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Tamas R.D.,Constantza Maritime University
2016 International Workshop on Antenna Technology, iWAT 2016 | Year: 2016

Previously, the author has described a method for measuring the antenna gain in non-anechoic sites. The effects of reflection and diffraction on the neighboring objects can be dramatically reduced by averaging, over a set of distances, a normalized transfer function of the system consisting of the antenna under test and the measuring antenna. The method was successfully tested on dipole type, ultra-wide band antennas. This paper, presents further results on measuring narrow band, monopole antennas. It comes out that averaging does not remove the effect of the diffraction on scatterers close to the radiating element, such as the edges of the antenna ground plane; conversely, it reasonably reduces the effects of scatterers placed at several wavelengths away from the antenna under test. © 2016 IEEE.

Scupi A.A.,Constantza Maritime University
IOP Conference Series: Materials Science and Engineering | Year: 2016

This paper is conceived on the idea that numerical programs using computer models of physical processes can be used both for scientific research and academic teaching to study different phenomena. Computational Fluid Dynamics (CFD) is used today on a large scale in research and academic institutions. CFD development is not limited to computer simulations of fluid flow phenomena. Analytical solutions for most fluid dynamics problems are already available for ideal or simplified situations for different situations. CFD is based on the Navier- Stokes (N-S) equations characterizing the flow of a single phase of any liquid. For multiphase flows the integrated N-S equations are complemented with equations of the Volume of Fluid Model (VOF) and with energy equations. Different turbulent models were used in the paper, each one of them with practical engineering applications: the flow around aerodynamic surfaces used as unconventional propulsion system, multiphase flows in a settling chamber and pneumatic transport systems, heat transfer in a heat exchanger etc. Some of them numerical results were validated by experimental results. Numerical programs are also used in academic institutions where certain aspects of various phenomena are presented to students (Bachelor, Master and PhD) for a better understanding of the phenomenon itself. © Published under licence by IOP Publishing Ltd.

Constantin S.L.,Constantza Maritime University
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

This study presents numerical and experimental results concerning a test impeller of a centrifugal pump. From the experimental point of view, the cavitation was visualized at different Inlet Pressure values. Image processing and statistical treatment of the photographs taken at given impeller position allowed to quantify the attached and cloud cavitation extent. A numerical model of 3D cavitating flows, based on the CFD code Fluent 6.1, has been developed to predict the cavitation behavior in the presented model which is considering the entire pump, the impeller and also the casing of the pump, with all its complex geometry and flow parameters. Non-cavitating and cavitating conditions were investigated. Calculations were found to be in good agreement with experimental measurements and visualisations. Experimental and numerical results concerning the pump parameters were investigated. The overall conclusion is the obvious knowledge that the Net Positive Suction Head (NPSH) is indeed affecting the cavitation condition in the centrifugal pumps, having direct impact on the magnitude of static pressures in various locations inside the pump, but is not altering too much the velocities distributions of fluid. © 2012 SPIE.

Ciucur V.-V.,Constantza Maritime University
Electronics and Electrical Engineering - Proceedings of the Asia-Pacific Conference on Electronics and Electrical Engineering, EEEC 2014 | Year: 2015

The control system for the speed position of a DC motor, generally can be controlled by a microprocessor, or microcomputer, all these components which can determine the values for speed for each movement and passes. The system can contain a D/A converter. In order to obtain signals which can then be processed by a converter an optical encoder can be used, mounted on the shaft of a DC motor. © 2015 Taylor & Francis Group, London.

Liviu-Constantin S.,Constantza Maritime University
2010 The 2nd International Conference on Computer and Automation Engineering, ICCAE 2010 | Year: 2010

This paper represents a step forward toward the introduction of engineering advanced research methods for the study of dynamic behavior of marine propulsion systems. The large dimensions of this work and its both theoretical and research material developed in it via numerical simulation are witnessing of the author effort for an exhaustive treatment of the proposed theme. ©2010 IEEE.

Scurtu I.C.,Constantza Maritime University
IOP Conference Series: Materials Science and Engineering | Year: 2015

Manufacturing steps for a modern three - column semi-submersible structure are delivered using CFD/CAE software and actual Froude scaled model testing. The three- column offshore is part of the Wind Float Project already realized as prototype for wind energy extraction in water depths more than 40 meters, and the actual model will not consider the wind turbine. The model will have heave plates for a smaller heave motion in order to compare it with the case without heave plates. The heave plates will be part of the Froude scale model.. Using a smaller model will determine a smaller heave motion and this will affect predictions of the vertical movement of the three- column offshore structure in real sea. The Froude criterion is used for the time, speed and acceleration scale. The scale model is manufactured from steel and fiberglass and all parts are subjected to software analysis in order to get the smallest stress in connections inside the model. The model mass was restricted by scale dimensions and also the vertical position of centre gravity will be considered during the manufacturing and design process of the Froude scale offshore structure. All conditions must converge in model manufacturing and design in order to get the best results to compare with real sea states and heave motion data..

