Akdeniz bölgesine taşınımı 26 – 29 Ağustos episodik periyodunda incelenmiştir. 3 ve 2 boyutlu meteorolojik değişkenlerin ve hava sirkülasyonunun öngörüsünü yapmak için Mezo-ölçekli meteorolojik model, MM5 kullanılmıştır. Hava parsellerinin yörünge simülasyonları MM5/RIP ve HYSPLIT modelleriyle tahmin edilerek Avrupa’dan kaynaklanan 3 ana yörünge kaynağı sektörü bulunmuştur. PSO42- ve SO2 gibi türlerin derişimi, birikmesi ve taşınımının simülasyonunun tahmini üç boyutlu Eulerian CAMx modeliyle yapılmıştır. Sülfatın Avrupa’dan Doğu Akdeniz bölgesine taşınması sırasında iki ana geçidi izlediği saptanmıştır. CAMx simülasyonlarının, HYSPLIT ve MM5/RIP modelleriyle üretilen yörünge simülasyonlarıyla büyük bir uyum sağladığı görülmüştür. Türkiye’de ilk defa kullanılan bu modelleme sistemi yüksek bir performans göstermiştir. Anahtar Kelimeler: Uzun menzilli hava kirliliği taşınımı, geriye doğru yörüngeler, MM5, CAMx, HYSPLIT
Modeling Electrocardiogram (ECG) signals via signature and envelope functions
Get PDFBu çalışmada, EKG işaretlerinin Temel Tanım ve Zarf Fonksiyonları ile modellenmesine yönelik yeni bir yöntem sunulmaktadır. Sunulan yöntem, herhangi bir EKG işaretine ilişkin Xi(t) çerçeve fonksiyonunu biçiminde modellemektedir. Bu modelde, jR(t), Temel Tanım Fonksiyonu olarak adlandırılmakta ve bir Ci katsayısı ile Xi çerçeve vektörünün en yüksek enerjisini taşımaktadır. aK(t), Zarf Fonksiyonu olarak adlandırılmakta ve Xi çerçeve vektörünün zarfını oluşturmaktadır. Ci katsayısı da Çerçeve Ölçekleme Katsayısı olarak adlandırılmaktadır. Temel Tanım ve Zarf Fonksiyonları iletim bandının herbir düğümüne yerleştirilerek EKG işaretinin iletimi, Temel Tanım ve Zarf Vektör Bankasının R ve K indislerinin ve Ci katsayısının iletimine indirgenerek önemli bir sıkıştırma oranı gerçeklenmiştir.Anahtar Kelimeler: Sıkıştırma, Modelleme, EKG.In this paper, a new method to model ECG signals by means of "Signature and Envelope Functions" is presented. In this work, on a frame basis, any ECG signal Xi(t) is modeled by the form of . In this model, jR(t) is defined as the Signature Function since it carries almost maximum energy of the frame vector Xi with a constant Ci. aK(t) is referred to as Envelope Function since it matches the envelope of CijR(t) to the original frame vector Xi; and Ci is called the Frame-Scaling Coefficient. It has been demonstrated that the sets F={jr(t)} and A={ak(t)} constitute a "Signature and Envelope Functional Banks" to describe any measured ECG signal. Thus, ECG signal for each frame is described in terms of the two indices "R" and "K" of Signature and Envelope Functional Banks and the frame-scaling coefficient Ci. It has been shown that the new method of modeling provides significant data compression with low level reconstruction error while preserving diagnostic information in the reconstructed ECG signal.. Furthermore, once Signature and Envelope Functional Banks are stored on each communication node, transmission of ECG signals reduces to the transmission of indexes "R" and "K" of [ak(t),jr(t)] pairs and the coefficient Ci, which also result in considerable saving in the transmission band. Keywords: Compression, Modeling, ECG.
