Probabilistic Damage Stability Research Articles

A dynamic simulation tool for ship's response during damage-generated compartment flooding

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.

Criticality analysis of probabilistic damage stability of ships with aggregation operators and additive ratio assessment

Damage stability criteria vary from ship to ship and contain very important factors about the overall stability of the ship. It is necessary to evaluate the modes that would endanger the stability and, therefore, the survival of a ship. It is also significant for ship designers to analyze the criticality of parameters on damage stability. This manuscript aims to rationally evaluate parameters based on the four key factors that are important in probabilistic damage stability (PDS) calculations. For this purpose, a method based on aggregation operators and the additive ratio assessment has been employed. In addition, a sensitivity analysis was conducted to determine how important the weight changes of critical parameters and factors are in prioritizing damage cases to verify the effect of change in expert weighting on outcomes.

Parameter space exploration for the probabilistic damage stability method for dry cargo ships

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.

An analysis of stability requirements for large inland passenger ships

The regulatory approach to stability assessment of seagoing ships has significantly evolved during the last two decades, which resulted in the introduction of the probabilistic damage stability regulations and development of the Second Generation Intact Stability Criteria by the International Maritime Organization. The ship stability regulations for inland vessels, however, have not followed a similar path. This paper investigates the present intact and damage stability requirements intended for large inland passenger ships (LIPS), offers a critical analysis of the present stability regulations, highlights the need for a global harmonization of regulations, and probes into the hierarchy of the stability requirements for LIPS. The investigation is performed on two ships which belong to the classes of the largest inland passenger ships presently used for river cruises in Europe. It was found that damage stability generally dominates the stability requirements of LIPS, and that the stability assessment may substantially depend on the choice of Flag, even if the ships are intended for the same inland waterway. Significant discrepancies in stability assessments performed according to different regulations bring into focus the question of reliability of the present regulatory framework for stability of LIPS.

A framework for onboard assessment and monitoring of flooding risk due to open watertight doors for passenger ships

Post-accident safety of ships is governed by damage stability, affected by watertight subdivisions which limit accidental flooding. This is important for passenger ships with watertight doors (WTDs) often fitted in the bulkheads. Awareness of the ship flooding risk due to open WTDs and the conditions under which the associated risk level changes are prerequisites for proactive risk mitigation.Accident risk is often expressed as a combination of accident likelihood and its consequences. Current solutions for flooding risk mitigation often treat these elements separately, or the adopted metrics are based on quantities not allowing proper active control of risk.In this paper an attempt is made to fill this gap by introducing a novel concept for rapidly assessing the flooding risk onboard passenger ships, accounting for the two dimensions of flooding accidents. The likelihood part is based on the complexity of surrounding traffic, operational conditions, and human reliability assessment. The consequences are based on precalculated probabilistic damage stability results of ship survivability.The presented case studies indicate that active monitoring of flooding risk can increase the crew's situational awareness of the effect of open WTDs on the flooding risk, thus positively influencing the safety culture onboard the ship.

Evaluating Capsize Boundary of Damaged Ro-Ro Ship Using Chaos Theory and Probabilistic Analysis

Instability in intact condition occurs when a ship’s motion changes periodically with time i.e. frequency of motion will match with free- roll frequency or multiples. In case of damage stability, the instability occurs due to flood water sloshing, a series of vibration occur along with free surface effect, which changes the metacentric height of ship. Mathieu's effect is the linear theory behind instability. Probabilistic damage stability analysis is performed in damage cases for the Ro-Ro vessel to understand the most critical loading condition. Phase plots and radial plots are used to find critical stability parameters for ship at intact condition. A new method for modeling the nonlinear dynamic behavior of ship in the chaotic flooded condition is developed and the results indicate that the vessel behaviour of flooded ship is similar to the Duffings oscillation equation and the stability conditions can be captured by this model.

The influence of damage breach sampling process on the direct assessment of ship survivability

The current damage stability regulatory framework for passenger and dry cargo ships allows addressing vessel survivability after flooding due to collisions with probabilistic requirements. This methodology also applies to other hazards responsible for the flooding of a ship such as bottom and side groundings. Traditionally, the application of Monte Carlo sampling of pertinent distributions allows for assessing ship survivability. Such a method introduces randomness in the process, leading to a dispersion of the attained survivability index within multiple sets of generated damages. The present work investigates sampling methods alternative to Monte Carlo, based on Latin Hypercube and Randomised Quasi-Monte Carlo processes. The sampling methods application for collisions, side and bottom groundings on a reference barge available in the literature for benchmark purposes shows that the Randomised Quasi-Monte Carlo method based on multidimensional Sobol sequences grants lower dispersion of the final survivability index data within samples of equivalent size. Finally, the application on a sample cruise ship of Monte Carlo and Randomised Quasi-Monte Carlo methods highlights the possibility to reduce the number of damage breaches necessary to evaluate the survivability index within an engineering confidence interval, thus improving accuracy and efficiency in the amplification of probabilistic damage stability methods by the industry.

