Dynamic on-bottom stability analysis of subsea pipelines using finite element model-based general offshore analysis software: a case study

Abstract

Abstract Background The dynamic on-bottom stability analysis represents a fundamental task in the design process of the subsea pipelines. Such analysis ensures the stability of the as-laid pipeline on the seabed against the lateral displacements, which are induced by the surrounding hydrodynamic forces. In this paper, the dynamic on-bottom stability analysis of a subsea pipeline is performed using finite element-based advanced offshore engineering simulation software called Flexcom. The latter predicts the pipeline response in a time-domain simulation based on a given environmental condition (i.e., the sea state, the soil frictional resistance, and the nonlinear behavior of the pipeline). A case study is conducted on a 22-in.-diameter pipeline, which is placed on a sandy soil in shallow water, under different loading combinations from two-dimensional irregular waves and a steady current. Results The resultant maximum lateral displacements and the associated stresses decreased by increasing the concrete weight coating thickness. Pipeline response due to drag, lift, and inertia forces increased by increasing the total water particle velocity induced from the summation of wave-induced particle velocity and current velocity. Different random wave patterns generated from different random seed numbers assigned to wave components are important to verify the selection of the concrete weight coating thickness. Ignoring passive soil resistance reduced the total soil resistance significantly and resulted in conservative stability weight requirement. Conclusions Several factors influence the pipeline stability such as pipeline submerged weight, hydrodynamic loads induced by random sea states, and soil friction model being used. The dynamic on-bottom stability analysis can optimize the design and results in less concrete weight coating if the actual case is modeled accurately; therefore, ignoring passive soil resistance reduced the prime advantage of this analysis compared to other simplified methods.