This research project is concerned with ship and offshore plant safety, and focuses on problems that can arise in the context of offshore wind turbines (OWT) in the Baltic and North Seas. Safety problems in connection with ships can occur during the installation, operation, maintenance and decomposition phases of offshore plants. While these safety problems may involve various scenarios, the physical reasons will have a high level of similarity. A deep understanding of the physical phenomena and the interdisciplinary development of the simulation models in the numerical methods is crucial in generating efficient technical solutions for safety issues without disproportionally increasing project costs or time.

The aim of this research project is to support the wind energy industry as well as national and international organisations by providing numerical methods in an effort to increase ship and offshore plant safety, to reduce the risks for humans, and to decrease the danger for environmental damage.

The research project focuses on computational strategies devoted to the prognosis of accident event sequences and possible consequences from resulting damages. A database for capsizing and sinking accidents with ships will be developed in order to provide test cases for other research projects and to validate numerical methods currently under development. These methods can be applied to analyse accident scenarios and to improve the safety performance of new ships and offshore plant designs. The evaluation of numerical results can also be used to define various categories of preventive and operational measures that can decrease the likelihood of accidents as well as damages and their consequences. Preventive measures would change the design characteristics in such a way that a particular problem would not arise and/or would have less serious consequences. Operational measures would reduce the consequences of an accident. These measures can be implemented during an accident in order to decrease its magnitude and to minimize the consequences; for example, the development of evacuation plans depending on the extent of the damage incurred.

A special feature of the planned numerical investigations is the simultaneous consideration of complex interaction between different phenomena. Examples included refer to the change in hydrostatic behaviour of offshore plants during installation, ship collision, global failure of ship structure due to local failure, and flooding simulation in rough seas under the influence of limited manoeuvring capabilities caused by damages of control devices in heavy weather conditions.

Six work packages (WP) on numerical simulation of dynamic ship and OWT behaviour in critical safety situations are included in the research program. A short summary of the six work packages is given below.

The sinking and capsizing of ships result in the largest number of sea-related fatalities. The offshore segment of OWT installation, maintenance and decomposition is especially high-risk in this regard, because larger structures are handled either by crane operations or by floating procedures, which can potentially lead to capsizing or sinking events. These kinds of events are extremely complex, as the event chain depends on many influences. The computation of such event chains requires a set of highly specialised numerical simulation methods, which, of course, must be adequately validated. This validation, however, can only be carried out on full-scale events, as model tests neglect too many important influences. It is, therefore, the aim of the project to establish a database of selected full-scale capsizing or sinking events which can then be used for the validation of numerical methods. The database will consist of ship and compartment models, major environmental data and a computed event chain that re-simulates the accident. Several steps for each individual accident can be derived from the event chain that can then serve as a validation basis for the other work packages.

Gravity foundations are favourable concepts for future installations of wind turbines located in German offshore fields. The foundation consists of cylindrical- and/or girder-shaped elements made of concrete or preferably steel. Prior to the final assembly of the power plant, the foundations are towed to their location and subsequently lowered to the ground. Filled with dense material, the foundation rests on the seabed. Their design is subjected to cost-related weight restrictions, but not to hydrodynamic aspects. This poses severe challenges to the towing and installation process where hydrodynamic issues are of relevance. The hydrodynamic performance of a foundation during towing and sinking is fairly complex and has not yet been given detailed attention. The complexity occurs when emphasis is given to the interactions of seaways, ground topography, various fluid-phases and free surfaces as well as arbitrary body motions and hydrodynamically interacting floating bodies. Such interactions can only be investigated using numerical methods for viscous multi-phase flows in combination with either meshless or overset-grid techniques.

The main objective of this research is the development of mathematical models for critical offshore operations using realistic wave and wind forces, which are modelled by stochastic diffusion processes. The dynamics of floating and fixed structures and supply vessels under extreme conditions during offshore operations have to be calculated. Furthermore, the influence of strong tidal currents will be analysed. The grounding of jack-up vessels is a very critical operation which involves impacts of jack-up legs into the seabed leading to an instantaneous change of ship stability behaviour, and operation limits of jack-up vessels and floating cranes need to be determined and compared.

The project is funded by

Forschungs- und Wissenschaftsstiftung Hamburg

Prof. Dr.-Ing. Moustafa Abdel-Maksoud
E-Mail: m.abdel-maksoud(at)tuhh(dot)de