Wave forces on a seawater intake caisson

The wave force on a seawater intake structure consisting of a perforated square caisson of 400 mm×400 mm size encircling a vertical suction pipe of 160-mm diameter is investigated using physical model studies. The porosity of caisson was varied from 1.6 to 16.9%. Regular and random waves of wide range of heights and periods were used. It is found that the force ratio (ratio of the force on perforated caisson to the force on caisson with zero percent porosity) reduces to an extent of up to 60% with increase in porosity of the caisson from 1.6 to 16.9%. The force ratio was found to increase with increase in relative wave height and reduces with increase in relative width. Multiple regression analysis of the measured data points was carried out and predictive equations for wave force ratios are obtained both for regular and random waves. The results of this investigation can be used in the hydrodynamic design of perforated caissons, which are widely used as seawater intake structures.     

Damage Localization of Offshore Platforms Under Ambient Excitation

In this paper Nondestructive Damage Detection (NDD) for offshore platforms is investigated under operational conditions. As is known, there is no easy way to measure ambient excitation, so damage detection methods based on ambient excitation have become very vital for the Structural Health Monitoring (SHM) of offshore platforms. The modal parameters (natural frequencies, damping ratios and mode shapes) are identified from structural response data with the Natural Excitation Technique (NExT) in conjunction with the Eigensystem Realization Algorithm (ERA) . A new method of damage detection is presented, which utilizes the invariance property of element modal strain energy. This method is to assign element modal strain energy to two parts, and defines two damage detection indicators. One is compression modal strain energy change ratio (CMSECR); the other is flexural modal strain energy change ratio (FMSECR). The present modal strain energy is obtained by incomplete modal shape and structural stiffness matr     

Test and Numerical Analysis of the Constitutive Relation of a Diatomaceous Soft Rock

A kind of diatomaceous soft rock and its constitutive model are studied in this article. Based on Yin and Graham's (1999) 3-D elastic viscoplastic constitutive model, the formulation under a triaxial stress state is established, and it is used to simulate the time-dependent stress-strain behavior and effective stress path of consolidated undrained triaxial tests of both normally consolidated and overconsolidated soft rock. The comparison between the model predictions and measured results shows that their agreement is good. This demonstrates that the constitutive equation established here can be used to simulate the time-dependent stress-strain behavior of the soft rock under triaxial stress condition.     

Application of Tube-Packaged FBG Strain Sensor in Vibration Experiment of Submarine Pipeline Model

1 .IntroductionSubmarine pipelines have been worldwide utilizedinthe field of offshore oil/gas exploitation.Inmany cases ,the pipelinesinitiallyresting onthe seabed may become suspended due toseveral reasonssuch as installation on an uneven seabed or scou…     

Simulation of T-bar penetration in soft clay with adhesive contact

Abstract

To model the deep penetration process of T-bar in soft clay, an adhesive contact algorithm was developed in conjunction with the Coupled Eulerian–Lagrangian approach with consideration of the effect of strain softening. Numerical results show the simulated penetration resistance agrees well with the previous centrifuge experimental data. The failure mechanisms of the clay around the T-bar can be divided into three stages, including shallow penetration stage with global failure mechanism, partially and fully back-flow stages with local failure mechanism. Fluctuations of the penetration resistance can be explained by the formation and evolution of shear bands around the T-bar. Newly formed shear bands would intersect the previously formed shear bands in the partially back-flow stage, which results in the formation of “ear-shaped” areas rotating anticlockwise around the T-bar. The evolution of shear bands would form a similar fabric structure in the fully back-flow stage.     

Nonlinear Behaviour of Coflexip Risers

A modified Newton-Raphson iterative technique is formulated for obtaining the static configuration of the Lazy "S" flexible marine riser between the floater and mid-arch buoy under its submerged self weight and the applied top tension. The geometrically non-linear problem is solved by finite difference with the above technique. The problem is formulated as a regular boundary value problem with specified moments and deflections at both ends. Usually the bending stiffness of the flexible riser made of Coflexip pipe is very low. By use of the above analysis, several flexible riser configurations are analyzed and their characteristic behaviors are investigated. Also, changes in the riser characteristics due to quasi-static motion of the floater end are estimated for the safety of the riser layout.     

Brief Account of Breakwater Construction in China

-The construction of breakwaters in China in more than 40 years since the founding of the People's Republic of China is reviewed. The construction of two main types of breakwater, upright breakwaters and rubble mound breakwaters, and the way in which they are built are expounded. Recommendations to improve the technology for future breakwater construction are presented.     

Acceptance criteria of defects in undersea pipeline using internal inspection

The purpose of this paper is to establish acceptance criteria for interpretation of the internal inspection results of undersea pipelines. There are no specific rules or guidelines for the acceptance criteria of existing pipelines using a certain internal inspection method. Acceptable criteria were established with a case study of a 609.6 mm (24 in.) diameter, concrete weight coated pipeline delivers fuel oil to a thermal power plant, Ghana. Parameters to be considered in the uncertainties of flaw sizing include the crack length, depth, orientation of the flaw, whether or not the flaw is surface breaking, and number of flaws. Fitness-for-services of other pipelines can be determined using the established criteria in this study. The method of inspection also affects the acceptance criteria. Imposing limitations at or beyond the limits of detection capability would obviously be counter-productive.     

Correlation of strain with anisotropy of magnetic susceptibility (AMS)

Existing correlations between strain and anisotropy of low-field magnetic susceptibility (AMS) have been re-assessed using a single parameter to express both anisotropies. TheP parameter (Hrouda, 1982) shows potential as a powerful single expression of the intensity of strain and of AMS. Previous correlations are improved by use of this parameter. Cautious optimism is justified for correlations between strain and susceptibility in a certain strain window between a lower limit (excluding the incomplete overprint of predeformation anisotropy) and an upper limit (excluding the effects of saturation anisotropy). For successful correlations the influence of stress-controlled recrystallisation should be minimal and the mineralogical sources of susceptibility must predate deformation.