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For ships navigating in ice floe fields, ship-ice-wave interactions may affect ship performance and ice impact forces. This is because the added mass and hydrodynamic damping may influence hydromechanics and associated ship-ice interactions. This paper presents an approach to evaluate the cross-coupling added mass and hydrodynamic damping between a passing ship and a free-floating small/medium size ice floe based on the Boundary Element Method (BEM). The influences of added mass and hydrodynamic damping are explored for different wave frequencies and headings. Preliminary results are presented for a regular waves scenario whereby a tanker progressing at low speed is passing by a free-floating ice floe modelled as a round disk in close proximity. Radiation and diffraction potentials of the interacting floating bodies are linearly superimposed to reflect the influence of hydromechanical coupling on responses. Parametric analysis of Response Amplitude Operators (RAOs) indicates that the cross-coupling terms of added mass and hydrodynamic damping are of the same order of magnitude as those of the ice floe but smaller by one or two orders of magnitude than those of the ship. It is concluded that whereas the influence of hydrodynamic interactions primarily influences the motions of the ice floe, hydrodynamic interactions are significant attributes of the ship-ice system dynamics.

We present a preliminary assessment on the influence of the hydrodynamic assumptions associated with ship motions, for vessels maneuvering in calm waters. Three approaches are considered: (a) Model 1 idealising the maneuvering of a ship in 3-dof as per Brix (1993); (b) Model 2 representing the 6-dof hybrid time domain unified seakeeping / maneuvering model of Matusiak (2017); and (c) Model 3 - idealising combined seakeeping and maneuvering nonlinear characteristics in 6-dof by the time domain Green function method of McTaggart (2005). Simulations of turning circle and zig-zag manoeuvers are assessed and compared against available data for two tankers (KVLCC2 & Esso Osaka) and a container ship (DTC). It is concluded that in calm waters simplified models with hydrodynamic derivatives from either RANSE CFD or model tests can be used. However, implementation of well-validated CFD hydrodynamic coefficients may be more economic for the development of practical engineering tools, such as rapid assessment tools accounting for evasiveness in ship crashworthiness.… Read more

openaire: EC/H2020/730888/EU//RESET Safety assurance of autonomous ships is one of the major long-term challenges faced by the maritime world. Applying systemic hazard analysis methods at this early stage will guide the design and operation of safe autonomous ships. This paper proposes an initial hierarchical ship systems structure that could be the basis for a systemic hazard analysis of autonomous ship systems and operations. The approach is based on the systems theory and the principle of hierarchy and has been developed via the combination of models used in past research projects and requirements of the STCW convention. For enabling the operation of autonomous ships, the ship crew functions are either replaced by ship technical systems or assigned to the Shore-Based Control Centre (SCC).

The concept of autonomous merchant ships is quite recent. The increasing interest in autonomous vessels is nowadays calling for smart technologies that are supposed to replace the human actions on board. This involves troublesome issues related to ship safety. In the future, decision-making processes that are conventionally performed by human beings on board ship will be moved ashore to the control centre and maybe even completely replaced by computers and smart technologies. This paper proposes a method suitable for oceangoing ships, providing an autonomous routine for the avoidance of two dangerous phenomena involving excessive motions of the ship, e.g. the synchronous roll and the parametric resonance, both taking place in rough seas. The method is two-fold, since it pertains to the process of route planning and route monitoring and it encompasses two submethods (A and B). Submethod A is used to define a set of operational scenarios to be avoided due to excessive accelerations, with the use of a numerical ship motion model. This is applied at the route-planning stage. Submethod B is developed to monitor ship motions and to detect large roll motion for a ship in the seaway. It also raises alerts at two levels, first when the large roll motions are expected to develop (leaving ample time for remotely located operators to react), second when the large roll motions are developing (leaving a short time window for action taken on board the ship). The main sources of uncertainty are defined and the solutions to address those are proposed. Finally, the method is applied on simulated time histories of ship motion, which is a container ship traversing the Pacific Ocean. The obtained results are promising; however, further work is required with respect to various manoeuvers performed by a ship in the seaway.

