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The International Maritime Organization aims for net-zero carbon emissions in the maritime industry by 2050. Among various alternatives, route optimization holds an important place as it does not require any additional component-related costs. Especially for wind-assisted ships, the effectiveness of different sailing systems can be improved significantly through route optimization. However, finding the ship's optimal route is computationally expensive when the totality of possible weather conditions is taken into consideration. To determine the optimal route that minimizes energy consumption, an energy model based on the environmental conditions, ship route and ship speed was built using artificial neural networks. The energy consumed for given input data was calculated using a ship dynamics model and a database was generated to train the artificial neural networks, which predict how much energy is consumed depending on the route followed in given environmental conditions. Then, such networks were exploited to derive the optimal routes for all the relevant operational conditions. It was found that route optimization can reduce the overall ship energy consumption depending on the weather conditions of the environment by up to 9.7% without any increase in voyage time and by up to 35% with a 10% delay in voyage time. The proposed methodology can be applied to any ship by training real weather conditions and provides a framework for reducing energy consumption and greenhouse gas emissions during the service life of ships. [ABSTRACT FROM AUTHOR]

This paper presents an analysis of the acceleration of a fast boat using a simulation model. Mathematical equations of ship motion dynamics with two types of propeller capabilities are developed using MATLAB and Simulink as simulation tools. The equations are extended to include the acting thrust, resistance, propeller’s performance curves, and the PID governor curve for the acceleration manoeuvre. The application models the dynamic differential equations representing the vessel dynamics in one degree of freedom. MATLAB code was used to develop the ship acceleration as a multibody system. Modules of hydrodynamic forces, resistance, moments, and propeller performances were implemented to simulate the ship manoeuvring process. A comparison of the results for the boat’s propulsion performance with two different propellers and the characteristics of the PID governor, which controls the fuel dose in the gas turbines, was carried out. We present a summary including a comparative analysis of the results for the boat dynamics with and without the PID governor. The results obtained here confirm significant discrepancies between the results of numerical simulations with and without the PID governor.

Ship dynamic models serve as the foundation for designing ship controllers, trajectory planning, and obstacle avoidance. Support vector regression (SVR) is a commonly used nonparametric modelling method for ship dynamics. Achieving high accuracy SVR models requires a substantial amount of training samples. Additionally, as the number of training samples increases, the computational efficiency for solving the quadratic programming problem (QPP) of SVR decreases. Ship controllers demand dynamic models with both high accuracy and computational efficiency. Therefore, to enhance the prediction accuracy and computational efficiency of SVR, this paper proposes a nonparametric modelling method based on twin SVR (TSVR). TSVR replaces a large QPP with a set of smaller QPPs, significantly enhancing generalizability and computational efficiency. To further improve the predictive accuracy of TSVR, the puma optimizer algorithm is employed to determine the optimal hyperparameters. The performance of the proposed method is validated using a Mariner class vessel. Gaussian white noise is introduced into the modelling data to simulate measurement error. The TSVR model accurately predicts various zigzag and turning circle manoeuvring motions under disturbance conditions, demonstrating its robustness and generalizability. Compared to the SVR model, the TSVR model achieves lower root mean square error and computational time, confirming its superior predictive accuracy and computational efficiency. [ABSTRACT FROM AUTHOR]

The International Maritime Organization aims for net-zero carbon emissions in the maritime industry by 2050. Among various alternatives, route optimization holds an important place as it does not require any additional component-related costs. Especially for wind-assisted ships, the effectiveness of different sailing systems can be improved significantly through route optimization. However, finding the ship’s optimal route is computationally expensive when the totality of possible weather conditions is taken into consideration. To determine the optimal route that minimizes energy consumption, an energy model based on the environmental conditions, ship route and ship speed was built using artificial neural networks. The energy consumed for given input data was calculated using a ship dynamics model and a database was generated to train the artificial neural networks, which predict how much energy is consumed depending on the route followed in given environmental conditions. Then, such networks were exploited to derive the optimal routes for all the relevant operational conditions. It was found that route optimization can reduce the overall ship energy consumption depending on the weather conditions of the environment by up to 9.7% without any increase in voyage time and by up to 35% with a 10% delay in voyage time. The proposed methodology can be applied to any ship by training real weather conditions and provides a framework for reducing energy consumption and greenhouse gas emissions during the service life of ships.

