FROTH: Fundamentals and Reliability of Offshore Structure Hydrodynamics

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.

This project aims to address the important but unsolved issues of wave impact on various marine structures that may be fixed and floating with free responses. The examples of fixed structures are jack up platform for oil and gas exploration, the offshore wind tower in shallow water, coastal defence structures and nuclear plant structures built along the coastline. Examples of floating structures are the oil/gas carrier, oil/gas storage and production tankers (such as FPSOs), floating offshore wind energy systems in deepwater, offshore wave energy structures and ships. In many cases, the structures were damaged due to wave impact and slamming. Examples include (1) tearing the bow of Norwegian cruise tanker Wilstar in 1974 (2) bow damage to FPSO Schiehallion in 1998; (3) oil tanker Prestige split into two parts in 2002, causing oil spill disaster. (4) sea wall in the front of Fukushima Nuclear plant hit by the recent Japan tsunami in 2011, causing nuclear disasters. It can be seen that the issues of wave impact can reach a broad range of engineering sectors and directly affects society.
Therefore the achievements of this project, including computer codes, numerical and experimental results as well as the guidance produced, will directly benefit the classification organisations and engineering consultant and service companies who have provided the support letters and have agreed to take part in the End User Management Group. These organisations and companies can use these project results and computer codes to improve their standards and their designs, and to assess if the existing structures would be suitable to serve in the longer term under changed environmental conditions.
The results and computer codes can also be employed by the owners of Liquefied Natural Gas (LNG) tankers, who can use them to assess the wave impact loads on the tank wall due to sloshing waves inside the tank; by the owners of FPSOs, who can use them to assess the weather conditions to see if they would cause damage; by coastal engineering consultancies who may use them to design safer sea walls and coastal defence structures. In addition, they may also benefit the companies who design, manufacture and install the offshore wind energy and wave energy structures as their project designs are based on better understanding of wave-structure interaction physics.
Furthermore, governmental agencies, such as the Health and Safety Executive (HSE) and environment agency (EA), UK, may benefit as well because they can develop better policy to address safety issues related to wave impact on many kinds of structures.
Apart from the above, the computer code would provide the opportunities for increasing the service and therefore creating additional jobs in the UK and worldwide Oil & Gas, coastal engineering and marine renewable energy sectors, which have been and will continue to be important contributors to UK GDP. It may also benefit the general public in the sense that the project results could help reduce the risk of failure of a structure, which could avoid or reduce the loss of lives and injuries, and could help prevent oil spill or other loss of cargo leading to environmental disaster.
In order to make the impact happen, we proposal to carry out the following activities:
1) Involve key stakeholders (e.g. Lloyds Register, Germanischer Lloyd, Bureau Veritas, Trinity House, Saipem) and establish an End User Management Group of offshore classification societies and key industrialists in order that they are directly informed of the project achievements;
2) Create a website to allow to open access to the information produced;
3) Organise two project workshops to widen the awareness of these achievements;
4) Organise special sessions in International Offshore and Polar Engineering Conference & Exhibition to maximise the international of reach of the developments;
5) Arrange public awareness events so that the interested public is well informed.