نشریه مهندسی شناورهای تندرو
پیاپی 60 (بهار و تابستان 1401)

The jet pump thrust system is one of the types of marine propulsion systems that creates the thrust force based on the momentum difference method. The jet pump is primarily designed for underwater vehicles. The jet pump propulsion system has been widely used due to its stealth and excellent performance, but due to its secrecy and complexity, few details have been published. The behavior of this propulsion system is similar to axial flow pumps. The main components of jet pump thrust system include duct, motor, stator, hub and boss. The motor is installed on the hub with a specific number of blades and the stator is attached to the hub from the root side and to the inner surface of the duct from the tip side.Jet pumps are classified into four categories according to the placement of the motor and stator inside the duct as well as the rotation mechanism: pre-rotation, post-rotation, driving ring and double anisotropy. The pre-rotation type has less noise and efficiency than the post-rotation type and is considered a type of ultra-silent propulsion system. Considering the numerous advantages of using nuclear propulsion in submarines and other marine vehicles, the jet pump seems to be a suitable candidate for marine propulsion systems with nuclear propulsion, considering the acoustic advantages as well as the limitations of the phenomenon of xenon poisoning and power reduction in nuclear reactors. arrives. In this research, an attempt is made to introduce this type of engine and examine its advantages.

In recent decades, speedboats have become extremely important and various hull shapes have been proposed, designed and built to achieve high speeds. High-speed vessels are divided into four groups: single-hull, hydrophilic, surface-effect and multi-hull vessels. Here, the main focus is on the wave piercing vessel with spray rail. Speedboats face various challenges to reach the high speeds intended by the designer. V-shaped transverse vessels do not generate hydrodynamic lifting force well. One way to create a hydrodynamic lifting force in fast vessels is to add a spray rail in the longitudinal direction of the hull. When water flows to the side of the float, the water flow is directed downwards using a spray rail, causing a hydrodynamic lifting force. In this dissertation, with the laboratory analysis of the wave piercing vessel, which includes trim, resistance and displacement of the height of the center of gravity (VCG) of vessel, once in calm water conditions with spray rail at a location of 24%T and once without installing spray rail, it has been compared by numerical analysis under exactly the same conditions, which has an acceptable error rate. This optimization, which is done by applying spray rail, significantly reduces trim and resistance at high speeds, as well as increasing center of gravity height changes. This dissertation can be a reliable reference for improving the performance of planning body vessels in the future

The passage of time and the progress of science and the need for materials with special efficiency in the industry have led to the creation of materials with specified properties in which the defects and weaknesses of one material are improved by another material. In fact, these composite materials, which are known as composites, consist of one component called the matrix or another component called the reinforcement. Now, if the dimensions of one of the constituent components of the composite are on the nanoscale, these materials are called nanocomposite. In this article, firstly, the definition of composites and nanocomposites is discussed and how they appear, and then the classification of composites is discussed in terms of whether they are natural or artificial; Then nanocomposites will be divided based on their base or context. In the next section, explanations are provided about polymer nanocomposite materials and its special type, i.e. carbon nanotubes, and the types of carbon nanotubes and their strengths and weaknesses are discussed, and at the end, the challenges ahead in the manufacture of polymer nanocomposite materials will be mentioned.

The wake produced by moving ships, which can be seen with the human eye, may extend for tens of kilometers in the open ocean and be detectable from a distance. This wake has different components and parts that are completely subject to the movement and geometric conditions of the ships and many studies have been done on their recognition. The main importance of these studies may be for the automatic and remote identification of these ships based on the patterns of wakes produced by them by various sensors such as visible photography, infrared measurement and microwave radars installed on satellites, radars and drones. In this article, the components of this phenomenon have been studied from the point of view of a drone, or in other words, from the optical point of view, and it has been shown that although this wake is complex and has 5 general components, three of its components are clearly visible from the optical point of view: Kelvin wake, turbulent wake, and internal waves generated by the ship.

Localization has many applications and there are different methods to do it. This research has focused on the Geolocationing of the moving marine target with emphasis on the simultaneous use of GEO satellites and the Kalman filter. For Geolocationing using GEO satellites, the technique of simultaneous use of TDOA and FDOA was used. Due to the presence of motion and non-zero velocity for the target, the relationships used in the localization equations by GEO satellite lose their effectiveness and the number of unknowns becomes more than the number of equations. For this purpose, we use the Kalman filter to reduce these unknowns by using the predicted speed given by the Kalman filter and to be able to do the localization by the GEO satellite equations. Additionally, the Kalman filter uses the position obtained by the GEO equations and makes them smoother. According to the findings of this research, the Kalman filter was able to accurately estimate the location and speed of the moving sea target.

Ultrasonic systems use quartz and ceramic transducers to generate sound power. The main limitation is insufficient input electrical power due to low power factor and high impedance. In this work, by presenting a new integrated method, with the help of the so-called direct calculation of the real frequency and the CAD method for piezoelectric transducers, it has been used. The design and construction process includes the following: 1-Determining the equivalent circuit of the piezoelectric transducer based on the admittance measured in the desired frequency range and under real working conditions with a 100-meter cable and a suitable depth in a non-reflecting pool 2- Designing a set of impedance matching networks, using From the computerized Smith chart with ADS and SMITCHCHART.V.4 software 3-Extracting and implementing the simulation model of the converter with adaptation to evaluate the gain and return power and the bandwidth of the designed impedance matching networks and to check the effectiveness of the presented approach through design, implementation, and characterization Impedance matching networks for broadband audio propagation converter 4- Design of peripheral circuits for smartness and selection of suitable IMN; 5) Construction of the desired intelligent EIMN and final testing. The results of this research, in the best matching and ideal conditions, in the simulation with ADS, provide 85 dB improvement for S11 and 26 dB improvement for S21. In working conditions and using real size filter elements, 58 dB improvement was obtained in S11 and 26 dB improvement in S21.