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CONTENTS
Volume 4, Number 4, December 2014
 

Abstract
The spudcan requires the suitable design considering the soil, platform, and environmental conditions. Its shape needs to be designed to secure sufficient reaction of soil so that it can prevent overturning accidents. Its shape also has to minimize the installation and extraction time. Even in the same soil condition, the reaction of soil may be different depending on the shape of spud can, mainly the slope of top and bottom plates. Therefore, in this study, the relation between the slope of plates and the reaction of soil with and without water jetting is analyzed to better understand their interactions and correlations. For the investigation, a wind turbine installation jack-up rig (WTIJ) is selected as the target platform and the Gulf of Mexico is considered as the target site. A multi layered (sand overlying two clays) soil profile is applied as the assumed soil condition and the soil-structure interaction (SSI) analysis is performed by using ANSYS to analyze the effect of the slope change of the bottom plate and water jetting on the reaction of soil. This kind of investigation and simulation is needed to develop optimal and smart spudcan with water-jetting control in the future.

Key Words
jack-up platform; spudcan; top and bottom plates; soil-structure interaction model; punch through; peak resistance; water jetting; structural design; finite element analysis

Address
Dong-Seop Han: 1Research Institute of Green Energy Equipment, Dong-A University, Busan, 604-714, Korea
Seung-Jun Kim and Moo-Hyun Kim: Coastal and Ocean Engineering Division, Zachry Department of Civil Engineering, Texas A&M University,College Station, Texas, 77843, USA


Abstract
Smart flanges are used for pipeline and riser repair in subsea. In a typical case in the gas export pipeline project, the end cap bolts of a 4inch smart flange were broken during operation, and in turn leakage occurred. This work presents the detail of three dimensional finite element analysis of the smart flange to support the observed end cap bolts failure. From finite element analysis it turns out that in the presence of external bending moment, an uneven contact distribution is present between seal and end cap, which in turn changes the uniform load distribution on bolts and threaten the integrity of bolts. On the other hand, 3D finite element analysis of interaction between pipeline and seabed is presented by means of Abaqus to explore the distribution of bending moment along the pipeline route. It is found that lateral buckling occurs in the pipeline which introduces large bending moment.

Key Words
smart flanges; subsea pipeline; end cap bolts; seabed topography; 3D finite element

Address
Ali Shaghaghi Moghaddam: Young Researchers and Elite Club, Takestan Branch, Islamic Azad University, Takestan, Iran
Saeid Mohammadnia: Pipeline Engineer, Iranian offshore and construction company (IOEC), Vila street, Tehran, Iran

Abstract
Unlike the traditional displacement type vessels, the high speed planing crafts are supported by the lift forces which are highly non-linear. This non-linear phenomenon causes their motions in an irregular seaway to be non-Gaussian. In general, it may not be possible to express the probability distribution of such processes by an analytical formula. Also the process might not be stationary or ergodic in which case the statistical behavior of the motion to be constantly changing with time. Therefore the extreme values of such a process can no longer be calculated using the analytical formulae applicable to Gaussian processes. Since closed form analytical solutions do not exist, recourse is taken to fitting a distribution to the data and estimating the statistical properties of the process from this fitted probability distribution. The peaks over threshold analysis and fitting of the Generalized Pareto Distribution are explored in this paper as an alternative to Weibull, Generalized Gamma and Rayleigh distributions in predicting the short term extreme value of a random process.

Key Words
eaks over threshold; generalized pareto distribution; goodness of fit; extreme value prediction; return level plot

Address
Abhilash Somayajula and Jeffrey M. Falzaranoa: Marine Dynamics Laboratory, Texas A&M University, College Station, Texas 77843, USA

Abstract
Geotextile tubes are basically a huge sack filled with sand or dredged soil. Geotextile tubes are made of permeable woven or non-woven synthetic fibers (i.e., polyester or PET and polypropylene or PP). The geotextile tubes performances in strength, dewatering, retaining solid particles and stacked stability have been studied extensively in the past. However, only little research has been done in the observation of the deformation behavior of geotextile tubes. In this paper, a large-scale apparatus for geotextile tube experiment is introduced. The apparatus is equipped with a slurry mixing station, pumping and delivery station, an observation station and a data station. For this study the large-scale apparatus was utilized in the studies regarding the stresses on the geotextile and the deformation behavior of the geotextile tube. Model tests were conducted using a custom-made woven geotextile tubes. Load cells placed at the inner belly of the geotextile tube to monitor the total soil pressure. Strain gauges were also placed on the outer skin of the tube to measure the geotextile strain. The pressure and strain sensors are attached to a data logger that sends the collected data to a desktop computer. The experiment results showed that the maximum geotextile strain occurs at the sides of the tube and the soil pressure distribution varies at each geotextile tube section.

Key Words
geotextile tube; stress; strain; scale model test

Address
Hyeong-Joo Kim: Department of Civil Engineering, Kunsan National University, Gunsan 573-701, Republic of Korea; Kwang-Hyung Lee, Sung-Kyeong Jo and Jay C. Jamin: Department of Civil and Environmental Engineering, Kunsan National University, Gunsan 573-701,
Republic of Korea


Abstract
The tension leg platform (TLP) is one of the compliant structures which are generally used for deep water oil exploration. With respect to the horizontal degrees of freedom, it behaves like a floating structure moored by vertical tethers which are pretension due to the excess buoyancy of the platform, whereas with respect to the vertical degrees of freedom, it is stiff and resembles a fixed structure and is not allowed to float freely. In the current study, a numerical study for square TLP using modified Morison equation was carried out in the time domain with water particle kinematics using Airy\'s linear wave theory to investigate the effect of changing the tether tension force on the stiffness matrix of TLP\'s, the dynamic behavior of TLP\'s; and on the fatigue stresses in the cables. The effect was investigated for different parameters of the hydrodynamic forces such as wave periods, and wave heights. The numerical study takes into consideration the effect of coupling between various degrees of freedom. The stiffness of the TLP was derived from a combination of hydrostatic restoring forces and restoring forces due to cables. Nonlinear equation was solved using Newmar\'s beta integration method. Only uni-directional waves in the surge direction was considered in the analysis. It was found that for short wave periods (i.e., 10 sec.), the surge response consisted of small amplitude oscillations about a displaced position that is significantly dependent on tether tension force, wave height; whereas for longer wave periods, the surge response showed high amplitude oscillations that is significantly dependent on wave height, and that special attention should be given to tethers fatigue because of their high tensile static and dynamic stress.

Key Words
tethers tension; tension leg platforms; hydrodynamic wave forces; wave characteristic

Address
Amr R. El-gamal: Department of Civil Engineering, Faculty of Engineering at Benha, Benha University, Assistant Lecturer, Egypt
Ashraf Essa: Department of Civil Engineering, National Building Research Center, Egypt
Ayman Ismail: Department of Steel and Structure Engineering, National Building Research Center, Egypt


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