Safe and smooth through a shallow fairway

Since the ever growing dimensions of all vessel types coming to the Flemish harbours which started in the mid 80’s of last century, the research at Flanders Hydraulics Research, a laboratory belonging to the Flemish Government, concerning harbour infrastructure and fairways was shifting from structural based examinations to ship related examinations. The key question was and is: how can an existing or new-built ship access the shallow water areas in Belgium safely and smoothly? With the installation of the first ship manoeuvring simulator in 1989 and the Towing Tank for Manoeuvres in Shallow water (co-operation Flanders Hydraulics Research- Ghent University) in 1992 fundamental and applied research studies followed successively. In May 2008 this joint work resulted in the Knowledge Centre Manoeuvring in Shallow and Confined Water (www.shallowwater.be) established to fix, extend and provide the scientific know-how on the behaviour of vessels in shallow and confined navigation areas. The presentation will give an overview of the latest fundamental researches executed at FHR and UGent concerning the influence of shallow water manoeuvring, bank effects and ship-ship interaction. Based on model tests with scale models of about 4 m length forces have been measured and the influence of different test parameters have been examined. Combining these measurements with mathematical models incorporated in the simulators gives the opportunity to evaluate new situations together with the pilots of the Flemish Pilotage. This research has been used to evaluate the accessibility of the largest containerships (the E-type vessel of Maersk Sealand and the 366 m vessels of other shipping companies as MSC and CMA-CGM) to the port of Antwerp and the port of Zeebrugge and the largest LNG carriers to the LNG terminal in Zeebrugge. New limits have been examined for the West lock in Terneuzen for Kamsarmax vessels where the useful width of 38 m for the lock is compared with the vessel’s beam of 37 m. This high blockage introduces lock effects that determines the behaviour entering the lock

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

Experiment based mathematical modelling of ship-bank interaction

The forces and moments induced by the vicinity of banks on a sailing vessel are known as bank effects. An extensive set of model tests have been carried out in a towing tank to investigate bank effects induced by irregular bank geometries. Tests along sloped surface-piercing as well as submerged banks are carried out. A mathematical model (for the longitudinal force and sway forces) found on these tests is formulated

Controlling the yawing of an Aframax tanker during a lightering manoeuvre

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Captive model testing for ship to ship operations

Applications of ship-to-ship operations for liquid cargo transfer, in particular for crude oil and LNG, will to be increasing in the future. Moreover, such operations are expected to take place in more severe environmental conditions. In order to have a better understanding of the hydrodynamic phenomena that are of importance for this kind of manoeuvres, a research project entitled “Investigating hydrodynamic aspects and control strategies for ship-to-ship operations” has been initiated, co-ordinated by MARINTEK (Trondheim, Norway) and supported financially by the Research Council of Norway. The main objective is to improve existing simulator based training activities for personnel involved in complex ship-to-ship operations in open seas through increased knowledge and understanding of the complex water flow between two ships operating in close proximity. As a final goal, a new generation simulation tools for ship-to-ship operations incorporating up-to-date knowledge of fluid dynamics has to be established. The project consists of four work packages: (1) Computational Fluid Dynamics; (2) Particle Image Velocimetry; (3) Mathematical models for simulators; (4) Nautical safety and control aspects. In the frame of the third work package, captive model tests are being carried out at the Towing tank for manoeuvres in shallow water (co-operation Flanders Hydraulics Research – Ghent University) in Antwerp, Belgium. While the model of an Aframax tanker is attached to the computer controlled planar motion carriage, a VLCC model is attached to the towing carriage as well. Two types of tests are considered: steady state tests, during which the main tests parameters (ships’ speed, relative longitudinal and lateral position, propeller rates, drift angle of the Aframax tanker, rudder angle) are kept constant, and dynamic tests, characterised by a varying lateral distance and/or heading. Horizontal forces and moments, propeller thrust and torque, and vertical motions are measured on both ship models, while the vertical motions of the free surface are monitored in three fixed points of the towing tank. The paper intends to give a summary of the test results, that will be used for validation of mathematical manoeuvring simulation models and CFD calculations

Longitudinally directed bank effects

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Hydrodynamic interaction between ships and restricted waterways

In open and unrestricted waters the water displaced by a forward sailing vessel can travel without major obstruction underneath and along the ship. In restricted and shallow sailing conditions, the displaced water is squeezed between the hull and the bottom and/or the bank. This results in higher flow velocities and as a consequence a pressure drop around the same hull. In the vicinity of a bank this pressure drop generates a combination of forces and moments on the vessel, known as bank effects. The major achievement of the presented research is the development of a realistic and robust formulation for these bank effects. This knowledge is acquired with an extensive literature study on one hand and with dedicated model tests carried out in different towing tanks on the other. The majority of the utilised model tests were carried out in the shallow water towing tank at Flanders Hydraulics Research in Antwerp, Belgium. The data set on bank effects consists of more than 8 000 unique model test setups (which is by far the most elaborate research ever carried out on this subject). These model tests provide the input for the analysis of bank effects and the creation of the mathematical model. Overall the magnitude of the bank induced forces increase with: A higher forward speed of the ship A higher propeller load A lower under keel clearance A more confined navigation area: steeper banks, smaller channel width A smaller distance between ship and bank The mathematical model copes with a wide range of ship types and bank configurations and is suitable for implementation (and has been implemented) in full mission bridge simulators which can be used for training purposes as well as for research to support the admittance policy or exploitation of ports and waterways