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1
Sarch, Martin G. "Fin stabilizers as maneuver control surfaces." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03Dec%5FSarch.pdf.
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Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, December 2003.<br>Thesis advisor(s): Fotis A. Papoulias, Charles N. Calvano. Includes bibliographical references (p. 111-112). Also available online.
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Deybach, Frédéric. "Intact stability criteria for naval ships." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/42609.
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Darvazehnoie, Akbar Shahrbaf. "Stability of ships with forward speed." Thesis, University College London (University of London), 2008. http://discovery.ucl.ac.uk/1446111/.
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The initial stability of a ship is currently evaluated by empirical formula based largely on a static approach. Evidently stability is affected by speed that causes variation of pressure distribution on the wetted surface of a ship's hull, and generated waves on the surface of water by the vessel's motion. Forces and moments resulting from bottom pressures, as the speed of the ship changes, are significantly different for the ship at rest and in a seaway. The principal aim of the research is to investigate the effect of variations of forward speed on stability of a ship in calm water. The thesis presents theoretical and experimental approaches of the research. The novelty of the research results leads to the conclusion that although increasing speed may improve the stability of a ship in some cases, it also depends on heeling angle or on any asymmetry of the wetted area of a hull. Taking into account asymmetry effects, unbalanced pressure distribution acting on the wetted surface of the hull, in some cases, hence, decrease of stability is also possible. On a moving, partially immersed body, hydrodynamic and hydrostatic forces predominate. These forces arise owing to interaction between the body's motion and its weight with respect to the surrounding water. In order to calculate these forces, the panel method of Computational Fluid Dynamics (CFD) has been applied to identify the velocity and pressure distribution on the wetted surface of a ship's hull. The mathematical model adopted is based on the source distribution on the ship's hull, known as the Kelvin source. The model for a body travelling with steady forward speed, where its motion does not disturb the free surface, is known as double body theory. For consideration of waves generated by the motion of the ship on the free surface, a three dimensional linearised potential flow solution has been utilised. Comprehensive tests conducted in the UCL towing tank have established a better understanding of the significance of variation of ship's stability associated with forward speed in calm water. It is shown that an accurate judgement regarding the ship's stability cannot be made if only the effect of forward speed, as a single parameter, is considered. The heeling angle is another important parameter that must also be taken into account. The effects of a combination of both variables have been investigated, and are reported herein. The research is presented showing that the applied CFD method may be developed as an alternative method to assess stability of a ship in seaway, but there is a long way for the CFD approach to replace towing tank testing. At present, CFD may be used for consideration as a precursor to improve ship's stability during the design stage, for modification, and before operation. It is hoped that in future the findings of the experimental approach of this form of research could be used as additional guidance to be incorporated within the stability documentation for individual ships at the design stage, and ship trials.
4
Sadat, Hosseini Seyed Hamid Stern Frederick Carrica Pablo M. "CFD prediction of ship capsize parametric rolling, broaching, surf-riding, and periodic motions /." [Iowa City, Iowa] : University of Iowa, 2009. http://ir.uiowa.edu/etd/427.
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Kreider, Marc Alan. "A numerical investigation of the global stability of ship roll : invariant manifolds, Melnikov's method, and transient basins /." Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-03142009-040740/.
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Kapasakis, Panos E. "Stability analysis of ship steering in canals." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1997. http://handle.dtic.mil/100.2/ADA333848.
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Kolthoff, David Lee. "Parametric study of the stability of towed ships." Thesis, Monterey, California. Naval Postgraduate School, 1989. http://hdl.handle.net/10945/26152.
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Allievi, Alejandro. "Experimental and numerical analysis of a fishing vessel motions and stability in a longitudinal seaway." Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/26680.
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Motions and stability of a typical B.C. fishing vessel were experimentally and numerically investigated in a longitudinal seaway condition. The experimental model was self-propelled, radio-controlled and equipped with an on-board data acquisition system. Pitch, roll, yaw, surge, and heave responses to regular waves of predetermined frequencies and amplitudes generated along a 220-ft model basin were obtained. Different displacement conditions and GM configurations were tested.
The numerical model for the dynamic analysis of the fishing vessel motions has been implemented using strip theory. A computer program was developed to study the nonlinear motions of the vessel. The velocity dependent coupling terms, responsible for a major part of the nonlinear behavior, were included. A time dependent component analysis of the roll damping has been performed. Regular linear and nonlinear waves were used.
A parametric study of the fishing vessel stability has been carried out by considering its dynamic response in waves of varying characteristics. Unstable behaviour was found to be closely related to waves of length of similar magnitude to the ship length. The effects of wave amplitude and rudder usage were found to be of capital importance in the capsizing process. Experimental and numerical results showed good agreement.<br>Applied Science, Faculty of<br>Mechanical Engineering, Department of<br>Graduate
9
Nord, Thomas. "Voltage Stability in an Electric Propulsion System for Ships." Thesis, KTH, Elektriska energisystem, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-118932.
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This Master of Science thesis was written based on the shipbuilder Kockums AB feasibility study regarding the development of an All- Electric Ship for the Swedish Navy. The thesis was aiming at addressing voltage stability issues in a dc system fed by PWM rectifiers operating in parallel when supplying constant power loads. A basic computer model was developed for investigating the influence from various parameters on the system. It was shown that the voltage stability is dependent upon the ability to store energy in large capacitors. It was also shown that a voltage droop must be implemented maintaining load sharing within acceptable limits. Different cases of operation were modelled, faults were discussed, and the principal behaviour of the system during a short-circuit was investigated. It was shown that the short-circuit current is much more limited in this type of system in comparison to an ac system. It was concluded that more research and development regarding the components of the system must be performed.
10
Sebastian, James W. "Parametric prediction of the transverse dynamic stability of ships." Monterey, California. Naval Postgraduate School, 1997. http://hdl.handle.net/10945/8800.
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There currently exists no direct method for predicting the righting energy of a ship based on key geometric hull properties. Consequently, naval architects traditionally select hull parameters based on other constraints and merely check the dynamic stability indicators after designing the preliminary body plan. Quantifying these relationships would allow such indicators to be used as design variables in optimizing a hull form. Additionally, the hull form has a considerable impact on ship motion theory and dynamic stability criteria. This thesis suggests possible functional relationships, to predict the residuary stability of a design using basic hull parameters
11
Logsdon, Mary J. "Coupled roll and directional stability characteristics of surface ships." Thesis, Monterey, California. Naval Postgraduate School, 1992. http://hdl.handle.net/10945/23602.
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Wimalsiri, Walallawita K. "Design of ro-ro cargo ships with particular reference to damage survivability." Thesis, University of Newcastle Upon Tyne, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239572.
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Deakins, Eric. "Prediction of the risk of capsize of small ships." Thesis, University of Plymouth, 1988. http://hdl.handle.net/10026.1/2343.
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The lack of a necessary rational framework for assessing ship stability was the main concern of this research. The aim was to develop a rational philosophy and a logical procedure of assessing intact stability in order to ensure a consistent and unified approach to design for operation and for survival. The method uniquely brings together a linearised analysis for assessing a potentially dangerous roll motion with a probabilistic assessment of ship performance in rough seas on a standard test-track. This represents a significant advance on previous research. A novel feature of the analysis was that prediction of the extreme capsize roll motion was not attempted per se. Instead a reduced level of roll response termed "potentially dangerous" roll motion was selected (based on discussions with seagoing personnel) beyond which there was evidence that loss of the vessel is likely. Validation of the linear spectral analysis used in the simulations was performed using full scale trial results of a fisheries protection vessel. Provided that measured values of roll damping coefficient were used, the predicted values of extreme roll closely matched the maximum values experienced on sea trials up to the chosen value of critical roll angle of 30 degrees. Particular attention was paid to the realistic modelling of total system behaviour in rough seas. Families of wave spectra were used to represent the complete range of wave conditions encountered in nature. Avoidance and pacifying seamanship were incorporated based on the results of available trials data and discussions with serving masters. Independent (Bernoulli) trials procedures were used to calculate the cumulative probability of a critical roll motion being exceeded at least once during the vessel's passage through the test-track. The value of critical motion exceedance obtained was 5x10ˉ² for the fisheries protection vessel which has a large metacentic height and is reported to have good seakeeping characteristics.
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Saydan, Deniz. "Damage stability of ships as a safety criterion for optimisation tools." Thesis, University of Southampton, 2006. https://eprints.soton.ac.uk/142587/.
