Modeling the dynamic cutting behavior of a cutter suction dredger in hard rock types

In order to allow the new Super Post Panamax ships (19000 TEU, 16 m draft) a greater draft is needed in ports and access channels. The realization of these larger depths requires dredging, whereby soil under water is removed. Geologically speaking, however, deeper often means harder. Recent experience shows that the number of projects is increasing where hard to very hard rock has to be dredged. The cutter suction dredger is the ultimate dredging tool for dredging rock. Dredging of soil with a cutter suction dredger always takes place in a number of phases that mutually influence each other: breaking out of the soil, mixing the broken soil with water, suctioning, pressing and depositing the mixture. This research project focuses exclusively on the first phase of rock outbreak. Other dredging phases and soil types are not included. When rock breaks out, two processes influence each other: the breakout and the wear process, both strongly dependent on the very heterogeneous rock mass with respect to the dimensions of the working area of a cutter suction dredger. All these effects negatively influence the cost price of a project. In the first part of this research, a model of the cutter suction dredger is built. This is a purely mechanical model, in which the interactions between the different drives are modeled (rotation axis, side winches with anchors, ladder, spud). A simplified force model approaches the contact forces with the rock (teeth, spud, anchors). By inverse force identification, the cutter suction dredger model and the force model are calibrated and validated in a second part. The unpredictability and variability of the soil interaction (break out and wear process of teeth at the most detailed level, anchoring the vessel in the environment at the most general level) cause an uncertainty and spread on the loads, which forms a third part of the investigation. Moreover, the heterogeneity of the rock mass further promotes this uncertainty and distribution. The relatively large heterogeneity with respect to the few available soil measuring points and the large working area of a cutter suction dredger causes a great deal of uncertainty and spread on the rock parameters. The model will not only allow the production of cutter suction dredgers to be optimized before and during the project, but it will also be useful within the company to, among other things, - reduce vibration transmission to improve onboard ergonomics, and - optimize cutter head and tooth systems, and - train employees better by implementing the results in the cutter simulator. In addition, the model will provide a unique picture of the power spectrum on a cutter suction dredger, which can be an impetus for attracting maritime suppliers to Flanders. More generally speaking, the generic method whereby finite element modeling is combined with uncertainty models can also be applied in other industries characterized by complex and irregular processes such as the installation of monopiles for offshore wind energy.