Browsing by Subject "Frequency domains"

Now showing 1 - 6 of 6

Open Access
Analysis of errors in zero-free-parameter modeling approach to predict the voltage of electrochemical energy storage systems under arbitrary load
(Electrochemical Society, 2017) Ulgut, Burak; Uzundal, Can Berk; Özdemir, Elif
In a recently published article (J. Electrochem. Soc. 164 (2017) A1274-A1280), we described a new method to predict the voltage response of electrochemical energy storage systems during arbitrary load profiles. Our work shows that the impedance spectrum can be employed in the frequency domain in order to ultimately calculate the time domain behavior of the electrochemical energy storage system. The big advantage of this method is the fact that there are no free parameters and fits throughout. The present work deals with the sources of error in the above-mentioned prediction approach and looks for the effects of the various sources of error. The current analysis concludes that two big contributors to the overall error are the inaccuracies in the DC part of the prediction and the non-linearities that are not modeled by a linear impedance spectrum. Discussions are also made regarding ways to improve the performance of the modeling approach the most and where future work is going to be looking to improve.
Open Access
An audio watermarking algorithm via zero assigned filter banks
(IEEE, 2005) Yücel, Zeynep; Özgüler, A. Bülent
In order to identify the owner and distributor of digital data, a watermarking scheme for audio files is proposed in frequency domain. The scheme satisfies the imperceptibility and persistence requirements and is robust against additive noise. It consists of a few stages of wavelet decomposition of several frames of the original signal using special zero assigned filter banks. By assigning zeros to filters on the high frequency portion of the spectrum, filter banks with frequency selective response is obtained. Text information is then inserted in the wavelet-decomposed and compressed signal. Several robustness tests are performed on male voice, female voice, and music files.
Open Access
A compression method for 3-D laser range scans of indoor environments based on compressive sensing
(IEEE, 2011-08-09) Dobrucalı, Oğuzcan; Barshan, Biilur
Modeling and representing 3-D environments require the transmission and storage of vast amount of measurements that need to be compressed efficiently. We propose a novel compression technique based on compressive sensing for 3-D range measurements that are found to be correlated with each other. The main issue here is finding a highly sparse representation of the range measurements, since they do not have highly sparse representations in common domains, such as the frequency domain. To solve this problem, we generate sparse innovations between consecutive range measurements along the axis of the sensor's motion. We obtain highly sparse innovations compared with other possible ones generated by estimation and filtering. Being a lossy technique, the proposed method performs reasonably well compared with widely used compression techniques. © 2011 EURASIP.
Open Access
Kesirli fourier dönüşümünün zaman bölgesinde sonlu farklar yöntemine uygulanması
(IEEE, 2010-04) Sayın, I.; Arıkan F.; Arıkan, Orhan
Bilgisayarların hız ve belleklerinin gelişmesi ile birlikte elektromanyetik problemlerin çözümünde saysal yöntemler sıkça kullanılmaya başlanmış ve bu konuda çok sayda araştırma yapılmıştır. Saysal Elektromanyetik yöntemleri genel olarak zaman ve frekans tabanlı yöntemler olarak sınıflandırılabilir. Zaman tabanlı yöntemler geçici tepkilerin ve geniş bantlı problemlerin incelenmesinde kullanışlı olurken, frekans tabanlı yöntemler durağan hal tepkilerin ve dar bantlı problemlerin incelenmesinde en iyi çözümü vermektedir. Her iki yaklaşımın da avantajlarını ön plana çıkarabilecek bir yöntem geliştirilebileceği düşünülmektedir. Uzayda ve/veya zamanda Kesirli Fourier Dönüşümü uygulanarak bazı durumlarda hesaplama karmaşıklığı azaltılabilir. Kesirli Fourier Dönüşümü, sürekli Fourier Dönüşümünün genelleştirilmiş halidir. Son yıllarda bu konu üzerinde çeşitli çalışmalar yapılmakta ve uygulama alanları genişlemektedir. Genel olarak, sinyal işleme ve gürültü süzme gibi alanlarda kullanılmaktadır. Bu çalmada Kesirli Fourier Dönüşümü, ilk kez Maxwell denklemlerine zaman bölgesinde uygulanmış ve elde edilen diferansiyel denklemler sonlu farklar yaklaşımı ile ayrık hale getirilmiştir. Elde edilen ayrık sonlu fark denklemlerinin çözümü için öneriler sunulmuştur.
Open Access
SOS methods for stability analysis of neutral differential systems
(Springer, 2009) Peet, M. M.; Bonnet, C.; Özbay, Hitay
This paper gives a description of how "sum-of-squares" (SOS) techniques can be used to check frequency-domain conditions for the stability of neutral differential systems. For delay-dependent stability, we adapt an approach of Zhang et al. [10] and show how the associated conditions can be expressed as the infeasibility of certain semialgebraic sets. For delay-independent stability, we propose an alternative method of reducing the problem to infeasibility of certain semialgebraic sets. Then, using Positivstellensatz results from semi-algebraic geometry, we convert these infeasibility conditions to feasibility problems using sum-of-squares variables. By bounding the degree of the variables and using the Matlab toolbox SOSTOOLS [7], these conditions can be checked using semidefinite programming.
Open Access
Stability analysis of the heat equation with time-delayed feedback
(IFAC, 2009-06) Çalışkan, Sina Yamaç; Özbay, Hitay
In this paper we consider the heat equation with time delayed feedback. Recently, stability analysis of this system, with possibly time-varying delay, is done by Fridman and Orlov (2007, 2009); and a sufficient condition is obtained for stability in terms of a linear matrix inequality. Here we consider the same system, but with constant delay, and perform the stability analysis in the frequency domain. A necessary and sufficient condition is obtained in terms of the system parameters. The result is illustrated with numerical examples. © 2009 IFAC.