Journal of Naval Sciences and Engineering

11

Authors: Erinç DOBUCALI

The dispersion of exhaust smoke is affected by a large number of parameters such as efflux velocity and temperature of smoke, level of turbulence, wind velocity and direction, geometry of the structures on ship’s deck etc. For this reason, Analyzing of the dispersion of exhaust smoke from ship stack is really complex. Traditionally, the behavior of the exhaust gases by using scale models in wind tunnels can be investigated. In nowadays, however, as a result of technological advances in numerical computational methods and computers, dispersion of the exhaust gases from Marine ship’s stack can be calculated and high performance funnels of the ship can be designed during pre-design phase. While cruising, ship has a boundary layer. In the sailing ships, these harmful emissions from funnel and high exhaust temperature affects the electronic devices in the ship’s deck and also the health of the crew in the deck. In this study, as a result of this literature review of this topic, a short summary of these studies will be presented.

16

Authors: Yusuf KAVURUCU

Subgraphs that occur in complex networks with significantly higher frequency than those in randomized networks are called Network Motifs. Such subgraphs are the basic building blocks of complex networks. They often play important roles on functioning of those networks. Finding network motifs is a computationally challenging problem. Finding network motifs often requires solving subgraph isomorphism problem which is NP-complete. Instead of this, several methods apply similarity queries on biological networks to find similar patterns that exist frequently according to given threshold values. As these networks are stored in databases, we need efficient methods for accessing and querying these databases. As these networks are generally represented as graphs in theory, several graph indexing methods are developed for answering queries on them. This paper summarizes network motifs and indexing techniques in biological networks.

30

Authors: Cüneyt EZGİ, M.Turhan ÇOBAN

Fuel cells provide great potential for electric power generation on-board ships. Ships use marine diesel fuel for marine main and auxiliary engines . In this work, this paper presents the performance analysis of a planar solid-oxide fuel cell (SOFC) under reformed diesel fuel. A detailed solid-oxide fuel cell model is used to study the influences of various operating parameters on cell performance. Significant differences in efficiency and power density are observed for isothermal operational regimes. In the model, electrochemical kinetics, gas dynamics and species are coupled. The model predicts polarization curve, velocity and species concentration and current distribution in the cell depending on fuel cell temperature and electrodes/ electrolyte materials used in the components

13

Authors: M. Turhan ÇOBAN

Pressure drop in pipes can be calculated by using Darcy-Weisbach formula. In order to use this formula, Darcy friction factor should be known. The best approximation to Darcy friction factor for turbulent flow is given by Colebrook-White equation. This equation can only be solved by numerical root finding methods. There are several other approximate equations to Darcy friction factor with some relative error compared to Colebrook-White equation. In some of these equations the percentage error is so small that they can be used directly in place of Colebrook equation. In this study relative error of several equations are re-evaluated.

19

Authors: İbrahim GİRGİN1, Mehmet TÜRKER

Acoustic waves hold oscillations of pressure, displacement and temperature. The interaction of these effects in gas close to a solid surface generates thermoacoustic oscillations. Some prototypes of coolers are being constructed using the principles of thermoacoustics nowadays. Even though the coefficient of performance of thermoacoustic systems is lower than the conventional coolers, the concern on the thermoacoustic systems has been increased since these systems are cheap, simple and do not use harmful gases for the atmosphere and do not have any moving parts compared to the conventional coolers. Thermoacoustic coolers are one of the potential cooling technologies of the future.