Journal of Naval Sciences and Engineering

12

Authors: Cüneyt EZGİ

Seawater is employed as the cooling media for a variety of heat exchanger applications on ships, offshore platforms, and at coastal locations. Although seawater is used extensively as a coolant medium, it has two main disadvantages: Corrosion and fouling. Selection of material must be met to ensure economical design and reliable performance.

16

Authors: Hüseyin Yavuz YÜCESOY, Prof. Dr. Murat VURAL

Beside the fact that austenitic stainless steels are used in various industrial applications, they are also widely used in naval applications. Especially, in shipbuilding sector, construction of corrugates and corrugate supports of tankers, chemical tankers, non-magnetic ships which are supposed to be working in polar areas and in construction of some naval war ships, as well as in piping systems of those, the need of having welded structures of non-magnetic stainless material has been increased. Within this scope, the prediction of the distortions of welded joints of austenitic stainless steel becomes more important and comes forward among the others. Most stainless steels are considered to have good weldability and may be welded by several processes including the arc welding processes, resistance welding, electron and laser beam welding, friction welding and brazing. For any of these processes, joint surfaces and any filler material must be clean. The coefficient of thermal expansion for the austenitic types is 50 % greater than that of carbon steel and this must be considered to minimize distortion. The low thermal and electrical conductivity of austenitic stainless steel is generally helpful in welding. Less welding heat is required to make a weld because the heat is not conducted away from a joint as rapidly as in carbon steel. In resistance welding, lower current can be used because resistivity is higher. Filler material for austenitic stainless steels should match or exceed the alloy content of the correct of the base metal. If a filler material of the correct match is not available, a filler metal with higher alloy content normally should be used. These filler metals can be in such a composition that a ferrite structure is obtained in order to prevent hot cracking. Filler metals for welding stainless steels are produced as coated electrodes, solid and metal cored wire and flux cored wire. In this study, it is aimed to analyze the welding distortions of austenitic stainless steels by using a sample steel (AISI 321 – 1.4541– UNS: S32100) and having it welded experimentally in two different positions (Butt Welding and Fillet Welding) and comparing the resulted deformations with Finite Element Method (FEM) modeling ones of the same joints.

20

Authors: Erinç DOBRUCALI

Computational fluid dynamics (CFD) is nowadays widely used to simulate smoke spread and temperature distribution as well as ventilation measures in a fire scenario. It allows improving fire fighting strategies and precaution measures in order to suppress the fire as fast as possible and help people to evacuate. In recent years, it has become apparent that computational fluid dynamics (CFD) can play an important and useful role in fire safety problems. The application of CFD to fire problems is also known as field modeling. Field modeling is based on the fundamental laws which govern the fire phenomena. Therefore, it is a valuable alternative for experimental investigations and empirical correlations and can be applied as a predictive tool. In this paper, field modeling is applied to tunnel fires in order to predict the critical ventilation velocity.

6

Authors: M.Oğuzhan ÜN, Mustafa YAĞIMLI, Hayriye KORKMAZ

In this study, the shape which gives a fine estimation about what may the object be is handled by Generalized Hough Transform via LABVIEW Graphical Interface Program. The template of any object with a distinguishable shape is learned first and then tracked via LABVIEW. The templates are searched in the video of a webcam which has the capability of 30 frames in a second. The matches taking a score over defined level are considered as real matches and bounded by a bounding box. In this way the target recognized and tracked real time.

16

Authors: Gökhan GÜRLEK, Necdet ÖZBALTA

The swirl flow devices like twisted tape, winglet, groove, conical ring, wire coil etc. have been used as passive heat transfer augmentation technique. Especially, twisted tape devices have been applied in thermal engineering systems such as boilers, heat exchangers, water heater. Many researches using swirl flow devices particularly twisted tape with different geometries for heat transfer enhancement have been published. In this paper, different modified twisted tapes which had examined in previous studies were compared with each other with regard to heat transfer augmentation. Heat transfer, friction factor and thermal-hydraulic performance factor characteristics were investigated separately under the same conditions such as same twisted ratios and same Reynolds number values. Twisted tape which gives best heat transfer and friction factor results was determined. Derived empirical correlations which had been found by researchers were used for comparison between twisted tapes.

17

Authors: Erinç DOBRUCALI

Recent concerns over the environment like global warning, weather changes increasing fuel prices and scarcity of its supply have promoted the interest in development of the alternative sources for petroleum fuels. Biyodiesel is one of the most important renewable, alternative fuels that no need any modification in diesel engines. If we think of our foreign fuel dependence, determining the abilities of biodiesel as a fuel in diesel engines is really crucial. In this study, early studies about alternative fuels are obtained and these are presented.

14

Authors: Erdal KARADENİZ, Mehmet TÜRKER, Fatih SERDAROĞLU, Yasin K. KUTUCU

Stainless steel flanged pipe formed by the welding are used commonly in nuclear, chemical, petroleum and food industries in which the corrosion resistance has importance. In the stainless steels, the distortions are occurred at an important rate due to excess heat input in welding method. This situation causes time, labor force and repair costs. In this study, angular distortion values - the most effective distortion - observed in welded flanged pipes was investigated. Austenitic stainless steel flanged pipes were produced by tungsten inert gas (TIG) method with or without filler rod. The most important parameter affecting the temperature rise in heat affected zone (HAZ) is the welding current. Therefore, experimental study was carried out by using welding current (70, 80, 90, 100 and 110 A) deemed worthy of researching.

18

Authors: Erinç DOBRUCALI

Fire is the heat and light energy released during a chemical reaction, in particular a combustion reaction. Depending on the substances alight, and any impurities outside, the color of the flame and the fire's intensity might vary. Fire in its most common form can result in conflagration, and has the potential to cause physical damage through burning. Fires in buildings and transportation systems are a threat to human lives and also to buildings and cultural heritage. In a fire inferno, most of the victims die due to late detection of the fire and consequent inhalation of toxic smoke gases. In addition to the human consequences, the economic and cultural loss is significant.

27

Authors: Güzide Öncü EROĞLU PEKTAŞ, Mustafa KARADENİZ, Gülçin SERBEST

Recently in business environment, the competition is not only between the individual firms but also the networks of the companies. Therefore, the supply chain of the firms has a critical role in the success and also it is very important for supply chains to be cost-effective, high quality and be able to response quickly. Supply chain is an umbrella term used for the activities a business undertakes in order to link their supply of goods with customer demand. And the bullwhip effect is the phenomenon of increasing demand variability in the supply chain from downstream echelons (retail) to upstream echelons (manufacturing). Loyalty means the positive trends of consumers towards a store or brand. And this consists after the result of the judgment or assessment from purchasing a particular product or service. The objective of this study is to analyze the impact of bullwhip effect on customer loyalty. Customer loyalty, supply chain and bullwhip effect in relation to each other contributes to the literature aimed.

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.