Nonlinear system identification using deterministic multilevel sequences
Get PDFBu çalışmada sınırlı doğrusalsızlık derecesine sahip Volterra süzgeçleri için yeni bir gösterilim geliştirilmektedir. Bu gösterilim kullanılarak Volterra süzgeçleri için kesin bir tanılama yöntemi sunulmaktadır. Bu yeni yöntem, giriş işareti olarak farklı seviyelere sahip impulslardan oluşan gerekirci diziler kullanmaktadır. Yeni tanılama yöntemi doğrusal, zamanla-değişmez sistemlerdeki birim impuls cevabının doğrusal olmayan sistemlere başarılı bir uyarlaması olarak düşünülebilir. Çalışmada sunulan tanılama yöntemi kesindir; böylece gözlem gürültüsü olmadığında Volterra çekirdeklerini hatasız kestirmektedir. Bilgisayar benzetimleriyle tanılama yönteminin literatürde yakın zamanda sunulmuş olan yöntemlerden daha iyi kestirim sonuçları verdiği gösterilmiştir.Anahtar Kelimeler: Doğrusal olmayan sistem tanılama, Volterra süzgeçleri.In this paper we develop a new representation for the finite-order Volterra filters. This representation introduces a novel partitioning of the Volterra kernels.Using this representation, we formulate a novel exact identification method for Volterra filters, which uses deterministic sequences consisting of impulses with distinct levels. The identification method might be considered as a successful extension of the impulse response of the linear, time-invariant systems to the realm of nonlinear systems. The developed method indeed includes identification using the unit impulse response as a subcase when the system under consideration is a linear system. Our identification method is exact; hence, it calculates the exact Volterra kernels in the absence of noise for very short length input sequences. Our method calculates each Volterra kernel individually. The kernel estimates are not utilized in the calculation of further kernel estimates. This property hinders error propagation among kernel estimates. Our method calculates directly the Volterra kernels, instead of calculating first some intermediary representation such as the Wiener kernels, which do not have any directly interpretable results. Our method does not introduce and identify any kernels which are redundant for the regular Volterra filter. We demonstrate with simulations that the identification algorithm can produce better parameter estimates than some most recent algorithms in the literature. Keywords: Nonlinear system identification, Volterra filters
Equivalence transformations of the general first order balance equations
Get PDFVerilmiş bir diferansiyel denklemler grubu keyfi fonksiyonlar, parametreler içeriyorsa, elimizde aynı yapıda denklemler grubunun ailesi var demektir. Eşdeğerlik grupları, verilen denklem ailesini değişmez bırakan dönüşümlerin grubu olarak tanımlanır. Simetri dönüşümleri diferansiyel denklemlerin bir çözümünü başka çözümlere götürürken, eşdeğerlik dönüşümleri ailenin bir üyesini diğer üyesine götürür ve denklemler grubunun bir çözümünü aynı ailenin başka grubunun çözümüne dönüştürür. Çalışmada birinci mertebe genel denklik denklemleri sisteminin eşdeğerlik dönüşümleri izovektör yöntemi ile incelenmiştir. Klasik sürekli fiziğin bir çok denklemi bu grupta ifade edilebildiğinden, sonuçları geniş uygulama alanına sahiptir. Eşdeğerlik dönüşümlerinin belirleyici denklemleri elde edildikten sonra açık çözümleri belirlenmiş, genel şema elektromagnetizmanın Maxwell denklemlerine uygulanmıştır. Anahtar Kelimeler: Eşdeğerlik dönüşümleri, denklik denklemleri, izovektör yöntemi.If a given set of equations contains some arbitrary functions or parameters we have in fact a family of sets of equations of the same structure. Almost all field equations of classical continuum physics possess this property since they describe certain common or similar behaviors of diverse materials. Equivalence groups are defined as groups of continuous transformations which leave a given family of equations invariant. In other words, they map an arbitrary member of the family onto another member of the same family and they transform a solution of a set of equations onto a solution of another set in the same family whereas the symmetry transformations map a solution of a system to another solution of the same system. In this work equivalence transformations of first order general balance equations involving arbitrary number of dependent and independent variables are investigated by using isovector method. To study system of balance equations occupies a privileged position since many equations in classical physics are of this form. The method consists of determining isovector fields of a closed ideal of certain exterior forms defined on a properly extended manifold. Isovector fields are defined as such vector fields whose orbits generate transformations under which the ideal remains invariant.. After obtaining determining equations of equivalence transformations, their explicit solutions are found. The general results are applied to Maxwell equations.Keywords: Equivalence transformations, balance equations, isovector method
