Dracos Vassalos

• University of Strathclyde

Evacuation and abandonment of large passenger ships is still a challenging process and a critical aspect of maritime safety. Technology can offer greater insight into the precursors of evacuation as well as its successful execution. New data-driven techniques and alternative evacuation procedures aided by smart technologies have become readily a...

This study presents a deterministic novel methodology, in the context of shipboard fire safety, able to derive realistic design fire scenarios without the necessity of probabilistic models. Utilisation of thermogravimetric analysis tests and differential scanning calorimetry along with other relevant fire parameters allow for the modelling of th...

The design of a passenger ship is a complex process covering multiple aspects of naval architecture and marine engineering to address performance, functionality safety, and cost as primary objectives. Between them, safety is a key element focusing on the people on board. In this sense, ship safety in the case of flooding events needs proper estimat...

This paper forms part of a wider study in the form of a Formal Safety Assessment of the domestic passenger ships operating in the Philippines, undertaken on behalf of the Philippines Government, and financed by the World Bank and the International Maritime Organisation. The paper focuses on design deficiencies of the domestic RoPax ships, primarily...

Fire models are categorised as zone models and field models. Field models excel in accuracy, whereas zone models outperform field models in terms of computational time and cost efficiency. Through comparison between Consolidated Fire and Smoke Transport (CFAST), representing zone models, and Fire Dynamics Simulator (FDS), a benchmark field model, t...

Estimating shallow water resistance for a vessel is an issue of primary importance for inland water navigation, not only for determining the total power absorbed by the propulsors but also for predicting the far-field wave pattern necessary to assess the wake-washing effect on the shores. Once it is not possible performing model tests for a specifi...

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 con...

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 subject of damaged stability has greatly profited from the development of new tools and techniques in recent history. Specifically, the increased computational power and the probabilistic approach have transformed the subject, increasing accuracy and fidelity, hence allowing for a universal application and the inclusion of the most probable sce...

This paper describes the background and provides the rationale and the framework to embrace the whole spectrum of measures (regulatory, design, operational and emergency response) for improving the damage survivability of existing RoRo passenger vessels. The damage stability workshop elaborated here is the first step of a process initiated by INTER...

Recent developments in damage stability legislation have drawn from ships with simple internal architecture such as RoPax and cargo ships. However, ships with complex internal architecture, such as cruise ships, have been rather neglected. In a regulatory context, cruise ships are currently grouped with RoPax and other passenger ships and this can...

Roll damping is probably the most intriguing of the components of hydrodynamic reaction in ship dynamics. It is also a problematic one—small, nonlinear, difficult to measure or predict and crucially, a key determinant of ship stability. Undoubtedly, some of the problems in computing or predicting roll damping are intrinsic. It can be argued, howeve...

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...

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. Not...

A more contemporary damaged stability assessment of a passenger ship can be addressed with a non-zonal approach, assessing multiple damage types and environmental conditions and employing dynamic analysis for ship survivability. This direct method necessitates the generation and simulation of many damage scenarios. However, the probabilistic models...

Against the background of using the Index of Subdivision as a reference to address the safety level of ships when damaged, following primarily collision accidents, the EC-funded FLARE project is making inroads towards a direct assessment of the flooding risk, which is ship specific and considers the operating conditions and all accident-types leadi...

This work focuses on investigating the correlation between the evolution of liquid bridges and moisture migration in solid bulk cargo liquefaction. We experimentally investigate the stability of liquid bridges in static and dynamic particles. The liquid-holding capacity of static particles is determined and the formation and fracturing of liquid br...

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 damag...

Mitigating flooding risk through passive and active measures is a key step in further increasing the safety of shipping, reducing loss of life and damage to the environment. This paper presents key findings from the EU Horizons 2020 project FLARE (FLooding Accident REsponse) that introduces a novel risk-based methodology beyond the state-of-the-art...

This work focuses on investigating the correlation between the evolution of liquid bridges and moisture migration in solid bulk cargo liquefaction. We experimentally investigate the stability of liquid bridges in static and dynamic particles. The liquid-holding capacity of static particles is determined and the formation and fracturing of liquid br...

