Session: 04-03-01 Rigid Risers

Submission Number: 180238

A Comparison of Numerical Simulations of the Dynamic Response of a Lazy–Wave Riser Conveying Multiphase Flow 

Production risers are an important class of systems present in offshore oil and gas engineering, being essential for transporting fluids from seabed wells to floating production units. The steel lazy-wave riser concept is particularly interesting, allowing installations at ultra deep water. In this scenario, a multitude of phenomena is present, with loading conditions being determined by both internal and external fluid flows, the motion of the floating unit, and interaction with the seabed.

In this paper, a lazy-wave riser (SLWR) is numerically modelled by means of two different software. The first one is Orcaflex™, which is a well-known alternative, commonly used in the offshore industry. The second is the in-house open-source software GIRAFFE, a finite element computational tool with all models and their implementations open for evaluation and further development, what makes it a valuable benchmarking asset.

The SLWR is subjected to some internal multiphase flow conditions, to critically address the differences and similarities that may arise from both software. The internal flow conditions are tailored to excite different modes and shapes for the vibrations of the riser, under a plug flow scenario.

Comparisons are made using scalogram visualizations of the displacement fields, time-series of selected points of interest at the sag and the hog regions, besides full-length spectral analysis, to investigate the frequency content of the system’s response along the structural length, among others that are deemed useful to assess the dynamic behaviour of the structure.

It was found that some important differences may arise depending on how the internal flow is implemented in Orcaflex™, by using its native tools for this type of simulation. Such results will also be used to emphasize the necessary care that must be taken concerning the input regarding the internal flow in Orcaflex™, and what kind of behaviour in the structural response can be used to point out the need for adjustments. Finally, with the two software being properly used and providing results in qualitative agreement with each other, further effects of the different conditions simulated for the internal flow over the dynamic response of the riser are investigated. Special attention is paid to the line slope variation, which could cause pattern transitions in multiphase flow, in the case a two-way coupling scheme may be further considered.

Presenting Author: Guilherme Jorge Vernizzi Universidade de São Paulo

Presenting Author Biography: Dr Vernizzi holds a faculty position in the Department of Mechanical Engineering at the Escola Politécnica of the University of São Paulo. His research interests include nonlinear dynamics, fluid–structure interaction, and the behavior of slender and offshore structures under dynamic excitation. His main publications focus on structural dynamics and reduced-order modeling.

Authors:

Guilherme Jorge Vernizzi Universidade de São Paulo
Gabriel Vicentin Pereira Lapa Universidade de São Paulo
Ramon Rangel Dos Santos Universidade de São Paulo
Rodrigo Provasi Universidade de São Paulo
Daniel De Oliveira Tomin Universidade de São Paulo
Clóvis De Arruda Martins Universidade de São Paulo
Alfredo Gay Neto Universidade de São Paulo
Renato Maia Matarazzo Orsino Universidade de São Paulo
Celso Pupo Pesce Universidade de São Paulo