Effects of local soil conditions on dynamic response of trapezoidal valleys
Get PDFGeoteknik deprem mühendisliğinde karşılaşılan en önemli problemlerden biri, zemin tabakalarının deprem sırasında gösterdiği davranışın belirlenmesidir. Bir sahada oluşan deprem hareketinin özellikleri tektonik yapı, kırılma mekanizması, doğrultu etkisi, merkez üstü uzaklığı, jeolojik yapının ve yerel zemin koşullarının etkisi gibi birçok faktöre bağlıdır. Zemin tabakalarının dinamik analizi için geliştirilen hesap yöntemleri bir, iki ve üç boyutlu olarak tanımlanmaktadır. İki ve üç boyutlu analizlerde, zemin kesitindeki tabakaların iki veya üç boyutlu geometrisi gerektiği için, bir boyutlu yaklaşımın kullanımı daha fazla tercih edilmektedir. Ancak zemin tabakalarının bir boyutlu dinamik analizinde; yüzey topografyası, tabakaların eğimi ve tabakaların sınırlı enine genişliğinin etkisi ihmal edilmektedir. Zemin tabakalarının yatay yönde sınırlı genişliğe sahip olması, vadi kenarlarında dalga hareketi dönüşümlerine sebep olmakta, dolayısıyla yer hareketinin frekans içeriği ve yüzeydeki etkisi vadilerin ortasından kenarlarına doğru değişebilmektedir. Bu çalışmada, seçilen trapez kesitli simetrik vadi modellerinde yerel zemin koşullarının zemin büyütmesine etkisi incelenmiştir. Bu amaçla, kenarlarda anakaya eğimi sabit olan, derinlik ve genişliği farklı vadi modelleri kullanılarak, farklı anakaya ivme kayıtları için bir ve iki boyutlu dinamik analizler yapılmış, elde edilen sonuçlar karşılaştırılmıştır. Her modelde zemin kesitinde en üstte kil tabakasının yer aldığı kabul edilmiştir. Yapılan analizler sonucunda, vadi yüzeyindeki ivme spektrumları, Afet Bölgelerinde Yapılacak Yapılar Hakkında Yönetmelik’te tanımlanan yerel zemin sınıfları için elde edilmiştir. Yüzeyde hesaplanan en büyük ivme değerleri, anakaya ivmelerine oranlanarak zaman ortamındaki zemin büyütmeleri elde edilmiş ve uzaklığa bağlı değişimleri incelenmiştir. Anahtar Kelimeler: Yerel zemin sınıfı, zemin büyütmesi, vadi modeli, dinamik analiz.One of the most commonly encountered problems in geotechnical earthquake engineering is the evaluation of ground response. The characteristics of ground motion at a particular site depend on many factors such as tectonics of the region, epicentral distance, geological formations, bedrock depth, geotechnical site conditions, local surface and subsurface topography. The topographical characteristics include the effects of surface formations, the two and three dimensional geometry of the subsurface soil layers and bedrock to the local site ground response. The calculation methods developed for the dynamic analysis of the soil layers are usually defined as two and three dimensional according to the necessity of the problem met. The two and three dimensional geometry of the soil layers and bedrock is required to perform two and three dimensional ground response analysis, so because of the application convenience one dimensional dynamic analysis is mostly preferred. However in one dimensional ground response analysis the surface topography, two or three dimensional geometry of the subsurface and the effects of the limited width of the soil layers are being neglected. In fact because of the limited lateral width of the soil layers wave transformations at the basin edges occur, surface waves are being focused to the valley center, two dimensional resonance models may occur and consequently the amplitude and frequency content of the ground motion may change from the center of the valley to the edges. In this paper, in order to study the effects of local site conditions, the depth and width of soil layers, the frequency content and amplitude of strong ground motion to the site amplification and frequency content of surface wave motion, one and two dimensional dynamic analyses were performed for five different bedrock acceleration records by using idealized trapezoidal symmetrical valley models. The results of the one and two dimensional analyses were compared, and the variations of the amplifications with the distance