A practical criterion which can be used for assessing the course-keeping capability of a ship in following waves, is proposed and evaluated. Presently, it accounts for regular waves and it accrued from an analytical estimation of the course instability region's boundary by applying the method of harmonic balance. The calculation is performed with regard to the third-order yaw equation, derived from a classic sway--yaw-rudder model of ship maneuvering motions, with time-dependent coefficients at two places, which is like a Mathieu-type equation extended to third order. The proposed analytical criterion was evaluated thoroughly against simulations with regard to this sway--yaw model and it was found to be adequately accurate. A supplementary quasi-static yaw stability criterion (fitting to ship operation with frequency of encounter, with respect to the waves, close to zero) was also considered in order to determine which one yields more stringent requirements, for various operating conditions. The proposed criterion could be an extra vulnerability check for broaching-to, in the context of the Second Generation Intact Stability Criteria. [ABSTRACT FROM AUTHOR]

Ship dynamic models serve as the foundation for designing ship controllers, trajectory planning, and obstacle avoidance. Support vector regression (SVR) is a commonly used nonparametric modelling method for ship dynamics. Achieving high accuracy SVR models requires a substantial amount of training samples. Additionally, as the number of training samples increases, the computational efficiency for solving the quadratic programming problem (QPP) of SVR decreases. Ship controllers demand dynamic models with both high accuracy and computational efficiency. Therefore, to enhance the prediction accuracy and computational efficiency of SVR, this paper proposes a nonparametric modelling method based on twin SVR (TSVR). TSVR replaces a large QPP with a set of smaller QPPs, significantly enhancing generalizability and computational efficiency. To further improve the predictive accuracy of TSVR, the puma optimizer algorithm is employed to determine the optimal hyperparameters. The performance of the proposed method is validated using a Mariner class vessel. Gaussian white noise is introduced into the modelling data to simulate measurement error. The TSVR model accurately predicts various zigzag and turning circle manoeuvring motions under disturbance conditions, demonstrating its robustness and generalizability. Compared to the SVR model, the TSVR model achieves lower root mean square error and computational time, confirming its superior predictive accuracy and computational efficiency.

In this study, the impact of propeller emergence on the performance of a ship (speed), propeller (thrust, torque, and RPM), a diesel engine (torque and RPM) and fuel consumption are analysed under severe sea conditions. The goal is to describe the variation in the system variables and fuel consumption rather than analysing the motion of the ship or the phenomenon of propeller ventilation in itself. A mathematical model of the hull, propeller, and engine interactions is developed in which the propeller emergence is included. The system parameters are set using model experiments, empirical formulae, and available data for the engine. The dynamic response of the system is examined in regular head waves under submerged and emerged conditions of the propeller. The pulsatility and the extent of variation of 20 selected variables for the coupled system of hull, propeller, and engine are elaborated using quantitative and qualitative terms and absolute and relative scales. The simulation begins with a ship moving on a straight path, in calm water, with a constant speed for the ship, propeller and engine under steady conditions. The ship then encounters regular head waves with a known time series of the total resistance of the ship in waves. Large motions of the ship create propeller emergence, which in turn reduces the propeller thrust and torque. This study shows that for a specific ship, the mean ship speed, shaft angular velocity, and engine power were slightly reduced in submerged conditions with respect to calm water. We compared the mean values of the variables to those in the emerged condition, and found that the shaft angular velocity was almost the same, the ship speed was considerably reduced, and the engine power significantly dropped with respect to calm water. The ratios of the amplitude of fluctuation to the mean (Amp/Mean) for the ship speed and angular velocity of the shaft under both conditions were considerable, while the Amp/Mean for the power delivered by the engine was extremely high. The outcomes of the study show the degree of influence of propeller emergence on these variables. We identify the extent of each change and categorise the variables into three main groups based on the results.