An experiment was carried out to study the ice loads of level ice and ridge on the vertical and slope structures. The prototype of the model is the lighthouse Nordströmsgrund, which is a vertical structure and locates in the north Baltic sea. Nevertheless, a conical part was added to the model to study the ice load on slope structures in addition to the study of the ice loads on vertical structures. Three ice sheets with ridges were targeted to design the ice condition around Nordströmsgrund, including the flexural strength, ice thickness, geometrical cross-sectional profile of ridge, etc. Every ice sheet had a constant thickness, ranging from 0.04m to 0.043m in model-scale, but its flexural strength could be changed by using tempering procedure. Eight tests were successfully conducted and the ice loads were measured and recorded with three components divided according to the Cartesian coordinate system. The effect of ice properties and degrees of consolidation were also observed and analyzed with the measured data. The history curve and its envelope were utilized to study the ice loads on structures. The ice loads were decomposed into rubble loads (loads induced by accumulated rubbles) and level ice/consolidated layer loads (loads induced by breaking the level ice/consolidated layer). The upper envelope was assumed to represent the total ice loads and the lower envelope was assumed to represent the rubble loads. Thus, the difference between the upper and lower envelopes could be considered the level ice/consolidated layer loads. Fast Fourier Transform was applied to study the energy distribution of ice loads. The splitting of level ice was observed in front of the ridge at three tests. The histogram and return period are employed to study the distribution of ice loads and affecting parameters. The most important discovery of this research was that the horizontal range of rubbles moved by the structure had stronger influence on the ice ridge loads than the depth of rubble accumulation in front of the structure. Actually, the ridge loads were proportional to the volume of rubble accumulation and the strength of freeze bond in the keel. The zigzag pattern in the curve of horizontal range reflected the process of breaking the keel. This resulted in that the accumulation volume increased with a zigzag pattern in the curve of volume against the structure’s penetration distance into the ridge.

The main features of our simulation platform aimed for autonomous marine navigation research are described in this paper. The platform includes a Collision Avoidance System featuring two sub-systems: a decision-making protocol and an autopilot. The decision-making subsystem navigates the vessel according to the collision avoidance regulations (COLREGs), whereas the autopilot commands propulsors and control de, vices. The utilized autopilot features three modes: track-, heading- and docking modes. During an evasive action, the autopilot mode is changed from the track mode to heading mode. However, the location of the ship related to the track and track limits is monitored in the heading mode also. For harbor maneuvering, the function of the track mode is extended to slow speeds. The system has been implemented to a ship handling simulator environment and selected simulation scenario with object crossings is presented in this paper. The developed system can be used for the design and evaluation of autonomous ship systems. More specifically, we suggest the following application fields for the system: 1) development of autonomous navigation systems, 2) human factors studies with potential users, 3) verification and validation activities, and 4) scenario tests before real implementations on autonomous vessels. Finally, the general requirements and boundary conditions related to autonomous navigation systems are also discussed in the paper.

Digitalisation of ship design, construction and operation are gaining increasing attention in the marine industry as ships become eco-friendlier and smarter. ‘Smart designs’ can be applied under this digital revolution as an intelligent design process that is highly automated and collaborative with ‘smart manufactur-ing’ and ‘smart ships’ through-life. Focusing on smart design, we introduce a hybrid evolutionary algorithm and morphing (HEAM) approach which combines an evolutionary algorithm with an efficient morphing-based shape variation approach to optimise and automate the hull form design process. By combining the process of design exploration, geometry modification and performance evaluation, it enables highly automated design process where new hull forms are created, compared and analysed so as to reduce the overall design cycle and produce more optimal designs. This paper a) introduces a framework on how smart design process can be connected with smart manufacturing and smart ships to form into through-life smart shipping network, b) de-scribes the proposed HEAM approach to optimise and automate the hull form design process and c) provides result of the HEAM approach to demonstrate the design efficiency and performance improvement.