JOURNAL OF MARINE ENGINEERING
Year:2019 | Volume:15 | Issue:29 |Papers Count:18

Precision and reliability are two main performance characteristic in low-cost Inertial Navigation System(INS). Increase of precision in low-cost INS without auxiliary sensors is main challenge. Bias instability leads to position drift error in inertial navigation system. In addition, fault occurrence makes the sensor reliability is decreased. Rotation of Inertial Measurement Unit(RIMU) and use of redundant IMUs despite single unit is an approach for precision and reliability incensement. In this paper three units IMU is placed in rotational table. The mean of three units IMU is considered as virtual IMU, then INS mechanization is solved after rotation compensation. Experimental results show that the position estimation error without rotation is 10 times of estimation error in rotary case. Attitude estimation is stable in rotatory case despite instability in conventional case.

Ports are among the important economic, military and political bottlenecks for countries that have the gift of maritime boundary. One of the main structures in ports is the wharves, which are important for many uses. Thereby, design and performance of wharves under critical conditions and the enemy's military and terrorist threats is indispensable for passive defense. In this research, the responses and the vulnerable points of pile-supported wharves against the underwater blast load are being investigated. For this purpose, one of the pile-supported wharves in south of Iran is selected and one of its frames is studied. For modeling, Abaqus software and its Undex method are used. The method used to simulate the pile-supported wharf was first verified and, after ensuring the validity of the model, the effect of underwater explosion on the overall behavior of the structure and the effect of different parameters on the structure response were determined. Investigations have shown that, with the damage and even the withdrawal of several piles around the source of explosion, in most cases the entire structure does not go out of use, and without being removed from the operating conditions, can be repaired and upgraded it.

Breakwaters have changed a lot during their design history. Overtopping is an important parameter that its evaluation and reduction has always been noticed. In this study, the wave overtopping of composite berm breakwater as a new conceptual structure has been investigated numerical modeling was performed using FLOW-3D software. Then, based on a laboratory model conducted by Losada et al, calibration and verification was done for our numerical model. After numerical model performance confidence, composite berm breakwater was designed in three types. The wave overtopping of the composite berm breakwater was analysed and compared with rubble mound and horizontally caisson breakwaters. The results show a decrease of 84. 01% of the overtopping in the composit berm breakwater compared to the rubble mound breakwater. Also, the overtopping in the composite berm breakwater had a 61. 42% reduction compared to the horizontal caisson breakwater.

In this paper, the governing equations of sea waves are analyzed nonlinearly and the energy extraction from the waves in the Lark and Faror islands in the Persian Gulf is determined. According to the data in the last 31 years, the waves of these two islands have the most incidence for the height of 0-0. 4 m and 0. 4-0. 8 m corresponding for the time periodicity of 2. 4-3 s and 3-3. 6 s, respectively. Therefore, waves with an average period of 3 s and a height of 0. 5 m are used in the design process. The Cylindrical Energy Transfer Oscillatory (CETO) mechanism is chosen and the conceptual design is carried out with an in-house FORTRAN code, in which the results are in favorable agreement with the available experimental data. Investigations show that optimum power production requires the range of 2. 8 to 3. 2 for the ratio of the height to the radius of the buoy. Also, it is possible to access 25 kW power for each mechanism in the optimum conditions.

In this paper, selecting of an appropriate mooring system for spar platform of a wind turbine consisting of chain– cable– chain is investigated based on a meta-heuristic method. The purpose is to investigate the hydrodynamic behavior of the structure and the mooring system in a normal and damaged conditions. ANSYS-AQWA software is applied to hydrodynamics analysis and the numerical results were first verified by experimental results. According to the characteristics of the experimental mooring system and designed stiffness in the desired depth of the sea, an appropriate chain is selected for the prototype model and then by investigating the changes applied to it and replacing a chain mooring system with a mooring system including chain– cable– chain, the survival behavior of the structure and mooring system evaluated for the 100-years return period, considering one of the mooring line disconnection. According to the controlling role of the initial chain connected to the structure, it was also observed that the decreasing the length of the initial chain and increasing the anchor chain length, the tension as well as the amplitude of the structural movements in the degrees of surge, heave and pitch increases.

