Evaluation by a Quantitative Index about Intact Stability Performance in Waves of a Set of Megayacht Units

Intact stability represents one of the most important topics when addressing ship safety, and it is ruled by the IMO Intact Stability code, evaluating ship stability in a calm water scenario. However, the interest in ship stability in waves has increased in recent years and this has led to the formulation of the second generation intact stability criteria (SGISc), finalized at IMO in 2020. In this research, an approach to quantitatively and comprehensively evaluate the ship stability performance in waves has been pursued. A methodology is developed with reference to the SGISc. The intact stability in waves index (ISWI) has been proposed, with the aim to become a complementary tool for designers and shipbuilders in the assessment of stability performance in waves. The ISWI represents a comprehensive stability index, able to capture the stability in waves performance of a vessel. The stability index has been verified on a set of megayacht units and its sensitivity to the wave characteristics has been tested, changing the environmental conditions. The outcomes point to a good agreement between the ISWI and the influence of environmental condition changes on the stability performance

A SGISC-Based Study about operational Profiles of Navy Vessels

In this paper, for selected navy vessels, a study of operational profiles in terms of intact stability performance in waves has been carried out. As an assessment tool, operational measures formulated within the Second Generation Intact Stability Criteria (SGISc) have been considered suitable for the analysis, as further detailed in the relevant guidelines. An application to different naval vessel typologies has been undertaken for the different stability failure modes. Results are analysed also in the view to evaluate how decisions in terms of ship speed may affect also ship stability besides range

Free Surface Hydrodynamics of Submarine Masts Configurations

Sailing at snorkel depth is a necessary but dangerous operating scenario for submarines. The main and straightforward reason is that such an operating condition represents a time of possible vulnerability of the vessel. From a design perspective this condition affects the so-called indiscretion rate, that is exactly the ratio between this time of greater vulnerability and the total operating time. Moreover, when the vessel operates at snorkel depths there are some relevant operations that might be accomplished related to both snorkeling, communications and threats detection. These operations are typically carried out by using a certain number of masts, of slightly different shapes and sizes, that might be used in various configurations. The proposed study aims at providing some insights into the unsteady, turbulent, hydrodynamics of several submarine masts configurations. The analysis is carried out in terms of behaviors of the developed free surface, considering the nonlinear interactions rising among the masts considered. The maximum height and length of the breaking wave generated at the bow of each mast is analyzed. Both the near field and the far field unsteady wave patterns are discussed comparing several configurations and focusing on the interaction effects. The computational study is carried out by using an open-source Smoothed Particle Hydrodynamic solver called DualSPHysics, able to exploit the computational acceleration provided by GP-GPU cards

A Boundary Element Method for Motions and Added Resistance of Ships in Waves

The accurate prediction of ship resistance in waves is nowadays of increased importance since it greatly influences ship performance regarding sustainable service speed and fuel consumption in seaways. Added resistance is considered as the longitudinal component of the second order mean force acting on a ship in waves and can be calculated from the first order ship motions by integrating the corresponding second-order pressure on the body surface. The purpose of this paper is to present a methodology for the prediction of motions and added resistance by a three dimensional Rankine panel method and to discuss and validate its results by comparing them with experimental data. The prediction in the short wave range, where forces due to wave reflection dominate, has been made applying semi-empirical corrections proposed by Kuroda. Experimental data for the heave, pitch, and added resistance of an ITTC benchmark KRISO container ship have been compared with numerical ones, and the applicability of the proposed method is discussed

A New Approach for Human Factor Integration into Ship Design Process

Ship safety and operations are driving issues of ship design and it is well recognized that such performances are strongly related to Human Factor (HF). In the paper a methodology to integrate HF into the ship design process since an early stage is envisaged, with the aim to improve the overall ship resilience when dealing with uncertainty of performance implied by HF element. The System-Theoretic Accident Model Process (STAMP, Leveson 2003) is investigated as a suitable methodology able to provide a significant asset in such perspective. The approach is widely applied in many industrial and transportation fields but in order to better understand its application into the marine context, a specific application will be briefly commented. In the attempt to define a comprehensive procedure, as a preliminary overview, some selected models suitable to classify the human behavior will be considered with specific focus on the reasons for performance degrade and/or uncertainty

Application of 2nd Generation Intact Stability Criteria on Naval Ships

The second generation intact stability criteria are currently under finalization and validation at the IMO. These criteria are organized in five stability failure modes and three levels of vulnerability assessment in each failure mode. Although this new regulation will not apply to naval ships, it is interesting to investigate the behavior of this vessel typology as well, due to their geometry and typical Froude number. This paper deals with of the pure loss of stability and parametric roll phenomena. Level one and level two vulnerability criteria for three naval ships of different size (helicopter carrier, destroyer, offshore patrol vessel) are applied. Results show an overall satisfactory behavior of the three ships investigated by the new regulation, for both failure stability modes

Digital Twin in Naval Environment

A naval vessel is usually engaged in demanding operations that take place in a multifaceted environment. This requires a solid design of the ship as a platform and a prompt decision-making response. To support both the design and operation phases, digital tools and techniques have been widely implemented, along with a significant number of sensors and probes installed onboard. All of these features pave the way for the development of a Digital Twin model, which will be beneficial for the naval sector. In this work, relevant applications and a use case have been presented and discussed, with the goal of highlighting the added value and critical issues in the perspective of gathering them in a Digital Twin environment. The steps required to develop a shared reference digital architecture have been identified, as well as the gaps that need to be filled

An Overview of Warships Damage Data from 1967 to 2013

In the last decade, in the field of merchant ships, a long harmonization process has taken place at IMO, resulting in the enforcement of the so called probabilistic SOLAS2009 for the residual buoyancy and stability assessment of a ship in a damaged condition. In the warships design process, the probabilistic methodology might represent a consistent approach to complement the fundamental overall ship survivability assessment. Nevertheless among the most critical issues, while discussing the possible implementation of this innovative approach, are the lack of a damage database and the significantly different threat typology. In this perspective, significant damage cases in the field of warships are investigated and critically analyzed. The observed time period will regard the period from 1967 (sinking of the Eilat) to 2013

A prediction tool for maintenance costs estimation during the design process of a ship engine room

When dealing with maintenance in ships engine room, the space available around machinery and systems (clearance) plays an important role and may significantly affect the cost of the maintenance intervention. In a first part of a current research study Gualeni et al. (Ship Technol Res, 10.1080/09377255.2021.2020949, 2022), a quantitative relation between the maintenance costs increment due to the clearance reduction is determined, using a Bayesian approach to General Linear Model (GLM), with reference to a single item/component of a larger system Sanchez-Herguedas et al. (Reliability Eng Syst Saf 207: 107394, 2021). This paper represents the second part of the activity and it enforces a systemic view over the whole machinery or system Sanders and Klein (Proc Comput Sci 8:413-419, 2012). The aim is to identify not only the relation between maintenance costs and clearance reduction, but also how the clearance reductions of the single components/items interact and affect the whole system/machinery accessibility and maintainability, meant as relevant emerging properties.The system emerging properties are investigated through the design and application of a Hidden Markov Model Salvatier et al. (Peer J Comput Sci 2: e55, 2016); i.e., the system is modeled by a Markov process with unobservable states. The sequence of states is the maintainability of the system (which incorporates each one of the single components) while the evidence is the increase in cost of maintenance related to the space reduction.By predicting a sequence of states, it is therefore possible to predict the interactions between the system components clearances and determine how the emerging maintainability property is affected by the engine room design