This paper focuses on the direct assessment of crashworthiness for ship collisions. A systematic methodology for quantitive risk analysis is being proposed to enhance damage survivability cost-effectively through crashworthy designs. The latter is used as risk control options for prevention or mitigation purposes from flooding risks within the curr...

Historically speaking, the primary driving force behind vessel layout has come in the form of rules and regulations. In such instances, change has occurred slowly, often in a reactive manner in the wake of accidents. The nature of internal layout that is favourable for operation is often in conflict with that for safety and hence objectives pertain...

Ships are designed on the basis of three basic objectives pertaining to ship performance, functionally and safety, all dictated by external shape, internal layout, deadweight, payload, permeable volume and their distributions. All, with the exception of one are calculated to extremely small tolerances and are subjected to rules and regulations that...

Against the background of using the Index of Subdivision as 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 ancient type specific by addressing all the underlying...

The survivability of a passenger ship after an accident is assessed by a probabilistic framework covering hazards like collisions and groundings. Such assessments are a key determinant for the internal ship arrangement and layout, affecting ship design and operation, The framework pertains to static assessment, but it is common to use the same dama...

Featured Application The present study highlights the possible benefits for passenger ship safety by installing passive and active risk control options realised with high-expansion foam. The application of foams with proper permeability characteristics may improve the survivability of a passenger ship after an accident, as highlighted in the provid...

The autonomous ships’ introduction is associated with a number of challenges including the lack of suitable risk acceptance criteria to support the risk assessment process during the initial design phases. The aim of this research is to develop a rational methodology for selecting appropriate risk matrix ratings, which are required to perform the r...

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...

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....

The dynamic response of ships following grounding and collision accidents may be influenced by structural topology as well as operational and environmental conditions. Traditionally, the consequences of such events may be assessed by crude empirical methods or laborious experiments. Computational methods offer a useful alternative in terms of accur...

The resistance of a cargo ship is calculated by numerical towing tank. RANSE multi-phase parallel solver with K-Z SSTturbulent model and VOF formulation is applied. Computational results from double model (without free surface) areused to obtain 1+k in Hughes’ method and those with free surface are analyzed by both Froude and Hughes’ approachesto i...

Effectively addressing safety, security and cyber-security challenges is quintessential for progressing the development of next generation maritime autonomous shipping. This study aims at developing a novel hybrid, semi-structured process for the hazardous scenarios identification and ranking. This method integrates the operational and functional h...

Collision accidents may lead to significant asset damage and human casualties. This paper introduces a direct analysis methodology that makes use of Automatic Identification System (AIS) data to estimate collision probability and generate scenarios for use in ship damage stability assessment. Potential collision scenarios are detected from AIS data...

Damage stability is the “Achilles” heel for all ship types, responsible for 90% of the risk to human lives in maritime accidents of large passenger ships. “Unsinkable” ship is treated as a misnomer in the maritime industry after the Titanic disaster, which marred the idea for ever. However, Titanic was designed using one damage scenario whilst desi...

The paper provides a full description and explanation of the probabilistic method for ship damage stability assessment from its conception to date with focus on the probability of survival (s-factor), explaining pertinent assumptions and limitations and describing its evolution for specific application to passenger ships, using contemporary numeric...

Probabilistic distributions of ship collision and grounding damages is an essential part in the design of crashworthy ships. SOLAS 2020 damage distribution for collision is developed based on all ship types; however, large differences in the ship design, operation and safety regulations, may render such assumptions invalid. Moreover, the number of...

Crashworthiness as one of the risk control options for damage stability has been around since the 1990s, potentially earlier. Yet, it has never managed to gain inroads for routine use in ship design and operation to enhance ship damage stability cost-effectively. A key reason relates to lack of understanding of how the concept can be used in ship d...

Modern optimisation methodologies have revolutionised the engineering sector and pave the way for innovation. In ship design, this has been spearheaded by the introduction of the Holistic Design approach that allows more attributes and performances of the end product to be assessed accurately and concurrently even at the early design phase. In this...

Over the past few decades, there has been an increased presence of large passenger ships, namely RoPAX and Cruise ships. Besides the continuous change in the ship design, regulatory requirements, and operational restrictions accounting for increased trade, movements and density of ship traffic, there exists, increased risk in terms of high conseque...

