Influences of pipe–soil interaction on dynamic behaviour of deepwater S-lay pipeline under random sea states

Abstract

The pipe-soil interactions have an important influence on the dynamic behaviour of offshore pipelines in the touchdown zone (TDZ) during deepwater S-lay. This paper mainly aims to reveal the dynamic behaviour of the pipeline in the TDZ, and its actual dynamic lay effects. A full finite element model for deepwater S-lay systems is primarily developed to simulate the dynamic responses of offshore pipeline from the pipelay vessel via the stinger to the seabed, in which pipelay vessel motions, pipeline hydrodynamics, clashing contacts between the pipeline and the stinger rollers and pipe-seabed interactions are considered particularly. The numerical analysis of an illustrative case for a gas export pipeline being installed to a water depth of 1500 m in the South China Sea is carried out in the time domain using the commercial computer code OrcaFlex. The influences of seabed soil models, soil characteristics, submerged self-weight of the pipe, surface waves, and pipelay vessel motions on the dynamic behaviour of the pipeline in the TDZ have been quantitatively studied in view of non-linear hysteretic soil model. The results indicate that the soil characteristics and the pipelay vessel motions induced by the surface wave have great influence on the bending moment and embedment of the pipeline, and the seabed resistance.

Numerical Investigation into Freak Wave Effects on Deepwater Pipeline Installation

“…When the lateral displacement y exceeds the range between −ybreakout and +ybreakout, the friction force of the pipe is equal to ) (z P μ , where P(z) is the vertical seabed resistance and μ is the soil friction coefficient. This model could effectively avoid the discontinuous nature of the friction force at zero lateral displacement and was conveniently implemented in the numerical program [30].…”

“…When the lateral displacement y exceeds the range between −ybreakout and +ybreakout, the friction force of the pipe is equal to ) (z P μ , where P(z) is the vertical seabed resistance and μ is the soil friction coefficient. This model could effectively avoid the discontinuous nature of the friction force at zero lateral displacement and was conveniently implemented in the numerical program [30]. In another view of the horizontal plane, the lateral and axial pipe-seabed interactions were simulated by the modified Coulomb friction model, which expressed the lateral resistance and axial friction force with the deflection as a bilinear equation, as illustrated in Figure 5.…”

Elastic buckling analysis of an embedded infinitely long rod under combined axial and torsional loads

“…The zerothand first-order terms of k 1 , k 2 , k 3 are given in Equation (A15) in Appendix A2, while the zeroth-and first-order terms of f 1 , f 2 , f 3 are given by Equations ( 23) and (24). Substituting the zeroth-and first-order terms of k 1 , k 2 , k 3 , f 1 , f 2 , f 3 into the six Governing equations and keep only the terms up to first order, we can obtain the first-order Kirchhoff equations as…”

“…However, this assumption is typically an oversimplification. For example, a torsional stress can be generated on DNA strands as proteins move along them [1,21]; the flow of intracellular fluid could induce torsional moment on microtubules in cells [22,23]; shear stress is produced due to the anisotropic growth of plant roots [10]; a torsional moment on pipelines on the seabed can also be induced by a lateral current [24]. However, the effects of an ambient elastic medium on the buckling of a rod under pure torsion or combined axial and torsional loading remain poorly understood, as highlighted by the summary of previous works given in Table 1.…”

Numerical Assessment on the Dynamic Behaviour of Submarine Hoses Attached to CALM Buoy Configured as Lazy-S under Water Waves

“…Examples are paired-column submersibles (PC Semis) [31][32][33][34][35] and CALM buoys [36][37][38][39]. Orcaflex has also found a notable application in pipeline/hoseline strength assessment [40][41][42] and pipeline installation/laying [43][44][45].…”