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Survivability of ships in damaged condition is an issue of paramount importance. Therefore, the regulatory framework is constantly updated, in response to the societal aversion towards accidents with severe impact on human life and on the environment. The introduction of the probabilistic damage stability framework was a major step towards the rationalization of the procedure for the assessment of survivability of ships in damaged condition. Subsequent revisions of SOLAS 2009 included the increase of the safety standard via the new formulations for the R-Index and for the calculation of the probability of survival (s-factor), which however is still performed by a hydrostatic approach. Flooding simulation tools can be used for an in-depth investigation of the transient response of a damaged ship, aiming to identify conditions that could jeopardize her survivability during the initial phases of flooding, or to assist in the improvement of the s-factor formulation. In this work, a newly developed flooding simulation tool, employing the Smoothed Particles Hydrodynamics (SPH) method coupled with a ship motions solver, is presented. The developed methodology predicts the dynamic response of the ship during the flooding process, primarily focusing on the initial stages, when particularly violent flow phenomena may be observed. • Application of SPH in damage stability flooding simulations. • SPH modeling of water inflow (and outflow) in a damaged compartment. • Simulation of box-shaped barge dynamics in symmetric and non-symmetric damages. • Comparison between non-linear dynamic SPH method and quasi-static method. [ABSTRACT FROM AUTHOR]

This paper focuses on the design stage of an electrical energy storage system which is intended to be used to level the power required by ships for propulsion when sailing in irregular seas. Particularly, a preliminary analysis has been carried out aimed at choosing, between two storage technologies namely battery and ultracapacitor, the more adequate storage system for the levelling action with respect to the period of the sea waves. A sizing procedure based upon a Hilbert transform decomposition of load demand is used. More specifically, a specified threshold frequency has been identified such that, power fluctuations related to irregular seas which are characterized by frequencies higher than the specified threshold, indicate the ultracapacitor as the more appropriate device for load levelling. For sizing the storage device, the load demand has been decomposed into two signals without overlapping frequencies. An optimal control strategy is proposed, by exploiting the decomposition of the load power, which allows simulating ultracapacitor real-time operation within the previously determined size constraints. Numerical results have been carried out referring to a Ro-Pax ferry powered by an electrical motor. • Onboard electrical energy storage is used for load levelling. • The use of the storage refers to a ship sailing in irregular sea states. • A threshold frequency is identified for the choice of storage technology. • A proper decomposition of the load request signal is performed. • An optimal control strategy based on an autoregressive model is used. [ABSTRACT FROM AUTHOR]

This paper presents a big data analytics method for the proactive mitigation of grounding risk. The model encompasses the dynamics of ship motion trajectories while accounting for kinematic uncertainties in real operational conditions. The approach combines K-means and DB-SCAN (Density-Based Spatial Clustering of Applications with Noise) big data clustering methods with Principal Component Analysis (PCA) to group environmental factors. A Multiple-Output Gaussian Process Regression (MOGPR) method is consequently used to predict selected ship motion dynamics. Ship sway is defined as the deviation between a ship and her motion trajectory centreline. Surge accelerations are used to idealise the time-varying manoeuvring of ships in various routes. Operational conditions are simulated by Automatic Identification System (AIS), General Bathymetric Chart of the Oceans (GEBCO), and nowcast hydro-meteorological data records. A Dynamic Time Warping (DTW) method is adopted to identify ship centre-line trajectories along selected paths. The machine learning algorithm is applied for ship motion predictions of Ro-Pax ships operating between two ports in the Gulf of Finland. Ship motion dynamics are visualised along the ship's route using a Gaussian Progress Regression (GPR) flow method. Results indicate that the present methodology may assist with predicting the probabilistic distribution of ship dynamics (speed, sway distance, drift angle, and surge accelerations) and grounding risk along selected ship routes. • Machine learning methods can be used to model the kinematics of ship motions. • Results can be used for the predictive mitigation of grounding risk in adverse conditions. • Uncertainties are minimised by application of a five-fold iteration process. • Examples of application are presented for Ro-Pax ships operating in the Gulf of Finland. • The method proposed may be used in intelligent decision support systems. [ABSTRACT FROM AUTHOR]

