Ship Behavior Research Articles

Preliminary Study on Characteristics of Motions of Side-by-side Moored Vessels during Waves in Port

Recently FSRU (Floating storage and regasification unit) system has been applied to not only offshore region but also ports and harbors region. The motions and mooring loads of a ship moored along jetty and side-by-side moored two ships are influenced by wave conditions such as wave height, period and its direction, and shallow water effect. In this study, we have conducted several physical model tests on ship behaviors for a single moored ship (Ship-to-jetty: STJ) and side-by-side two vessels where one ship is moored along dolphins (STJ+STS: Ship-to-ship: STS) during waves to obtain the property of ship motions and mooring loads. Also a numerical simulation system has been developed for the side-by-side moored two vessels to investigate the property of ship motions and mooring loads.

ANALYSIS OF SHIP BEHAVIOR UNDER INFLUENCE OF WAVES AND CURRENTS

The most important environmental factors related to safety of ship and performance on high sea are surface winds and waves. In order to obtain an optimal trajectory of a ship route, it is a prerequisite to know the sea state condition, as well as, the behavior of the ship in waves and currents. The purpose of this study is to analyze the ship behavior under the influence of 3 different sea state conditions over the Southern Brazilian inner shelf near the Rio Grande coastal region. SHIPMOVE and TOMAWAC + TELEMAC3D system were simulated under three different wave scenarios. Day 4 showed the shortest traveled distance and lowest velocity. The sea state of Day 33 deflected the initial vessel path northeasterly and generated high rotational motions. Day 100 depicted the longest final displacement and highest average velocity, where this event showed the most smooth sea state condition. Lastly, the ship behavior seems to be strongly influenced by the sea state condition for the three events.

Risk perceptions on cruise ships among young people: Concepts, approaches and directions

Cruising is becoming a more popular form of tourism, leading to the increasingly sophisticated demand and expectations of cruise passengers and the growing number of young cruise passengers. Therefore, it is essential that cruise operators develop a thorough understanding of their customers and determinants influencing the decision-making process. Risk perception plays a key role in affecting purchase intention and retention, and shaping consumer experiences and satisfaction. This paper synthesises the existing knowledge on the role of risk perception in cruising, explores theories underpinning risk perception and its measurements, and identifies key factors influencing risk perception. The paper offers a comprehensive conceptual framework for risk perception on cruise ships, and identifies knowledge gaps that have not yet been explored in the extant cruising literature. This paper contributes to the advancement of risk knowledge in cruise ship behaviour, and allows cruise operators to better understand customer behaviour, especially the youth.

Numerical investigation of the behaviour and performance of ships advancing through restricted shallow waters

Upon entering shallow waters, ships experience a number of changes due to the hydrodynamic interaction between the hull and the seabed. Some of these changes are expressed in a pronounced increase in sinkage, trim and resistance. In this paper, a numerical study is performed on the Duisburg Test Case (DTC) container ship using Computational Fluid Dynamics (CFD), the Slender-Body theory and various empirical methods. A parametric comparison of the behaviour and performance estimation techniques in shallow waters for varying channel cross-sections and ship speeds is performed. The main objective of this research is to quantify the effect a step in the channel topography on ship sinkage, trim and resistance. Significant differences are shown in the computed parameters for the DTC advancing through dredged channels and conventional shallow water topographies. The different techniques employed show good agreement, especially in the low speed range.

