Guillaume Delefortrie

Validation of ship manoeuvring in shallow water through free-running tests

The shallow water effect on ship manoeuvring cannot be neglected. Most sea-going ships become more course stable when they sail from deep to (very) shallow water. International collaborations such as SIMMAN intend to grade up the knowledge on ship manoeuvring prediction through model tests and system based and numerical methods. Free-running model tests executed with the very large crude carrier KVLCC2 at two laboratories have been compared with the results of simulated turning circles and zigzag manoeuvres from two different mathematical models. It was concluded that the type of mathematical model has an important influence on the simulated behaviour. Moreover, further research is necessary as simulations result into a more course stable behaviour compared to free-running tests at model scale.

The Towing Tank for Manoeuvres in Shallow Water

cm Centimetre FHR Flanders Hydraulic Research GSP Groningen Seaports kHz Kilohertz kn Knots (nautical speed) KSN Keep Sediments Navigable N.A.P. Normaal Amsterdams Peil (reference height) m Meter Pa.s Pascal second UKC Under Keel Clearance W&P Wiertsema & Partners UKC210kHz UKC with respect to 210kHz based on survey of 2 of May 2015 UKC33kHz UKC with respect to 33kHz based on survey of 2 of May 2015

Running sinkage and trim of the DTC container carrier in harmonic sway and yaw motion : open model test data for validation purposes

After successful conferences on bank effects, ship – ship interaction and ship behaviour in locks, the Fourth International Conference on Ship Manoeuvring in Shallow and Confined Water (MASHCON) has a non-exclusive focus on ship – bottom interaction. With increasing ship sizes in vertical and horizontal dimensions, a clear understanding of the interaction between a ship and the bottom of the waterway will help to improve the operations and increase the safety of manoeuvring ships. To open a joined research effort on the validation and verification of the different research methods, the Knowledge Centre Manoeuvring in Shallow and Confined Water has selected model test data which were obtained while executing tests with the DTC container carrier in the framework of the European SHOPERA project. The benchmark data are harmonic yaw and harmonic sway tests with the bare hull of the DTC at full draft and 20% under keel clearance at rest.

The influence of the ship’s speed and distance to an arbitrarily shaped bank on bank effects

A displacement vessel – obviously – displaces a (large) amount of water. In open and deep navigation areas this water can travel almost without any restriction underneath and along the ship’s hull. In restricted and shallow waterways, however, the displaced water is squeezed under and along the hull. These bathymetric restrictions result in increased velocities of the return flow along the hull. The resulting pressure distribution on the hull causes a combination of forces and moments on the vessel. If generated because of asymmetric flow due to the presence of a bank, this combination of forces and moment is known as bank effects. By far the most comprehensive and systematic experimental research program on bank effects has been carried out in the Towing Tank for Manoeuvres in Shallow Water (cooperation Flanders Hydraulics Research – Ghent University) at Flanders Hydraulics Research (FHR) in Antwerp, Belgium. The obtained data set on bank effects consists of more than 14 000 unique model test setups. Different ship models have been tested in a broad range of draft to water depth ratios, forward speeds and propeller actions. The tests were carried out along several bank geometries at different lateral positions between the ship and the installed bank. The output consists of forces and moments on hull, rudder and propeller as well as vertical ship motions. An analysis of this extensive database has led to an increased insight into the parameters which are relevant for bank effects. Two important parameters are linked to the relative distance between ship and bank and the ship’s forward speed. The relative position and distance between a ship and an arbitrarily shaped bank is ambiguous. Therefore a definition for a dimensionless distance to the bank will be introduced. In this way the properties of a random cross section are taken into account without exaggerating the bathymetry at a distance far away from the ship or without underestimating the bank shape at close proximity to the ship. The dimensionless velocity, named the Tuck number (Tu), considers the water depth and blockage, and is based on the velocity relative to the critical speed. The latter is dependent on the cross section (and thus the bank geometry) of the waterway.

Application of Potential Flow Methods to Ship Squat in Different Canal Widths

This paper presents a comparison of numerical methods with model test results for squat (sinkage and trim) of a 1:75 KVLCC2 model in the Flanders Hydraulics Research towing tank, at a range of rectangular canal widths and depths. The numerical methods are the Linear-2D and Nonlinear-1D methods in ShallowFlow, the Double-Body method in HullWave and the Rankine-Source method in GL Rankine. Analysis of the model tests showed that in the narrowest canals, mass flux past the ship was not conserved, nevertheless it appears that the Nonlinear-1D method may give good results for the narrowest canals. The Linear-2D method was found to give good results in the widest canal, particularly at the shallowest water depth. The Rankine-Source method was found to give good results for the widest canal, particularly at high speed. The Double-Body method was found to give quite consistently good results across all conditions.

