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Advance modeling of the excavation process for control of Hopper Dredgers

Subject: Advance modeling of the excavation process for control of Hopper Dredgers
Staff Mentor: prof. R. Babuška
Other Mentor(s): Pawel Stano;
Keywords: Modeling and analysis; Nonlinear and LPV systems; Industrial processes

A Trailing Suction Hopper Dredger (TSHD) is a ship that is used to excavate soil at sea, rivers, lakes and ports. The largest ships are used to reclaim land from the sea, such as for the prestigious projects Palm Island and The World in Dubai, whereas the smaller units are maintaining the depth in ports or rivers.

The draghead is the most important component of the excavation system in a TSHD. Its task is to break the coherence of the bottom soil which allows the loosened material to be sucked by the dredge pump and be transported to the storage tank (hopper). The overall production comes from three factors: production by the water jets, production by cutting and production by erosion. The water jets are placed in the heel of the draghead. They are powered by the onboard jet pump which supplies the energy to jet the water under high pressure into the bottom. This loosens the material and allows it to be sucked by the dredge pump into the transport pipe. Production by cutting is obtained by the cutting device which is placed on the other side of the draghead. It consists of a blade or several knives which cut through the soil making it possible to be transported to the hopper. The necessary energy is supplied by the propulsion of the ship. Production by erosion occurs when the water velocity in the draghead creates a local decrease of pressure and an increase of pressure difference over the soil packet. As a result outside the draghead a water current is formed. Such a current breaks the cohesion between the grains and carries them into the transport pipe.

Over the past years, extensive research has been conducted to develop an automatic controller of the excavation system where the controlled inputs are, among others, the position of the draghead, the angle of the transport pipe and the speed of the jet pump. One of the most important part of this research is modeling of the draghead behavior. This is a very challenging problem due to the limited number of sensors, multiple operating regimes and uncertainty caused a dynamically changing environment. Simplified models have been derived from basic physical and mechanical principles. These models contain several uncertain parameters that need to be estimated online during the dredging.

The goal of this project is to investigate the excavation process in order to derive an improved draghead model. The research should start with the cross-validation of the existing models using the most recent field data. Next, the main objective will be to derive more accurate model for the draghead which incorporates the latest technological advances in the field. The new model should cope with the operating modes that were previously omitted in modeling due to insufficient knowledge or lack of appropriate data. The project is in cooperation with IHC Systems for obtaining data and to do experiments.

TSHD Marieke at the North See ( © Jelmer Braaksma).

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Last modified: 19 May 2011, 15:25 UTC
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