Probabilistic Damage Stability for Passenger Ships—The p-Factor Illusion and Reality

The paper complements an earlier publication by the authors addressing the probability of survival in the IMO framework for damage stability assessment, the s-factor. The focus here is on the probability of occurrence of a certain damage scenario (breach), conditional on its dimensions and location (centre and port or starboard side), the p-factor. Pertinent assumptions and limitations are explained, following its evolution for specific application to passenger ships. Attempts to provide analytical descriptions of the damage breach distributions as tetrahedra shapes positioned along the ship length whilst accounting for changes in ship geometry, structural arrangements, and subdivision for consumption by the wider profession has led to misconceptions and misunderstandings of what exactly the p-factor is in the context of probabilistic damage stability calculations. This is evidenced by the fact that the same original damage breach distributions, derived in Project HARDER, based on largely cargo ships with the age spread over the last three decades of the previous century, are still being used today for all ship types, including modern passenger ships. Filling this gap, a new database for passenger ships developed in the EC-funded Project FLARE, is briefly presented, leading to new damage breach distributions specifically for passenger ships. It is believed that this paper will throw considerable light in enhancing understanding on the p-factor, which has been cluttered with unnecessary complexity from the outset.

A comparative method for scaling SOLAS collision damage distributions based on ship crashworthiness – application to probabilistic damage stability analysis of a passenger ship

ABSTRACT SOLAS2020 damage stability regulations are based on probabilistic damage distributions. Those originate from the pooled analysis of collision accidents across a fleet with bias towards cargo ships. This paper introduces a method that accounts for collision-based crashworthiness on ship damage distributions. The method reshapes statistical SOLAS damage distributions for a given ship or structural details for a reference ship section and her reinforced version. Damage reductions may differ depending on ship characteristics and operational scenarios. To mitigate this, a high number of collision scenarios was simulated using the super-element method. It is shown that risk control in terms of damage reduction over the whole range of damages is possible by adding a double hull or by deck reinforcement. Damage reduction is quantified by damage stability analysis of a cruise vessel. It is concluded that installing a double hull on ship vulnerable zones leads to increased A-index.

Stability Assessment of Drill Ship Using Probabilistic Damage Stability Analysis

Drill ship is a ship-shaped structure with a drilling unit at its center and with oil compartments, which is moored and kept in position using anchors. These ships should be capable of working in deep sea for a long time, hence affected by harsh ocean environment. Drill units are said to have greater heave motion, and the height of the derrick influences the vessel’s stability. MARPOL Oil Outflow Analysis is performed for damaged crude oil carriers or tankers and Mobile offshore drilling units (MODU) in damaged condition. In the present study, probabilistic analysis is performed on drill ship to understand its stability behavior under damaged condition. Stability assessments are carried out by considering single and multiple damage locations. Oil outflow analysis is carried out for different damage cases of oil tank. Probabilistic damage assessment is done for load cases up to 50% flooding, to obtain stability charts. These charts will be useful to understand variations in stability parameters under damaged conditions.

Complementing SOLAS damage ship stability framework with a probabilistic description for the extent of collision damage below the waterline

SOLAS probabilistic damage stability regulations assess the ship safety level through the attained subdivision index, which is a probabilistic measure of ship survivability combining, in principle, the probability of flooding of (groups of) compartments and the corresponding conditional survivability (the s-factor). However, the present SOLAS framework does not embed a probabilistic model for the extent of collision damage below the waterline. A “worst-case approach” is therefore used for the s-factor when there are horizontal subdivision boundaries below the waterline. This leads to a systematic underestimation of the ship survivability in presence of horizontal subdivision boundaries below the waterline, and it prevents an effective assessment of the impact of such boundaries. To make a step forward, the paper presents a probabilistic model for the extent of damage below the waterline, derived from statistical analysis of collision accidents data. From this model, a “u-factor” is defined, and it is described how the “u-factor” could be straightforwardly embedded in the SOLAS framework, in combination with “p-factor”, “r-factor” and “v-factor”, to consistently account for horizontal subdivision boundaries below the waterline, thus avoiding the need for using the “worst-case approach”. An example application is reported to quantitatively assess the effect of the “u-factor”.

