Weather Downtime Prediction for Cutter Suction Dredgers
Type:
Presented during:
WODCON XXII - Enhance the Harmony between Dredging and Ecology
Authors:
T.M. Tessler, A.N. Simos
Abstract
"The dredging activity is increasing worldwide because of ships that require bigger drafts, and consequently deeper navigation channels. Some dredging projects require the operation of cutter suction dredgers in open waters, since these are capable of removing compact sediments and rocks, also maintaining a good productivity. These facts prompted the creation of a weather driven downtime prediction software for this type of operation, based on simplified calculations of the main dredging systems of a Cutter Suction Dredger (CSD). The motions caused by waves and the forces and moments caused on these dredgers by winds, waves and currents were analyzed in order to evaluate the influence of each parameter magnitude and direction on the behavior of the vessel. The main criteria of the dredger influenced by these conditions have been determined in a literature review, and consist in the swing winch required power, the interaction between the cutterhead and the soil, and the anchoring system resistance. The latter can be described either by the stresses on a spud pole system or the by the tensions on a Christmas tree mooring configuration. In this research, only the bending stresses on the spud pole system were considered. Three mathematical models were developed to represent those systems. Since the non-linearity of the relation between the reaction forces of the dredger and the soil was not an object of the study, this process was represented by means of a constant user defined reaction force and a horizontal cutterhead velocity model. The efficiency of these models was tested by applying them on a case study considering a possible scenario of a dredging activity on the southeast coast of Brazil, and available data of jumbo, sea going cutter suction dredgers. Simultaneous wind, wave and current data were used as input to these models, both by creating a time series scenario of the operation period and by joint correlation diagrams. The results for both scenarios showed that the operation would be unfeasible during most of the time due to dynamic stresses on the spud pole caused by motions of the dredger."
Keywords: Dredging operation, Weather downtime, Cutter suction dredger.