Ship manoeuvring behaviour in muddy navigation areas : state of the art

The manoeuvring behaviour of vessels is highly affected by their small under keel clearance in access channels and harbours. If sedimentation and the formation of mud layers occur in these areas the manoeuvring behaviour becomes even more challenged, especially because the exact location of the bottom is not unequivocally determined. In such areas the nautical bottom definition, as stated by PIANC, is useful: The nautical bottom is the level where physical characteristics of the bottom reach a critical limit beyond which contact with a ship’s keel causes either damage or unacceptable effects on controllability and manoeuvrability. Over the past decades research has been focussing on both the determination of the physical characteristics of the mud and the manoeuvring behaviour in such areas. The paper tends to give an overview of this research and of practical applications in harbours worldwide, and to provide an outlook for future research.

The Influence of the Ship’s Speed and Distance to an Arbitrarily Shaped Bank on Bank Effects

A displacement vessel — obviously — displaces a (large) amount of water. In open and deep navigation areas this water can travel almost without any restriction underneath and along the ship’s hull. In restricted and shallow waterways, however, the displaced water is squeezed under and along the hull. These bathymetric restrictions result in increased velocities of the return flow along the hull. The resulting pressure distribution on the hull causes a combination of forces and moments on the vessel. If generated because of asymmetric flow due to the presence of a bank, this combination of forces and moment is known as bank effects.By far the most comprehensive and systematic experimental research program on bank effects has been carried out in the Towing Tank for Manoeuvres in Shallow Water (cooperation Flanders Hydraulics Research – Ghent University) at Flanders Hydraulics Research (FHR) in Antwerp, Belgium. The obtained data set on bank effects consists of more than 14 000 unique model test setups. Different ship models have been tested in a broad range of draft to water depth ratios, forward speeds and propeller actions. The tests were carried out along several bank geometries at different lateral positions between the ship and the installed bank.The output consists of forces and moments on hull, rudder and propeller as well as vertical ship motions. An analysis of this extensive database has led to an increased insight into the parameters which are relevant for bank effects.Two important parameters are linked to the relative distance between ship and bank and the ship’s forward speed. The relative position and distance between a ship and an arbitrarily shaped bank is ambiguous. Therefore a definition for a dimensionless distance to the bank will be introduced. In this way the properties of a random cross section are taken into account without exaggerating the bathymetry at a distance far away from the ship or without underestimating the bank shape at close proximity to the ship.The dimensionless velocity, named the Tuck number (Tu), considers the water depth and blockage, and is based on the velocity relative to the critical speed. The latter is dependent on the cross section (and thus the bank geometry) of the waterway.Copyright

Controlling the Yawing of an Aframax Tanker During a Lightering Manoeuvre

Abstract Lightering is the process where a larger ship (the ship to be lightered, STBL) transfers (parts of) its cargo to a smaller vessel, known as service ship. This transfer occurs at a slow sailing speed (about 4 knots) while both ships are moored to each other. A knowledge-building project with user involvement entitled “Investigating Hydrodynamic Aspects and Control Strategies for Ship-to-Ship Operations” was carried out in 2007-2011 to offer more insight in lightering operations. The actual forces acting on both vessels while preparing for lightering can be analysed based upon more than two thousand captive model tests carried out at the Towing tank for manoeuvres in shallow water (co-operation Flanders Hydraulics Research – Ghent University) in Antwerp, Belgium. The tests were executed with a scale model of a very large crude oil carrier (VLCC) attached to the main frame of the towing carriage and a scale model of an Aframax tanker attached to the computer controlled planar motion carriage. Forces, moments and vertical positions were measured on both models. In this article particular attention is given to the comparison, in deep and shallow water, of the yawing moment induced on the service ship during the lightering operation and the yawing moment induced by the rudder of the same ship during open water tests. The combination of both allows defining ranges of relative positions between both vessels with an equal degree of controllability of the service ship during the lightering operation. In shallow water, the acceptable meeting area appears to be reduced significantly.

Ship Manoeuvring at Very Small and Negative Under Keel Clearance

Abstract A selection of results of systematic captive manoeuvring test series with a container carrier model above a solid bottom as well as above and in simulated mud layers is presented. The effect of under keel clearance - with emphasis on very small and even negative values referred to the water-mud interface - on linear manoeuvring coefficients and dynamic stability parameters is discussed. Controllability and manoeuvrability appear to be affected particularly by the influence of water depth on the lateral force due to yaw, as at very small under keel clearance the centrifugal inertia force is completely compensated by a hydrodynamic centripetal force.