Autonomous trajectory generation plays an essential role in the navigation of vehicles in space as well as in terrestrial scenarios, i.e. in the air, on solid ground, or water. For the latter, the navigation of ships in ports has specific challenges since ship dynamics are highly nonlinear with limited agility, while the manoeuvre space in ports is limited. Nevertheless, for providing support to humanly designed control strategies, autonomously generated trajectories have not only to be feasible, i.e. collision-free but shall also be optimal with respect to manoeuvre time and control effort. This article presents a novel approach to autonomous trajectory planning on the basis of precomputed and connectable trajectory segments, the so-called motion primitives, and an A*-search algorithm. Sequences of motion primitives provide an initial guess for a subsequent optimization by which optimal trajectories are found even in terrains with many obstacles. We illustrate the approach with different navigation scenarios.

According to the International Maritime Organization (IMO)'s Greenhouse Gas (GHG) strategy whose aim is to reduce the shipping industry's total carbon emissions by 50% by the year 2050, it is desirable to increase ships energy efficiency to reduce GHG emissions and fuel costs. To do so, a short-term measure is to develop innovative engine control strategies in waves that will reduce ship's GHG emissions. In this study, a mathematical model is developed to assess two engine control strategies: the standard constant rotational speed mode and an innovative constant fuel rack approach. The coupled model is made of a mean value engine, propeller curves and a ship behavior simulator. Emphasis is placed on the presentation of the engine model and references are given for further details on the ship simulator. After verifying the coupling between the engine model and the ship simulator, the fuel consumption is compared, for the two strategies, at the same average speed and for three head regular waves. This paper presents the basics of a further long time research project and shows that coupling ship simulators with engine simulators leads to promising simulation tools for a ship's GHG emissions reduction. Results from a first application case show that the constant fuel rack approach reduces fuel consumption (up to 1.6%). [ABSTRACT FROM AUTHOR]

Autonomous trajectory generation plays an essential role in the navigation of vehicles in space as well as in terrestrial scenarios, i.e. in the air, on solid ground, or water. For the latter, the navigation of ships in ports has specific challenges since ship dynamics are highly nonlinear with limited agility, while the manoeuvre space in ports is limited. Nevertheless, for providing support to humanly designed control strategies, autonomously generated trajectories have not only to be feasible, i.e. collision-free but shall also be optimal with respect to manoeuvre time and control effort. This article presents a novel approach to autonomous trajectory planning on the basis of precomputed and connectable trajectory segments, the so-called motion primitives, and an A*-search algorithm. Sequences of motion primitives provide an initial guess for a subsequent optimization by which optimal trajectories are found even in terrains with many obstacles. We illustrate the approach with different navigation scenarios. [ABSTRACT FROM AUTHOR]

Two nonlinear models of the roll motion of ships are discussed and analytically solved. Both models are second-order differential equations with nonlinear restoring and damping moments. A new approach to the homotopy perturbation method is applied to derive analytical expressions for the roll angle, velocity, acceleration and restoring and damping moments. The analytical results are validated by direct comparison with the fourth-order Runge-Kutta method. The analytical approach of this paper can be efficiently extended to various vibrating dynamical models arising in mechanical systems. [ABSTRACT FROM AUTHOR]

This article introduces a novel nonlinear control approach for quadrotor landing on a moving ship. The dynamics of the relative position and attitude dynamics with uncertainties, unmodeled dynamics, external disturbances, and control input saturation is derived. Then, a novel robust adaptive constrained backstepping control law for the propeller and torques of the quadrotor is designed. To deal with uncertainties and un-modeled dynamics, radial basis function is employed. The bounded-in-probability stability is used to alleviate the destructive influence of the stochastic Wiener process on the system positions and attitudes. Whereas the quadrotor is under-actuated, a redundant control input technique, which affects the attitude commands, is presented. The actual control input saturation limits are turned into unknown saturation limits of the redundant control inputs. Also, since two phases for the landing problem are considered, a smooth switching mechanism between the control inputs is developed. Simulation results show the merits and applicability of the developed robust adaptive nonlinear controller. [ABSTRACT FROM AUTHOR]

