During the operation and installation of offshore pipelines, high axial forces and pressures are experienced, and their effects cannot be neglected. In this article, the effect of internal flow velocity and functional...During the operation and installation of offshore pipelines, high axial forces and pressures are experienced, and their effects cannot be neglected. In this article, the effect of internal flow velocity and functional loads on vortex-induced vibration （VIV） response is investigated. On the basis of the Hamilton principle, a differential equation was derived to describe the motion of a pinned-pinned tensioned spanning pipeline conveying fluid. The VIV response was calculated according to DNV-RP-F105 under different functional loads. The results showed that functional loads influence free spanning pipeline VIV response by changing the natural frequency. Internal flow velocity was found less important for VIV response than other functional load factors, such as effective axial force, because the speed in reality is not high enough to be significant. The research may provide a reference for sensitivity studies of the effect of functional loads on allowable free span lengths.展开更多
To investigate the mechanical behavior of segmental lining, a three-dimensional numerical analysis and test using three actual segments were used to analyze the effects of axial force and reinforcement ratio on the fa...To investigate the mechanical behavior of segmental lining, a three-dimensional numerical analysis and test using three actual segments were used to analyze the effects of axial force and reinforcement ratio on the failure mechanism and ultimate bearing capacity of segmental lining. Both numerical and test results confirmed that the cracking load, yield and ultimate load were strongly influenced by axial force, and it was also proved that the yield and ultimate load would increase with the increase of reinforcement ratio, but the cracking load was almost not affected. The cracking load, yield and ultimate load are about 28.7%, 500% and 460% larger due to the effect of axial force respectively. The comparison between numerical calculation and test results showed that the finite element analysis resuits were in good agreement with the test results.展开更多
Splash zone crossing of the structures with large horizontal surface （e.g. manifolds） and the structures having large weight variation in water and air （e.g. suction anchors） is a critical marine operation. This i...Splash zone crossing of the structures with large horizontal surface （e.g. manifolds） and the structures having large weight variation in water and air （e.g. suction anchors） is a critical marine operation. This is due to the large slamming forces and added mass of the structure, which results in high dynamic loads on the crane. The solution to this could be attaching a PHC （Passive Heave Compensator） between the crane hook and the payload. This paper analyzes the deployment of a subsea manifold with and without PHC unit in North Sea at a water depth of approximately 370 m. A detailed dynamic analysis is done for a seastate of 3 m significant wave height （Hs） over a range of zero up-crossing period （Tz） varying from 3s to 13 s. For better understanding of the result analysis has been done in two stages. The first stage covers the lowering of manifold through the splash zone while second stage covers the seabed landing of the manifold. Based on the results of the analyses it is concluded that PHC tends to reduce the dynamic peak load on the crane. Besides this, it also mitigates the risk of slack wire situations during splash zone crossing of the payload. Furthermore, reduction in both landing velocity and crane tip velocity is also achieved by using a well-designed PHC unit.展开更多
The instability of the tensile armor wire of flexible pipes is a failure mode associated with deep and ultra-deep water applications. Real compressive forces acting on the pipe are necessary to trigger this process. T...The instability of the tensile armor wire of flexible pipes is a failure mode associated with deep and ultra-deep water applications. Real compressive forces acting on the pipe are necessary to trigger this process. The loss of stability may be divided into two distinct processes, according to the main direction of the wire＇s displacement： radial or lateral instability. This study aims at proposing a numerical tool for predicting lateral and radial critical buckling loads for the tensile armor wires of flexible pipes. A simple finite element model, based on springs and beams elements, was developed in ABAQUS~ to deal with this problem in an efficient and reliable manner. A parametric study was conducted concerning the behavior of the critical load when the laying angle, the initial curvature and the total pipe length are varied. The results were consistent with previously published literature data and analytical expressions, proving its applicability to pipe engineering projects. It also has the advantage of approaching the problem three-dimensionally, which allows further modelling modifications, such as including friction effects.展开更多
基金Supported by the National Natural Science Foundation of China (No. 50879013)China National 111 Project (No.B07019)
文摘During the operation and installation of offshore pipelines, high axial forces and pressures are experienced, and their effects cannot be neglected. In this article, the effect of internal flow velocity and functional loads on vortex-induced vibration （VIV） response is investigated. On the basis of the Hamilton principle, a differential equation was derived to describe the motion of a pinned-pinned tensioned spanning pipeline conveying fluid. The VIV response was calculated according to DNV-RP-F105 under different functional loads. The results showed that functional loads influence free spanning pipeline VIV response by changing the natural frequency. Internal flow velocity was found less important for VIV response than other functional load factors, such as effective axial force, because the speed in reality is not high enough to be significant. The research may provide a reference for sensitivity studies of the effect of functional loads on allowable free span lengths.
基金Supported by National Natural Science Foundation of China (No. 10902073)
文摘To investigate the mechanical behavior of segmental lining, a three-dimensional numerical analysis and test using three actual segments were used to analyze the effects of axial force and reinforcement ratio on the failure mechanism and ultimate bearing capacity of segmental lining. Both numerical and test results confirmed that the cracking load, yield and ultimate load were strongly influenced by axial force, and it was also proved that the yield and ultimate load would increase with the increase of reinforcement ratio, but the cracking load was almost not affected. The cracking load, yield and ultimate load are about 28.7%, 500% and 460% larger due to the effect of axial force respectively. The comparison between numerical calculation and test results showed that the finite element analysis resuits were in good agreement with the test results.
文摘Splash zone crossing of the structures with large horizontal surface （e.g. manifolds） and the structures having large weight variation in water and air （e.g. suction anchors） is a critical marine operation. This is due to the large slamming forces and added mass of the structure, which results in high dynamic loads on the crane. The solution to this could be attaching a PHC （Passive Heave Compensator） between the crane hook and the payload. This paper analyzes the deployment of a subsea manifold with and without PHC unit in North Sea at a water depth of approximately 370 m. A detailed dynamic analysis is done for a seastate of 3 m significant wave height （Hs） over a range of zero up-crossing period （Tz） varying from 3s to 13 s. For better understanding of the result analysis has been done in two stages. The first stage covers the lowering of manifold through the splash zone while second stage covers the seabed landing of the manifold. Based on the results of the analyses it is concluded that PHC tends to reduce the dynamic peak load on the crane. Besides this, it also mitigates the risk of slack wire situations during splash zone crossing of the payload. Furthermore, reduction in both landing velocity and crane tip velocity is also achieved by using a well-designed PHC unit.
文摘The instability of the tensile armor wire of flexible pipes is a failure mode associated with deep and ultra-deep water applications. Real compressive forces acting on the pipe are necessary to trigger this process. The loss of stability may be divided into two distinct processes, according to the main direction of the wire＇s displacement： radial or lateral instability. This study aims at proposing a numerical tool for predicting lateral and radial critical buckling loads for the tensile armor wires of flexible pipes. A simple finite element model, based on springs and beams elements, was developed in ABAQUS~ to deal with this problem in an efficient and reliable manner. A parametric study was conducted concerning the behavior of the critical load when the laying angle, the initial curvature and the total pipe length are varied. The results were consistent with previously published literature data and analytical expressions, proving its applicability to pipe engineering projects. It also has the advantage of approaching the problem three-dimensionally, which allows further modelling modifications, such as including friction effects.
