Experimental and Numerical Model Investigations of the Underwater Towing of a Subsea Module

Yingfei Zan,Ruinan Guo,Zhaohui Wu,Lihao Yuan

doi:10.3390/jmse7110384

Abstract

In underwater towing operations, the drag force and vertical offset angle of towropes are important considerations when choosing and setting up towing equipment. The aim of this paper is to study the variation in drag force, vertical offset angle, resistance, and attitude for towing operations with a view to optimizing these operations. An underwater experiment was conducted using a 1:8 scale physical model of a subsea module. A comprehensive series of viscous Computational Fluid Dynamics (CFD) simulations were carried out based on Reynolds-averaged Navier–Stokes equations for uniform velocity towing. The results of the simulation were compared with experimental data and showed good agreement. Numerical results of the vorticity field and streamlines at the towing speeds were presented to analyze the distribution of vortexes and flow patterns. The resistance components were analyzed based on the numerical result. It was found that the lateral direction was a better direction for towing operations because of the smaller drag force, resistance, and offset angle. Similar patterns and locations of streamlines and vortexes were present in both the longitudinal and lateral directions, the total resistance coefficient decreases at a Reynolds number greater than that of a cylinder.

Highlights

The oil and gas industry are engaging in offshore operations in deeper and more distant areas
The numerical simulation results for the drag force coefficient and offsets angle were in agreement with the physical model results
Most of the differences in the drag force coefficients and offset angles were less than 10%

Summary

Introduction

The oil and gas industry are engaging in offshore operations in deeper and more distant areas. Most approaches to addressing these issues can be divided into two categories: (1) the subsea module can be transported on the deck of a vessel and lowered through the surface near the subsea module site, and (2) in wet tow methods, the module can be lowered through the splash zone at inshore sheltered areas and towed on the surface of the water or underwater [4]. Unlike the surface towing method, the body is totally underwater and away from the surface, the wave and wind loads are no longer significant parameters. Subsea towing does not require vessels with large decks and high lifting capacity and avoids the effects of working in extreme sea states [7]

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