نشریه مهندسی دریا
پیاپی 34 (پاییز و زمستان 1400)

The main goal of the present study is to use satellite data to extract bathymetry maps of coastlines and especially the shores of the Caspian Sea. For this purpose, the area between the Neka power plant and Amirabad port in Mazandaran province was selected as a pilot. Landsat-OLI satellite image was used to extract the bathymetry map of the study area. Simultaneously with the path of the satellite, about 2700 points from the depths of 2 to 11 meters of the Caspian Sea, was measurement, of which 500 points were used as control points and the rest as training samples. The polynomial linear regression method was used to extract the bathymetry map. Also, a stepwise regression method was used to identify the best regression model and select the best independent variables to estimate the depth. Comparison between the water depth map extracted from the Landsat-OLI satellite image with the control points showed that the RMSE value of this sensor in estimating the coastal water depth was about 0.4 m with an average standard error of 7.6%. By considering the turbidity and roughness of the seawater of Caspian Sea, the obtained result is an acceptable accuracy.

Tropical cyclone storm surge is one of the key parameters in the design of coastal structures and shoreline management plans. Therefore, the storm surge of the Nanauk and Ashooba tropical cyclone has been investigated on the Makran coasts. In this study, in addition to the analysis of the global sea level monitoring station data, the effects of boundary conditions and wind field accuracy of reanalysis, parametric and WRF model data have been investigated in storm surge modeling. Analysis of water level observations shows that the maximum storm surge (0.38 and 0.36 m) occurred after the tropical cyclone landfall. Furthermore, the secondary effects of tropical cyclones cause the movement of the water body and storm surge for several days. Considering the Sea Surface Anomaly (SSA) as the open boundary condition has led to improved numerical model results. The storm surge results of the ERA5 and WRF wind field have appropriate accuracy in Makran coasts. The maximum value of storm surge obtained based on ERA5 wind field at Chabahar station in Nanauk and Ashooba tropical cyclone is 0.25 and 0.34 m, respectively.

Ordinary projectiles in the water usually experience a sharp drop in speed and a have a very short range of several meters. Super cavitation causes the entire body of the projectile to be covered by a cavity of gas (relative vacume). For this result the amount of frictional resistance under super cavitation conditions decreases significantly. In fact, the analysis of super-cavitation projectile is strongly dependent on cavitator diameter and its shape, ratio of length to projectile diameter, projectile mass, projectile diameter, final projectile range, recoil energy of the weapon. In this paper, the mass of projectile assumed to be independent paremeter. On the other hand because of bubble requirements, for cavitator some diameters are assumed. For this reason, design variables reduses to three quantity: mas and final range of projectile and recoil energy of weapon. According to required maximum range and minimum cost with trade off   beatween recoil energy and range, final options are limited. In this article the effects of each of these parameters and how they are analyzed by analytical relationships and their validation are explained.

Nowadays, the development of ports and the construction of artificial harbors using seabed sediments is widespread. However, due to the nature of the material used and the method of implementation, often have weakness in engineering characteristics, especially bearing capacity and settlement of the soil. To solve many of these problems, this is essential to improve these characteristics in the soil. One of the common soil improvement methods is soil reinforcement methods, which are often costly because of the costs of supply of material and the implementation. The addition of waste materials to the soil is a proper way to reinforce the ground because of its environmental benefits and the ease of adding it during embankment implementation. Moreover, due to the increase in plastics production in recent decades, it was decided to use waste polyethylene terephthalates for soil improvement in this study. After sample preparation, dynamic tests were performed on soil samples (Bandar Anzali sand) in two treated and untreated cases under various vertical loads by the dynamic Simple Shear apparatus. Then the effect of adding this material on dynamic parameters of the soil was investigated. Afterward, by performing the bender element Tests on similar samples, the additive effect on shear wave velocity and maximum shear modulus has been considered.

In this paper, an analytical method for evaluating single piles under lateral loading by stiffness matrix method has been developed in which nonlinear behavior for soil stiffness and flexural stiffness of piles. In this method, the implicit limit state functions are used and the analysis is based on the reliability method. Two types of failures have been investigated in this study, which include lateral displacement of the pile head as well as the maximum bending moment along the pile. The reliability index is evaluated using an algorithm for the first-order reliability method (FORM) and based on the elliptical method using random variables. In this study, spatial variability of soil characteristics is also considered using spatial autocorrelation method. In this research, validation of the results using numerical derivation and comparison with Monte Carlo simulations based on important sampling was done and also sensitivity analysis was conducted too.

After years of using fossil fuels, the use of renewable energy is now growing. Offshore wind turbines are one of the ways to benefit from clean energy. This article studies the dynamic reactions of offshore wind turbine (OWT) supported on monopile foundation in saturated soil under wave and wind loads separately and combined. The wind load was calculated using the power spectral density function with different velocities and applied to the turbine blade and the turbine tower. To modeling the random waves the Pierson-Moskowitz spectrum is used and the force of sea waves on the body of monopile calculation is based on the diffraction theory. The models are simulated in three-dimensional and written with the help of TCL programming language and analyzed with open-source software OpenSees. The effects of several factors on the dynamic responses of the models are investigated. The results are shown that it is essential to examine the combination of wave and wind loads in the analysis and design of OWT.