In this paper, the application of artificial neural network in ship course control systems is investigated. Two-multilayered feed-forward neural network course control system is proposed. The first neural network plays the role of ship forward dynamic approximator. The second one is the course controller. Both neural networks are trained in a quasi-online regime using training data acquired from system functional process to cope with changing ship dynamics. A cost function is used in control action calculation. The performance of the proposed system is evaluated in different conditions. The system stability is verified via simulation. The simulation results show that the course control system is able to keep the predefined direction in various sea conditions and the proposed approach serves the consideration on developing and applying in designing real ship autopilot systems. [ABSTRACT FROM AUTHOR]

This paper presents a methodology to develop the control systems of a surface vessel by using both computational fluid dynamics techniques and model-based control design. The model-based control design is supported by a simulation platform where both the ship hydrodynamics and the propulsion plant are modelled together. The application of CFD is related to the direct evaluation of the hull forces in the ship hydrodynamic model, for different manoeuvring conditions. The developed design tool is essential in the preliminary design phase, as a benchmark to test the control algorithms for autonomous ships. The comparison between numerical assessment and regression-based formulae has been performed on non-standard manoeuvres to quantify the difference in thrust allocation from the point of view of control design. Eventually, to validate the effectiveness of the proposed methodology, the results of the sea trials for different manoeuvres are shown. [ABSTRACT FROM AUTHOR]

Survivability of ships in damaged condition is an issue of paramount importance. Therefore, the regulatory framework is constantly updated, in response to the societal aversion towards accidents with severe impact on human life and on the environment. The introduction of the probabilistic damage stability framework was a major step towards the rationalization of the procedure for the assessment of survivability of ships in damaged condition. Subsequent revisions of SOLAS 2009 included the increase of the safety standard via the new formulations for the R-Index and for the calculation of the probability of survival (s-factor), which however is still performed by a hydrostatic approach. Flooding simulation tools can be used for an in-depth investigation of the transient response of a damaged ship, aiming to identify conditions that could jeopardize her survivability during the initial phases of flooding, or to assist in the improvement of the s-factor formulation. In this work, a newly developed flooding simulation tool, employing the Smoothed Particles Hydrodynamics (SPH) method coupled with a ship motions solver, is presented. The developed methodology predicts the dynamic response of the ship during the flooding process, primarily focusing on the initial stages, when particularly violent flow phenomena may be observed. • Application of SPH in damage stability flooding simulations. • SPH modeling of water inflow (and outflow) in a damaged compartment. • Simulation of box-shaped barge dynamics in symmetric and non-symmetric damages. • Comparison between non-linear dynamic SPH method and quasi-static method. [ABSTRACT FROM AUTHOR]

The system identification of a ship dynamics model is crucial for the intelligent navigation and design of the ship’s controller. The fluid dynamic effect and the complicated geometry of the hull surface cause a nonlinear or asymmetrical behavior, and it is extremely difficult to establish a ship dynamics model. A nonparametric model based on sparse Gaussian process regression with similarity was proposed for the dynamic modeling of a ship. It solves the problem, wherein the kernel method is difficult to apply to big data, using similarity to sparse large sample datasets. In addition, the experimental data of the KVLCC2 ship are used to verify the validity of the proposed method. The results show that sparse Gaussian process regression with similarity can be applied to the learning of a large sample data, in order to obtain ship motion prediction with higher accuracy than the parameterized model. Moreover, in the case of sensor signal loss, the identified model continues to provide accurate ship speed and trajectory information in the future, and the maximum prediction error of the motion trajectory within 100 s is only 0.59 m.

This paper focuses on the design stage of an electrical energy storage system which is intended to be used to level the power required by ships for propulsion when sailing in irregular seas. Particularly, a preliminary analysis has been carried out aimed at choosing, between two storage technologies namely battery and ultracapacitor, the more adequate storage system for the levelling action with respect to the period of the sea waves. A sizing procedure based upon a Hilbert transform decomposition of load demand is used. More specifically, a specified threshold frequency has been identified such that, power fluctuations related to irregular seas which are characterized by frequencies higher than the specified threshold, indicate the ultracapacitor as the more appropriate device for load levelling. For sizing the storage device, the load demand has been decomposed into two signals without overlapping frequencies. An optimal control strategy is proposed, by exploiting the decomposition of the load power, which allows simulating ultracapacitor real-time operation within the previously determined size constraints. Numerical results have been carried out referring to a Ro-Pax ferry powered by an electrical motor. • Onboard electrical energy storage is used for load levelling. • The use of the storage refers to a ship sailing in irregular sea states. • A threshold frequency is identified for the choice of storage technology. • A proper decomposition of the load request signal is performed. • An optimal control strategy based on an autoregressive model is used. [ABSTRACT FROM AUTHOR]