Impact of drafts on the damage survivability of cruise ships

Abstract The prevailing probabilistic damage stability concept, as outlined within SOLAS 2009 for passenger ships, calculates the Attained Subdivision Index based upon three loading conditions which combine to form a theoretical draft range for a given vessel. To each of these loading conditions a weighting factor is then applied to account for the probability that a vessel will be operating at or near any of these drafts at the time of collision, should one occur. Currently the weighting factors are applied in a ‘one-size-fits-all’ manner, with the same weightings to be applied in the case of cargo and passenger vessels despite the fact that these ship types are known to have very different tendencies when it comes to the nature of their operation. This in turn, calls into question the suitability of these weightings concerning what degree they, in fact, reflect the operational profile of the vessels covered by the standard. With this in mind, the present paper aims to investigate the suitability and accuracy of the currently assumed draft weighting factors with regards to cruise vessels. This study is conducted using operational loading condition data sourced from 18 cruise ships and spanning up to a period of two years in some cases. On the basis of this data, draft probability distributions are derived and new weighting factors are formed specifically pertaining to cruise ships and the nature of their operation. Finally, an assessment is conducted looking into the impact of the newly derived weighting factors on the magnitude of the Attained Subdivision Index and recommendations are made on how best to implement them.

Application Side Casing on Open Deck RoRo to Improve Ship Stability

RoRo is a vessel that can transport passengers, cargo, container and cars. Open Car Deck is favourite RoRo Vessel in developing countries due to its small GT, small tax and spacious car deck, but it has poor survival of stability. Many accident involve Open Car Deck RoRo which cause fatalities and victim. In order to ensure the safety of the ship, IMO had applied intact stability criteria IS Code 2008 which adapted from Rahola’s Research, but since 2008 IMO improved criteria become probabilistic damage stability SOLAS 2009. The RoRo type Open Car Deck has wide Breadth (B), small Draft (D) and small freeboard. It has difficulties to satisfy the ship’s stability criteria. Side Casings which has been applied in some RoRo have be known reduce freeboard or improve ship’s safety. In this paper investigated the effect side casings to survival of intact dan damage ship’s stability. Calculation has been conducted for four ships without, existing and full side casings. The investigation results shows that defect stability of Open Deck RoRo can be reduce with fitting side casing.

Damage Survivability of Passenger Ships—Re-Engineering the Safety Factor

This paper presents a brief summary of the work carried out by SSRC and Brookes Bell Safety at Sea within the EC-funded project GOALDS on the development of a new formulation for assessing the survivability of damaged ships in waves. The proposed formula is meant to be an alternative or replacement to the s-factor in use within the current SOLAS regulations for probabilistic damage stability. The authors briefly discuss concerns related to the current survivability model and present the process of development that led to the re-engineered formulation.

Damage stability and survivability – ‘nailing’ passenger ship safety problems

With artefacts on human endeavours at sea dating as far back as 6500 BC, it is mind boggling to think that it was not until 250 BC when the first recorded steps to establish the foundation of naval architecture, floatability and stability, were made by Archimedes. It is even more astonishing that practical pertinence and function of these two very basic principles remained dormant for nearly two millennia after this, before the first attempts to convey the meaning of stability to men of practice took place in the eighteenth century by Hoste and Bouguer. Pertinent regulations, especially after accidents involving water ingress and flooding (through subdivision and damage stability), were introduced even much later. Notably, the first Merchant Shipping Act of 1854 addressed subdivision and led eventually and after heavy loss of life to the adoption of the first internationally agreed system of subdivision in SOLAS 1929 (Safety of Life at Sea), while the first specific criterion on residual static stability standards was introduced at the 1960 SOLAS Convention. This ‘tortoise’ pace gave way to the steepest learning curve in the history of naval architecture with the introduction of the probabilistic damage stability rules in the late 60s as an alternative to the deterministic requirements. Prompting and motivating the adoption of a more rational approach to damage stability and survivability necessitated the development of appropriate methods, tools and techniques capable of meaningfully addressing the physical phenomena involved. Within 50 years, this new impetus has climaxed to the ‘zero tolerance’ concept of Safe Return to Port, introduced in July 2009, and to an open proclamation by the Secretary of the International Maritime Organization (IMO) that deterministic requirements have no future. More important, the use of a probabilistic framework and of first-principles tools to address ship safety quantitatively and consistently has given rise to aspirations and henceforth capability in identifying and evaluating the key contributors to passenger ship safety. The revelation was plain and clear, namely: damage stability or, more precisely, lack thereof constitutes by far the key risk contributor for passenger ships. Resolving this problem will be equivalent to solving (‘nailing’) passenger ship safety problems. The author, having played a protagonist role in contemporary developments on damage stability and survivability and having been involved closely in implementing such developments to the design of modern mega-ships, will attempt to provide a succinct account of pertinent developments on damage stability and survivability and demonstrate their implications on passenger ship design and operation.

