Maritime University of Constanta

Constanţa, Romania

Maritime University of Constanta

Constanţa, Romania
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Elisei-Iliescu C.,Polytechnic University of Bucharest | Paleologu C.,Polytechnic University of Bucharest | Tamas R.,Maritime University of Constanta
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2016

The recursive least-squares (RLS) is a very popular adaptive algorithm, which is widely used in many system identification problems. The parameter that crucially influences the performance of the RLS algorithm is the forgetting factor. The value of this parameter leads to a compromise between tracking, misadjustment, and stability. In this paper, we present some insights on the performance of variable forgetting factor RLS (VFF-RLS) algorithms, in the context of system identification. Besides the classical RLS algorithm, we mainly focus on two recently proposed VFF-RLS algorithms. The novelty of the experimental setup is that we use real-world signals provided by Romanian Air Traffic Services Administration, i.e., voice and noise signals corresponding to real communication channels. In this context, the Air Traffic Control (ATC) communication represents a challenging task, usually involving non-stationary environments and stability issues. © 2016 SPIE.

Dumitrascu A.,Maritime University of Constanta | Tamas R.D.,Maritime University of Constanta | Dragulinescu M.,Polytechnic University of Bucharest | Caruntu G.,Maritime University of Constanta
21st Saint Petersburg International Conference on Integrated Navigation Systems, ICINS 2014 - Proceedings | Year: 2014

In this paper, we propose a Method of Moments (MoM) approach for decomposition of a complex displacement into elementary movements. Data from an inertial navigation system is used to compute accelerations of different orders, as well as amplitudes of oscillatory movement. We used as basis functions a set of polynoms, sine and cosine functions. The results were compared to those calculated by integrating the instantaneous acceleration and a good agreement could be noted.

Tamas R.D.,Maritime University of Constanta | Caruntu G.,Maritime University of Constanta | Petrescu T.,Polytechnic University of Bucharest
Final Program and Book of Abstracts - iWAT 2011: 2011 IEEE International Workshop on Antenna Technology: Small Antennas, Novel Structures and Innovative Metamaterials | Year: 2011

Antenna synthesis can yield optimal radiating structures in terms of pattern diagram, gain, bandwidth or other figures of merit. Although the synthesis might be more difficult for continuous sources than for antenna arrays the resulting radiating structures are cheaper and easy to manufacture. In this paper, we propose a time-domain synthesis approach for ultra-wide band antennas. The method is based on a finite expansion of the antenna time-domain response. The synthesis is performed with regard to the resemblance between the time-domain radiated waveform and the waveform at the antenna input. The approach is validated by synthesizing a planar, ultra-wide band antenna designed for a particular waveform of excitation. © 2011 IEEE.

Tamas R.D.,Maritime University of Constanta | Petrescu T.,Polytechnic University of Bucharest | Caruntu G.,Maritime University of Constanta
2012 IEEE International Workshop on Antenna Technology, iWAT 2012 | Year: 2012

Low-distortion antennas for pulsed excitation can be synthesized by using a technique based on a finite expansion of the antenna time-domain response. Current profiles can therefore be generated in order to achieve optimal response for a given waveform of excitation. However, the simplest radiating structures resulting from synthesis might neither provide acceptable input matching, nor omnidirectional radiation. This paper addresses these two issues and further proposes two antenna structures. © 2012 IEEE.

Caranica A.,Maritime University of Constanta | Burileanu C.,Polytechnic University of Bucharest
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2015

The novelty of this work relies on the application of an open source research software toolkit (CMU Sphinx) to train, build and evaluate a speech recognition system, with speaker-independent support, for voice-controlled hardware applications. Moreover, we propose to use the trained acoustic model to successfully decode offline voice commands on embedded hardware, such as an ARMv6 low-cost SoC, Raspberry PI. This type of single-board computer, mainly used for educational and research activities, can serve as a proof-of-concept software and hardware stack for low cost voice automation systems. © 2015 SPIE.

George Z.,Maritime University of Constanta
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

The success of terrestrial wireless sensor networks in monitoring various phenomena caused an increased interest to develop underwater sensor networks by the underwater acoustics community. These networks are based on underwater acoustic modems for real-time data transmission. The high cost and fixed architecture of these devises makes it impossible to implement dense wireless sensor networks adapted to the environment. We propose an adaptive architecture for a low cost underwater acoustic modem. Designing such a modem with adaptable parameters is determined by the zonal variability of the underwater channel. This article presents the results of a frequency dependent simulation for a particular underwater channel in the Black Sea for which we determined the distance dependent impulse response. The simulation results reinforce the idea of variability of the transmission channel and support the idea of designing an adaptive underwater acoustic modem. Underwater acoustic modem, frequency dependent simulation, underwater wireless sensor network, underwater acoustic channel. © 2012 SPIE.

