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.