Intact Stability Analysis of Dead Ship Conditions using FORM

The international Maritime Organization (IMO) Weather Criterion has proven to be the governing stability criteria regarding minimum metacentric height for e.g., small ferries and large passenger ships. The formulation of the Weather Criterion is based on some empirical relations derived many years ago for vessels not necessarily representative for current new buildings with large superstructures. Thus, it seems reasonable to investigate the possibility of capsizing in beam sea under the joint action of waves and wind using direct time domain simulations. This has already been done in several studies. Here, it is combined with the first order reliability method (FORM) to define possible combined critical wave and wind scenarios leading to capsize and corresponding probability of capsize. The FORM results for a fictitious vessel are compared with Monte Carlo simulations, and good agreement is found at a much lesser computational effort. Finally, the results for an existing small ferry will be discussed in the light of the current weather criterion. 1. Introduction Recently, the International Maritime Organization (IMO) has initiated a thorough revision of the intact stability rules in the framework of goal-based design, e.g., Peters et al. (2013). Several draft guidelines have been issued, e.g., SDC 1/INF.8 (IMO 2013) discussing in details the requirements for the hydrodynamic software to be applied including qualitative and quantitative assessment procedures. The focus so far has been mostly on failure modes related to the change of righting lever in waves, notably parametric rolling and pure loss of stability, whereas the dead ship behavior in beam sea still is based on the existing Weather Criterion issued by IMO (1985) as Resolution A.562. This criterion is based to a large extent on model tests of older hull forms and does not provide any probability of capsize for a given vessel, just a pass/no pass result. Furthermore, the wave environment is not explicitly specified in the criterion thus leading to the same requirement whether the ship is sailing in restricted areas or not. A very detailed and precise description of the drawbacks in the IMO Weather Criterion, as applied to modern ships, is given in Bulian and Francescutto (2004). In a recent study by Tompuri et al. (2015), a detailed investigation on application of the second generation intact stability criteria has been done. However, the criterion for dead ship condition is excluded from this thorough study because the criterion is thought to be still in the early phase of development.

Nonlinear surge motions of a ship in bi-chromatic following waves

Unintended motions of a ship operating in steep and long following waves are investigated. A well-known such case is “surf-riding” where a ship is carried forward by a single wave, an event invoking sometimes lateral instability and even capsize. The dynamics underlying this behavior has been clarified earlier for monochromatic waves. However, the unsteadiness of the phase space associated with ship behavior in a multichromatic sea, combined with the intrinsically strong system nonlinearity, pose new challenges. Here, current theory is extended to cover surging and surf-riding behavior in unidirectional bi-chromatic waves encountering a ship from the stern. Excitation is provided by two unidirectional harmonic wave components having their lengths comparable to the ship length and their frequencies in rational ratio. The techniques applied include (a) continuation analysis; (b) tracking of Lagrangian coherent structures in phase space, approximated through a finite-time Lyapunov exponents’ calculation; and (c) large scale simulation. A profound feature of surf-riding in bi-chromatic waves is that it is turned oscillatory. Initially it appears as a frequency-locked motion, ruled by the harmonic wave component dominating the excitation. Transformations of oscillatory surf-riding are realized as the waves become steeper. In particular, heteroclinic tanglings are identified, governing abrupt transitions between qualitatively different motions. Chaotic transients, as well as long-term chaotic motions, exist near to these events. Some extraordinary patterns of ship motion are discovered. These include a counterintuitive low speed motion at very high wave excitation level; and a hybrid motion characterized by a wildly fluctuating velocity. Due to the quite generic nature of the core mathematical model of our investigation, the current results are believed to offer clues about the behavior of a class of nonlinear dynamical systems having in their modeling some analogy with a perturbed pendulum with bias.

Sensitivity analysis of traffic efficiency in restricted channel influenced by the variance of ship speed

Enhancing the traffic efficiency of restricted channels is one of the most important objectives for maritime transportation, especially in busy waterways and ports. In many cases, the variance of ship speed would impede the traffic efficiency in restricted channels where overtaking between ships is not allowed. The ship behaviors in restricted channels are studied in this article. Two indicators are applied to evaluate traffic efficiency, which are the percentage of ships that reduce speed and the increase of navigating time in the channel due to speed reduction. Screening method is introduced to make sensitivity analysis considering five factors, which are the mean value of ship speed, variance of ship speed, channel length, safety distance and arriving rate. The results indicate that the mean value of ship speed is most sensitive to traffic efficiency, followed by the variance of ship speed and arriving rate. The safety distance is the least sensitive to channel efficiency. Quadratic equation models and response surface method are further used to make interaction analysis between the factors. High degree of interactions among the mean value, variance of ship speed, arriving rate and channel length are identified. These findings are valuable for the guidance of making effective measurements to make full use of channel resource to promote its efficiency.