The maritime industry has been progressing towards autonomous shipping with a main barrier and scepticism being on the safety assurance of the next-generation autonomous ships. This study aims to perform a safety analysis of the autonomous navigation of a Short Sea Shipping vessel. A conceptual system for the investigated of the system is proposed...

This paper introduces a method that makes use of AIS data to estimate collision frequencies and scenarios for use in ship damage stability. Collision scenarios are studied by crash analysis to obtain a probabilistic description of the damage, relevant to the ship studied and an area of operation. Due to the extensive number of collision scenarios t...

SOLAS2020 damage stability regulations are based on probabilistic distributions of damage characteristics that originate from pooled analysis of collision accidents across the total fleet at risk. This paper introduces a method that explicitly considers the influence of collisions-based crashworthiness on ship damage distributions for ultimate use...

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 dam...

Development of damage stability as a scientific subject, specifically in 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. Notwithstandi...

The intricate nature of ship stability has resulted in a slow and discontinuous evolution of the subject and its measurement in Naval Architecture despite two millennia having lapsed since its initial conception and measurement. This has been influenced by two major factors; Naval Architects of the past were primarily "men of practice" and hence no...

The paper provides a full description and explanation of the probabilistic concept of ship damage stability from its conception to date, explaining its assumptions and limitations and describing its evolution for specific application to passenger ships, using contemporary numerical and experimental tools and data. It also provides comparisons in re...

Development of damage stability as a scientific subject, specifically in 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. Notwithstandi...

The safe operation of any vessel is challenged by the constraints posed through design, proper maintenance and operation of the available safety barriers ensuring their effectiveness. This requires a direct linkage between barrier performance and operational risk management accounting for barrier degradation and ensuing corrective actions. This pap...

This study aims at developing a CFD model for large marine two-stroke dual fuel engine with gaseous fuel direct injection at high pressure. For the gaseous fuel, the shock tube theory and the pseudo-diameter concept are employed to model the injection, jet penetration and air entrainment processes, whereas its non-premixed combustion is represented...

As wind farms are moving farther offshore, logistical concepts increasingly include service operation vessels (SOVs) as the prime means of service delivery. However, given the complexity of SOV operations in hostile environments, their safety management is challenging. The objective of this paper is to propose a quantitative, non-probabilistic metr...

Recent advances in the maritime industry include research and development of new sophisticated ships with a number of smart functionalities and enhanced autonomy. The new functions and autonomy levels though come at the cost of increased connectivity. This results in increased ship vulnerability to cyber-attacks, which may lead to financial loss, e...

Dynamics of damaged ships has repelled close attention until the 1980s, following ground shaking accidents (Herald of Free Enterprise, 1987 and Estonia, 1994). Research since then continues unabated, in the knowledge that damage stability is responsible for 90% of deaths in the maritime industry. Notwithstanding this, safety even in the most advanc...

The research presented in this paper emanates from Ph.D. research (Karolius, 2019), directed at the development of a framework where sensors and analytics serve to improve the quality of information in risk assessment and, hence, provide means for a more comprehensive life-cycle flooding risk management framework for large cruise vessels. This pape...

The traditional risk control option adopted in naval architecture to meet safety-related objectives is by regulations, targeting damage limitation, nominally instigated in the wake of maritime accidents claiming heavy loss of life. These primarily concern the introduction of watertight bulkheads, i.e., permanent (passive) reconfiguration of the int...

The evacuation of a ship is the last line of defence against human loses in case of emergencies in extreme fire and flooding casualties. Since the establishment of the International Maritime Organisation (IMO), Maritime Safety is its cornerstone with the Safety of Life at Sea Convention (SOLAS) spearheading its relentless efforts to reduce risks to...

The stringent regulatory framework for the emissions and safety from shipping operations as well as the market pressure to reduce the operational costs has led the cruise ship industry to pursue and investigate alternative solutions for both the new-built and the existing ships by using multi-objective optimisation methods. This study aims at inves...

The intrinsic complexity of the flooding process on ships renders accurate quantification of the flooding risk a highly arduous task, particularly in the context of emergency management. This is especially true for large cruise vessels where convolution stems from innovative designs and complex internal subdivision resulting in a multitude of varia...