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A literature overview of past optimisation studies revealed that whilst satisfaction of intact stability requirements has been built into existing alternative hull form optimisation packages, seeking improved hydrodynamic hull forms in terms of seakeeping, calm water resistance and added resistance, damage stability is not an automated feature. Within the context of the hydrodynamic hull form optimisation techniques their application to novel hull forms would only permit use of deterministic damage stability analysis and as this is not straight-forward damage is applied after the hull is optimised. The damage must be relevant to ship type and applied in appropriate locations with sensible extents of damage. To fulfil this need both the Marine Accident Investigation Branch (MAIB) damage data base and a damage data base generated by Lutzen (2002) are interrogated and findings are reported. The hydrodynamic analysis of the optimised hull and basis hull for the intact and damage cases is thereafter carried out using a three-dimensional singularity distribution method. The relative vertical motion responses of both intact and damaged hull forms are determined with greater structural cross-coupling than is usually applied in the solution of the equations of ship motions. This has necessitated the development of a novel approach to implement the calculation of the pure and product moment of inertias for the intact and damaged hull forms to facilitate meaningful comparison of intact and damaged ship motions. The processes are equally applicable to any kind of ship.
15
Sánchez, Néstor E. "Stability of nonlinear oscillatory systems with application to ship dynamics." Diss., Virginia Polytechnic Institute and State University, 1989. http://hdl.handle.net/10919/54410.
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A procedure to generate an approximate bifurcation diagram for a single-degree-of-freedom system in a selected parameter space is developed. The procedure is based on the application of Floquet analysis to determine the stability of second-order perturbation approximations of the solutions of the system in the neighborhoods of specific resonances. As a control parameter is varied, a combination of elementary concepts of bifurcation theory and the proposed method are used to detect the first bifurcation from the periodic solutions and hence infer the qualitative changes that the system experiences. Codimension-one bifurcations are investigated in a two-dimensional parameter space composed of the amplitude and frequency of the excitation. The behavior of a softening Duffing oscillator is analyzed under external and parametric excitation. The dynamics of a ship rolling in waves is also considered and three types of excitations are treated: external, parametric, and a combination of both.
Analog- and digital-computer simulations are used to verify the accuracy of the analytical predictions. It is found that the predictions based on the first bifurcation of the analytical solution give a good estimate of the actual behavior of the system. The stability regions of the solutions near each of the resonances display a self-similar structure in the parameter space. The physical implications of these bifurcation patterns are important for the prediction of the capsizing of ships. The dangerous regions of the parameter space where capsizing might occur are identified for a given system.
Capsizing is found to occur via two distinct scenarios: one evolving from a large oscillation through a disappearance of a chaotic attractor (crises) and a second, potentially more dangerous, developing from a small oscillation through a sudden tangent instability. These scenarios agree with previous experimental studies.<br>Ph. D.
16
Fryer, David Kenneth. "The application of random signals to models for evaluating the performance of ships." Thesis, University of Portsmouth, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306154.
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Brumley, Adam Timothy 1972. "Human performance during the evacuation of passenger ships." Monash University, Dept. of Mechanical Engineering, 2001. http://arrow.monash.edu.au/hdl/1959.1/9289.
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Turan, Osman. "Dynamic stability assessment of damaged passenger ships using a time simulation approach." Thesis, University of Strathclyde, 1993. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=21964.
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In the transition from deterministic to probabilistic approaches to assessing the damage survivability of passenger ships this PhD study seeks to draw attention to the key need in regard to loss prevention - the need to address damage survivability by taking full account of vessel dynamics in realistic environments. The thesis begins by critically reviewing the development of subdivision and damage stability requirements, emphasising the inherent weaknesses in the existing approaches to assessing damage survivability. The approach adopted in this thesis is then described. This is based on real time simulation of the dynamic behaviour of the damaged vessel in realistic wind and wave conditions. The mathematical model comprises coupled sway-heave-roll motions in beam seas while taking into consideration progressive flooding as well as water accumulation. A series of comprehensive model experiments have been specifically designed and undertaken to investigate the nature and magnitude of couplings in the above modes of motion in upright and inclined conditions. The damage survivability of the vessel is examined by considering a number of damage scenarios, chosen on the basis of maximising the danger of potential capsize (or sinkage) while taking into account actual accident records. The practical applicability of the proposed procedure is demonstrated by means of a parametric investigation aimed at identifying the effect of a number of key parameters on the damage survivability of a modern car/passenger ferry. These include: wave height; wave length; wind speed; flooding; water accumulation; location and extent of flooding; loading. The results of the investigation are presented and discussed. On the basis of these results boundary stability curves are proposed as a substitute for existing still-water damage stability criteria. These curves involve relationships between design and environmental parameters and inherent stability-related parameters.
19
McBride, William M. "The effect of wing wall geometry and well deck configuration on the stability characteristics of amphibious landing ship dock (LSD) class ships." Thesis, Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/101234.
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Amphibious ships, configured with floodable well decks, present a unique challenge to the Ship Design Team to incorporate maximum troop, cargo and vehicle capacity, along with sufficient well deck size, to facilitate efficient operation of LCAC (Landing Craft Air Cushion) and other amphibious assault craft in support of power projection operations. Analysis of the various LSD 49 Class alternative designs, revealed significant variance in the stability limits for each design. These variations appeared to be directly attributable to wing wall size, as well as to the geometry of the well deck. In order to better understand the effect of these items, and to develop guidelines for future design efforts, this study concentrated on evaluating the stability limitations for various combinations of beam, well deck configuration, and wing wall size using an LSD 49 Class proposed hull form. The results indicated that the most significant parameter affecting the stability of the LSD 49 Class is the height of the well deck above the baseline. The higher the well deck, the smaller the loss of waterplane inertia caused by the entrance of flooding water into the well deck compartment. For lower well decks, the loss of waterplane inertia is more critical at smaller values of beam, but becomes less critical at the upper values of beam considered. In these cases, off-center wing wall flooding becomes more critical, and it is more advantageous to devote larger percentages of beam to the well deck compartment.<br>M.S.
20
Matsubara, Shinsuke Mechanical & Manufacturing Engineering Faculty of Engineering UNSW. "A study of the desingularised boundary-element method and viscous roll damping." Awarded by:University of New South Wales. School of Mechanical and Manufacturing Engineering, 2005. http://handle.unsw.edu.au/1959.4/20566.
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Two major areas were studied in this research to achieve more efficient and optimised method for the prediction of ship motion, and this research has two aims. The first aim was to improve an algorithm of the oscillatory problems for strip theory by means of reducing numerical integration using the desingularised method. A new way of distributing point sources was developed by the author in order to solve the boundary problem on the source distribution. Results showed that desingularsation can be utilised on rounded hull shapes. Although the desingularsation process reduces the computational time, the conventional method is more robust and stable due to the simple source panel distribution. The second aim was an investigation of viscous roll damping of ship motion with the influence of forward velocity, and several numerical simulations were developed in order to support wind-tunnel experimentation. The wind tunnel experimentation was conducted by using a 1.2 m NACA6521 modified cylindrical-bulb model to investigate the viscous effect on the rolling motion of the ship. Since viscous damping was very small under restrictions from the experimental condition, a normal method of collecting data of roll motion, in which a device is physically attached on the bulb model, was not suitable. As a solution, remote sensing was utilised to capture the motion picture by a digital video camera. A visual analysis was then conducted to obtain data of the roll motion of the bulb model inside the wind-tunnel test section. Two different numerical simulations were developed under the hypothesis that the forward velocity influences the boundary layer generation to cause viscous roll damping on the ship model hull. The first numerical simulation uses the energy method to produce damping coefficients, and the second numerical simulation requires solving the motion of equation numerically. It was discovered that the increase of forward velocity results in a linear increase of the viscous damping coefficient. The numerical simulation and experimental data agree closely. Therefore, the theory used to predict the viscous roll damping was shown to be reasonably accurate.
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Filho, Odilon Rodrigues. "Estudo da influência do nível de alagamento sobre a estabilidade dinâmica de pesqueiros." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/3/3135/tde-19092006-165959/.