Tamas R.D.,Constantza Maritime University
IOP Conference Series: Materials Science and Engineering | Year: 2015

Numerical methods are widely used for modeling different physical phenomena in engineering, especially when an analytic approach is not possible. Time-domain or frequency- domain type variations are generally investigated, depending on the nature of the process under consideration. Some methods originate from mechanics, although most of their applications belong to other fields, such as electromagnetism. Conversely, other methods were firstly developed for electromagnetism, but their field of application was extended to other fields. This paper presents some results that we have obtained by using a general purpose method for solving linear equations, i.e., the method of moments (MoM), and a time-domain method derived for electromagnetism, i.e., the Transmission Line Matrix method (TLM)..

Deacu D.,Constantza Maritime University
Advanced Materials Research | Year: 2014

Modeling of radio wave propagation onboard ship should take into account multipath effects, i.e., reflection and scattering on the ship conductive superstructure. Novel ultra-wide band communication technology consists of series of short pulses carrying information by changing the polarity as 0 or 1 bits are transmitted. Multipath effects actually impact on the interference free time-slots to be provided between carrier pulses. Narrow-band radio channels are presently modeled either deterministic or stochastic. Although accurate, deterministic models are rather complicated and difficult to use when the configuration of the propagation channel changes. Stochastic models are less sensitive with respect to the configuration of the channel if the distribution of the scatterers and their type do not change dramatically. This paper extends the stochastic, narrow-band logdistance model to ultra-wide band channels. The coefficients of the model are calculated from a set of real data measured onboard a maritime ship. The accuracy of our model is then investigated by comparing the real channel response to the calculated one. Finally, we investigate the channel response to a usual pulse waveform, i.e. the first time-derivative of the Gauss function. The figure of merit to be analyzed is the normalized correlation coefficient or fidelity factor. It should be noted that the dispersion of the measuring antennas was compensated by knowing the gain variation as a function of frequency. This study also leads to minimal values for the time slots between pulses. © (2014) Trans Tech Publications, Switzerland.

Dragomir C.,Constantza Maritime University
Advanced Materials Research | Year: 2014

This Finite element method is one of the most advanced calculating methods for approximation of accurate solutions to engineering problems. Optimization of grab's quay cranes is necessary because most port operators use this type of equipment for loading and unloading bulk cargo. Initial research methods applied in this study are based on observations and surveys conducted on Bocşa 16 t - 32 m mobile quay cranes of MinMetal S.A. Constanta port operator. Modeling and analysis for grab's structure optimization was made with FEMAP and NX NASTRAN - version 10.3.1 applications, which use the finite element method and finite element analysis. After calculations and analysis, the following optimizations resulted: -to increase the grab's closing force (in order to minimize the loss of cargo between jaws and to increase digging force) the lower beam weight must be reduced. -to reduce the amount of cargo drained from the grab's jaws at loading, rubber jaws barriers can be fixed or bars can be welded at grab's jaws. - if cargo has high granulation, in order to reduce grab's weight the plate of the jaw can be cropped. -cups' supporting tie rods could be replaced by hydraulic cylinders. The greatest tension is located in the cups' supportive arms and in the area where cups are attached to arms. Shafts' tensions are larger than the grab's metal structure and are located in shafts-arms contact areas, ie support bearings. In these areas, an optimization can be made by installing ball bearings to reduce friction. The largest deformations occur in the middle area of the arms. To increase safety in operation it is necessary to change the material of the four arms supporting cups, given that deformation of 89.7 mm (~ 9 cm) combined with external factors and / or shock loads can lead to permanent deformation or even material breaks. After changing the material, the model showed that the deformations in the middle area of the arms are substantially reduced, at only 4 mm. In the contact area of the upper arms with the two bars of the upper beam, hazardous tensions may be minimized if there are inserted bearings. © (2014) Trans Tech Publications, Switzerland.

Ciucur V.,Constantza Maritime University
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2015

Of three-phase alternating current electric machines, it brings into question which of them is more advantageous to be used in electrical energy storage system by pumping water. The two major categories among which are given dispute are synchronous and the asynchronous machine. To consider the synchronous machine with permanent magnet configuration because it brings advantages compared with conventional synchronous machine, first by removing the necessary additional excitation winding. From the point of view of loss of the two types of machines, the optimal adjustment of the magnetic flux density is obtained to minimize the copper loss by hysteresis and eddy currents. © 2015 SPIE.

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