فصلنامه علوم و فناوری دریا
سال بیستم شماره 79 (پاییز 1395)

GPS provides accurate measuring of velocity and positioning for marine navigation. Phase Lock Loop (PLL) is used to measure signal carrier phase accurately. Thanks to easy architecture of Costas loop, it has been one of the most-used PLL in GPS software receiver. Phase noise and high dynamic situation effects on PLL designing. To track high dynamic signals, wider loop noise bandwidth is desirable. However, a wide bandwidth allows noises to pass through the loop filter. To reduce the thermal noise, the filter loop with narrow loop noise bandwidth should be designed. But it degrades the tracking loop robustness in high dynamic situation and result in loosing lock. To solve this problem, we have used a Fuzzy Logic Controller (FLC) to tune loop noise bandwidth in an adaptive manner. This FLC is a two inputs and one output system which its membership functions has been optimized with Genetic Algorithm (GA). Carrier phase and its delay version go to FLC as input data. According to changes of input, the loop noise bandwidth changes adaptively. This work has been compared with some traditional methods and the performance of the proposed tracking loop is verified by several simulations.

Nanotechnology is the understanding and control a wide range of due to high pollution sources a considerable impact on the development and solving environmental issues. The purpose of this study was the use of nanocatalysts and nano-adsorbents used in the offshore industry and military and petroleum hydrocarbons absorb pollution from cargo ships. The most effective catalysts can be used to nanoparticles of titanium dioxide (TiO2), combined with high energy gap at approximately 380 nm wavelength light of shows photocatalytic properties. Titanium nanoparticles coated on suitable substrates and the puddles are irradiated with ultraviolet light. Energy band gap of the semiconductor is about 3 eV. Tests shown that waste oil contaminated with organic material after 7 days of completely decomposed. To improve the efficiency of nanoparticles of titanium the Fe and Er have also been used. The use of nano-composites and nano-catalysts and review its performance in different situations can help a lot in solving environmental problems when accidents have oil.

Maritime transportation industry; as the backbone of global trade; provides more than 90 percent of cargo transportation overseas. Accordingly, safety at sea is highly regarded. On the other hand, safety management requires risk assessment as its prerequisite. In maritime transportation, vessel collision is the most destructive and most frequent accident. Accordingly, collision risk assessment is the most important task when talking about the safety of transportation. In this article, the concept is reviewed including frequency of occurrence as well as its consequence. Then with a focus on the frequency of collisions; which includes high risk locations and causation factor; four approaches to evaluate high risk locations are fully investigated as statistical, analytic, network-based and simulation-based ones. The study clearly shows a good potential to develop software in this area. It becomes more important when looking at sea transportation at the region as well Iran’s port development projects.

Although, calculating of the hydrodynamic resistance is an important activity in design process of conventional ships, but for the planning vessels that usually has a minimum draft in planning phase and most of the vessel's body is subjected to the wind flows and the aerodynamics can not be neglected. it is more important for the vessels are moving at higher speeds than about 40 knots. At these cases, form design of the vessel’s superstructure would be important. At this paper, using the computational fluid dynamics the aerodynamic flow about a monohull planning hull in the range of 40 to 100 knots are simulated numerically. The governing equations of mass and momentum conversations and the SST –Transition turbulence model are utilized. Aerodynamic loading such as the lift and drag forces and the aerodynamic’s lost of power are calculated and the contours of pressure and flow fields are also presented.

Geochemical studies of sediments, water bodies like rivers, estuaries and the sea bed, can be an effective step to find the source and distribution model assessment of environmental pollutants in a region.Sediments are the final destination of heavy metals in aqueous environments contamination, including arsenic entering the water resources in different ways, causing hazards such as poisoning, and carcinogenesis in living bodies. Study arsenic levels in the eastern part of the Caspian Sea, 30 stations were selected. After graining size and organic mater analysis, arsenic concentration in in two seasons summer and winter was determined by using Inductively Coupled Plasma- Mass spectrometry (ICP-MS). Geochemical index, Enrichment factor and pollution index showed low pollution to non pollution area and primary cause of arsenic distribution to this environment, geology and upstream sediment erosion and transport by rivers leading to Gorgan Bay and surrounding areas. compare these results with other parts of the Caspian Sea show that arsenic levels observed in this study in the Gorgan Bay and surrounding areas has been less than other part of the Caspian Sea.

In this study, possibility of establishing sound channel in the southern coastal waters of the Caspian Sea has been evaluated. The research is based on data analysis from field measurement data of temperature, salinity and pressure in the southern boundary of the Caspian Sea. The results show that water temperature changed between 17.9 and 9.2 degree from surface to the bottom and vertical changes of salinity were between 12.06-12.67. Sound speed in the water column varied between 1488 to 1460 m/s from surface to depth of 42 m with a rapid decrease across thermocline layer. Vertical structure of seawater temperature follows the vertical sound speed changes which indicate a high correlation between these parameters. According to the results, the sound channel in the shallow waters of the eastern part of the southern coast of the Caspian Sea was not observed.

Common methods include the use of sound waves and underwater detection equipment such as sonar (which is divided into two types: active and passive) and Sonobuoy that functions like a sonar is used. In this paper, we introduce new algorithms in this field and the best and most reliable way of Magnetic Anomaly Detection called MAD briefly explain. This detection algorithm, is a method based on the measurement of the smallest changes or disruptions in the Earth's magnetic field by passing a ferromagnetic object and magnetic dipole field generated around it is based. In this paper, the detection of subsurface using the principles and methods of detection of this method are discussed and compared.

Unmanned underwater model is a non-linear system that various methods have been proposed for the depth control. Sliding mode control (SMC) is a state feedback robust control for non-linear systems that will change its structure to achieve optimal performance. In this method, it is assumed that the process control can be instantly changed from one structure to another structure. In classic SMC, Computational delays and restrictions on operators leads to the phenomenon of chattering in control signal. In this paper, depth control of an unmanned underwater vehicle system of two degrees of freedom is considered. It is shown that the use of the sliding mode controller for the depth controlling of the system under study, will lead to the chattering phenomenon. To solve the problem for the system under study, there is tried to use the fuzzy sliding mode control. Simulation results indicates that the fuzzy sliding mode method is solved the problem in which the system properly is controlled with low chattering control signal.