Influence of freeboard on ship stability in rough weather: A probabilistic analysis

Slobodni bok morskih brodova određuje se pomoću determinističkih odredbi Međunarodne konvencije o teretnoj vodnoj liniji. U ovom radu, međutim, koristi se probabilistički postupak kako bi se ocenio uticaj slobodnog boka na dinamičku stabilnost broda u oluji. Serijom numeričkih eksperimenata, procenjuje se verovatnoća gubitka stabiliteta malog višenamenskog teretnog broda izloženog istovremenom dejstvu neregularnih bočnih talasa i udara stohastički promenljivog bočnog vetra, pri čemu je visina slobodnog boka sistematski varirana. Uticaj slobodnog boka kvantifikovan je opsegom metacentarskih visina pri kojima se brod može smatrati stabilnim sa probabilističke tačke gledišta. Rad predstavlja korak ka uspostavljanju procedure čijom bi se upotrebom u postupku projektovanja mogla postići bolja ravnoteža između sigurnosti i ekonomičnosti broda. PR Projekat Ministarstva nauke Republike Srbije, br. TR35009. The research presented in the paper was performed within the framework of the project: Development of next generation of safe, efficient, ecological (SE-ECO) ships, executed by Department of Naval Architecture, Faculty of Mechanical Engineering University of Belgrade.Freeboard assignment for seagoing vessels is carried out according to the deterministic provisions of the International Convention on Load Lines. In present investigation, however, an attempt is made to evaluate the influence of freeboard on the dynamic stability of ships in storms using a probabilistic approach. The probability of a stability failure of a small multipurpose cargo ship exposed to irregular beam waves and stochastic beam wind is estimated in a series of numerical experiments, whereby the freeboard of the examined vessel is systematically varied. The effect of freeboard is quantified in terms of a range of metacentric heights ensuring sufficient stability from the probabilistic point of view. The paper presents a step towards a procedure that could enable a better balance of safety and cost-efficiency in the ship design framework

