Gunes Yilmaz

An Assessment of the Methods for Calculating Ampacity of Underground Power Cables

Endurance of an insulation material to high temperatures determines the maximum current-carrying capacity (ampacity) of an underground power cable. Cable ampacity is calculated conventionally using the installation conditions and maximum steady-state operation temperature according to IEC-60287 standard. In this article, finite element method results are compared with IEC-60287. A further verification has also been made with experiments. In this work, ampacity analyzes of 154 kV high voltage XLPE underground power cable are made using ANSYS 5.61 finite element analysis software. An experimental set-up is developed to measure conductor and surface temperature of the cable in underground conditions. The results of experiments and numerical calculations are compared to the IEC-60287 standard. Additionally, the thermal regions of three cables in flat installation are investigated to show the versatility of the finite element method. The effects of insulation thickness and external thermal source on ampacity are also analyzed using the finite element method.

Solution of Raman fiber amplifier equations using MATLAB BVP solvers

Purpose – The purpose of this paper is to demonstrate an effective and robust numerical solution for Raman fiber amplifier (RFA) equations which have no explicit solution. MATLAB BVP solvers are addressed for the solution.Design/methodology/approach – The continuation method proposed for the solution of RFA equations using MATLAB BVP solvers is explained. Scripts for improving the power values at the boundaries with continuation, extending fiber length with continuation and calculation of the analytical partial derivatives using the MATLAB Symbolic toolbox are introduced. Comparisons among the different MATLAB BVP solvers have been made. Using the continuation method, signal evolutions for different kinds of RFA amplifier configurations are plotted.Findings – The paper finds that MATLAB BVP solver with the continuation method can be used in the design of various kinds of RFAs for high powers/long gain fiber spans.Research limitations/implications – The paper will assist the fiber optic research community ...

Novel guess functions for efficient analysis of Raman fiber amplifiers

Purpose – The aim of the paper is to demonstrate a fast numerical solution for Raman fiber amplifier equations using proposed guess functions and MATLAB intrinsic properties. MATLAB BVP solvers are addressed for the solution.Design/methodology/approach – The guess functions proposed for the solution of RFA equations using MATLAB BVP solvers are derived from Taylor expansion of pump and signal wave near the boundary to specifically obtain convergence for the initial mesh point. The guess functions increase simulation speed significantly. In order to improve the simulation speed further, vectorization and analytical Jacobians are introduced. Comparisons among bvp4c and bvp5c have been made with respect to total pump power, number of signals, vectorization with/without analytical Jacobians, fiber length, relative tolerance and continuation method. The simulations are performed to determine the effect of the run time on the choice of the number of equally spaced mesh points (N) in the initial guess, and thus ...

Numerical solution of Brillouin and Raman fiber amplifiers using bvp6c

Purpose – The purpose of this paper is to demonstrate an effective and faster numerical solution for nonlinear‐coupled differential equations describing fiber amplifiers which have no explicit solution. MATLAB boundary value problem (BVP) solver of bvp6c function is addressed for the solution.Design/methodology/approach – Coding method with the bvp6c is introduced, signal evolution, threshold calculation method is introduced, gain and noise figure are plotted and superiority of the bvp6c solver is compared with the Newton‐Raphson method.Findings – bvp6c function appears to be an effective tool for the solution fiber amplifier equations and can be used for different pump configurations of BFAs and RFAs. The excellent agreement between the proposed and reported results shows the reliability of the proposed threshold power calculation method.Research limitations/implications – The paper eases the work of the fiber optic research community, who suffer from two point BVPs. Moreover, the stiffness of the signal...

Performance Analysis of the Differential Evolution and Particle Swarm Optimization Algorithms in Cooperative Wireless Communications

In this study, we evaluate the performance of differential evolution (DE) and particle swarm optimization (PSO) algorithms in free-space optical (FSO) and mobile radio communications systems. In particular, we obtain the optimal transmission distances for multiple-relay nodes in FSO communication systems and optimal relay locations in mobile radio communications systems for the cooperative-diversity networks, using both algorithms. We investigate the performance comparison of DE and PSO algorithms for the parallel decode-and-forward (DF) relaying. Then, we analyze the cost functions. Furthermore, we present the execution time and the stability of the DE and PSO algorithms.

Fresnel reflection based fiber optic refractive index sensor for liquid concentration dedection

Measurement of refractive index which is one of the distinctive properties of materials is commonly used in many fields such as quality control of food industry, biomedical applications, biochemical analysis and measurement of environmental pollution. From the refractive index measurement methods, the one based on fiber optic stands out with their provided advantages. In this study, firstly, a simple, reliable and highly sensitive Fresnel reflection based fiber optic refractometer was setup, then the refractive indexes of various liquids were measured using this setup at different times. When the measurement results are compared with material science data sheet (MSDS) values, the percent error was found to be less than %1. Moreover, the long term stability of ethanols refractive index was examined and the refractive index variation of salt-water was obtained as a function of the salt concentration.

Analysis of interactions between node induced crosstalk and fiber nonlinearities in optical metropolitan area networks

The problems that occur at the nodes of a metropolitan area network (MAN) can interact with optical fiber nonlinearities. In this paper, impacts of such interactions, in particular the one between crosstalks occurring at the optical add/drop multiplexers (OADMs) of metropolitan network nodes and optical fiber nonlinearities, on transmission performances of optical fiber systems are investigated. The optical fiber systems are a non-zero dispersion shifted fiber (NZDF) system and a standard single mode fiber (SMF) system where dispersion compensating fiber (DCF) is used for dispersion management, shortly a SMF+DCF system. Significant impairments on transmission performances are observed in simulations. The results show that such interactions should be carefully considered during the design of metropolitan WDM networks.

A Novel Protocol Proposal for Integratıon of SIP Based Telephony Services To IPTV System

In this study, a novel architecture that will provide integration of session initiation protocol (SIP) based call server telephony services with IPTV system has been proposed, a novel protocol (Independent Notification Protocol) has been designed for this aim and advantages of the developed architecture have been analyzed. The proposed architecture and supporting protocols eliminate the need for a middleware layer in the notification architecture. Therefore, one layer is reduced from the notification architecture and dependence to a special middleware finishes, i.e. the notification architecture can be built up with any kind of middleware layer. Test results for the proposed architecture and the protocol have showed that notification bandwidth reduces to 10 % of that of conventional notification architecture and the proposed architecture works successfully.