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Embarcações pesqueiras representam uma parcela expressiva nas estatísticas de acidentes ocorridos no mar. Dentre estas, aquela que se destaca por impor uma perda sensível em vidas humanas é a ocorrência de emborcamentos. Quando tais embarcações passam a ser submetidas a um alagamento intermediário, sua situação de estabilidade pode ser diferente daquela prevista pela Arquitetura Naval Clássica que considera apenas efeitos estáticos. Assim, este trabalho propõe, a partir de duas simples modelagens, caracterizar o comportamento dinâmico do alagamento sob diferentes níveis e sua influência positiva ou negativa sobre a estabilidade da embarcação pesqueira realizando análises sobre o regime transiente e permanente do movimento.<br>When a large compartment of a ship is flooded the water will affect the ship dynamic behaviour, and may have a significant impact on the vessels ability to withstand the action of waves. It is well known that complex dynamics can be associated with the loss of dynamic stability even for an intact ship, and these phenomena have been shown to be particularly relevant for fishing. We investigate here the effect of several levels of partial flooding on the dynamic processes that lead to loss of dynamic stability and capsize in waves. Two mathematical models are used in the present analysis. The first is a simplified model in which the vessel is acted upon by trains of regular beam waves. The free surface in this model is assumed to remain flat. The dynamic interaction between the vessel and the water inside it is modeled in such a way that the ensuing equations are those of a nonlinear inverted double pendulum. Drawing on this observation, an even simpler model was developed based on the idea of an equivalent mechanical pendulum. Since transient capsize in waves is a rapid phenomenon when compared to the flooding of a compartment, the analyses consider the percentage of flooding as a varying parameter.
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Xing, Zhiliang. "Identification of the variance of the wave exciting rolling moment using ship's random response /." Internet access available to MUN users only, 2003. http://collections.mun.ca/u?/theses,170296.
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Bosich, Daniele. "Medium Voltage DC integrated power systems for large all electric ships." Doctoral thesis, Università degli studi di Padova, 2014. http://hdl.handle.net/11577/3423756.
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The Medium Voltage Direct Current (MVDC) distribution represents a promising technology for future shipboard power systems. In such a topic, during the last years, universities and reserch centers have proposed technical solutions to achieve the important targets of MVDC technology, for instance fuel saving, reducing power system weight/space, reconfigurability in case of fault and enhanced power quality. Conversely, the main challenge to face regards voltage control, which has to be capable for guaranteeing the paramount requirement of stability. In regards to this aspect, a possible instability may arise due to the presence of high-bandwidth controlled load converters, modeled as Constant Power Loads (CPLs). Such non-linear loads are seen from the system as negative incremental resistances which are the cause of voltage instability in presence of a perturbation (e.g. load connection, generating system disconnection).
The thesis has been realized in the Laboratory of Grid Connected and Marine Electric Power Generation and Control (EPGC Lab.), at the University of Trieste. The aim is to develop voltage control strategies to solve the CPL issue in a realistic multi-converter MVDC Integrated Power System, which is conveniently designed considering a real cruise line MVAC distribution. In such a system, voltage instability may be engage by different approaches, exploiting plant solutions (addition of dedicated filters, addition of energy storage devices) or control solutions. The latter is followed in this thesis: in this case voltage actuators (DC/DC power converters) are used to compensate for the voltage instability: therefore, on one hand (load side) power converters are responsible for the non-linear loads’ issue but, on the other (generators side), they may be utilized to contribute in its solution, thus ensuring a stable behavior. The stabilizing approach foresees the employment of different control techniques, whose theory is focused in the thesis. Starting from the simplier State Feedback (SF), two techniques are mostly studied in the multi-converter arrangement, i.e the Active Damping (AD) and the Linearization via State Feedback (LSF).
The AD is a control method to transiently increase the filter resistances in order to damp the voltage oscillations: one of the main pros is the simple implementation on digital controllers, whereas the drawback regards its limited stabilizing action. Therefore, strategies based on Active Damping are to be used to stabilize non-critical systems. Conversely, LSF is a well-performing technique to obtain a notable cancellation of the non-linearities related to CPLs, by exploiting the DC/DC converters to apply a proper non-linear control function. Against the notable capability in stabilizing critical systems, great attention is to be paid in control function’s estimation: inaccurate system parameters or errors in controller’ feedbacks may invalidate the LSF approach, determining a partial loop-cancellation, therefore a non-linear resulting power system. Final simulations are aimed in testing AD and LSF, implemented in global and local control strategies: the former strategy has the purpose to solve the instability directly on CPLs, whereas the second one ensures the bus stability.<br>La distribuzione in media tensione continua (Medium Voltage Direct Current, MVDC) rappresenta una tecnologia promettente per i sistemi elettrici navali del futuro. A tal riguardo, negli ultimi anni, università e centri di ricerca hanno proposto soluzioni tecniche tali da raggiungere gli obiettivi propri della tecnologia MVDC: fra gli altri, risparmio di carburante, riduzione del peso/ingombro dell’impianto elettrico, riconfigurabilità a fronte di guasti e miglioramento della power quality. D’altra parte, la più grande sfida da affrontare riguarda la regolazione della tensione che deve risultare in grado di garantire il requisito fondamentale della stabilità. Relativamente a questo aspetto, una possibile instabilità si manifesta in presenza di convertitori di carico a banda elevata, modellizzabili come carichi a potenza costante (Constant Power Loads, CPLs). Tali carichi non-lineari vengono visti dal sistema come resistenze incrementali negative, le quali rappresentano la causa dell’instabilità della tensione a fronte di un disturbo (per esempio connessione di carico, disconnessione di un sistema di genenerazione).
La tesi è stata realizzata presso il Laboratorio Grid Connected and Marine Electric Power Generation and Control (EPGC Lab.), presso l’Università degli Studi di Trieste. Lo scopo è quello di sviluppare strategie per il controllo della tensione in grado di risolvere la questione CPL, considerando un possibile impianto elettrico integrato (multi-convertitore) in MVDC, convenientemente progettato a partire dalla distribuzione reale MVAC di una nave da crociera. Nel sistema visto, l’instabilità di tensione può essere affrontata secondo diversi approcci, sfruttando soluzioni impiantistiche (aggiunta di filtraggio dedicato, aggiunta di energy storage) oppure soluzioni controllistiche. Il secondo approccio è quello seguito nella presente tesi: gli attuatori di tensione (convertitori DC/DC) vengono usati in questo caso per compensare l’instabilità di tensione. Quindi, da una parte (lato carico) i convertitori sono responsabili del problema dei carichi non-lineari, dall’altro (lato generatori) possono essere utilizzati per contribuire alla sua soluzione, garantendo un comportamento stabile. L’approccio stabilizzante previsto prevede l’utilizzo di diverse tecniche di controllo, analizzate nella tesi dal punto di vista teorico. A partire dalla tecnica semplice State Feedback (SF), altre due tecniche sono state studiate per il caso di sistema multi-converter, ovvero l’Active Damping (AD) e il Linearization via State Feedback (LSF).
L’AD è un metodo di controllo per incrementare transitorialmente la resistenza dei filtri, in modo tale da smorzare le oscillazioni di tensione: uno dei principali vantaggi è quello relativo alla semplice ingegnerizzazione su controllori digitali, mentre lo svantaggio riguarda la limitata azione stabilizzante. Pertanto, strategie basate sull’AD devono considerarsi valide per stabilizzare sistemi non critici. D’altra parte, LSF è una tecnica molto valida per ottenere una buona cancellazione delle non-linearità dei CPL, per mezzo dell’azione di convertitori DC/DC in grado di applicare un’opportuna funzione di controllo non-lineare. A fronte di una notevole capacità nello stabilizzare sistemi critici, grande attenzione va posta nella stima della funzione di controllo: conoscenza inaccurata dei parametri o errori nei feedback ai controllori possono invalidare l’approccio LSF, causando una parziale cancellazione, quindi un sistema risultante non-lineare. Le simulazioni finali hanno lo scopo di testare le tecniche AD e LSF, implementate in strategie di controllo locale e globale: la prima strategia ha lo scopo di risolvere l’instabilità direttamente sui CPL, mentre la seconda assicura la stabilità del bus.
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Khaniya, Dina. "Development of three-phase continuation power flow for voltage stability analysis of distribution systems." Master's thesis, Mississippi State : Mississippi State University, 2008. http://library.msstate.edu/etd/show.asp?etd=etd-11142008-101009.
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Gildenhuys, Fourie. "An improved device to measure human response to dorsiflexion and plantar flexion perturbations." Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/96000.
