Evert Lataire

Ship Motions in Shallow Water As the Base for a Probabilistic Approach Policy

A calculation tool has been developed for determining tidal windows for deep-drafted ships approaching and leaving the Belgian harbors according to probabilistic criteria. The calculations are based on a database containing response functions for the vertical motions in waves and squat data for a selection of representative ships. The database contains both results of model tests carried out in the Towing tank for maneuvers in shallow water – co-operation Flanders Hydraulics Research & Ghent University in Antwerp (Belgium), as well as calculated values. During the experiments, draft, trim, under keel clearance (7 to 20% of draft) and speed have been varied. The tests were performed in regular waves with lengths which are small compared to ship length, and in wave spectra that are typical for the Belgian coastal area. For given input data (ship characteristics, speed, tide, directional wave spectra, bottom, trajectory, current, departure time), the tool calculates the probability of bottom touch during the transit, so that a tidal window can be determined. Other restrictions, such as penetration into fluid mud layers and current, are taken into account as well.Copyright

Comparison of AQWA, GL Rankine, MOSES, OCTOPUS, PDStrip and WAMIT with model test results for cargo ship wave-induced motions in shallow water

A benchmarking study is carried out concerning wave induced ship motions in shallow water, predicted with commercially available codes AQWA, GL Rankine, MOSES, OCTOPUS, PDStrip and WAMIT. Comparison is made with experiments for three cargo ship models tested at Flanders Hydraulics Research. The same IGES models of the ship hulls were used in all codes to ensure consistent representation of the model geometry. The comparisons may be used to assess the suitability of each code for zero-speed applications such as berthed ship motions and under-keel clearance, as well as forward-speed applications such as under-keel clearance in navigation channels. Another, quickly developing, application area that requires analysis of seaway-induced ship motions in shallow water, is analysis of motions, accelerations and loads on cargo transport, installation and service vessels for offshore wind parks.

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.

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.