The dynamics of a damaged ship in waves is a complex phenomenon regarding fluid and structure interactions. Flooded water motions in the damaged compartment could be influenced by decks, obstructions and obstacles in the compartment. This becomes particularly relevant in case of flooding in the engine room that is usually characterized by the presence of large objects such as engines and machineries. In such cases the possibility to better understand the behavior of a damaged ship, influenced by the fluid and structure interactions, could provide novel outcomes and thus enhance the damaged ship safety. In this paper an experimental campaign is conducted on a passenger ferry hull. The effects of obstacles in the engine room compartment, such as decks and engines, on ship roll responses, are studied. Roll decay in still water and steady roll responses in beam regular waves at zero speed are measured for the empty compartment and for the compartment with obstructions, as defined above. The main outcomes from the conducted experiments disclose a mitigation of the resonant behavior of the coupled system, ship with damaged compartment, by having engine shapes occupying the flooded engine room. Moreover it is possible to observe how the resonant frequency of the ship modifies having a more realistic arrangement of damaged compartment and how motion RAOs and roll decay characteristics modify accordingly. [ABSTRACT FROM AUTHOR]

Guaranteeing a sufficient level of safety from the point of view of stability is typically considered to be a matter of design. The overall level of safety of a ship, however, can only be guaranteed when considering passive design measures in conjunction with active operational measures, in a holistic, balanced and cost-effective manner. Time could therefore be coming for systematically considering operational measures as a recognised and normed integral part of a holistic approach to ship safety from the point of view of stability. In this respect, the scope of this paper is to identify open challenges and to provide, in general, food for thought for stimulating a discussion on the topic of operational measures, with specific attention to the damaged ship condition. The aim is to provide ground for further proceeding towards the goal of implementing a virtuous integrated approach to ship stability safety which gives due credit to effective and robust operational risk control options. [ABSTRACT FROM AUTHOR]

Attaining a sufficient level of safety from the point of view of stability is typically considered to be a matter of design. However, it is impossible to ensure safety only by design measures, and operational measures can then represent a complementary tool for efficiently and cost-effectively increasing the overall safety of the vessel. Time could therefore be coming for systematically considering operational measures as a recognised and regulated integral part of a holistic approach to ship safety from the point of view of stability. This paper therefore aims at capturing recent trends of research targeting operational safety measures, with specific attention to the intact ship condition. Open challenges and opportunities for research are identified, potential benefits and shortcomings of different options are discussed, and needs and possibilities for further developments in this area are explored. As an overall goal, this paper aims at providing food for thoughts as well as a ground for further proceeding towards the target of implementing a virtuous integrated approach to intact ship safety, from the point of view of stability, which gives due credit to effective and robust operational risk control options. [ABSTRACT FROM AUTHOR]

Ship motions after damage are difficult to evaluate since they are affected by complex phenomena regarding fluid and structures interactions. The possibility to better understand how ship behavior in damage is influenced by these phenomena is important for improving ship safety, especially for passenger vessel. In this paper an experimental campaign is carried out on a passenger ferry hull, to show the effects of the water dynamics across damage openings on ship motions. Novel aspects of this research include the study of the effects of the damage position on the ship roll response. The study is carried out for still water and for beam regular waves at zero speed. Results from the experiments carried out underline that the roll behavior of a damaged ship is affected by the position of damage opening and not only by its size. Assuming the same final equilibrium conditions after flooding but characterized by different damage openings it is possible to observe how motions RAOs and roll decay characteristics modify according to the opening locations. [ABSTRACT FROM AUTHOR]

In Naval Architecture, the concept of “stability” has a very wide meaning, embracing ship stability fundamentals with ship dynamics and ultimately ship safety. As such, the subject is of paramount importance for its wide implications on design and operation of ships and floating units. Research in this field has, therefore, an important impact on the fleet safety, and the International Conferences on Stability of Ships and Ocean Vehicles (STAB Conferences) and the International Ship Stability Workshops (ISSW) are certainly the venues where expertise and contemporary developments in this specific field tend to be collected and thoroughly debated. With the aim of analysing the current status and possible future perspectives of research in the field of ship stability, dynamics and safety, this paper provides an extensive review of the findings presented at STAB Conferences and ISSW events in the period 2009–2014. The reviewed material is organised according to a set of identified macro-topics of research. On the basis of the reviewed material, consolidated research topics as well as emerging subjects are laid out, and ideas for possible future research are also brought forward. Discussion is also provided regarding the link between research and educational aspects. [ABSTRACT FROM AUTHOR]