Two different propulsion systems are analyzed from point of view of future control applications. The traditional one consists of a pushing single screw propeller and a blade rudder. The other system is based on pod (pods): pulling or pushing ones. The equations describing forces and moments generated in both systems, are presented. Exemplary results of a simulation in comparison to the real-time experiments for two ships are also shown.

Traditionally, the evaluation of global loads experienced by passenger ships has been based on closed-form Classification Society Rule formulae or quasi direct analysis procedures. These approaches do not account for the combined influence of hull flexibility, slenderness, and environmental actions on global dynamic response. This paper presents a procedure for the prediction of the global wave-induced loads of a medium-size passenger ship using a potential flow Flexible Fluid Structure Interaction (FFSI) model. The study compares results from direct long-term hydro-structural computations against Classification Society Rules. It is demonstrated that for the specific vessel under consideration: (a) the elastic contributions of the responses on loads are negligible as springing effects occur outside of the wave energy spectrum, (b) deviations of the order of 28% arise by way of amidships when comparing direct hydrodynamic analysis predictions encompassing IACS UR S11A hog/sag nonlinear correction factors and the longitudinal strength standard, and (c) the interpretation of the wave scatter diagram influences predictions by approximately 20%. Based on these indications, it is recommended that further parametric studies over a range of passenger ship designs could help draw unified conclusions on the total influence of global and local hydrodynamic actions on passenger ship loads and dynamic response.

This paper presents a series of dynamic simulations for a ship towed by kite. To ensure time efficient computations, seakeeping analysis with forward speed correction factors is carried out in the frequency domain and then transformed in the time domain by convolution. The seakeeping modeling is coupled with a zero-mass kite modeling assuming linear dependence of aerodynamic characteristics with respect to turning rate. Decoupled (segregated) and coupled (monolithic) approaches are assessed and compared in different environmental conditions. Results show that in regular beam waves, strong interactions between the kite and the ship motions are captured by the monolithic approach. Around the wave frequency, especially for the lower one tested (0.4 rad/s), a kite lock-in phenomenon is revealed. It is concluded that the mean kite towing force can be increased whereas the ship roll amplitude can even be decreased compared to a non-kite assisted ship propulsion configuration.

This paper presents a numerical model for the smart detection of synchronous and parametric roll resonance of a ship. The model implements manoeuvring equations superimposed onto ship dynamics in waves. It also features suited autopilot and rudder actuator models, aiming at a fair depiction of the control delay. The developed method is able to identify and distinguish between synchronous and parametric roll resonance, based on the estimation of encounter wave period from ship motions. Therefore, it could be useful as a smart tool for manned vessels and, also, in the perspective of unmanned and autonomous vessels (in the paper it is assumed a hypothetical remote crew). Once the resonance threat is identified, different evasive actions are simulated and compared, based on course and speed change. Calculations are carried out on a ro-ro pax vessel vulnerable to parametric roll. We conclude that, in roll resonance situations, and in the absence of roll stabilisation systems on-board, course change could be the most effective countermeasure.

