فصلنامه دریا فنون
سال دوم شماره 1 (پیاپی 3، بهار و تابستان 1394)

The Global Positioning System (GPS) has changed the world. This is especially true for marine operations, including search and rescue. Safety and security of marine navigation GPS system is vulnerable to spoofing attack. Therefore, in recent years, the study of spoofing and related countermeasures has become one of the important topics of scientific research especially in marine navigation . One of the basic requirements and major challenges in designing anti-spoof methods and evaluating a successful GPS spoofing countermeasure is the collection of actual spoofing data used to verify the proposed algorithm. Since actual spoofing data is acquired through an expensive spoofer-receiver device which is not possible in most cases, preparing genuine spoofing data without expensive spoofing devices including extra software or hardware can be helpful in the development of anti-spoofing studies. In this paper, a new and low-cost technique is proposed that help to generate a set of spoofing data only with the employment of software receiver and a set of real GPS signals. In this way, a spoofing data is resulted by utilizing delay and mixing procedure. This data will be generated in victim receiver antenna in marin navigation system, if a spoofer-receiver device is used in practice. After explanation of spoofing algorithm, the validation of proposed method is proved by appropriate tests.

Due to excellent piezoelectric properties, lead-based ferroelectric materials and more particularly the Pb(Zr,Ti)O3 (PZT) are widely used in actuators, sensors and transducers. However, these ceramics contain more than 60% PbO. With regard to the toxicity of lead, many efforts have been made to develop environmentally friendly and non-hazardous materials. In the present work, Potassium-Sodium Niobate (KNN) ceramics as the most important family of lead-free piezoceramics were fabricated by mechanical-Alloying reaction route and the synthesis and sintering processes as well as electrical properties of these ceramics were investigated. Characterization of synthesized powders by XRD, SEM revealed that calcination of raw materials at 850°C leads to a homogeneous and single-phase KNN powders. At optimum sintering temperature of 1000°C, the desirable values of 643, 140 pC/N and 0/01 were obtained for dielectric constant(εr),piezoelectric charge coefficient (d33) and loss factor, respectively.

Utilizing transverse steps for high-speed planning hulls is one of the methods for reducing of their resistance and thereafter increasing of their speed. Similar to regular planning hulls, the stepped hulls also have a hump in their resistance-speed curves during the transition from displacement to planning stage. Overcome to the hump usually follows with a heavy load on propulsion systems. In this paper, hydrodynamic characteristics of two planning boat model, a regular V-bottom hull and a hull with one transverse step, are investigated experimentally using towing tank tests. After that the tests for the stepped hull are repeated while a ventilation system is also added behind the transverse step. The results show in preplanning stage, resistance of the stepped hull increased about 30 to 40 percent whereas at the planning stage their resistance reduced about 5 percent respect to the regular planning hull. Using a natural ventilated system for stepped planning hulls reduced both the hump resistance (about 21 percent) and preplanning resistance respect to non-ventilated stepped hull. So, it can be used as a low cost system for practical issues.

Trust force is one of the most dynamic forces that in all periods of wind turbine operation is to be expected. Usually, dynamic response of the wind turbine tower under trust forces is calculated using the finite element method. Finite element method has high accuracy but it can considerably increases the computational works depending on the modeling type of foundation and modeling axial force variations. In this paper, transfer matrix method is used to reduce computational works and increase the speed of analysis instead of the finite elements method. For this purpose, the wind turbine foundation is modeled using DS model and required relations are extracted to determine of wind turbine response.Then, factors affecting the dynamic response such as induction factor, wind speed variations and nacelle mass variations are examined in several case studies. Finally, the transfer matrix method obtained results are compared with the results of the finite elements method, multi body dynamics, analytical method and experimental data which show good agreement in spite of low computational cost. The study shows that the vibrations from thrust force, wind turbine towers is resonance at frequencies equal to twice the natural frequency. Therefore, in the design of wind turbine towers, tower response at 0.5×ωn also be studied.

Tension leg platform (TLP) is a comparative platform used for extracting petroleum in deep waters. It is necessary to study Caspian Sea's tension leg platforms in deep water conditions due to its deep oil-rich areas. One of the most important parameters in TLP design is to calculate horizontal, vertical and angular relocations of platform. Relocations have enormous effect on tendon stresses. Since the main characteristic of TLP is to restrain these platforms by tendons, it is important to calculate these relocations and monitor the tension of tendons in all steps of design and production. By considering the conditions of the Caspian Sea’s waves on the platform modeled by ABAQUS software, the wave force have been calculated by Morison’s equation and the platform’s response had been studied for surge, sway and heave motions and roll, pitch and yaw angular motions by dynamic and static analyses. By changing the angle of incident wave and also platform’s loading, different responses of structure have been shown. The ideal of this research is analyses dynamic and static for a kind of this platform in deep water of Caspian Sea and show the final result of the platform’s response in different motions regarding to hydrodynamic calculations of platform.