The paper presents an overall methodology on how to improve ship survivability using actual damage probabilities based on crashworthiness analysis. The methodology comprises four parts. First, calculate the damage stability/survivability for the struck vessel according to current SOLAS regulations. Second, identify vulnerable zones with high risk u...

Accidents such as the Costa Concordia and more recently the Viking Sky incident cause a societal pressure for improving safety and emergency response in passenger ships. Finding realistic solutions for improvement requires first and foremost an understanding of the current regulatory landscape and the corresponding performance assessment standards....

Abstract. As windfarms are moving further offshore, logistical concepts increasingly include service operation vessels (SOV) as the prime means of service delivery. However, given the complexity of SOV operations in hostile environments, their safety management is challenging. The objective of this paper is to bring awareness of hazards that may ha...

This study aims at the parametric investigation of the gas injection system settings of a large marine two-stroke dual fuel engine by using a developed and customized CFD method in the ANSYS Fluent software. The investigated engine injection system parameters include the gas injection timing, the gas injection duration, the gas injector lateral ang...

As windfarms are moving further offshore, their maintenance has to be supported by the new generation Service Operation Vessels (SOV) with Dynamic Positioning capabilities. For the SOV safe operations it is crucial that any hazardous scenario is properly controlled. Whilst international regulations require the implementation of Failure Modes and Ef...

Recent advances in the maritime industry include the research and development of new sophisticated ships including the autonomous ships. The new autonomy concept though comes at the cost of additional complexity introduced by the number of systems that need to be installed on-board and onshore, the software intensiveness of the complete system, the...

Solid bulk cargo liquefaction has been prominent on the agenda for shipping in recent years, which resulted in a cargo shift and loss of stability, causing the loss of many lives. When the cargo is subject to cyclic forces, such as the rolling movement of the ship, the cargo shift will contribute an extra moment on the ship hold and may result in s...

The primary cause of machinery space fires is cited as the release of flammable oil mist contacting unprotected hot surfaces. With this being common knowledge why do we continue to see this type of incident reoccurring on ships carrying thousands of passengers to precarious destinations? We review regulatory and Class requirements with respect to f...

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 probabil...

In the new era of direct stability assessment (DSA) for ship survivability in intact and damaged conditions, direct and accurate evaluation of the safety level achieved by the design plays a vital role. Two are the most popular methods for DSA namely, time domain numerical simulation (TDNS) and Computational Fluid Dynamics (CFD). Both can be used f...

Stability has been a primary focus of the maritime industry and of immense interest to the IMO from the outset. Despite several attempts to resolve stability-related issues, the problem of stability remains one that has yet to be resolved. Reasons for this, range from the complexity of the problem itself to misconceptions in its very nature, partic...

Recent developments in damage stability legislation have been drawn from ships with simple internal watertight architecture such as RoPax and cargo ships. However, ships with complex internal architecture, such as cruise ships, have been rather neglected. In a regulatory context, cruise ships are currently grouped with RoPax and other passenger shi...

Large cruise vessels have subdivision and compartment connectivity of unique complexity, making predictions of floodwater propagation a particularly challenging task. Evermore so, the plethora of internal openings leads to a large number of opening status combinations, a well-known problem in identifying flooding paths and assessing progressive flo...

The stringent regulatory framework for both emissions and safety as well as the market pressure to reduce the operational costs led the cruise ship industry to pursue alternative solutions. In this respect, multi-objective optimisation methods can be employed for decision-making for identifying optimal solutions with improved efficiency, lower envi...

As the cruise ship industry enjoys continuous growth and penetration into new markets, good safety records must be maintained to achieve business objectives. Unfortunately, serious incidents and accidents reoccur on modern cruise ships and hence a better understanding of why this continues to happen is needed. This paper contributes towards a bette...

Accidents such as the Costa Concordia and more recently the Viking Sky incident cause a societal pressure for improving safety and emergency response in passenger ships. Finding realistic solutions for improvement requires first and foremost an understanding of the current regulatory landscape and the corresponding performance assessment standards....

