A trailing suction hopper dredge draghead production model

Abstract

Estimators at the production department of Great Lakes Dredge & Dock Company use a number of models to make production estimates for a job. These models require the slurry concentration in the suction arm of a trailing suction hopper dredge (TSHD) as an input. Currently this concentration is estimated based on results of previous projects. To aid in the estimation of the slurry concentration a model that calculates the in situ production and slurry concentration has to be developed.

During this research a model was developed that calculates in situ production by iteratively finding equilibrium between the actuator moments and the cutting moments around a draghead visor hinge. The slurry concentration is then calculated using the in situ production and a function describing the relationship between slurry concentration and dredge pump flow based on data of an existing TSHD.An extension to existing cutting theory was made to model the effects of the presence of water jets in the cutting teeth of the draghead. In this extension water jets were modeled as a pressure source which provides water to reduce the pore under pressures that cause cutting forces.The production model was evaluated by performing sensitivity analyses. In general the course of the production as a function of the trailing speed that was found could be described as a linear increase followed by a steep drop in production after which production started increasing again at a lower rate. It was found that it was mainly the geometry of the draghead that caused this steep drop. Another finding is that the production at operational trailing speeds (1 to 2 knots) is only of a realistic order of magnitude (between 36 and 125 m^3/min in this case) when still in the linear increase.

The conclusions that were drawn during the development of the model and the sensitivity analyses are that the TSHD draghead production might actually be best described as a linear function of the trailing speed and that the angle of internal friction of the sand is the parameter with the largest influence on the production. Of controllable parameters the pressure in the actuator had the largest influence on the production. That the results of the tooth jet extension correspond sufficiently well with an energy-based type of approach.