The dynamics of a damaged ship in waves is a complex phenomenon regarding fluid and structure interactions. Flooded water motions in the damaged compartment could be influenced by decks, obstructions and obstacles in the compartment. This becomes particularly relevant in case of flooding in the engine room that is usually characterized by the presence of large objects such as engines and machineries. In such cases the possibility to better understand the behavior of a damaged ship, influenced by the fluid and structure interactions, could provide novel outcomes and thus enhance the damaged ship safety. In this paper an experimental campaign is conducted on a passenger ferry hull. The effects of obstacles in the engine room compartment, such as decks and engines, on ship roll responses, are studied. Roll decay in still water and steady roll responses in beam regular waves at zero speed are measured for the empty compartment and for the compartment with obstructions, as defined above. The main outcomes from the conducted experiments disclose a mitigation of the resonant behavior of the coupled system, ship with damaged compartment, by having engine shapes occupying the flooded engine room. Moreover it is possible to observe how the resonant frequency of the ship modifies having a more realistic arrangement of damaged compartment and how motion RAOs and roll decay characteristics modify accordingly. [ABSTRACT FROM AUTHOR]

The demands for lower Energy Efficiency Operational Index (EEOI) reflect the requirements of international conventions for green shipping. Within this context it is believed that practical solutions for the dynamic optimization of a ship’s main engine and the reduction of EEOI in real conditions are useful in terms of improving sustainable shipping operations. In this paper, we introduce a model for dynamic optimization of the main engine that can improve fuel efficiency and decrease EEOI. The model considers as input environmental factors that influence overall ship dynamics (e.g., wind speed, wind direction, wave height, water flow speed) and engine revolutions. Fuel consumption rate and ship speed are taken as outputs. Consequently, a genetic algorithm is applied to optimize the initial connection weight and threshold of nodes of a neural network (NN) that is used to predict fuel consumption rate and ship speed. Navigation data from the training ship “YUMING” are applied to train the network. The genetic algorithm is used to optimize engine revolution and obtain the lowest EEOI. Results show that the optimization method proposed may assist with the prediction of lower EEOI in different environmental conditions and operational speed.

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Guaranteeing a sufficient level of safety from the point of view of stability is typically considered to be a matter of design. The overall level of safety of a ship, however, can only be guaranteed when considering passive design measures in conjunction with active operational measures, in a holistic, balanced and cost-effective manner. Time could therefore be coming for systematically considering operational measures as a recognised and normed integral part of a holistic approach to ship safety from the point of view of stability. In this respect, the scope of this paper is to identify open challenges and to provide, in general, food for thought for stimulating a discussion on the topic of operational measures, with specific attention to the damaged ship condition. The aim is to provide ground for further proceeding towards the goal of implementing a virtuous integrated approach to ship stability safety which gives due credit to effective and robust operational risk control options. [ABSTRACT FROM AUTHOR]

Attaining a sufficient level of safety from the point of view of stability is typically considered to be a matter of design. However, it is impossible to ensure safety only by design measures, and operational measures can then represent a complementary tool for efficiently and cost-effectively increasing the overall safety of the vessel. Time could therefore be coming for systematically considering operational measures as a recognised and regulated integral part of a holistic approach to ship safety from the point of view of stability. This paper therefore aims at capturing recent trends of research targeting operational safety measures, with specific attention to the intact ship condition. Open challenges and opportunities for research are identified, potential benefits and shortcomings of different options are discussed, and needs and possibilities for further developments in this area are explored. As an overall goal, this paper aims at providing food for thoughts as well as a ground for further proceeding towards the target of implementing a virtuous integrated approach to intact ship safety, from the point of view of stability, which gives due credit to effective and robust operational risk control options. [ABSTRACT FROM AUTHOR]

Ship motions after damage are difficult to evaluate since they are affected by complex phenomena regarding fluid and structures interactions. The possibility to better understand how ship behavior in damage is influenced by these phenomena is important for improving ship safety, especially for passenger vessel. In this paper an experimental campaign is carried out on a passenger ferry hull, to show the effects of the water dynamics across damage openings on ship motions. Novel aspects of this research include the study of the effects of the damage position on the ship roll response. The study is carried out for still water and for beam regular waves at zero speed. Results from the experiments carried out underline that the roll behavior of a damaged ship is affected by the position of damage opening and not only by its size. Assuming the same final equilibrium conditions after flooding but characterized by different damage openings it is possible to observe how motions RAOs and roll decay characteristics modify according to the opening locations. [ABSTRACT FROM AUTHOR]