Stiffened plates are the main supporting members of structures like offshore and ships. They typically consist of conventional stiffeners like T- of Flat bars. Recently some new structures were invented like Y-bar stiffeners. Whereas collision is one of the most important limit states of ships, analysis of collision and its failure mechanism is took in to consideration. Finite element method is a powerful tool for analyzing ship collision problem and has been seen more and more applications in the recent years. The accuracy of numerical modeling results significantly depends on the proper modeling and defining of critical parameters such as rupture criteria. A series of nonlinear FEM indentation analysis have been carried out quasi-statically that implemented into ANSYS/LS-DYNA. In this paper investigation of parameters on the collision of stiffened aluminum panels with Y-stiffeners was done and finally compared with T-stiffeners. With the aid of different analysis, It was showed that In general, increase in panel bending rigidity will result increase contact force. YB panels have higher contact force to weight than TB panels.

The offshore structures are always under water wave force. One of the effects of waves on the jacketsis is deformed and collapse phenomena. We know if the natural frequency of structure was near the frequency of the applied wave force, the resonance phenomenon will take place intensified. To prevent this phenomenon can with changes in the structure prevent from resonance phenomenon. In the paper we modify the boundary conditions of the jacket legs attached to the bed of the sea floor, it is shown which boundary conditions the natural frequency of the structure will be more distance from forced frequency of the wave. Finally,appropriate boundary condition is applied.

Moonpool is a wetted opening, located near the mid-ship, which allows researchers take their tools and vehicles into the water in a safer and more protected area. In this paper, in order to investigate the effect of the moon pool on the increase of motion resistance of the Supporter surface vessel, a set of experiments at various Froude number in the range of 0.139-0.370 are conducted in the IUT towing tank, using a scaled model of 1:37.2. Experiments are conducted for two cases; when the model has a moonpool near the mid-ship and when the moonpool entrance at the bottom of the ship is closed. The increase in the motion resistance of the vessel model is measured. The obtained results are compared with those obtained by HSVA towing tank, which used a 1:17.2 scaled model. A CFD simulation is also conducted, using Ansys-CFX. A two phase flow model is used to simulate the steady state motion of the vessel. The domain is consisted of water and air fluids. The results showed that introducing an open moonpool increases the ship resistance significantly.

A major problem in the development of the maritime industries is the unpleasant accumulation of some sea micro-organisms, plants and other sea species on the surfaces of ships and other floated sea constructions. This phenomenon, as a result, has caused some damages to the maritime industries by increasing the maintenance expenses due to corrosion, lowering the speed of the ships, increasing the use of fuel, increasing the docking, and so forth.
One of the most efficient ways to overcome this problem is the use of coatings which from the economy as well as the environment crisis point of views fulfill the international standards.
In part of our study, for the first time, a polymeric metal complex containing silver(I) and iron(II) ions was synthesized and characterized using the conventional methods such as NMR spectroscopy, Electrospray Ionization Mass Spectrometry, UV-vis Spectrophotometry, single X-ray Crystallography and elemental analysis. Considering the chemical structure of the obtained metal complex, one can conclude that this compound has a great potential to use as an efficient biofouling material in the formulation for marine coatings. In this paper, we report the synthesis and characterization of such class of compounds.

Nowadays, seawater usage in mineral processing has become a fairly topical issue. Due to rapid population growth and industrial development, the amount of fresh water is decreasing rapidly, so that fresh water is a critical component, especially in many industrialized arid countries, such as Iran. One of the main methods of mineral processing is flotation process that occurs in aquatic environments and consumes large volumes of water. The purpose of this paper was to investigate the use of sea water in the Cu-Mo ores froth flotation. In the experimental work, seawater was utilized as process water in the laboratory rougher flotation tests and compare the results with fresh water. The ore sample was porphyry Cu-Mo ore, which was delivered from Sarcheshmeh Copper complex. Results show that recovery of copper maintained almost the same level in both mediums. However, lime consumption was observed to be increased significantly under flotation conditions in seawater. In addition, the floatability of molybdenum was affected negatively above the pH 9.5-10. Recovery reduction of molybdenum was suggested to occur due to the magnesium hydroxide complexes and magnesium hydroxide precipitates, which began to form in seawater in higher pH levels. The experimental work showed that the conventional flotation of Cu-Mo ore conducted in seawater has serious conflicts, when pyrite is depressed with lime.