Production Estimation of Water Jets in Drag Heads
Type:
Presented during:
WODCON XXII - Enhance the Harmony between Dredging and Ecology
Authors:
S.A. Miedema
Abstract
"Many models have been derived for the forces, power and specific energy of soil cutting, sand, clay and rock. Very often modern drag heads also use waterjets to excavate the soil, in this case sand. A good model to determine the production, power and specific energy of waterjets in a drag head has never been published. In order to develop a model for the production and thus mixture density in a drag head, such a model is required. The mixture density and mixture velocity in its turn are required for existing hopper sedimentation models. Now these inputs are a best guess. This paper shows the derivation and validation of a model to determine production, power and specific energy of the waterjets in a drag head. The model assumes that the jet production does not depend on the water depth and the assumption that for cutting sand at zero water depth, the specific energy is equal for a certain blade angle. The law of conservation of misery, in this case conservation of a minimum amount of energy required. By making the jet power and the non-cavitating cutting power equal, a useful equation is derived, including the sand soil mechanical parameters. A simplification of the dilatancy to permeability ratio makes the equation practical. With some data available, the model (equation) is validated/calibrated. Based on the non-cavitational cutting process and an assumption regarding the equilibrium of moments on the visor, the cut production is added to the jet production, so the total production can be determined. Depending on the modeling, a maximum can be found or a slightly increasing production with increasing trailing speed is found. Part of the model derived is already in use for TSHD production and overflow loss estimations (see Miedema (2016))."
Keywords: Water jets, Production estimation, Specific energy, Overflow losses.