An optimal dredging process by using new draghead control concepts
Type:
Presented during:
CEDA Dredging Days 2015 - Innovative Dredging Solutions for Ports, Rotterdam
Authors:
Van den Bergh PM and Osnabrugge J - IHC Systems, the Netherlands; de Keizer C - C. de Keizer Controls, the Netherlands
Abstract: The dredging process of a Trailing Suction Hopper Dredger (TSHD) is influenced by a large number of actuators such as propulsion (to control trail speed), dredge pump (to influence mixture velocity and pump efficiency), draghead visor (to control excavation height and trail force), jet pumps (to loosen the bottom), swell compensator pressure (to control the draghead vertical force) and intermediate suction tube winch (to control the lower suction tube angle). All these processes interact with each other and are furthermore strongly influenced by the soil type, water depth, dredger's draught, water current, waves and bottom irregularities. Therefore, there is no unique set of fixed settings for the actuators that give highest production and lowest trail force and fuel consumption. The operator has to find out how to set the actuators and it appears hardly possible to do it manually in an optimal way under continuously changing circumstances. Therefore IHC Systems started 10 years ago to develop a fully automated dredging process by using Model Predictive Control. This method is successfully demonstrated on board of TSHD’s. Nowadays most IHC built TSHD’s are equipped with advanced controllers for trail speed and dredge pumps.
Further improvement is made by controlling also the excavation process to maximize the dredging production with lowest capital and operational costs. The best actuator for that job is the visor of the draghead, which conventionally is controlled by complex, vulnerable and expensive hydraulic and electric equipment on the draghead under water. With the visor both the dredging production and trail force are influenced. In this paper the dredging process is explained in detail and it shows how an optimal suction production is achieved theoretically. Furthermore, the effectivity and efficiency of the different controllable actuators that influence the suction production are addressed.
Finally, this paper presents an inventive new draghead concept that uses a simple hardware and measurement setup to generate a larger control range compared to a conventional active draghead. The new type of controlled draghead that is demonstrated does not require active hydraulic or electric equipment on the draghead or suction tube. Instead, the visor of the drag head is controlled via the force in the hoisting wire, which is adjustable via the swell compensator pressure. In this paper the principle is explained and solutions are demonstrated, as well as its vital role within the automation and optimization of the dredging process.
Key words: dredging, advanced control, optimization, controlled draghead, excavation