Numerical estimation of shallow water effect on multipurpose amphibious vehicle resistance

This research paper investigated the hydrodynamic resistance of Multipurpose Amphibious Vehicles (MAV) due to navigate in low water depth numerically. This type of vehicle and other coastal floating vehicles encounter the problem of a small under keel clearance with river bed. The proper estimation of ship resistance and squat is influence largely on the power calculation in the design stage. The present work describes the effect of shallow water on the Multipurpose Amphibious Vehicles (MAV) resistance at different speed using Computational Fluid Dynamics (CFD) techniques. A comparison in the drag on the hull is illustrated between depth restriction and infinite depth water. This paper provides a wide introduction into the problems of modelling of the restricted water depth effects on the ship behaviour, specifically hydrodynamic resistance and squat using CFD which is applied by ANSYS-CFX14.0.

On the structural behavior of ship's shell structures due to impact loading

When collision accident between ships or between ship and offshore platform occurs, a common phenomenon that occurs in structures is the plastic deformation accompanied by a large strain such as fracture. In this study, for the rational design against accidental limit state, the plastic material constants of steel plate which is heated by line heating and steel plate formed by cold bending procedure have been defined through the numerical simulation for the high speed tension test. The usefulness of the material constants included in Cowper–Symonds model and Johnson–Cook model and the assumption that strain rate can be neglected when strain rate is less than the intermediate speed are verified through free drop test as well as comparing with numerical results in several references. This paper ends with describing the future study.

Effects of the rebounding of a striking ship on structural crashworthiness during ship-ship collision

The purpose of this paper is to study the rebounding phenomenon of a striking ship and its effect on the structural crashworthiness of the struck ship. Pioneer works on ship collision and mathematical formulations to assess energy after collision are described to summarize the behaviour of the ship structure under collision between ships in various scenarios. A benchmark study is conducted using laboratory tests of the resistance to penetration of a stiffened plate to validate the methodology of the present work, which uses finite element methods to model a series of dynamic collision scenarios. The setting and configuration of a full-scale collision analysis is introduced, along with the configurations of the defined scenarios. External and internal ship collision parameters are considered as parameters that will affect structural behaviour prior to and after ruptures. The results of the evaluation indicate that in the event of a side collision, the striking ship can either fully stuck or rebounding phenomena. These phenomena produce significant differences in term of internal energy and crushing force, which are included as crashworthiness criteria. The type of striking ship, as well as its velocity, significantly affects the rebounding of the striking ship and behaviour of the struck ship. A notable gap between medium and high-carbon steels is not found during observations of the structural crashworthiness accounting for structure materials. Finally, other criteria for assessing the mechanisms and effects of rebounding during a collision are summarized, i.e. kinetic energy, acceleration, and extent of damage.

MPS法による大型船舶の津波中挙動と構造物に作用する衝突荷重特性に関する研究

Most of the loss suffered in the Great East Japan Earthquake was due to the tsunami rather than to the earthquake itself. An unusual aspect of these disasters was that much of the structural wreckage that was swept up by the tsunami remained and drifted on the sea. Some of the wreckage caused subsequent damage to coastal structures. These drifting objects caused by the tsunami included containers, boats and ships, cars, caissons, and other objects from the harbors. Thus, it is necessary to solve these problems in order to plan the safe coastal zone. However, there is no effective method in order to verify this subject, and few reports are available on characteristics of collision behavior of huge ship in tsunami. These problems can be resolved by the hydraulic model experiment. However, it is difficult to verify the scale model experiment, in addition these need enormous cost. On the other hand, numerical simulation method is suitable for analyze the collision phenomena of huge ship in tsunami. The MPS method is a particle based method originally proposed by Koshizuka et al. and is a Lagrangian procedure for simulating a flow field employing the moment-to-moment motions of particles distributed in a space. The most distinctive aspect of particle methods is that they do not require consideration of connections between calculation points. Because of this, the MPS method is well suited for analysis of strongly non-linear phenomena accompanying large deformations of free surfaces. The objective in this paper is following items, 1) to propose and evaluate the friction elastic body model for collision phenomena using MPS method, 2) to clarify characteristics of collision behavior of huge ship. The present numerical model of the MPS method is applied the dynamic analysis of elastic solids developed by Koshizuka et al. And, the authors approach the new method of the MPS which can analisys friction phenomena between solid in this research. As these results, the authors found that present model is suitable for calculation of collision phenomena through the verifications of the wave tank experiment and the analytical solution. In addition, the authors confirmed basic characteristics of behavior of collision phenomena of huge ship in tsunamis. Further, it was concluded that, the impulse due to collision force without friction force on the surface of the huge ship is 55% larger than the impulse of only tsunami waves in case of reflection tsunami flow from the land structure is small.

