نشریه مهندسی دریا
پیاپی 38 (بهار 1402)

Prediction of a ship’s trajectory during a maneuvering motion is so important. In this study, the acceleration maneuver for a twin-screw vessel is directly investigated using computational fluid dynamic (CFD) environment and unsteady RANS (Reynolds Averaged Navier-Stokes) solver. For this purpose, the self-propulsion and acceleration simulations with hull and propeller interaction for the well-known ONRT vessel were investigated. All simulations were performed by using Star-CCM+ software at two Froude numbers i.e. (0.2 and 0.3). The propeller rotational motion has been simulated using sliding mesh technique. Besides, numerical verification and validation are performed based on the procedures proposed by the ITTC. The validation of the self-propulsion results with the available experimental data shows a very good agreement among them. Also, changes in wave pattern, wake flow field during the acceleration maneuver were investigated.

In this research paper, five centrifuge lateral loading tests of long piles with a considerable load eccentricity were carried out in the sand to investigate the impacts of the load eccentricity and pile length changes on the lateral behavior of a flexible pile beside the determination of experimental p-y curves.Comparing experimental test results with the recommended API (American Petroleum Institute) curves clarifies what is nowadays identified as the difference between the behaviors of monopiles and flexible piles how far can be affected by the load eccentricity. Additionally, the efficiency and accuracy of the available equipment at the University of Tehran have also been investigated. Results show that although the load eccentricity affects p-y curves, the current design approach can lead to a proper design even at high load eccentricities. In most tests, the initial stiffness in p-y curves is lower than that of the guidelines. Also, the hyperbolic model shows a closer estimation to the experimental test results.

This study deals with the numerical modeling of symmetrical water entry of tunneled sections. In this study, firstly, the water entry problem of a wedge section without tunnel in four different deadrise angles was numerically modeled. The obtained results related to the pressure distribution on these sections and the maximum pressure have been compared with the experiment results. In the next step, the numerical simulation of the water entry problem with the tunnel section has been done. For this purpose, a tunneled section was created by adding a tunnel to a simple wedge section. Finally, the effects of changing the deadrise angle and also changing the radius of the tunnel section have been modeled. In this study, the viscous Navier-Stokes (N-S) equations are used to simulate water flow around the section and also a Volume of Fluid (VOF)-type method, is employed to capture the free surface. The results of pressure changes and maximum pressure in three different areas of the tunnel section have been obtained. These three areas include the area before the tunnel, in the tunnel area and the area after the tunnel. The results of this research indicate the occurrence of severe pressure changes in the tunnel area. Also, with the increase of the radius of the tunnel, it was observed that the amount of pressure on the section also increases. The results of this study can be used in the hydrodynamic analysis of tunneled vessels.

Increase in the accuracy of hydrodynamic coefficient calculation cause to increase in the prediction of vessel maneuvering ability. Different methods of determining hydrodynamic coefficients will be effective in determining the accuracy of coefficients, especially in numerical simulation. In this paper, we do planar motion mechanism (PMM) test, oblique towing test, and rotating arm test simulations to compare the accuracy of their results with experimental data. The accuracy of the simulation results of K-ε Realizable and K-ω SST turbulence model has been investigated in the simulation of the rotating arm test. Also, a method to reduce the dimensions of the domain and the run-time in the simulation of the motion of pure-Sway and pure-heave has been presented, discussed, and evaluated. The results show that by hybridizing these methods we can calculate the sway and heave damping coefficients with an error under 8.5% and their added mass coefficients with an error under 20%, the yaw and pitch damping coefficient with an error under 9.5%, and the yaw and pitch added-mass coefficient with an error under 15%.

Maneuverability is an important aspect of marine vehicle design. With the development and utilization of ocean resources, maritime transportation is becoming increasingly busy. Stopping ability has great effect on the safety of ship maneuvering for those large ships. Therefore, it is necessary to study the behavior of the ship during the stopping maneuver to ensure the safety of navigation. In this study, the stopping maneuver has been investigated directly and with interaction between the ship's hull and propeller, Reynolds Averaged Navier-Stokes (RANS) equations and Star-CCM+ commercial software. well-known vessel KVLCC2 have been selected to study the parameters of the stopping maneuver. In order to reach the design speed of the ship, the self-propulsion test has been carried out using a PI integral controller. Verification and validation of the results have been studied according to ITTC recommendations. By comparing the results obtained in the self-propulsion test as well as the stopping maneuver with some available experimental data, a good accuracy was obtained and the details of the flow parameters, including pressure distribution and wake pattern, were analyzed

In this study, the damping sheets were attached to a semi-submersible platform to mitigate the heave motions. We first examined a typical GVA4000 semi-sub under a monochromatic linear wave train in deep water. an analytical method based on diffraction theory was used to determine the heave motion response. The results revealed that the analytical results show good agreement with available experimental data. Then, the damping sheets were attached to the pontoons of the GVA4000 semi-sub under study. The heave motion response was evaluated with the changing numbers and widths of sheets under constant thickness in different sea waves conditions. The results showed that with increasing damping sheet width, the heave motion response is improved. Moreover, the heave natural frequency of semi-sub is shifted far away from the monochromatic wave frequency, so, the resonant phenomenon significantly decreases. Based on the proposed method, it is concluded that the solution to reducing heave motion response of the semi-submersible platform is simple, effective, economical and practicable.

