International Journal of Maritime Technology
Volume:6 Issue: 9, Autumn-Winter 2018

In this paper, symmetric water entry of twin wedges is investigated for deadrise angle of 30 degree. Three numerical simulation of a symmetric impact, considering rigid body dynamic equations of motion in two-phase flow is presented. The two-phase flow around the wedges is solved by Finite Element based on Finite Volume method (FEM-FVM) which is used in conjunction with Volume of Fluid (VOF) scheme in ANSYS Fluent and ANSYS CFX and Phase Field scheme in COMSOL Multiphysics. The method and scheme of simulation are validated by experimental data for geometry with one wedge. The dynamic mesh, mesh motion and moving mesh models are used to simulate dynamic motion of the wedges in ANSYS Fluent, ANSYS CFX and COMSOL Multiphysics, respectively. The vertical velocity and pressure coefficient versus time are determined and comparisons of the computed mentioned parameters against experimental data are performed. The eight characteristics effects of fluid flow are investigated till 0.25 second after wedges falling including impact event. It is demonstrated that the ANSYS Fluent and k-ε were the best software and viscous model, respectively.

Iranian offshore oil and gas platforms are mostly located in the Persian Gulf. Technical and environmental challenges resulted from an off-design running condition of processes on a platform are important issues. The weakness of strategies to stop or decrease the amount of greenhouse gas emission production rate in the Persian Gulf; which is intensively increasing, is another matter of concern. modern methods of energy generation from available renewable potentials near offshore platforms are suggested. Integration of renewable energy converters with offshore oil and gas platforms can solve both problems with machinery and environment to an acceptable extent. In this study, the economics of the Soroush offshore complex is subjected to two scenarios. The first scenario defines the present condition in which the total power demand of the complex is supplied by burning the associated extracted natural gas on board the platform in its thermal power plant and the second scenario considers a wind farm located near Bardekhun in Bushehr province to be connected to the complex power network and shares its renewable source generated power with the platform. The economics of both scenarios are compared in terms of total annual power cost. The second scenario shows more beneficial, although there are some conservative assumptions included due to a shortage of data and limitations.

Free-span occurs normally in a pipeline at uneven seabed, dynamic seabed and pipeline crossing. Free spanning in pipeline causes Vortex Induced Vibration (VIV) fatigue, fracture and bursting. In this paper, a pipeline located in South Pars Gas Field is assessed against local buckling and VIV fatigue using probability of failure theory based on the recommended methodology by Det Norske Veritas (DNV) corresponding to different soil classes and different span length to pipeline diameter and also different water depths by applying First-Order Reliability Method (FORM) and Monte-Carlo Sampling (MCS), separately. Furthermore, the simultaneous effect of local buckling and VIV fatigue is assessed in terms of probability of failure. Finally, in order to determine the effect of each parameter on failure probability, sensitivity analysis is carried out using the alpha index.

Nowadays, application of high speed crafts with large tonnage is of our country's essences. In order to gain high speed, new multi hull crafts are traditional. A hull form having been used recently in frigates is the Trimaran. Trimaran hull form and motion have been extensively studied due to the development of numerical and analytical methods as well as the exploitation of experimental setup. In this article, we investigate the possibility to move the side hulls longitudinal and transversal with respect to the main hull in order to find the optimum situation for minimum drag. The mathematical approach is numerical method CFD with the help of VOF. Moreover the experimental measurement was provided for some cases. The simulation results indicated good agreement with the experimental results. The investigations undertaken within the scope of this article provide a starting point to investigate the flow pattern and performance of such ships.

Single Point Mooring (SPM) is a type of offshore facility that is used for the loading and unloading of oil and gas tankers in the sea. In Iran, it is briefly called “floating buoy”. The present study discussed floating type, fixed to the seabed with mooring chain. The mooring chain of SPM, which is considered one of the important parameters of its design, will be evaluated with regard to reliability in different environmental conditions. Reliability is the likelihood of a healthy and flawless functionality for a specific time according to existing and predetermined conditions. OrcaFlex Ver. 9.4e (UK) software, by Orcina Company was used for moorings analysis. For this purpose and to calculate the environmental forces in the mooring chains (in our case 6 mooring chains with a 60 degree angle), the researchers used the diffraction analysis and time history. The results revealed that; by decreasing and increasing the diameter of the mooring chain, the force applied to the mooring also decreased and increased, respectively. Also, the effects of chain diameter, direction, and amount of wave and current were studied. The behavior of wave and current showed that when the direction of the wave and the current were closer to the direction of each mooring chain, the force applied to the mooring increased. To calculate the reliability, the FORM method was employed, and to find the target point on the function, the MPP method was used. The reliability of mooring was intended to control, the value of reliability index (β), using a software program written in MATLAB, for the environment loads with a return period of 100 years. The reliability index for mooring lines of SPM was greater than 3.51, representing the safe performance of the mooring lines under environmental load.

The important and hazardous of the rescue mission in oceans and seas, autonomous vessels now are one of the most appropriate applications among others. Due to safety, reliability, and accessibility of smart, Autonomous and Cooperative vessels today has attracted much attention from the industry. Regard to the complication of the mono vessel for different objects, the multi- agent system was proposed by the researchers. A group of vessels which are connected to each other through different communication systems like GPS, INS and etc., could easily act their duties in the different situations. Design a strategy controller for a group of underwater vessels with the aid of Lyapanove and Graph theory is addressed in this brief. Realistic dynamics is considered in this paper which is novel things in the fields of control system design to demonstrate the performances of the designed controller. Using realistic dynamics makes it possible to really analyze the behavior of the system and consider all the problems which the systems might be faced in reality. The main features of the proposed controller are the decentralized and scalable controller which convert the controller to be applicable to the different number of agents also in the different situation without any external monitoring and this is while all the previous work were based on the external Control. Due to the realistic agent dynamics, non-holonomic dynamics and turning constraints of the vessels are considered in the design process. Advantages of the proposed controller could be represented as follow: domestic information is used between vessels. Based on the realistic dynamics of motion, damping and inertia matrix which in previous works used to be diagonal and constant, are considered as non-diagonal and variable. Also to represent the effectiveness of the proposed controllers, MATLAB and SIMULINK are used to simulate the effectiveness of the controller. As the simulation results show, designed controllers perform well on the system and the objective duty is achieved appropriately.