Greenhouse gas emissions and atmospheric pollutants, economic savings, as well as alignment with the new rules of the shipping industry's leading is a new concern. In order to meet and achieve these goals, many efforts have been made. In this paper, some methods for reducing fuel consumption, including optimization of floating trim, have been considered in design draught. In this regard, the body resistance of model of the KCS container ship is calculated in design draught; This analysis was performed by numerical solution and experimental test for-0. 1 to +0. 1 trim range. And the results of ship model analysis was generalized to the main body. In this regard, the mathematical model of ship propulsion system is implemented in the MATLAB-Simulink software; and by using this model for different trims, rates of ship specific fuel consumption presented. According to the results of modeling and simulation of the floating body, a reduction of 1. 5% of fuel consumption has been achieved due to optimization of the trim.

The underwater Gliders are a kind of autonomous vehicles that have a special role in ocean surveys which demand continuous monitoring and long endurance. Because of low energy consumption and long endurance, these vehicles are favorite for these missions. Among this, a type of gliders can harvest ocean thermal energy, causing significant endurance increase. These vehicles need at least 680 meters sea depth to operate their propulsion system. In this paper, by analyzing a propulsion system of a typical glider, heat transfer and its operation depth is assessed. For decreased operational depth, an approach is presented for possibility of using this technology in shallower seas, which provides the utilization of this type of gliders at wider range of the Gulf of Oman.

Skirted foundations are an appropriate alternative to deep foundations in onshore and offshore structures, which have the ability to withstand uplift loads, are also easy to be installed. The tensile performance of skirted foundations on sand was studied by physical and numerical modeling. Laboratory tests were carried out on small-scale foundation models with peripheral skirts. Numerical modeling was performed by 3D finite element analysis for verifying the results of physical tests, as well as generalizing the results to the large-scale models. The effects of geometry and soil properties parameters including foundation diameter, sand shear strength, skirt depth, surface roughness, and load inclination angle were investigated. The results showed that the presence of peripheral skirt improves the behavior of tension bearing capacity of foundations on sand; Improvement values increase with increasing skirt depth, sand shear strength, roughness of foundation surfaces, and also, with decreasing the load inclination angle relative to vertical direction.

Considering the increase in number of offshore oil production projects and for better understanding of plume dynamics in accidental underwater oil blowouts, a series of laboratory experiments in a square cross section open top basin were carried out to investigate the effect of changes in seawater stratification and water column stability on plume dynamics and peeling height. Accordingly the open top basin was filled with stratified salt water at different buoyancy frequencies and the results of experiments were numerically expanded to marine condition of shallow waters. Non-dimensionalized form of experimental and numerical results showed that decrease in basin buoyancy frequency increases the plume peeling height and reduces the plume width. Experimental results showed that the neutral buoyancy level was the applicable transition criterion from plume dynamic phase to advective and diffusive phase.

Single Point Mooring (SPM) are floating Structures that are deployed in deep water which their duties are vessel mooring and transferring oil and gas productions by pipelines from shore to petroleum tankers and conversely. One of the most important components of SPM is mooring system. Which bears not only environmental loads but also petroleum tanker loads which conducted by two thick ropes. Mooring system of SPM regarding the important responsibility it has, has been pay attention to a lot. Proper mooring system leads to efficiency improvement in different environmental conditions and mooring system life increase. In this research SPM with four mooring lines are simulated by ANSYS AQWA Software and forces on the SPM calculated diffraction theorem and Boundary Element and mooring lines are calculated by Morrison theorem.

This paper presents the effect of hydrodynamic parameters of the two-body converters of a point wave absorber on the amount of power output. This converter includes two submerged and floating bodies which are connected to the spring-damper system. The whole of the converter is connected to the sea bed by mooring catenary. The relative displacement of the floating body and the submerged body is the main factor in generating electrical energy. Since the calculation of hydrodynamic coefficients has a significant effect on the solution of dynamic equations, this study focused on the calculation of added mass and hydrodynamic damping by boundary element method using the ANSYS-AQWA software. Also, this paper investigates the effect of floating borehole geometry on the hydrodynamic parameters and the extracted power of the converter using complementary analysis on the domain of time and frequency. Comparison of numerical simulation outputs and the results from the laboratory work which had carried out by Sandiego researchers in 2011, shows the suitable accuracy of the simulation. According to the results, with the two meters increase in buoy diameter, the power output will increase by 20%, and the output power for the half-conical is 17% more than the hemisphere.