Speed estimation is one of the important parameters in navigation of an Autonomous Underwater Vehicle (AUV). Varied underwater speed sensors exist that they use of different technologies for measuring of an underwater speed. For example, ultrasonic, electromagnetic, optical and paddlewheel speed sensors and Doppler Velocity Log (DVL) are used for water speed measuring. The purpose of the article is designing and manufacturing of a differential pressure based speed sensor that measures an AUV speed by using of Bernoulli’s low. For analyzing of the proposed sensor, it is tested in the towing tank of the National Iranian Marin Laboratory (NIMALA). For determining of the sensor measurement accuracy, the sensor data is compared with an accurate speedometer that is installed on the towing tank. With analyzing of the results, the sensor accuracy is 0.05 (m/sec) in speed range 0.5-4.5 (m/sec).

The mooring design of floating structures is one of the important parts in the design process of offshore structures. To design and evaluate the performance of mooring lines, criteria such as ultimate strength and fatigue have been defined. In real conditions, mooring forces are random variables, so to check the strength, the statistical distribution of mooring forces under the influence of environmental condition must be calculated at first. In this article, a statistical study of the mooring force of a semi-submersible offshore wind turbine, which is stabled by three catenary-chain mooring lines, has been considered. Hydrodynamic analysis of the structure was performed by ANSYS-AQWA software and the environmental characteristics of the area were extracted from the DNVGL standard for the Mediterranean Sea. During the life of the structure, due to corrosion, the diameter of the mooring chain decreases. Therefore, in this research, the condition of the mooring lines from the perspective of tensile forces has been investigated by considering the corrosion at a constant annual rate. During the life of the structure, due to corrosion and as a result the reduction of the axial stiffness, the tension of the mooring lines will be reduced. This amount of reduction for the critical mooring line in 10-year intervals of its 30-year lifetime is 5.4, 13.1 and 21.3 percent, respectively.

One of the most important policies of water-scarce countries such as Iran is the desalination of seawater for industrial, agricultural and drinking use. Before desalinating seawater, it needs to be transferred, which is a costly process. In this research, the flap-type wave energy converter was considered to provide the necessary energy to transfer seawater to a desalination plant by merely using wave energy. For this purpose, the effects of wave energy converter parameters (paddle width and height), flow properties (water depth and wave frequency), and the slope of the shore on the performance of the wave energy convertor were investigated in a laboratory study. Although the efficiency naturally increased with increasing width of the flap, it should not exceed a certain limit. In short, with 35% and 71% increase in the width of the flap, the output pressure increased 1.58 and 2.82 times, respectively. An increase of 13% and 27 % in water depth first led to a maximum increase of 3.44 times in water pressure and then led to a decrease of a maximum of 1.68 times. Experiments with the height of the flap also showed that when the rotating flap was non-submerged, the water pressure of the device was at least 2.05 times higher than that in its submerged state. For the slope of the shore, with 63% increase in slope (from 1: 5 slope to 1: 3 slope), the pressure increased by 47.25%, and when the slope was increased five times (from 1: 5 slope to vertical slope), the pressure increased by 2.14 times.  For the period of the wave, with a 15% increase in the period, the pressure decreased by 17.02%, and for a 25% increase in the period, the pressure decreased by 81.58%. In this study, a total of 165 experiments were performed and the flap-type wave energy converter was evaluated as a suitable and low-cost method for transferring seawater to shore.

The presence of switchable communication topologies in a multi-agent system‏ causes the adjacency, degree, and Laplacian matrices of the group, and finally, its Fiedler eigenvalue, to constantly change, thereby affecting the group consensus. The key motivation of this study is to design an appropriate control law to achieve group consensus and create a hexagonal motion formation in a group of autonomous underwater vehicles by considering switching communication topologies between agents. For this purpose, first, the six degrees of freedom mathematical model of each AUV is presented and then the relationship between the agents of the group is modelled through the graph theory. The leader-follower consensus control algorithm is then designed to form a hexagonal arrangement between the leader and the follower robots. The proposed consensus control algorithm has been assessed in two different scenarios: 1- Switching communication topology between the follower robots, 2- Switching communication topology between the follower robots with time delay factor.

This article presents a new innovative method to reduce the motions and stabilizing the ships using the ordinary fishing net. The study of ship motions in the waves has been the main concerns of ship designers. Some methods have been used to stabilize the ship in the waves, such as stabilizing tanks, gyro stabilizers and fin stabilizer, which these have their own advantages and disadvantages. In this paper, the study of the net element to reduce the amplitude of Pitch motion in the regular waves in the static state has been done by experiments in a towing tank. The model experiments were performed in the towing tank of National Iranian Marine Laboratory (NIMALA) using two kinds of net with different meshes to compare the effects. The innovative idea of using the fishing net element to reduce the ship motions in the waves was presented for the first time in this research. The findings of this study for the planing craft show a reduction in Pitch motion of up to 20% in regular waves. The length of the model is 2.5 meters and the requirements of the test method are based on the ITTC marine testing instructions.

Estimation of the hydrodynamic forces due to the motion of the ship on wave and the resulting vibrational response is of great importance in the design procedure of ship structure. In this paper, modal analysis and force study of loads on the catamaran float in the frequency and time domain and in the direction of Heave and Pitch and taking into account the inherent damping of the hull has been done. In proposed analyzes, the forces acting on the vessel such as Frude-Krylov, diffraction, added mass and damping are investigated. Then, using the finite element method and using the structure-fluid interaction method, the ship motion is modeled on regular waves. By examining the simulation results and comparing it with the past numerical-experimental methods, it can be seen that the obtained results have a good accuracy and also an error of less than 10%, so the proposed method can be used to estimate the forces on the ship.