Research carried out at the Ship Hydromechanics and Ship and Offshore Structures (SHS) research group is linked to the educational programme mainly by means of the numerous master thesis projects that are carried out in our main research fields:
- Sea keeping, Resistance and Propulsion of Fast Vessels
The Ship Hydromechanics and Structures research group has come to play an important role in research into the sea keeping, resistance and propulsion of fast vessels. A semi-empirical calculation model, termed ‘Fastship’, has been set up for the prediction of the sea keeping behaviour of fast vessels. This model is still currently under development and has been successfully applied in the design stage of fast vessels.
The concepts upon which two very successful designs are based, the enlarged ship concept and the axe bow concept, were developed by the research group based on extensive experience with high speed craft. Together with partners in industry, the design concepts have been translated into very successful high speed vessels that are now in great demand as patrol vessels and fast offshore crew suppliers, among other things.
- Fatigue of Fast Aluminium Vessels
The maritime industry requires high speed craft for surveillance duties, security, rescue and interception operations (Figure 1 and 2) to combat terrorism, piracy and drugs. In addition, high-speed craft are employed as crew transport vessels and pilot boats. They are typically built of welded joined aluminium because of substantial structural weight savings compared to steel craft, resulting in reduced installed power and fuel consumption.
The aim of the ‘VOMAS project’ is to develop a modern tool that predicts hydrodynamic loading and fatigue of (critical) structural elements of high speed aluminium craft, using methods developed in the FAST project. Results will be related to a state-of-the-art fatigue life calculation method.
- Performance Prediction of Sailing Yachts
Over the last 35 years, research has been carried out on the Delft Systematic Yacht Hull Series. This research has focused on the influence of various parameters (hull parameters or heel and trim of the yacht) on the total resistance and sideforce production of the yacht. A total of around 60 yachts have been tested, and this number is still rising.
Findings derived from this research have been used to devise a hydrodynamic model that can be used to calculate the resistance components on a sailing yacht based on hull parameters. These expressions have been used to create a Velocity Prediction Programme (or VPP), in which the performance of a generic yacht can be predicted. In addition, a computer simulation model has been developed allowing for the simulation of sailing yacht manoeuvring and the study of the yacht manoeuvring behaviour.
- Cavitation Research
The cavitation research carried out in the Delft cavitation tunnel focuses on sheet and vortex cavitation and in particular on the shedding mechanism of three-dimensional sheet cavitation on a twisted hydrofoil in unsteady inflow conditions. Using video recordings at frame rates up to 3000 fps to produce time-resolved ‘particle image velocimetry’ (PIV) videos, a detailed and accurate database of benchmark tests of the unsteady cavity has been created for the validation of computational methods. Lift and pressure on the hydrofoil can also be measured under a variety of conditions.
The most recent research has focused on the interaction between sheet and vortex cavitation. The research helps to provide a better understanding of the behaviour of cavitation, to improve cavitation prediction, and to form guidelines for propeller design.
- Deterministic Motion Prediction of Offshore Structures in Waves
Very often, the operability of offshore operations involving floating structures (e.g. LNG off-loading, helicopter landing, installations by floating crane barges, dynamic positioning) is governed by the motions of these floating structures in waves. New remote sensing techniques (e.g. the special application of X-band radar) make it possible to measure the wave field at a considerable distance from a floating structure.
In the ship hydromechanics research group, research is being carried out on how to use remote wave measurements to make a deterministic prediction of the structure’s motions in order to allow for the continuation of operations in heavier sea states. Remote wave measurements can also be used to predict wave forces on structures. These predicted hydrodynamic forces can be used for more sophisticated control of dynamic positioning systems, making them more accurate and energy efficient.
Below, the three most important research facilities of the Ship Hydromechanics and Structures research group are presented.
- Large towing tank
This basin, measuring 150 m x 4 m x 2.5 m, is equipped with a towing carriage that can tow ship models through the basin at speeds up to 8 m per second, while allowing for the measurement of forces on and/or motions of the towed ship model. The carriage is equipped with a high-tech camera system that can measure the motions of the model in 6 degrees of freedom, and with a 6 degrees of freedom oscillator.
- Small towing tank
- This basin, measuring 80 m x 2.75 m x 1.25 m, is equipped with a towing carriage that can tow ship models through the basin at speeds up to 5 m per second, while allowing for the measurement of forces on and/or motions of the towed ship model.
- Cavitation tunnel
This facility is used to test the cavitation behaviour of propellers. Specifications of the Cavitation tunnel are as follows:
- Test section dimensions: L x B x H = 600 x 300 x 300 mm^3
- Water-speed: 7 m.s^(-1) Brand Kempf und Remmers, closed recirculation tunnel
- Drive System: 4-bladed axial flow propeller with Ward Leonard control.
- Engine Power: 15 Kw, (total) - 2920 rpm
- Pressures: 102 kPa (max) - I I kPa (min)
- Instrumentation: Propeller dynamometer, 5-hole pitot-tube, various pressure sensors, Laser Doppler Anemometry Type and location of torque and thrust dynamometer Balance T- and Q dynamometer at the end of propeller shaft, Tmax 400 N, Qmax 10 Nm Propeller or model size range, Propeller diameters from 50 - 160 mm
- Tests performed: Propeller tests in uniform flows; Forces and pressure distributions on rudder, fins etc.
An excellent relationship has been established with the shipbuilding industry, both nationally and internationally. Most of the research carried out is in close cooperation with industry partners such as ship yards, navies and coast guards, SAR operators, with research institutes, in particular Marin and TNO, and with the marine services industry, such as classification societies and engineering and design bureaus. Besides fundamental research, contract work, often concerning feasibility studies of new designs, is carried out in the fields of offshore structures, high speed vessels and sailing yachts.
These extensive contacts are often used to place master students at external companies for the second year traineeship and graduation projects, including at firms and institutes such as: Damen Shipyards, Gusto/MSC, MARIN, TNO, SBM Offshore, and Dockwise.