Theory and applications of coupled fluid-structure interactions of ships in waves and ocean acoustic environment

Wave induced motions and structural distortions, and machinery or propeller excited vibrations and acoustic radiations of a ship are two kinds of important fluid-structure interaction problems. The branch of ship science that describes the coupled wave induced dynamic behavior of fluid-structure interaction system is referred to as hydroelasticity. During the past three decades the development of three-dimensional hydroelasticity theories and applications gained great progress. Recently the 3-D hydroelasticity theory was further extended to account for the fluid compressibility and the effect of the ocean acoustic environment with finite water depth. A three-dimensional sono-elasticity theory was then produced. In this paper, the 3-D hydroelasticity theory and the 3-D sono-elasticity theory of ships are briefly described. To illustrate the applicability and feasibility of these theories and the corresponding numerical approaches, several examples are presented including the predictions of wave loads, rigid-body and flexible-body responses, springing and fatigue behaviors, machinery or propeller excited coupled structural vibrations and acoustic radiations, as well as design optimizations for improving safety and acoustic behaviors of ships.

Peculiarities of Zigzag Behaviour in Linear Models of Ship Yaw Motion

Abstract The present survey, as part of larger project, is devoted to properties of pure linear models of yaw motion for directionally stable ships, of the first- and second-order, sometimes referred to as the Nomoto models. In rather exhaustive way, it exactly compares and explains both models in that what is being lost in the zigzag behaviour, if the reduction to the simpler, first-order dynamics (K-T model) is attempted with the very famous [Nomoto et al., 1957] approximation: T = T1 + T2 - T3. The latter three time constants of the second-order model, more physically sound, are strictly dependent on the hydrodynamic coefficients of an essential part of the background full-mission manoeuvring model. The approximation of real ship behaviour in either of the mentioned linearity orders, and the corresponding complex parameters may facilitate designing and evaluating ship steering, and identifying some regions of advanced nonlinear models, where linearisation is valid.As a novel outcome of the conducted investigation, a huge inadequacy of such a first- -order model for zigzag simulation is reported. If this procedure is used for determining steering quality indices, those would be of course inadequate, and the process of utilizing them (e.g. autopilot) inefficient.

A Computationally Efficient Implementation of Nonzero-Speed Transient Green Functions for Zero-Speed Nonlinear Seakeeping Problems

The proposed methodology is a time-domain panel method where the transient Green functions (GFs) used for the estimation and implementation of the free-surface effects on the vessel's motions are estimated assuming constant low lateral speed, instead of the common practice zero-speed influence functions. The main difference between the proposed method and standard practice lies in the use of the proposed scheme on a typical zero-speed problem, as the solution scheme is conditioned to the mean drift velocity instead of zero-speed. Furthermore, in this way, a significant improvement in accuracy accompanied by a large reduction in computational times is also achieved. The low lateral-speed GFs are computed for a speed similar to the one that the vessel is expected to drift. Estimation of this speed can be initially based on model tests or by means of an iterative process where we start the computations with the zero-speed GFs and adjust the latter's input speed according to the calculated drift speed until convergence is obtained. As a representative case study, we apply this method for the simulation of seakeeping behavior of a cruise ship in extreme dead ship conditions. For the validation of the proposed methodology, the first- and second-order motions, i.e., heave, roll, and the drift velocity, respectively, as well as lateral accelerations of the vessel were investigated for two cases of severe beam seas further combined with a constant strong wind load. The results were compared against experimental model tests.

