نشریه مهندسی دریا
پیاپی 6 (تابستان 1386)

Tension leg platforms are compliant structures for oil extraction in deep water consisting of hull, deck foundation, tendons and risers. The hull is very important part of a TLP from functionality, weight and cost point of views that is made of vertical column and horizontal pontoon with circular and rectangular sections. The hull geometry plays very important rule in optimum action of the structure. The ratio of columns volume to total volume (), that is the function of pontoon length (), column length (), pontoon diameter (), column diameter (), is an important parameter in structure response against waves loading. In the present research a parametric study has been carried out to investigate the effect of hull geometry on TLP’s responses under wave attack. A wide range of geometric parameters have been considered. A number of models have been set up by changing pontoon length, column length, pontoon diameter and column diameter. In these models the displacement volume, total volume and tendons’ tension were kept constant. Then the structural models were analyzed under wave load using a finite element software. In this paper, results of this parametric study is presented and discussed. Based on these results, appropriate range of dimensionless geometry parameters are proposed for conceptual design of TLPs hull.

In this paper, using two different methods, probability of failure is calculated for three offshore platforms in Persian Gulf. In first method, uncertainties are applied as a magnification factor in calculation of failure probability, whereas in the second method these uncertainties are considered directly for uncertainty parameters. The parameters of wave height hazard curve for eight directions of platforms with statistical analysis were obtained. These parameters are necessary for calculation of failure probability. Finally an analytical comparison has been carried out between two mentioned methods. These methods can be used for assessment of existing platforms and capacity analyses of new platforms.

Transferring patients under critical conditions such as heart attack, stroke or transient ischemic attack (TIA), and head and backbones injuries is very important, specially transportation on sea because of high level of vibration of ship due to the sea waves is very critical. Many injured persons who work on ships or offshore platform with specialist hospitals are under critical dangers of their life because of their transportation with sea vehicles. In this paper a dynamic analysis is presented to investigate the effect of sea wave on the peak acceleration of critically seek persons during transporting them on a sea. With this information equipments can be designed and installed to transfer patients safer and healthier on sea.

This paper is presents The computation of the wave-making drag of underwater vehicle by boundary element method (BEM). The method is employed constant strength doublet and source distributions on each quadrilateral element representing the body and free surface. Using Green’s function, boundary integral equation is constituted for all elements by a matrix form to determine the potential on each element, and then calculate the pressure and wave-making drag at different vehicle speeds and water depths. The computed results indicate that the present method is in good agreement with other results and, its results are shown that the method is more capable and powerful tool for prediction and analysis of wave-making drag of underwater (UV11) vehicle.

This paper presents results of an experimental investigation on stability of reshaping breakwaters. Results of 82 test cases have been used to study the reshaped profile condition of such breakwaters during the process of wave attacks. In this research, first 7 independent parameters having significant effects on structure stability have been identified and their consequence on geometric parameters of stability (6 parameters) have been studied. These 6 dependant parameters are selected so that they show completely the deformed geometry of the structure with the least probable tries. Then, using experimental data and fitting them to various statistical models, some formulae are suggested for estimation of geometrical parameters of reshaped profiles. Also efforts to increase the validity of these experimental formulae are presented. Finally a software called IB has been developed using results of the present research. Then comparisons have been made between IB and BREAKWAT program. Results show that BREAKWAT fails to predict the reshaped profile in some test cases.

This paper discusses the disturbance velocity and potential as well as the total velocity formulation for non lifting potential flow problem. The problem is derived based on the Cauchy method formulation. The adding and subtracting back technique is used to desingularize the integral equations. The desingularized boundary integral equations are then discretized. The discretized equations can be evaluated using an arbitrary high order Gaussian quadrature or any other numerical integration method. Numerical examples for ellipse and Joukowski airfoil are calculated and compared with the analytical solution. It is shown that the usage of a desingularized Cauchy's formula in potential flow computation leads to an efficient and an accurate determination of the velocity and pressure on the body surface.