Controlling the yawing of an Aframax tanker during a lightering manoeuvre

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Manoeuvreergedrag van containerschepen in slibrijke vaarwateren Manoeuvring Behaviour of Container Vessels in Muddy Navigation Areas

English version below *** Vele havens en toegangsgeulen hebben te lijden onder de vorming van sliblagen op de bodem van de vaargeul. Om de toegang te garanderen zijn onderhoudsbaggerwerken noodzakelijk. Nu is de vraag welke vaardiepte nodig is voor een veilige scheepvaart. In het geval van sliblagen is de grens tussen water en bodem niet erg duidelijk, en wordt vaak het concept nautische bodem gebruikt. Dit is de positie waar de karakteristieken van de sliblaag een kritische limiet bereiken. Wanneer de kiel van het schip met deze limiet in aanraking komt dan ontstaat er schade of is het schip niet langer manoeuvreerbaar. Door toepassing van dit concept kan men toelaten dat de scheepskiel in contact komt met de bovenste sliblagen, op voorwaarde dat het schip nog onder controle kan gehouden worden. Om het gedrag van de manoeuvreerbaarheid te beoordelen werd een uitgebreid programma modelproeven uitgevoerd in de sleeptank , waarbij het gedrag van het schip boven en in een serie kunstsliblagen werd beproefd. Aan de hand van de meetgegevens werd eerst een wiskundig model opgesteld dat toelaat om per combinatie van kielspeling en sliblaagconditie het manoeuvreergedrag na te bootsen in een scheepsmanoeuvreersimulator. Vervolgens werd een veralgemeend wiskundig model opgesteld dat rekening houdt met kielspeling en sliblaagkarakteristieken en zo toelaat om het gedrag van eender welk diepstekend containerschip in realistische slibrijke vaarwateren te voorspellen. Als praktische toepassing werden de theoretische ontwikkelingen gebruikt voor het bepalen van een optimale nautische bodem en operationele grenzen voor de doorvaarbaarheid van het slib in de haven van Zeebrugge, wat heeft geleid tot efficiëntere onderhoudsbaggerwerken en de toelating van grotere containerschepen. *** Many harbours and access channels suffer from the formation of mud layers on the bottom. Maintenance dredging works are necessary to guarantee the accessibility. The question is which navigation depth guarantees a safe shipping traffic. In case of mud layers the border between water and bottom is not unambiguous. Therefore the nautical bottom concept is used. This is the position where the characteristics of the bottom reach a critical limit. If the ship’s keel touches this limit damage occurs or the ship cannot longer be controlled. The implementation of the nautical bottom concept allows the ship to penetrate the upper mud layers if at least the ship can be controlled. To assess the manoeuvrability a comprehensive experimental program has been carried out in the Towing Tank for Manoeuvres in Shallow Water – collaboration Flanders Hydraulics Research – Ghent University in Antwerp. During this program the ship’s behaviour has been measured above and in contact with a series of artificial mud layers. Based on the measurements a mathematical model was built which allows to simulate the manoeuvring behaviour for each combination of bottom condition and under keel clearance on a ship manoeuvring simulator. Subsequently a consolidated mathematical model has been built, which takes into account the under keel clearance and mud characteristics. This model allows to predict the manoeuvrability of any deep drafted container vessel in fairways with any realistic mud layer. An example of application was the determination of the nautical bottom and operational limits for the penetrability of the mud in the harbour of Zeebrugge. This lead to a more efficient maintenance dredging and the admission of larger container vessels

Estuary traffic: an alternative hinterland connection for coastal ports

In 2007, the Belgian Federal Authorities issued a Royal Decree concerning "inland vessels that can also be utilised for non-international sea voyages", allowing inland vessels to operate in coastal areas between the Belgian coastal harbours and the Belgian inland waterway network via the Western Scheldt, provided that – among other requirements – a risk analysis demonstrates that the probability of adverse events such as bottom slamming, overtaking of water on deck and ingress of water in open cargo holds is limited to an acceptable level. Several tankers and container vessels are nowadays operating in significant wave heights up to 1.90 m. The present paper intends to provide background into the present regulations, to describe the methodology used for performing risk analyses, and give an overview of the present and future research at Flanders Hydraulics Research and Ghent University on estuary container vessels

Longitudinally directed bank effects

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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

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