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Thesis (MEng) -- Stellenbosch University, 2014.<br>ENGLISH ABSTRACT: The Dorsiflexometer is a device designed and built for the assessment of a
patient’s balance capabilities. The birth of the Dorsiflexometer is due to a
serious need for physiological balance assessment equipment, capable of conducting
dynamic tests in the clinical setting. This is accomplished by recording
and analysing the patient’s response to sagittal plane perturbations. The Dorsiflexometer
is operated from a computer software interface program. It uses
the measurements from a single force plate to calculate four balance metrics’
characterising a patient’s ability to maintain balance. These balance metrics
include the sway index, equilibrium score, postural stability index and radius
parameter.
A single and a double inverted pendulum model of the human body is derived
to calculate a patient’s centre of mass movement in the sagittal plane
with the measured force plate data and body parameters. Three experiments,
involving 48 subjects, were conducted. The experimental tests proved the
competency of the machine, the accuracy of both inverted pendulum models
and the balance response of seafarers aboard an Antarctic research and supply
vessel during rough sea conditions.
The tests concluded that the inverted pendulum models can be used to calculate
the body centre of mass displacement. The double inverted pendulum
model results are more accurate compared with the single inverted pendulum
model. During rough sea conditions, the body movement and postural
response of seafarers are increased in order to keep themselves upright. The
body is furthermore exposed to a fluctuating ground reaction force which may
lead to the progression of osteoarthritis and musculoskeletal injuries. The Dorsiflexometer
proved to be capable of conducting repeatable assessments and yielding accurate results which can be used to distinguish between balance
capabilities.<br>AFRIKKANSE OPSOMMING: Die Dorsiflexometer is ’n apparaat wat die balansvermoë van pasiënte analiseer.
Die masjien is ontwerp en vervaardig weens die groot behoefte aan
fisiologiese balans assesserings toerusting wat dinamiese toetse in die mediese
sektor kan bepaal. Dit word bereik deur pasiënte se liggaamsreaksie in die
sagittale vlak te meet en te assesseer.
Die Dorsiflexometer is beheerbaar vanaf ’n rekenaar sagteware koppelvlak
program. Die masjien maak gebruik van ’n enkele kragplaat om pasiënte se
balans statistieke te meet. Hierdie balans statistieke wat die pasiënte se balans
vermoë beskryf en karakteriseer behels die sogenaamde: swaai indeks, balans
telling, posturale stabiliteit indeks en die radius parameter.
’n Enkel en dubbel inverse slinger model van die liggaam is afgelei. Hierdie
modelle maak gebruik van ’n pasiënt se kragplaat metings en sy liggaamlike
parameters om die swaartepunt tydens beweging te bereken.
Drie eksperimente, waarin 48 persone betrokke was, is gedoen. Die eksperimente
is gedoen om die apparaat se bevoegdheid te bewys, die akkuraatheid
van altwee inverse slinger modelle te toets en verder die balans van seevaarders
op die Antarktiese navorsings en toevoer skip tydens rowwe see toestande
te analiseer. Die toetse het bewys dat die inverse modelle gebruik kan word
om die liggaam se swaartepunt te bereken. Die dubbel inverse slinger model
resultate is wel akkurater as die enkel slinger model. Daar is bevind dat seevaarders
van meer liggaamsbeweging en posturale reaksies gebruik moet maak om orent te bly tydens rowwe seetoestande. Verder word hul liggame blootgestel
aan ’n wisselende grond reaksie krag wat kan lei tot die ontwikkeling van
osteoarthritis en muskuloskeletale beserings.
Die Dorsiflexometer is bewys as ’n aparaat wat wat akurate resultate lewer
vir herhaalbare assesserings. Dit kan gebruik word om te onderskei tussen verskillende balans vermoëns.
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Babaoglu, Ufuk. "Coupled directional stability of multiple ship formations." Monterey, California: Naval Postgraduate School, 2013. http://hdl.handle.net/10945/34620.
Full textAbstract:
Approved for public release; distribution is unlimited<br>This thesis addresses the problem of coordinated motion control and the stability loss of surface marine vehicles. The mathematical model is based on Nomotos second order model which captures the fundamental dynamics of turning on the horizontal plane with no side slip. A state feedback control law is coupled with a line of sight guidance law to provide path control. A string of three vehicles is considered where each vehicle is using the vehicle in the front as a reference point. The coupled motion stability of the formation is analyzed by linearization. It is shown that under the assumed dynamics, guidance, and control laws, the stability properties of the system decoupled into individual vehicles. This makes it possible to obtain exact analytical results that can be used in design. Parametric runs and sensitivity analysis studies show the effect of main vehicle geometric parameters on formation control and motion stability.
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Gokce, Mersin. "Coupled stability analysis of close proximity ship towing." Thesis, Monterey California. Naval Postgraduate School, 2002. http://hdl.handle.net/10945/6060.
Full textAbstract:
Approved for public release, distribution is unlimited<br>The scope of this thesis is to study the stability of two ships in close proximity towing. Unlike previous studies in the past, the lateral dynamics of both ships are included in the formulation. The equations of motion of the system consist of the sway and yaw motions of the two ships and a control law for the leading ship. An eigenvalue stability analysis of the coupled system confirms the results that are obtained through numerical simulations. It is shown that it is possible for the system to be unstable even through the classical criteria for the towing stability are satisfied. A series of parametric studies is conducted in order to analyze the sensitivity of the system for different towline lengths, tension, and control time constant.
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Grinnaert, François. "Etude et implémentation des critères de seconde génération dans un code de stabilité." Thesis, Brest, 2017. http://www.theses.fr/2017BRES0003/document.
Full textAbstract:
Les critères de stabilité à l’état intact de seconde génération sont en cours de finalisation par l’Organisation Maritime Internationale. Ils doivent compléter les critères actuels en apportant une sécurité accrue dans les vagues. Ils sont organisés en cinq modes de défaillance et trois niveaux d’évaluation dans chaque mode de défaillance. Le premier niveau est basé sur une approche déterministe simplifiée des phénomènes et assure des marges de sécurité importantes. Le second niveau requiert des calculs plus complexes basés sur des considérations hydrostatiques dans les vagues. Il est supposé assurer des marges de sécurité réduites. Le troisième niveau, actuellement en cours de développement, devrait consister en des simulations numériques du comportement du navire sur des états de mer réels réalisés par des instituts spécialisés. Les deux premiers niveaux des modes de défaillance perte pure de stabilité et roulis paramétrique ont été implémentés dans un code de stabilité. Les courbes de KGmax associées à ces critères sont calculées pour une sélection de navires civils et militaires de différents types ayant des comportements connus ou supposés différents vis-à-vis de ces modes de défaillance. Les exigences et la pertinence des critères sont analysées. La seconde vérification du critère de niveau deux en roulis paramétrique est étudiée en détail. Une méthode simplifiée de calcul de l’angle maximum de roulis paramétrique supposant un GZ linéaire est proposée et implémentée dans le critère correspondant<br>The second generation intact stability criteria are currently under finalization by the International Maritime Organization. They are intended to improve the current intact stability rules by adding safety in waves. They are structured in five failure modes and three levels of assessment in each failure mode. The first level is based on a simplified deterministic approach of the phenomena and ensures high safety margins. The second level requires more complex computations based on hydrostatic considerations with regard to static waves and is expected to provide reduced safety margins. The third level, currently under development, would consist of numerical simulations of the ship’s behavior in real sea states performed by specialized institutes. Level-one and level-two criteria of both pure loss of stability and parametric roll failure modes have been implemented in a stability code. The KGmax curves associated with these future criteria are computed for a selection of different ships of different types, both civilian and military, expected or known to have different behaviors with regard to the considered failure modes. The requirement and the relevance of the criteria are analyzed. The second check of parametric roll level-two criterion is thoroughly analyzed. A simplified method providing the maximum parametric roll angle assuming a linear GZ is developed and implemented in the corresponding criterion
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Barrie, D. A. "The influence of ship and environmental parameters on stability assessment." Thesis, University of Strathclyde, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381518.
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Alexander, J. G. M. "Design excitations for dynamic stability assessment based on mapping weighted responses." Thesis, University of Strathclyde, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382277.
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Jahnke, Joshua James. "Hydrostatic and intact stability analysis for a surface ship." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/58868.
