نشریه مهندسی شناورهای تندرو
پیاپی 45 (پاییز و زمستان 1393)

Nowadays, speed in high speed crafts is of particular importance. Creation in of moss on the hull is one of the factors slowing down the vessel. Among the methods of removing moss, Painting hull is the most effective and the cheapest method among other methods used to remove moss. Antifouling paints, were introduced to the market from the early 20th century among them TBT- SPC Free and tin-free glossy paints has been highly regarded (in terms of quality and economical). This sample of the paints, reduces friction force between water and draught, as well as reducing the surface roughness resulting in less fuel consumption and an increase in speed of the vessel. However, they are rarely used for the vessels, due to environmental pollution this article is about the maintenance of the hull against seaweeds using antifouling paints.

Research on radio equipment and remote control with unprecedented speed being done, above all, too many applications off this technology in the arena military has made the governments do huge investments in this sector. Despite a good performance and very high achievements of electromagnetic radiation, if not control very dangerous for human and irreversible effects it will have its effects will remain even after thousands of years.
A variety of telecommunication and communication equipment such as mobile phones, communication device and etc. that emits electromagnetic waves with biological tissues they will create a change such as electronic burn. naturally The use of this equipment to endanger life, because electromagnetic waves from passing any object and then exit it after creating wastes that are very harmful.

Shell and tube heat exchangers equipped with segmental baffles are the most widely used kind of heat exchangers in industrial applications. Nowadays, substitution of the heat exchangers equipped with helical baffles is a new methodology to improve of the heat exchangers efficiencies. In this paper, heat and fluid flow fields through the heat exchangers equipped with continuous helical baffles are analyzed numerically using the computational fluid dynamics, CFD. Also the effects of two major geometrical ratios: the shell to pipe diameters, D/d, and the baffle pitch to shell diameter, B/D, on the efficiency of the heat exchangers are studied. Numerical methodology of solution and governing equations is validated by repetition numerical analyze of a heat exchanger that have experimental data for comparison. Consistency between the numerical and experimental are occurred. The results show that in both cases of baffles, for D/d near to 11.5, the variations of temperature difference between output and input of the shell with respect to D/d, changes from decreasing manner to increasing manner, while the variations of the pressure drop changes inversely, i.e. from increasing to decreasing manner. Similar results to the above also occurred near to the ratio of the baffle pitch to shell diameter, B/D of about 2. Comparison between the segmental and continuous helical baffles shows lower pressure drop and upper temperature differences for heat exchangers equipped with the later baffles.

The main characteristic of sound propagation in shallow waters in that graph of sound speed is almost constant or it has a downward fracture. Therefore, the sound propagation is shallow waters areas is that each beam emitted from the sound source during the propagation time is constantly reflected from the seabed reflectivity of the seabed is more important than the reflectivity of the surface of the sea.
Is this paper, the characteristics of geographical environment in the Persian Gulf and HORMUZ strait and the way of sound propagation in these areas has been explained. The effect of heat, cold, salinity and water flow on the speed will also be evaluated. The Persian Gulf and its coastal areas with less than 200 meters is a type of shallow waters environments.

The main characteristic of sound propagation in shallow waters is that graph of sound speed is almost constant or it has a down ward fracture. Therefore, the sound propagation is shallow waters areas is that each beam emitted from the sound source during the propagation time is constantly reflected from the seabed reflectivity of the seabed is more important than the reflectivity of the surface of the sea. In this paper, the characteristics of geographical environment in the Persian Gulf and hormuz strait and the way of sound propagation in these areas has been explained. The effect of heat, cold, salinity and water flow on the speed of sound will also be evaluated. The Persian Gulf and its coastal areas with depth less than 100 meters is a type of shallow waters environments.

In this paper, some variations have been described in designs of conventional pressure chamber. Two numbers of these designs include cylindrical/conical body and head-end bodies. Third design, also, is the case that pressure chamber has enforced by environmental tubes. It is demonstrated that the design of folded pressure chamber is more efficient than cases that enforced by conventional rings. For enforced cylinder by thin walled ring, response is based on elastic bar- on- bed theory, while, for cones and thin & thick walled heads, responses are based on finite element method. Solutions have been described for unstable cylinders, cones and thin walled heads under uniform external pressure. Some of theories are based on analytical approach and some others are based on numerical finite element method.

During recent several years, the game theory was one of the most important research fields and has been used in politic, biology, military and engineering applications in addition to economic and mathematics. Game theory is the science of strategies which presents a logical and mathematical form of decisions to players to approach their best possible payoffs. This theory tries to find optimum strategies of all players by modeling of the mathematical behavior exist in the game; i.e. the payoff of any player is affected by the strategies of all other players. The importance of game theory is that we can model the real problems as a game and then solve it. This paper aims to introduce this theory and its applications. First the research history and basic definitions and concepts of game theory are expressed and then different games, applications and their mathematical modeling are described.