Nonlinear rolling of ships due to wind and waves

Proračun valjanja broda na uzburkanom moru predstavlja jedan od najznačajnijih problema dinamike broda. Uobičajeno je da se problem rešava linearnom jednačinom valjanja broda na talasima, pri čemu se uticaj vetra zanemaruje, a dobijena rešenja važe samo za male uglove nakretanja. Nasuprot tome, istraživanje predstavljeno u ovom radu zasniva se na nelinearnim diferencijalnim jednačinama kretanja broda izloženog stohastičkom dejstvu neregularnih bočnih talasa i udara bočnog vetra koje simuliraju ponašanje broda u realnoj bočnoj oluji. Statističkom analizom zakona valjanja određuje se verovatnoća gubitka stabiliteta broda: prevrtanja, velikih uglova nakretanja ili naplavljivanja kroz nezaštićene otvore. Ovaj postupak nazvan je probabilistička analiza sigurnosti broda u oluji. U radu su predstavljeni matematički modeli sa jednim i sa dva stepena slobode: nezavisne nelinearne jednačine valjanja i spregnute nelinearne nezavisne jednačine valjanja i zanošenja morskih brodova izloženih dejstvu promenljivog bočnog vetra i neregularnih talasa i rečnih brodova pod dejstvom promenljivog bočnog vetra. Svaki model sadrži više izvora nelinearnosti: moment stabiliteta aproksimiran polinomom visokog stepena, nelinearno prigušenje kretanja, moment vetra. Posebna pažnja poklonjena je ispravnom modelovanju haotičnog, udarnog vetra. Probabilistička analiza može se koristiti u raznovrsnim problemima sigurnosti broda. Razvoj novih propisa o stabilitetu broda jedna je od oblasti u kojima ovaj pristup nalazi primenu. U radu je predstavljen koncept mogućih probabilističkih propisa o stabilitetu morskih i rečnih brodova. Probabilistički postupak primenjen je i u istraživanju uzroka pomorskih nesreća (nesreća broda Kugar Ejs, iz 2006. godine). Primena probabilističke analize u postupku projektovanja na osnovu rizika omogućava uvođenje inovativnih tehničkih rešenja nastalih u cilju povećane efikasnosti i sigurnosti. Definicije opsega prihvatljivih metacentarskih visina i optimalne metacentarske visine morskih brodova predstavljaju verovatno najznačajniji doprinos rada projektovanju na osnovu rizika. Osim toga, rezultati analize sigurnosti brodova unutrašnje plovidbe, dobijeni probabilističkim postupkom, iskorišćeni su kako bi se dobile neke smernice za projektovanje rečnih kontejnerskih brodova.Rolling of ships in severe weather is one of the most important problems of ship dynamics, which is typically solved by using a linear differential equation of rolling; the influence of wind is neglected and the obtained solutions are valid for small roll angles only. However, the research presented in this thesis makes use of a very dissimilar approach, based on dynamics of a ship subjected to stochastic action of irregular beam waves and gusting beam wind. Acquired time history is statistically analyzed in order to assess the probability of a ship stability failure: capsize, large amplitude rolling or flooding through unsecured openings. This approach is denoted as the probabilistic analysis of ship safety. The thesis introduces following mathematical models, developed in the course of the research: nonlinear differential equations of roll and coupled nonlinear differential equations of sway and roll of seagoing ships exposed to beam waves and wind gusts and inland vessels subjected to gusting wind. Probabilistic analysis may be used in a variety of ship safety problems. The thesis introduces concepts of possible future probabilistic ship stability regulations, both for the seagoing and inland vessels. The thesis also proposes options for the improvement of the present stability regulations for inland container vessels. The probabilistic approach was used to conduct analysis of one of the most significant maritime accidents in 2006, the car carrier Cougar Ace case. The application of the probabilistic analysis in the risk-based ship design emerges as a promising technique for introduction of innovative solutions that may provide increased efficiency and safety. Probably the most significant contribution of the thesis to the field of risk-based design is the definition of the range of acceptable metacentric heights of seagoing ships. Additionally, the probabilistic analysis was used to develop some guidelines for design of inland container vessels

On safety of inland container vessels designed for different waterways

U prethodnim istraživanjima autori su razvili nov "probabilistički" metod analize sigurnosti rečnih brodova izloženih bočnom olujnom vetru. U ovom radu metod se koristi za analizu ponašanja rečnih kontejnerskih brodova projektovanih za različite plovne puteve. Pokazano je da rizik od zalivanja i naplavljivanja usled valjanja broda izazvanog udarima bočnog vetra raste sa smanjenjem projektovanog gaza broda. Dalje, utvrđeno je da postojeći propisi ne uračunavaju ovaj efekat ispravno. Propisi bolje odgovaraju brodovima s većim gazom (kakvi su npr. brodovi na Rajni), dok su brodovi za pliće plovne puteve (kakav je npr. Dunav) izloženi većem riziku od zalivanja. Konačno, autori predlažu poboljšanje postojećih propisa o sigurnosti rečnih kontejnerskih brodova, kako bi se ispravno uračunali različiti uslovi plovidbe na unutrašnjim plovnim putevima. .In their previous investigation, the authors developed a new, risk-based method for the analysis of inland vessel safety, when exposed to the beam gusting wind. In the present paper, the method is used to analyze the behavior of container vessels designed for different inland waterways. It shows that the risk of flooding due to beam wind increases with the decrease of vessel drought. Furthermore, it proves that the present safety regulations do not account this effect properly. The regulations are more appropriate for the vessels with large droughts (e.g. the Rhine vessels), while the vessels for shallower waterways (as the Danube) are put to the higher risk of the accidents. Finally, the authors propose the improvement of the present safety rules, which would account properly the conditions on the different inland waterways.

