Evaluation of the Double Snap-Through Mechanism on the Wave Energy Converter’s Performance

Lower efficiencies induce higher energy costs and pose a barrier to wave energy devices'commercial applications.Therefore,the efficiency enhancement of wave energy converters has received much attention in recent decades.The reported research presents the double snap-through mechanism applied to a hemispheric point absorber type wave energy converter(WEC)to improve the energy absorption perfomance.The double snap-through mechanism comprises four oblique springs mounted in an X-configuration.This provides the WEC with different dynamic stability behaviors depending on the particular geometric and physical parameters employed.The efficiency of these different WEC behaviors(linear,bistable,and tristable)was initially evaluated under the action of regular waves.The results for bistable or tristable responses indicated significant improvements in the WEC's energy capture efficiency.Furthermore,the WEC frequency bandwidth was shown to be significantly enlarged when the tristable mode was in operation.However,the corresponding tristable trajectory showed intra-well behavior in the middle potential well,which induced a more severe low-energy absorption when a small wave amplitude acted on the WEC compared to when the bistable WEC was employed.Nevertheless,positive effects were observed when appropriate initial conditions were imposed.The results also showed that for bistable or tristable responses,a suitable spring stiffness may cause the buoy to oscillate in high energy modes.

Buckling Properties of a Subsea Function Chamber for Oil/Gas Processing in Deep Waters

Due to the complexity of installations and connections of subsea production equipment and the massive structures involved in a challenging environment,the failure of subsea production equipment could induce enormous loss to the safety and reliability of structures in addition to the cost of the oilfield development.One of the challenges that the subsea production structures face,as it moves to ultra-deep water and polar underwater equipment,is to design subsea shell structures capable of withstanding high external pressures.Hence,a subsea function chamber(SFC)has been lately proposed as a viable solution,which has a high level of safety and reliability,and a technique for the subsea production system.This paper presents a general and efficient buckling and collapse analysis strategy.In this work,the SFC is composed of cylindrical and hemispherical shaped steel material.Initial imperfection-based nonlinear buckling analysis has been carried out to investigate the buckling and risks associated with different thicknesses of the structure.Linear and nonlinear static buckling analyses have been carried out using ABAQUS software.By introducing the nonlinear properties of materials,the nonlinear numerical model of SFC is established.The effects of the thickness of differentmodels and the number of stiffeners on the bucklingmodes are discussed.The wall thickness is calculated by the Donnell equation and Timoshenko’s classical method.It has been found that the classical solutions given by the Donnell and Timoshenko equations are more accurate for structures with larger lengths and diam.The thickness and number of stiffeners have a great influence on the ultimate buckling external pressure load of SFC structure.

Correction to:Buckling Properties of a Subsea Function Chamber for Oil/Gas Processing in Deep Waters

The article“Buckling Properties of a Subsea Function Chamber for Oil/Gas Processing in Deep Waters”,written by Amer Ali Al-Hamati,Menglan Duan,Chen An,C.Guedes Soares and Segen Estefen,was originally published Online First without Open Access.After publication in volume 19,issue 4,page 642–657 the author decided to opt for Open Choice and to make the article an Open Access publication.

Risk and Reliability Analysis of Deepwater Reel-Lay Installation: A Scenario Study of Pipeline during the Process of Tensioning

In terms of reel-lay installation in deep water, studies on the pipeline during the process of tensioning have been completed based on theories of risk and reliability analysis and Ergonomics. Qualitative risk results, including minimum cut sets, structural importance and probability expression of system failure, are obtained from fault tree analysis. Also, quantitative risk results, mainly consisting of failure probability and reliability index of pipeline plastic deformation, are worked out through Monte Carlo simulation. Simultaneously, scientific suggestions based on Ergonomics are provided. Conclusions drawn from this paper can, to some extent, provide certain references for reel-lay installation in deep water.