Finding realistic solutions for improvement of passenger ship evacuation and emergency response requires first and foremost an understanding of the current regulatory landscape and the corresponding performance standards. The first part of this paper is dedicated into providing an as practically possible comprehensive overview of the regulatory fra...

Passenger vessel safety remains one of the most important challenges facing the maritime industry today and flooding remains the highest risk. Consequently, much of what exists within naval architecture discourse revolves around how best to assess vessel damage stability performance and to what level the safety requirement should be set. However, f...

Cruise ship industry is rapidly developing, with both the vessels size and number constantly growing up, which renders ensuring passengers, crew and ship safety a paramount necessity. Collision, grounding and fire are among the most frequent accidents on cruise ships with high consequences. In this study, a hazard analysis of diesel-electric and hy...

The cruise industry represents one of the fastest growing shipping industries, supported by a 62% demand increase for the last decade, and an order-book in excess of $25bn. The sustained growth in demand is complemented by increasing vessel size, which represent investments in the order of billions. Mega-ships serve a specific market segment, with...

A painstaking evolutionary development on damage stability of ships is giving way to unprecedented scientific and technological developments that has raised understanding on the subject as well as the capability to respond to the most demanding societal expectations on the safety of human life and to do so cost-effectively. Within less than half a...

An integrated numerical method, which couples a seakeeping solver and a Navier-Stokes (NS) solver with the volume of fluid (VOF) model, has been developed to study the behavior of a damage ship in waves. The dynamics of water flooding and sloshing in the compartments were calculated by the NS solver, while the hydrodynamic forces induced by the sea...

This paper addresses the survivability assessment of damaged ships with respect to the coupled effects of structural degradation and damage stability in the context of the Safe Return to Port (SRtP) framework for passenger ship safety. The survivability is evaluated in the time domain with varying wave loads. The proposed methodology is demonstrate...

A concept for analytical representation of the capsize rate, a measure directly related to damage ship survivability, has attracted attention ever since the first attempts were made to explain the behaviour of a damaged ship in waves. Attempts in the late 1990s helped to enhance understanding and facilitate characterisation of phenomena pertaining...

The major benefit of switching from the deterministic frameworks for damage stability of the past to the current performance-based state of the art is the ability to have a measurement of the level of survivability of any given design. The required level of survivability is probably the key parameter in any probabilistic framework, in essence answe...

This paper presents results of the physical experiments carried out at the SSRC, aiming at measurements of hydrodynamic reactions on a cylindrical body forced to roll in calm water with an open-to-sea compartment. The research addresses the problem of ship-floodwater interaction—an issue of fundamental importance in predicting roll damping for ship...

Although aviation, nuclear, processing, etc. industries have long ago adopted and established preventative frameworks and procedures to safeguard against unwanted outcomes of daily operations, the maritime industry still places the emphasis on the mitigation of consequences following an accident. Despite the widely expressed opinion that prevention...

The present study focuses on the modelling of a marine dual fuel engine and its control system with an aim to study the engine response at transient conditions and identify and discuss potential safety implications. This investigation is based on an integrated engine model developed in GT-ISE™ software, capable of predicting the steady state perfor...

The vertical centre of gravity (VCG) is paramount in assessing intact and damage stability being the baseline for any condition of loading. It is well known that the Classical method used to calculate the VCG is limited by assuming an unchanged metacentre position and may produce error prone results. An alternative method, namely the Polar method,...

From the perspective of the design-stage evolution of damage stability, it is recognised that only certain combinations of damaged compartments will result in critical flooding cases with high risk of vessel loss. This knowledge may be utilised to identify optimised location of flooding sensors for the purpose of survivability prediction during act...

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 probabil...

The paper describes the background and provides the rationale and the framework to embrace the whole spectrum of measures (design, operational and emergency response) for improving the damage survivability of existing and newbuilding passenger vessels. Damage control, evacuation, Life- Saving Appliances, rescue and crisis management are all topics...

As Cyber-Physical Systems (CPSs) are a class of systems advancing in a number of safety critical application areas, it is crucial to ensure that they operate without causing any harm to people, environment and assets. The complexity of CPSs though, render them vulnerable and accident-prone. In this study, the sources of complexity are meticulously...