FROTH: Fundamentals and Reliability of Offshore Structure Hydrodynamics

Lead Research Organisation: Manchester Metropolitan University
Department Name: Sch of Computing, Maths and Digital Tech

Abstract

The FROTH project is a close collaboration between five universities with significant experience in research into wave interactions with fixed and floating structures working together to combine and apply their expertise to different aspects of the problem. The aim is to investigate the detailed physics of violent hydrodynamic impact loading on rigid and elastic structures through a carefully integrated programme of numerical modelling and physical experiments at large scale. Open source numerical code will be developed to simulate laboratory experiments to be carried out in the new national wave and current facility at the UoP [http://www.plymouth.ac.uk/pages/view.asp?page=34369].
It is well known that climate change will lead to sea level rise and increased storm activity (either more severe individual storms or more storms overall, or both) in the offshore marine environment around the UK and north-western Europe. This has critical implications for the safety of personnel on existing offshore structures and for the safe operation of existing and new classes of LNG carrier vessels whose structures are subject to large instantaneous loadings due to violent sloshing of transported liquids in severe seas. Some existing oil and gas offshore structures in UK waters are already up to 40 years old and these aging structures need to be re-assessed to ensure that they can withstand increased loading due to climate change, and to confirm that their life can be extended into the next 25 years. The cost of upgrading these existing structures and of ensuring the survivability and safe operation of new structures and vessels will depend critically on the reliability of hydrodynamic impact load predictions. These loadings cause severe damage to sea walls, tanks providing containment to sloshing liquids (such as in LNG carriers) and damage to FPSOs and other offshore marine floating structures such as wave energy converters.
Whilst the hydrodynamics in the bulk of a fluid is relatively well understood, the violent motion and break-up of the water surface remains a major challenge to simulate with sufficient accuracy for engineering design. Although free surface elevations and average loadings are often predicted relatively well by analysis techniques, observed instantaneous peak pressures are not reliably predicted in such extreme conditions and are often not repeatable even in carefully controlled laboratory experiments. There remain a number of deeply fundamental open questions as to the detailed physics of hydrodynamic impact loading, even for fixed structures and the extremely high-pressure impulse that may occur. In particular, uncertainty exists in the understanding of the influence of: the presence of air in the water (both entrapped pockets and entrained bubbles) as the acoustic properties of the water change leading to variability of wave impact pressures measured in experiments; flexibility of the structure leading to hydroelastic response; steepness and three dimensionality of the incident wave.
This proposal seeks to directly attack this fundamentally difficult and safety-critical problem with a tightly integrated set of laboratory experiments and state of the art numerical simulations with the ultimate aim of providing improved guidance to the designers of offshore, marine and coastal structures, both fixed and floating.

Publications

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Gao F. (2015) Simulation of breaking wave impact on a vertical wall with a compressible two-phase flow model in Proceedings of the International Offshore and Polar Engineering Conference

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Gu H (2013) Development of a free surface flow solver for the simulation of wave/body interactions in European Journal of Mechanics - B/Fluids

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Ma Z (2016) Pure and aerated water entry of a flat plate in Physics of Fluids

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Ma Z (2014) A compressible multiphase flow model for violent aerated wave impact problems in Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences

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Ma Z.H. (2015) The role of fluid compressibility in predicting slamming loads during water entry of flat plates in Proceedings of the International Offshore and Polar Engineering Conference

 
Description Will be inputted by the lead organization (Plymouth University) of the project.
Exploitation Route Journal paper citation.
Sectors Aerospace, Defence and Marine,Environment