نشریه مهندسی شناورهای تندرو
پیاپی 63 (پاییز و زمستان 1402)

Marine propellers are important and vital members that establish a connection between the floating engine and the water, and most of the power generated by them turns into the forward movement of the floating. The phenomenon of cavitation is one of the important issues in the design of floating propellers, and it can be mentioned as a criterion for design, because if this unwanted phenomenon occurs, the acoustic benefits of the ship's propeller will be reduced, and in some cases irreparable damage will occur. Sees. In the design of vessels, noise creates relatively different limitations, which are discussed in two areas, firstly, the effect of noise on the sensors and systems of internal weapons, and secondly, the effect of this noise around the ship, which is one of the factors of identification by enemy identification systems. In subsurface floats, the most important parameter in propeller design is the amount of concealment and reduction of the emission noise level. The vortex of the tip of the propeller blade can be introduced as one of the strongest sources of noise generation, reduction of thrust and efficiency, and the cause of induced vibrations on the body. Therefore, the geometric factors affecting the blade tip geometry should be optimized to achieve this goal. In this research, an attempt is made to introduce the phenomenon of cavitation and examine its disadvantages.

Wigcrafts are vessels that fly by force from surface or wall effect. This phenomenon arises from the compression of the trapped air between the wing and the surface, which in the case, this surface is the sea. In this paper, the performance of Wigcrafts under the influence of wing geometry is evaluated. The wing has been fixed with three types of progressive designs, swept forward, swept back and rectangular wing with 4° mounting angle to the body. The hull and tail of the vessel are the same in all three models. The angle of sweep forward and sweep back wing is 45 degrees. Conceptual design with IGES format in AutoCAD software. Numerical calculations are simulated in the star CCM+ software assuming a non-uniform flow, k Epsilone Tourbulent, and in two phases with the aulerian multi-phazes model. The surface of the water is flat and without waves. The dimensionless parameters of the lift, drag and torque of all three models were compared. In the discussion of stability, only the pitch of all three vessels is free. From the free surface view, pressure contours, shear stress and sheil friction are presented on the model and water level in all three simulations. The results of all three are similar. The results of all three simulations are summarized and examined by the assumptions of flying bodies and the aerodynamics laws of different wing designs.

Steganography is one of the most important methods of safe transmission of sensitive information in electronic warfare and audio data hiding due to its higher capacity and complexity than other methods, making it similar to entropy. And the interest of researchers is in the field of information security. The most important part of conducting this research is the decoding of LPC, CELP, and MELP audio encoders, which is considered an important innovation in the field of national information security and electronic warfare because these encoders are among the most powerful audio coding methods used by NATO forces. They are used to transmit Speech. In this article the proposed method, the least significant bit method was used to hide the secret information in the carrier audio. The results of simulation and evaluation according to Table 1 show that this method has a large number of security due to its high resistance compared to other methods, and compared with this code, it shows that the MELP method has a higher security than others.

Ship's watertight doors are used in watertight places and compartments such as the engine room. In addition to being watertight, these doors should be strong enough to withstand explosive loads or high-speed impacts. The use of these doors in high-speed vessels, where the weight of the vessel is very important, should be based on weight reduction. This study presents a design of watertight doors in which the weight is relatively optimized. The working method is as follows: first, by using Navier's theory for sheets and according to the boundary conditions and loading on the door, the thickness of the sheet resistant to explosive load is obtained, and in the next step, by equating the moment of inertia and using from the sheet and beam section standard, the structure is strengthened in terms of resistance to impact and explosion, and also relatively light in terms of the weight. The obtained results are satisfactory compared to the numerical results of the finite element method.

Until now, various calculation methods have been used to analyze CRP propellers that are used in submarines and some ships. Open water and self-propulsion tests are the most common tests in the evaluation of propellers. In this research, one of the common methods of results extrapolation of the propeller test in open water (POW) has been tried to evaluate scientifically based on experimental data, and its accuracy in results generalizing from the model to the base sample in different advance ratio has been determined. The experimental data includes the test results of the POW model of a CRP propeller in the superimposition mode of the effect of the propellers and also the model test results for each single propeller of this CRP system. The way of checking the accuracy and efficiency of the method studied in this article is that with the raw data of the model test, the increase in the Kt and Kq coefficients of the CRP propeller compared to the single propellers of the model was determined. Then, with the help of the result extrapolation code, by extracting the coefficients of Kt and Kq for base sample propellers, the increase of Kt and Kq coefficients of the CRP propeller compared to single propeller was evaluated. By comparing the amount of these increases in the model and the base sample, it is possible to estimate result extrapolation accuracy of CRP propeller open water test at different advance ratio.

Fast vessels can perhaps be considered the most obvious characteristic of the Islamic Republic of Iran's maritime power in the Persian Gulf and Strait of Hormuz region, and at the same time, the biggest operational and tactical challenge for the US Navy fleet in this region. High-speed boats are used in other parts of the world, but what happened in Iran is considered the production of science. In this regard, the use and application of emerging technologies (artificial intelligence, machine learning, reinforcement learning, deep learning,...) in the field of high-speed vessels is very important. Machine learning is becoming a powerful tool for designers and builders of speedboats. This technology can be applied at various stages of the design and construction process to result in more efficient, safer and cost-effective vessels. Machine learning can be used to predict float performance under various operating conditions. This can help designers and manufacturers to create vessels that meet the specific needs of customers. Machine learning can be used to optimize the performance of floating propulsion systems, such as engines and propellers. This can help reduce fuel consumption. Machine learning can be used to analyze sensor data from the vessel to predict potential failures. This can help with preventive maintenance and reduce downtime. In this article, the application of machine learning in the design and construction of high-speed vessels is discussed, the most cited articles are reviewed and products based on artificial intelligence and machine learning are reported in this field.

Calculation of ship sound source level in shallow waters using acoustic propagation models has attracted the attention of many researchers in recent decades. Source level measurement is important because of its wide application in subsurface communication and telecommunications, marine life and biology of marine animals such as whales and dolphins, and many other diverse applications.In this article, we first measure the bandwidth source level in the frequency range of less than 2500 Hz under specific operational and environmental conditions and under a specific standard. Then, the source level was measured for different floats in one-third octave of normal frequencies (25, 63, 125, 250 and 1000 Hz) and the sound transmission loss was calculated using acoustic models. This paper introduces a new modeling technique formulated based on finite difference time domain (FDTD).In this modeling method, factors such as layering of water and bed and depth changes of transmitter and receiver are considered and calculated as inevitable variables in field measurements. This technique can provide a suitable computational approach for standard source level measurement in shallow water.

Target classification in military radars is one of the most important issues in these systems. In this article, a model called rectangular approximation is introduced at the beginning. In this model, the physical shape of each float is approximated by a rectangle with proportional dimensions. Each range cell is determined according to the radar's transmitted wavelength and its resolution. Then, a specific process is provided by counting the number of range cells in the direction radiated to a given sea target by two high-resolution radars. In front of the radar, it determines the number of distance cells in this direction. With this method, it is possible to estimate the radiation angle of the radar towards the target and finally the class of the target is determined in terms of its physical size. The result of this article will determine the angle of view of the radar relative to the target vessel. It means which direction the radar is radiating to the target vessel at any moment.