Full textAbstract:
Thesis (S.M. in Naval Architecture and Marine Engineering)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (p. 53).<br>Ship's lines are designed such that they are fair. To the naval architect, fairness means that the lines exhibit a continuous second derivative. This is the definition of a spline. Before the advent of digital computers, naval architects checked every line on a lines plan for fairness by bending a thin stick of wood, called a batten, on the line. If the line followed the natural bend of the batten, the line was fair. This phenomenon follows from the beam equation, which shows that the minimum energy in the beam occurs when the beam has a continuous second derivative of position. Hydrostatics lies at the heart of naval architecture. The hydrostatic properties of a hull are determined by the lines and their interpretation using rules of integration. The resulting analysis is presented in the form of graphs, termed the "curves of form" or "displacement and other curves." An intact stability analysis follows naturally from the hydrostatic analysis. Hydrostatics (determination of KM) coupled with a KG value can be used to predict initial stability. This intact stability analysis evaluates the range of stability at both small and large angles of inclination. The responses of the hull to static and dynamic loading situations can be inferred from the curves of form. Their most basic use is to determine the static waterline in various loading scenarios. A more subtle use is to determine the correct placement of the vertical center of gravity to ensure a sea kindly roll period, stability in beam winds, and stability in high speed turns. Various computational tools can be used to compute the hydrostatic and stability properties of a ship. This thesis explores the results from two computer aided design tools used by the U.S. Navy and commercial industry; Advanced Surface Ship and Submarine Evaluation Tool (ASSET) and Program for Operational Ship Salvage Engineering (POSSE).<br>by Joshua James Jahnke.<br>S.M.in Naval Architecture and Marine Engineering
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Story, William Robert. "Application of Lyapunov Exponents to Strange Attractors and Intact & Damaged Ship Stability." Thesis, Virginia Tech, 2009. http://hdl.handle.net/10919/33047.
Full textAbstract:
The threat of capsize in unpredictable seas has been a risk to vessels, sailors, and cargo since the beginning of a seafaring culture. The event is a nonlinear, chaotic phenomenon that is highly sensitive to initial conditions and difficult to repeatedly predict. In extreme sea states most ships depend on an operating envelope, relying on the operatorâ s detailed knowledge of headings and maneuvers to reduce the risk of capsize. While in some cases this mitigates this risk, the nonlinear nature of the event precludes any certainty of dynamic vessel stability.
This research presents the use of Lyapunov exponents, a quantity that measures the rate of trajectory separation in phase space, to predict capsize events for both intact and damaged stability cases. The algorithm searches backwards in ship motion time histories to gather neighboring points for each instant in time, and then calculates the exponent to measure the stretching of nearby orbits. By measuring the periods between exponent maxima, the lead-time between period spike and extreme motion event can be calculated. The neighbor-searching algorithm is also used to predict these events, and in many cases proves to be the superior method for prediction.
In addition to the ship stability research, the Lyapunov exponents are used in conjunction with bifurcation analysis to determine regions of stable behavior in strange attractors when the system parameters are varied. The boundaries of stability are important for algorithm validation, where these transitions between stable and unstable behavior must be accounted for.<br>Master of Science
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Weidle, William Scott. "Influence of Trimaran Geometric Parameters on Intact and Damaged Ship Stability." Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/81101.
Full textAbstract:
Multi-hull vessels have been considered for high-speed, military and commercial applications for decades. More recently the trimaran vessel, with three hulls, has captured interest among naval ship designers and stakeholders. A definition of multi-hulls is introduced as a continuum with monohulls on one end, catamarans on the other, and trimarans in-between. A review of methods to assess intact and damaged stability follows in addition to an overview of current research in the area of dynamic stability for monohulls and trimarans. An investigation of intact stability characteristics for multi-hulls along the continuum is presented and their trends are examined. Next, a series of trimaran configurations are modeled in CAD with subdivision to determine their allowable KG according to USN deterministic criteria and using quasi-static methods. A response surface model was determined for allowable KG as a function of center hull length to beam, side hull beam to draft, transverse position, and displacement for use as a rule of thumb measure and potential optimization constraint.<br>Master of Science
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Cotton, Ben. "The application of nonlinear dynamics to ship roll and capsize." Thesis, University College London (University of London), 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327011.
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Julitz, David. "Numerical analysis of random dynamical systems in the context of ship stability." Universitätsbibliothek Chemnitz, 2004. http://nbn-resolving.de/urn:nbn:de:swb:ch1-200401234.
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We introduce numerical methods for the analysis of random dynamical systems.
The subdivision and the continuation algorithm are powerful tools which will be
demonstrated for a system from ship dynamics. With our software package we are
able to show that the well known safe basin is a moving fractal set. We will also
give a numerical approximation of the attracting invariant set (which contains a
local attractor) and its evolution.
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PETACCO, NICOLA. "Second Generation Intact Stability criteria: Analysis, Implementation and Applications to significant ship typologies." Doctoral thesis, Università degli studi di Genova, 2019. http://hdl.handle.net/11567/945565.
Full textAbstract:
The following doctoral thesis addresses all the stability failures embraced by the
Second-Generation Intact Stability criteria (SGISc). These criteria are under
finalization within the sub-Committee at the International Maritime Organization
(IMO). SGISc are one of the most discussed topic since the session in 2008 and
they drew the attentions not only of the international scientific community but
also of other stakeholders such as designers and shipyards. It is forecast that the
second-generation criteria will be finalized and published in an official document
at IMO by 2020 session. The new regulation has introduced a modern method
to apply the criteria that is called multi-layered approach: it consist of three
different vulnerability level with increasing accuracy and complexity.
One of the aims of this dissertation is to evaluate, both qualitatively and
quantitatively, how the SGISc will affect existing vessels and new projects. To
chase this main object, it has been necessary to develop a set of computational
codes, for each stability failure and vulnerability level, integrated with an existing
in-house software already developed. Before beginning to compile the codes,
the phenomena physics behind each stability failure has been studied together
with a detailed analysis of the regulations texts. Subsequently, a comprehensive
campaign of application on a representative mega yacht unit and on a Ro-Ro pax
ferry has been carried out in order to verify and validate the computational codes
developed. Navy vessel and container-ship have been included in the analysis because
they are deemed to be vulnerable to the phenomena addressed by SGISc.
To identify a relationship between the stability failures and main design parameters,
a set of parent hull variations has been carried out. To better understand
which parameters are more relevant in each specific phenomenon, it has relied
on a useful tool adopted in systems engineering: the Design Structure Matrix
(DSM). Thanks to DSM it has been possible to classify the direction and the
magnitude of relationships among parameters introduced by the SGISc.
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McGowan, Gerald K. "Application of VAX/VMS graphics for solving preliminary ship design problems." Thesis, Monterey, California : Naval Postgraduate School, 1989. http://hdl.handle.net/10945/27529.
Full textAbstract:
Approved for public release; distribution is unlimited<br>The VAX/VMS UIS graphics library routines were used in the creation of a menu driven, interactive program which solves basic preliminary ship design problems. The program uses a menu with active mouse and keyboard to select options, enter data, and control program execution. At present, the program solves transverse and longitudinal static stability problems and predicts the effects of shifting weight in three planes. It also calculates the hydrodynamic derivatives for maneuvering performance and predicts the turning circle characteristics of the ship. Provisions for a hardcopy, detailed report are also included. Space has been allocated to include future program modules or user supplied programs.
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Larson, David F. H. "A framework for ship stability in a seastate using the state-space Fokker-Planck method." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/118706.
Full textAbstract:
Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 91-93).<br>Ships sailing on the ocean have many inherent dangers. One of the most compelling is when they interact with severe stochastic waves, resulting in a loss of stability and adversely affecting their operation. This can result in extreme motions, at the very least making life difficult for crew, to potentially the most catastrophic events capsize, and loss of cargo and life. This compels the need to reliably predict vessel responses to wave interactions in order to aid the decision-making process for operating the ship safely. Despite the advances in computational methods and stochastic hydrodynamic theories to this date, a general framework, capable of handling nonlinear three-dimensional effects, arbitrary wave headings and unconventional hull geometries, is still missing from the engineer's toolbox. This thesis presents a new methodology for modeling the nonlinear responses and stability of a ship in stochastic waves. Invoking the weak-scatterer hypothesis, the radiation and diffraction effects are linearized, computed via a panel method, and cast into a state-space form, aided by applying the ESPRIT algorithm. Strong free surface nonlinearities present in the Froude-Krylov exciting and hydrostatic restoring forces are modeled by Fluid Impulse Theory. In parallel, the ambient seastate is represented by a multidimensional stochastic differential equation (SDE) conforming to a prescribed spectrum. Combining the state-space and seastate models capacitates the study of the nonlinear seakeeping and stability of a ship in a broad range of stationary seastates via stochastic calculus methods. Chief among them is the use of the Fokker-Planck equation (FPE), a deterministic partial differential equation governing the joint probability density function of the states of the SDE. The formulation for a rectangular barge rolling in beam waves is presented, with the approach readily extendable to six-degree-of-freedom responses. By deriving a state-space stochastic differential equation for the states governing the vessel response motions, the joint probability density can be found either by numerical Monte-Carlo simulation of the SDE, or by numerically solving the associated FPE.<br>by David F.H. Larson.<br>S.M.
