Description of hydro/meteo data in ship manoeuvring simulators : a survey on the state of the art

This paper describes the results of a survey performed by the authors to assess how hydro/meteo conditions are presently modelled in ship manoeuvring simulators. While mathematical models for the manoeuvring behaviour of ships are well documented in literature, an overview concerning hydro/meteo modelling did not exist yet, despite the crucial role of this aspect on the global level of realism which could be achieved in manoeuvring simulations. A questionnaire regarding current, waves, wind and water levels was therefore sent to a large list of simulator developers and users, with the explicit aim to compile the results in a research paper. The received answers were thoroughly analysed and are summarized in this paper as an overview of the state of the art in hydro/meteo data for ship simulators at the time of writing. All the results are published in an anonymous form to guarantee a high discretion level to all parties who answered the survey. The information which is publicly summarized in this paper could benefit the whole community of ship simulator users and developers by making everyone more aware of the present common practices, while also fixing a starting point for future research and improvements

Wave effects on the turning ability of an ultra large container ship in shallow water

The influence of waves on ship behaviour can lead to hazardous scenarios which put at risk the ship, the crew and the surroundings. For this reason, investigating the effect of waves on manoeuvring is of relevant interest. Waves may impair the overall manoeuvring performance of ships hence increasing risks such as collisions, which are of critical importance when considering dense traffic around harbour entrances and in unsheltered access channels. These are conditions met by Ultra Large Container Ships (ULCS) when approaching a port, e.g. in the North Sea access channels to the main sea ports of Belgium. Note that due to the large draft of ULCS and the limited water depth, shallow water effects will also influenced the ship. Thus, in such scenarios the combined effects of shallow water and waves on the ship's manoeuvring need to be studied. The present work investigates the effect of waves on the turning ability of an ULCS in shallow water. Simulations are carried out using the two time scale approach. The restricted water depth corresponds to 50% Under Keel Clearance (UKC). To gain a better insight on the forces acting on the ship, the propulsion, and the rudder behaviour in waves experimental studies were conducted. These tests were carried out in the Towing Tank for Manoeuvres in Confined Water at Flanders Hydraulics Research (in co-operation with Ghent University) with a scale model of an ULCS. Different wave lengths, wave amplitudes, ships speeds, propeller rates, and rudder angles were tested. The turning ability characteristics obtained from simulations in waves and calm water are presented, and discussed

Numerical modelling of a mussel line system by means of lumped-mass approach

This paper describes a numerical model to simulate the behavior of a mussel longline system, subjected to environmental loads such as waves and current. The mussel line system consists of an anchor, a mooring chain, a long backbone line, mussel collector lines and buoys. The lumped-mass open-source code MoorDyn is modified for the current application. Waves are modelled as a directional spectrum, and the current as a homogeneous velocity field with an exponential vertical distribution. A Coulomb model is implemented to model the horizontal friction between nodes and the seabed. Cylindrical buoys with three translational degrees-of-freedom are modelled by extending the simplified hydrodynamic model in use for line's internal nodes with additional properties like cylinder height, diameter and mass. Clump weights are modelled in a similar way. For validation purposes, the results of the present software are compared with the commercially available lumped-mass based mooring dynamic software, OrcaFlex

Wind modeling for large container vessels : a critical review of the calculation procedure

With the increasing size of container ships, accurate methods to model manoeuvring and mooring conditions are indispensable. Especially in confined waters, where the ship speed is low or even zero, wind forces add a significant contribution to the force balance. The calculation of wind forces is typically done using wind coefficients based on wind tunnel tests. In these computations, a reference wind pressure must be used which is often based on the wind speed at 10 m height. When the wind blows over a rough surface however, the wind profiles become non-uniform, resulting in much higher wind speeds near the top of the ship, for the same wind speed at 10 m height. In case of differences between the wind profile used in the wind tunnel and the one expected in the reality, an appropriate reference pressure should be used. A method proposed by Blendermann to calculate such reference pressure is applied in this paper to a wind force calculation for an ULCS. It is shown that, depending on the roughness of the surface, the reference pressure can be a factor 2 to 3 higher than the one corresponding to 10 m height. This means that wind forces are potentially highly underestimated. The results of the method are compared with CFD simulations with a uniform and non-uniform inlet profile. The comparison shows a good agreement between Blendermann’s method and CFD results for the surge force and roll moment. On the other hand, Blendermann’s method seems to overestimate the sway force, but more simulations are needed before a firm conclusion can be draw

Wind modeling for large container vessels : a critical review of the calculation procedure

With the increasing size of container ships, accurate methods to model manoeuvring and mooring conditions are indispensable. Especially in confined waters, where the ship speed is low or even zero, wind forces add a significant contribution to the force balance. The calculation of wind forces is typically done using wind coefficients based on wind tunnel tests. In these computations, a reference wind pressure must be used which is often based on the wind speed at 10 m height. When the wind blows over a rough surface however, the wind profiles become non-uniform, resulting in much higher wind speeds near the top of the ship, for the same wind speed at 10 m height. In case of differences between the wind profile used in the wind tunnel and the one expected in the reality, an appropriate reference pressure should be used. A method proposed by Blendermann to calculate such reference pressure is applied in this paper to a wind force calculation for an ULCS. It is shown that, depending on the roughness of the surface, the reference pressure can be a factor 2 to 3 higher than the one corresponding to 10 m height. This means that wind forces are potentially highly underestimated. The results of the method are compared with CFD simulations with a uniform and non-uniform inlet profile. The comparison shows a good agreement between Blendermann’s method and CFD results for the surge force and roll moment. On the other hand, Blendermann’s method seems to overestimate the sway force, but more simulations are needed before a firm conclusion can be draw

Experimental and numerical evaluation of the added wave resistance for an ultra large container ship in shallow water

In this paper, the added wave resistance of an Ultra Large Container Ship (ULCS) in shallow water is investigated both experimentally and numerically. The experimental results come from a series of tests performed in the Towing Tank for Manoeuvres in Confined Water (co-operation Flanders Hydraulics Research and Ghent University) in Antwerp (Belgium) in 2016. Tests were executed for head and following waves, with two wave amplitudes, and using two different beam frames to attach the ship to the towing tank’s carriage. One of the frames restrained the heave and pitch motions while the other one allowed the free motion of both. The results of experiments outline the proportionality of added resistance on the square of the wave amplitude in shallow water conditions. Moreover, the expected behaviour of added resistance at different wave lengths can be observed: in long waves, the added resistance is tightly related to the ship motions, while in short waves it achieves an asymptotic trend. In following waves, a peculiar phenomenon is noticed: at moderate forward speeds a positive added resistance of substantial magnitude is measured for a specific, speed dependent interval of wave lengths. This phenomenon is investigated and preliminary ascribed to the interaction between the incident wave field and the return current originated by the motion of the ship in shallow water. Numerical simulations are performed with two potential codes: one based on strip theory and one 3D panel code. The 3D panel code performs better than the strip theory code. An in-depth analysis of the added resistance and vertical motions is performed, and the discrepancies of simulated added resistance with respect to experiments are mainly ascribed to the inaccuracies of numerical codes in the calculation of heave and pitch RAOs and phases