In Naval Architecture, the concept of “stability” has a very wide meaning, embracing ship stability fundamentals with ship dynamics and ultimately ship safety. As such, the subject is of paramount importance for its wide implications on design and operation of ships and floating units. Research in this field has, therefore, an important impact on the fleet safety, and the International Conferences on Stability of Ships and Ocean Vehicles (STAB Conferences) and the International Ship Stability Workshops (ISSW) are certainly the venues where expertise and contemporary developments in this specific field tend to be collected and thoroughly debated. With the aim of analysing the current status and possible future perspectives of research in the field of ship stability, dynamics and safety, this paper provides an extensive review of the findings presented at STAB Conferences and ISSW events in the period 2009–2014. The reviewed material is organised according to a set of identified macro-topics of research. On the basis of the reviewed material, consolidated research topics as well as emerging subjects are laid out, and ideas for possible future research are also brought forward. Discussion is also provided regarding the link between research and educational aspects. [ABSTRACT FROM AUTHOR]

The focus of this paper is to update the classic criterion for the determination of the safe keel clearance for ships sailing in restricted waterways. Ship׳s dynamics is taken into account by integrating the notion of the unsteady squat. This paper shows the existence of unstable equilibrium position of the ship during heave motion. Furthermore, it proposes a new mathematical expression to evaluate it as a function of canal and ship parameters. It is shown that this unstable equilibrium position can be considered as a virtual bottom for ship. It should not be reached during ship motion in order to avoid grounding. The importance of this result, confirmed both by an analytical model as well as by a numerical model with Finite Elements Method, lies in the reduction of the safety margin actually allowed for pilots. So this result points out the knowledge of a virtual bottom that could lie above the real nautical bottom. [ABSTRACT FROM AUTHOR]

The dynamic characteristics of ship structures are becoming more important as the flexibility of modern ships increases, for example, to predict reliable design life. This requires an accurate dynamic model of the structure, which, because of complex vibration environment and complex boundary conditions, can only be validated by measurements. In the present paper the use of operational modal analysis (OMA) for dynamic characterization of a ship structure based on experimental data, from a full-scale measurement of a 210-m long Ro-Lo ship during sea trial, is presented. The measurements contain three different data sets obtained under different operating conditions of the ship: 10 knots cruising speed, 18 knots cruising speed, and at anchor. Natural frequencies, modal damping ratios, and mode shapes have been successfully estimated for the first 10 global modes. Damping ratios for the current ship were found within the range 0.9%-1.9% and natural frequencies were found to range from 0.8 to 4.1 Hz for the first 10 global modes of the ship at design speed (18 knots). The three different operating conditions showed, in addition, a speed dependency of the natural frequencies and damping ratios. The natural frequencies were found to be lower for the 18-knots condition compared with the two other conditions, most significantly for the vertical bending modes. Also, for the vertical bending modes, the damping ratios increased by 28%-288% when the speed increased from 10 to 18 knots. Other modes were not found to have the same strong speed dependency. [ABSTRACT FROM AUTHOR]

The ship's dynamic performance (acceleration, turning ability, crash stop) strongly depends on both the propulsion system and its control. The steady-state performance analysis of propulsion systems has shown that onboard energy usage benefits from the employment of simulation techniques. Besides, these techniques provide significant advantages in designing the control logic of sophisticated and complex systems. The present work summarizes the research activities conducted to develop suitable simulation framework for the propulsion systems of naval vessels. Theoretical and mathematical models have thus been developed in this paper to simulate the propulsion of ships. Model-scale experiments and full-scale trials have been used to increase the fidelity of the models. The research outcome is a conceptual framework and a fully validated parametric software representing the vessel's dynamic behaviour and propulsion system in steady-state and abrupt manoeuvres. Thanks to this simulation framework, the propulsion control system could be designed, validated, and calibrated before its installation on board, reducing the commissioning time and minimising the propulsion control system's onboard calibration during the acceptance sea trials. • A new holistic approach for designing complex propulsion plant is shown. • Mathematical models to simulate the dynamics of several ship' subsystems have been conceptualised. • Real-time ship simulation platform has been developed. • Validation by sea trials demonstrates the methodology validity. [ABSTRACT FROM AUTHOR]