Session: 04-03-01 Rigid Risers

Submission Number: 180310

Numerical Simulation of Steel Lazy-Wave Riser Dynamics Considering Internal Multiphase Flow Transients 

Riser systems are essential components in offshore production, conveying oil and gas between subsea equipment and floating production units. The structural integrity of flexible riser systems is a critical aspect in offshore engineering, particularly in deepwater, where the interaction between harsh environmental conditions, complex internal fluid dynamics, and sophisticated geometrical configurations introduces significant nonlinear behavior. This paper presents a comprehensive numerical study of a steel lazy-wave riser deployed at a water depth of 2,000 m. The riser is modeled using the open-source software GIRAFFE, a finite element–based computational tool that employs the Geometrically Exact Beam Theory (GEBT) to account for large displacements and rotations, which are typical in deepwater riser behavior. The riser is considered fixed at a hang-off structure, and the environmental loads are incorporated using Morison’s equation, accounting for hydrodynamic drag and inertia effects due to ocean currents and waves. A key focus of this study is the influence of internal multiphase flow on the riser response, analyzed through three representative scenarios: (1) gradual transitions between flow regimes throughout the riser, during standard operation; (2) the occurrence of severe slugging, which introduces pronounced pressure and velocity fluctuations; and (3) anomalous operational conditions arising from unexpected internal flow transients. Internal flow parameters—including pressure, density, and velocity distributions—were obtained from commercial multiphase flow simulation software and implemented as distributed loads within a one-way fluid–structure interaction (FSI) framework. Dynamic time-domain simulations were conducted for the three scenarios, with riser deformation and stress distribution visualized through heatmaps to facilitate global assessment. In addition to these analyses, local variations in riser inclination caused by internal fluid transients were evaluated along selected sections of the riser, indicating geometric changes that might influence internal flow behavior. Critical regions such as the touchdown zone, sag bend, and hog bend were examined in detail, given their susceptibility to fatigue damage and failure. Complementary modal analysis was also performed, incorporating the effects of internal fluid to determine natural frequencies and mode shapes, which were compared against frequency-domain representations of the simulation results. Although this study adopts a one-way coupling strategy, findings indicate that such an approach may not be enough to simulate dynamic responses properly in highly transient multiphase flow conditions. Furthermore, the observed inclination variations suggest potential effects between structural motion and internal flow, which could modify flow regimes and intensify dynamic loads. These results emphasize the importance of advancing toward two-way coupling methodologies in future research to more accurately predict fatigue life, ensure structural integrity, and improve the overall reliability of deepwater riser design.

Presenting Author: Gabriel Lapa Universidade de São Paulo

Presenting Author Biography: Gabriel Lapa is a civil engineer specializing in structural engineering, with an emphasis on offshore structures and fluid–structure interaction. He is currently pursuing a Ph.D. in Civil Engineering at the University of São Paulo, where he conducts research on the dynamic analysis of risers considering multiphase flow, employing finite element modeling and consistent fluid–structure interaction formulations for offshore applications.
He earned his Master’s degree in Civil Engineering from the University of São Paulo (2023), where he investigated the fluid–structure interaction of wind turbine blades using the finite element method and the Blade Element Momentum (BEM) method.

Authors:

Gabriel Lapa Universidade de São Paulo
Bruna Naidek ISDB Flowtech
João Carneiro ISDB Flowtech
Afredo Gay Neto Universidade de São Paulo
Oscar Rodriguez Universidade de São Paulo
Celso Pesce Universidade de São Paulo