Deleanu D.N.,Maritime University of Constanta
ECCOMAS 2012 - European Congress on Computational Methods in Applied Sciences and Engineering, e-Book Full Papers | Year: 2012

Investigating a discrete or continuous dynamical system, one of the most important challenges is to distinguish between its ordered or chaotic orbits. This distinction is of great interest because in the case of ordered motions we have predictability whereas for chaotic motions we are unable to predict the time evolution of the dynamical system after a short time period. After we have studied a significant number of papers concerning this subject, we would try in the present paper to emphasize the strong and weak points of three recent indicators of chaos and order, namely Fast Lyapunov Indicator (FLI), Smaller Alignment Indices (SALI), and the Dynamic Lyapunov Indicator (DLI). For this, we first recall the definitions of FLI, SALI and DLI. Then, we demonstrate the usefulness of the above-mentioned indicators by applying them to the Tinkerbell map, the Lorentz BD map, the Rucklidge oscillator and the double-pendulum system. The main observations of our study refer both at the "traditional" behavior of every indicator as well as their deviations to this.

In this analysis, the variable configuration requires a variable distribution. This takes account of the areas offered by the valves and resistance gazodynamic coefficients. All at once the law of efficiency variation describes the variation of the power law. Cycle behavior was analyzed for the following values of the pressure drop coefficient on admission: 5%, 10%, 20% and 40%. For the calculations is necessary to determine the dimensionless heat developed by combustion. I used the following values: for the pressure drop coefficient on admission I use ψa=10 % and for the share of gazodynamic on the suction route conductance in total conductance I use Ka 0,5. With this configuration imposed and with Qcb 3,71 (dimensionless heat developed by combustion) resulted: pmi 10,255 (mean indicated pressure cycle); ηv = 0,876 (cylinder filling coefficient); α = 1,515 (excess air coefficient) and ηi = 0,499 (indicated cycle efficiency); Pi 1,851 (dimensionless indicated power); Qg 3,37 (dimensionless heat taken combustion gas);Q0 1534, (dimensionless heat taken environment). After numerical analysis result a maximum efficiency with relatively low dissipation. © (2014) Trans Tech Publications, Switzerland.

Omocea I.,Maritime University of Constanta
Advanced Materials Research | Year: 2014

We use a model that is based on the cycle behavior inlet pressure variation. This analysis revealed the two main regimes of operation marine propulsion engines. Pressure drop in the suction process can be seen from two points of view: this pressure drop is an active dissipation and at the same time is a passive dissipation, contributing to the deterioration of cycle infrastructure. Interference of the two effects is reflected by the appearance of a ψa opt=0,3...0,35, for which indicated power Pi becomes maximum in terms of given geometric and gazodynamic configurations. Respectively for a weighting of conductance gazodynamic Ka imposed. When fuel flow is imposed, the analysis revealed that the share of shall be amended to variation of ψa, which involves the geometric and gazodynamic configuration variable. In this numerical analysis showed the existence of ψa opt=0,1...0,15, for which indicated efficiency ηi is maximum. © (2014) Trans Tech Publications, Switzerland.

George Z.,Maritime University of Constanta
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2015

In a shallow underwater acoustic channel the delayed replicas of a transmitted signal are mainly due to the interactions with the sea surface and the bottom layer. If a specific underwater region on the globe is considered, for which the sedimentary layer structure is constant across the transmission distance, then the variability of the amplitude-delay profile is determined by daily and seasonal changes of the sound speed profile (SSP) and by weather changes, such as variations of the wind speed. Such a parameter will influence the attenuation at the surface, the noise level and the profile of the sea surface. The temporal variation of the impulse response in a shallow underwater acoustic channel determines the variability of the optimal transmission frequency. If the ways in which the optimal frequency changes can be predicted, then an adaptive analog transceiver can be easily designed for an underwater acoustic modem or it can be found when a communication link has high throughput. In this article it will be highlighted the way in which the amplitude-delay profile is affected by the sound speed profile, wind speed and channel depth and also will be emphasized the changes of the optimal transmission frequency in a configuration, where the transmitter and receiver are placed on the seafloor and the bathymetry profile will be considered flat, having a given composition. © 2015 SPIE.

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