The Persian Gulf is an important region in the world regarding energy supply, transportation, shipping, and military missions. Therefore, studying the annual circulation of water current in the Persian Gulf is very important for marine experts. In the present study, the simulation of current circulation in the Persian Gulf has been studied using ROMS numerical model and field observations. The numerical model results are in good agreement with TMD dataset as well as field data. In addition, the circulation patterns in the summer and winter seasons are well simulated. However, the numerical simulation results showed that the modeling accuracy in summer was lower than in winter, probably due to the model's boundary data quality.

In this article, the most important specifications of hydrofoil floats, i.e. their seakeeping under regular and irregular waves under different encounter angles of wave, has been investigated. Numerical simulation has been done using STAR CCM+ software. Surge, heave, roll and pitch motions are kept free at the same time and their effects on each other are taken into account. USV01 model, whose laboratory test results are available, was used to validate the simulation. The results show that the increase and change in the regular wave components and speed of the craft, cause less changes in the movements of the hydrofoil craft compared to the planing craft, except in the following sea, where planing craft performs better overall. Therefore, it should be said that the most dangerous situation for a hydrofoil craft is encounter angles less than 90 degrees, especially zero-degree encounter angle, i.e. following sea.

Gliders are new marine vehicles which have research and military uses and they move by sequent diving and climbing. Suitable design of its main body and wings are important for the most advance velocity. hydrodynamic design variables are main body form, wings (cross section, dimensions, shape, longitudinal and vertical position) and hydrostatic parameters (static trim angle, amount of added force). Spray marine glider is selected as the initial design and changing each of its component in numerical simulation show its effects on the glider performance then the appropriate ones are chosen. The glider is simulated by computational fluid dynamics method in Star CCM+ that its error is less than 10% according to a validation. The main body of Spray has the least resistance force. Symmetry sections performance are better for the wings, and NACA 0012 foil is chosen. smaller wings are better. by moving the wings to back of the glider the advance velocity increases. Increasing the static trim angle and the added force causes increasing the advance velocity.

Sea-oriented development is one of the most important concepts raised in the last few decades. In fact, sea-oriented development is a shortcut to development for maritime countries. Iran is also one of the maritime countries and the Makran coast is one of its most important maritime areas. In this research, using the descriptive analytical method, the sea-oriented development of the coast of Makran, with an emphasis on the upstream documents, was subjected to pathology. The findings of this research show that the coasts of Makran are of great importance and potential from a strategic, economic, and logistic point of view, especially in various areas of sea-oriented development, such as sea transportation, energy, sea tourism, and seafood resources. In general, the lack of development in this region is due to the lack of efficient and effective internal and external investment, which is also related to many political, economic, cultural, environmental, and of course legal reasons. In examining the legal reasons, it is possible to point out the lack of attention to the category of sea-oriented development in a normative, structural, and behavioral manner in an efficient and effective way, in upstream documents such as the programs of economic, social and cultural development, and the weakness in the implementation of some laws and regulations related to the development of Makran beaches. In the international dimension, sanctions in the field of foreign investment are one of the factors for the lack of development of these coasts. Finally, in order to realize sea-oriented development, it is necessary to take some measures and internal requirements from the normative, structural, and behavioral perspective by the Legislature and executive powers, the private sector, and non-governmental institutions. From an international point of view, some measures such as deepening friendly relations between Iran, the Coastal countries of the Persian Gulf, the Oman Sea, the Indian Ocean, and countries with advanced marine technologies are of fundamental importance for the realization of maritime-oriented development.

Platform decommissioning is the process of ending the exploration, extraction, drilling, etc. operations in a marine platform and returning that part of the sea to its natural condition. Different countries of the world have adopted different approaches and frameworks for environmental impact management and platform decommissioning, but the lack of a suitable legal framework as a guide for this field is felt in Iran. The purpose of this study is to review the necessary approaches to improve safety and environmental protection.Therefore, first, the most important international regulations for offshore decommissioning are reviewed and then information related to the methods, techniques and engineering considerations related to the decommissioning assets has been prepared, which includes all aspects of the platform installation including from planning to cleaning of the site, Then the Decommissioning cost is briefly explained. As a case study, considerations and approaches for a platform located in the Persian Gulf have been carried out and decommissioning techniques have been selected. At the end, the powerful internal organizations of this field are examined

Today, researchers are looking for ways to intelligentize and eliminate human wrong to reduce the amount of errors and costs of sea voyages.  The purpose of this study is to design an intelligent system for the displacement vessel model of a tanker in order to track trajectory and appropriate state.  Since the dynamics of vessel is nonlinear, in this research, the behavior of the system in nonlinear mode is investigated by considering the controller.  PID control method and sliding mode control (SMC) have been used to control actuators, which have the ability to control vessel movements in different directions and modes.  To check the performance of the designed controller, various missions such as controlling speed and heading angle, trajectory tracking have been investigated.  The obtained results show that each controller has ability of speed and heading angle control with acceptable accuracy and slight difference.  In the trajectory tracking mode, if movement speed is not significant, we can expect a proportional performance from the intelligent system.  In sliding mode control, which is a non-linear control, it shows better performance with favorable fluctuations in controlling the rudder angle and tracking.  However PID, it performs better in controlling propeller rotating, but it performs more unstable in controlling direction.

Offshore open intakes are built to supply feed water for desalination plants, power plants, and many other coastal industries. They have positive effects on supplying water demands for the coastal cities, however, adverse effects on the life of marine organisms and their habitats have been reported. As the barnacles and biofouling may change the roughness of the intake opening, in this study, their effects on changing roughness from 0.001, 0.19 and 0.5 mm were numerically simulated and the intake performance, including flow velocity between screen rods and flow rate, were evaluated. Changes in flow velocity around the opening of the intake show that an increase in roughness will decrease flow velocity and flow rate up to 4 percent