Concurrent Treatment of Safety Aspects in Ship Design and Construction Process

This paper presents a fascinating overview of many concurrent topics having Ship Safety as common denominator. It is a voyage in the recently explored waters of innovation - promoting dissemination of R&D findings, best practices and application techniques successfully implemented by the European Shipbuilding industry - as well as a continuation of the adventure towards uncharted waters of future challenges. From the perspective of the European Shipyards, insight is given into the work in progress on direct assessment of safety and the possible implications on the future regulatory framework.Every year, safety regulations are modified and updated to keep the pace with new technologies and developments in the maritime industry. There is an impressive range of topics marking the evolution of safety aspects in ship design, including, but not limited to: Safe Return to Port, Formal Safety Assessment, Goal-based/Performance-based design, new generation Intact Stability Criteria, Probabilistic Damage Stability implementation, Water on Deck, Collision and Grounding, Time to Flood/Sink/Capsize, Evacuation Analysis, Alternative Design, Innovative Life-Saving Equipment, Navigation and Bridge Equipment, Fire prevention, Accident prevention.Such design and operation developments have been promoted and implemented with the valuable support and contribution of a number of EC-funded projects. Each of these projects somehow paved the way to specific innovation, or offered answers to the primary challenges of the European maritime industry.

On the safety level of the SOLAS 2009 damage stability rules for RoPax vessels

Heading The new probabilistic damage stability rules in SOLAS 2009 and their impact on the safety of the ship subdivi- sion design have been widely discussed. Especially the safety level of RoPax designs are considered for further investigations. This paper describes a methodology to compare the safety provided by different damage stability regulations for a certain ship design. The determination of the dam- age cases probabilities are based on a Monte Carlo si- mulation for the damage distributions. The damage cube itself is modeled by distribution functions retrieved from statistics based on the HARDER project. This gives a very elegant, fast and direct approach of damage calculations. Together with the calculation of the survi- vability of all damage cases, this allows to identify and compare the safety level indices of different damage stability standards. The method has been used in the "EMSA Study on Damage Stability of ROPAX vessels". The theory of the simulation methodology and some extracts of the results of the EMSA study will be presented in the following. It has been shown in the study that for the investigated RoPax designs the new SOLAS 2009 rules are less stringent than the old, deterministic rules according to the Stockholm agreement. This means that especially the old water-on-deck requirement results in more se- vere designs and that the required index of the new damage rules is too low for the investigated RoPax

A Novel Ship Subdivision Method and its Application in Constraint Management of Ship Layout Design

Conventionally, the rooms and spaces of a ship are either modeled as volumetric entities, or with the aid of bulkheads and decks. According to our knowledge, no simple representation exists where both entities can be modeled independently, and where automated conversion from one view (volumetric) to the other (planes) is possible. This paper introduces a simple yet effective approach, where a ship designer can mix the use of volumes and planes in any fashion. Furthermore, this modeling method is applied in a novel tool to manage ship subdivision constraints. As quite a few numerical constraints are known a priori, they can be defined in a list and assigned to specific subdivision elements. Examples are bulkhead locations or required tank volumes or deck areas. A constraint management tool is developed that evaluates the ship layout design during the design process. The designer will be able to modify or add constraints, and the tool will support the designer by managing these constraints during the design process. If the hull form changes, all submitted rules will be updated according to the new main particulars. If one of the constraints does not comply, an adjustment or alternative can be chosen at that moment and the impact of this change is directly visible. The designer can also ask the tool to provide a ship layout design that complies best with the constraints entered. When the Constraint Management program is used, a feasible ship compartment design can be made in a quick manner and the designer is kept from making errors. This means that a correct ship layout model is available on which probabilistic damage stability calculations and weight estimations can be performed in an early stage. This method has been implemented in a computer program, so actual design examples are discussed.

Sensitivity analysis of the probabilistic damage stability regulations for RoPax vessels

In the light of the newly developed harmonised probabilistic damage stability regulations, set to come into force in 2009, this article presents a systematic and thorough analysis of the sensitivity of the Attained Subdivision Index with reference to a wide range of related design parameters. The sensitivity of the probabilistic regulations was investigated for a typical large RoPax vessel, with variation of parameters, such as the number, positioning and local optimisation of transverse bulkheads; the presence and position of longitudinal bulkheads below the main vehicle deck; the presence of side casings; and the height of the main deck and double bottom. The effects of water on deck and of operational parameters (draught, centre of gravity and trim) were also investigated. The results of the study, presented in graphical form, can provide valuable assistance to the designer when determining subdivision characteristics at the very early stage of the design process, resulting in optimal, efficient and safe ships.

A New Method and Program for Probabilistic Damage Stability

Fundamental application problems can be experienced with the current probabilistic damage stability rules. A novel application approach is based on numerical integration of the probability functions.