Nonlinear rolling of ships due to wind and waves

Proračun valjanja broda na uzburkanom moru predstavlja jedan od najznačajnijih problema dinamike broda. Uobičajeno je da se problem rešava linearnom jednačinom valjanja broda na talasima, pri čemu se uticaj vetra zanemaruje, a dobijena rešenja važe samo za male uglove nakretanja. Nasuprot tome, istraživanje predstavljeno u ovom radu zasniva se na nelinearnim diferencijalnim jednačinama kretanja broda izloženog stohastičkom dejstvu neregularnih bočnih talasa i udara bočnog vetra koje simuliraju ponašanje broda u realnoj bočnoj oluji. Statističkom analizom zakona valjanja određuje se verovatnoća gubitka stabiliteta broda: prevrtanja, velikih uglova nakretanja ili naplavljivanja kroz nezaštićene otvore. Ovaj postupak nazvan je probabilistička analiza sigurnosti broda u oluji. U radu su predstavljeni matematički modeli sa jednim i sa dva stepena slobode: nezavisne nelinearne jednačine valjanja i spregnute nelinearne nezavisne jednačine valjanja i zanošenja morskih brodova izloženih dejstvu promenljivog bočnog vetra i neregularnih talasa i rečnih brodova pod dejstvom promenljivog bočnog vetra. Svaki model sadrži više izvora nelinearnosti: moment stabiliteta aproksimiran polinomom visokog stepena, nelinearno prigušenje kretanja, moment vetra. Posebna pažnja poklonjena je ispravnom modelovanju haotičnog, udarnog vetra. Probabilistička analiza može se koristiti u raznovrsnim problemima sigurnosti broda. Razvoj novih propisa o stabilitetu broda jedna je od oblasti u kojima ovaj pristup nalazi primenu. U radu je predstavljen koncept mogućih probabilističkih propisa o stabilitetu morskih i rečnih brodova. Probabilistički postupak primenjen je i u istraživanju uzroka pomorskih nesreća (nesreća broda Kugar Ejs, iz 2006. godine). Primena probabilističke analize u postupku projektovanja na osnovu rizika omogućava uvođenje inovativnih tehničkih rešenja nastalih u cilju povećane efikasnosti i sigurnosti. Definicije opsega prihvatljivih metacentarskih visina i optimalne metacentarske visine morskih brodova predstavljaju verovatno najznačajniji doprinos rada projektovanju na osnovu rizika. Osim toga, rezultati analize sigurnosti brodova unutrašnje plovidbe, dobijeni probabilističkim postupkom, iskorišćeni su kako bi se dobile neke smernice za projektovanje rečnih kontejnerskih brodova.Rolling of ships in severe weather is one of the most important problems of ship dynamics, which is typically solved by using a linear differential equation of rolling; the influence of wind is neglected and the obtained solutions are valid for small roll angles only. However, the research presented in this thesis makes use of a very dissimilar approach, based on dynamics of a ship subjected to stochastic action of irregular beam waves and gusting beam wind. Acquired time history is statistically analyzed in order to assess the probability of a ship stability failure: capsize, large amplitude rolling or flooding through unsecured openings. This approach is denoted as the probabilistic analysis of ship safety. The thesis introduces following mathematical models, developed in the course of the research: nonlinear differential equations of roll and coupled nonlinear differential equations of sway and roll of seagoing ships exposed to beam waves and wind gusts and inland vessels subjected to gusting wind. Probabilistic analysis may be used in a variety of ship safety problems. The thesis introduces concepts of possible future probabilistic ship stability regulations, both for the seagoing and inland vessels. The thesis also proposes options for the improvement of the present stability regulations for inland container vessels. The probabilistic approach was used to conduct analysis of one of the most significant maritime accidents in 2006, the car carrier Cougar Ace case. The application of the probabilistic analysis in the risk-based ship design emerges as a promising technique for introduction of innovative solutions that may provide increased efficiency and safety. Probably the most significant contribution of the thesis to the field of risk-based design is the definition of the range of acceptable metacentric heights of seagoing ships. Additionally, the probabilistic analysis was used to develop some guidelines for design of inland container vessels

