The seaway trade market has expanded in the last years and container ship dimensions are constantly increasing for higher cargo capacity. In the early design stage, main dimensions are usually determined based on an existing ship database from which regression formulas are derived. In the present paper, a database of 260 non-sister container ships built from 1979 to 2022, representing 20% of the world fleet, has been considered to derive and compare different types of regressions. Simple regressions have been developed and compared with equivalent formulations available in literature, proving better approximations of the trends. The study has been further extended by multivariable regressions and forest tree algorithms, which allow the use of more than one independent variable and provide a better fitting compared to simple regressions. Forest tree regressions return the highest values of fitting coefficients, but the technique is not of easy application due to the absence of mathematical expressions. The main contribution is the updated set of simple and multivariable regression formulas which have a higher goodness of fit than previous works and can be easily employed by designers in the early design stage and in multi-attribute design procedures.

The traditional way of assessing the operational risk of passenger ships is based on the concept of susceptibility and vulnerability to an accident. Such an approach is mainly used to study the possible risk in given operational scenarios, adopting simplified quasi-static methods to assess the vulnerability of the vessel and using empirical definitions for the damage breach modelling. These methods are not employing first-principles methods for the risk evaluation and are not suitable for the development of onboard real-time risk assessment. To this end, developments in the EU-founded project FLARE led to a multi-level risk assessment framework based on first principle methods, that can be applied as a basis for an onboard risk assessment in real-time. The framework for real-time assessment is based on the development of databases for damage locations and dimensions and survivability. Here, the development of a suitable database of damages is discussed, concerning the employment of direct crash simulations with the software SHARP, aiming at developing a database of collisions suitable for a general operational scenario. The resulting database can be used as a data source for the development of a surrogate model for fast application in real time. This paper addresses the application of the process to a reference cruise vessel.

The increasing demand for offshore operations in deep water implies the necessity to predict station-keeping ability of offshore vessels since the early stages of design. To this end, besides developing sufficiently fast and accurate methodologies for the equilibrium resolution of the forces acting on the ship, it is of utmost importance to estimate, in a reliable way, the external forces acting on the vessel. This work focuses on the current loads, aiming at developing a model for fast current load prediction based on high-fidelity Computational Fluid Dynamics (CFD) computations. Selecting the drill-ships as reference vessel-type for the study, starting from the actual fleet operating worldwide, a systematic series of hulls has been generated varying the main hull-form parameters inside the database, according to a Box-Behnken scheme. CFD calculations based on RANS equations have been performed on the whole ship set, for a set of incidence angle varying from 0 to 180 degrees considering the hull symmetric. As numerical analyses are not suitable for fast calculations the results on the systematic series have been used as input for developing a surrogate model based on Multiple Linear Regressions (MLR). The method allows for scaling the results as a function of the Reynolds number, allowing for general and flexible applicability among different vessel dimensions. The results obtained with the developed model are compared with the conventional current loads estimation methods, and the obtained results are compared on the capability plot, highlighting the higher reliability of the proposed model for early-stage predictions.

Real-time assessment of flooding risk associated with the collision between two ships, requires a fast estimation of damage dimensions and associated survivability. The state-of-the-art frameworks for risk assessment on passenger ships do not consider a direct evaluation of damages through crash simulations but refer to probabilistic considerations, modelling damage characteristics according to statutory marginal distributions of damage breaches too old to be any longer relevant. In any case, such an approach is not possible for the real-time risk assessment process developed in project FLARE, aimed at promoting the employment of first-principles tools for risk evaluation. In this spirit, the present work investigates the possibility of developing a database-oriented damage breach model, which employs direct crash analyses with the super-element code SHARP. However, the sole usage of crash simulations is not suitable for real-time applications. Therefore, starting from the collision simulation database, surrogate models have to be derived for real-time application. In this specific case, three different strategies have been used for the models creation namely: multiple linear regressions, neural networks and decision trees. Here, the strategy to build the database and application on a reference passenger ship is described, highlighting the differences in accuracy and calculation time between the proposed surrogate models.

