نشریه مهندسی شناورهای تندرو
پیاپی 55 (پاییز و زمستان 1398)

Man is always looking for ways to do his daily work at a higher speed. The ability to move individuals and objects in the shortest possible time has always been one of the main concerns of humans. The marine industry is not an exception to this requirement. The use of planing boats to increase displacement speed as well as agility has received a lot of attention from industries that have not been excluded. The design and construction of these vessels requires dynamic understanding and control of their instability. One of the most important instabilities in planing boats is porpoising under the influence of various factors. In this paper, we investigate the effect of aspect ratio on the stability of planing boats by studying prismatic body. First, the numerical parameters were selected using numerical analysis results on three models with different ratio and then the effect of the aspect ratio on the occurrence of porpoising was investigated using Mr. Suitsky's regression equation.

No doubt the sound production in the last century has increased greatly from sources such as sonar, oil cargo ships, seismic devices, oil and gas drilling exploration, offshore pile-driving, etc. This is a kind of pollution called noise pollution. Noise can cause stress in animals, increase their risk of being hunted, and disrupt the reproductive system of some species. These effects can be a function of the frequency and intensity of the sound and the duration of the sound exposure. It is necessary to measure floating noise in shallow waters by sound simulation to calculate the transmission loss according to the standard. In this study, in addition to field measurement of the noise of a rigid buoy using standard measurement principles, the effect of buoyant noise waves and other sources of noise generation in seas and oceans on marine life for different species has been investigated. In this research, first, different sources of noise generation are produced and the effect of different sources of noise on marine and marine life is expressed. In the next part, the transmission loss in the environment is calculated by simulating the environment and in the last part, the noise level of the three fast crafts is measured. We deal with different issues and, finally, offer some suggestions for reducing the noise of the hard-hover.

An underwater vehicle, which is able to carry out missions like chasing, hunting, pursuing or going along with a robot or a surface or subsurface organism with appropriate accuracy, must possess high maneuverability. In this article, a new hovering type underwater vehicle is proposed, simulated and controlled in order to chase a surface or subsurface object. With the help of proper control algorithms, the underwater vehicle is able to obtain the necessary information of the target position in order to travel the shortest path to reach the target and also, keep the target within line of sight at all times. In this paper, the controller is first designed and simulated based on a linearized dynamic model and then applied to a nonlinear dynamic model, and finally, the validation has been done. The proposed controller has three loops: A loop to control the path in the vertical plane, a loop to control the path in the horizontal plane and a third controller to control the speed of the robot's advance at a specified value. In order to investigate the controller's resistance, this paper also investigates the effect of currents in the form of disturbance forces on the underwater vehicle.

Due to benefits of passive radars, implementation of these radars are considered in recent years. Among the different opportunistic signals that is used in passive radars, digital video broadcasting-terrestrial (DVB-T) signal is a good candidate, because of wide bandwidth and appropriate range resolution, high transmitted power and long coverage area. Using software defined radio (SDR), decreases the hardware dependency and implementation costs. In this paper, a DVB-T based passive radar is implemented on SDR platform. In the proposed algorithm, the cross correlation between the direct DVB-T transmitter signal and the scattered signal from the target is computed. Then the maximum value of the fast Fourier transformation (FFT) of output is computed and the target position is estimated. In order to evaluate the performance of the proposed algorithm, the direct DVB-T transmitter signal is received using SDRPLAY hardware and an antenna. The signal processing units of proposed algorithm are implemented in the GNURadio software. Simulation results show the appropriate performance of the proposed algorithm in target detection.

During the assembly process of aluminum structures with welded joints, usually the life of the structure due to the unwanted stress of the welding process and possibly the presence of undesired defects due to the strength of the initial design of the reduced structure will cause cracking and eventually cause fracture near the support sections. ؛ In this paper, to prevent the propagation of microscopic cracks, first, based on field investigations, the exact location of crack damage in rigid floating structure with specific application is identified, and then numerical methods are used to investigate the behavior of model floating structure under cyclic or periodic impact loads. Due to the knocking of waves and firing c Has been discarded. In addition, by analyzing the data output, by changing the component parts of the rigid float superstructure, and by modifying the new positioning of the structural member locally, the optimal design has been achieved, and the new geometry design responds to the needs of the floating user and stops Growth is cracking.

One of the most important craft motions is the movement around its longitudinal direction, which is called transverse roll.This motion can reduce the range of craft performance and in many cases lead to problems for crew, cargo, weapons and craft equipment.Therefore, its stabilization is of particular importance.To achieve this goal, several methods and equipment have been designed to reduce craft fluctuations, especially transverse roll oscillations.These include the correct layout of the loads, the Bilge keels, the balancing weights, the transverse anti-rolling tanks, the steering system and the active fins.The purpose of this study is to investigate the different stabilizers of craft transverse roll motion and to select and evaluate a suitable stabilizer.For this purpose, among the many methods, stabilizing craft transverse roll using a ball stabilizer due to its high efficiency, relatively large torque, and relatively simple design is desirable.This is the best stabilization, which, due to its location (in the middle and close to the craft waterline), creates the least coupling with other movements. Analyze with a degree of freedom.The Marine System Simulator (MSS) Toolbox has been used to evaluate the performance of the stabilizer.The simulation results show that in the case of using fin stabilizers with linear quadratic regulator (LQR), there is a significant decrease in transverse roll motion.