The focus of this paper is to update the classic criterion for the determination of the safe keel clearance for ships sailing in restricted waterways. Ship׳s dynamics is taken into account by integrating the notion of the unsteady squat. This paper shows the existence of unstable equilibrium position of the ship during heave motion. Furthermore, it proposes a new mathematical expression to evaluate it as a function of canal and ship parameters. It is shown that this unstable equilibrium position can be considered as a virtual bottom for ship. It should not be reached during ship motion in order to avoid grounding. The importance of this result, confirmed both by an analytical model as well as by a numerical model with Finite Elements Method, lies in the reduction of the safety margin actually allowed for pilots. So this result points out the knowledge of a virtual bottom that could lie above the real nautical bottom. [ABSTRACT FROM AUTHOR]

The ship's dynamic performance (acceleration, turning ability, crash stop) strongly depends on both the propulsion system and its control. The steady-state performance analysis of propulsion systems has shown that onboard energy usage benefits from the employment of simulation techniques. Besides, these techniques provide significant advantages in designing the control logic of sophisticated and complex systems. The present work summarizes the research activities conducted to develop suitable simulation framework for the propulsion systems of naval vessels. Theoretical and mathematical models have thus been developed in this paper to simulate the propulsion of ships. Model-scale experiments and full-scale trials have been used to increase the fidelity of the models. The research outcome is a conceptual framework and a fully validated parametric software representing the vessel's dynamic behaviour and propulsion system in steady-state and abrupt manoeuvres. Thanks to this simulation framework, the propulsion control system could be designed, validated, and calibrated before its installation on board, reducing the commissioning time and minimising the propulsion control system's onboard calibration during the acceptance sea trials. • A new holistic approach for designing complex propulsion plant is shown. • Mathematical models to simulate the dynamics of several ship' subsystems have been conceptualised. • Real-time ship simulation platform has been developed. • Validation by sea trials demonstrates the methodology validity. [ABSTRACT FROM AUTHOR]

Abstract: Oscillations of solid bodies like boats interacting with liquids like water are commonly studied in the marine science community but less so in the broader mechanical sciences. This paper presents a clear and simple exposition of a basic problem in this field, for a general nonspecialist audience. A two dimensional analysis is developed from first principles of small free oscillations of a boat in inviscid water in a finite tank. The water motions obey the Laplace equation. The boat motions are not imposed, but rather found as a part of the overall solution using rigid body dynamics under time-varying pressures on the hull. The importance is clarified of the difference between nominal and displaced configurations of the boat. The equations for water, boat, and boundary conditions are assembled into an eigenvalue problem that determines the oscillation frequencies and mode shapes. The equations are discretized using a boundary element formulation, and the corresponding discrete version of the eigenvalue problem is constructed and solved. The mode shapes thus found include (i) a well defined roll-dominated oscillation, (ii) easily interpretible nearby equilibrium solutions (“rigid body” modes), and (iii) tank-scale sloshing-dominated modes. The roll frequency is found to vary negligibly with tank size, and goes to zero as the boat center of mass is moved to the metacenter. The net added inertia implied by the roll frequency is discussed. Finally, experiments conducted with two boat models, one round bottomed and one square, match roll frequencies predicted by the above calculations. [Copyright &y& Elsevier]

Abstract: Seakeeping qualities are one of the most important aspects for passenger ships, since a collateral effect of seakeeping, the seasickness, can avoid the use of ships and ferries among passengers who can choose a different way of transport. Therefore, it is important for ship designers and ship owners to predict and evaluate the seasickness effects at the design stage. In this paper, a review of the seasickness causes and effects is made, and a mathematical model that includes several human factors is proposed. This model is applicable especially in big passenger ships where different kind of spaces or activities for the passengers can be found inside the ship. The way to present the large amount of information obtained in seakeeping calculations is important, and it is useful to detect the most conflictive parts of the ship''s general arrangement. Calculations for an example ferry are presented. [Copyright &y& Elsevier]