Monopiles are the most common type of foundation for offshore wind turbines (OWT). Monopiles have been used in more than 80% of the offshore wind turbines. A monopile will be affected by millions of lateral load cycles during the operating period, which will cause its rotation and lateral deformation. The rotation and the deformation are dependent on the soil properties, monopile specification, and lateral loading characteristics. Current methods are only for the design of piles with less than 1meter in diameter. Due to this fact that monopiles are hollow cylindrical steel tubes with a diameter of 2 to 8 meters, in this research the behavior of these structures due to monotonic and cyclic lateral loads in sandy soils has been studied by physical modeling in a geotechnical centrifuge. One monotonic test and six cyclic tests were designed and implemented to investigate the effect of lateral load characteristics. According to the results of 7 tests, the effect of different loading parameters on monopile cumulative displacement and soil stiffness is discussed. In all tests, the monopile deflection is a rigid body, and the cumulative displacement of the monopile head is increasing with power functions. Also, the monopile stiffness in terms of the number of cycles is ascending, and the rate of the increase is decreasing.

The biomimetic and hydrodynamic study of aquatic animals is one of the most challenging computational fluid dynamics topics in recent studies due to the complexity of body geometry and the type of flow field. The movement of the aquatic body, and particularly the tail section and the corresponding movement of fluid around the body, causes an unsteady flow and requires a comprehensive study of the interaction of fluid and aquatic body which makes the analysis more complicated. In this research, the main purpose is to investigate the numerical simulation of hydrodynamic flow around the aquatic body regarding dolphin swimming condition. Specifically, considering the precise 2D geometry of a dolphin body, the studied parameters include the drag and lift coefficients, body movement and its effect on vorticity, pressure and velocity fields immediately around the body. According to the results it can be claimed that the body movement frequency and the length of tail motion highly affect the mentioned parameters.

In this research, the application of multilayer perceptron (MLP) neural networks and support vector machine (SVM) for modeling the hydrodynamic behavior of Permeable Breakwaters with Porous Core has been investigated. For this purpose, experimental data have been used on the physical model to relate the reflection and transition coefficients of incident waves as the output parameters to the width of the breakwater chamber, the ratio of the height of rockfill material to the water depth, the ratio of the width of the chamber to the wavelength, Wave number in water depth and wave steepness. The results indicate that the MPL model has better performance in modeling the hydrodynamic behavior than the SVM model and is largely correlated to real data (R = 0. 8689 for reflection coefficient and 0. 96629 R = for transient coefficient). In order to reveal the response of reflection and transition coefficients to each input parameter, a parametric study was performed. Also, using the sensitivity analysis, the participation rate of each input parameters in the prediction of reflection and transient coefficients has been studied.

Simulation of the flow around propeller is a complex fluid flow problem, especially when the propeller is close to free surface. In this study, the effect of different depths on the performance and efficiency of a B-Wageningen series close to surface of water have been numerically investigated. For this purpose the ANSYS-FLUENT commercial software has been used to solve the viscous, incompressible and two phase flow field. The rotation of the propeller has been implemented using the rotating reference frame model for steady flow and the sliding mesh for unsteady flow. For turbulent flow modeling and free surface simulation, the k-ω SST model and the volume of fluid method have been used, respectively. For validation of numerical results due to lack of access to experimental results of propeller close to surface, numerical solution in open water condition has been performed and performance coefficients have been calculated. The results of the numerical solution show that the propeller coefficient decreases at different depths with increasing forward ratios.

Makran subduction located at the northwest of the Indian Ocean nearby the southern coast of Iran and Pakistan. Makran subduction is the source of tsunamis that threaten southern coast of Iran. In this article, generation and propagation of 1945’ s tsunami initiated by Makran subduction is simulated. For the three dimensional generation of the wave, advanced algorithm of Okada is adopted. The CFD based software of Flow 3D is applied for global and regional numerical simulation of tsunami wave propagation. In the first stage the 3D propagation of the wave in Oman sea and Indan Ocean is simulated. The presented approach in this paper including the accurate 3D generation of the tsunami wave using the Okada algorithm and two stages propagation in the global and regional models results in a more accurate results in terms of time duration and tsunami wave run-up.