from the valley edges were investigated. These models have different depths and widths. In the valley models, the soil layers were assumed to extend horizontally limited with valley edges having a constant slope angle of 45°. The topsoil layer was selected as high plasticity clay for each model. The parameters such as the thickness and initial shear wave velocities of the soil layers above bedrock, which play the main role in the determination of dynamic response, were selected in accordance with the soil groups and soil classes defined in Turkish Earthquake Design Code (1998). With this aim, the valley models were subjected to 1D and 2D dynamic analyses by using five different bedrock strong ground motion records and the results were compared .The results that will be obtained from the 1D and 2D analyses were aimed to reflect the seismotectonical structure of the North Anatolian fault in Turkey. Therefore two bedrock acceleration time histories were selected among the Turkey earthquakes. The vertical and horizontal boundary conditions become important especially in the dynamic analyses of 2D models. In this study viscous dashpots, which are, calculated proportional to the shear and pressure waves of the relevant layers were put at the vertical and horizontal layers. High amplification values were calculated at the surface of rigid valley models having local site class of Z2. In the models having local site class of Z3 or Z4, the amplifications decreased at the high bedrock acceleration values. At the models with sudden rigidity change in the soil profile, the amplifications relatively increased for the surface sections, which are located at the beginning of valley edge (X/H=1). For the deeper valley models having a graded rigidity decrement from bottom to upper layers, the amplifications decreased noticeably and the increase in the peak bedrock acceleration values made this situation more remarkable. The bedrock topography must be carefully investigated to obtain the 2D dynamic behaviour of laterally limited soil layers under earthquake excitation. So the geological and geotechnical investigations should be done carefully to satisfy this condition. When the data about the topography of soil layers and bedrock is insufficient, it will be obligatory to prefer 1D dynamic analysis based upon the assumption of horizontal soil layers extending to infinity. However 1D and 2D dynamic analyses give similar results only for the sections near the middle part of very wide valleys. Keywords: Local site condition, soil amplification, valley model, dynamic analysis
Development of a new method for the boric acid production process from colemanite ore
Get PDFKolemanitten borik asit üretiminde mevcut teknolojideki temel sorun kolemanit cevheri içindeki yan minerallerin reaksiyon ortamında bozunmasıyla safsızlık sorunu yaratarak prosesten, verim düşüklüğüne neden olan çözelti deşarjı gerektirmesidir. Çalışmanın amacı, reaksiyonun sülfürik asit yanında propionik asit veya kalsiyum propionat katkılı ortamda gerçekleştirilerek proseste safsızlık kontrolünün mümkünlüğünü araştırmak, uygun proses koşullarını belirlemek ve yeni bir üretim prosesi geliştirmektir. Farklı proses alternatifleri değerlendirilerek proseste devreden bileşenin kalsiyum propionat olduğu yöntem seçilerek modellenmiştir. Kimyasal ve mineralojik yapıları belirlenmiş beş değişik tenörlü kolemanit cevherlerinin %10’luk propionik ve sülfürik asitlerle bozundurulmasıyla çözeltiye safsızlık geçişleri incelenmiş ve propionik asitli ortamda kil minerallerinin bozunmasının engellenebileceği belirlenmiştir. Değişik oranda propionik asit-sülfürik asit karışımları ve değişik tenörlü kolemanit cevherleri kullanılarak kesikli veya sürekli çalışan reaktörde reaksiyonun yürüyüşü ve çözeltiye geçen safsızlıklar izlenmiş ve reaksiyonda oluşan süspansiyonların filtrasyon hızları ölçülmüştür. Deneylerden, kalsiyum propionat varlığının çözeltiye geçen magnezyum ve silis konsantrasyonlarını önemli ölçüde azalttığı, sodyum ve potasyum geçişini ise hemen hemen engellendiği görülmüştür. Ortamdaki kalsiyum propionat oranı arttıkça, kalsiyum propionatın kil minerallerini dağıtması nedeni ile filtrasyon hızının düştüğü belirlenmiştir. Sonuç olarak, kolemanitten sülfürik asit yanında kalsiyum propionat kullanılmasına dayanan yeni borik asit üretim prosesinde çözeltiye safsızlık geçişi azaltılarak proses veriminin yükseltilebileceği gösterilmiştir. Anahtar Kelimeler: Borik asit, kolemanit, propionik asit, proses geliştirme, safsızlık kontrolü.The most