Nonlinear rolling of ships due to wind and waves

Прорачун ваљања брода на узбурканом мору представља један од најзначајнијих проблема динамике брода. Уобичајено је да се проблем решава линеарном једначином ваљања брода на таласима, при чему се утицај ветра занемарује, а добијена решења важе само за мале углове накретања. Насупрот томе, истраживање представљено у овом раду заснива се на нелинеарним диференцијалним једначинама кретања брода изложеног стохастичком дејству нерегуларних бочних таласа и удара бочног ветра које симулирају понашање брода у реалној бочној олуји. Статистичком анализом закона ваљања одређује се вероватноћа губитка стабилитета брода: превртања, великих углова накретања или наплављивања кроз незаштићене отворе. Овај поступак назван је пробабилистичка анализа сигурности брода у олуји. У раду су представљени математички модели са једним и са два степена слободе: независне нелинеарне једначине ваљања и спрегнуте нелинеарне независне једначине ваљања и заношења морских бродова изложених дејству променљивог бочног ветра и нерегуларних таласа и речних бродова под дејством променљивог бочног ветра. Сваки модел садржи више извора нелинеарности: момент стабилитета апроксимиран полиномом високог степена, нелинеарно пригушење кретања, момент ветра. Посебна пажња поклоњена је исправном моделовању хаотичног, ударног ветра. Пробабилистичка анализа може се користити у разноврсним проблемима сигурности брода. Развој нових прописа о стабилитету брода једна је од области у којима овај приступ налази примену. У раду је представљен концепт могућих пробабилистичких прописа о стабилитету морских и речних бродова. Пробабилистички поступак примењен је и у истраживању узрока поморских несрећа (несрећа брода Кугар Ејс, из 2006. године). Примена пробабилистичке анализе у поступку пројектовања на основу ризика омогућава увођење иновативних техничких решења насталих у циљу повећане ефикасности и сигурности. Дефиниције опсега прихватљивих метацентарских висина и оптималне метацентарске висине морских бродова представљају вероватно најзначајнији допринос рада пројектовању на основу ризика. Осим тога, резултати анализе сигурности бродова унутрашње пловидбе, добијени пробабилистичким поступком, искоришћени су како би се добиле неке смернице за пројектовање речних контејнерских бродова.Rolling of ships in severe weather is one of the most important problems of ship dynamics, which is typically solved by using a linear differential equation of rolling; the influence of wind is neglected and the obtained solutions are valid for small roll angles only. However, the research presented in this thesis makes use of a very dissimilar approach, based on dynamics of a ship subjected to stochastic action of irregular beam waves and gusting beam wind. Acquired time history is statistically analyzed in order to assess the probability of a ship stability failure: capsize, large amplitude rolling or flooding through unsecured openings. This approach is denoted as the probabilistic analysis of ship safety. The thesis introduces following mathematical models, developed in the course of the research: nonlinear differential equations of roll and coupled nonlinear differential equations of sway and roll of seagoing ships exposed to beam waves and wind gusts and inland vessels subjected to gusting wind. Probabilistic analysis may be used in a variety of ship safety problems. The thesis introduces concepts of possible future probabilistic ship stability regulations, both for the seagoing and inland vessels. The thesis also proposes options for the improvement of the present stability regulations for inland container vessels. The probabilistic approach was used to conduct analysis of one of the most significant maritime accidents in 2006, the car carrier Cougar Ace case. The application of the probabilistic analysis in the risk-based ship design emerges as a promising technique for introduction of innovative solutions that may provide increased efficiency and safety. Probably the most significant contribution of the thesis to the field of risk-based design is the definition of the range of acceptable metacentric heights of seagoing ships. Additionally, the probabilistic analysis was used to develop some guidelines for design of inland container vessels