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Ariffin, Arman. "Etude des critères de seconde génération de la stabilité du navire à l'état intact." Thesis, Brest, 2017. http://www.theses.fr/2017BRES0043/document.
Full textAbstract:
Le Sous-comité de la conception et de la construction navale de l'Organisation maritime internationale (OMI) a entrepris l'élaboration de critères de stabilité intacts de deuxième génération (SGISC). Le SGISC est une règle supplémentaire qui complète les règles actuelles.En outre, ces critères sont structurés en trois niveaux, à savoir le premier niveau, le deuxième niveau et l'évaluation directe. Les procédures d'évaluation directe pour chaque échec de stabilité sont développées avec la technologie de pointe la plus avancée disponible soit par analyse numérique, soit par travail expérimental pour une analyse quantitative. Dans cette thèse, on présente une implémentation des niveaux 1 et 2 du SGISC dans le solveur hydrostatique, une approche expérimentale pour le navire en détresse dans une tempête et des simulations RANS du même critère. En conclusion, il est possible de mettre en oeuvre les critères de stabilité du navire intact de deuxième génération dans le code de stabilité GHS ©, un code couramment utilisé par les industriels dans le domaine. Cinq navires ont été considérés pour vérifier cette mise en oeuvre. Une méthode expérimentale utilisant une grande soufflerie et une méthode de calcul CFD simplifiée ont été appliquées sur deux modèles. Dans les deux cas, les résultats montrent que l'angle de roulis maximal atteint par les deux navires étudiés est inférieur à celui donné par le calcul réglementaire. La méthode expérimentale est certainement plus proche de la réalité et le calcul CFD reste conservateur sans être aussi contraignant que la réglementation. En conclusion les méthodes expérimentale et numérique développées et utilisées dans ce travail de thèse peuvent être proposées pour l’évaluation directe du critère<br>The Sub-Committee of Ship Design and Construction of International Maritime Organisation (IMO) has undertaken the development of Second Generation Intact Stability Criteria (SGISC). The GISC is an additional rule that complement present rules. Five failure modes will be address in SGISC are excessive roll in dead ship condition, pure loss of stability, broaching, parametric roll, and excessive acceleration. Moreover, these criteria are structured in three levels namely, first level, second level and direct assessment. Direct assessment procedures for every stability failure are developed with the most advanced state-of-the art technology available either by numerical analysis or experimental work for quantitative analysis. In this thesis, implementations of Level 1 and Level 2 of the SGISC in the hydrostatic solver, experimental approached for dead ship condition and RANS simulation are presented.In conclusion, it was possible to implement the stability criteria of the intact second-generation vessel in the GHS © code of stability, a code commonly used by industrialists in the field. Five vessels were considered to verify this implementation. An experimental wind tunnel method and a simplified CFD calculation method were used on two different models. In both cases, the results show that the maximum roll angle reached by the two vessels studied is lower than the one given by the regulatory calculation. The experimental method is certainly closer to reality and the calculation CFD remains conservative without being as binding as the regulation.Therefore, the two approaches, numerical and experimental can be proposed to be used for Direct Assessment of the criterion
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Gao, Qiuxin. "The effect of free surface on classical ship hydrodynamics using RANSE : resistance, manoeuvring, propulsion, seakeeping and stability." Thesis, University of Strathclyde, 2012. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=16924.
Full textAbstract:
In this research, the Computational Fluid Dynamics (CFD) approach, based on the solution of the Reynolds Averaged Navier-Stokes (RANS) equations is used to study the classical ship hydrodynamic problems, all being affected markedly by the presence of free-surface, namely: ship resistance, propulsion, manoeuvring, seakeeping and stability, the latter focusing on flooding of a damaged ship. In this respect, this thesis represents a marked deviation from classical approaches and a unique contribution to ship dynamics and hydrodynamics. The RANS equations with SST K-w two-equation turbulence model and Volume Of Fluid (VOF) formulation were discretised by the finite volume (FV) method and the pressure-coupled governing equations were solved by the SIMPLE algorithm. The geometric reconstruction algorithm was adopted to locate transient free surfaces. The second order upwinding scheme was used for the discretisation of the convection flux and Multi-grid Acceleration was applied to improve convergence. In addressing ship resistance, grid sensitivity studies were carried out according to the “ITTC guideline of quality” manual. The computed results were verified and validated against available model test data. Additionally, the results of the effects of the turbulence models were investigated by comparing turbulence quantities predicted by SST K-w and RSM. In addressing ship propulsion, the propeller was modelled as an actuator disk of equivalent thrust and torque. Distributions of the body force were compared with results from a parametric study and the implementation of the body force approach was validated by model test data. In addressing ship manoeuvring, numerical PMM simulations of pure sway and yaw motions were performed. The numerical results were benchmarked against physical experiments. The computed hydrodynamic derivatives were compared with empirical formulae and subsequently implemented in manoeuvring simulations. In addressing seakeeping, incident waves were generated by a numerical wave maker and the computed results for wave diffraction were validated against physical measurements. Furthermore, RANS simulation for roll decay was undertaken and validated against results from model tests. Finally, a numerical roll tank was established to study the hydrodynamic coefficients of the roll motion in intact and damaged conditions and the corresponding results were compared with available model test data. In conclusion, systematic studies and ensuing results from numerical simulations of classical ship hydrodynamic problems using RANS demonstrated beyond doubt that CFD could and should play an important role in the design, analysis and evaluation of ship hydrodynamic performance. In addition, they provide unshakeable evidence of the level of capability to make the next important step: rendering CFD a routine "tool" in ship dynamics and hydrodynamics.
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Anggoro, Suryo Mechanical & Manufacturing Engineering Faculty of Engineering UNSW. "Analysis of the intact stability of Indonesian small open-deck roll-on/roll-off passenger ferries." Publisher:University of New South Wales. Mechanical & Manufacturing Engineering, 2008. http://handle.unsw.edu.au/1959.4/44412.
Full textAbstract:
Small open-deck roll-on/roll-off passenger ferries in Indonesia have a poor safety record. The Indonesian Government is interested in means by which the safety of these vessels can be improved, and this was the main catalyst for commencing research in this area. Any solution should be capable of being retrofitted to both existing vessels and new designs to improve their stability and, hence, their safety. The research therefore focused on the intact stability of the bare hulls, and with addition of side casings, for the vessels for which data was made available by the Indonesian Government. The research covered both quasi-static analysis, based on the objective of meeting the IMO intact stability criteria, and a dynamic approach using time-domain simulation in regular beam waves. A parametric study of the stability parameters of the twenty vessels demonstrated that, without the presence of side casings, the vessels had difficulties in complying with the IMO intact stability criteria. The problems were solved by introducing side casings (watertight spaces above the vehicle deck) either inboard of the vessels side-shell plating, or partially inboard and partially outboard of the side shell. The minimum extent (breadth) of side casings required was determined by iteration on each of the twenty vessels, incorporating variations in the height of the centre of gravity and loading conditions. The implementation of the minimum side casings showed that each vessel then met the IMO intact stability criteria. However, the assessment of the vessels dynamic stability characteristics using time-domain simulation provided inconsistent results for these vessels with side casings which met the IMO intact stability criteria. For some particular conditions, the existence and the different forms of side casings could decrease vessel survivability by increasing the roll motion amplitudes for both inside and outside casings and could lead the vessel to capsize. The results of the dynamic stability analysis also confirmed the vulnerability of small vessels with small stability parameters to large waves, and the different roll seakeeping behavior of the different vessel stability parameters.
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Holden, Christian. "Modeling and Control of Parametric Roll Resonance." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for teknisk kybernetikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-12736.
