نشریه مهندسی دریا
پیاپی 39 (تابستان 1402)

Tides continuously change the water level in seas, and due to the continuity and dominance of currents caused by tides in bays, straits and estuaries, it is necessary to investigate the phenomena related to sediment transport and scouring in the surroundings of the structures located in the above areas will be illuminated more than before. In this research, by numerical simulation of the flow field and sediment transport, the scouring phenomenon under the pipelines caused by bidirectional currents has been investigated, and according to the values ​​of movement threshold speed, depth and number of tidal cycles to reach equilibrium, the characteristics of the scouring profile has been drawn. The obtained results indicate an increase in the depth and surface of the scour pit caused by the tidal current due to the alternating changes in the flow direction compared to the scour caused by the unidirectional current, and the vortex shedding process affects the final shape of the scour profile.

Today, navigation systems have become an integral part of the control of the floating unit. Today, ECDIS navigation system is considered as the most important navigation assistance system. The presence of electronic maps in the memory of the Ecdys device, along with the processing ability of this device, has caused the officer guarding the command bridge to navigate the ocean routes without any worries. One of the disadvantages of conventional navigation systems (such as Ecdis and integrated navigation system) is the lack of meteorological data in these systems.In this study, a navigation system has been developed that has calculated the sea route according to the turning points. And performs estimated navigation. In this system, climatic data of wind, temperature, pressure are calculated on estimated points over a period of forty years. Calculating climatic data on estimated points can help navigating officers decide on a seafaring route.

In the field of port design or protection of marine structures, one of the important things is predicting the performance of breakwaters against radiation waves. A type of breakwater that today, in addition to being able to be quickly installed, moved and reused in areas with similar conditions, maintains the water connection between protected space and open waters, is a floating breakwater. One of the factors influencing the performance of floating breakwaters is the geometrical parameters of the floating breakwater section. In this research, the numerical investigation of the effect of geometrical parameters of rectangular floating breakwater in single-row and double-row state on its hydrodynamic performance and wave transmission coefficient in ANSYS-AQWA software for wave periods in the range of 3 to 7 seconds has been investigated. For verification, the results of the present numerical model were compared with the laboratory results of Ji Deng et al. in (2019), which is in good agreement. The results showed that the use of a rectangular floating breakwater with the ratio of the height of the structure to the width of the structure in the range of 0.35 to 0.45 has the best performance. Also, increasing the mass of the structure against short-period waves improves performance and reduces the forces on the restraining cable and while in the face of long-period waves, reducing the mass of the structure improves the performance of the rectangular floating breakwater.

Since various relationships have been presented to calculate the recession in the berm breakwater, the evaluation of these relationships in the form of probabilistic is one of the most basic topics in marine engineering. In this study, the failure probability or in complementary the reliability for recession of Shahid Beheshti port berm breakwater is investigated based on six models of Torum (2007), Moghim et al. (2011), Lykke Andersen et al. (2014), Moghim and Alizadeh (2014), Van Der Meer and Sigurdarson (2016) and Ehsani et al. (2020). Four methods of First-Order Reliability Method (FORM), Second-Order Reliability Method (SORM), Monte Carlo Simulation (MCS) and Importance Sampling (IS) are applied to obtained the failure probability and reliability index for breakwater at the maximum water depth and 100-year wave height. The results of the MCS show the highest failure probability belongs to Moghim et al. (2011) model with a value of about 0.69, and the lowest value possess to the Torum (2007) model with a value of about 0.29. In addition, Van der Meer and Sigurdarson (2016) and Moghim and Alizadeh (2014) models give the failure probabilities of 0.57 and 0.50 respectively and Likke Andersen et al. (2014) and Ehsani et al. (2020) models presented the failure probabilities of 0.42 and 0.38 respectively. According to these results, Ehsani et al. (2020) and Torum (2007) models which developed for Icelandic breakwaters have the lowest probability of failure. Furthermore, Models of Moghim et al. (2011) and Moghim and Alizadeh (2014) which presented for reshaping breakwaters have the highest probability of failure. Next, sensitivity analysis was performed and the impact of different variables on the probability of failure was investigated.

One of the challenges of the autonomous underwater vehicles (AUV) navigation is measuring their velocity. The usual method for measuring the velocity of AUV is to use a Doppler Velocity Logger (DVL), but it is not possible to use this sensor due to its placement in the category of expensive sensors, as well as the increase in time and even the lack of data collection due to high depth or sudden changes in depth in some cases. The aim of this research is to provide a cheap and economical method of speed identification based on an autoregressive exogenous (NARX) neural network with the least number of neural network inputs in 2-D floating motion. In the proposed algorithm, by removing the inputs of the neural network obtained from the output of low-cost sensors, the measurement error of the sensors is removed from the identification process and the accuracy of the velocity model output is improved. The proper performance of the proposed algorithm, compared to the output of the DVL and also the output obtained from the differential model identification method with the help of Least Square (LS) and Recursive Least Square (RLS) algorithms, confirms the advantage and efficiency of this method in identifying the velocity of AUV.