important problem of the current boric acid production process from colemanite ore is the decomposition of side minerals in colemanite ore in the reaction media, which leads to impurity problems and causes some of the process liquor to be purged, therefore process efficiency decreases and environmental problems arise. The aim of this study is to investigate the possibility of impurity control in the process by performing the reaction in the presence of propionic acid or calcium propionate beside sulfuric acid, to determine the appropriate process conditions and to develop a new process that can be an alternative to the conventional one using solely sulfuric acid. Since intake of the impurities into the solution is sourced from the side minerals in the colemanite ore in the boric acid production process, it is necessary to determine the chemical and mineralogical structure of the colemanite ores and their interaction with acids. For this purpose, firstly, chemical and mineralogical structures of different colemanite ores were determined. Subsequently, the concentration of impurities captured by the solution in the presence of solely propionic acid by decomposing these ores with 10% propionic acid solutions, and, the amount, the chemical and mineralogical structure of the remaining solid obtained from these decompositions were determined. Concentrations of impurities transferred into the solution were determined by also decomposing these ores with 10% sulfuric acid solutions. By comparing the concentrations of sodium, potassium, magnesium and aluminum in solutions obtained by decomposing ores in propionic and sulfuric acid solutions, where these impurities do not precipitate, it was concluded that in the presence of propionic acid the decomposition of clay and feldspar minerals could be prevented. After assessing alternative models, the process model in which calcium propionate is the recycling component was selected and modeled. Batch and continuous reaction and filtration experiments were performed in accordance with this model. Advance of the reaction was followed by chemical analysis, transfer rates of the impurities into the solution were determined during batch reactions of different colemanite ores with different propionic acid-sulfuric acid mixtures and the filtration rates of the suspensions obtained from the reactions were measured under constant pressure difference. It was determined that the reactions could be performed in conformity with the model, provided that the concentration of calcium propionate is lower than 3% in the production liquor in order to prevent calcium borate precipitation. Impurity concentrations captured by 18% boric acid solution in reaction conditions were determined and considered as the unavoidable impurity concentrations. By taking these unavoidable concentrations into consideration, it was shown that the concentrations of magnesium and silica transferred into the solution could dramatically be decreased and the transfer of the sodium and potassium could practically be prevented in the presence of propionic acid. Based on the filtration rate measurements of reaction products, it was determined that the filtration rates were decreased by increasing concentrations of calcium propionate in the media and the cause of this decrease was the swelling and consequently the dispersion of the clay minerals in the presence of calcium propionate. It was investigated whether the reactions are performed in accordance with the model in the reac-tions of different colemanite ores with different sulfuric acid-propionic acid mixtures in the continuous reaction system. The impurity intake of the solutions obtained from the reactions was determined. Similar to the results obtained from batch reaction experiments, it was found out that the intake of magnesium, silica, sodium and potassium to the solution was decreased dramatically. From the measurements of first and second filtration rates under constant pressure difference, similar results were obtained to those obtained from batch experiments. In conclusion, it was shown that product quality and process efficiency could be increased and the environmental impact of the process could be decreased by decreasing the impurity intake of the solution in the new boric acid production process based on the reaction of colemanite ore with sulfuric acid in the presence of calcium propionate. Keywords: Boric acid, colemanite, propionic acid, process development, impurity control
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