Full textAbstract:
Parametric roll resonance is a dangerous resonance phenomenon affecting several types of ships, such as destroyers, RO-RO paxes, cruise ships, fishing vessels and especially container ships. Worst case, parametric roll is capable of causing roll angles of at least 50 degrees, and damage in the tens of millions of US dollars. Empirical and mathematical investigations have concluded that parametric roll occurs due to periodic changes in the waterplane area of the ship. If the vessel is sailing in longitudinal seas, with waves of approximately the same length as the ship, and encounter frequency of about twice the natural roll frequency, then parametric resonance can occur. While there is a significant amount of literature on the hydrodynamics of parametric roll, there is less on controlling and stopping the phenomenon through active control. The main goal of this thesis has been to develop controllers capable of stopping parametric roll. Two main results on control are presented. To derive, analyze and simulate the controllers, it proved necessary to develop novel models. The thesis thus contains four major contributions on modeling. The main results are (presented in order of appearance in the thesis): Six-DOF computer model for parametric roll One-DOF model of parametric roll for non-constant velocity Three-DOF model of parametric roll Seven-DOF model for ships with u-tanks of arbitrary shape Frequency detuning controller Active u-tank based controller for parametric roll
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Koshiro, Tsuyoshi. "Large-Scale Variability in Marine Low Stratiform Cloud Amount and Its Relationship to Lower-Tropospheric Static Stability in Terms of Cloud Types." Kyoto University, 2018. http://hdl.handle.net/2433/233820.
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Wu, Wan. "Analytical and Numerical Methods Applied to Nonlinear Vessel Dynamics and Code Verification for Chaotic Systems." Diss., Virginia Tech, 2009. http://hdl.handle.net/10919/30099.
Full textAbstract:
In this dissertation, the extended Melnikov's method has been applied to several nonlinear ship dynamics models, which are related to the new generation of stability criteria in the International Maritime Organization (IMO). The advantage of this extended Melnikov's method is it overcomes the limitation of small damping that is intrinsic to the implementation of the standard Melnikov's method.
The extended Melnikv's method is first applied to two published roll motion models. One is a simple roll model with nonlinear damping and cubic restoring moment. The other is a model with a biased restoring moment. Numerical simulations are investigated for both models. The effectiveness and accuracy of the extended Melnikov's method is demonstrated.
Then this method is used to predict more accurately the threshold of global surf-riding for a ship operating in steep following seas. A reference ITTC ship is used here by way of example and the result is compared to that obtained from previously published standard analysis as well as numerical simulations. Because the primary drawback of the extended Melnikov's method is the inability to arrive at a closed form equation, a 'best fit'approximation is given for the extended Melnikov numerically predicted result.
The extended Melnikov's method for slowly varying system is applied to a roll-heave-sway coupled ship model. The Melnikov's functions are calculated based on a fishing boat model. And the results are compared with those from standard Melnikov's method. This work is a preliminary research on the application of Melnikov's method to multi-degree-of-freedom ship dynamics.
In the last part of the dissertation, the method of manufactured solution is applied to systems with chaotic behavior. The purpose is to identify points with potential numerical discrepancies, and to improve computational efficiency. The numerical discrepancies may be due to the selection of error tolerances, precisions, etc. Two classical chaotic models and two ship capsize models are examined. The current approach overlaps entrainment in chaotic control theory. Here entrainment means two dynamical systems have the same period, phase and amplitude. The convergent region from control theory is used to give a rough guideline on identifying numerical discrepancies for the classical chaotic models. The effectiveness of this method in improving computational efficiency is demonstrated for the ship capsize models.<br>Ph. D.
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Bigi, Nedeleg. "Investigation of the dynamic motions and operability of a ship towed by kite." Thesis, Brest, 2017. http://www.theses.fr/2017BRES0133/document.
Full textAbstract:
Afin de réduire les émissions de gaz à effet de serre et le coût du transport maritime, l'utilisation des cerfs-volants comme système de propulsion auxiliaire des navires est prometteuse. Pour estimer les performances et l’opérabilité d’un navire tracté par cerf-volant, une modélisation dynamique du système est alors mise en oeuvre. Une modélisation analytique de cerf-volant est utilisée. Ce modèle néglige la masse du cerf-volant et suppose que les lignes sont droites et indéformables. Ces hypothèses conduisent à un modèle cinématique dépendant du coefficient de portance et de la finesse aérodynamique. Une évolution linéaire des coefficients aérodynamiques en fonction de la courbure de la trajectoire de vol est proposée. Par ailleurs, en développant un modèle quasi analytique de ligne, il est montré qu’à partir de 2 m.s-1 de vent relatif que l’hypothèse de ligne droite est raisonnable. En se basant sur un modèle de ligne, un critère analytique de vitesse de vent minimum permettant un vol quasi-statique est présenté. Dans le but de résoudre l’ensemble des termes d’interaction entre le cerf-volant et le navire, un modèle linéarisé de tenue à la mer temporelle est développé. Le produit de convolution de la réponse impulsionnelle du navire est calculé avec des systèmes d’états. Cependant comme celle-ci représente mal les mouvements horizontaux des navires, le modèle développé est alors couplé à un modèle de manoeuvrabilité. Pour étudier les interactions entre le cerf-volant et le navire un couplage monolithique et un couplage dissocié sont comparés. Le couplage dissocié néglige l’influence des mouvements du navire sur le vol du cerf-volant. En cas de mer calme, les résultats obtenus par les deux types de couplage sont très proches. En cas de houle régulière les mouvements du navire sont principalement causés par la houle. Le couplage monolithique montre qu’un réseau de sous-harmoniques basse fréquence apparait alors dans le spectre d’excitation du navire. La fréquence fondamentale des sous-harmoniques est donnée par la différence entre la fréquence de vague et la fréquence de l’harmonique la plus proche de l’excitation du kite. Quand cette différence est suffisamment petite, un phénomène d’accrochage apparait. Ce phénomène est bénéfique pour le cerf-volant et le navire quand le décalage des harmoniques d'excitation correspond à une augmentation. Par ailleurs, une étude de la stabilité de route montre qu'il est nécessaire de contrôler activement le safran<br>In order to reduce greenhouse gas emissions and shipping costs, the use of kites as an auxiliary propulsion device for ships is promising. In order to estimate the performance and the operability of a kite-towed vessel, a dynamic modeling of the system is implemented. A classical kite modeling is used. This model neglects the mass of the kite and assumes straight and inelastic tethers. These assumptions lead to a kinematic model depending on the lift coefficient and the aerodynamic lift to drag ration angle. A linear evolution of these aerodynamic coefficients as a function of the curvature of the flight path is proposed. In addition, by developing a quasi-analytical line model, it is shown that from 2 m.s-1 of relative wind the straight tether assumption is reasonable. Based on the tether model, an analytical criterion assessing the minimum wind speed to enable a quasi-static kite flight is developed. To solve all the interaction terms between the kite and the ship, a time domain seakeeping model based on the linearized ship equation of motion assuming a potential flow is developed. The convolution product of the impulse response of the ship is computed with state-space systems. However, since horizontal ship motions are not well represented by such theories, a coupling with a maneuvering model is presented.Comparisons to experimental data tests show good agreements. To study the interactions between the kite and the ship, a monolithic coupling and a dissociated coupling are compared. The dissociated coupling neglects the influence of ship motions on the kite flight. In a calm water case, results obtained by the two types of coupling are very close. In regular waves, ship motions are dominated by the wave influence. Thus, with the monolithic coupling, a network of low frequency subharmonic appears in the kite excitation spectrum. The fundamental frequency of the subharmonic is given by the difference between the wave frequency and the frequency of the nearest kite excitation harmonic. When this difference is small enough, a lock-in phenomenon appears. This phenomenon is a benefit for the kite and the ship when the shift of the excitation harmonics corresponds to an increase. Furthermore, a course keeping stability study shows that the rudder needs to be actively controlled
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Duffy, JT. "Modelling of ship-bank interaction and ship squat for ship-handling simulation." Thesis, 2008. https://eprints.utas.edu.au/19864/1/whole_DuffyJonathanTerrance2008_thesis.pdf.
Full textAbstract:
This thesis reports on an investigation into the simulation of ship manoeuvring in restricted waters; in particular ship squat and ship-bank interaction.