On safety of inland container vessels designed for different waterways

U prethodnim istraživanjima autori su razvili nov "probabilistički" metod analize sigurnosti rečnih brodova izloženih bočnom olujnom vetru. U ovom radu metod se koristi za analizu ponašanja rečnih kontejnerskih brodova projektovanih za različite plovne puteve. Pokazano je da rizik od zalivanja i naplavljivanja usled valjanja broda izazvanog udarima bočnog vetra raste sa smanjenjem projektovanog gaza broda. Dalje, utvrđeno je da postojeći propisi ne uračunavaju ovaj efekat ispravno. Propisi bolje odgovaraju brodovima s većim gazom (kakvi su npr. brodovi na Rajni), dok su brodovi za pliće plovne puteve (kakav je npr. Dunav) izloženi većem riziku od zalivanja. Konačno, autori predlažu poboljšanje postojećih propisa o sigurnosti rečnih kontejnerskih brodova, kako bi se ispravno uračunali različiti uslovi plovidbe na unutrašnjim plovnim putevima. .In their previous investigation, the authors developed a new, risk-based method for the analysis of inland vessel safety, when exposed to the beam gusting wind. In the present paper, the method is used to analyze the behavior of container vessels designed for different inland waterways. It shows that the risk of flooding due to beam wind increases with the decrease of vessel drought. Furthermore, it proves that the present safety regulations do not account this effect properly. The regulations are more appropriate for the vessels with large droughts (e.g. the Rhine vessels), while the vessels for shallower waterways (as the Danube) are put to the higher risk of the accidents. Finally, the authors propose the improvement of the present safety rules, which would account properly the conditions on the different inland waterways.

Stability assessment of the river-sea Vessel Train

Vessel Train is a novel waterborne transport concept which implies several digitally connected vessels sailing in a convoy. Vessel Train is consisted of a "lead vessel" and one or more "following vessels". The lead vessel is fully manned, while the following vessels are remotely controlled from the lead vessel via a control system. This could allow the following vessels to sail either with a reduced crew or with a crew off-duty. This paper addresses the stability assessment of the Vessel Train consisted of the river-sea ships, which are subject to operational limitations when sailing in maritime environment. Using the Second Generation Intact Stability Criteria framework, it is investigated how sailing in the Vessel Train would affect the operational limitations of the river-sea ships depending on their design and operational features

On application of standard methods for roll damping prediction to inland vessels

Proper estimation of roll damping moment is of paramount importance for adequate assessment of dynamic stability of ships. However, experimental data on roll damping of inland vessels are scarce and unreliable. Thus the applicability of classic Ikeda's method and its simplified version on typical European inland vessels is investigated, with specific focus on eddy making component. It is found that the simplified Ikeda's method, in comparison to the classic method, may considerably underestimate the eddy making component of damping of full hull forms, or even return negative values, although the block coefficient is within the limits of method applicability. Hence, the paper explores possibilities of adjusting the simplified Ikeda's method in order to improve the observed shortcoming, as well as to extend its application to stability analysis of inland ships

On application of standard methods for roll damping prediction to inland vessels

Proper estimation of roll damping moment is of paramount importance for adequate assessment of dynamic stability of ships. However, experimental data on roll damping of inland vessels are scarce and unreliable. Thus the applicability of classic Ikeda's method and its simplified version on typical European inland vessels is investigated, with specific focus on eddy making component. It is found that the simplified Ikeda's method, in comparison to the classic method, may considerably underestimate the eddy making component of damping of full hull forms, or even return negative values, although the block coefficient is within the limits of method applicability. Hence, the paper explores possibilities of adjusting the simplified Ikeda's method in order to improve the observed shortcoming, as well as to extend its application to stability analysis of inland ships

Natural roll period of river-sea ships

The natural roll period is an important component of stability assessment. The need for development of a proper estimation method is particularly important for river-sea ships, which represent inland vessels intended for operations in maritime environment. The overall goal of this study is to contribute to the development of a suitable method for the natural roll period estimation for river-sea ships. For this purpose, a method based on the linear potential hydrodynamics is applied on a database consisted of 31 river-sea ships. The obtained results are analysed and compared with those calculated using semi-empirical methods, and a practical natural roll period estimation method for river-sea ships is proposed