Probabilistic approach for collision risk analysis of powered vessel with offshore platforms

The continuous increase in marine traffic and the construction of several offshore installations has led to a serious concern regarding the risks to offshore platforms from ship collisions. The main aim of this study was to carry out a probabilistic collision-risk analysis for offshore platforms exposed to powered collisions with passing vessels using an automatic identification system (AIS) database. The paper first describes the statistical distribution of the ship traffic under study and then considers how this information can be effectively used to estimate collision frequencies and impact energies for various categories of vessel, based on a simple probabilistic method. The effects of various collision mitigation measures, such as the use of enhanced collision alarming devices and the ability of platforms to rotate using thrusters, are considered in the frequency calculations. The risk method presented in this paper can be applied in the design and development phase of both new and existing platforms

Computational models for the structural crashworthiness analysis of a fixed-type offshore platform in collisions with an offshore supply vessel

The aim of this paper was to develop practical modelling techniques for the structural crashworthiness analysis in collisions between a fixed-type offshore platform and an offshore supply vessel (OSV). The computational models used nonlinear finite element method involving large deformations (strains) of both vessel and offshore platform, dynamic effects of material (e.g., strain rate and dynamic fracture strain), and the influence of surrounding waters. The applicability of the modelling techniques was demonstrated with an applied example to collisions between an OSV and a jacket-type offshore platform, where a sensitivity analysis was carried out for different collision parameters (e.g., collision velocities and impact locations). It is concluded that the computational models can ultimately be employed for quantitative risk assessment of fixed-type offshore structures collided with an OSV, which requires to perform the structural crashworthiness analysis

Process, methods and tools for ship damage stability and flooding risk assessment

Development of damage stability as a scientific subject, specifically in damage ship hydrodynamics and, generally, flooding risk assessment, has evolved primarily by inquisitive academics with support by people with vision and passion towards maritime safety enhancement from industry and Government, the latter in the wake of serious accidents. Notwithstanding this, the subject has seen remarkable development in a short period of time in terms of understanding process, and developing methods and tools for practical implementation of such developments. The stage has now been reached where large-scale EC and industry-funded projects are bringing all requisite knowledge and experience together towards implementation by end users with the view to institutionalizing such developments. The paper critically traces and presents key developments starting from basic concepts to a complete framework for performing numerical simulations of ship survivability in operational conditions in the seaway, leading to flooding risk assessment with application potential for new and existing ships with focus on the design phase but with operation potential in ship operation, the latter involving emergencies

A new method for predicting site-specific wave-induced hull girder loads acting on ship-shaped offshore installations in benign conditions

The aim of this study is to develop a new method for predicting wave-induced hull girder loads acting on ship-shaped offshore installations in benign conditions. Unlike in trading ships, current classification society rules provide procedures to define the design values of wave-induced hull girder loads for ship-shaped offshore installations in survival conditions with site-specific metocean data considering that the installations always remain on site. However, ship-shaped offshore units with single-point or turret mooring systems can be disconnected to temporally evacuate from the fields during the severe storm. Also, some areas may be fully benign accommodating spread mooring systems. In these cases, their design wave-induced hull girder loads may be defined in a similar way to those of trading ships but associated with site-specific metocean data. This study proposes a probabilistic approach to determine the site-specific design values of wave-induced loads acting on ship-shaped offshore installations in benign conditions that also accounts for the effects of mooring system type. Six target regions – the North Sea, Gulf of Mexico, western coast of Africa, eastern coast of South America, south eastern coast of Asia and north western coast of Australia – were studied to compare the results corresponding to various sea states. A set of wave scenarios representing all possible wave events for each target region were selected using the Latin hypercube sampling technique. To demonstrate this method, the design values of the wave-induced vertical bending moments were determined for a very large crude oil carrier (VLCC)-class structure with a hypothetical floating, production, storage and offloading (FPSO) unit. The effects of the mooring system type (e.g., single-point mooring versus spread mooring) on the wave-induced hull girder loads of the ship-shaped offshore installations were also evaluated. A case study of the developed method was made by comparison with existing results in the literature and design values provided by classification society rules. The novelty of this study is associated with a new approach that can accurately determine wave-induced hull girder loads of ship-shaped offshore installations in benign conditions, taking into account the effects of site-specific ocean environmental conditions and mooring system type, and its main contribution to industry is to provide a practical technology for the safe and economical design of ship-shaped offshore hull structures