Performance analysis of a horn-type rudder implementing the Coanda effect

The Coanda effect is the phenomenon of a fluid jet to stay attached to a curved surface; when a jet stream is applied tangentially to a convex surface, lift force is generated by increase in the circulation. The Coanda effect has great potential to be applied practically applied to marine hydrodynamics where various lifting surfaces are being widely used to control the behavior of ships and offshore structures. In the present study, Numerical simulations and corresponding experiments were performed to ascertain the applicability of the Coanda effect to a horn-type rudder. It was found that the Coanda jet increases the lift coefficient of the rudder by as much as 52% at a jet momentum coefficient of 0.1 and rudder angle of 10°.

Analysis of ship drifting in a narrow channel using Automatic Identification System (AIS) data

With maritime transportation has played an important role in global economy development, ship traffic has become more congested. Therefore, ships navigate under risk conditions, and thus maritime accidents have occurred frequently. Especially, ship passing through a narrow channel is even more dangerous. Because, the ships are easy to be affected by external forces such as wind and currents that can cause ship drifts. Many latent risks are present during navigation. In order for the development of a sensible and appropriate traffic model for the safety and efficiency ship navigation, this study has focused on the actual ship behavior to understand the ship drift in the Kurushima Strait, Japan, which is one of the most dangerous routes in Japan. The analysis of ship behavior was carried out using the Automatic Identification System (AIS) data. As a result, the ships drift was understood in detail, and the latent risk was unveiled when ships pass through the narrow route. Moreover, the risk areas were obtained and visualized by the ship drift behavior analysis. The obtained results can be applied to ensure safe navigation and the development of an eco-friendly and economy efficient for ship navigation.

Assessment of current criteria for dynamic stability of container vessels

Container vessels sailing through heavy weather are exposed to a significant variation of stability due to specific shape of the hull combined with the action of the waves. Even if the weather forecast is transmitted to vessels, the way of acting it is a matter of officers’ experience. The Maritime Safety Committee, under the International Maritime Organization, has approved the Guidance to the master for avoiding dangerous situations in adverse weather and sea conditions. Adverse weather conditions include wind induced waves or heavy swell. The development of dangerous phenomena such as surf-riding and broaching to, syncronious and parametric rollings is a result of a these adverse conditions which has to be encountered by the vessels. Understanding the dynamic stability of the vessel in the waves and ship's behaviour based on mathematical and physical rules is a difficult task, any effort in order to assess these components are salutary. To avoid excessive acceleration and forces which can damage the hull of the vessel, lashing and integrity of containers, course and speed may need to be changed for the vessel's motion in heavy seas. Specific software have been developed as aids for evaluating the response of the vessel in heavy seas according to parameters variations. The paper aims at assessing of current criteria for dynamic stability of a container vessel model ship in order to determine the ways for avoiding dangerous conditions. The results should be regarded as a supporting tool during the decision making process.

SPH simulation of ship behaviour in severe water-shipping situations

Fishing vessels, having relatively small freeboard, are prone to encounter a water-shipping event in severe sea states. The water impact and accumulated water effects could make fishing vessels be unstable and capsize in the worst-case scenario. Therefore securing the safety of fishing vessels under water-shipping situations is an important subject, but it is not easy to predict the water behaviour in water-shipping situations, where over-topping, water impact, largely deformed free-surface and strong coupling with ship motions appear compositely. In this paper, SPH simulations using GPU are applied to the prediction of 6DoF ship motions in severe water-shipping condition. Then the prediction accuracy of the SPH method is systematically investigated through comparisons with dedicated captive and free motion tests.

CPA Calculation Method based on AIS Position Prediction

The information on the Closest Point of Approach (CPA) of another vessel to own ship is required in a potential collision situation as it helps determines the risk to each vessel. CPA is usually calculated based on the speed and direction of the approaching ship neglecting the Change Of Speed (COS) and the Rate Of Turn (ROT). This will make the CPA less useful. To improve the CPA calculation, Automatic Identification System (AIS) information containing the Speed Over Ground (SOG), Course Over Ground (COG), COS and ROT is used. Firstly, a model using these four factors is built to predict ship positions better. Secondly, a three-step CPA searching method is developed. The developed CPA calculation method can assist in informing the navigation decisions and reducing unnecessary manoeuvres. Through the analysis of a real collision scenario, this paper shows that the proposed method can help identify and warn of anomalous ship behaviours in a realistic time frame.

An experimental investigation into the influence of the damage openings on ship response

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.