Abstract: The motions of a high speed craft are highly influenced by speed and dynamic forces that begin to be important for high Froude numbers. Classical ship motions theories and some seakeeping programs do not include the effect of these dynamic forces that mainly affect to the damping of vertical motions, and have to be corrected to model high speed crafts. In any other way, the use of these theories or programs would be unrealistic. In this paper, some theories that can be used to predict the seakeeping behaviour of high speed crafts, considering dynamic forces, are studied and validated against seakeeping tests of some fast monohulls models. Tests and results focus on vertical motions in head seas, which are the most severe for these fast crafts. Experimental results of vertical motions are compared with numerical calculations and conclusions about the range of application of the presented theories are obtained. [Copyright &y& Elsevier]

A nonparametric identification method based on ν ('nu')-support vector regression (ν -SVR) is proposed to establish robust models of ship maneuvering motion in an easy-to-operate way. Assisted by the kernel trick, the nonlinear model learns implicitly in high-dimensional feature space without a priori model structure. The ν -SVR controls the sparsity automatically, resulting in high efficiency. To improve the practicality, a parameter tuning scheme combining the hold-out validation and the simulation of dynamic processes is designed to avoid overfitting. Taking the KVLCC2 ship as the study object, the experimental data from the SIMMAN database are used to evaluate the method. The selection and pre-processing of training data are discussed. The identified model shows good generalization performance in the prediction of multiple maneuvers not involved in the training set, verifying the effectiveness of the method. • A novel nonparametric identification scheme is proposed for modeling ship maneuvering motion in an easy-to-operate way. • The method is based on "nu"-SVR that can control the sparsity automatically, resulting in high efficiency. • Assisted by the RBF kernel, the nonlinear model is implicitly learned in high-dimensional feature space. • A parameter tuning scheme combining hold-out validation and simulation of dynamic processes is designed to avoid overfitting. • A systematic evaluation based on real data from the model tests is conducted. [ABSTRACT FROM AUTHOR]

In setting a safe route for a ship, one of the problems to face is represented by excessive roll motions deriving from resonance phenomena in adverse weather conditions. An effective prediction of the roll motion amplification is related to a proper mathematical modelling of the ship motions. Linear models may result to be inadequate in case of large roll motions, where non-linear effects dominate. This paper investigates the roll response resonance in irregular waves. The developed method aims at demonstrating the influence of the non-linear immersed hull geometry, as already acknowledged in literature for regular seas. A 6-Dof non-linear model is applied for generating the time histories of ship roll motions in irregular waves. These are fed into an optimization routine, able of finding the linear system (focusing at its natural roll frequency) that better approximates the non-linear one at a certain mean roll amplitude. The outcomes of this research are meant to support the estimation of roll resonance period accounting for non-linearities of immersed hull geometry, allowing for a more reliable solution of weather routing problems. • Analysis of the non-linearities on roll resonance period in irregular seas. • Procedure for the estimation of resonance period from ship roll time histories. • Roll signal filtering by empirical mode decomposition technique. • Comparison of the estimated roll resonance periods with reference trends. • Study of the sensitivity of roll resonance period to the amplitude spectrum and phase spectrum. [ABSTRACT FROM AUTHOR]

The paper provides an insight into contemporary research on ship stability and identifies the possible directions for future research by reviewing a selection of papers published in STAB 2015, ISSW 2016 & 2017. These works have been organized in different sections, according to the main thematic areas of research, covering intact and damage stability, regulatory issues including probabilistic approaches, advanced numerical methods for ship motion and stability failure prediction including roll damping, operational issues related to ship stability and environmental modelling. Furthermore, the educational potential of STAB/ISSW is exemplified. This review paper is a joint effort within the SRDC (Stability R&D Committee). • The manuscript covers the recent research on the stability of ships and ocean vehicles and categorizes it in a useful manner. • The most relevant references are presented providing an overview and a starting point to research on the ship stability. • The paper exposes the important advances and challenges in the main thematic areas of the research on the stability. • The importance of STAB and ISSW for education in ship stability is highlighted. [ABSTRACT FROM AUTHOR]