A time-domain mathematical model has been developed to predict unsteady squat and dynamic acceleration effects for a vessel travelling in non-uniform water depth. A quasi-steady approach was adopted, where the prediction at each time step is based on steady-state heave force and pitch moment in uniform water depth. A comprehensive set of model scale experiments was conducted to investigate squat in both uniform and non-uniform water depth. Regression analysis was performed on the uniform water depth test data to develop empirical equations for steady-state squat, which were used as input to the mathematical model. The equations apply to a full form vessel and are dependent on under keel clearance parameters, channel width parameters and depth Froude number. Empirical correction factors were also developed to estimate the effect of propulsion on squat.
Good correlation was observed between predictions from the squat mathematical model and steady-state sinkage measurements for a wide range of water depth to draught ratios. Predictions from the mathematical model were also compared with unsteady sinkage measurements on a ship model travelling over a simplified ramp bank. The general trend of the predicted unsteady sinkage was reasonable, improving the realism of simulation for abrupt changes in water depth compared to predictions where acceleration effects in the vertical plane are neglected. However, the maximum unsteady sinkage was not always predicted accurately, which may be attributable to limitations and assumptions associated with the technique.
A comprehensive model scale experiment program was conducted to investigate ship-bank interaction. The following parameters were systematically varied for three different hull forms: flooded bank height, water depth, bank slope, lateral ship to bank distance, vessel speed and vessel draught. The results from these experiments were used to develop a bank parameter to estimate the effects of lateral surface piercing and flooded banks. This parameter was utilised in regression analyses to develop empirical formulae for steady-state bank induced sway force and yaw moment.
The empirical formulae were validated against independent model scale measurements from literature and showed reasonable agreement for a range of cases. The formulae were then incorporated into the existing mathematical model of the AMC ship-handling simulator. The quasi-steady technique was used to predict the path of a vessel for a real-life manoeuvre where bank induced yaw moment is used to aid a turn. The proposed bank effect simulation method was found to provide a satisfactory solution to the problem of ship-bank interaction simulation.
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Watson, NL. "Wave-induced motions on high Froude number slender twin-hull vessels." Thesis, 2004. https://eprints.utas.edu.au/22126/1/whole_WatsonNigelLeslie2004_thesis.pdf.
Full textAbstract:
A study of the wave-induced motions experienced by slender twin-hull vessels was conducted through experimental measurements and numerical computation. Particular attention was required in the analysis of measured data for comparison with the predicted motions. The difficulties of analysing measured data from a vessel that had encountered sea waves of a random nature were addressed by grouping the data into subsets based on primary wave direction, vessel speed, and hull configuration. The primary wave direction was determined by considering the motions of the vessel as for a directional wave buoy. The data acquisition system consisted of hardware and software that was developed and assembled on two twin-hull full-scale vessels for periods of up to 12 months each. Designed to operate mostly unsupervised whilst collecting data in remote locations, a data recording sequence was initiated through a preset trigger level from a motion sensor. In the subsequent analysis, transfer functions were obtained from the measured data based on the sorted data subsets.
Numerical modelling of the vessels in head sea waves used an existing strip theory code that defined the hull as sectional boundary elements that contributed to solving a Green function problem for the free surface and sectional motion in the time domain. A modification to the code allowed the effects of motion control surfaces on the motion transfer functions to be determined through selection of appropriate gain setting that minimised the average vertical hull accelerations. With the damping effect of control surfaces not scaling linearly with wave height, the controls were modelled to minimise the hull average vertical acceleration in a 2.5 metre Bretschneider wave spectrum of 7 second average period. The inclusion of control surfaces in the motion computation combined with non-linear wave height effects in some instances greatly improved the correlation between the numerical and measured motion transfer functions by reducing the frequency of maximum response.
The accelerations and motion sickness incidence (MSI) distributions derived through computations on an 86 metre vessel indicate the presence of high accelerations that are not fully counteracted by a motion control system of practicable size. Future advances in numerical prediction codes may require verification with detailed full-scale measurements to ensure the scale effects are adequately considered. Fullscale measurements should therefore constitute part of a complete testing and analysis program for motions, but due to the high cost of these trials the measurements required for analysis may best be obtained from data supplied from on board monitoring systems during regular service operations.
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Nakhata, Tongchate. "Stability analysis of nonlinear coupled barge motions." Thesis, 2002. http://hdl.handle.net/1957/31491.
Full textAbstract:
The present research investigates nonlinear barge motions through analyses
of coupled multi-degree-of-freedom (MDOF) deterministic and stochastic models.
Roll-Heave-Sway and other lower-ordered models are developed to predict the
nonlinear motions and analyze the stability of a class of ship-to-shore cargo barges.
The governing equations of motion contain coupled rigid body Roll-Heave-Sway
relations, hydrostatic and hydrodynamic terms. The rigid body relationships are a
part of the general six-degree-of-freedom model. Hydrostatic terms include effects of
the barge's sharp edge and of relative Roll-Heave states. Hydrodynamic terms are in
a "Morison" form. The characteristics of the excitation wave field are based on
linear wave theory.
Predictive capabilities of the Roll-Heave-Sway and the Roll-Heave models
are investigated. System parameters are calibrated to match experimental test results
using several regular wave test cases. Potential theory predictions provide initial
estimates of several key system parameters. With the identified system parameters,
numerical predictions obtained from time domain simulations of both models are
compared with experimental test results for a random wave case, and compared to
each other to investigate the coupling effects of sway on roll and heave motions.
Reliability against capsizing of a barge in random seas is investigated using
stochastic analysis techniques. With the Markov process assumption, the barge
response density to random waves is derived as a solution to the corresponding
Fokker-Planck equation. The path integral solution technique is employed to obtain
numerical solutions for the Roll-Heave and the Roll models. A quasi-2DOF model
is introduced to improve the accuracy of the 1DOF Roll model. The reliability of a
barge in a variety of sea conditions is analyzed as a first passage problem using the
quasi-2DOF model. Mean times to reach specified capsizing probabilities for a
barge operating in sea states 1 through 9 are obtained.<br>Graduation date: 2003
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Köse, Ercan. "A stability monitoring and advisory system for small ships." Thesis, 1994. http://hdl.handle.net/2429/7249.
Full textAbstract:
Considering the loss of lives and money as a result of marine accidents, the importance
of reducing or preventing capsizing of small boats is clearly evident.
The research described in this thesis addresses the development of a monitoring and
advisory system for the safety of fishing vessels. This system uses environmental information
obtained from a number of sensors and proposes corrective action based on a
rule-base derived from experiments, theoretical research and human expertise.
Improvements in computer technology and the low prices of measurement equipment
facilitates the integration of a system based on off-the-shelf devices and subsystems such
as a ship's radar system to measure wave properties. The thesis demonstrates that such
off-the-shelf devices and subsystems can be used with special purpose software developed
to produce a low cost, intelligent safety monitoring and advisory system.
This monitoring system is designed based on the following requirements :
• The system should measure the minimum amount of data. In order to make system
practical and least costly, the equipments already existing onboard should be used.
• The system should not interfere with the operation of the ship, since anything
interfering with operation is expected to be discarded by the captain or crew.
In view of the need for the evaluation of wave parameters at a fast rate, in the order
of 30 - 60 seconds, for input into the advisory system, two new techniques (Boxing and
thinning techniques) have been developed. Reasonable agreement has been found between
these two techniques and conventional techniques, such as Fourier transforms.
A fuzzy expert system has been developed as a decision making process for the monitoring
and advisory system. Rules forming the basis for the advisory system are presented.
An advantage of this modular structure is that new rules may be easily appended
to the existing rule-base in view of further knowledge gained through interviewing experts,
experiments or theoretical developments.
Finally, feasibility of this approach has been demonstrated through numerical simulations
of various sea conditions on a range of ship forms.
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Lin, Rong-Jyun, and 林嶸鈞. "Study on Regulations for Probabilistic Damaged Stability of Ships." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/52388406662558255701.
Full textAbstract:
碩士<br>國立高雄海洋科技大學<br>造船及海洋工程研究所<br>101<br>The main objective of this paper is to study on regulations for SOLAS probabilistic damaged stability of ship. A comprehensive comparative analysis work has been proceeded for damaged stability of past and in-force regulation. Firstly, collates and explains the origin and history of ship’s damaged stability regulations. Then explains and discusses to every rules of the new and old regulations, and focus has put on calculation the required subdivision index (R) and parameters of attained subdivision index (A) of probabilistic damaged stability. Compares the different and change of regulations. In the end, an example ship has been used to calculation the parameters of probabilistic damaged stability, and it was more carefully compared for regulations. The analysis results of this thesis, could effective enhance design results of damaged stability of ship.