Due to the strategic importance of coastal areas from various aspects, their protection against waves is considered a necessity in the management and sustainable development of beaches, in this research, an attempt has been made to investigate the effective method of protecting the coastal environment, such as trees, in addition to protective structures and compared to the purely structural method, the depreciation of coastal waves and as a result the protection of beaches should be investigated in a more comprehensive way. The method used in the flow modeling is Reynolds Averaged Navier-Stokes (RANS) and (k-ω, SST) model, which is done in Open FOAM software platform. The coastal wall structure of the coastal dike structure in combination with trees was investigated under the influence of 5 different incoming wave heights. The research done with the help of the numerical model showed that the damping and weakening of the waves in the mentioned conditions compared to the beach without protection has provided acceptable results. In the most influencing of wave weakening in terms of power, the presence of coastal wall structure, dyke structure and forest cover of the coastal forest was able to help absorb the force of the waves by 1.2 times compared to the unobstructed beach, and on the other hand, the height of the wave passing by the beach was also 4.36 times compared to unobstructed mode, reduce further. The results were compared with the laboratory data. The results of numerical models were compared with the corresponding laboratory model. In this comparison, the root mean square of the normal error was 0.42 and the correlation coefficient was 0.98, which indicates the good accuracy of the numerical model and the appropriate performance of the Open FOAM software in modeling.

Over the past few decades, the idea of using underwater vehicles with inspiration from nature has created a significant interest in these areas. This interest is due to the potential benefits of swimming as compared to conventional methods.
Advantages include increased speed, improved energy consumption, high efficiency of the driveline system, increased maneuverability, greater stability, optimized hydrodynamic performance in order to increase the efficiency and dispersion of the surrounding water. Today, subsurface robots modeled from the aquarium are called Shahbad, which are used as military robots to identify and neutralize offshore mines. The use of these robots has a lot of economic savings over submarines.The purpose of this research is to first provide a model inspired by the actual sample of a mantle clay and its hydrodynamic survey. In this research, the hydrodynamic dynamics of the fluctuating fin flange with the help of computational fluid dynamics (Anise Fluent, in 3D) based on the initial model and extraction motion equations are investigated. After that, a laboratory robot model is made and the numerical simulation results are compared with experimental results.

This article has reviewed the dynamic equations of naval submarines by considering all parameters affecting them and summarized a complete set of existing equations. Usually, submarine dynamic equations are complicated and difficult due to the multitude of parameters in them, especially in military submarines that have both normal and emergency conditions such as emergency ascent. These parameters include the following, all of which have been compactly reviewed in this article: Weight and buoyancy distribution, load changes and water changes inside the trim and compensation tanks, metacentric height, amount of thrust force and vertical distance between the thrust direction and the center of gravity, the position of the hydroplanes and their moments, the center of pressure and the effects of speed on Submarine dynamic behavior. Also, a speed is defined in the submarine maneuver that the control of the submarine by after hydroplanes is not possible. Due to the importance of this phenomenon, the reverse speed and its formulation are also presented in this article.

The present study is for the feasibility of using the OWC wave energy converter to supply electrical power to a refinery unit near the shores of the Persian Gulf over a 20-year horizon. Considering the potential of other renewable energy sources in the study area, a combined system of wind turbine, photovoltaic panel, wave converter, electrolyzer, battery and fuel cell is proposed. A comparison between using a reformer instead of an electrolyzer has also been studied. The effect of OWC energy converters on the hybrid system has been evaluated as a new approach in generating the required power. The results show that the hybrid system including the OWC converter with NPC and COE costs $ 26.5 and $ 0.205, respectively, is more cost-effective than the hybrid system without the OWC converter to meet the refinery unit power demand. About 30.7% of the required power is supplied by the wave energy converter. The use of wave energy converters is reduced in the months with low wave energy potential and the role of other renewable energy sources becomes more colorful.

Planning vessels have a special significance in the marine industry. The main and most significant aspect of designing these types of vessels is achieving high speed by having low body resistance. One of the key modifications applied to the hulls of planning vessels was the development of the chine. This research aims to analyze the impact of the chine on planning hulls using numerical analysis. After analyzing the results, improved chine can be specified in terms of the hydrodynamic performance of the hulls. The chosen method to analyze the flow around the planning hull forms is numerical simulation. This method calculates the resistance force, lift force, pitch angle, and heave amount of the intended hulls. The numerical simulations of different modifications of the C planning hulls were compared to the hydrodynamic behavior of the C-hull after verifying the results of the numerical simulations and validation of results with the laboratory results of the former reference. Based on the results obtained from the numerical simulations, the hull with 5.43% chine width to beam ratio recorded the lowest resistance. The highest trim was observed in the hull with 5.43% chine width to beam ratio, and the hull with 5.87% chine width to beam ratio registered the highest heave. Moreover, the hull with 4.57% chine width to beam ratio exhibited the highest resistance in the simulations.