The focus on digitalisation in manufacturing is spreading to other industry fields, including large and complex objects like ships. Such interest introduces the concept of Digital Twins in supporting designers and operators through the whole ship-life cycle. However, the term Digital Twin is typically abused in the shipping industry, many times erroneously referring to any virtual version of a model-based system as a Digital Twin of the ship. The mutual data exchange between the physical and virtual environment, which is the basis of a true Digital Twin, is mostly missing, confusing a virtual model with a sophisticated living virtual environment. Few reviews are available in the literature for Digital Twins on ships. This systematic review proposes the identification of weaknesses and correlations between current Digital Twin applications in the maritime industry and other industry fields. Furthermore, the methodology applied here may be repeated in future studies to provide a fair and objective overview of the research advancements in the topic. The study highlighted how literature scarcely addresses the design and decommissioning phases, indicating that research should focus on these topics, especially concerning the design of future ships.

Flooding risk identification is a task always treated within a very narrow scope between the life-cycle of a passenger ship. Therefore, different approaches and methods are available for design, operational or onboard applications. Furthermore, the models employed and proposed solutions use simplified methods based on empirical or probabilistic concepts. One of the aims of the EC-founded project FLARE was to promote the use of first principle methods throughout the whole vessel life-cycle, from the design phase up to the onboard risk management. To this end, this work presents the challenges and potential applicability of a real-time flooding risk evaluation methodology for ship-to-ship collisions, based on first-principles calculations. The possibility to perform direct calculations for survivability allows us to define a multi-level approach to flooding risk, separating Level-1 predictions, purely based on semi-empirical models and databases, from Level-2 predictions based on the concept of Potential Loss of Life (PLL). Here, besides a description of the multi-level risk assessment based on PLL, the different tasks of design and operational phases are addressed. Such issues are then linked to the real-time flooding risk evaluation for onboard applications, potentially working for different hazard types but conceptualised for the case of ship-to-ship collisions. The developed method applied to an arbitrary set of models, shows that the approach and tools employed for creating the framework are suitable for a real-time calculation of flooding risk.

The in-force probabilistic framework for passenger ship survivability assessment covers collision hazards. The framework primarily pertains to a static approach. Nonetheless, more complex dynamic analyses usually employ the same damage definitions, adding besides the breach characteristics, the environmental condition selection or, more precisely, the irregular wave environment necessary to simulate the damage scenarios. The traditional dynamic approaches to survivability consider only the significant wave height sampled from statistical formulations, with the wave period deriving from a constant steepness assumption. However, wave height and period influence ship dynamics in waves differently, especially concerning survivability after damage. Therefore, aiming at a direct assessment of ship survivability and the probability of loss of lives determination in realistic operational scenarios, it is essential to properly study the influence of combined variations of wave height and periods and their occurrence. The present study proposes a methodology for dynamic simulations in site-specific conditions derived from the Global Wave Statistics. The study documents the process in two critical collision damages for a reference passenger ship, using wave height and period combinations typical of the main sea areas of interest for passenger ships and performing a sensitivity analysis on the simulations needed to evaluate survivability. This enhanced analysis allows identifying the limiting environmental conditions for the critical damage cases, including the effect of heading variations, determining the ship's survivability to specific damage in an operational area.

Theory and application of damage stability followed over the years two dissociated paths: static assessments and dynamic simulations. The first approach, being easy to apply and understand, has been preferred by ship designers and regulators; the second, more advanced and first-principle oriented, has been mainly reserved for research or high-level consultancy, especially for passenger ships. Nowadays, the availability of numerical flooding simulation tools across the scientific community and calculation power in the industry allows for a possible definitive transition of damage stability assessment towards direct numerical analyses. However, research should softly drive designers towards more advanced processes via a suitable didascalic calculation framework. The multi-level approach pursued in project FLARE is an example of such a transition from static to dynamic damage stability assessment. The present work initially carefully reviews the probabilistic concept of damage stability, critically comparing the prescriptive statistical methods with direct ones and providing insights and guidance on how researchers and designers can reconcile with the original implicit assumption of the probabilistic approach. Secondly, the development of the multi-level framework highlights incongruences concerning modelling of damages between static and dynamic assessments, disfavouring the comprehension of dynamic results to designers. Two detailed examples highlight the differences in dynamic simulation results between different damage breach modelling, leading to completely different flooding paths for the same damage case. Finally, the paper indicates how a compromise between academic approach and application could help designers to start their transition towards direct numerical damage stability analyses.

