JOURNAL OF MARINE ENGINEERING
Year:2009 | Volume:4 | Issue:8|Papers Count:6

Guyed tower is a compliant offshore platform used for drilling and extraction of oil in deep water. This platform has a flexible body and needs proper mooring system to control the deck movements. In present study this platform is analyzed in frequency domain due to irregular waves. The exiting force extracted from Pierson Moskovits spectrum using Morrison Equation. Modeling of moorings is difficult due to their variable stiffness and non linear interaction with main structure. Therefore first using static analysis data the diagram for mooring force excursion was obtained and fitted to a polynomial of order 5. Then using this equation the spring force of moorings was linearized. Furthermore the drag term was linearized and both of these two linearized terms used in dynamic equation of motion. The results of analysis showed that errors due to this linearization on final results are negligible. Results of this research can be used for optimum design of guyed towers in deep water and its special application in Caspian Sea can be considered.

In this paper, the flow pattern around the perpendicular and inclined groynes were simulated in three-dimensional using the fluent software, which solves the flow equations using the finite volume method and cell-center scheme. The prismatic grids were used to descretize the computational domain. The perpendicular groyne was first investigated to verify the model results and the inclined groyne with 60° to the flow direction was then considered. From the available turbulence models in the software, the two equation k - e turbulence model was used in this research study. In order to include the free surface effect, the rigid-lid and volume of fluid schemes were used. The result of the latter scheme showed good agreement with the experimental results.

The goal of this study was to simulate the Gonu cyclone and its resulting waves in the Gulf of Oman. The Gonu cyclone wind field was simulated using CGW module of Mike 21 and cyclone track data. Then, using SW module of Mike 21, the simulated wind field and ECMWF parametric boundary condition, the resulting wave field was simulated. The maximum significant wave height of 10.5 m in the Gulf of Oman and 3.8 m in Chabahar was simulated during Gonu cyclone occurrence. This wave height in Chabahar is 12% more than the buoy measurement which is in the safe side for design purposes. Uncertainty in the cyclone radius and insufficiency of the wind measurement points in the study area are major limitations of this research. The wave forecast study of this cyclone is useful in studying the wave climate in the Gulf of Oman and will provide engineers with valuable data for designing coastal structures. This model enables us to estimate the maximum significant wave height during cyclone occurrences. The results were re orted to responsible authorities leading to a successful evacuation of the costal regions and saving a significant number of lives.

Waves exert one of the most important forces on offshore and coastal structures as well as floating vessels. However, due to the random nature of waves, estimation of their hydrodynamic forces on marine structures is very complicated. Morison's semi-empirical model is one of the models capable of estimating wave forces on slender cylindrical elements of marine structures. In this research using large scale experimental results in wave flume, the effect of random waves on rough vertical cylinders will be considered. Water particle kinematics was estimated using non-linear Stokes fifth order theory (i.e. Fenton Method). Finally, System Identification method known as SI method was utilized in order to determine hydrodynamic coefficients in Morison's equation. Comparison of measured and estimated hydrodynamic force by Morison's equation showed that although Morison's equation is most applicable and available routine for estimation of wave forces on slender cylindrical elements, its errors in safe side is considerable.

The goal of this study was to provide quality assurance for QuikSCAT wind speed and direction in Iranian adjacent seas including the Caspian Sea, the Persian Gulf and the Gulf of Oman. Synoptic station wind data and numerical atmospheric models in the study area were compared with QuikSCAT wind field. Time difference and spatial separation between the QuikSCAT and synoptic observations were limited to less than 1 hr and 45 km, respectively. The average and standard deviation of QuikSCAT wind speeds are more than those of synoptic stations and numerical atmospheric models. The accuracy of the QuikSCAT wind direction at low wind speed range is less satisfactory than that at moderate to high wind ranges. QuikSCAT wind speeds in the range of 5-15 m/s have an acceptable level of accuracy in southern seas. Large spatial separation between some of the synoptic stations in Iranian coastline and islands is a major limitation of this research. This is the first time that QuikSCAT wind field was evaluated against observed and modeled data in Iranian seas. QuikSCAT wind field can be used as a valuable source in wave hindcast/forecast modeling.

In this paper, in order to understand the flow-pipe interaction more clearly, the variations on flow pattern around semi-buried pipelines due to steady current have physically and numerically been investigated. In physical modeling section, the experiments have been carried out in a flume with 10 meter length, 0.3 meter width and 0.5 meter depth using a P.V.C pipe with 6.35 cm in diameter (for different burial depth-diameter ratios). To visualize the flow patterns, the polystyrene particles with 0.4 mm in diameter and 1.05gr/cm3 in density have been used. In order to understand the phenomenon as well as possible, the whole processes of tests have been recorded using a digital camera. For the numerical simulation section, the flow field has been analyzed using a computational fluid dynamics software "FLUENT". For the soft are, the governing equations are discredited using the finite volume method. Geometry and mesh production have been done using pre-processor software called "GAMBIT".