Aligning intact and damage stability in a multi-level-assessment framework

Against the background of using the Index of Subdivision as a reference to address the safety level of ships when damaged, following primarily collision incidents, the EC-funded FLARE project is making inroads towards a direct assessment of flooding risk, which is ship, operating environment, and accident-type specific by addressing all the underlying elements, using a two-level approach; level 1 being semi-empirical with risk models informed through a newly composed accident database and level 2 with flooding risk, in the form of Potential Loss of Life, calculated from first principles, using time-domain flooding simulation tools and evacuation analyses in pertinent emergencies. In addition to addressing all accident types and modes of loss, the FLARE framework and methodology target active and passive measures of risk prevention and control, hence with application potential to both newbuildings and existing ships as well as facilitate real-time flooding risk evaluation for risk monitoring and effective control in emergencies. A key objective of the FLARE project is to provide the technical basis and a proposal for the revision of relevant IMO regulations towards a risk-based approach to contain and control flooding emergencies. The paper provides a complete example of one cruise ship and one RoPax where levels 1 and 2 of flooding risk evaluation are presented and discussed, and a summary of results for a further 8 sample ships from Project FLARE, leading to conclusions on the progress made and recommendations for the way forward

Regulatory gap analysis for risk assessment of ammonia-fuelled ships

The concept and design of ammonia as a marine fuel are still in the embryonic stage which requires an in-depth investigation of its applicability in terms of its safety and potential risks, both in the design and operational phases of a ship's lifecycle. The paper examines and compares the state-of-the-art safety regulations, rules, standards and guidelines relevant to ammonia-fuelled ships available in various classification societies reports and international regulations such as the IGF codes and summarises their gaps and limitations. The paper critically analyses three major hazards namely toxicity, chemical corrosion, fire and explosion and their potential impact on the human, environment and ship in the event of ammonia leakage. Various hazardous areas considered include ammonia leakage at the bunkering station, fuel preparation room, engine room and storage room and its impact on the ship's general arrangement. In addition, this study reviews and discusses various qualitative and quantitative risk assessment methods employed in ships using low-flashpoint fuels and their relevance and potential suitability for ships powered by ammonia. The paper concludes with important findings and recommendations to aid designers, operators, safety experts, and policymakers in the further development of safety within the framework of risk assessment and management. Overall, this study provides valuable insights into the safety considerations of using ammonia as a marine fuel and highlights the need for further research and development in this area

Effect of mooring line layout on the loads of ship-shaped offshore installations

An offshore mooring system stations a ship-shaped offshore installation in place while withstanding incoming loads from the marine environment with short-term and long-term uncertainties. This study aims to develop a novel framework for analysing the loads on floating systems, namely mooring line tension, mooring line fatigue damage, and hull bending moment, as a function of the mooring layout design variables and environmental random variables. The nonlinear influence of those variables is assessed by means of advanced techniques using response charts, response divergence charts, and Sobol's total-effect sensitivity indexes. The developed procedure includes a probabilistic selection of mooring scenarios, station-keeping numerical analyses, and metamodel selection to define input loads. An example of a hypothetical floating production storage and offloading (FPSO) unit with taut legs in the Gulf of Mexico illustrates the procedure. The details of the computations are documented, and the findings show that the mooring line top-tension has a high total-effect index for the wave-induced bending moment and the total mooring line tension, whereas the fatigue damage is mostly affected by the chain diameter. The results of this research offer useful insights to designers and propose the use of a surrogate model to be used in the reliability-based design of mooring systems