The Dynamic Positioning system allows a vessel to keep a precise position and heading during stationing operations in a rough sea by using onboard actuators only. During the design phase, it is mandatory to identify the capability of the system actuators to counteract the environmental forces. Conventional predictions are limited to the estimation of a maximum sustainable wind speed on predefined encounter angles by estimating the corresponding wave parameters with questionable standard deterministic correlations. The proposed approach aims at determining the dynamic positioning performances by using site-specific long-term environmental conditions which are modelled with joint distributions of wind and wave parameters. To this end, the operability of the dynamic positioning system is evaluated as a non-deterministic multidimensional Monte Carlo integration process, based on the sampling of environmental joint distributions. For each environmental condition, a quasi-static dynamic positioning analysis is performed solving the equilibrium between external forces and the vessel's actuators through a non-linear thrust allocation algorithm. The proposed methodology is applied to a reference offshore ship in five different operative geographic areas, highlighting the suitability of the calculation methodology for site-specific operability predictions.

The prediction of the statutory attained subdivision index is a challenging issue for the initial design of ships due to the design freedom offered by a probabilistic damage stability assessment. To this end, optimisation techniques integrated with a parametric model of the internal layout may generate a preliminary subdivision design, fulfilling damage stability regulations and cargo volume requirements. The present study explores using a multi-objective constrained optimisation algorithm coupled with a parametric model of a single hold cargo vessel, first investigating two design goal alternatives and secondly performing a global sensitivity analysis on the design variables for the most promising solution. The adoption, in parallel, of state-of-the-art practices shows the validity of the obtained solutions and the time benefits for designers. Nonetheless, the non-linear nature of probabilistic damage stability does not allow for clearly identifying the most impactful parameters on the attained survivability index.

Installation of jacket platforms requires simultaneous and combined operations of multiple assets. When the whole process has to be planned, it is necessary to predict in a fast and reliable way the possible weather limitations that may occur during the operations. The paper will present the major challenges of this unusual and innovative Dynamic Positioning analysis which has been carried out for Ana Jacket installation. The obtained results show that the Dynamic Positioning system of the core vessel in intact configuration is capable to hold the position for the investigated vessels' arrangements and design operative weather conditions. Lifting, upending and installation of Ana Jacket were carried out successfully in 2021.

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.

The damaged stability assessment for a passenger ship is a process requiring the simulation of multiple damage scenarios. Nevertheless, the stochastic nature of the damage stability framework requires the analysis of a statistically significant number of cases. On the other hand, the probability density functions used to estimate the possible damage dimensions and locations along the ship generate many scenarios that are not critical for the ship's survivability, especially for large passenger ships. It is standard to apply empirical rules to restrict the number of damage scenarios, such as critical damages is only above two compartments, considering that damage stability regulations currently in force ensure survivability levels beyond this extent of breaches. However, a rigorous approach is lacking. To this end, in the present work, it is proposed to use more scientific-based methods to identify critical damages. This paper presents three original approaches developed in the context of a multi-level damage stability assessment. The first method relies on preliminary static calculations, the second on the energy absorbed by the ship during an impact, and the third on a purely dynamic approach. Here, the methods are critically compared on two sample passenger ships for collision damages, showing their respective advantages and disadvantages.

Large cruise ships can carry 10 000 persons onboard, and consequently, survivability of the ship in the event of a flooding accident is essential. Many designers are already conducting advanced damage stability analyses beyond the regulatory requirements. With increased computing capacity, survivability analyses, by using time-domain simulation tools, are already commonly applied in the design of new cruise ships. Consequently, it is essential that such tools are properly validated, in terms of ship response and detailed flooding behavior, to assess the capability and applicability of the tools. For this purpose, an international benchmark study on simulation of flooding and motions of damaged cruise ships was conducted within the EU Horizon 2020 project FLARE, using experimental data from new dedicated model tests as a reference. The test cases include transient and progressive flooding, both in calm water and in irregular beam seas. The results indicate that capsize is properly captured by simulation codes, but there are notable differences in the flooding progression and capsize mechanisms, especially when flooding takes place in high waves.