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Earthquake performance evaluation of three-dimensional roller compacted concrete dams

Kartal M.E. | Karabulut M.

Article | 2018 | Earthquake and Structures14 ( 2 ) , pp.167 - 178

A roller compacted concrete (RCC) dam should be analyzed under seismic ground motions for different conditions such as empty reservoir and full reservoir conditions. This study presents three-dimensional earthquake response and performance of a RCC dam considering materially non-linearity. For this purpose, Cine RCC dam constructed in Aydin, Turkey, is selected in applications. The three-dimensional finite element model of Cine RCC dam is obtained using ANSYS software. The Drucker-Prager material model is considered in the materially nonlinear time history analyses for concrete and foundation rock. Furthermore, hydrodynamic effect w . . .as investigated in linear and non-linear dynamic analyses. Researchers observe that how the tensile and compressive stresses change by hydrodynamic pressure effect. The hydrodynamic pressure of the reservoir water is modeled with the fluid finite elements based on the Lagrangian approach. In this study, dam body and foundation are modeled with welded contact. The displacements and principle stress components obtained from the linear and non-linear analyses with and without reservoir water are compared each other. Principle stresses during earthquake were obtained at the most critical point in the upstream face of dam body. Besides, the change of displacements and stresses by crest length were investigated. Moreover demand-capacity ratio criteria were also studied under linear dynamic and nonlinear analysis. Earthquake performance analyses were carried out for different cases and evaluated. According to linear and nonlinear analysis, hydrodynamic water effect is obvious in full reservoir situation. On the other hand, higher tensile stresses were observed in linear analyses and then non-linear analyses were performed and compared with each other. © 2018 Techno-Press, Ltd Daha fazlası Daha az

Performance analysis of multi chip/data rate DS-CDMA signals over multipath Rayleigh fading channels

Öztürk E.

Conference Object | 2006 | IWCMC 2006 - Proceedings of the 2006 International Wireless Communications and Mobile Computing Conference2006 , pp.15 - 20

This paper investigates the Probability error (Pe) performance of Multi-Chip/Data Rate Direct Sequence Code Divisions Multiple Access (MCDR/DS-CDMA) systems over multi-path Rayleigh fading channels. Two chip waveforms, raised cosine (RC) and an orthogonal wavelet, are compared numerically in terms of the Pe. The results represent that the wavelet based system significantly outperforms the RC based system in terms of the P e. On the other hand, the wavelets have greater bandwidths than the RC waveforms. Thus, two systems are also compared in terms of the capacity (the number of users per Hertz) for the same Pe level. The results for . . .the capacity show that the wavelet based design has 3% and 41% more capacity than the RC based system for the medium and low rate users, respectively, while the RC based system provides 7% higher capacity than the wavelet based system for high data rate users. Since the average power of wavelets is zero, they can utilize a Single Side Band (SSB) transmission. With the SSB transmission, the wavelet based system has 86%, 106% and 182% more capacity for the high, medium and low data rate users, respectively. Copyright 2006 ACM Daha fazlası Daha az

Performance of wavelet based Multi-Chip Rate DS-CDMA signals over multi-path Nakagami-m fading channels

Öztürk E.

Article | 2008 | Wireless Communications and Mobile Computing8 ( 6 ) , pp.745 - 757

Multi-Chip Rate/Direct Sequence-Code Division Multiple Access (MCR/DS-CDMA) technique using scaled chip waveforms has been designed as an alternative to multi-data rate DS-CDMA techniques having constant chip rates. In this work, the probability of error (Pe) expression for MCR/DS-CDMA signals is derived over multi-path Nakagami-m fading channels to investigate the effects of chip waveforms on it. This paper also proposes the use of orthogonal wavelets as chip waveforms of MCR/DS-CDMA signals over the considered channel. For numerical calculations, Daubechies-22 (D22) wavelet is used because its side lobes are 40 dB below its main l . . .obe in frequency domain. D22 is compared with a Square Root Raised Cosine (SRRC) chip waveform. In the numerical calculations, only first four scales of the chip waveforms relating to four different chip/data rates are considered. The results for the Pe performance and the capacity (the number of user per Hertz for a same P e level) show that D22 significantly outperforms the SRRC chip waveform at all data rates, due to low cross correlations among different scales of orthogonal wavelets. Besides, by increasing the number of scales, the advantage of the use of orthogonal wavelets will increase furthermore. Copyright © 2007 John Wiley & Sons, Ltd Daha fazlası Daha az

Spatial multiple access (SMA): Enhancing performances of MIMO-NOMA systems

Kara F. | Kaya H.

Conference Object | 2019 | 2019 42nd International Conference on Telecommunications and Signal Processing, TSP 2019 , pp.466 - 471

The error performance of the Non-Orthogonal Multiple Access (NOMA) technique suffers from inter-user interference (IUI) although it is a promising technique for future wireless systems in terms of the achievable sum rate. Hence, a multiple access technique design with limited IUI and competitive to NOMA in terms of spectral efficiency is essential. In this paper, we consider so-called spatial multiple access (SMA) which is based on applying the principle of spatial modulation (SM) through the different users' data streams, as a strong alternative to multiple-input and multiple-output (MIMO)-NOMA systems. The analytical expressions o . . .f bit error probability (BEP), ergodic sum rate and outage probability are derived for the SMA. The derivations are validated via computer simulations. In addition, the comparison of the SMA system with NOMA is presented. The results reveal that SMA outperforms NOMA in terms of the all performance metrics (i.e., bit error rate (BER), outage probability and ergodic sum rate) besides it provides low implementation complexity. © 2019 IEEE Daha fazlası Daha az

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